Experimental Study of Geopolymer Concrete Produced from Waste Concrete

AbstractThis paper investigates complete recycling of waste concrete to produce new geopolymer concrete (GPC). Specifically, GPC was produced using waste concrete fines (WCF) and class-F fly ash (FA) together with mixed sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solution as the geopolymer binder and waste concrete aggregates (both coarse and fine) as the aggregate. The effect of NaOH concentration, Na2SiO3 solution to NaOH solution mass ratio (SS/N), cement (WCF and FA) to aggregate ratio (C/A), water-to-cement ratio (W/C), and curing temperature on the initial setting time and the 7-day unconfined compressive strength (UCS) of the GPC was systematically studied. For comparison, GPC using natural aggregate (NA) was also produced and studied at similar conditions. The results indicated that the GPC produced from recycled aggregate (RA) has higher UCS than the GPC from NA at both room (23°C) and 35°C curing temperatures. This is mainly due to the stronger interfacial transition zones (ITZs) in the RA-based GPC than in the NA-based GPC. Based on this study, it can be concluded that waste concrete can be completely recycled (both WCF and RA are reused and no NA is needed) to produce new structural geopolymer concrete with sufficiently high compressive strength.