Aghayarzadeh, M, Khabbaz, H, Fatahi, B & Terzaghi, S 2020, 'Interpretation of Dynamic Pile Load Testing for Open-Ended Tubular Piles Using Finite-Element Method', International Journal of Geomechanics, vol. 20, no. 2, pp. 04019169-04019169.
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© 2019 American Society of Civil Engineers. For a foundation to perform safely, the ultimate strength of each pile must satisfy the structural and geotechnical requirements. Pile load testing is considered to be a direct method for determining the ultimate geotechnical capacity of piles. In this paper the dynamic and static response of a driven steel pipe pile monitored as part of a highway bridge construction project in New South Wales, Australia, has been simulated and then numerically analyzed using the finite-element method. A continuum numerical model has been established to simulate the dynamic load testing of steel pipe piles with unplugged behavior in which adopting measured soil properties resulted in a reasonable match between the measured and predicted results and without needing random signal matching in an iterative process. Settlement at the head and toe of the pile was then calculated when a static load represented by a dead load plus a heavy platform load of a bridge was applied over the pile head. During the dynamic and static load testing simulation, a hardening soil model with small strain stiffness was used to obtain the best correlation between the large and small strains, which occurred while the pile was under static load and being driven. The numerical predictions obtained using continuum finite-element simulations were then compared with the corresponding predictions obtained from the Case Western Reserve University (CASE) method and CASE Pile Wave Analysis Program (CAPWAP) to evaluate the predictions. The results show that the hardening soil model with small strain stiffness exhibits a reasonable correlation with the field measurements during static and dynamic loading. Moreover, parametric studies have been carried out in the established continuum numerical model to evaluate how the interface properties between the pile and soil and the reference shear strain define the backbone on the velocity at the head of the pile and trac...
Boyd-Weetman, B & Thomas, P 2020, 'Assessment of the ground aggregate paste (GAP) test for aggregate alkali–silica reactivity screening', Journal of Thermal Analysis and Calorimetry, vol. 142, no. 5, pp. 1635-1641.
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This paper investigates the potential of a laboratory test for the screening of aggregate reactivity to alkali–silica reaction (ASR) through phase analysis of the phases developed in ground aggregate paste (GAP) specimens subjected to accelerated ageing. GAPs were prepared using two aggregates categorised as non-reactive and potentially reactive by standard expansion test methods and were aged at 40, 60 and 80 °C in 1 M NaOH solution over periods up to 84 days. Phase development was monitored using TG, XRD and FTIR, and the reactivity was correlated with quartz and calcium hydroxide consumption. The data demonstrate that this test has the potential to be developed as a screening test, based on the correlation of phase consumption with Australian standard expansion test reactivity categorisation.
Cao, S, Wu, C & Wang, W 2020, 'Behavior of FRP confined UHPFRC-filled steel tube columns under axial compressive loading', Journal of Building Engineering, vol. 32, pp. 101511-101511.
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© 2020 Elsevier Ltd Ultra-high performance fiber-reinforced concrete (UHPFRC) has been widely investigated in recent years. This study focusses on the experimental results of FRP confined UHPFRC filled steel tube (UHPFRCFST) specimens under axial compression. In total 37 specimens, both square and circular, were prepared and tested to investigate the axial compressive behaviors of FRP confined UHPFRCFST specimens. The main investigated parameters were the FRP layers, the concrete type and the steel fiber addition. The experimental results indicate that axial load capacity of concrete filled steel tube (CFST) specimens can be effectively enhanced by the FRP confinement. However, the performance enhancement was less significant for square UHPFRCFST specimens as compared to circular UHPFRCFST specimens. Comparisons of these results demonstrate that FRP confined CFST specimens exhibit a higher load-bearing capacity in the post-peak stage than the non-wrapped CFST specimens. Moreover, prediction equations were proposed to predict the ultimate axial load capacity of FRP confined UHPFRCFST specimens, and the predicted results matched well with the experimental results.
Chauviré, B & Thomas, PS 2020, 'DSC of natural opal: insights into the incorporation of crystallisable water in the opal microstructure', Journal of Thermal Analysis and Calorimetry, vol. 140, no. 5, pp. 2077-2085.
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© 2019, Akadémiai Kiadó, Budapest, Hungary. Low-temperature DSC on a wide range of opal-A and opal-CT samples was carried out to estimate the proportion of crystallisable water and to determine the size of water-filled cavities. A wide range of crystallisable water contents in the range 4.9 to 41.9% of the water contained in opals were observed, although the proportion of crystallisable water did not correlate with structure. Pore size and pore size distribution were estimated from the melt temperature depression and heat flow data, respectively. Opal-CT was observed to have smaller water-filled pores (radii < 2 nm) than opal-A (radii from 2.5 to 4.9 nm), suggesting that molecular water may be contained between nanograins in the microstructural units (spheres or lepispheres). A narrower pore size distribution was calculated for opal-CT, and no melting of the crystallisable water was observed where bulk water would be expected to melt, suggesting the absence of larger voids. The melting peaks for opal-A, on the other hand, transitioned into the melting of bulk water suggesting the presence of significantly larger water-filled pores, an observation consistent with the microstructure observed in SEM micrographs.
Cheshomi, A, Bakhtiyari, E & Khabbaz, H 2020, 'A comparison between undrained shear strength of clayey soils acquired by “PMT” and laboratory tests', Arabian Journal of Geosciences, vol. 13, no. 14, p. 640.
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© 2020, Saudi Society for Geosciences. A pressuremeter test (PMT) is one of the in situ tests, which is used to evaluate deformation and strength parameters of soils for various projects, including subway projects. The limit pressure (PL) and undrained shear strength (Su) are the key parameters that are obtained directly and indirectly from the pressuremeter testing results. This research was carried out using geotechnical information obtained from a subway project in Qom city, Iran. Based on 44 PMT and uniaxial tests on very stiff to hard saturated clayey soils, a linear empirical equation between Su − PL and Su − PL* = (PL − σH) with R2 = 0.68 was proposed and it was found that σH had an insignificant effect on the proposed relationship. The effect of physical properties of soil, including plastic index (PI), liquid limit (LL), and water content (ω), was evaluated, and a multivariate equation was proposed between them. A comparison between the equations obtained in this research and those proposed by other researchers reveals that the empirical relationships between Su and PL are associated with the consistency of soils; the stiffer the soil is, the slope of relationship between Su and PL is less.
Dinh, TH, Phung, MD & Ha, QP 2020, 'Summit Navigator: A Novel Approach for Local Maxima Extraction', IEEE Transactions on Image Processing, vol. 29, pp. 551-564.
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© 1992-2012 IEEE. This paper presents a novel method, called the Summit Navigator, to effectively extract local maxima of an image histogram for multi-object segmentation of images. After smoothing with a moving average filter, the obtained histogram is analyzed, based on the data density and distribution to find the best observing location. An observability index for each initial peak is proposed to evaluate if it can be considered as dominant by using the calculated observing location. Recursive algorithms are then developed for peak searching and merging to remove any false detection of peaks that are located on one side of each mode. Experimental results demonstrated the advantages of the proposed approach in terms of accuracy and consistency in different reputable datasets.
Doan, S & Fatahi, B 2020, 'Analytical solution for free strain consolidation of stone column-reinforced soft ground considering spatial variation of total stress and drain resistance', Computers and Geotechnics, vol. 118, pp. 103291-103291.
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© 2019 Elsevier Ltd This paper provides an analytical solution for consolidation problem of a stone column-improved soft soil layer subjected to an instantly applied loading under free strain condition. The radial and vertical consolidation equations are solved in a coupled fashion for both the stone column and its surrounding soil. A general solution of excess pore water pressure at any point of a unit cell model in terms of a Fourier-Bessel series was achieved using the combination of separation of variables method and orthogonal expansion technique. The obtained solution can capture the drain (well) resistance effect and the space-dependent distribution of total vertical stress induced by the external loading. Indeed, since the permeability and size of the stone column are directly utilised in the governing equations and the analytical solution, the drain resistance is directly captured. The capabilities of the proposed solution are exhibited through a comprehensive worked example, while the accuracy of the solution is verified against a finite element simulation and field measurements of a case history with good agreements. To examine the effect of various factors on consolidation behaviour of the composite ground, a parametric study involving column spacing, modulus and permeability of soft soil along with distribution pattern of total stress and thickness of soil layer is also conducted. A decrease in the column spacing or an increase in the modulus or permeability of soft soil led to the acceleration of the consolidation process of the soil region, while the variation of the total stress with depth and the thickness of soil deposit primarily affected the consolidation rate of stone column. Under the free strain condition, the average differential settlement between the stone column and encircling soil was indeed considerable during the consolidation process.
Dong, W, Li, W, Guo, Y, He, X & Sheng, D 2020, 'Effects of silica fume on physicochemical properties and piezoresistivity of intelligent carbon black-cementitious composites', Construction and Building Materials, vol. 259, pp. 120399-120399.
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© 2020 Elsevier Ltd Carbon black (CB) filled cementitious composites as cement-based sensors with intrinsic piezoresistivity have the potential applications for structural health monitoring (SHM). Effect of silica fume (SF) replacement ratio on the physicochemical, mechanical and piezoresistive properties, and microstructure of CB-cementitious composite were experimentally investigated in this study. The results show that 5% or 10% replacement ratio of SF can improve the water impermeability, setting time and electrical conductivity, but decrease the fresh flowability. Cementitious composite with 10% SF exhibiteds excellent compressive and flexural strengths. Moreover, cement hydration in the acceleration stage decreased with the increase of SF content in the early stage, but the phase analysis after 28 days curing demonstrates that with the addition of SF, there are more hydrated products and less ettringite. In addition, the microstructures of cementitious composites without SF present more porous structures and CB agglomerations. In contrast, the amount of micropores or voids was significantly reduced by the addition of SF due to the physical filling effect and less CB agglomerations. In terms of piezoresistivity, SF can obviously improve the fractional changes of resistivity (FCR) under cyclic compression. With 10% SF, CB-cementitious composites as cement-based sensors exhibited excellent FCR and electrical stability, which will promote their development and application in the SHM for smart infrastructures.
Dong, W, Li, W, Luo, Z, Guo, Y & Wang, K 2020, 'Effect of layer-distributed carbon nanotube (CNT) on mechanical and piezoresistive performance of intelligent cement-based sensor', Nanotechnology, vol. 31, no. 50, pp. 505503-505503.
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Abstract Agglomerated carbon nanotube (CNT) powder was scattered into a cement paste layer-by-layer to form layer-distributed CNT composite (LDCC) as intelligent cement-based sensor. The characteristic of the CNT agglomerations and its effect on the mechanical and piezoresistive properties of cement paste were investigated in this study, and the results were compared with those of uniformly-dispersed CNT composites (UDCC). Based on the statistics of CNT agglomerations, it was found that the sizes of agglomerations varied from several to dozens of micrometres. The larger sized agglomerations with poorer roundness exhibited a higher possibility to cause the pores or voids accompanied with stress concentration when subjected to external forces. Hence, it is necessary to control the agglomeration sizes to reduce the porosity with edges and corners. The UDCC reached the highest compressive strength, followed by the plain cement paste and then LDCC. The mechanical strength of LDCC decreased with the increase of CNT layers. The piezoresistivity occurred in both the UDCC and LDCC, with the former possessing stable and repeatable performance. In addition, the strain-sensing ability of LDCC with moderate CNT layers presented similar sensing efficiency and repeatability to that of UDCC. The related results provide insight into the intelligent cement-based sensors with layer-distributed CNT and agglomerations, which can improve the efficiency and effectively reduce the cost for practical application.
Dong, W, Li, W, Luo, Z, Long, G, Vessalas, K & Sheng, D 2020, 'Structural response monitoring of concrete beam under flexural loading using smart carbon black/cement-based sensors', Smart Materials and Structures, vol. 29, no. 6, pp. 065001-065001.
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© 2020 IOP Publishing Ltd. The fractional changes of resistivity (FCR) of cement-based sensors with various carbon black (CB) contents were firstly investigated under uniaxial compression in this study. Then the piezoresistive behaviours of embedded cement-based sensors in unreinforced small-scale concrete beams were investigated under flexural bending load. As for the embedded cement-based sensors in the compression zones of the beam, the stress magnitude and crack failure initiation of the beams can be detected and monitored by a gradual decrease and then a sharp increase in the FRC. On the other hand, as for the counterpart sensors in the tension zones of the beam, the stress magnitude and crack failure initiation can be recognized by the gradual increase in resistivity and then a rapid jump in the FRC. During the stress monitoring of the concrete beam, the FCR values of cement-based sensors in both the compression and tension zones were consistent with the flexural stress changes, which exhibit acceptable sensitivity and reversibility. Moreover, very firm and dense interfaces in the boundaries indicate the excellent cohesion between embedded CB/cement-based sensors and beams. The related results demonstrate that the CB/cement-based sensors embedded in concrete exhibit excellent piezoresistive behaviours to potentially monitor the stress magnitude and failure process of concrete structures and pavements.
Dong, W, Li, W, Shen, L, Sun, Z & Sheng, D 2020, 'Piezoresistivity of smart carbon nanotubes (CNTs) reinforced cementitious composite under integrated cyclic compression and impact', Composite Structures, vol. 241, pp. 112106-112106.
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© 2020 Elsevier Ltd The cyclic compression and four series of fixed magnitude impact loads with an increment of 50 times were conducted alternatively on the smart carbon nanotubes (CNTs) reinforced cementitious composites, to evaluate the piezoresistive sensitivity and repeatability of composites after exposed to different drop impact energies. The results show that the impacts procedure suddenly increased in electrical resistivity due to the emerged micro-cracks and pores, and higher impact energy led to faster resistivity increase. On the other hand, when the impact is repeatedly applied, a high impact resistance of the cementitious composites could be observed, which was attributed to the dense microstructures. Moreover, instead of instable and uneven output of electrical resistivity during cyclical compression, more stable and uniform fractional changes of resistivity were achieved after exposed to impact load. However, severe nonlinearity with swift resistivity reduction of cementitious composites under low loads was observed at the beginning and the end of cyclic compression after subjected to many impacts with impact energy of 18.72 × 10−4 J/cm3. The related outcomes of smart conductive cementitious composites subjected to cyclic compression and impact will provide an insight into the stable electrical signal output and promote the applications of cement-based sensors for structural health monitoring under various loading conditions.
Dong, W, Li, W, Vessalas, K & Wang, K 2020, 'Mechanical and Conductive Properties of Smart Cementitious Composites with Conductive Rubber Crumbs', ES Materials & Manufacturing, vol. 7, pp. 51-63.
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Dong, W, Li, W, Wang, K, Guo, Y, Sheng, D & Shah, SP 2020, 'Piezoresistivity enhancement of functional carbon black filled cement-based sensor using polypropylene fibre', Powder Technology, vol. 373, pp. 184-194.
