Temperature-dependent compressive stress-strain behaviors of alkali-activated slag-based ultra-high strength concrete

•A clinkerless ultra-high strength concrete (UHSC) was developed at room temperature.•The damage evolution and plasticity development of UHSC were investigated.•A unified temperature-dependent constitutive model was proposed. In this work, the uniaxial compressive behaviors of alkali-activated slag-based ultra-high strength concrete (AAS-UHSC) subjected to different temperatures were investigated, with an emphasis on the temperature-dependent stress-strain relation. To this end, 104 cylinder specimens with three steel fiber contents (0.5%, 1.0%, and 1.5%) and two water-to-binder (W/B) ratios (0.20 and 0.25) were tested upon the monotonic and cyclic compression performed at ambient temperature (20 ℃) and four elevated temperatures (200, 400, 600, and 800 ℃). The test results showed that the mechanical properties of AAS-UHSC in terms of elastic modulus, ultimate strength, energy dissipation, and post-peak softening can be effectively improved with the fiber inclusion, regardless of the W/B ratio. Moreover, AAS-UHSC exhibited a quite different plastic strain evolution law featured as two discontinuous stages due to the damage localization and possessed better energy dissipation capacity compared to OPC-based concretes. After being exposed to elevated temperatures, a consistent decline in compressive strength was observed as the temperature increased, with residual strength at 800 ℃ remaining around 10% of the ultimate compressive strength at 20 ℃. Based on the test results, a unified empirical temperature-dependent model was proposed to capture the main features of the constitutive compressive stress-strain relations of AAS-UHSC. The fairly good comparisons between test results and model predictions in different loading scenarios demonstrated a compromise between the accuracy and the generality of the model and contributed a beneficial addition to the understanding of nonlinear responses of AAS-UHSC.