Dr Wengui Li is a Senior Lecturer in School of Civil and Environmental Engineering at University of Technology Sydney (UTS), Australia. Dr Li received his Joint Doctoral Degree of Structural Engineering from Tongji University and Northwestern University (USA). From 2010 to 2013, he studied in the Center for Advanced Cement-Based Materials (ACBM) with Prof Surendra P. Shah at Northwestern University, USA. In 2015, Dr. Li was awarded the Australia Research Council Discovery Early Career Researcher Award (ARC DECRA Fellow).
Dr Li’s research motivation is to connect material properties of concrete to structure performances. His current research interests basically include smart concrete and sustainable construction materials. He is a member of American Institute of Concrete (ACI-555 and ACI-241), American Society of Civil Engineers (ASCE), International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM-273-RAC, 283-CAM and 278-CHA) and Concrete Institute of Australia (CIA). Dr Li is also the editorial member of two international journals.
Dr Li has published more than 100 international journal papers, and also reviewed papers of 20 international journals in the areas of concrete materials and structures. He is the member of the following professional societies.
- American Concrete Institute (ACI)
- Concrete Institute of Australia (CIA)
- American Society of Civil Engineers (ASCE)
- International Union of Testing and Research Laboratories for Materials and Structures (RILEM)
The Australian Network of Structural Health Monitoring (ANSHM)
The International Association of Protective Structures (IAPS)
- Committee of Recycled Aggregate Concrete of China (China Civil Engineering Society)
Can supervise: YES
Dr Li’s research interests are in the field of connecting material properties to structural responses of concrete, including
- Multifunctional concrete (self-sensing, self-healing and self-cleaning)
- Recycled concrete
- Concrete nanotechnology
- Solid waste recycling
- Concrete durability
- Seawater and sea sand concrete
- Construction materials (48352), Coordinator
- Design for durability (42907)
- Reinforced concrete and masonry structures (CIV2226)
- Introduction to Civil and Environmental Engineering (48310)
Dong, W, Li, W, Vessalas, K & Wang, K 2020, 'Mechanical and Conductive Properties of Smart Cementitious Composites with Conductive Rubber Crumbs', ES Materials & Manufacturing.View/Download from: Publisher's site
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.View/Download from: Publisher's site
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.View/Download from: Publisher's site
Lei, B, Li, W, Luo, Z, Li, X, Tam, VWY & Tang, Z 2020, 'Performance deterioration of sustainable recycled aggregate concrete under combined cyclic loading and environmental actions', Journal of Sustainable Cement-Based Materials.View/Download from: Publisher's site
© 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group. The effects of strength grades, loading modes, and stress levels on the performance deterioration of sustainable recycled aggregate concrete (RAC) subjected to mechanical loading or coupled mechanical loading and environmental actions are investigated in this study. Comparison analysis of residual properties of RAC suffered from single mechanical loading, coupled actions of mechanical loading, and salt-solution freeze-thaw cycles, as well as the combined actions of mechanical loading and salt-solution corrosion were experimentally studied. The results indicate that the stress level is the most influential factor affecting the durability of RAC followed by the RAC strength grade and the number of times the alternating load applied. Moreover, applying novel intermittent loading mode to simulate the durability of RAC under the coupled actions of sustained loading and environmental factors is feasible and reasonable. Additionally, the fitting equations were proposed to discuss the effects of number of times the alternating load applied, stress level, and mechanical strength on the mechanical strength loss and durability of RAC.
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.View/Download from: Publisher's site
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.View/Download from: Publisher's site
© 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, 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.View/Download from: Publisher's site
Ling, Y, Wang, K, Wang, X & Li, W 2020, 'Prediction of engineering properties of fly ash-based geopolymer using artificial neural networks', Neural Computing and Applications.View/Download from: Publisher's site
© 2019, Springer-Verlag London Ltd., part of Springer Nature. Fly ash-based geopolymer has been studied extensively in recent years due to its comparable properties to Portland cement and its environmental benefits. However, the uncertainty and complexity of design parameters, such as the SiO2/Na2O mole ratio in alkaline solution, the alkaline solution concentration in liquid phase, and the liquid-to-fly ash mass ratio (L/F), have made it very difficult to create a systematic approach for geopolymer mix design. These mix design parameters, along with fly ash properties and curing conditions (temperature and time), significantly influence key properties of the material, such as setting time and compressive strength. In this study, an artificial neural network (ANN) was used to develop models for predicting the key properties of high-calcium fly ash-based geopolymer according to its mix design parameters. The correlations between experimental measurements and ANN model predictions of setting time, compressive strength, and heat of geopolymerization were established based on the results of tests on 36, 273, and 72 geopolymer mixes, respectively. The results show that the correlations between the experimental measurements and ANN model predictions of the properties studied are all strong. ANN modeling was found to be a suitable computing method to analyze the effects of design parameters on geopolymer properties and showed that L/F exhibited the greatest effect on setting time, alkaline solution concentration had the greatest influence on compressive strength, and a mole ratio larger than 1.5 significantly impacted heat at the geopolymerization peak. The developed ANN models can be used as guidance for mix design of high-calcium fly ash geopolymer in engineering applications.
Lu, ZH, Wang, HJ, Qu, F, Zhao, YG, 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.View/Download from: Publisher's site
© 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.View/Download from: Publisher's site
© 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.View/Download from: Publisher's site
© 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.
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.View/Download from: Publisher's site
© 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.
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.View/Download from: Publisher's site
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 and Recycling: X, vol. 6.View/Download from: Publisher's site
© 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.View/Download from: Publisher's site
© 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.View/Download from: Publisher's site
© 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.
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.View/Download from: Publisher's site
© 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.
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.View/Download from: Publisher's site
© 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.
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/Materiaux et Constructions, vol. 53, no. 4.View/Download from: Publisher's site
© 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.
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.View/Download from: Publisher's site
© 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, 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.View/Download from: Publisher's site
© 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, 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.View/Download from: Publisher's site
© 2020 Elsevier B.V. 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.View/Download from: Publisher's site
© 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.View/Download from: Publisher's site
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.View/Download from: Publisher's site
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.View/Download from: Publisher's site
© 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.
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.View/Download from: Publisher's site
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.View/Download from: Publisher's site
© 2020 Elsevier B.V. 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.
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.View/Download from: Publisher's site
Dong, W, Li, W, Tao, Z & Wang, K 2019, 'Piezoresistive properties of cement-based sensors: Review and perspective', Construction and Building Materials, vol. 203, pp. 146-163.View/Download from: Publisher's site
© 2019 Elsevier Ltd Cement-based sensors are increasingly used in smart concrete to self-sense and monitor the damages and cracks through the measurements of concrete electrical resistivity. The fundamental concepts, key components, manufacturing process, piezoresistivity measurements, and primary applications of cement-based sensors are reviewed in this paper. Various materials, mechanical and environmental factors affecting concrete piezoresistive properties are explicated. Some contradictory results from different studies are reported and discussed. Future perspectives of piezoresistive cement-based sensors are also delineated. The review reveals that there is an optimal conductor content, below which the sensor would perform more like plain concrete with high resistivity and low sensitivity, while excessively higher than which, the dispersion of the conductive phase could become difficult, thus increasing resistivity. The manufacturing process, such as the dispersion method of conductors and curing condition, plays a significant role in conductor distribution, matrix density and pore structure of the sensors, which, together with rheology of the sensor composite, consequently alters the piezoresistive properties of the sensors. In addition to responding to mechanical loading, cement-based piezoresistive sensor also has a great potential for monitoring behaviour of concrete under freeze-thaw cycling. It is expected that this review will provide not only an orientation for new researchers to explore and engage in related studies but also an insight for experienced researchers to perform transformational examinations into cement-based piezoresistive sensors.
Hu, Y, Tang, Z, Li, W, Li, Y & Tam, VWY 2019, 'Physical-mechanical properties of fly ash/GGBFS geopolymer composites with recycled aggregates', CONSTRUCTION AND BUILDING MATERIALS, vol. 226, pp. 139-151.View/Download from: Publisher's site
Jahandari, S, Saberian, M, Tao, Z, Mojtahedi, SF, Li, J, Ghasemi, M, Rezvani, SS & Li, W 2019, 'Effects of saturation degrees, freezing-thawing, and curing on geotechnical properties of lime and lime-cement concretes', Cold Regions Science and Technology, vol. 160, pp. 242-251.View/Download from: Publisher's site
© 2019 Elsevier B.V. There are very limited researches carried out to investigate the influence of saturation degrees, freezing-thawing, and curing times on geotechnical properties of lime concrete (LC) and lime-cement concrete (LCC) due to the capillary action and changes in groundwater table. Subsequently, the primary goal of this research is to investigate the influence of these parameters on mechanical properties of LC and LCC using unconfined compression tests, namely uniaxial compressive strength (UCS), stress-strain behavior, deformability index (I D ), secant modulus (E S ), failure strain, bulk modulus (K), resilient modulus (M R ), brittleness index (I B ), and shear modulus (G). At first, the mechanical and chemical characteristics of the utilized materials were measured. Then, samples were made with an optimal amount of cement, lime, coarse-grained soil, fine-grained soil, and water. The samples were then exposed to saturation points extending from 0 to 100% after 14, 28, 45 and 60 curing days. Then, to consider the effect of amount of saturation on the mechanical properties, UCS tests were performed on some of the samples. Other LCC specimens were exposed to freezing-thawing conditions to consider the effect of this phenomenon on the mechanical properties as well. The results of more than 250 UCS tests demonstrated that the curing times significantly affected the strength of LC and LCC specimens. Moreover, it is not ideal and logical to utilize LC and LC columns at a profundity underneath or near the groundwater level, though it is reasonable to adopt LCC and LCC columns at a profundity beneath or near the groundwater level because of the immaterial effect of degrees of saturation on LCC. In addition, this study showed that extending the curing period and diminishing the saturation degree would increase the strength and mechanical properties of the LCC specimens. The results of freezing-thawing demonstrated a negligible increase in the strength of t...
Li, CY, Chen, SJ, Li, WG, Li, XY, Ruan, D & Duan, WH 2019, 'Dynamic increased reinforcing effect of graphene oxide on cementitious nanocomposite', Construction and Building Materials, vol. 206, pp. 694-702.View/Download from: Publisher's site
© 2019 The reinforcing effect of graphene oxide on cementitious materials under high strain rate remains largely unknown. Existing studies on microfiber reinforced cementitious composites showed that the dynamic increase factor (DIF) decreases due to these fibres. This study reports that the reinforcing effect of graphene oxide nanosheets can, in contrast, increase with strain rate. Tensile splitting and compression tests were conducted under both static and dynamic loadings. High strain rate, up to 1700 s −1 , is achieved using a split Hopkinson pressure bar apparatus. It is found that the DIF of graphene oxide nanocomposite only increase when the DIF is higher than a threshold which is about 780 and 30 s −1 for compression and tensile test respectively. The increased of DIF was correlated with the speed of crack development and pull-out of the graphene oxide nanosheets. Also, the pull-out or fracture of graphene oxide on fragmented sand was also found a possible contributing factor to the increased DIF. The findings of this study indicate the future potential of atomic-thin nanosheets for materials under extreme impact and blast loading.