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In this study, different dosages of carbon black (CB) and polypropylene (PP) were added to develop functional cementitious composites as cement-based sensors. The results show that electrical conductivity increased with the amount of PP fibres, due to the enclosed CB nanoparticles and more conductive passages. The compressive strength slightly decreased, while the flexural strength was significantly increased with the increased amount of PP fibres. The improvement is mainly achieved by the reduced CB concentration in cement matrix and the excellent tensile strength of PP fibres. Under the cyclic compression, the piezoresistivity increased by three times for 0.4 wt% PP fibres filled CB/cementitious composite, regardless of the loading rates. The flexural stress sensing efficiency was considerably lower than that of compressive stress sensing, but it increased with the amount of PP fibres. Moreover, fitting formulas were proposed and used to evaluate the self-sensing capacity, with the attempts to apply cement-based sensors for structural health monitoring.
Dong, W, Li, W, Wang, K, Han, B, Sheng, D & Shah, SP 2020, 'Investigation on physicochemical and piezoresistive properties of smart MWCNT/cementitious composite exposed to elevated temperatures', Cement and Concrete Composites, vol. 112, pp. 103675-103675.
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© 2020 Elsevier Ltd Piezoresistivity of smart carbon nanotube/cementitious composite has been experimentally investigated, but the piezoresistive performance had been rarely studied when exposed to elevated temperatures. In this study, the physicochemical and mechanical properties, and piezoresistive behaviours of multi-walled carbon nanotube (MWCNT) reinforced smart cementitious composite were investigated under heat treatments of elevated temperatures of 300 °C and 600 °C. The microstructures, crystal deterioration and thermal gravity relationships were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and thermos-gravimetric (TG) analysis. The results show that the compressive strength and elastic modulus of MWCNT/cementitious composite after heat treatments gradually decreased, especially under the high temperature of 600 °C. There was a sudden growth of fractional changes of resistivity (FCR) after heat treatment. The higher temperature treatments led to more extensive sudden increase in the piezoresistivity. In the linear part of the relationship curves of FCR to the strain, the gauge factor even increased at the temperature of 300 °C. Moreover, the mechanism for the altered piezoresistivity was fundamentally explained and discussed by the MWCNT purification and destructions of MWCNT, cement matrix and agglomerations after heat treatments. Therefore, the related outcomes will promote the understanding and application of smart MWCNT/cementitious composite for structural health monitoring (SHM) under extreme environments.
Dong, W, Li, W, Wang, K, Luo, Z & Sheng, D 2020, 'Self-sensing capabilities of cement-based sensor with layer-distributed conductive rubber fibres', Sensors and Actuators A: Physical, vol. 301, pp. 111763-111763.
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Dong, W, Li, W, Wang, K, Vessalas, K & Zhang, S 2020, 'Mechanical strength and self-sensing capacity of smart cementitious composite containing conductive rubber crumbs', Journal of Intelligent Material Systems and Structures, vol. 31, no. 10, pp. 1325-1340.
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The effects of conductive rubber crumbs on the mechanical properties and self-sensing capacities of cementitious composites are investigated in this study. The rubberized cementitious composites with five different contents of conductive rubber crumbs are incorporated, ranging from 0%, 10%, 20%, 30% and 40% by mass of fine aggregate. Under the uniaxial cyclic compression, all the conductive rubber crumbs–filled cement composites exhibit excellent repeatability of piezoresistivity. The mortar with 20% conductive rubber crumbs at a water-to-binder ratio of 0.42 displayed the best piezoresistive sensitivity. Based on the relative positions of conductive rubber crumbs in the rubberized cement mortar, three conductive mechanisms were proposed for the conductive rubber crumbs, including complete isolation state, neighbouring state and the contact state. The isolation state plays a dominant role when the content of the conductive rubber crumbs is low, in which the piezoresistive behaviour is mainly controlled by the resistivity changes in cement matrix. In the neighbouring state, pores or voids in the gaps between nearby conductive rubber crumbs make the conductive rubber crumbs easier to connect, thus decreasing the resistivity under uniaxial compression. As for the contact state, the decreased contact resistance and the absence of sand between conductive rubber crumbs lead to higher resistivity changes under cyclic compression. The related results indicate that conductive rubber crumbs in cement mortar have application potentials for structural health monitoring.
Dong, Y & Fatahi, B 2020, 'Discrete element simulation of cavity expansion in lightly cemented sands considering cementation degradation', Computers and Geotechnics, vol. 124, pp. 103628-103628.
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© 2020 Elsevier Ltd This study aims to investigate the influence of cementation on the stress-strain and strength characteristics of soil during cavity expansion in lightly cemented sand deposit using three-dimensional discrete element simulations. Contact models, simulating the cementation effects of bonded clumps and capturing the interlocking effects between discrete sand particles, are incorporated to mimic the cemented sands with various cement contents. The microscopic parameters are calibrated and validated against existing experimental results. Real scale cylindrical cavity expansion models starting from zero initial cavity radius with different levels of cementation are developed, and each proposed model consists of 150,000 particles with boundary conditions carefully selected to reproduce the realistic scenario. The embedded scripting is utilised to precisely measure both the local and global stress–strain variations, and record and analyse the cementation bond breakage during the cavity expansion process. The results confirm that the cementation enhances the material strength through the increase in cohesion and tensile strength at the contacting interfaces, whereas the friction angle is not altered notably. Hence, the failure envelope of the cemented sand gradually merges with the critical state line due to the cementation degradation, particularly at a high confining pressure. It was found that the failure mode of the lightly cemented sand adopted in this study, was mainly controlled by the shear rather than tensile strength at the contacting interfaces. Referring to the numerical predictions it is evident that the zone with significant cementation degradation due to the cavity expansion extends as far as 4af for all cemented specimens (af being the final cavity radius). In addition, specimens with higher cement content experience a more pronounced dilation at the internal cavity wall, while an inverse trend is captured at a greater radial ...
Dong, Y, Fatahi, B & Khabbaz, H 2020, 'Three dimensional discrete element simulation of cylindrical cavity expansion from zero initial radius in sand', Computers and Geotechnics, vol. 117, pp. 103230-103230.
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© 2019 Elsevier Ltd This study seeks to assess the influence of choice of initial cavity radius on the soil response during cavity expansion in sandy soil adopting three-dimensional discrete element simulations and obtaining the size of the influence zone when the expansion starts from zero initial radius. Sandy soil is modelled adopting rolling resistance contact model to capture the effects of particle interlocking, and the microscopic parameters are calibrated utilising linear model deformability method for both loose and dense sands against experimental results. Four cylindrical cavity expansions that commenced from different initial radii are simulated in dense and loose sand specimens. The large-scale three-dimensional model is proposed with more than 500,000 particles, enabling precise volumetric dilation and contraction predictions using strain rate tensors. During the cavity expansion process, cavity pressure is constantly recorded by appropriate subroutines, while the stress-strain and void ratio variations are continuously monitored using an array of prediction spheres situated close to the internal cavities. The results confirm that the initial cavity radius chosen has conspicuous effects on the cavity pressure, the stress path, the volumetric strain and the deviatoric stress, especially at the initial stage of expansion; however, these effects become less pronounced and are ultimately minor as the cavity reaches full expansion. The results confirmed that given the same expansion volume, the pressure required to create a cavity is significantly larger than expanding an existing cavity in the same soil medium, whereas the pressure needed to maintain an already expanded cavity is not sensitive to the choice of initial cavity radius. The results obtained were further validated adopting the variations of stress path, deviatoric stress and volumetric strain in the vicinity of the cavity wall. The findings from this study may provide practicing en...
Fatahi, B, Huang, B, Yeganeh, N, Terzaghi, S & Banerjee, S 2020, 'Three-Dimensional Simulation of Seismic Slope–Foundation–Structure Interaction for Buildings Near Shallow Slopes', International Journal of Geomechanics, vol. 20, no. 1, pp. 04019140-04019140.
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© 2019 American Society of Civil Engineers. Buildings constructed adjacent to the slope crest in seismically active areas might be exposed to serious danger when they are subjected to strong earthquake excitations. The ground conditions can influence the seismic response of structures through a phenomenon known as the slope-foundation-structure interaction. Indeed, the presence of the slope in the vicinity of a building foundation can significantly affect the seismic response of the superstructure. In this study, the impact of shallow slopes on the seismic performance of nearby buildings was numerically assessed. In the adopted three-dimensional finite-element simulation, the nonlinear variations of the soil stiffness and damping with the cyclic shear strain plus varying distances between the edge of the foundation and crest of the slope were employed. A 15-story moment-resisting structure, a 30-m-thick clayey deposit, and a 2-m-high shallow slope were considered as the benchmark model, being simulated using the direct method in the time domain. According to the results of the analyses, the seismic response of a building could be highly sensitive to the distance between the slope crest and foundation. Particularly, the building closer to the slope crest experienced more severe foundation rocking, lateral deformation, and interstory drifts owing to the amplified effect of the slope-foundation-structure interaction. Moreover, the results highlighted the importance of the slope-foundation-structure interaction in altering the natural period and damping of the system. Hence, it is critical for practicing engineers to assess the impact of nearby slopes on the seismic performance of structures with extreme care to ensure the reliability and safety of the design.
Gokuldas, S, Banerjee, S & Nimbalkar, SS 2020, 'Effects of Tunneling-Induced Ground Movements on Stability of Piled Raft Foundation: Three-Dimensional Finite-Element Approach', International Journal of Geomechanics, vol. 20, no. 8, pp. 04020104-04020104.
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Gomes, SDC, Zhou, JL, Li, W & Qu, F 2020, 'Recycling of raw water treatment sludge in cementitious composites: effects on heat evolution, compressive strength and microstructure', Resources, Conservation and Recycling, vol. 161, pp. 104970-104970.
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Water treatment sludge (WTS) is produced daily and represents a globally significant solid waste stream. The application of this sludge as construction materials has been studied although most studies have modified the sludge before its incorporation, hence involving significant energy consumption. This study aims to use raw sludge as a novel cementitious material, by determining the effects of sludge addition on the composition and performance of cementitious composites. Important aspects such as the physicochemical interaction of the raw sludge with the Portland cement, the heat evolution of the cement paste and the compressive strength of the composite cement were carefully studied. The results show that for 1-2% of WTS addition, the compressive strength and heat evolution of the cement paste was well maintained being close to the reference specimen after 28 days of curing. However, for sludge addition above 5%, a delay in the hydration reaction was observed, together with about 25% reduction in compressive strength at 28 days of curing. The mineralogical and thermal analysis showed decreasing portlandite content and increasing calcite in the WTS-amended composites. Scanning electron microscope analysis demonstrated that the addition of sludge induced more porous and weak surface structures compared to the reference specimen.
Gu, X, Li, J & Li, Y 2020, 'Experimental realisation of the real‐time controlled smart magnetorheological elastomer seismic isolation system with shake table', Structural Control and Health Monitoring, vol. 27, no. 1.
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© 2019 John Wiley & Sons, Ltd. Traditional base isolation protects structures against severe seismic events by providing a designated lateral flexibility at the base level of the structures. Due to its inherent passive nature, in the design process, compromises have to be made among performance of different design targets (displacements, interstorey drifts, accelerations, etc.). In addition, as the working principle, the effectiveness of a base isolation relies on the degree of “decoupling” between ground excitation and superstructure. However, a higher degree of decoupling compromises the stability of the structures. In other words, for a base solation system, it possesses inherent conflicts between the effectiveness of the isolation and the lateral stability of the structure. A concept of new smart base isolation system is proposed, in which real-time controllable decoupling for a base isolation structure is achieved by employing magnetorheological elastomer (MRE) base isolators. With controllable lateral stiffness, the smart base isolation system can achieve an optimal decoupling by instantly shifting the structure's natural frequencies to a nonresonant region. This paper aims at experimentally proving and validating this innovative concept, including designing a three-storey shear building model equipped with MRE base isolators, demonstrating the feasibility and evaluating the performance of the proposed system by a series of shake table testing. The comprehensive experimental design and results of shake table testing have concept-proved the proposed smart MRE base isolation system for future development in practical applications.
He, X, Xu, H, Li, W & Sheng, D 2020, 'An improved VOF-DEM model for soil-water interaction with particle size scaling', Computers and Geotechnics, vol. 128, pp. 103818-103818.
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© 2020 This study presents an improved VOF-DEM model where the Darcian velocity and a compound variable are treated as unknowns in the pressure-velocity calculation procedure such that the use of interpolated porosity at cell faces is minimised and stability is ensured even if the porosity field is not smooth or even ragged. A higher-order porosity estimation method is also used such that the porosity and interaction force are evaluated correctly when the CFD cell size is of the same order as the DEM particle size. Additionally, a particle size scaling technique is proposed to let the DEM particle size different from the real soil particle size and soil-water interaction forces are the same as when the real soil particle size is used. This is achieved by modifying the calculation of drag force. The solution scheme is verified in two case where analytical solutions exist. Particle size scaling technique is also used and tested in permeability tests and wave interaction with porous structure. Subsequently, the settling and collision of particles in water, dambreak of soil-water mixture and submerged landslides are simulated. With the present improvements and the particle size scaling, the capability of the VOF-DEM is extended in soil-water interaction problems.
Hoang, VT, Phung, MD, Dinh, TH & Ha, QP 2020, 'System Architecture for Real-Time Surface Inspection Using Multiple UAVs', IEEE Systems Journal, vol. 14, no. 2, pp. 2925-2936.
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Jayawardane, VS, Anggraini, V, Li-Shen, AT, Paul, SC & Nimbalkar, S 2020, 'Strength Enhancement of Geotextile-Reinforced Fly-Ash-Based Geopolymer Stabilized Residual Soil', International Journal of Geosynthetics and Ground Engineering, vol. 6, no. 4.
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© 2020, Springer Nature Switzerland AG. Soils in their natural form are often deemed unsatisfactory to be directly used as a construction material for their respective applications. Under such circumtances, employment of ground improvement techniques to better suit the soil for its function is typically the most economical approach. Consequently, the present research investigated into the beneficial effect of modernized soil treatment techniques, i.e., geopolymer stabilization using fly ash as the precursor and geotextile reinforcement, on the strength enhancement of natural residual soil. A series of unconsolidated undrained (UU) triaxial compression tests were carried out to assess variation of geopolymer stabilized residual soil strength based on the varying number of geotextile layers, geotextile arrangement, and confining pressures. It was found that the increase in the number of geotextile layers resulted in a corresponding rise in soil strength and stiffness. It was also discovered that placement of geotextile layers at sample regions which suffered the maximum tensile stress–strain during loading was more effective compared to random placement. Soil strength was observed to reduce with increasing confining pressure which demonstrated the effectiveness of utilizing geotextile reinforcement at greater depths below the ground to be less. Failure patterns showed that while unreinforced soil resulted in failure along a shear plane at an approximate angle of 45 + φ/2 (φ: angle of internal friction), reinforced samples demonstrated a bulging failure where the soil between adjacent layers of geotextiles appeared to bulge. The findings deemed the employment of geopolymer stabilization and geotextile reinforcement on natural residual soil very effective with regards to the enhancement of soil strength and stiffness.
