Impact behaviour of fly ash and slag-based geopolymeric concrete: The effects of recycled aggregate content, water-binder ratio and curing age

Using recycled concrete aggregate as substitution for natural aggregate in geopolymeric concrete to produce geopolymeric recycled aggregate concrete (GRAC), is becoming a desirable solution to handle the huge amount of construction and demolition waste, meanwhile, can harness the eco-friendly benefits from geopolymer binders. This study aims to investigate the dynamic compressive behaviour of GRAC based on fly ash and ground granulated blast furnace slag, focusing on the effects of recycled coarse aggregate (RCA) content (0, 50% and 100%), water-binder ratio (0.3, 0.4 and 0.5) and curing age (7 days and 28 days). By using a Ø100-mm split Hopkinson pressure bar apparatus, extensive experimental investigations were carried out for understanding the impact properties of GRAC under different strain rates ranged from 30 s−1 to 150 s−1. The compressive properties of GRAC under impact loading, including failure modes, stress-strain curves, compressive strength and energy absorption capability were analyzed and compared to those under quasi-static loading. Then, a new model has been developed for the dynamic increase factor (DIF) of GRAC. The results show that GRAC exhibited a lower strain rate sensitivity than OPC-based concrete, and the addition of RCA improved the strain rate sensitivity of geopolymeric concrete. The dynamic compressive strength and impact toughness of geopolymeric concrete decreased with increasing RCA content and water-binder ratio. The proposed model, which considered the effect of RCA content to predict the DIF of GRAC, agreed well with the test results.