Ling, Y, Wang, K, Li, W, Shi, G & Lu, P 2019, 'Effect of slag on the mechanical properties and bond strength of fly ash-based engineered geopolymer composites', Composites Part B: Engineering, vol. 164, pp. 747-757.View/Download from: Publisher's site
© 2019 Recently, the concept of engineered cementitious composites (ECCs) has been extended to the creation of engineered geopolymer composites (EGCs). Although showing similar mechanical characteristics (e. g., strain hardening and multiple cracking) to conventional ECC, the strength of existing EGC is generally low, and this sometimes restrains its applications. In the present study, a low-calcium (Class F) fly ash-based, polyvinyl alcohol (PVA) fiber reinforced EGC was developed and further modified by a ground-granulated blast-furnace slag (slag). The slag was used to replace the fly ash at content of 0%, 10%, 20%, and 30% (by weight). The effects of the slag on the mechanical properties (e.g., compressive strength, modulus of elasticity, uniaxial tensile behavior, flexural bending strength, and pullout bond strength) of the EGCs were investigated. The results revealed that all EGCs studied exhibited a strain/deflection hardening behavior under tension/flexure, and all slag replacements for fly ash enhanced strength-related properties but reduced ductility-related properties of the EGCs. The EGC mix with 20% slag replacement for fly ash (FA-20%S) had 102.3 MPa compressive strength, 6.8 MPa tensile strength, and 6.2 MPa bond strength, while the EGC mix with no slag (FA-0%S) had 72.6 MPa compressive strength, 4.7 MPa tensile strength, and 3.5 MPa bond strength at 28 days. These strength enhancements were mainly attributed to the improved density of the EGC matrix and the bond between the matrix and fiber. There are close relationships between the bond strength and other strengths, especially the tensile and flexural strengths, of the EGCs.
Lu, ZH, Li, H, Li, W, Zhao, YG, Tang, Z & Sun, Z 2019, 'Shear behavior degradation and failure pattern of reinforced concrete beam with chloride-induced stirrup corrosion', Advances in Structural Engineering, vol. 22, no. 14, pp. 2998-3010.View/Download from: Publisher's site
© The Author(s) 2019. Reinforcement corrosion exhibits an adverse effect on the shear strength of reinforced concrete structures. In order to investigate the effects of chloride-induced corrosion of reinforcing steel on the shear behavior and failure pattern of reinforced concrete beams, a total of 24 reinforced concrete beams with different concrete strength grades and arrangements of stirrups were fabricated, among which 22 beams were subjected to accelerated corrosion to achieve different degrees of reinforcement corrosion. The failure pattern, crack propagation, load–displacement response, and ultimate strength of these beams were investigated under a standard four-point loading test in this study. Extensive comparative analysis was conducted to investigate the effects of the concrete strength, shear span-to-depth ratio, and stirrup type on the shear behavior of the corroded reinforced concrete beams. The results show that increasing the stirrup yielding strength is more effective in improving the shear strength of corroded reinforced concrete beams than that of concrete compressive strength. In terms of three types of stirrups, the shear strength of the beams with deformed HRB-335 is least sensitive to stirrup corrosion, followed by the beams with smooth HPB-235 and the beams with deformed HRB-400. The effect of the different stirrups on the shear strength depends on the corrosion degree of stirrup and shear span-to-depth ratio of the beam. The predicted results of shear strength of corroded reinforced concrete beams by a proposed analytical model are well consistent with the experimental results.
Lu, ZH, Lun, PY, Li, W, Luo, Z, Li, Y & Liu, P 2019, 'Empirical model of corrosion rate for steel reinforced concrete structures in chloride-laden environments', Advances in Structural Engineering, vol. 22, no. 1, pp. 223-239.View/Download from: Publisher's site
© The Author(s) 2018. The corrosion rate of reinforcing steel is an important factor to determine the corrosion propagation of reinforced concrete structures in the chloride-laden environments. Since the corrosion rate of reinforcing steel is affected by several coupled parameters, the efficient prediction of which remains challenging. In this study, a total of 156 experimental data on corrosion rate from the literature were collected and compared. Seven empirical models for predicting the corrosion rate were reviewed and investigated using the collected experimental data. Based on the investigations, a new empirical model is proposed for predicting the corrosion rate in corrosion-affected reinforced concrete structures considering parameters including concrete resistivity, temperature, relative humidity, corrosion duration and concrete chloride content. The comparison between the experimental data and those predicted using the new empirical model demonstrates that the new model gives a good prediction of the corrosion rate. Furthermore, the uncertainty and probability characteristics of these empirical models are also investigated. It is found that the probability distributions of the model errors can be described as lognormal, normal, Weibull or Gumbel distributions. As a result, the new empirical model can provide an efficient prediction of the corrosion rate of reinforcing steel, and the model error analysis results can be utilized for reliability-based service life prediction of reinforced concrete structures under chloride-laden environments.
Luo, Z, Li, W, Tam, VWY, Xiao, J & Shah, SP 2019, 'Current progress on nanotechnology application in recycled aggregate concrete', Journal of Sustainable Cement-Based Materials, vol. 8, no. 2, pp. 79-96.View/Download from: Publisher's site
© 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group. As a very promising sustainable construction material, recycled aggregate concrete (RAC) has become a hot research topic and attracted wide attention. Although many investigations have been conducted, it is still a great challenge to product RAC with satisfactory and stable performance for practical engineering application. In recent years, nanotechnology has been introduced to RAC research and displayed distinct advantages over many traditional methods. This article is devoted to reviewing the current research on nanotechnology application in RAC, including nanoengineering and nanoscience. The corresponding results involving microstructure characteristics, mechanical properties, workability, and durability were summarized and discussed. It has been found that nanoscience has promoted better understanding of microstructure and various internal mechanism of RAC, while nanoengineering has helped RAC achieve dense microstructure, improved mechanical properties and durability. However, further efforts are required to realize the potential of nanotechnology and to bring breakthroughs in research and application of RAC.
Tan, X, Li, W, Zhao, M & Tam, VWY 2019, 'Numerical discrete-element method investigation on failure process of recycled aggregate concrete', Journal of Materials in Civil Engineering, vol. 31, no. 1.View/Download from: Publisher's site
© 2018 American Society of Civil Engineers. This study numerically investigates the failure processes of recycled aggregate concrete (RAC) and natural aggregate concrete (NAC). A two-dimensional simulation based on a discrete-element method (DEM) is conducted with a universal distinct-element code (UDEC) program. RAC is modeled by a combination of rigid Voronoi blocks cemented to each other using contacts for interfaces. The determination procedure of contact microparameters is analyzed, and a series of microscopic contact parameters in different components of modeled recycled aggregate concrete (MRAC) is calibrated using nanoindentation results. The complete stress-strain curves, fracture process, and failure pattern of numerical model are verified by experimental results, proving its accuracy and validation. The initiation, propagation, and coalescence of microcracks and subsequent nonlinear deformation behaviors of cement mortar, modeled natural aggregate, and recycled aggregate concrete are captured through DEM numerical simulations and compared with digital image correlation (DIC) results. It is found that both the new interfacial transition zone and the old interfacial transition zone are the weak links in RAC, where most microcracks initiate and propagate into the cement mortar region. The failure behaviors of MRAC revealed by both experimental and numerical results can effectively provide insights into the failure mechanism and enhancement of RAC.
Tang, Z, Hu, Y, Tam, VWY & Li, W 2019, 'Uniaxial compressive behaviors of fly ash/slag-based geopolymeric concrete with recycled aggregates', Cement and Concrete Composites, vol. 104.View/Download from: Publisher's site
© 2019 Elsevier Ltd The uniaxial compressive stress-strain behaviors of fly ash/ground granulated blast furnace slag (GGBFS) geopolymeric concrete containing recycled aggregate were investigated in this study. Geopolymeric concretes with the variations of three recycled aggregate replacement ratios (i.e., 0%, 50% and 100%) and four contents of slag (i.e., 0%, 10%, 20% and 30% of the mass of total binder) were tested under uniaxial compression. Special attention was devoted to the failure behaviors and patterns, stress-strain characteristics (such as the peak stress, the elastic modulus, the peak strain, and the ultimate strain) and energy absorption capacity. The results showed that the peak stress, elastic modulus and energy absorption (toughness) decreased with the increase of the replacement ratio of recycled aggregate, while these mechanical properties increased when the content of slag increased. The reverse trend was observed with respect to the ductility. Moreover, the inclusion of slag could alleviate the nagative effects of the recycled aggregate replacement on the stress-strain characteristics of geopolymeric concrete. Additionally, a stress-strain model was developed in this study by modifying the parameters of the existing stress-strain model with the best prediction. This new proposed model can satisfactorily describe the stress-strain behaviors for both geopolymeric natural aggregate concrete and geopolymeric recycled aggregate concrete.
© 2019 Elsevier Ltd Glubam, a new type of engineered bamboo composites, is a promising structural material characterized by outstanding mechanical performance and environmental friendliness. In this study, glubam I-joists, with the spans ranging from 2.4 m to 7.5 m, were prepared and tested to evaluate their structural behavior. The glubam I-joists were lengthened by finger joints, and two kinds of connections were used to connect the web and flanges. Four-point bending tests were conducted to examine the failure modes, load-deflection relationships and load carrying capacity of glubam I-joists. Test results indicated that the dominant failure modes of glubam I-joists included shear failure at the finger joint in the web, bending failure at the finger joint in the bottom flange and lateral buckling. Correspondingly, the load carrying capacity of glubam I-joists was governed by the bending strength, shear capacity and critical bending moment. Glubam I-joists have relatively higher mechanical performance compared with other engineered bamboo or timber I-joists with similar dimension, and the bending capacity of the glubam I-joist with continuous web-to-flange connection meets the requirement specified in Chinese code. Based on the experimental findings and existing methods, theoretical methods were proposed for predicting the stiffness and load carrying capacity of glubam I-joist and were also validated by the test results.