Lei, B, Li, W, Liu, H, Tang, Z & Tam, VWY 2020, 'Synergistic Effects of Polypropylene and Glass Fiber on Mechanical Properties and Durability of Recycled Aggregate Concrete', International Journal of Concrete Structures and Materials, vol. 14, no. 1.
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AbstractTo better understand the synergistic effects of combined fibers on mechanical properties and durability of recycled aggregate concrete (RAC), different types of fibers with various lengths and mass ratios were adopted in this study. Experimental investigations were conducted to study the 28-day compressive strength and strength loss after exposed to salt-solution freeze–thaw cycles and the coupled action of mechanical loading and salt-solution freeze–thaw cycles. The microstructure was also characterized to evaluate the mechanism of this synergistic effect. To determine the effectiveness of the combined fibers on improving the mechanical properties and durability of RAC, the synergistic coefficient was proposed and applied for various combinations of fibers. The results indicate that the incorporation of fibers slightly decreased the 28-day compressive strength of RAC, but combining different sizes and types of fibers can mitigate this negative effect. Moreover, the incorporation of fibers greatly improves the freeze–thaw resistance of RAC. The combining different fibers exhibited a synergistic effect on the enhancement in properties of RAC, which could not be predicted with only one simplistic rule of fibre mixtures. In addition, microstructural characterization shows that the bonding strength of the interfacial transition zone (ITZ) between the fiber and cement matrix is mainly determined by the chemical bonding force which is due to the hydration reaction between fiber surface and cement matrix.
Lei, B, Li, W, Luo, Z, Tam, VWY, Dong, W & Wang, K 2020, 'Performance Enhancement of Permeable Asphalt Mixtures With Recycled Aggregate for Concrete Pavement Application', Frontiers in Materials, vol. 7.
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© Copyright © 2020 Lei, Li, Luo, Tam, Dong and Wang. The incorporation of recycled concrete aggregate (RCA) in permeable asphalt mixtures (PAMs) is an efficient method of utilizing construction demolished waste. It not only conforms to the trend of building sponge cities, but also alleviates the problem of overexploitation of natural aggregate resources. As the performance of PAM containing recycled aggregate is not comparable to natural aggregate, modification treatments and the addition of hybrid fibers are adopted as two enhancement methods to improve the performance of PAM with RAC in this study. It is found that replacing natural aggregate with recycled aggregate increases the optimum asphalt content (OAC) but decreases the residual stability. The OAC is increased by 45% when the RCA ratio is 100%, whereas applying silicone resin can give a 16.2% decrease in the OAC. Enhancing RCA with silicone resin can increase the water stability to be comparable with natural aggregate. Moreover, with modification treatment using calcium hydroxide solution, the mechanical strength of PAM is enhanced to even higher than that of natural coarse aggregate mixture alone. Improvements in both mechanical strength and water stability are also achieved by strengthening recycled aggregate with cement slurry, although the performance is less effective than using silicone resin. With the increase in the content of RCA, the permeability coefficients of PAM first decrease and then exhibit an increasing trend. The results indicate that the PAM with RCA and modification treatments can perform satisfactorily as a pavement material in practice. Applying probable modification, PAM incorporating RCA meets the criteria for use in concrete pavement applications.
Lei, B, Li, W, Tang, Z, Li, Z & Tam, VWY 2020, 'Effects of environmental actions, recycled aggregate quality and modification treatments on durability performance of recycled concrete', Journal of Materials Research and Technology, vol. 9, no. 6, pp. 13375-13389.
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© 2020 The Author(s). The durability performance of recycled concrete (RC) subjected to different environmental actions, including salt-solution, mechanical load, salt-solution freeze-thaw cycles, and coupled mechanical load and salt-solution freeze-thaw cycles was investigated in this paper. To evaluate the effects of recycled aggregate (RA) quality on the RC durability, modeled recycled concrete (MRC) containing modeled recycled aggregate (MRA) with various thickness and coverage of old mortar, along with different degrees of initial damage, was fabricated and tested. Moreover, several modification treatments were employed to study the effects of modification treatments on the RC durability, which included the impregnation of RA with polyvinyl alcohol (PVA) emulsion or nano-SiO2 solutions, and the enhancement of RC with the incorporations of fly ash or hybrid fly ash and silica fume. The results reveal that the deterioration of RC under coupled actions of mechanical load and salt-solution freeze-thaw cycles was the most severe, which was followed by the salt-solution freeze-thaw cycles, mechanical load and salt-solution. The old interface in RA was determined as the weakest zone in RC. With the increase in the thickness or coverage of old mortar, or the initial damage of RA, the durability performance of RC declined, and the effect of initial damage of RA was more significant compared to the thickness or coverage of old mortar. Additionally, modifying RC with 1.5% nano-SiO2 solution or PVA emulsion, and replacing cement with 10% fly ash can significantly enhance the RC durability.
Li, H, Li, Y & Li, J 2020, 'Negative stiffness devices for vibration isolation applications: A review', Advances in Structural Engineering, vol. 23, no. 8, pp. 1739-1755.
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In recent years, negative stiffness vibration isolation device with nonlinear characteristic has become an emerging research area and attracted a significant amount of attentions in the community due to the promising potentials it brought into the field. Its high-static-low-dynamic stiffness property endows the capacity to realize effective vibration isolation and in the meantime to maintain the system stability. This article presents a comprehensive review of the recent research and developments on negative stiffness vibration isolation device. It begins with an introduction on the concept of negative stiffness and then provides a summary and discussion regarding the realization and characteristics of negative stiffness vibration isolation device. The article places its special interest on the principles, structure design, and device characterisation of different types of negative stiffness vibration isolation devices, including spring type, pre-bucked beam type, magnetism type, geometrically nonlinear structural type, and composite structural type. Besides, the applications of negative stiffness vibration isolation device, as well as negative stiffness damper, are summarized and discussed based on the current state-of-the-art. Finally, the conclusions and further discussion provide highlights of the investigation.
Li, P, Gao, X, Wang, K, Tam, VWY & Li, W 2020, 'Hydration mechanism and early frost resistance of calcium sulfoaluminate cement concrete', Construction and Building Materials, vol. 239, pp. 117862-117862.
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© 2019 Elsevier Ltd This study investigated the hydration mechanism and mechanical properties of ordinary Portland cement (OPC) blended with calcium sulfoaluminate (CSA) cement. Heat evolution, hydration products, pore size distribution, and microstructure were investigated for OPC-CSA blends concrete with different contents of CSA cement. Macroscopic properties, such as internal temperature, dynamic elastic modulus, and compressive strength, are also studied through concrete subjected to early frost conditions. The results show that the OPC-CSA blended cement displayed a higher early strength and exhibited enhanced resistance to the early frost damage compared to OPC. The OPC-CSA blended cement also exhibits a higher hydration rate and a larger amount of heat of hydration than that in the OPC at the early stage. The increased heat of hydration can effectively prolong the hydration duration at sub-zero temperatures. However, incorporating CSA delayed the hydration of C3S at the late stage, thus affecting the development of compressive strength and dynamic elastic modulus. On the other hand, the hardened blended cement exhibited an higher porosity, which was corresponding to the increasing proportion of macropores (diameter over 1000 nm). If concrete directly is suffered from early frost after casting, blended cement with 20% of CSA can effectively reduce strength loss from frost damage by 100% at −5 °C, and that from frost damage by 80% at −15 °C respectively. Furthermore, when the calcium nitrite is incorporated as the antifreeze admixture with OPC-CSA blended concrete, the early stage frost resistance of concrete infrastructures can be significantly improved.
Li, P, Li, W, Yu, T, Qu, F & Tam, VWY 2020, 'Investigation on early-age hydration, mechanical properties and microstructure of seawater sea sand cement mortar', Construction and Building Materials, vol. 249, pp. 118776-118776.
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© 2020 Elsevier Ltd Using seawater for concrete manufacturing promisingly provides significant economical and environmental benefits. In this study, ordinary Portland cement (OPC) hydration in distilled water and seawater and the corresponding evolution of solid phases was investigated by heat evolution, hydrated phase, hydration kinetics, and microstructure characterization. The results show that seawater can promote the early hydration of tricalcium silicate (C3S) during the hydration acceleration period. The hydrated phase assemblage was affected by the dissolved ions in seawater. Friedel's salt was detected as a specific hydration phase in seawater, which was formed by chemical combination between the aluminate ferrite monosulfate (AFm) phase and chloride ions. The monocarboaluminate can be converted into a stable phase as Friedel's salt in the seawater, due to the reaction with chloride ions. Furthermore, the ettringite becomes more stable when coexists with Friedel's salt than that with monocarboaluminate, and thus ettringite formed in seawater remains 67% higher than that formed in distilled water at the later curing age. Moreover, additional unhydrated cement and less amorphous calcium silicate hydrate (C-S-H) were formed in seawater, which might be responsible for the slightly lower compressive strength of cement mortar prepared by seawater and sea sand. A modeled evolution of the solid phase and pore solution have been established, which agrees well with the characteristics of the dissolution of mineral phase, precipitation of hydration products and changes of pore solution. The related results can provide an insight into the applications of seawater and sea sand concrete for marine infrastructures.
Li, S, Tian, T, Wang, H, Li, Y, Li, J, Zhou, Y & Wu, J 2020, 'Development of a four-parameter phenomenological model for the nonlinear viscoelastic behaviour of magnetorheological gels', Materials & Design, vol. 194, pp. 108935-108935.
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Li, S, Watterson, PA, Li, Y, Wen, Q & Li, J 2020, 'Improved magnetic circuit analysis of a laminated magnetorheological elastomer device featuring both permanent magnets and electromagnets', Smart Materials and Structures, vol. 29, no. 8, pp. 085054-085054.
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As an essential and critical step, magnetic circuit modelling is usually implemented in the design of efficient and compact magnetorheological (MR) devices, such as MR dampers and MR elastomer isolators. Conventional magnetic circuit analysis simplifies the analysis by ignoring the magnetic flux leakage and magnetic fringing effect. These assumptions are sufficiently accurate in dealing with less complicated designs, featuring short magnetic path lengths such as in an MR damper. However, when dealing with MR elastomer devices, such simplification in magnetic circuit analysis results in inaccuracy of dimensioning and performance estimation of the devices due to their sophisticated design and complex magnetic paths. Modelling permanent magnets also imposes challenges in the magnetic circuit analysis. This work proposes an improved approach to include magnetic flux fringing effect in magnetic circuit analysis for MR elastomer devices. An MRE-based isolator containing multiple MRE layers and both a permanent magnet and an exciting coil was designed and built as a case study. The results of the proposed method are compared to those of conventional magnetic circuit modelling, finite element analysis and experimental measurements to demonstrate the effectiveness of the proposed approach.
Li, W, Dong, W, Shen, L, Castel, A & Shah, SP 2020, 'Conductivity and piezoresistivity of nano-carbon black (NCB) enhanced functional cement-based sensors using polypropylene fibres', Materials Letters, vol. 270, pp. 127736-127736.
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© 2020 Elsevier B.V. The cement-based sensors have a great potential for structural health monitoring, especially functional sensors filled with nano-carbon black (NCB) particles. To improve the sensing efficiency of NCB filled cementitious composite, polypropylene (PP) fibres were premixed with NCB during the manufacturing of cement-based sensor. Although the compressive strength is slightly decreased, the electrical conductivity and piezoresistivity of the NCB filled cementitious composite are improved by PP fibres. Microstructural characterization indicated that NCB attached to the surface of PP fibres significantly promotes the generation of conductive paths and contact points in cement-based sensors. The results can provide a new insight into the application of nonconductive fibres to enhance the conductivity and piezoresistivity of spherical conductors filled cement-based sensor.
Li, W, Tang, Z, Tam, VWY, Zhao, X & Wang, K 2020, 'A Review on Durability of Alkali-activated System from Sustainable Construction Materials to Infrastructures', ES Materials & Manufacturing, vol. 4, pp. 2-19.
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Li, Z, Tao, M, Du, K, Cao, W & Wu, C 2020, 'Dynamic stress state around shallow-buried cavity under transient P wave loads in different conditions', Tunnelling and Underground Space Technology, vol. 97, pp. 103228-103228.
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Liu, K, Li, Q, Wu, C, Li, X & Li, J 2020, 'Optimization of spherical cartridge blasting mode in one-step raise excavation using pre-split blasting', International Journal of Rock Mechanics and Mining Sciences, vol. 126, pp. 104182-104182.
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© 2019 Elsevier Ltd In one-step raise excavation, spherical cartridge blasting mode is easy to be implemented due to minimal requirement of the hole-deviation. Nevertheless, it may induce cumulative damage to the country rock. This study firstly uses a validated rock model (Johnson-Holmquist model) to simulate the damage evolution process of a raise by spherical cartridge blasting mode in LS-DYNA software. Then a field test is carried out to examine the numerical results of spherical cartridge blasting mode. Both the numerical and test results indicate that because of highly confined rock mass and restricted free face in deep raise, a large charge is required in spherical cartridge blasting mode which leads to extensive damage on the wall of the raise. In order to solve such a problem, the pre-split blasting technique is developed to optimize spherical cartridge blasting mode. According to the subsequent numerical results, the improved spherical cartridge blasting mode is successfully applied in another filling raise. This study provides an effective solution to the difficulties that are encountered in one-step raise excavation by spherical cartridge blasting mode.
Liu, K, Wu, C, Li, X, Li, Q, Fang, J & Liu, J 2020, 'A modified HJC model for improved dynamic response of brittle materials under blasting loads', Computers and Geotechnics, vol. 123, pp. 103584-103584.
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Long, G, Xie, Y, Luo, Z, Qu, L, Zhou, JL & Li, W 2020, 'Deterioration mechanism of steam-cured concrete subjected to coupled environmental acid and drying action', Journal of Infrastructure Preservation and Resilience, vol. 1, no. 1, p. 5.
