Mechanical properties of ambient cured one-part hybrid OPC-geopolymer concrete

To produce geopolymers, a large amount of highly corrosive and hygroscopic alkaline activators, i.e, sodium hydroxide and potassium hydroxide, are commonly used. In this study, one-part hybrid ordinary Portland cement (OPC)-geopolymer concrete mixes were developed, in which solid potassium carbonate (7.5 wt% of the total geopolymeric raw materials) was used as the main activator and the OPC as a source of silicate and poly silicate was blended with geopolymeric raw materials (fly ash and ground granulated blast furnace slag) in different proportions. The influence of OPC content on the workability, setting time, compressive strength development and microstructure of the concrete mixes was investigated. It was found that the inclusion of OPC in geopolymer mixes reduced the workability and setting time but significantly increased the early age and ultimate compressive strength due to the quick reaction of OPC with alkali activators. By the inclusion of just 10% OPC in the binder system, the compressive strength at 28 days increased from 11.4 MPa to 33.4 MPa. Furthermore, control OPC concrete mixes were also prepared and tested. It was found that the percentage of strength increase at 28 days due to alkali activation decreased from 82.5% to 24.4% as the OPC content increased from 10% to 60%. Microstructural analysis was also conducted, which confirmed the coexistence of geopolymeric and CSH gels in the one-part hybrid OPC-geopolymer binder system.