Xue, C, Li, W, Li, J & Wang, K 2019, 'Numerical investigation on interface crack initiation and propagation behaviour of self-healing cementitious materials', CEMENT AND CONCRETE RESEARCH, vol. 122, pp. 1-16.View/Download from: Publisher's site
Xue, C, Li, W, Li, J, Tam, VWY & Ye, G 2019, 'A review study on encapsulation-based self-healing for cementitious materials', Structural Concrete, vol. 20, no. 1, pp. 198-212.View/Download from: Publisher's site
© 2018 fib. International Federation for Structural Concrete Encapsulation-based self-healing technology is an effective method for healing the crack-deteriorated cementitious material. Encapsulation-based self-healing initiates by crack occurrence and progresses by chemical reaction of released self-healing agents in the cracks, which are contained in capsules. In this paper, a review has been conducted on various healing agents, encapsulation techniques, as well as experimental approaches, basing on existing substantial studies. Recently, there is no consistent agreement on the effective criteria for evaluating encapsulation-based self-healing and mature solution for increasing the survival ratio of capsules during mixing. However, the polyurethane-based healing agents filled in glass or ceramic tubes are popularly applied for self-healing cementitious materials. Besides, the polymer capsules present promising attractions for engineering application. Mechanical strength and durability are the most widely used self-healing efficiency assessment indexes. On the other hand, nondestructive technique and numerical modeling have also extensively adopted to visualize and evaluate the self-healing behavior of cementitious materials. However, there are still some challenges, which require further investigations, such as behavior of crack propagation, kinetics of healing agent in discrete crack surfaces, effect of inserted capsules on the mechanical properties of self-healed cementitious materials.
Dong, W, Li, W, Lu, N, Qu, F, Vessalas, K & Sheng, D 2019, 'Piezoresistive behaviours of cement-based sensor with carbon black subjected to various temperature and water content', COMPOSITES PART B-ENGINEERING, vol. 178.View/Download from: Publisher's site
Dong, W, Li, W, Shen, L & Sheng, D 2019, 'Piezoresistive behaviours of carbon black cement-based sensors with layer-distributed conductive rubber fibres', MATERIALS & DESIGN, vol. 182.View/Download from: Publisher's site
Dong, W, Li, W, Long, G, Tao, Z, Li, J & Wang, K 2019, 'Electrical resistivity and mechanical properties of cementitious composite incorporating conductive rubber fibres', Smart Materials and Structures, vol. 28, no. 8.View/Download from: Publisher's site
© 2019 IOP Publishing Ltd. Conductive cementitious composites with excellent conductivity and piezoresistivity can be potentially used for pavement deicing, concrete corrosion evaluations or structural health monitoring. Inspired by the practice of recycling rubber wastes for concrete manufacturing, the conductive rubbers are first added as enhanced fillers to improve the electrical conductivity of cementitious composite in this study. Based on the experimental investigations on electrical resistivity, mechanical properties and microstructure, the results show that cementitious composites containing conductive rubber fibres exhibit relatively low resistivity with nearly one order of magnitude to approximately 1 × 104 Ω cm. On the other hand, cementitious composites with aluminium/silver filled rubber (AR) exhibit better conductivity than the counterparts with carbon black filled rubber (CR). For CR reinforced composites (CRC) and AR reinforced composite (ARC) with more than 40 rubber fibres (0.64 vol%), the higher the rubber fibre content, the better is the conductivity but the slightly lower the compressive strength. The cementitious composites reinforced by 100 conductive rubber fibres (1.6 vol%) not only display excellent conductivity but also provides acceptable mechanical properties, with up to 30.6% increase in ultimate strain but only 17.3% reduction in compressive strength. Furthermore, cementitious composites with rubber fibres demonstrate better damping capacity by enlarging stress-strain hysteresis loops compared to the counterpart without rubber. Such promising conductivity and damping properties provide the cementitious composites with great potentials for being used as cementitious composite sensors and smart composites to self-monitor the structural health or traffic load of various transportation infrastructures, such as bridges, highways and pavements.
De Carvalho Gomes, S, Zhou, JL, Li, W & Long, G 2019, 'Progress in manufacture and properties of construction materials incorporating water treatment sludge: A review', Resources, Conservation and Recycling, vol. 145, pp. 148-159.View/Download from: Publisher's site
© 2019 Elsevier B.V. Water treatment sludge (WTS) management is a growing global problem for water treatment plants (WTPs) and governments. Considering the scarcity of raw materials in many parts of the planet and unique properties of WTS, extensive research has been conducted on the application of WTS in the production of construction materials such as roof tiles, bricks, lightweight aggregates, cement, concrete and geopolymers. This paper critically reviews the progress in the application of WTS in construction materials, by synthesizing results from recent studies. Research findings have revealed that incorporation of ≤10% alum-based sludge in ceramic bricks is satisfactory with a small reduction of mechanical performance. Using the iron-based sludge, the bricks presented better mechanical strength than the reference clay-bricks. Concerning WTS application in concrete, 5% replacement of cement or sand by WTS was considered as the ideal value for the application in a variety of structural and non-structural concrete without adverse effect on concrete mechanical performance. Furthermore, this paper discusses sludge-amended concrete in terms of durability, potential leaching of toxic elements and cost, and suggests topics for future research on the sustainable management of WTS.
Long, G, Li, L, Li, W, Ma, K, Dong, W, Bai, C & Zhou, JL 2019, 'Enhanced mechanical properties and durability of coal gangue reinforced cement-soil mixture for foundation treatments', JOURNAL OF CLEANER PRODUCTION, vol. 231, pp. 468-482.View/Download from: Publisher's site
Tang, Z, Li, W, Hu, Y, Zhou, JL & Tam, VWY 2019, 'Review on designs and properties of multifunctional alkali-activated materials (AAMs)', Construction and Building Materials, vol. 200, pp. 474-489.View/Download from: Publisher's site
© 2018 Elsevier Ltd The stream of research on alkali-activated materials (AAMs) has expanded rapidly during the last decades owing to the potential as a viable alternative to cement-based materials. In addition to the load-carrying function, AAMs have been integrated with other functions to develop advanced construction materials, namely multifunctional AAMs. Multifunctional AAMs are intelligent systems not only serve a basic structural function but also exhibit other functional properties or have the abilities to react upon external stimuli or disturbances. Materials of this kind have tremendous potential to enhance the mechanical performance and durability of structure, improve the reliability and longevity of infrastructure, as well as reduce life-cycle service and maintenance cost. These multifunctional properties are mainly achieved through materials composition design, incorporation of functional elements, or microstructure modification. This paper presents an overview on designs and properties of multifunctional AAMs covering the smart functions, mechanical functions, and electrical functions, and with special attention to their definition, principles, and current progress. Furthermore, the challenges in the research of multifunctional AAMs have been discussed, as well as the future directions to increase the innovation and engineering application of these materials and structures.
Tang, Z, Li, W, Ke, G, Zhou, JL & Tam, VWY 2019, 'Sulfate attack resistance of sustainable concrete incorporating various industrial solid wastes', Journal of Cleaner Production, vol. 218, pp. 810-822.View/Download from: Publisher's site
© 2019 Elsevier Ltd Industrial solid wastes are inducing severe environmental problems, but the problem can be overcame by reusing them as construction materials. The sulfate resistances of sustainable concrete incorporating various solid waste materials, including waste glass powder (WGP), coal gangue powder (CGP) and fly ash (FA) were investigated in this study. Concrete mixes with different water to binder (w/b) ratios and containing various solid waste materials as partial replacement of Portland cement by ratios of 10%, 20%, and 30% were prepared. These mixes were immersed in the 5% Na 2 SO 4 solution for a total period of 22 months. The sulfate attack resistances were evaluated extensively based on visual appearance, mass change, compressive strength, splitting tensile strength, ultrasonic pulse velocity, mineralogy, and microstructure. The results indicate that regardless of the type and content of solid waste materials, the replacement of cement by solid waste materials exhibit a positive impact on the sulfate attack resistance. Under the same substitution level, WGP appear to be the most effective in offsetting the destructive effect of sulfate attack, followed by CGP and FA. Therefore, sustainable concrete incorporating solid waste materials can not only promote the recycling of solid waste, but also provide high sulfate attack resistance.
Yu, Y, Li, W, Li, J & Nguyen, TN 2018, 'A novel optimised self-learning method for compressive strength prediction of high performance concrete', Construction and Building Materials, vol. 184, pp. 229-247.View/Download from: Publisher's site
© 2018 Elsevier Ltd Concrete strength (CS) is one of the most important performance parameters that are crucial in the design of concrete structure. The reliable prediction of strength can reduce the cost and time in design and avoid the waste of materials caused by a large number of mixture trials. In this study, a novel predictive model is put forward to predict the CS of high performance concrete (HPC) using support vector machine (SVM) approach, which has benefits of nonlinear mapping, high robustness and great generalisation capacity. In the proposed model, the input variables include the contents of water, cement, blast furnace slag, fly ash, super plasticiser, coarse and fine aggregates and curing age, which produces the CS of HPC as the output. In order to improve the model performance, a type of enhanced cat swarm optimisation (ECSO) is adopted to optimise the key parameters of SVM. Finally, the model is trained and evaluated using a total of 1761 data records, which are collected from existing literatures. The results indicate that the proposed SVM-based model exhibits better recognition ability and higher prediction accuracy than other commonly used models, and it can be considered as an effective method to predict the CS property of HPC in infrastructure practice.
Chuah, S, Li, W, Chen, SJ, Sanjayan, JG & Duan, WH 2018, 'Investigation on dispersion of graphene oxide in cement composite using different surfactant treatments', Construction and Building Materials, vol. 161, pp. 519-527.View/Download from: Publisher's site
© 2017 Elsevier Ltd Graphene oxide (GO) is a novel class of two-dimensional nanoscale sheet material due to its excellent dispersibility in water, high aspect ratio and good intrinsic strengths. In order to obtain a well-distributed GO-reinforced cement composites, the dispersion of GO in water, alkali and several ionic species are investigated with the aid of UV–vis spectroscopy. High alkalinity and calcium ions are key factors inducing the agglomeration of GO in cement system. Dispersion of GO in simulated pore solution is the culmination of the alkali and salt experiments. Agglomeration of GO occurred when GO contacted with the simulated pore solution, highlighting the necessity to protect GO against such aggressive media. The test on surfactant compatibility was then carried out to ensure GO was effectively dispersed in polycarboxylate, air-entrainment and Gum Arabic admixtures within the pore solution. Polycarboxylate-based superplasticisers gave the most promising results to disperse GO in cement alkaline environment. Flexural experiments was performed to highlight the importance of fabrication protocol on the mechanical properties of GO-cement composites. The result shows that the amount of 0.03% GO by weight of cement can increase the flexural strength of GO-cement composite up to 67%.
