Min Wei

The mechanical characteristics of steel fiber-reinforced lightweight concrete (SFLWC) under high temperatures are studied in this paper. Different concrete matrices, including all-lightweight concrete (ALWC) and semi-lightweight concrete (SLWC), and different steel fibers with hooked ends and crimped shapes are considered as objects. In addition, normal-weight limestone aggregates concrete (NWC), no-fiber ALWC, and SLWC were tested after high-temperature treatment as a control group. The temperature effects on the splitting tensile strength, ultrasonic pulse velocity, compressive stress–strain curve, elastic module, peak strain, and axial compressive strength of the SFLWC were investigated. The results showed that, with increasing exposure temperature, both the axial compressive strength and the elastic modulus decreased, while the axial peak strain has a certain increase, and hence the stress–strain curves were gradually flattened. The toughness of all the concretes increased first and then reduced with increasing temperature, while the specific toughness of all the concretes increased with the increase in temperature. Compared with NWC and SLWC, ALWC had a better capacity to resist high temperatures, especially temperatures > 400 °C. Adding steel fibers can improve the capacity of energy absorption, specific toughness, and residual splitting tensile strength of lightweight concrete (LWC) before and after it is exposed to high temperatures. Based on a regression analysis, a segmented constitutive equation for LWC and SFLWC under uniaxial compression was derived from fitting the experimental findings, and the fitting curve agrees well with the test results.

This paper investigated the performance of actively confined geopolymer concrete (GPC) through experiments. The mechanical properties of GPC under triaxial stress states were analyzed and discussed from the prospects of failure modes, axial peak stress and strain, monotonic and cyclic constitutive relationships. The experimental results demonstrated that the loading modes (monotonic loading and cyclic loading) had little effect on the failure mode and axial peak stress and strain. The improvement of the strength and ductility of GPC with the increase in confinement level was consistent with that of the conventional cement concrete while the strain enhancement of confined GPC was lower than that of confined conventional cement concrete at the same confinement level. The curves of the monotonic stress–strain and the envelop of cyclic compression were predicted through Mander’s model with good accuracy. The unloading/reloading models proposed by Lokuge were modified and the predicted cyclic hysteresis curves for actively confined GPC were in good agreement with the cyclic compression results. Findings from this study provide references for the application of geopolymer concrete.