Suitability of heat-cured low-calcium fly ash-based geopolymer concrete for precast applications

This paper discusses the advantages of using low-calcium fly ash (FA)-based geopolymer concrete (GPC) for precast applications when high early-age strength is required. Heat curing is known to be the reaction accelerator for both Portland cement (OPC) concrete and the newly emerged GPC. Here, the influence of 12 different heat-curing regimes, as well as internal curing, on mechanical properties of an FA-based GPC is investigated. The curing regimes include three temperatures of 60, 75 and 90°C, and four curing durations of 8, 12, 18 and 24 h. Results are compared with that of OPC concrete counterpart, with the same amount of binder and aggregate. Test results show that, in optimum heat-curing conditions, GPC can achieve more than 90% of its 28 d compressive strength after 1 d, compared to only 55% to 71% for normal concrete. The optimum heat-curing regime for GPC, combining best performance and energy efficiency, is found to be 75°C for 18 h. Contrary to conventional concrete, heat curing has no detrimental effect on the long-term compressive strength of GPC. It is concluded that, for precast applications, FA-based GPC appears to perform better than OPC concrete in terms of both early and long-term compressive strength using the same amount of binder.