Ke, G, Li, W, Li, R, Li, Y & Wang, G 2018, 'Mitigation Effect of Waste Glass Powders on Alkali–Silica Reaction (ASR) Expansion in Cementitious Composite', International Journal of Concrete Structures and Materials, vol. 12.View/Download from: Publisher's site
© 2018, The Author(s). The effects of different contents and particle sizes of waste glass powder on alkali–silica reaction (ASR) expansion of cementitious composite bar were investigated in this study. Waste glass powder with particle size less than 300 μm exhibits an excellent mitigation effect on ASR expansion. With larger content and smaller particle size, the mitigation effect of waste glass powder on ASR expansion gradually increases. The mitigation effect of waste glass powder with particle size ranging from 38 to 53 μm and 20% by weight of cement seems relatively better than that of fly ash. When the waste glass powder content reaches 30%, the mitigation effect is still effective and almost the same as that of fly ash. However, the waste glass powder with particle size larger than 300 μm presents negative mitigation effect on ASR expansion when the replacement rate is larger than 30%. On the other hand, the waste glass powder and calcium hydroxide (CH) further react, and produce more calcium–silicate–hydrate gels, which apparently reduce the amount of CH. Moreover, the increasing content of waste glass powder results in a lower pH value in the pore solution of cementitious composite.
Lei, B, Li, W, Li, Z, Wang, G & Sun, Z 2018, 'Effect of cyclic loading deterioration on concrete durability: Water absorption, freeze-thaw, and carbonation', Journal of Materials in Civil Engineering, vol. 30, no. 9.View/Download from: Publisher's site
© 2018 American Society of Civil Engineers. The effect of cyclic loading deterioration on freeze-thaw and carbonation resistances of concrete were experimentally investigated in this study. A novel loading method was designed, which simultaneously considers both mechanical loading and environmental actions for concrete. It shows that with the increase of cyclic compressive loading, the porosity and water absorption of concrete initially decrease but then increase when the stress is above a threshold level because of the cracking initiation caused by cyclic compression. With the increase of concrete porosity, both dynamic elastic modulus loss and carbonation depth obviously exhibit an increasing trend. On the other hand, under the same stress level, the freeze-thaw and carbonation resistances of high-strength concrete are relatively superior to those of low-strength concrete. Compared with the unloaded concrete, the carbonation depth and dynamic elastic modulus loss after mechanical loading below the stress level threshold are lower. This is probably due to the denser microstructure compacted by the compression. However, if the loading level becomes above the threshold level, both the carbonation depth and dynamic elastic modulus loss dramatically increase, which is due to the cracks initiation and propagation after cyclic loading deterioration. Therefore, the combination of mechanical and environmental actions is more severe than a single environmental action without considering the mechanical loading.
Lei, B, Li, W, Tang, Z, Tam, VWY & Sun, Z 2018, 'Durability of recycled aggregate concrete under coupling mechanical loading and freeze-thaw cycle in salt-solution', Construction and Building Materials, vol. 163, pp. 840-849.View/Download from: Publisher's site
© 2017 Elsevier Ltd In this study, a novel coupling testing protocol with separated repetitive loading and freezing-thaw cycles in salt-solution is designed to simulate coupling mechanical loading and complex environmental effects on durability and deterioration of recycled aggregate concrete (RAC). The Micromechanical properties and porosity of RAC were also characterized by scanning electron microscopy (SEM) and microhardness. The results show that the number and width of cracks of RAC and NAC under freeze-thaw cycles obviously increased with the increase of alternating times of repetitive load and the compressive stress level. The compressive strength losses for both RAC and NAC increase with the increase of compressive stress level and alternative times of repetitive load. However, the compressive strength of natural aggregate concrete (NAC) became lower than that of RAC after freeze-thaw cycles. It was found that the freeze-thaw resistance of RAC seems even better than that of NAC under the same freeze-thaw attacks and cyclic mechanical loading. It indicates that after freeze-thaw cycles in salt-solution, the durability of RAC is better than that of NAC. On the other hand, the microhardness and SEM characterization results indicate that the interface transition zone (ITZ) was a weak part in both RAC and NAC, and the ITZ in NAC obviously deteriorated faster than that of RAC.
Li, W, Luo, Z, Long, C, Huang, Z, Huang, L, Yu, Q & Sun, Z 2018, 'Mechanical strengths and microstructures of recycled aggregate concrete incorporating nanoparticles', Advances in Civil Engineering Materials, vol. 7, no. 1, pp. 188-205.View/Download from: Publisher's site
Copyright © 2018 by ASTM International The influences of nanoparticles on the mechanical properties and microstructures of recycled aggregate concrete (RAC) were investigated in this study. The compressive and flexural strengths of RAC with different dosages of nanoSiO2 (NS) and nanoCaCO3 (NC) were tested. Both the scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques were applied to analyze the microstructures and porosity of interfacial transition zones (ITZs) in RAC. Based on the comparison on compressive strength and flexural strength, the NS is more effective than the NC for improving the mechanical properties of RAC. Dispersion of NC particles by a superplasticizer can somewhat improve the early-age strength of RAC but is unlikely to enhance the 28-day mechanical strengths. This may be attributed to the better dispersion and pozzolanic activity of NS compared to NC. The results show that a denser microstructure and a reduction of porosity within ITZs were observed by incorporating NS, which occurred along with the improvement of the mechanical strengths of RAC. Moreover, the NS-modified RAC exhibits less total porosity than the NC-modified RAC. The NS-modified RAC mainly contains small size pores, but the NC-modified RAC has more large pores than the NS-modified RAC, which has negative effects on the mechanical properties of RAC.
Li, W, Luo, Z, Sun, Z, Hu, Y & Duan, WH 2018, 'Numerical modelling of plastic-damage response and crack propagation in RAC under uniaxial loading', MAGAZINE OF CONCRETE RESEARCH, vol. 70, no. 9, pp. 459-472.View/Download from: Publisher's site
Li, X, Liu, YM, Li, WG, Li, CY, Sanjayan, JG, Duan, WH & Li, Z 2018, 'Corrigendum to "Effects of graphene oxide agglomerates on workability, hydration, microstructure and compressive strength of cement paste" [Constr. Build. Mater. 145 (2017) 402–410] (S0950061817307110) (10.1016/j.conbuildmat.2017.04.058))', Construction and Building Materials, vol. 179, pp. 537-538.View/Download from: Publisher's site
© 2018 The authors regret that the SEM image of GO (Fig. 1) should be replaced by a more representative one, which is provided by the material supplier, as given below. The workability measurement (Fig. 2) was plotted incorrect and should be revised by the following. Consequently, the sentence in Abstract should read as follows: The mini-slump diameter was reduced by 27% with the incorporation of 0.03% by weight GO in cement paste. The sentence in Section 4.1 should read as follows: However, when 0.03% by weight GO was added, the mini-slump diameter showed a sudden decrease to a level that was about 27% lower than that of the plain cement paste C. The Acknowledgement should read: The authors are grateful for the financial support of the Australian Research Council in conducting this study. Thanks also go to Mr. Samuel Chuah and Mr. Hongsen He for their great support in materials testing during their stay at the Monash University. The authors would like to apologise for any inconvenience caused.
Li, X, Wang, L, Liu, Y, Li, W, Dong, B & Duan, WH 2018, 'Dispersion of graphene oxide agglomerates in cement paste and its effects on electrical resistivity and flexural strength', CEMENT & CONCRETE COMPOSITES, vol. 92, pp. 145-154.View/Download from: Publisher's site
Li, Y, Li, W, Deng, D, Wang, K & Duan, WH 2018, 'Reinforcement effects of polyvinyl alcohol and polypropylene fibers on flexural behaviors of sulfoaluminate cement matrices', Cement and Concrete Composites, vol. 88, pp. 139-149.View/Download from: Publisher's site
© 2018 Elsevier Ltd The fracture behavior of unoiled/uncoated polyvinyl alcohol (PVA) fiber reinforced sulphoaluminate cement (SAC) matrices was experimentally investigated and compared with those of polypropylene (PP) fiber reinforced SAC and PVA fiber reinforced Portland cement (PC) matrices in this study. In the experimental investigation, three-point bending tests were carried out for notched fiber reinforced cement beams. Special attentions were paid on their deflection-hardening and multiple crack patterns. The different flexural behaviors between the plain SAC and PC matrices were evaluated using the double-K fracture model. The results indicate that the PVA fiber reinforced SAC matrices exhibited better flexural behaviors when compared with the PVA fiber reinforced PC matrix having comparable matrix strength. The bond strength between SAC matrix and PVA fiber are relatively better than that between the counterpart PC matrix and PVA fiber, while the bond strength between SAC matrix and PVA fiber is obviously stronger than that between the SAC and PP fibers.
Liu, Q, Gao, R, Tam, VWY, Li, W & Xiao, J 2018, 'Strain monitoring for a bending concrete beam by using piezoresistive cement-based sensors', Construction and Building Materials, vol. 167, pp. 338-347.View/Download from: Publisher's site
© 2018 Elsevier Ltd Graphite nanoplatelets (GNPs), promising in improving electrical properties of cement-based materials and its smartness, were used to prepare piezoresistive cement-based strain sensors (PCSSs) in this study. Their piezoresistive responses along vertical, horizontal and inclined directions were measured during applying a vertical cyclic compression. After calibrating free PCSSs by analyzing their gauge factors, three PCSSs are embedded in a four-point bending beam at different stress zones, i.e. uniaxial compression, uniaxial tension and combined shear and compression. In addition to investigating piezoresistive responses of PCSSs embedded in the beam, traditional strain gauges and finite element method (FEM) were also used to grasp the strains at relevant positions for comparison. For free PCSSs, It was found that the electrical resistances along vertical, horizontal and diagonal directions drop by amplitudes of 5.5%, 1.8% and 6.7% respectively, as the increasing of vertical compression. The gauge factor along loading direction was calculated to be −160.8, which illustrated a better sensitivity. In the four-point bending beam, the PCSSs in compressive zone and tensile zone can be used to presume the strain variation by considering the gauge factor obtained from the free PCSS. The reaction of the PCSS in shear zone can illustrate its strain features because a slight volume variation happened in this area, which can also be testified to be only 0.012‰with FEM analysis.
