Multiphase lightweight aggregate concrete (MLAC) is a green composite building material prepared by replacing part of the crushed stone in concrete with other coarse aggregates to save construction ore resources. For the best MLAC performance in this paper, four kinds of coarse aggregate—coal gangue ceramsite, fly ash ceramsite, pumice and coral—were used in different dosages (10%, 20%, 30% and 40%) of the total coarse aggregate replacement. Mechanical property and impact resistance tests on each MLAC group showed that, when coal gangue ceramsite was 20%, the mechanical properties and impact resistance of concrete were the best. The compressive, flexural and splitting tensile strength and impact energy dissipation increased by 29.25, 19.93, 13.89 and 8.2%, respectively, compared with benchmark concrete. The impact loss evolution equation established by the two-parameter Weibull distribution model effectively describes the damage evolution process of MLAC under dynamic loading. The results of a comprehensive performance evaluation of four multiphase light aggregate concretes are coal gangue ceramsite concrete (CGC) > fly ash ceramsite concrete (FAC) > coral aggregate concrete (CC) > pumice aggregate concrete (PC).

Engineered cementitious composites (ECCs) are cement-based composite materials with strain-hardening and multiple-cracking characteristics. ECCs have multiscale defects, including nanoscale hydrated silicate gels, micron-scale capillary pores, and millimetre-scale cracks. By using millimetre-scale polyethylene (PE) fibres, microscale calcium carbonate whiskers (CWs), and nanoscale carbon nanotubes (CNTs) as exo-doped fibres, a multiscale enhancement system was formed, and the effects of multiscale fibres on the mechanical properties of ECCs were tested. The Box-Behnken experimental design method, which is a response surface methodology, was used to construct a quadratic polynomial regression equation to optimise ECC design and provide an optimisation of ECC mix proportions. The results of this study showed that a multiscale reinforcement system consisting of PE fibres, CWs, and CNTs enhanced the mechanical properties of ECCs. CWs had the greatest effect on the compressive strengths of highly ductile-fibre-reinforced cementitious composites, followed by CNTs and PE fibres. PE fibres had the greatest effect on the flexural and tensile strengths of high-ductility fibre-reinforced cementitious composites, followed by CWs and CNTs. The final optimisation results showed that when the ECC matrix was doped with 1.55% PE fibres, 2.17% CWs, and 0.154% CNTs, the compressive strength, flexural strength, and tensile strength of the matrix were optimal.

Cement-matrix composite are typical multi-scale composite materials, the failure process has the characteristics of gradual, multi-scale and multi-stage damage. In order to delay the multi-stage damage process of cement-matrix composites, the defects of different scales are suppressed by using different scales of fibres and fly ash (FA), and the overall performance of cement-matrix composites is improved, a new multi-scale fibre-reinforced cement-based composite composed of millimetre-scale polyvinyl alcohol fibre (PVA), micron-scale calcium carbonate whisker (CW), and nano-scale carbon nanotubes (CNTs) was designed in this study. The compressive strength, flexural strength, splitting tensile strength, and chloride ion permeability coefficient were used as assessment indices by the orthogonal test design. The impacts of the three fibre scales and fly ash on each individual index were examined, and the overall performance of the multi-scale fibre-reinforced cementitious materials (MSFRCC) was then optimized using grey correlation analysis. The optimized mix ratio for overall performance was PVA: 1.5%, CW: 2%, CNTs: 0.1%, FA: 40%. Compared with the optimal results for each group, the compressive strength of the final optimized MSFRCC group decreased by 8.9%, the flexural strength increased by 28.4%, the splitting tensile strength increased by 10%, and the chloride ion permeability coefficient decreased by 5.7%. The results show that the compressive performance and resistance to chloride ion penetration of the optimized group are slightly worse than those of the optimal group in the orthogonal test, but its flexural performance and splitting tensile performance are significantly improved.

Silica-fume–polyvinyl-alcohol-fiber-reinforced concrete (SPRC) is a green and environmentally friendly composite material incorporating silica fume and polyvinyl alcohol fiber into concrete. To study the impact resistance of SPRC, compressive-strength and drop hammer impact tests were conducted on SPRC with different silica-fume and polyvinyl-alcohol-fiber contents. The mechanical and impact resistance properties of the SPRC were comprehensively analyzed in terms of the compressive strength, ductility ratio and impact-energy-dissipation variation. Based on the impact resistance of the SPRC, the impact life of SPRC with different failure probabilities was predicted by incorporating the Weibull distribution model, and an impact damage evolution equation for SPRC was established. The impact life of SPRC under the action of silica-fume content, polyvinyl-alcohol-fiber content and failure probability was analyzed in depth by the response surface method (RSM). The research results show that, when the content of silica fume is 10% and the content of polyvinyl alcohol fiber is 1%, the compressive strength and impact resistance of SPRC are the best. The RSM response model can effectively predict and describe the impact life of SPRC specimens under the action of three factors.