Mechanical properties of alkali-activated concrete subjected to impact load

Drop-weight tests are conducted to study the dynamic flexural properties of alkali-activated concrete (AAC) under four different impact velocities, corresponding to strain rates of 15, 35, 55, and 75 s-1. The effect of low temperature (-30°C) is also observed at the strain rate of 35 s-1. The replacement ratio of fly ash with slag, alkali concentration, modulus of alkali activator, and water:binder ratio are selected as parameters to study the strain rate effect of AAC. The quasi-static compressive strength, flexural strength, and elastic modulus are evaluated. For comparison, one mixture of ordinary portland cement concrete (OPCC) is also studied. The results show that, similar to OPCC, AAC is a strain rate-sensitive material; the flexural strength, energy consumption, and deformation at failure increase with the loading rate; the dynamic increase factor (DIF) of flexural strength is related to its quasi-static strength, and a lower quasi-static strength leads to a higher DIF; and the energy dissipation capacity of AAC increases almost linearly with the strain rate regardless of its quasi-static strength. In addition, different from OPCC, alkali-activated slag concrete (AASC) is found to exhibit less sensitivity to low temperature in terms of the flexural property, which might be attributed to the refinement of the microstructure, high proportion of micropores, and high concentration of pore solution in AASC.