Long, G, Liu, H, Ma, K, Xie, Y & Li, W 2018, 'Development of High-Performance Self-Compacting Concrete Applied as the Filling Layer of High-Speed Railway', JOURNAL OF MATERIALS IN CIVIL ENGINEERING, vol. 30, no. 2.View/Download from: Publisher's site
Lu, ZH, Li, H, Li, W, Zhao, YG & Dong, W 2018, 'An empirical model for the shear strength of corroded reinforced concrete beam', Construction and Building Materials, vol. 188, pp. 1234-1248.View/Download from: Publisher's site
© 2018 Elsevier Ltd A total of 158 experimental tests of shear behavior of corroded reinforced concrete (CRC) beams under action of concentrated load, published in the literature were collected and compiled into a shear strength database. This database was firstly used to discuss important parameters which affect the shear strength of CRC beams. The results show that the effect of stirrups' corrosion on shear capacity of CRC beams is greater than that of longitudinal reinforcement corrosion. The shear span-to-depth ratio is also an important factor on shear strength of CRC beams. Total 9 available empirical models for predicting the residual shear strength are evaluated and compared based on the test database. It is found that eight of the nine models underestimate the shear strength of CRC beams while the other model gives the overestimated results. It is in this regard that a new empirical model for predicting the residual shear strength of CRC beams is proposed, in which a reduction coefficient is incorporated with the consideration of the effect of stirrups' corrosion as well as shear span-to-depth ratio. The comparison studies demonstrate that the new proposal can provide an effective and accurate prediction of the shear capacity of CRC beams with a wide range of reinforcement corrosion damages.
Luo, Z, Li, W, Wang, K & Shah, SP 2018, 'Research progress in advanced nanomechanical characterization of cement-based materials', Cement and Concrete Composites, vol. 94, pp. 277-295.View/Download from: Publisher's site
© 2018 Elsevier Ltd Advanced characterization techniques have provided powerful tools for characterizations of materials at micro- and nano-scales worldwide. Although some overviews on nanomechanical characterizations of cement-based materials have been published, they have often focused on nanoindentation. Very limited reviews have been reported on the applications of modulus mapping, PeakForce quantitative nanomechanical mapping, and nanoscratch for researches on the micro and nanoscale compositions, structures and mechanical properties of modern cement-based materials. This paper is aimed at filling this blank. Based on an extensive literature review and authors' own experience, the basic knowledge (e.g., general concepts, developments, and progresses) involved in the state-of-the-art nanomechanical characterization techniques have been systematically summarized in this paper. The critical issues (e.g., sample preparation procedures and requirements, measurements, and data analysis methods) of these techniques have been discussed in details. The applications of these techniques, especially their suitability for critical characterization of different scales of interfaces of cement-based materials are compared. Finally, the future perspectives of these nanomechanical characterization techniques are highlighted. It is expected that the outlook of this paper can help future researchers make scientific justification on selection of nanomechanical characterization methods and steer inquisitive readers into substantial details that may lead them to successful applications of these advanced techniques.
Qin, L, Gao, X, Li, W & Ye, H 2018, 'Modification of magnesium oxysulfate cement by incorporating weak acids', Journal of Materials in Civil Engineering, vol. 30, no. 9.View/Download from: Publisher's site
© 2018 American Society of Civil Engineers. This paper investigates the effects of weak acids (citric acid, boric acid, and trisodium citrate) with dosages of 0.5, 1.5, and 2.5% of MgO weight on compressive strength, water resistance, and drying shrinkage of magnesium oxysulfate (MOS) cement. Hydration products and microstructure of typical samples are studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis-thermogravimetry (DTA-TG), and scanning electron microscope (SEM) facilities. The results show that compressive strength of MOS cement increases with an increasing MgO/MgSO4 molar ratio and decreasing H2O/MgSO4 molar ratio. The addition of citric acid, boric acid, or trisodium citrate significantly enhances compressive strength and water resistance and alleviates drying shrinkage of MOS cement paste. With the incorporation of weak acid, 5 · 1 · 7 [5Mg(OH)2 · MgSO4 · 7H2O] phase, which is a new magnesium subsulfate crystalline product with a needlelike crystal whisker shape, forms in cement paste. This substance behaves in a criss-crossing manner and fills in pores and microcracks, inducing the improved performance of MOS cement paste. With optimum dosages of 0.5, 2.5, and 0.5%, respectively, citric acid, trisodium citrate, and boric acid exhibit decreasing improvement effect.
Li, W, Luo, Z, Wu, C & Duan, WH 2018, 'Impact performances of steel tube-confined recycled aggregate concrete (STCRAC) after exposure to elevated temperatures', CEMENT & CONCRETE COMPOSITES, vol. 86, pp. 87-97.View/Download from: Publisher's site
Chen, SJ, Li, WG, Ruan, CK, Sagoe-Crentsil, K & Duan, WH 2017, 'Pore shape analysis using centrifuge driven metal intrusion: Indication on porosimetry equations, hydration and packing', Construction and Building Materials, vol. 154, pp. 95-104.View/Download from: Publisher's site
© 2017 Porosity is an intrinsic property of many cementitious materials. This study uses a new centrifugation-based low-melting-point metal intrusion technique to characterize and analyze the shape of pores in cementitious materials. Low energy electrons with ultra-long beam dwell time are used to obtain nano meter level resolution of the pore shape. Three descriptors, namely circularity, solidity, and aspect ratio, are proposed to represent the area-perimeter relationship, hydration and packing and 3D shape of the pores, respectively. Circularity is found to hold a consistent power correlation with pore size. Based on this correlation, the Washburn's equation is modified to correct the biased prediction of pore size using mercury intrusion porosimetry (MIP). Solidity, is found to decrease with increased pore size, denser packing of cement particles and more hydration products. Aspect ratio of the observed pores is found to average at about 2 representing an oblate ellipsoid shape of pore in 3D space.
Hou, P, Cai, Y, Cheng, X, Zhang, X, Zhou, Z, Ye, Z, Zhang, L, Li, W & Shah, SP 2017, 'Effects of the hydration reactivity of ultrafine magnesium oxide on cement-based materials', Magazine of Concrete Research, vol. 69, no. 22, pp. 1135-1145.View/Download from: Publisher's site
The size of magnesium oxide may greatly affect its behaviour in cement-based materials (CBMs), and this has not been fully investigated. The reactivity of ultrafine magnesium oxide (UFM) of size 40 nm to 20 μm was assessed, and its effects on the compressive strength and volume stability of cement mortar were investigated. The results showed that the hydration of UFM followed the first-order reaction mode in the first 3 d and then slowed down due to the alteration of the reaction to the diffusion-controlled mode. UFM contributed to an increase in compressive strength and a decrease in shrinkage of CBMs at the very early age, but hindered the hydration of cement at later ages, coarsened the microstructure, and decreased the later-age shrinkage to a much smaller extent than normal light-burnt magnesium oxide. The relatively high hydration reactivity of UFM may contribute to the formation of a more compact gel structure around cement particles at the very early age, which may hinder the reaction of cement at later ages, thus leading to the slowed property gain of CBMs at later ages. The findings from this study may help in the selection of magnesium oxide types for achieving a desired CBM with certain properties.
Li, W, Huang, Z, Hu, G, Hui Duan, W & Shah, SP 2017, 'Early-age shrinkage development of ultra-high-performance concrete under heat curing treatment', Construction and Building Materials, vol. 131, pp. 767-774.View/Download from: Publisher's site
© 2016 Elsevier LtdThe effects of a novel heat curing regime and longitudinal reinforcement ratio on early-age shrinkage of ultra-high performance concrete (UHPC) were experimentally investigated in this study. The microstructure, porosity and calcium hydroxide (CH) content of UHPC after different heat curing durations were characterized with scanning electron microscopy, mercury intrusion porosimetry and thermal analysis. The results indicate that slight shrinkage was observed when the heat curing duration was less than 60 min and curing temperature reached 48 °C. However, when the heat curing duration approached 70 min and curing temperature was around 55 °C, the early-age shrinkage increased dramatically. It was found that the early-age shrinkage is approximately 450 με after 48 h of heat curing. The results also show that the early-age shrinkage of UHPC significantly decreased by percentage of 33–60% with the increase of longitudinal steel reinforcement ratio from 2.0 to 4.52%. Meantime, after 10 h of heat curing, the cement hydration and secondary hydration in UHPC tend to finish, which consequently leads to dense microstructure and low CH content in UHPC.
Li, W, Li, X, Chen, SJ, Liu, YM, Duan, WH & Shah, SP 2017, 'Effects of graphene oxide on early-age hydration and electrical resistivity of Portland cement paste', Construction and Building Materials, vol. 136, pp. 506-514.View/Download from: Publisher's site
© 2017 Elsevier Ltd The effects of graphene oxide (GO) on the early-age hydration process and mechanical properties of Portland cement paste were experimentally investigated in this study. Based on an isothermal calorimeter measurement, the hydration rate of cement was observed to increase with the increase of GO content by nucleation effect. On the other hand, the electrical resistivity development of GO-cement paste was monitored using a non-contact electrical resistivity device. The result showed that electrical the resistivity of GO-cement paste was evidently higher than that of plain cement paste. However, cement paste with excessive amounts of GO exhibited a decreased electrical resistivity due to the massive ion diffusion caused by GO. Compared to plain cement paste, the GO-cement paste exhibited obviously higher compressive and flexural strengths, but the enhancements in compressive strength began to decline when the GO amount was greater than 0.04%. The microstructure characterization indicated that GO can apparently densify the cement pastes with less porosity and hydrates networking, which is consistent with the results of hydration acceleration and strength enhancement.
Li, W, Li, X, Chen, SJ, Long, G, Liu, YM & Duan, WH 2017, 'Effects of nanoalumina and graphene oxide on early-age hydration and mechanical properties of cement paste', Journal of Materials in Civil Engineering, vol. 29, no. 9.View/Download from: Publisher's site
© 2017 American Society of Civil Engineers. The effects of nanoalumina (NA) and graphene oxide (GO) on the early-age hydration and mechanical properties of portland cement pastes were investigated in this study. The hydration heat release rate and cumulative heat of cement pastes incorporating different dosages of NA and GO were evaluated using an isothermal calorimeter measurement method. Early-age electrical resistivity development was investigated by a noncontact electrical resistivity technique. The results show that both NA and GO could efficiently accelerate cement hydration. As a physical filler, NA significantly accelerates the hydration of tricalcium aluminate (C 3 A) in cement. On the other hand, GO is able to obviously reduce the dormant period of cement hydration and shift the heat flow peaks to the left by accelerating the hydration of tricalcium silicate (C 3 S) in cement. Compared to plain cement pastes, both the compressive and flexural strengths of cement pastes incorporating NA or GO are significantly increased. However, when NA and GO contents exceed the optimal amounts, improvements in flexural strength tend to decline, which is probably due to particle agglomeration. NA-cement paste exhibited slightly higher electrical resistivity than plain cement paste during hydration acceleration and deceleration stages. But GO-cement paste clearly showed lower electrical resistivity, which might be attributed to iron diffusion caused by GO with large surface areas.
