Dynamic fracture behavior of alkali-activated mortars: Effects of composition, curing time and loading rate

Abstract

Alkali-activated binders made from industrial waste have become a potential alternative of ordinary Portland cement (OPC) because of their low energy consumption and greenhouse gas emissions. This paper aims to evaluate the fracture properties of alkali-activated-binder-based mortars subjected to dynamic loading. We investigated the mortars containing low-calcium (i.e., fly ash) and high-calcium (i.e., ground granulated blast furnace slag (GGBFS)) alkali-activated binders, which have different chemical properties and microstructures. The activators in these mortars are NaOH and sodium silicate solutions. Two groups of specimens made with different water ratios were tested for both fly ash and GGBFS based mortars. Split Hopkinson pressure bar (SHPB) system with the notched semi-circular bend (NSCB) specimen was used to conduct dynamic fracture tests, and dynamic mode-I fracture toughness was measured to provide a comprehensive understanding of the dynamic fracture behaviors of alkali-activated-binder-based mortars. The results show that the fracture toughness of alkali-activated mortars increases with the loading rate and curing time. Moreover, the water content has little influence on the dynamic fracture toughness of fly-ash based mortars, but it significantly affects the dynamic fracture toughness of GGBFS based mortars. Finally, the dependence of dynamic fracture toughness for fly-ash and GGBFS based mortars on the loading rate and curing time is described by empirical formulas.