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This study aims to investigate the effect of calcium sulfate whisker (CSW) on the properties and microstructure of cement-based composites. Further, nanosilica (NS) was used as a comparison. The results show that the compressive strength and fracture toughness of cement-based composites increased by 10.3% and 10.2%, respectively, with 2% CSW. The flexural strength, splitting tensile strength, and fracture energy increased by 79.7, 34.8 and 28.7%, respectively, with 1% CSW. With the addition of CSW, shrinkage deformation was aggravated, and the capillary water absorption coefficients were clearly reduced. Compared with NS, CSW-reinforced cement-based composites show better tensile, flexural, and fracture properties and smaller shrinkage deformations and capillary water absorption coefficients. The residual mechanical properties of all groups improve when the treating temperature is lower than 400 °C and decline rapidly when the temperature goes over 600 °C. When treated at 900 °C, the residual mechanical properties are 40% less than those at ambient temperature, with the NS group showing the best performance, followed by the control group and the CSW group. X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests show that the addition of CSW improves the microstructure of the matrix. CSW can reinforce and toughen composites by generating ettringite and whisker pullout, whisker breakage, crack bridging, and crack deflection at the microstructure level. [ABSTRACT FROM AUTHOR]

The effects of cenospheres, an industrial waste residue, on the compressive strength, flexural strength, toughness, ductility, chemical component, microstructures, and micromechanics of lightweight toughness cement-based composites (LTCCs) by comprehensive experimental tests are explored in this paper. The results indicate that an increase in the amount of cenospheres leads to a decrease in the compressive and flexural strength of LTCCs. However, the specific strength of LTCCs increases with increasing cenosphere content. LTCCs containing 20% cenospheres and 1% fiber volume have the best toughness and ductility. Significant strain hardening occurs during the four-point bending and uniaxial tensile process. Furthermore, the incorporation of cenospheres promotes the hydration reaction of LTCCs due to its high pozzolanic activity. The LTCC cement paste has a low bonding strength to the fiber, which helps the fiber to be pulled out to produce greater bending deformation and tensile strain. The elastic modulus and hardness of the LTCC cement paste decrease linearly with increasing cenosphere content, which also causes the LTCC microstructure to become loose and more ettringite to generate. The weak interfacial transition zone between the cenospheres and the cement matrix is the important reason for the decreasing compressive strength of the LTCC. In conclusion, LTCC incorporating cenospheres is suitable for long-span steel deck pavements due to its light weight and excellent toughness. The successful application of cenospheres in engineering construction can save natural resources and contribute to sustainable development. [ABSTRACT FROM AUTHOR]

Strain hardening cementitious composites (SHCCs) are widely used in projects due to their excellent deformation resistance and large energy absorption capacity. However, determining tensile strain capacity is still a challenge for engineers. The current popular approach is to use inverse methods to predict the tensile behavior of SHCCs, such as the UM method (Qian and Li) and the JCI (Japan Concrete Institute) method. The key to these two approaches is to acquire the exact relationship between the bending and the uniaxial response. In this paper, a reasonable linear constitutive model of the SHCCs is modified. Initially, the moment-curvature diagrams are discussed by material parameters. The results reveal that the moment-curvature response is quite sensitive to the variations in the parameter of transition strain α, post-cracking tensile stiffness η, and strain softening stiffness μ, however, for the compressive parameters, the moment-curvature responses influence on flexural behavior is insignificant. Moreover, the load-deflection curve in the mid-span of SHCC, based on the consideration of shear effect, is simulated under a four-point bending test (FPBT). The results show a remarkable consistency with the experimental data when compared to the previous simulations. It is expected that this modified method can enhance an accurate program in order to obtain the tensile capacity. [ABSTRACT FROM AUTHOR]

• Some properties of lightweight cement-based composites with high toughness were investigated. • The effect of cenosphere content on the tensile ductility of the composites was analyzed based on the micromechanical design theory. • The incorporation of cenosphere could effectively reduce the shrinkage of the cement-based composites. • Lightweight cement-based composites with excellent mechanical properties can help mitigate environmental costs of construction. Cenosphere is an industrial waste residue used as lightweight aggregate in cement-based composites. In this work, we investigated the influences of cenosphere on the properties and applicability of cement-based composites. The compressive and flexural strength, bending toughness, tensile ductility, and shrinkage of the composites were measured. Meanwhile, the environmental and economic benefits of cenosphere were analyzed. Our results showed that cenosphere-added lightweight cement-based composites exhibited a density of 1477.52–1734.23 kg/m3, compressive strength of 63.94–70.69 MPa, and flexural strength of 9.50–14.71 MPa, depending on the cenosphere content. The calculated fracture energy of the matrix notably dropped with increasing cenosphere content due to the weak interface transition zone between the aggregate and cement paste. Moreover, the incorporation of cenosphere had a negative effect on the tensile strain capacity and tensile strength of composites. The high bridging stress of the fibers ensured the tensile ductility and bending properties of the cement-based composites. Due to internal curing effect of cenosphere, the shrinkage of lightweight toughness cement-based composites was effectively reduced with increasing cenosphere content. Compared with the control group, the embodied energy of the cement-based composites containing 30% cenosphere was reduced from 10.12 to 7.20 GJ/m3, while the global warming intensity was reduced by 37.85%. Therefore, developing eco-friendly cement-based composites with cenosphere is viable approach to mitigate the environmental costs of construction. [ABSTRACT FROM AUTHOR]