Li, W, Long, C, Luo, Z & Huang, Z 2017, 'Investigation on Failure Mechanism of Nanomodified Recycled Aggregate Concrete', Jianzhu Cailiao Xuebao/Journal of Building Materials, vol. 20, no. 5.View/Download from: Publisher's site
© 2017, Editorial Department of Journal of Building Materials. All right reserved. The crack evolution of recycled aggregate concrete (RAC) and the performance of RAC after incorporation of different amount of nanoparticles (nanosilica sol and nanolimestone) were studied. Under uniaxial compression, the crack development of RAC specimens with different water-cement ratios (0.4, 0.5 and 0.6) and aggregate replacement ratios were observed by high speed camera. Scanning electron microscopy (SEM) observation and mercury injection test were conducted for studying the microscopic morphology and pore structure of the interfacial transition zone (ITZ) of nanomodified RAC and the influences of different mass fraction of nanoparticles and different treatment processes on it were analyzed. The results indicate that the crack of RAC is usually derived from new ITZ or old ITZ (determined by the weaker one) and then it gradually extends to the surrounding area. The evolution of crack eventually leads to the longitudinal splitting failure of the RAC. Nanosilica sol could improve the microstructure of ITZ. Therefore, the strength of nanosilica sol modified RAC was enhanced. But the improvement by nanolimestone is not very significant for it can't enter the interface transition zone to fill the pore in it.
Li, W, Long, C, Tam, VWY, Poon, CS & Hui Duan, W 2017, 'Effects of nano-particles on failure process and microstructural properties of recycled aggregate concrete', Construction and Building Materials, vol. 142, pp. 42-50.View/Download from: Publisher's site
© 2017 Elsevier Ltd The effects of nano-particles including nano-silica (NS) and nano-limestone (NL) on the crack propagation and microstructure properties of recycled aggregate concrete (RAC) were experimentally investigated in this study. The crack initiation and propagation of nano-particles modified RAC with different nano-particle modification were evaluated using digital image correlation technique (DIC). The microstructures and porosity of interfacial transition zones (ITZ) in nano-modified RAC were also examined using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). It was found that the micro-cracks were typically derived from relatively weak ITZs in RAC, and then progressively propagated along the compressive loading direction. The meso-crack developments eventually led to final splitting failure. The results indicated that compared to NL, NS was more effective in improving the microstructure properties and enhance the mechanical strength of RAC. The porosity and water absorption of RAC were obviously reduced by the NS incorporation. However, due to particles agglomeration, NL could not effectively improve the microstructure of RAC for further enhancing the RAC mechanical properties. Furthermore, in terms of severe particles agglomeration, NL was even detrimental to the mechanical strength of RAC especially at the late-age.
Li, W, Luo, Z, Long, C & Huang, L 2017, 'Experimental Study on the Dynamical Mechanical Performance of Nanomodified Recycled Aggregate Concrete', Hunan Daxue Xuebao/Journal of Hunan University Natural Sciences, vol. 44, no. 9, pp. 92-99.View/Download from: Publisher's site
© 2017, Editorial Department of Journal of Hunan University. All right reserved. The dynamic mechanical performances of recycled aggregate concrete (RAC) incorporating with 1% to 2% nano-SiO2or nano-CaCO3were tested by Split Hopkinson Pressure Bar (SHPB). The effects of different kind is of nanoparticles and different dosages on the mechanical performances of RAC were investigated. The results revealed that RACs with nano-SiO2and nano-CaCO3all zhowed higher dynamic compressive strength than the control RAC, and the nano-SiO2was more effectire than nano-CaCO3in enhancing the dynamic compressive strength of RAC. But RACs with high dosage of nano-SiO2or nano-CaCO3usually showed lower dynamic compressive strength than that of low dosage one, and the RAC incorporating with 1% nano-SiO2achieved the highest dynamic compressive strength. Nano-CaCO3exhibited more advantage in improving the deformation performance and energy absorption capacity of RAC. Both nano-SiO2modified RAC and nano-CaCO3modified RAC showed lower dynamic increase factor than control RAC.
Li, W, Luo, Z, Tao, Z, Duan, WH & Shah, SP 2017, 'Mechanical behavior of recycled aggregate concrete-filled steel tube stub columns after exposure to elevated temperatures', Construction and Building Materials, vol. 146, pp. 571-581.View/Download from: Publisher's site
© 2017 Elsevier Ltd The compressive mechanical behaviors of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposure to elevated temperatures were experimentally investigated in this study. The RACFST stub columns incorporating different recycled coarse aggregate (RCA) replacement ratios of 0, 50% and 100% were heated under elevated temperatures of 200 °C, 500 °C, and 700 °C. The results show that the compressive strength and elastic modulus of RACFST columns were relatively inferior to those of the corresponding natural aggregate concrete-filled steel tube (NACFST) columns after exposure to the same elevated temperatures, and the degradations became more pronounced with increasing RCA replacement ratio and higher temperature. This phenomenon might be attributed to the lower resistance of recycled aggregate concrete (RAC) than natural aggregate concrete (NAC) when was exposed to elevated temperatures. However, after elevated temperature exposure, the peak strain of RACFST stub column was relatively higher than that of the NACFST counterpart. Degradation regression formulas of mechanical properties and deformation behaviors of RACFST stub columns after exposure to elevated temperatures were proposed and agreed well with the experimental results.
Li, W, Sun, Z, Luo, Z & Shah, SP 2017, 'Retraction: Influence of Relative Mechanical Strengths between New and Old Cement Mortars on the Crack Propagation of Recycled Aggregate Concrete', Journal of Advanced Concrete Technology, vol. 15, no. 3, pp. 110-125.View/Download from: Publisher's site
Li, W, Sun, Z, Luo, Z & Shah, SP 2017, 'Retraction: Influence of relative mechanical strengths between new and old cement mortars on the crack propagation of recycled aggregate concrete (Journal of Advanced Concrete Technology (2017) 15:3 (110-125) DOI: 10.3151/jact.15.110)', Journal of Advanced Concrete Technology, vol. 15, no. 3.
© 2017 Japan Concrete Institute. All rights reserved. We reported "Influence of Relative Mechanical Strengths between New and Old Cement Mortars on the Crack Propagation of Recycled Aggregate Concrete" in Journal of Advanced Concrete Technology, Vol. 15 (2017) No. 3 p. 110-125; doi: 10.3151/jact.15.110. After publication of the paper, we have become aware of the copyright violation from the original research. We therefore decided to retract the paper and apologize for any inconvenience caused by the retraction.
Li, X, Liu, YM, Li, WG, Li, CY, Sanjayan, JG, Duan, WH & Li, Z 2017, 'Effects of graphene oxide agglomerates on workability, hydration, microstructure and compressive strength of cement paste', Construction and Building Materials, vol. 145, pp. 402-410.View/Download from: Publisher's site
© 2017 Elsevier Ltd In this study, the effects of graphene oxide (GO) agglomerates on the workability, hydration, microstructure, and compressive strength of cement paste were addressed. The workability of cement paste was reduced because of the presence of GO agglomerates, which entrap a large amount of water. The mini-slump diameter was reduced by 21% with the incorporation of 0.03% by weight GO in cement paste. Hydration of the cement paste was accelerated due to nucleation sites provided by GO agglomerates serving as seeding material in the cement paste. The incorporation of GO refined the pore structure of the cement paste. The incorporation of GO was found to have much greater impact on macropores than on large and small mesopores. At 28 days, the incorporation of 0.04% by weight GO produced a 14% improvement in the compressive strength of cement paste. Below 0.03%, the incorporation of GO had no positive effects on compressive strength.
Li, X, Lu, Z, Chuah, S, Li, W, Liu, Y, Duan, WH & Li, Z 2017, 'Effects of graphene oxide aggregates on hydration degree, sorptivity, and tensile splitting strength of cement paste', Composites Part A: Applied Science and Manufacturing, vol. 100, pp. 1-8.View/Download from: Publisher's site
© 2017 Elsevier Ltd It has recently been found the graphene oxide (GO) aggregates form in cement paste due to the chemical cross-linking of calcium cations. Therefore, the effects of GO addition on the properties of cement based materials should be dependent on the properties of GO aggregates rather than GO nanosheets. In this study, GO aggregates were first characterized by particle size measurement. Then, the effects of GO aggregates on the degree of hydration, sorptivity, and tensile strength of cement paste were investigated. The aspect ratio of GO aggregates is much larger than that of the original GO nanosheets. Compared to plain cement paste, the increase of non-evaporable water content of the cement paste was found to be very limited, around 1.17% and 3.90% for cement pastes containing 0.02% and 0.04% by weight GO, respectively. The sorptivity of cement paste, especially the secondary sorptivity, was notably reduced for GO incorporated cement paste. The tensile strength was significantly improved by GO aggregates. Incorporation of 0.04% by weight GO increased the tensile strength by 67% compared to that of plain cement paste.
Su, Y, Wu, C, Li, J, Li, Z-X & Li, W 2017, 'Development of novel ultra-high performance concrete: From material to structure', CONSTRUCTION AND BUILDING MATERIALS, vol. 135, pp. 517-528.View/Download from: Publisher's site
Li, W, Luo, Z, Wu, C, Tam, VWY, Duan, WH & Shah, SP 2017, 'Experimental and numerical studies on impact behaviors of recycled aggregate concrete-filled steel tube after exposure to elevated temperature', Materials and Design, vol. 136, pp. 103-118.View/Download from: Publisher's site
© 2017 Elsevier Ltd This study investigated the impact behaviors of recycled aggregate concrete-filled steel tube (RACFST) after exposed to elevated temperatures by experimental and numerical studies. The impact test on RACFST was conducted by a split Hopkinson pressure bar (SHPB) with 100 mm-diameter. After the validation of finite element method simulation by the experimental results, parametric analysis were applied to analyze the effects of RAC strength, steel strength and steel ratio on the impact behaviors and deformation properties of the RACFSTs exposed to elevated temperatures ranging from 20 °C, 200 °C to 500 °C and to 700 °C. The results show that both the increases in RAC strength, steel strength and steel ratio significantly enhance the impact resistance of RACFST. However, when RAC strength deteriorates quickly after exposure to high temperature, the increase in RAC strength just slightly improves the impact properties of RACFST, especially after exposure to elevated temperatures higher than 500 °C. In conclusion, increasing steel ratio is an effective way for improving the impact behaviors of RACFST, but resulting in higher cost for practical application. For the impact design of RACFST, steel strength and steel ratio are two essential factors in terms of impact behavior enhancement and cost efficiency.