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AbstractIn order to investigate the deterioration mechanism of steam-cured concrete under severe environmental actions such as acid rain corrosion, salt corrosion, and cyclic thermal loading, accelerated corrosion tests were conducted in this study. Surface damage as well as deteriorative kinetics of steam-cured concrete and cement paste suffering from coupled acid-thermal actions was investigated by soaking-drying cycle experiments. The effects of mineral admixture, curing regime and corrosion condition on the durability were all comparatively studied, and the X-ray diffractograms and nanoindentation were applied to analyse the mechanism of corrosion deterioration. The results revealed that compared with the cementitious materials under standard curing, larger depth and faster corrosion were observed for steam-cured concrete and cement paste, which might be partly attributed to the lower content of hydrated production presented in steam-cured specimens. Besides, under acid solution soaking-drying cycle regime, there was significant higher corrosion depth compared to only soaking in acid solution. The corrosion depth under steam curing and soaking-drying condition increased by 156.68% and 44.17%, respectively, compared with those under standard curing and only soaking treatment. In addition, fly ash effectively decreased the corrosion depth of steam-cured cement paste and concrete by 64.98% and 16.33%, respectively.
Lu, Z-H, Wang, H-J, Qu, F, Zhao, Y-G, Li, P & Li, W 2020, 'Novel empirical model for predicting residual flexural capacity of corroded steel reinforced concrete beam', Frontiers of Structural and Civil Engineering, vol. 14, no. 4, pp. 888-906.
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© 2020, Higher Education Press. In this study, a total of 177 flexural experimental tests of corroded reinforced concrete (CRC) beams were collected from the published literature. The database of flexural capacity of CRC beam was established by using unified and standardized experimental data. Through this database, the effects of various parameters on the flexural capacity of CRC beams were discussed, including beam width, the effective height of beam section, ratio of strength between longitudinal reinforcement and concrete, concrete compressive strength, and longitudinal reinforcement corrosion ratio. The results indicate that the corrosion of longitudinal reinforcement has the greatest effect on the residual flexural capacity of CRC beams, while other parameters have much less effect. In addition, six available empirical models for calculating the residual flexural strength of CRC beams were also collected and compared with each other based on the established database. It indicates that though five of six existing empirical models underestimate the flexural capacity of CRC beams, there is one model overestimating the flexural capacity. Finally, a newly developed empirical model is proposed to provide accurate and effective predictions in a large range of corrosion ratio for safety assessment of flexural failure of CRC beams confirmed by the comparisons.
Luo, Z, Li, W, Gan, Y, Mendu, K & Shah, SP 2020, 'Applying grid nanoindentation and maximum likelihood estimation for N-A-S-H gel in geopolymer paste: Investigation and discussion', Cement and Concrete Research, vol. 135, pp. 106112-106112.
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© 2020 Elsevier Ltd Static nanoindentation and Maximum Likelihood Estimation (MLE) were applied for the nano/micromechanical properties investigation of alkali-activated fly ash (AAFA) in this study. Some critical issues of statistical nanoindentation were fully discussed, including properties of pure gel phase, influence of bin size when using least-square estimation (LSE), and suitable number of components for deconvolution. Results indicate that the model estimated by MLE method can effectively reflect the micromechanical distribution of AAFA. The number of components needed to separate sodium aluminosilicate hydrate (N-A-S-H) gels is sometimes more than the normally used 3 or 4, depending on the sample and testing factors. The gel phase does not always display as a prominent peak in the histogram and is easy to be mixed with other adjacent peaks even if the bin size is small, indicating the challenges of employing the LSE method to investigate the gel phase in highly heterogeneous materials, such as geopolymer.
Luo, Z, Li, W, Gan, Y, Mendu, K & Shah, SP 2020, 'Maximum likelihood estimation for nanoindentation on sodium aluminosilicate hydrate gel of geopolymer under different silica modulus and curing conditions', Composites Part B: Engineering, vol. 198, pp. 108185-108185.
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© 2020 Elsevier Ltd As an important inorganic material, geopolymer has been widely used for ceramics and sustainable cement in concrete. Sodium aluminosilicate hydrate (N-A-S-H) gel known as the zeolite precursor gel has the most critical impact on the performance of geopolymer. The nano/micromechanical properties of N-A-S-H have been investigated in several studies, but the resutls are always inconsistent. A novel “compromise approach” using Maximum Likelihood Estimation (MLE) for deconvolution of nanoindentation data is introduced to fundamentally further understand this issue in this study. Correlation and difference of different statistical techniques are compared to clarify the rationality of this method. Multiple characterization techniques including microstructure observation at micro -and nano-scale, element analysis, and crystal identification are applied to reveal the mechanisms. The results indicate that the elastic modulus and hardness of the N-A-S-H gel in geopolymer under different silica modulus and curing conditions vary in a small range from 10.50 to 14.30 GPa and from 0.40 to 0.57 GPa, respectively. When applying statistical nanoindentation in geopolymer, two kinds of spurious phases, mixed phases and sub-phases are unavoidable. For the MLE method adopted, the errors generated from analytical technique were estimated to be only 0.68 and 0.13 GPa for elastic modulus and hardness, respectively.
Ma, M, Tam, VWY, Le, KN & Li, W 2020, 'Challenges in current construction and demolition waste recycling: A China study', Waste Management, vol. 118, pp. 610-625.
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China produced a large amount of construction and demolition (C&D) waste, owing to the rapid development of construction industry. Although a set of policies and regulations are being drafted in China for promoting C&D waste recycling, execution of these policies in practice seems to be far from effective. Currently, approximately 75% of Chinese cities are still surrounded by large volumes of C&D waste. Therefore, identification of challenges in the development of C&D waste management, specially recycling, is essential. This paper employs site visits to 10 recycling plants in 10 Chinese cities (Shanghai, Hangzhou, Suzhou, Chongqing, Chengdu, Xi'an, Changsha, Shenzhen, Nanjing, and Zhoukou) and interviews with 25 industry practitioners for examining the challenges. Eight challenges are identified: (1) unstable source of C&D waste for recycling, (2) absence of subsidies for recycling activities and high cost for land use, (3) insufficient attention paid to design for waste minimisation, (4) absence of regulations on on-site sorting, (5) unregulated landfill activities, (6) a lack of coordination among different government administration departments, (7) a lack of accurate estimation of waste quantity and distribution, and (8) a lack of an effective waste tracing system. Recommendations to address these challenges are presented. The results of this study are expected to aid policy makers in formulation of proper C&D waste management in China and provide a useful reference for researchers who are interested in C&D waste recycling industry.
Meena, NK, Nimbalkar, S, Fatahi, B & Yang, G 2020, 'Effects of soil arching on behavior of pile-supported railway embankment: 2D FEM approach', Computers and Geotechnics, vol. 123, pp. 103601-103601.
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Meng, Q, Wu, C, Hao, H, Li, J, Wu, P, Yang, Y & Wang, Z 2020, 'Steel fibre reinforced alkali-activated geopolymer concrete slabs subjected to natural gas explosion in buried utility tunnel', Construction and Building Materials, vol. 246, pp. 118447-118447.
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© 2020 Elsevier Ltd Accidental gas explosions in the buried utility tunnels around the world have caused massive losses in economy and human lives. The buried utility tunnel with adequate blast resistance capacity is therefore required to withstand the possible accidental gas explosions. In this study, a novel construction material, alkali-activated steel fibre reinforced geopolymer composite is introduced and the blast resistance capacity of slabs made of this material is studied in a full-scale buried utility tunnel. Fly ash and S95 grade ground granulated blast-furnace slag powder (GGBS) were used as the major binders in this geopolymer concrete. The plain geopolymer concrete had a compressive strength of 61 MPa and the steel fibre reinforced geopolymer concrete had a compressive strength of 74 MPa. The elastic modulus of the plain geopolymer concrete was found to be lower than the conventional C30 concrete. The methane gas explosion test was conducted in a full-scale (12 m × 1.8 m × 0.6 m) tunnel segment to investigate the structural performance of selected slab specimen (1.8 m × 0.4 m × 0.09 m). The test results and numerical simulations of structural responses subjected to methane gas explosion are presented. The results indicate the fibre reinforced geopolymer concrete slab has good capacity to resist methane gas explosion load.
Meng, Q, Wu, C, Li, J, Liu, Z, Wu, P, Yang, Y & Wang, Z 2020, 'Steel/basalt rebar reinforced Ultra-High Performance Concrete components against methane-air explosion loads', Composites Part B: Engineering, vol. 198, pp. 108215-108215.
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© 2020 Elsevier Ltd Ultra-High Performance Concrete (UHPC) is a relatively new construction material, which has been investigated over the past few decades. Despite its exceptional mechanical strength, UHPC still requires passive steel reinforcement to maximise its bending capacity and the overall material cost will be high. The basalt fibre rebar has a higher mechanical strength than steel rebar with lower cost. In addition, it also has better alkali resistance and good cost-effectiveness. The basalt fibre rebar is therefore considered as a potential alternative reinforcement in the structural member. In this study, a recently developed UHPC formula was adopted, the conventional steel rebar and basalt fibre rebar were used as reinforcement. The developed components were tested against static flexural and methane-air explosion loads. In the four-point flexural tests, the basalt fibre rebar reinforced specimen (400 mm × 100 mm × 100 mm) performed more ductile structural behaviour with higher flexural strength. Two large scale methane-air explosion tests were conducted in buried utility tunnels with different length (i.e., 12000 mm × 1800 mm × 600 mm and 20000 mm × 1800 mm × 600 mm). The experimental test in shorter tunnel yielded lower explosion pressure [1] with marginal structural response. The test in longer tunnel achieved a higher explosion pressure on concrete elements. The C30 and UHPC specimens (1800 mm × 400 mm × 90 mm) with steel/basalt fibre rebar reinforcement were tested. The pressure and deflection data revealed that basalt fibre rebar reinforced UHPC component had a more ductile structural behaviour against accidental gas explosion.
Mi, Y, Liu, Z, Wang, W, Yang, Y & Wu, C 2020, 'Experimental study on residual axial bearing capacity of UHPFRC-filled steel tubes after lateral impact loading', Structures, vol. 26, pp. 549-561.
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Ngoc, TP, Fatahi, B, Khabbaz, H & Sheng, D 2020, 'Impacts of matric suction equalization on small strain shear modulus of soils during air drying', Canadian Geotechnical Journal, vol. 57, no. 12, pp. 1982-1997.
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In this study, a weight-control bender element system has been developed to investigate the impact of matric suction equalization on the measurement of small strain shear modulus (Gmax) during an air-drying process. The setup employed is capable of measuring the shear wave velocity and the corresponding Gmax of the soil sample in either an open system in which the soil sample evaporates freely or in a closed system that allows the process of matric suction equalization. The comparison between measurements of Gmax in the open and closed systems revealed underestimations of Gmax when matric suction equalization was ignored due to the nonuniform distribution of water content across the sample cross-sectional area. This study also investigated the time required for matric suction equalization tse to be established for samples with different sizes. The experimental results indicated two main mechanisms driving the matric suction equalization in a closed system during an air-drying process, namely the hydraulic flow of water and the flow of vapour. While the former played the key role when the micropores were still saturated at the high range of water content, effects of the latter increased and finally dominated when more air invaded the micropores at lower water contents.
Nguyen, DM, Ding, G & Runeson, G 2020, 'Energy and economic analysis of environmental upgrading of existing office buildings', Construction Economics and Building, vol. 20, no. 4, pp. 82-102.
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Over many decades, buildings have been recognised as a significant area contributing to the negative impacts on the environment over their lifecycle, accelerating climate change. In return, climate change also impacts on buildings with extreme heatwaves occurring more frequently and raising the earth’s temperature. The operation phase is the most extended period over a building’s lifespan. In this period, office buildings consume most energy and emit the highest amount of greenhouse gas pollution into the environment. Building upgrading to improve energy efficiency seems to be the best way to cut pollution as the existing building stock is massive. The paper presents an economic analysis of energy efficiency upgrade of buildings with a focus of office buildings. The paper identifies upgrading activities that are commonly undertaken to upgrade energy efficiency of office buildings and a case study of three office buildings in Sydney, Australia has been used to analyse the results. The upgrading activities can improve the energy performance of the case study buildings from 3 stars to 5 stars NABERS energy rating in compliance with the mandatory requirement in the Australian government’s energy policy. With the potential increase in energy price, energy efficiency upgrading will become more affordable, but currently, most of them, except solar panels and motion sensors show a negative return and would not be undertaken if they did not also contribute to higher rental income and an increased life span of the building. The upgrading discussed in the paper represent a potentially attractive alternative to demolition and building anew.
Nguyen, TN, Emre Erkmen, R, Sanchez, LFM & Li, J 2020, 'Stiffness Degradation of Concrete Due to Alkali-Silica Reaction: A Computational Homogenization Approach', ACI Materials Journal, vol. 117, no. 6, pp. 65-76.
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Alkali-silica reaction (ASR) is one of the most harmful distress mechanisms affecting concrete infrastructure worldwide. ASR is a chemical reaction that generates a secondary product, which induces expansive pressure within the reacting aggregate material and adjacent cement paste upon moisture uptake, leading to cracking, loss of material integrity, and functionality of the affected structure. In this work, a computational homogenization approach is proposed to model the impact of ASR-induced cracking on concrete stiffness as a function of its development. A representative volume element (RVE) of the material at the mesoscale is developed, which enables the input of the cracking pattern and extent observed from a series of experimental testing. The model is appraised on concrete mixtures presenting different mechanical properties and incorporating reactive coarse aggregates. The results have been compared with experimental results reported in the literature. The case studies considered for the analysis show that stiffness reduction of ASR-affected concrete presenting distinct damage degrees can be captured using the proposed mesoscale model as the predictions of the proposed methodology fall in between the upper and lower bounds of the experimental results.
Nimbalkar, S, Kolay, PK & Sun, Y 2020, 'Editorial: Geotechnical Innovation for Transport Infrastructures', Frontiers in Built Environment, vol. 6.
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Nimbalkar, S, Pain, A & Annapareddy, VSR 2020, 'A Strain Dependent Approach for Seismic Stability Assessment of Rigid Retaining Wall', Geotechnical and Geological Engineering, vol. 38, no. 6, pp. 6041-6055.
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© 2020, Springer Nature Switzerland AG. A new method is proposed to evaluate the seismic stability of a rigid retaining wall undergoing translation or rotational failure. In the present method, strain-dependent dynamic properties are used to assess the seismic stability of rigid retaining walls against sliding and overturning failure conditions. The effect of foundation soil properties on the stability of retaining walls is also considered. From the parametric study, it is observed that the foundation soil properties have a significant effect on both sliding and rotational stability of rigid retaining walls. This can be attributed to the use of strain-dependent dynamic properties and the consideration of foundation soil properties. The predictions of the proposed method are compared and verified against the results from other methods proposed in the past. The percentage increase in the results compared to the existing literature is a maximum of 10 and 28% for rigid (bedrock) and flexible (sand deposit) foundation, respectively.
Ou, T, Wang, D, Xin, Z, Tan, J, Wu, C, Guo, Q & Zhang, Y 2020, 'Full-scale tests on the mechanical behaviour of a continuously welded stainless steel roof under wind excitation', Thin-Walled Structures, vol. 150, pp. 106680-106680.
