Optimum Utilization of GGBS in Fly Ash Based Geopolymer Concrete

There have been increasing efforts in recent years to minimize the amount of cement used in concrete. Efforts at partial replacement have been successful and regulations have been promulgated to standardize and use such formulations. Research aimed at complete replacement of cement by activating industrial materials that are rich in silica and alumina with alkaline solutions is still on-going all over the world. The present study was aimed at complete elimination of cement through the development of a geopolymer concrete containing the mixture of fly ash and ground granulated blast furnace slag (GGBS), activated by sodium based alkaline activators. The effect of replacing up to 50% fly ash by GGBS was considered. The strength parameters were studied for a mixture of sodium silicate and sodium hydroxide solution having concentration 12M. The samples were cured under ambient conditions as well as in an oven at 60oC for 24 hours. Compressive and split tensile strengths of the samples were measured on 3rd, 7th, 14th, 28th, 56th and 90th days of casting. The cubes were also tested for durability parameters by ponding in NaCl and H2SO4 solution for 28 and 90 days. It was observed that replacing fly ash with 30% of GGBS gave the best results.