Gao, C, Huang, L, Yan, L, Kasal, B & Li, W 2016, 'Behavior of glass and carbon FRP tube encased recycled aggregate concrete with recycled clay brick aggregate', COMPOSITE STRUCTURES, vol. 155, pp. 245-254.View/Download from: Publisher's site
Li, W, Huang, Z, Zu, T, Shi, C, Duan, WH & Shah, SP 2016, 'Influence of Nanolimestone on the Hydration, Mechanical Strength, and Autogenous Shrinkage of Ultrahigh-Performance Concrete', JOURNAL OF MATERIALS IN CIVIL ENGINEERING, vol. 28, no. 1.View/Download from: Publisher's site
Li, W, Kawashima, S, Xiao, J, Corr, DJ, Shi, C & Shah, SP 2016, 'Comparative investigation on nanomechanical properties of hardened cement paste', Materials and Structures/Materiaux et Constructions, vol. 49, no. 5, pp. 1591-1604.View/Download from: Publisher's site
© 2015, RILEM. Three types of nanomechanical methods including static nanoindentation, modulus mapping and peak-force quantitative nanomechanical mapping (QNM) were applied to investigate the quantitative nanomechanical properties of the same indent location in hardened cement paste. Compared to the nanoindentation, modulus mapping and peak-force QNM allow for evaluating local mechanical properties of a smaller area with higher resolution. Beside, the ranges of elastic modulus distribution measured by modulus mapping and peak-force QNM are relatively greater than that obtained from nanoindentation, which may be due to a result of the shaper probe and local confinement effect between multiple phases. Moreover, the average value of elastic modulus obtained using peak-force QNM were consistent with those obtained by modulus mapping, while the different in modulus probability distribution could be related to the different nanomechancial theories and contact forces. The probability distributions of elastic modulus measured using nanomechanical methods to provide a basis for the different types of phases existing in cement paste. Based on the observation with high spatial resolution, cement paste can be likely found as nanocalse granular material, in which different submicron scale or basic nanoscale grain units pack together. It indicates that the peak-force QNM can effectively provide an effective insight into the nanostructure characteristic and corresponding nanomechanical properties of cement paste.
Ouyang, J, Han, B, Cao, Y, Zhou, W, Li, W & Shah, SP 2016, 'The role and interaction of superplasticizer and emulsifier in fresh cement asphalt emulsion paste through rheology study', CONSTRUCTION AND BUILDING MATERIALS, vol. 125, pp. 643-653.View/Download from: Publisher's site
Shi, C, Li, Y, Zhang, J, Li, W, Chong, L & Xie, Z 2016, 'Performance enhancement of recycled concrete aggregate - A review', JOURNAL OF CLEANER PRODUCTION, vol. 112, pp. 466-472.View/Download from: Publisher's site
Xiao, J, Qu, W, Li, W & Zhu, P 2016, 'Investigation on effect of aggregate on three non-destructive testing properties of concrete subjected to sulfuric acid attack', CONSTRUCTION AND BUILDING MATERIALS, vol. 115, pp. 486-495.View/Download from: Publisher's site
Li, W, Luo, Z, Long, C, Wu, C, Duan, WH & Shah, SP 2016, 'Effects of nanoparticle on the dynamic behaviors of recycled aggregate concrete under impact loading', MATERIALS & DESIGN, vol. 112, pp. 58-66.View/Download from: Publisher's site
Li, W, Huang, Z, Cao, F, Sun, Z & Shah, SP 2015, 'Effects of nano-silica and nano-limestone on flowability and mechanical properties of ultra-high-performance concrete matrix', CONSTRUCTION AND BUILDING MATERIALS, vol. 95, pp. 366-374.View/Download from: Publisher's site
Li, W, Xiao, J, Kawashima, S, Shekhawat, GS & Shah, SP 2015, 'Experimental investigation on quantitative nanomechanical properties of cement paste', ACI Materials Journal, vol. 112, no. 2, pp. 229-238.View/Download from: Publisher's site
Copyright © 2015, American Concrete Institute. All rights reserved. Nanoindentation, quantitative modulus mapping, and PeakForce quantitative nanomechanical mapping (QNM) are applied to investigate the quantitative nanomechanics of hardened cement paste at different spatial resolutions. The elastic modulus measured by static nanoindentation is slightly higher than those measured by the other methods. The average elastic modulus and probability obtained by PeakForce QNM are typically consistent with those found by modulus mapping. Both modulus mapping and PeakForce QNM can be used to discriminate different material phases in cement paste at the nanoscale. It concludes that cement paste is a granular material in which the sub-micron scale grains or basic nanoscale units pack together. Moreover, the high resolution Peak-Force QNM can provide an efficient tool for identifying nanomechanical properties, particle sizes, and thickness of the interface between different nanoscale grains.
Li, W, Xiao, J, Shi, C & Poon, CS 2015, 'Structural Behaviour of Composite Members with Recycled Aggregate Concrete - an Overview', ADVANCES IN STRUCTURAL ENGINEERING, vol. 18, no. 6, pp. 919-938.View/Download from: Publisher's site
Li, W, Xiao, J, Yi, W & Shah, SP 2014, 'Experimental study on failure mechanism of modeled recycled aggregate concrete under uniaxial compression', Jianzhu Jiegou Xuebao/Journal of Building Structures, vol. 35, pp. 340-348.View/Download from: Publisher's site
©, 2014, Science Press. All right reserved. In this study, systematic experimental research was carried out to investigate the crack propagation of modeled recycledag gregate concrete (MRAC) under uniaxial compressive loading. A two-dimensional nondestructive digital image correlation (DIC) technique was applied to record the initiation and propagation of surface micro-cracks. The obtained results indicate that the fracture process and crack pattern of MRAC are greatly affected by the relative strength of new interfacial transition zone (ITZ) and old ITZ. The bond cracks first appear around the weak ITZs and then propagate into the mortar region by connecting with each other. When the strength of the new ITZ is inferior to that of the old ITZ, the first visible crack mostly appears at the new ITZ region. Also, when the strength of the new ITZ is better than that of the old ITZ, the first visible crack mostly appears at the old ITZ region. When the strength of the new ITZ is equal to that of old ITZ, the first observable cracks appear around both the new and old ITZs. Based on the propagation and coalescence processes of the surface micro-crack, an in-depth analysis was carried out on the whole failure process to reveal the failure mechanism and the crack evolution of recycled aggregate concrete.
Li, WG, Xiao, JZ, Huang, L & Shah, SP 2014, 'Experimental study on mechanical properties of interfacial transition zones in recycled aggregate concrete', Hunan Daxue Xuebao/Journal of Hunan University Natural Sciences, vol. 41, no. 12, pp. 31-39.
©, 2014, Hunan University. All right reserved. The mechanical properties of Recycled Aggregate Concrete (RAC) with different mixing approaches were comparatively investigated. Based on the experiments on the Interfacial Transition Zone (ITZ) of RAC by nanoindentation technique and scanning electron microscopy, the results indicate that, for the new ITZ with Normal Mixing Approach (NMA), the elastic modulus distribution appears to decrease significantly from the old paste matrix surface, while for the new ITZ with Two-Stage Mixing Approach (TSMA), there is no obvious trend indicating that the elastic modulus increases or decreases with the increase of distance. For the old ITZ, the elastic modulus increases as the distance increases from original aggregate surface. The TSMA can improve the microstructures of the new ITZ by reducing the volume fraction of voids and calcium hydroxide. Correlating the nanomechanical properties of ITZ and microstructure with the compressive strength of RAC, it can be concluded that TSMA can enhance the mechanical properties of RAC by improving the mechanical properties and microstructure of the new ITZ.
Xiao, J, Li, W, Corr, DJ & Shah, SP 2013, 'Effects of interfacial transition zones on the stress-strain behavior of modeled recycled aggregate concrete', CEMENT AND CONCRETE RESEARCH, vol. 52, pp. 82-99.View/Download from: Publisher's site
Xiao, J, Li, W, Corr, DJ & Shah, SP 2013, 'Simulation Study on the Stress Distribution in Modeled Recycled Aggregate Concrete under Uniaxial Compression', JOURNAL OF MATERIALS IN CIVIL ENGINEERING, vol. 25, no. 4, pp. 504-518.View/Download from: Publisher's site
Xiao, J, Li, W, Sun, Z, Lange, DA & Shah, SP 2013, 'Properties of interfacial transition zones in recycled aggregate concrete tested by nanoindentation', CEMENT & CONCRETE COMPOSITES, vol. 37, pp. 276-292.View/Download from: Publisher's site
Li, W, Xiao, J & Yuan, J 2012, 'Stress distribution characteristics of modeled recycled aggregate concrete under uniaxial compression', Tongji Daxue Xuebao/Journal of Tongji University, vol. 40, no. 6, pp. 906-913.View/Download from: Publisher's site
Based on the mechanical properties of each material phase in recycled aggregate concrete (RAC), a two-dimensional modeled RAC was built, and the stress distribution characteristics of the modeled RAC under uniaxial compressive were obtained by meso-level numerical analysis. A parametric analysis was conducted to investigate the sensitivity of the stress distribution of the modeled RAC, which focused on different mechanical parameters of natural aggregate, interfacial transition zone (ITZ) and old hardened mortar. Results show that a concentration of tensile stress and shear stress produces at new and old interfacial transition zones between the natural aggregates. The higher elastic modulus of natural aggregates are, the higher the magnitude of stress concentration is, and the higher elastic modulus of the interfacial transition are, the lower the magnitude of stress concentration is. Whereas the effects of the elastic modulus of old hardened mortar on stress concentration are not evident.
Li, W, Xiao, J, Sun, Z & Shah, SP 2012, 'Failure processes of modeled recycled aggregate concrete under uniaxial compression', Cement and Concrete Composites, vol. 34, no. 10, pp. 1149-1158.View/Download from: Publisher's site
In order to investigate the failure processes of Recycled Aggregate Concrete (RAC), cracking behavior of modeled RAC specimens under compressive loading was investigated using Digital Image Correlation (DIC). Strain and displacement contour maps were produced to analyze the cracks' initiation and propagation during loading. The testing results indicate that the discrepancy between the elastic moduli of coarse aggregates and mortar matrix significantly influences the mechanical properties and crack patterns of the modeled materials. It is found that the failure process is related to the relative strength of coarse aggregate and mortar matrix. For modeled RAC, the first bond cracks appear around both the old and new interfacial transition zones (ITZ), and then propagate into the old and new mortar matrix by connecting each other. The observation implies that the initiations and propagations of microcracks are different between RAC and Natural Aggregate Concrete (NAC). The findings in this investigation are useful to improve the mechanical properties of RAC by optimizing the mix proportion. © 2012 Elsevier Ltd. All rights reserved.