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© 2020 Elsevier Ltd The wind uplift performance of the continuously welded stainless steel roof (CWSSR) system adopted in the Zhaoqing New District Sports (ZNDS) Center of China is investigated in this study. To determine the optimal welding program and examine the mechanical properties of the continuously welded stainless steel joints, uniaxial tensile testing is first conducted on 27 specimens with tension-shear and tension-bending types. Two CWSSR specimens, one that is square-shaped with a horizontal layout and one that is rectangular-shaped with an inclination layout of 10.71°, are further tested under dynamic and static ultimate wind uplift loadings to explore the wind uplift capacity. All specimens are full-size, and the corresponding materials, structural details and construction technologies are kept the same as the actual building to ensure the authenticity of the testing investigations. The testing results indicate that the integrated and sealed CWSSR system has a clear force transmission mechanism and a remarkable wind resistance performance. The welded joints achieve the best performance, and the mechanical behaviours are equivalent to those of the base material under the continuously welded conditions including an electric current of 65 A and a moving velocity of 750 mm/s. An excellent dynamic wind suction performance is achieved under 5000 five-level cumulative loading cycles with a maximum pressure of 5400 Pa. The static ultimate pressure reaches 9400 Pa for the square specimen and 10,400 Pa for the rectangular specimen. Damage observations show that no tearing or rupture failures are observed for the CWSSR system. The investigation results contribute the most to the safe design of the ZNDS Center and are expected to provide guidelines for future applications of the CWSSR system.
Pain, A, Nimbalkar, S & Hussain, M 2020, 'Applicability of Bouc-Wen Model to Capture Asymmetric Behavior of Sand at High Cyclic Shear Strain', International Journal of Geomechanics, vol. 20, no. 6, pp. 06020009-06020009.
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Pardeshi, V, Nimbalkar, S & Khabbaz, H 2020, 'Field Assessment of Gravel Loss on Unsealed Roads in Australia', Frontiers in Built Environment, vol. 6, pp. 1-11.
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The gravel loss is a major limitation for unsealed roads and it needs major maintenance annually. The continual process of gravel loss leads to the unsustainability of these roads. The unsealed road management faces several issues, viz., difficulty to forecast behavior, huge data collection needs, and a vulnerability in the service and maintenance practices. The quality of gravel material also plays a major role in the process of gravel loss. In view of the aforementioned, appropriate revisions to ARRB material specifications are proposed in this study. The gravel material as per modified ARRB specifications is used on the unsealed road network in the Scenic Rim Regional Council in the state of Queensland. Gravel loss monitoring stations were established over the entire region in order to assess the gravel loss and the implication of using a better quality of gravel material. This study discusses the gravel loss monitoring approaches, data analyses, and improved material specification for gravel. It is found that the modified gravel used on unsealed road performs better than conventionally used gravel.
Phung, MD & Ha, QP 2020, 'Motion-encoded particle swarm optimization for moving target search using UAVs', Applied Soft Computing, vol. 97, pp. 106705-106705.
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Punetha, P, Nimbalkar, S & Khabbaz, H 2020, 'Analytical Evaluation of Ballasted Track Substructure Response under Repeated Train Loads', International Journal of Geomechanics, vol. 20, no. 7, pp. 04020093-04020093.
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© 2020 American Society of Civil Engineers. The irrecoverable deformations in the substructure layers are detrimental to the track stability and demand frequent maintenance. With an escalation in axle load and traffic volume, the frequency of maintenance operations has remarkably increased. Consequently, there is an inevitable need to predict the long-term behavior of the track substructure layers. This article presents a methodology to evaluate the recoverable and irrecoverable responses of the substructure layers under the train-induced repetitive loads. The present method utilizes an integrated approach combining track loading, resiliency, and settlement models. The track substructure layers are simulated as lumped masses that are connected by springs and dashpots. The method is successfully validated against the field investigation data reported in the literature. A parametric study is conducted to investigate the influence of substructure layer properties on the track response. The results reveal that the response of each track layer is significantly influenced by the neighboring layer properties and the incorporation of multilayered track structure enables more accurate prediction of track behavior. The present analytical approach is simple, computationally efficient and may assist the practicing engineers in the safer design of the ballasted track.
Punetha, P, Nimbalkar, S & Khabbaz, H 2020, 'Evaluation of additional confinement for three-dimensional geoinclusions under general stress state', Canadian Geotechnical Journal, vol. 57, no. 3, pp. 453-461.
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Three-dimensional cellular geoinclusions (e.g., geocells, scrap tires) offer all-around confinement to the granular infill materials, thus improving their strength and stiffness. The accurate evaluation of extra confinement offered by these geoinclusions is essential for predicting their performance in the field. The existing models to evaluate the additional confinement are based on either a plane-strain or axisymmetric stress state. However, these geoinclusions are more likely to be subjected to the three-dimensional stresses in actual practice. This note proposes a semi-empirical model to evaluate the additional confinement provided by cellular geoinclusions under the three-dimensional stress state. The proposed model is successfully validated against the experimental data. A parametric study is conducted to investigate the influence of input parameters on additional confinement. Results reveal that the simplification of the three-dimensional stress state into axisymmetric or plane-strain condition has resulted in inaccurate and unreliable results. The extra confinement offered by the geoinclusion shows substantial variation along the intermediate and minor principal stress directions depending on the intermediate principal stress, infill soil, and geoinclusion properties. The magnitude of additional confinement increases with an increase in the geoinclusion modulus. The findings are crucial for accurate assessment of the in situ performance of three-dimensional cellular geoinclusions.
Qu, F, Li, W, Tao, Z, Castel, A & Wang, K 2020, 'High temperature resistance of fly ash/GGBFS-based geopolymer mortar with load-induced damage', Materials and Structures, vol. 53, no. 4.
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© 2020, RILEM. This study investigated the effect of elevated temperatures on the residual mechanical behaviors of geopolymer mortars with initial damage induced by mechanical load. Geopolymer mortar was prepared using different fly ash/ ground granulated blast furnace slag (GGBFS) ratios and was activated by sodium silicate and sodium hydroxide solution. The physical properties and residual mechanical strength were investigated and compared with those of Portland cement mortar (PCM). After elevated temperature exposure, microstructure of GSM was studied by various microcharacterizations. The results show that before the exposure to high temperature, the addition of GGBFS increased the compressive strength of GSM, but made it more sensitive to the preloading damage, leading to the increased strength loss. After exposed to combined preloading damage and high temperature exposure, the GSM exhibited lower residual strength than the ones only suffered from preloading damage or high temperature exposure. Compared to the PCM, GSM with GGBFS performed better at temperature of 300 °C, but became worse at temperatures of 500 and 700 °C due to severe damage caused by combined high load level and large heat exposure. Finally, a low percentage of GGBFS (less than 20%) can be considered as an optimal amount for the GSM to achieve excellent fire resistance capacity.
Qu, F, Li, W, Zeng, X, Luo, Z, Wang, K & Sheng, D 2020, 'Effect of microlimestone on properties of self-consolidating concrete with manufactured sand and mineral admixture', Frontiers of Structural and Civil Engineering, vol. 14, no. 6, pp. 1545-1560.
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© 2020, Higher Education Press. Self-consolidating concrete (SCC) with manufactured sand (MSCC) is crucial to guarantee the quality of concrete construction technology and the associated property. The properties of MSCC with different microlimestone powder (MLS) replacements of retreated manufactured sand (TMsand) are investigated in this study. The result indicates that high-performance SCC, made using TMsand (TMSCC), achieved high workability, good mechanical properties, and durability by optimizing MLS content and adding fly ash and silica fume. In particular, the TMSCC with 12% MLS content exhibits the best workability, and the TMSCC with 4% MLS content has the highest strength in the late age, which is even better than that of SCC made with the river sand (Rsand). Though MLS content slightly affects the hydration reaction of cement and mainly plays a role in the nucleation process in concrete structures compared to silica fume and fly ash, increasing MLS content can evidently have a significant impact on the early age hydration progress. TMsand with MLS content ranging from 8% to 12% may be a suitable alternative for the Rsand used in the SCC as fine aggregate. The obtained results can be used to promote the application of SCC made with manufactured sand and mineral admixtures for concrete-based infrastructure.
Rasouli, H & Fatahi, B 2020, 'Geofoam blocks to protect buried pipelines subjected to strike-slip fault rupture', Geotextiles and Geomembranes, vol. 48, no. 3, pp. 257-274.
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© 2019 Elsevier Ltd This paper proposes using geofoam blocks to improve the safety of buried steel pipelines under permanent ground deformation due to strike-slip fault rupture. Since these geofoam blocks are deformable, they can compress during fault rupture and thus reduce the pressure imposed on the pipeline by the surrounding soil. This means that the pipe can sustain a higher level of tectonic deformations. For the pipeline system adopted in this study, the geofoam blocks consist of two 1 m thick blocks at each side and another on the top of the pipeline. The effectiveness of this configuration is then assessed in comparison to the conventional buried pipeline by three dimensional numerical simulations that consider the interaction between soil and structure and the impact of critical parameters such as the pipeline-fault trace crossing angle, geofoam blocks thickness and the internal pressure of the pipeline. The results indicated that the geofoam blocks reduced the axial tensile strain of non-pressurised pipeline from the unacceptable 4.16% to the safe level of 0.75% when the crossing angle was 135°. In addition, geofoam blocks successfully decreased the maximum ovalisation parameter and compressive strain of the non-pressurised pipeline from 0.237 and −25.8% to 0.065 and −0.47%, respectively when the crossing angle was 65°.
Rasouli, H, Fatahi, B & Nimbalkar, S 2020, 'Liquefaction and post-liquefaction assessment of lightly cemented sands', Canadian Geotechnical Journal, vol. 57, no. 2, pp. 173-188.
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Post-liquefaction response of lightly cemented sands during an earthquake may change and become similar to uncemented sands due to bonding breakage. In the current study, the effect of degree of cementation on liquefaction and post-liquefaction behaviour of lightly cemented sands was studied through a series of cyclic and monotonic triaxial tests. Portland cement with high early strength and Sydney sand were used to reconstitute the lightly cemented specimens with unconfined compression strength ranging from 25 to 220 kPa. A series of multi-stage soil element tests including stress-controlled cyclic loading events with different amplitudes and post-cyclic undrained monotonic shearing tests were carried out on both uncemented and cemented specimens. Furthermore, a series of undrained monotonic shearing tests without cyclic loading history on different types of specimens was conducted to investigate the effect of cyclic loading history on the post-cyclic response of the specimens. The results show that residual excess pore-water pressure is correlated to the cyclic degradation of lightly cemented sands during cyclic loading. In addition, optical microstructure images of the cemented specimens after liquefaction showed that a major proportion of cementation bonds remained unbroken, which resulted in a superior post-liquefaction response with respect to initial stiffness and shear modulus in comparison to the uncemented sand.
Sadeghi, F, Li, J & Zhu, X 2020, 'A Steel-Concrete Composite Beam Element for Structural Damage Identification', International Journal of Structural Stability and Dynamics, vol. 20, no. 10, pp. 2042015-2042015.
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The composite action between the layers of steel and concrete is governed by the shear connection. Because of the complicated interconnection behavior of these composite layers, it is difficult to detect damage in the composite structures, especially, the interfacial integrity of the two layers. In this paper, anovel method has been developed for structural damage identification of composite structures based on a steel-concrete composite beam element with bonding interface. In displacement-based finite element (FE) formulation, three damage indicators have been embedded into stiffness matrix of the composite beam that are defined as a stiffness reduction in the concrete, steel and interface layers. An algorithm-based on recursive quadratic programming has been proposed to identify structural damage in the composite beam from static measurements. The analytical FE model is validated by adapting its static responses in undamaged state with those obtained from an equal experimental model as well as a FE model developed in commercial software ABAQUS. A convergence study is conducted to determine the number of the composite beam FEs. To verify the proposed method, the static responses of the FE model with different damage cases at a given loading are calculated, and the measurements are simulated by adding different levels of white noise. Then, the proposed algorithm is applied to identify damage of the composite beam. The effects of measurement noise, loading location and amplitude, measurement numbers and the sizes of FE mesh on the identified results have been investigated. The numerical results show that this method is efficient and accurate to separately identify small damage in the concrete slab, and the steel girder and bonding interface of the composite beam.
Senanayake, S, Pradhan, B, Huete, A & Brennan, J 2020, 'A Review on Assessing and Mapping Soil Erosion Hazard Using Geo-Informatics Technology for Farming System Management', Remote Sensing, vol. 12, no. 24, pp. 4063-4063.
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Soil erosion is a severe threat to food production systems globally. Food production in farming systems decreases with increasing soil erosion hazards. This review article focuses on geo-informatics applications for identifying, assessing and predicting erosion hazards for sustainable farming system development. Several researchers have used a variety of quantitative and qualitative methods with erosion models, integrating geo-informatics techniques for spatial interpretations to address soil erosion and land degradation issues. The review identified different geo-informatics methods of erosion hazard assessment and highlighted some research gaps that can provide a basis to develop appropriate novel methodologies for future studies. It was found that rainfall variation and land-use changes significantly contribute to soil erosion hazards. There is a need for more research on the spatial and temporal pattern of water erosion with rainfall variation, innovative techniques and strategies for landscape evaluation to improve the environmental conditions in a sustainable manner. Examining water erosion and predicting erosion hazards for future climate scenarios could also be approached with emerging algorithms in geo-informatics and spatiotemporal analysis at higher spatial resolutions. Further, geo-informatics can be applied with real-time data for continuous monitoring and evaluation of erosion hazards to risk reduction and prevent the damages in farming systems.
Senanayake, S, Pradhan, B, Huete, A & Brennan, J 2020, 'Assessing Soil Erosion Hazards Using Land-Use Change and Landslide Frequency Ratio Method: A Case Study of Sabaragamuwa Province, Sri Lanka', Remote Sensing, vol. 12, no. 9, pp. 1483-1483.
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This study aims to identify the vulnerable landscape areas using landslide frequency ratio and land-use change associated soil erosion hazard by employing geo-informatics techniques and the revised universal soil loss equation (RUSLE) model. Required datasets were collected from multiple sources, such as multi-temporal Landsat images, soil data, rainfall data, land-use land-cover (LULC) maps, topographic maps, and details of the past landslide incidents. Landsat satellite images from 2000, 2010, and 2019 were used to assess the land-use change. Geospatial input data on rainfall, soil type, terrain characteristics, and land cover were employed for soil erosion hazard classification and mapping. Landscape vulnerability was examined on the basis of land-use change, erosion hazard class, and landslide frequency ratio. Then the erodible hazard areas were identified and prioritized at the scale of river distribution zones. The image analysis of Sabaragamuwa Province in Sri Lanka from 2000 to 2019 indicates a significant increase in cropping areas (17.96%) and urban areas (3.07%), whereas less dense forest and dense forest coverage are significantly reduced (14.18% and 6.46%, respectively). The average annual soil erosion rate increased from 14.56 to 15.53 t/ha/year from year 2000 to 2019. The highest landslide frequency ratios are found in the less dense forest area and cropping area, and were identified as more prone to future landslides. The river distribution zones Athtanagalu Oya (A-2), Kalani River-south (A-3), and Kalani River- north (A-9), were identified as immediate priority areas for soil conservation.
