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

In this work, the uniaxial compressive behaviors of alkali-activated slag-based ultra-high strength concrete (AASUHSC) 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 degrees C) and four elevated temperatures (200, 400, 600, and 800 degrees C). 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 degrees C remaining around 10% of the ultimate compressive strength at 20 degrees C. Based on the test results, a unified empirical temperature-dependent model was proposed to capture the main features of the constitutive compressive stressstrain 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.