Li, W, Xiao, J, Sun, Z, Kawashima, S & Shah, SP 2012, 'Interfacial transition zones in recycled aggregate concrete with different mixing approaches', CONSTRUCTION AND BUILDING MATERIALS, vol. 35, pp. 1045-1055.View/Download from: Publisher's site
Xiao, J, Li, W & Poon, C 2012, 'Recent studies on mechanical properties of recycled aggregate concrete in China-A review', SCIENCE CHINA-TECHNOLOGICAL SCIENCES, vol. 55, no. 6, pp. 1463-1480.View/Download from: Publisher's site
Xiao, J, Li, W, Fan, Y & Huang, X 2012, 'An overview of study on recycled aggregate concrete in China (1996-2011)', CONSTRUCTION AND BUILDING MATERIALS, vol. 31, pp. 364-383.View/Download from: Publisher's site
Xiao, J, Li, W, Sun, Z & Shah, SP 2012, 'Crack Propagation in Recycled Aggregate Concrete under Uniaxial Compressive Loading', ACI MATERIALS JOURNAL, vol. 109, no. 4, pp. 451-461.
Xiao, J, Li, W & Liu, Q 2011, 'Meso-level numerical simulation on mechanical properties of modeled recycled concrete under uniaxial compression', Tongji Daxue Xuebao/Journal of Tongji University, vol. 39, no. 6, pp. 791-797.View/Download from: Publisher's site
A modeled recycled concrete is proposed. According to the meso- and micro-level mechanics parameters and constitutive relationships of the five-phase medium materials of recycled concrete, the failure mechanism of recycled concrete is numerically simulated. An investigation is made into the replacement of recycled coarse aggregate, the strength of the new or old hardened cement paste, the thickness of the old hardened cement paste, and the strength of interfacial transition zone (ITZ) on the mechanical properties of modeled recycled concrete under uniaxial compression. The results indicate that the strength of the new and old hardened cement paste have a remarkable influence on the initial elastic modulus and peak stress. The thickness of the old cement paste has some certain influence on the initial elastic modulus and peak strain. Furthermore, the influence of the strength of interfacial transition zones on the initial elastic modulus, peak stress and peak strain is not distinctive.
Liu, Q, Xiao, JZ & Li, WG 2010, 'Axial tensile test and lattice model simulation on recycled concrete', Sichuan Daxue Xuebao (Gongcheng Kexue Ban)/Journal of Sichuan University (Engineering Science Edition), vol. 42, no. SUPPL. 1, pp. 119-124.
The mechanical parameters of each phase of recycled concrete such as the old hardened mortar, new hardened mortar, and interfacial transition zone (ITZ) were obtained by axial tension tests, and the failure mechanism of recycled concrete under axial tensile loading was studied. Based on the relevant knowledge of solid mechanics and mechanical properties of each phase of recycled concrete, a new meso-level lattice model of recycled concrete was proposed. According to the material parameters of each phase of recycled concrete, lattice model simulation on the failure mechanisms of the recycled concrete under axial tension was carried out by the lattice model, the axial tensile stress-strain relationship curves for recycled concrete were attained, and the internal damage process and tensile failure mechanism of recycled concrete were discussed. The results showed that the tensile fracture occurred approximately in the old or new hardened mortar, and the results of lattice model simulation were consistent with those of axial tensile tests.
Xiao, J, Li, W & Tawana, MM 2010, 'On 4R Principle in the Rehabilitation of Concrete Historic Buildings', 7TH INTERNATIONAL CONFERENCE ON STRUCTURAL ANALYSIS OF HISTORIC CONSTRUCTIONS: STRENGTHENING AND RETROFITTING, PTS 1 AND 2, vol. 133-134, pp. 985-990.View/Download from: Publisher's site
© 2020, Springer Nature Singapore Pte Ltd. Solid waste disposal has been emerging as a challenging issue worldwide following the enhanced economic activities and rapid urbanization. Considerable efforts have been made to use solid waste materials as partial cement replacement in concrete. This work investigates the sulfate resistance of concrete containing different solid waste materials—waste glass powder, coal gangue powder and fly ash, at various substitution levels (10, 20, and 30%). Two water to binder ratios were adopted as 0.41 and 0.54. The sulfate resistance was evaluated by exposing the prepared concrete specimens to a 5% sodium sulfate solution for a total period of 22 months and examining the mass change, compressive strength, splitting tensile strength, ultrasonic pulse velocity, mineralogical and microstructural properties. Results obtained show that the sulfate resistance of concrete can be improved substantially by the addition of solid waste materials. Additionally, waste glass powder is found to be the most effective, followed by gangue coal powder and fly ash. These studies reveal that in addition to helping solid waste management, reusing of these solid waste materials in concrete improves the resistance to sulfate attack.
Li, W, Luo, Z, Xiao, J & Shah, SP 2019, 'Impact behaviors of recycled aggregate concrete with nanoparticles', FIB 2018 - Proceedings for the 2018 fib Congress: Better, Smarter, Stronger, pp. 3984-3992.
© 2019 by the fib. All rights reserved. A 100 mm-diameter split Hopkinson pressure bar (SHPB) was used to investigate effects of nanoparticles on the dynamic mechanical properties of recycled aggregate concrete (RAC) under impact loading. The nano-SiO2 (NS) and nano-CaCO3 (NC) were incorporated to replace cement by mass of 1 and 2% in RACs. The impact velocities were set as 7.7, 9.8 and 11.6 m/s in the SHPB tests. The effects of nanoparticles on failure patterns, compressive strengths, elastic modulus, peak strain and dynamic increase factor (DIF) of RACs under different strain rates were analyzed and discussed. The results show that nanomodified RACs exhibit higher both quasi-static and dynamic compressive strengths compared to control RAC. Dynamic elastic modulus of RAC seems not to be affected by nanoparticles dosages and impact velocities. Compared to NC, NS is more effective in improving dynamic compressive strengths of RAC.
Wu, C, Li, W & Tao, Z 2018, 'Influence of aggregate spatial distribution of concrete against projectile penetration', IOP Conference Series: Materials Science and Engineering, International Conference on Concrete Engineering and Technology, Kuala Lumpur, Malaysia.View/Download from: Publisher's site
© 2018 Institute of Physics Publishing. All rights reserved. Coarse aggregate settlement may occur during concrete pouring, which affects the ability to resist projectile attack. In order to study the anti-penetration performance of concrete, and obtain high penetration resistance concrete, mesoscale finite element model of different aggregate space distribution of concrete was established, the numerical simulation of long rod rigid projectile penetrating into different concrete was conducted. The results showed that aggregate settlement had great influence on target scabbing; aggregate size and settlement had limited influence on projectile residual velocity.
Li, WG, Luo, ZY, Long, C, Duan, WH & Shah, SP 2016, 'Influences of graphene oxide on electrical resistivity development of Portland cement paste', Mechanics of Structures and Materials: Advancements and Challenges - Proceedings of the 24th Australasian Conference on the Mechanics of Structures and Materials, ACMSM24 2016, Australian Conference on the Mechanics of Structures and Materials, CRC Press, Perth, Australia, pp. 449-452.
© 2017 Taylor & Francis Group, London. Investigation on effect of Graphene Oxide (GO) on hydration process of Portland cement paste was comprehensively conducted using non-contact electrical resistivity measurement. GO additions from 0.01 to 0.08% by weight of cement were incorporated into cement paste with water/cement ratio of 0.40. The electrical resistivity development of cement pastes incorporating GO additions were monitored by non-contacting measurement method. It shows that the electrical resistivity of GO-cement paste increased at early-age compared to pure cement paste. However, because of ions diffusion caused by GO in liquid phases, the electrical resistivity of GO-cement paste declined increased when high GO additions were incorporated. Moreover, the microstructure characterization indicated that GO can refine the microstructure of GO-cement pastes with more connected hydration products.
Zhang, Z, Shao, XD, Li, WG & Cao, JH 2014, 'A lightweight composite bridge deck system', Bridge Maintenance, Safety, Management and Life Extension - Proceedings of the 7th International Conference of Bridge Maintenance, Safety and Management, IABMAS 2014, International Conference of Bridge Maintenance, Safety and Management, Shanghai, China, pp. 1422-1427.
Based on some issues of existing Orthotropic Steel Deck (OSD) bridges, an innovative composite bridge deck system composed of OSD and Compact Reinforced Reactive Powder Concrete (CRRPC) overlay is presented. The Stress Reduction Factor (SRF) and tensile properties are targeted to evaluate its effectiveness. The SRF computation results reveal that thin CRRPC overlay drops the maximum stress from 178.20 MPa to 75.36 MPa in the deck plate and it extends the fatigue life by 13.22 times. Furthermore, several direct-tension tests of both with and without steel-bar reinforcement are implemented. Those tests demonstrate that the maximum post-cracking stresses are increased by four times when reinforced with steel-bars. Eventually, an overload fatigue test is employed to assess the fatigue resistance of the composite deck system. None of visible crack occurs after test under an equivalent stress range of 13.04 MPa. Therefore, OSDCRRPC composite bridge deck has a good potential to be successful. © 2014 Taylor & Francis Group.
Li, W, Xiao, J, Corr, DJ & Shah, SP 2013, 'Numerical modeling on the stress-strain response and fracture of modeled recycled aggregate concrete', 13th International Conference on Fracture 2013, ICF 2013, International Conference on Fracture, Beijing, China, pp. 749-759.
According to the nanoindentation tests, the constitutive relationship of the Interfacial Transition Zones (ITZs) in Recycled Aggregate Concrete (RAC) is proposed with a plastic-damage constitutive model. Based on the meso/micro-scale constitutive relations of mortar matrix, numerical studies were undertaken on Modeled Recycled Aggregate Concrete (MRAC) under uniaxial loadings to predict mechanical behavior, particularly the stress-strain response. The tensile stress tends to concentrate in the ITZs region, which leads to the development of microcracks. After the calibration and validation with experimental results, the effects of the mechanical properties of ITZs and new mortar matrix on the stress-strain response and fracture of MRAC were analyzed. The FEM modeling is capable of simulating the complete stress-strain relationship of MRAC, as well as the overall fracture pattern. It reveals that the mechanical properties of new mortar matrix and the corresponding new ITZ play a significant role in the overall stress-strain response and fracture process of MRAC.