Shakor, P, Nejadi, S & Paul, G 2020, 'Investigation into the effect of delays between printed layers on the mechanical strength of inkjet 3DP mortar', Manufacturing Letters, vol. 23, pp. 19-22.
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© 2019 Currently, additive manufacturing have enabled to fabricate the three-dimensional models. 3D-Printing technique is a multipurpose process for producing structural members using a sequential layering approach. The “feature quality” of 3DP specimens can be improved by optimising the build constraints. In this paper, a mortar mix powder-base has been prepared that consists of cementitious materials. Experiments are conducted to investigate the effects of different delays in printing time on the mechanical properties of the scaffolds. It has been shown that the compressive stress and strength of printed specimens with a delay of 200 ms were greater than specimens with other delay values.
Shakor, P, Nejadi, S, Paul, G & Sanjayan, J 2020, 'Dimensional accuracy, flowability, wettability, and porosity in inkjet 3DP for gypsum and cement mortar materials', Automation in Construction, vol. 110, pp. 102964-102964.
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© 2019 Inkjet (powder-based) 3D Printing is a popular and widely used technology, which can be applied to print a wide range of specimens using different powder materials. This paper discusses the use of inkjet 3DP technology for construction applications using custom-made powder instead of commercial gypsum powder (ZP 151). The paper aims to address the differences between ZP 151 and CP (a custom-made construction-specific cement mortar powder) with regard to powder flowability, wettability, powder bed porosity and apparent porosity in 3DP specimens. An inkjet 3D printer is employed and experimental results verify that ZP 151 has a lower angle of repose, a higher contact angle and noticeably less porosity in the powder bed compared with the CP powder. Additionally, specimens printed with ZP 151 have a lower apparent porosity compared with CP specimens. The wettability for each of the powders was tested using contact angle goniometer, while the Optronis Cam-Recorder was used at 1000 fps at 800 × 600 pixel resolution images for the powder flowability tests. The bulk density tester was utilised to find the apparent porosity in the printed specimens. The paper also discusses the details of the printing procedure and dimensional accuracy of printed specimens.
Shakor, P, Nejadi, S, Sutjipto, S, Paul, G & Gowripalan, N 2020, 'Effects of deposition velocity in the presence/absence of E6-glass fibre on extrusion-based 3D printed mortar', Additive Manufacturing, vol. 32, pp. 101069-101069.
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© 2020 Additive Manufacturing (AM) technologies are widely used in various fields of industry and research. Continual research has enabled AM technologies to be considered as a feasible substitute for certain applications in the construction industry, particularly given the advances in the use of glass fibre reinforced mortar. An investigation of the resulting mechanical properties of various mortar mixes extruded using a robotic arm is presented. The nozzle paths were projected via ‘spline’ interpolation to obtain the desired trajectory and deposition velocity in the reference frame of the manipulator. Along each path, various mortar mixes, with and without chopped glass fibre, were deposited at different velocities. Tests were conducted to determine their mechanical performance when incorporated in printed structures with different layers (1, 2, 4 and 6 layers). The results are compared with those of conventional cast-in-place mortar. In this study, the mixes consist of ordinary Portland cement, fine sand, chopped glass fibres (6 mm) and chemical admixtures, which are used to print prismatic- and cubic-shaped specimens. Mechanical strength tests were performed on the printed specimens to evaluate the behaviour of the materials in the presence and absence of glass fibre. Robot end-effector velocity tests were performed to examine the printability and extrudability of the mortar mixes. Finally, horizontal and vertical line printing tests were used to determine the workability, buildability and uniformity of the mortar mix and to monitor the fibre flow directions in the printed specimens. The results show that printed specimens with glass fibre have enhanced compressive strength compared with specimens without glass fibre.
Singh, RP, Nimbalkar, S, Singh, S & Choudhury, D 2020, 'Field assessment of railway ballast degradation and mitigation using geotextile', Geotextiles and Geomembranes, vol. 48, no. 3, pp. 275-283.
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© 2019 Elsevier Ltd Rail tracks continue to deform due to degradation of ballast under the application of heavy train traffic. The resulting track deformations often lead to drainage impairment as well as loss of resiliency. For track replenishment, deep screening of ballast is usually adopted by Indian Railway (IR) either after 10 years or passage of 500 MGT traffic, whichever is earlier. To study the effectiveness of geotextile on track stability and assess possible reductions in maintenance costs, a layer of woven geotextile was installed at the ballast-subgrade interface in Bhusawal-Akola central railway section of IR which is the present study area. The results show that the amount of degradation and fouling are different in UP and DN tracks due to inherent variation in traffic characteristics. This study also shows that the placement of geotextile in the track has led to prolonged maintenance cycle with favorable implications on cost and track shutdown periods. The findings of the present case study results will be useful for IR to reduce the ballast procurement and reuse of discarded material during deep screening in future.
Tam, VWY, Butera, A, Le, KN & Li, W 2020, 'Utilising CO2 technologies for recycled aggregate concrete: A critical review', Construction and Building Materials, vol. 250, pp. 118903-118903.
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© 2020 Elsevier Ltd Employment of recycled aggregate within concrete provides great potential for the reduction of landfilling. Unfortunately, recycled aggregate exhibits a high porosity and water absorption and consequently produces a substandard material when compared to the mainstream virgin aggregate concrete. Recently, the injection of CO2 into cementitious materials has been studied, for both improving the overall quality of recycled aggregate concrete as well as permanently chemically converting CO2 into stone. CO2 treatment can permit recycled aggregate concrete to rival virgin aggregate concrete in phycial and mechanical properties. Currently, there are two primary methodologies for the sequestration of CO2 into concrete: (1) carbon-conditioning is the injection of CO2 into recycled aggregate; and (2) carbon-curing involves sequestering CO2 into new concrete's cement paste. Whilst both technologies permit recycled aggregate concrete for achieving great mechanical property and durability, carbon-conditioning provides a practical implementation. Carbon-conditioning permits a prompt and complete carbonation of recycled aggregate which enhances the final concrete's mechanical property and durability. This paper provides an insight into the available CO2 technologies for concrete improvement.
Tan, X, Hu, Z, Li, W, Zhou, S & Li, T 2020, 'Micromechanical Numerical Modelling on Compressive Failure of Recycled Concrete using Discrete Element Method (DEM)', Materials, vol. 13, no. 19, pp. 4329-4329.
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This paper investigates the failure processes of recycled aggregate concrete by a model test and numerical simulations. A micromechanical numerical modeling approach to simulate the progressive cracking behavior of the modeled recycled aggregate concrete, considering its actual meso-structures, is established based on the discrete element method (DEM). The determination procedure of contact microparameters is analyzed, and a series of microscopic contact parameters for different components of modeled recycled aggregate concrete (MRAC) is calibrated using nanoindentation test results. The complete stress–strain curves, cracking process, and failure pattern of the numerical model are verified by the experimental results, proving their accuracy and validation. The initiation, growth, interaction, coalescence of microcracks, and subsequent macroscopic failure of the MRAC specimen are captured through DEM numerical simulations and compared with digital image correlation (DIC) results. The typical cracking modes controlled by meso-structures of MRAC are concluded according to numerical observations. A parameter study indicates the dominant influence of the macroscopic mechanical behaviors from the shear strength of the interfacial transition zones (ITZs).
Tang, Z, Li, W, Tam, VWY & Luo, Z 2020, 'Investigation on dynamic mechanical properties of fly ash/slag-based geopolymeric recycled aggregate concrete', Composites Part B: Engineering, vol. 185, pp. 107776-107776.
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By harnessing the benefits from both construction and demolition waste recycling and geopolymer binders, geopolymeric recycled aggregate concrete (GRAC) can contribute to the green and eco-friendly construction material products. In this study, the compressive behavior of GRAC based on fly ash and slag was experimentally investigated under both quasi-static and dynamic loadings. Quasi-static compressive tests were performed by using a high-force servo-hydraulic test system, while dynamic compressive tests were carried out by using a Ø80-mm split Hopkinson pressure bar (SHPB) apparatus. The compressive properties of GRAC under dynamic loading, including stress-strain curves, energy absorption capability, and failure modes were obtained and compared with those under quasi-static loading. The results show that the compressive properties of GRAC exhibit a strong strain rate dependency. Although the recycled aggregate replacement decreases the quasi-static compressive strength, it exhibits a slight effect on the compressive strength at high strain rates. The dynamic increase factor (DIF) for compressive strength exhibits an significant increasing trend with the recycled aggregate replacement. On the other hand, the incorporation of slag increases the quasi-static compressive strength, dynamic compressive strength, and DIF. As for the energy absorption capacity, a minor enhancement is achieved with the recycled aggregate replacement, while a significant improvement is identified after the inclusion of slag. Empirical DIF formulae for compressive strength of GRAC are proposed, in which the DIF increases approximately linearly with the strain rate in a logarithmic manner.
Tang, Z, Li, W, Tam, VWY & Xue, C 2020, 'Advanced progress in recycling municipal and construction solid wastes for manufacturing sustainable construction materials', Resources, Conservation & Recycling: X, vol. 6, pp. 100036-100036.
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© 2020 The sharply increasing solid waste generation has raised the environmental concerns worldwide which currently have been escalated to a worrying level. Intending to eliminate the negative environmental impacts of solid waste and meanwhile promote sustainability on the energy- and resource-intensive construction and building sector, considerable efforts have been devoted to recycling solid waste for the possible use in sustainable construction material products. This paper reviews the existing studies on recycling municipal and construction solid waste for the manufacture of geopolymer composites. Special attention is paid to the predominate performance of these geopolymer composite products. The principal findings of this work reveal that municipal and construction solid waste could be successfully incorporated into geopolymer composites in the forms of precursor, aggregate, additive, reinforcement fiber, or filling material. Additionally, the results indicate that although the inclusion of such waste might depress some of the attributes of geopolymer composites, proper proportion design and suitable treatment technique could alleviate these detrimental effects and further smooth the recycling progress. Finally, a brief discussion is provided to identify the important needs in the future research and development for promoting the utilization of solid waste materials in the forthcoming sustainable geopolymer industry. In summary, this work offers guidance for the better ecological choice to municipal and construction solid waste through developing waste materials into highly environmental-friendly construction materials.
Tang, Z, Li, W, Tam, VWY & Yan, L 2020, 'Mechanical behaviors of CFRP-confined sustainable geopolymeric recycled aggregate concrete under both static and cyclic compressions', Composite Structures, vol. 252, pp. 112750-112750.
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© 2020 Elsevier Ltd Geopolymeric recycled aggregate concrete (GRAC) can greatly facilitate sustainability in the construction industry by the simultaneous utilization of solid waste-based recycled aggregate and eco-friendly binder–geopolymer. This study presents an experimental investigation on the mechanical behaviors of GRAC confined by carbon fiber-reinforced polymer (CFRP) jackets under both monotonic and cyclic compressive loading. A total of 24 CFRP-confined GRAC specimens were fabricated and tested, in which four aggregate replacement ratios (i.e., 0%, 25%, 50%, and 100%) and two thicknesses of CFRP jackets (i.e., 1 and 2 layers) were considered. The failure patterns, compressive stress-strain behavior, and axial-lateral strain responses of CFRP-confined GRAC were investigated and compared. The characteristics of stress-strain relationships were also discussed in terms of the peak stress, ultimate strain, residual modulus, plastic strain, reloading modulus, and stress deterioration ratio. Moreover, the related results were analyzed by comparing to the prediction ones of the existing models for FRP-confined concrete, to evaluate their applicability and accuracies for CFRP-confined GRAC. The outcomes will enrich the experimental database of CFRP-confined concrete and provide insights into the practical application of CFRP-confined GRAC.
Tang, Z, Li, W, Tam, VWY & Yan, L 2020, 'Mechanical performance of CFRP-confined sustainable geopolymeric recycled concrete under axial compression', Engineering Structures, vol. 224, pp. 111246-111246.
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© 2020 Elsevier Ltd Sustainable geopolymeric recycled aggregate concrete (RAC) by utilizing environmentally-friendly binder-geopolymer and constructional solid waste-recycled aggregate (RA) will facilitate the sustainability in concrete industry. This study investigated the compressive behavior of sustainable geopolymeric RAC confined by carbon fiber-reinforced polymer (CFRP) jackets. A total of 72 cylindrical fly ash/slag-based geopolymeric concrete specimens, including 48 CFRP-confined specimens and 24 unconfined specimens were fabricated and tested. The testing variables included: coarse aggregate type (i.e., natural aggregate and RA), thickness of CFRP jackets (i.e., 1, 2, and 3 layers) and (iii) slag content (i.e., 0, 10%, 20% and 30% of the total binder by mass). The results indicate that the CFRP confinement remarkably enhances the compressive strength and ultimate strain of geopolymeric concrete, and the enhancement is more pronounced with the increase of CFRP jacket thickness. Moreover, the RA replacement and the inclusion of slag have minor influences on the CFRP confinement performance for the compressive strength, but have obvious effects on the CFRP confinement performance for the ultimate axial strain. Based on the test results, empirical stress and strain models were proposed to predict the ultimate condition of the CFRP-confined geopolymeric concrete.
Thanh, HT, Li, J & Zhang, YX 2020, 'Numerical simulation of self-consolidating engineered cementitious composite flow with the V-funnel and U-box', Construction and Building Materials, vol. 236, pp. 117467-117467.
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Thomas, P, Chauviré, B, Flower-Donaldson, K, Aldridge, L, Smallwood, A & Liu, B 2020, 'FT-NIR and DSC characterisation of water in opal', Ceramics International, vol. 46, no. 18, pp. 29443-29450.
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© 2020 Elsevier Ltd and Techna Group S.r.l. Opal is a hydrous silica (Si02.nH2O) formed through a dissolution-precipitation process. The formation process incorporates water into the structure as bound silanol and molecular water. As the water is distributed in a range of states, multiple methods of characterisation are required to identify each state. This study reports the results of temperature dependent FT-NIR and DSC investigation on natural opal samples of the opal-A (amorphous) and opal-CT (poorly crystalline cristobalite with tridymitic stacking faults) types. Significant differences in the melting behaviour of crystallisable water as well as differences in the spectral characteristics of the non-crystallisable molecular water are observed. These differences are ascribed to the different microstructures of the opal types.
Tran, AT, Ha, QP & Hunjet, R 2020, 'Reliability enhancement with dependable model predictive control', ISA Transactions, vol. 106, pp. 152-170.
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© 2020 ISA Operational Technology (OT) systems are merging towards a conjoint architecture with the advances in communication networks and emerging standards such as IEC/IEEE 60802 for industrial automation, automotive, power and energy and other areas. In this paper, we present a Dependable Control System (DepCS) with Model Predictive Control (MPC) algorithm that works in such architectures using multiple MPC controllers (of a feedback control loop) to enhance the operational reliability. We termed this as Dependable Model Predictive Control (DepMPC) system. The reliability enhancement of a DepMPC system is achievable thanks to the fault-tolerance of multiple MPC controllers and the tractable information flows with Time-Sensitive Networking (TSN). Here, our discussion was focused only on the logical connectivity and not the hardware architecture. The numerical simulations are studied with three multi-variable plants that have control constraints. In this study, we introduced a Replacement Controller (RC) to improve the control performance of the DepMPC system. The combination of both the Replacement Controller and Dependable Model Predictive Control (RC-DepMPC) system proves a promising solution for actual implementations.
Vakhshouri, B, Nejadi, S & Erkmen, E 2020, 'Advances in numerical analysis of creep effect in time-dependent deflection of light-weight concrete slabs', Mechanics of Advanced Materials and Structures, vol. 27, no. 18, pp. 1563-1570.
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© 2018, © 2018 Taylor & Francis Group, LLC. Using a wide range of creep models, the experimental results of long-term deflection of lightweight concrete slabs subjected to two levels of early-age loading are investigated. Different creep models give considerably different estimation of the experimental deflection of slabs. The included factors in each creep model to simulate the experimental creep behavior of the concrete, and loading level on the slabs are the main causes of different results. Among the investigated models, the BP1 and FIBMC-2010 models including the aggregate type and concrete density is shown to be in good agreement with the experimental data in both loading levels.
Vu, HNK, Ha, QP, Nguyen, DH, Nguyen, TTT, Nguyen, TT, Nguyen, TTH, Tran, ND & Ho, BQ 2020, 'Poor Air Quality and Its Association with Mortality in Ho Chi Minh City: Case Study', Atmosphere, vol. 11, no. 7, pp. 750-750.
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Along with its rapid urban development, Ho Chi Minh City (HCMC) in recent years has suffered a high concentration of air pollutants, especially fine particulate matters or PM2.5. A comprehensive study is required to evaluate the air quality conditions and their health impact in this city. Given the lack of adequate air quality monitoring data over a large area of the size of HCMC, an air quality modeling methodology is adopted to address the requirement. Here, by utilizing a corresponding emission inventory in combination with The Air Pollution Model-Chemical Transport Model (TAPM-CTM), the predicted concentration of air pollutants is first obtained for PM2.5, NOx, and SO2. Then by associating the pollutants exposed with the mortality rate from three causes, namely Ischemic Heart Disease (IHD), cardiopulmonary, and lung cancer, the impact of air pollution on human health is obtained for this purpose. Spatial distribution has shown a high amount of pollutants concentrated in the central city with a high density of combustion vehicles (motorcycles and automobiles). In addition, a significant amount of emissions can be observed from stevedoring and harbor activities, including ferries and cargo handling equipment located along the river. Other sources such as household activities also contribute to an even distribution of emission across the city. The results of air quality modeling showed that the annual average concentrations of NO2 were higher than the standard of Vietnam National Technical Regulation on Ambient Air Quality (QCVN 05: 2013 40 µg/m3) and World Health Organization (WHO) (40 µg/m3). The annual average concentrations of PM2.5 were 23 µg/m3 and were also much higher than the WHO (10 µg/m3) standard by about 2.3 times. In terms of public health impacts, PM2.5 was found to be responsible for about 1136 deaths, while the number of mortalities from exposure to NO2 and SO2 was 172 and 89 deaths, respectively. These figures demand some stri...
Wang, D, Wu, C, Zhang, Y, Xue, G & Xu, Y 2020, 'Study on seismic performance of a precast buckling-restrained composite shear wall system with three assembly arrangements', Bulletin of Earthquake Engineering, vol. 18, no. 10, pp. 4839-4872.
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© 2020, Springer Nature B.V. Precast buildings have attarcted worldwide attention because of their significant role in the realization of sustainable urbanization. In this study, a precast buckling-restrained composite shear wall (PBRSW) system is developed, which is assemblied by multiple composite shear wall modules on site. The PBRSW system with three assembly arrangements of the composite shear wall modules, vertical, horizontal and cross arrangements, are designed and explored comparatively to mitigate buckling phenomena and obtain beneficial mechanical behaviours with experiment and simulation methods. To bring insight the seismic performance of the developed system, traditional buckling-restrained shear wall (BRSW) system and steel plate shear wall (SPSW) system are further investigated. The results show that the PBRSW system achieves plumper hysteresis behaviors, higher force-bearing and energy-dissipation capacities, and better ductility performance than that of the other two systems. Buckling phenomena of the PBRSW system are restrined effectively, and its maximum out-of-plane displacement is only 1/18 and 1/15 of the SPSW and BRSW systems on average respectively. The PBRSW system with vertical arrangement of the composite shear wall modules shows the best mechanical behavior with the highest bearing capacity and energy dissipation among the three assembly arrangements. Experimental data coincides well with those from finite element model (FEM) analysis and therefore validates FEM.
Wang, W, Wu, C, Liu, Z, An, K & Zeng, J-J 2020, 'Experimental Investigation of the Hybrid FRP-UHPC-Steel Double-Skin Tubular Columns under Lateral Impact Loading', Journal of Composites for Construction, vol. 24, no. 5, pp. 04020041-04020041.
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© 2020 American Society of Civil Engineers. The lateral impact behavior of hybrid fiber-reinforced polymer (FRP)-ultrahigh-performance concrete (UHPC)-steel double-skin tubular columns (DSTCs) was experimentally investigated in this study. Seven specimens, which had an outer diameter of 168 mm and a length of 2,000 mm, were tested under lateral impact loading. Different parameters, including the axial force level, impact energy, concrete type, void ratio, FRP tube thickness, and the presence/absence of the FRP tube, were investigated. The dynamic responses, including global/local damage modes, lateral deflection-time histories, impact force-time histories, strain-time histories, and acceleration-time histories, were investigated. The test results prove that the hybrid UHPC DSTCs exhibit very ductile behavior under lateral impact loading. The hybrid UHPC DSTCs have a higher lateral impact resistance capacity as compared to the hybrid DSTCs infilled with normal-strength concrete. The lateral impact resistance capacity of hybrid UHPC DSTCs with an applied axial force of 200 kN can be improved to some extent compared with those without any axial force. The impact energy, the void ratio, the FRP tube thickness, and the presence/absence of the FRP tube can significantly affect the lateral impact behavior of hybrid UHPC DSTCs. Furthermore, the lateral impact behaviors of hybrid DSTCs, concrete-filled double-skin steel tubes (CFDSTs), and concrete-filled steel tubes (CFSTs) were compared and discussed based on the experimental results in this study as well as in other literature studies.
Wei, J, Li, J & Wu, C 2020, 'Behaviour of hollow-core and steel wire mesh reinforced ultra-high performance concrete columns under lateral impact loading', International Journal of Impact Engineering, vol. 146, pp. 103726-103726.
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© 2020 Elsevier Ltd Adopting UHPC in practical construction is very expensive due to the high steel fibre content (>2.5 vol%) and passive flexure reinforcement. Aiming at balancing the performance and cost, two UHPC column designs (2000 × 168 × 168 mm) are proposed in the present study. Hollow-core components and steel wire mesh reinforced components were cast with UHPC that contained 1.5 vol% steel fibre, and the impact resistance of both structural types was studied. The test specimens included two hollow-core UHPC columns with square and circular hollow shapes, and two steel wire mesh reinforced UHPC columns with 6 and 10 layers wire mesh reinforcement. The impact scenario was modelled with a 411 kg drop hammer falling freely from 1.25 m height to the mid-span of the test specimen. The results demonstrated that all UHPC specimens remained a flexural response with minimal damage. The developed numerical model captured the impact force, structural deformation and damage with reasonable accuracy. With the validated model, the energy evolution, dynamic shear and moment distribution, residual axial capacity and damage level of post-impact columns were evaluated. The effects of hollow section shape and ratio, axial load level, and longitudinal reinforcement ratio for hollow-core UHPC columns and the effects of layers of steel wire mesh for steel wire mesh reinforced UHPC columns were investigated. Compared with other hollow-core UHPC columns under the impact velocities between 4.95 m/s – 6.64 m/s, UHPC columns with a circular hollow section and 15% hollow ratio was the most effective in balancing the cost and impact resistance. For steel wire mesh reinforced UHPC columns, the column with steel wire mesh strengthening in the whole section had better impact resistance than its counterpart that only had wire mesh reinforcement in the tensile zone.
WU, P, WU, C, LIU, Z & XU, S 2020, 'Numerical simulation of SHPB test of ultra-high performance fiber reinforced concrete with meso-scale model', SCIENTIA SINICA Physica, Mechanica & Astronomica, vol. 50, no. 2, pp. 024614-024614.
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Xu, D-S, Xu, X-Y, Li, W & Fatahi, B 2020, 'Field experiments on laterally loaded piles for an offshore wind farm', Marine Structures, vol. 69, pp. 102684-102684.
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© 2019 Elsevier Ltd Pile foundations are widely used to support offshore wind turbines due to their cost effectiveness and rapid constructions. Offshore piles must be designed with enough capacity to withstand overturning moments caused by wind turbines and other environmental factors such as wave excitations and extreme winds. In this study, a full-scale field experimental test is undertaken to determine the pile behaviour under various lateral loading conditions. A distributed fiber optic sensing technology is used to measure strains along two instrumented piles. The bending moments and lateral deflections are calculated from distributed fiber optic sensors, and then analysed with the various p-y methods. Field measurements indicated that for two offshore piles ZK01 and ZK28 with diameter of 2 m and length of 71.5 m and 77.5 m, the maximum lateral movements under a given lateral load of 800 kN were 369.1 mm and 351.7 mm, respectively. The maximum bending moment occurred at 6.5 m and 5.5 m below seabed level with the corresponding depth of 12.15D and 11.95D for pile ZK01 and ZK28, respectively. The position of “zero crossing” of soil resistance for two instrumented piles is almost the same, even though the piles have different lengths. The lateral deflections and bending moments of the two instrumented piles are predicted by the API and hyperbolic method, which indicates that the hyperbolic method yields larger prediction errors than the API method. A modified p-y approach is then proposed for more reliable predictions when compared with field measurements.
Xu, S, Wu, P & Wu, C 2020, 'Calibration of KCC concrete model for UHPC against low-velocity impact', International Journal of Impact Engineering, vol. 144, pp. 103648-103648.
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Xue, C, Li, W, Castel, A, Wang, K & Sheng, D 2020, 'Effect of incompatibility between healing agent and cement matrix on self-healing performance of intelligent cementitious composite', Smart Materials and Structures, vol. 29, no. 11, pp. 115020-115020.
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Abstract Encapsulation-based intelligent self-healing cementitious composite with a potential of crack self-healing and closure is promising to recovery concrete from damage and improve the durability and serviceability of infrastructures. The efficiency of self-healing concrete were investigated, but limited studies have been conducted on effect of incompatibility between the self-healing agent and cement matrix on the cracking behaviour and recovery efficiency of crack-healed concrete. In this study, a coupled experimental and numerical investigations were adopted to understand the cracking behaviours of crack-healed cementitious composites using traction–separation law by extended finite element method (XFEM). Firstly, experimental investigation was conducted to characterize the properties and parameters of cement matrix and healing agent-crack interface to calibrate the traction–separation law. Then, various parameters of healing agent, cement matrix, and their interface on the performance of crack-healed cementitious composite was numerically analysed. The results indicate that to achieve excellent self-healing performance, it is vital to consider the incompatibility between healing agent and cement matrix in the design of intelligent self-healing cementitious composites.
Xue, C, Li, W, Qu, F, Sun, Z & Shah, SP 2020, 'Self-healing efficiency and crack closure of smart cementitious composite with crystalline admixture and structural polyurethane', Construction and Building Materials, vol. 260, pp. 119955-119955.
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© 2020 Elsevier Ltd The crack closure and self-healing efficiency of smart self-healing cementitious composite can effectively reveal the mechanism of self-healing performance recovery. This study focused on effects of crack healing on crack closure and mechanical performance recovery of crack-healed cementitious composite, including flexural compressive behaviours. Meanwhile, several parameters were defined to quantify the efficiency of mechanical performance recovery efficiency for self-healing cementitious composite. Furthermore, the interfaces between self-healing products and crack surface were analyzed and compared to provide understanding insight to the self-healing recovery. It is found that the bonding interface dominated the flexural strength recovery, and therefore autonomous self-healing yielded the maximum self-healing efficiency. On the other hand, the stiffness damage recovery index under compression is found to be an effective parameter to evaluate the inner crack healing, which slightly depends on the bonding interface. The related results indicate that the development of smart self-healing cementitious composite should consider the bonding between self-healing product and crack surface to improve the self-healing recovery efficiency for engineering application.
Xue, C, Li, W, Wang, K, Sheng, D & Shah, SP 2020, 'Novel experimental and numerical investigations on bonding behaviour of crack interface in smart self-healing concrete', Smart Materials and Structures, vol. 29, no. 8, pp. 085004-085004.
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© 2020 IOP Publishing Ltd. There are crack interfaces between self-healing agent and cement matrix in smart encapsulation-based self-healing concrete, whose mechanical properties significantly affects the load capacity recovery of crack-healed concrete. In this study, both experimental and numerical investigations were conducted on the crack-healed concrete under uniaxial tension to investigate the interface bonding behaviours and the self-healing agent distribution on the crack surface. The results show that the bonding behaviour of the crack interface depends on the content of healing agent and mechanical properties of the crack surface. However, it is still difficult to accurately understand their effects on the bonding behaviour by experimental investigation due to the high brittleness of the crack interface and the discrepancy of self-healing concrete. Therefore, based on the experimental results, a novel numerical model of the interface between self-healing agent and cement matrix was developed to investigate effects of aggregates, pores and interface properties on the bonding behaviour of crack interface by the cohesive surface technique (CS). Parametric analysis was also performed on the bonding behaviours and a method was proposed for assessing the load capacity of crack-healed concrete. Based on the experimental and numerical investigations on the healing agent-concrete crack interface in the smart encapsulation-based self-healing concrete, this novel numericla methods can be used to assess the recovery efficiency and performance of smart self-healing concrete structure.
Yang, T, Liu, Z, Yang, Y & Wu, C 2020, 'Experimental investigation on behavior of ultra-high performance concrete after high temperature', Tumu yu Huanjing Gongcheng Xuebao/Journal of Civil and Environmental Engineering, vol. 42, no. 3, pp. 115-126.
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The apparent characteristics, mass loss and mechanical properties of ultra-high performance concrete after exposure to high temperature were studied through the high temperature heating test and the cubic compressive strength test. The effects of steel fiber, polypropylene fiber, steel fiber and polypropylene fiber on cracking suppression of ultra-high performance concrete were compared. The effects of temperature, fiber type and content, aggregate (quartz sand and steel slag) on the strength of ultra-high performance concrete were investigated. The test results show that 1% steel fibers and 2% polypropylene fibers can effectively restrain high temperature explosion behavior, and the specimen remains intact after high temperature. Ultra-high performance concrete with steel slag aggregate and hybrid fiber has excellent high temperature mechanical properties, the residual strength of 67% can still be maintained after being exposed to high temperature at 1 000℃. With the increase of temperature, the cubic compressive strength of ultra-high performance concrete increases first and then decreases. High temperature enhances the compressive ductility of ultra-high performance concrete when the target temperature is more than 600℃.
Yao, Z & Li, W 2020, 'Microstructure and thermal analysis of APS nano PYSZ coated aluminum alloy piston', Journal of Alloys and Compounds, vol. 812, pp. 152162-152162.
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© 2019 Elsevier B.V. Aluminium alloys in internal combustion (IC) engines may suffer from heat damage. Such heat damage can be mitigated using thermal barrier coatings (TBCs). In this study, the TBC Nano yttria partially stabilized zirconia (PYSZ) is applied as an aggregated powder to an aluminum alloy piston using an atmospheric plasma spray (APS) method. The preparation and application of the Nano PYSZ aggregated powder are critical to its effectiveness as a TBC. IC engine bench experiments were undertaken to provide a baseline against which the effectiveness of the TBC could be judged. The microstructure of the Nano PYSZ aggregated powder and thermal barrier coatings were examined using three instruments: scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and X-ray powder diffraction (XRD). Results from this study show that the Nano PYSZ ceramic TBCs, applied to the aluminum alloy piston using a plasma spraying technique, (a) has a high quality Nano-structure, (b) can effectively resist the thermal shock of high temperature gas in the cylinder and (c) maintains both stable macro characteristics and micro structure during the working cycle of the IC engine. The thermal insulation properties of TBCs were also examined. The thermal analyses describe the distribution of temperature across both the piston and the aluminum alloy substrate. Results desmonstrate the effectiveness of the TBCs in reducing the temperature of the aluminium alloy substrate at the top of piston. One benefit is that the piston can operate effectively at higher temperatures. Specifically, as the thickness of ceramic coating increased from 0.1 mm to 1.4 mm, the maximum temperature of the pistons coated with the TBCs increased from 399 °C to 665 °C. The maximum temperature of the aluminum alloy substrates simultaneously decreased from 336 °C to 241 °C. This study clearly demonstrates the excellent thermal insulation properties of the TBCs and shows...
Ying, J, Han, Z, Shen, L & Li, W 2020, 'Influence of Parent Concrete Properties on Compressive Strength and Chloride Diffusion Coefficient of Concrete with Strengthened Recycled Aggregates', Materials, vol. 13, no. 20, pp. 4631-4631.
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Parent concrete coming from a wide range of sources can result in considerable differences in the properties of recycled coarse aggregate (RCA). In this study, the RCAs were obtained by crushing the parent concrete with water-to-cement ratios (W/Cparent) of 0.4, 0.5 and 0.6, respectively, and were strengthened by carbonation and nano-silica slurry wrapping methods. It was found that when W/Cparen was 0.3, 0.4 and 0.5, respectively, compared with the mortar in the untreated RCA, the capillary porosity of the mortar in the carbonated RCA decreased by 19%, 16% and 30%, respectively; the compressive strength of concrete containing the carbonated RCA increased by 13%, 11% and 13%, respectively; the chloride diffusion coefficient of RAC (DRAC) containing the nano-SiO2 slurry-treated RCA decreased by 17%, 16% and 11%; and that of RAC containing the carbonated RCA decreased by 21%, 25% and 26%, respectively. Regardless of being strengthened or not, both DRAC and porosity of old mortar in RCAs increased with increasing W/Cparent. For different types of RCAs, DRAC increased obviously with increasing water absorption of RCA. Finally, a theoretical model of DRAC considering the water absorption of RCA was established and verified by experiments, which can be used to predict the DRAC under the influence of different factors, especially the water absorption of RCA.
Ying, X, Wang, Y, Li, W, Liu, Z & Ding, G 2020, 'Group Layout Pattern and Outdoor Wind Environment of Enclosed Office Buildings in Hangzhou', Energies, vol. 13, no. 2, pp. 406-406.
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This paper presents a study of the effects of wind-induced airflow through the urban built layout pattern using statistical analysis. This study investigates the association between typically enclosed office building layout patterns and the wind environment. First of all, this study establishes an ideal site model of 200 m × 200 m and obtains four typical multi-story enclosed office building group layouts, namely the multi-yard parallel opening, the multi-yard returning shape opening, the overall courtyard parallel opening, and the overall courtyard returning shape opening. Then, the natural ventilation performance of different building morphologies is further evaluated via the computational fluid dynamics (CFD) simulation software Phoenics. This study compares wind speed distribution at an outdoor pedestrian height (1.5 m). Finally, the natural ventilation performance corresponding to the four layout forms is obtained, which showed that the outdoor wind environment of the multi-yard type is more comfortable than the overall courtyard type, and the degree of enclosure of the building group is related to the advantages and disadvantages of the outdoor wind environment. The quantitative relevance between building layout and wind environment is examined, according to which the results of an ameliorated layout proposal are presented and assessed by Phoenics. This research could provide a method to create a livable urban wind environment.
Yu, Y, Royel, S, Li, Y, Li, J, Yousefi, AM, Gu, X, Li, S & Li, H 2020, 'Dynamic modelling and control of shear-mode rotational MR damper for mitigating hazard vibration of building structures', Smart Materials and Structures, vol. 29, no. 11, pp. 114006-114006.
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Abstract Magneto-rheological (MR) materials and their devices are being rapidly developed and have drawn surge of interest for the potential application in vibration control. Among them, a novel shear-mode rotational MR damper (SM-RMRD) with adaptive variable stiffness and damping was developed for adaptive structural control in real-time against different types of earthquakes. To make use of this innovative device perfectly, a robust and reliable model should be developed to simulate the nonlinear and hysteretic behaviours for the application in adaptive control. Accordingly, this research initially presents a new phenomenological model to describe the force response of the SM-RMRD. Then, model parameters are estimated based on experimental data of force, displacement and velocity, which were directly or indirectly obtained from the device under different loading protocols. The field dependence of each model parameter is also investigated so that a general model with current-related parameters is acquired for designing the control strategy. Using the current-dependent model of SM-RMRD, a semi-active controller is developed and implemented to the SM-RMRD to produce the feedback control for the structures in real-time. Finally, the effectiveness of proposed control method is appraised by a numerical study, in which an SM-RMRDs-incorporated three-storey building model with different control strategies are subjected to various scaled benchmark earthquakes. The comparison result verifies the excellent capacity of the proposed controller based on the developed phenomenological model in terms of reducing the storey acceleration and inter-storey drift.
Yu, Y, Subhani, M, Hoshyar, AN, Li, J & Li, H 2020, 'Automated Health Condition Diagnosis of in situ Wood Utility Poles Using an Intelligent Non-Destructive Evaluation (NDE) Framework', International Journal of Structural Stability and Dynamics, vol. 20, no. 10, pp. 2042002-2042002.
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Wood utility poles are widely applied in power transmission and telecommunication systems in Australia. Because of a variety of external influence factors, such as fungi, termite and environmental conditions, failure of poles due to the wood degradation with time is of common occurrence with high degree uncertainty. The pole failure may result in serious consequences including both economic and public safety. Therefore, accurately and timely identifying the health condition of the utility poles is of great significance for economic and safe operation of electricity and communication networks. In this paper, a novel non-destructive evaluation (NDE) framework with advanced signal processing and artificial intelligence (AI) techniques is developed to diagnose the condition of utility pole in field. To begin with, the guided waves (GWs) generated within the pole is measured using multi-sensing technique, avoiding difficult interpretation of various wave modes which cannot be detected by only one sensor. Then, empirical mode decomposition (EMD) and principal component analysis (PCA) are employed to extract and select damage-sensitive features from the captured GW signals. Additionally, the up-to-date machine learning (ML) techniques are adopted to diagnose the health condition of the pole based on selected signal patterns. Eventually, the performance of the developed NDE framework is evaluated using the field testing data from 15 new and 24 decommissioned utility poles at the pole yard in Sydney.
Zhang, G, Li, Y, Yu, Y, Wang, H & Wang, J 2020, 'Modeling the non-linear rheological behavior of magnetorheological gel using a computationally efficient model', Smart Materials and Structures, vol. 29, no. 10, pp. 105021-105021.
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Abstract Magnetorheological (MR) gel is a novel generation of smart MR material, which has the inherent hysteretic properties and strain stiffening behaviors that are dependent on applied excitation, i.e. magnetic field. The main challenge for the application of the MR gel is the accurate reproduction of the above characteristics by a computationally efficient model that can predict the dynamic stress-strain/rate responses. In this work, parametric modeling on the non-linear rheological behavior of MR gel is conducted. Firstly, a composite MR gel sample was developed by dispersing carbon iron particles into the polyurethane matrix. The dynamic stress-strain/rate responses of the MR gel are obtained using a commercial rheometer with strain-controlled mode under harmonic excitation with frequencies of 0.1 Hz, 5 Hz and 15 Hz and current levels of 1 A and 2 A at a fixed amplitude of 10%. Following a mini-review on the available mathematical models, the experimental data is utilized to fit into the models to find the best candidate utilizing a genetic algorithm. Then, a statistical analysis is conducted to evaluate the model’s performance. The non-symmetrical Bouc–Wen model outperforms all other models in reproducing the non-linear behavior of MR gel. Finally, the parameter sensitivity analysis is employed to simplify the non-symmetrical Bouc–Wen model and then the parameter generalization is conducted and verified for the modified non-symmetrical Bouc–Wen model.
Zhang, P, Li, H, Ha, QP, Yin, Z-Y & Chen, R-P 2020, 'Reinforcement learning based optimizer for improvement of predicting tunneling-induced ground responses', Advanced Engineering Informatics, vol. 45, pp. 101097-101097.
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Zhang, X, Li, W, Tang, Z, Wang, X & Sheng, D 2020, 'Sustainable regenerated binding materials (RBM) utilizing industrial solid wastes for soil and aggregate stabilization', Journal of Cleaner Production, vol. 275, pp. 122991-122991.
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© 2020 Elsevier Ltd This study presents an experimental investigation on a sustainable regenerated binding material (RBM), which is derived from several industrial solid wastes. Initially, the hydration process, mechanical behaviors, and microstructural characteristics of the RBM were investigated. Subsequently, the feasibility of RBM for the stabilization of macadam, expansive soil, and weathered sand was evaluated. The results reveal that in comparison with the ordinary Portland cement (OPC), the RBM exhibits a slightly faster hydration rate at the initial stage and comparable mechanical performance. For the stabilized macadam, the one stabilized by the RBM exhibits better unconfined compressive strength, scouring resistance and freeze-thaw resistance than the counterpart stabilized by OPC. Furthermore, the RBM can significantly improve the performance index of the expansive soil and weathered sand, and this enhancement is more significant as the RBM content increasing. Additionally, the RBM has been successfully applied in practical engineering, manifesting the promising application potential of the RBM. Overall, the excellent performance of RBM as an alternative stabilizer of the subgrade soil and aggregates can promote the application of the RBM low-carbon pavement construction in the future.
Zhao, E & Wu, C 2020, 'Unified egg ellipse critical threshold estimation for the deformation behavior of ultrahigh arch dams', Engineering Structures, vol. 214, pp. 110598-110598.
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© 2020 Elsevier Ltd This paper presents an innovative critical threshold estimation approach using unified egg-shaped ellipsoid modelling to study the deformation behavior of ultrahigh arch dams. First, the deformation variation law is regarded as a direct indicator of the overall stability and potential damage of ultrahigh arch dams based on comprehensively comparison with the results of theoretical calculations, experimental tests, numerical simulations and monitoring data. Subsequently, a novel geometric center of an irregular deformation plane constituted by all the deflection curves is proposed according to the measured distribution characteristics of the deformation spatial fields of the Xiaowan and Jinping I arch dams. Furthermore, unified egg-shaped ellipse equations are proposed to systematically identify the deformation critical attributes of Jinping I dam. Eventually, based on the peaks over threshold model, critical indexes are estimated considering the abnormal probabilities. The proposed methods are applied to Xiaowan dam as well. Results demonstrate that unified ellipsoid modelling can uniformly describe the abnormal features of the deformation behaviors of different ultrahigh arch dams, thereby the universal structural evolution characteristics to be understood in a wider range during their long-term operations.
Zhao, E, Wu, C, Wang, S, Hu, J & Wang, W 2020, 'Seepage dissolution effect prediction on aging deformation of concrete dams by coupled chemo-mechanical model', Construction and Building Materials, vol. 237, pp. 117603-117603.
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© 2019 Elsevier Ltd Concrete dams undergo a seepage dissolution process because of huge reservoir water pressure and concrete permeability, and such dissolution weakens the mechanical properties of concrete and produces a certain amount of irreversible aging deformation. This study proposes a coupled chemo-mechanical model to predict the seepage dissolution effect on aging deformation of concrete dams. The interactions between elastic–plastic, chemical damage and mechanical damage are jointly explored combining with on-site inspection of long-term service performance of a concrete gravity dam firstly. Then an aging model of the seepage dissolution damage is digitized, and a novel model on chemo-mechanical coupled effect is put forward by introducing an overall chemo-mechanical damage scalar. The validity of the model is proved by a case study on the gravity dam through finite element simulation on its seepage dissolution and comparison with monitoring data. Finally, these methods are applied into an ultra-high arch dam to quantitatively calculate the irreversible aging deformation with the increase of the seepage dissolution degree. And the annual maximum aging deformation of the arch dam increases 0.65 mm after 100 years. The results indicate that the proposed model can effectively predict the aging deformation caused by the seepage dissolution during long-term operation of concrete dams.
Zheng, J, He, X, Li, Y, Zhao, B, Ye, F, Gao, C, Li, M, Li, X & E, S 2020, 'Viscoelastic and Magnetically Aligned Flaky Fe-Based Magnetorheological Elastomer Film for Wide-Bandwidth Electromagnetic Wave Absorption', Industrial & Engineering Chemistry Research, vol. 59, no. 8, pp. 3425-3437.
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