Micro-characterisation of alkali activated paste with fly ash-GGBS-metakaolin binder system with ambient setting characteristics

The study reports properties of a stable and high strength ternary binder matrix using Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), and Metakaolin (MK). The bulk of the binder system is composed of Fly Ash and Ground Granulated Blast Furnace Slag (GGBS), while Metakaolin is added in three levels of 20%, 10%, 5% by weight, as suggested by the design of experiments. Alkali solution consisting of sodium hydroxide flakes and sodium silicate solution was used as the alkali activator. Fresh properties of all the Alkali Activated binder Pastes were studied to understand the Setting time and Mini-Slump. Mechanical properties of the hardened fly ash based ternary binder mortar were tested for compressive strength and ultrasonic pulse velocity (UPV) after 3, 7,28, and 56 days of curing. X-Ray Diffraction (XRD), Field-Emission-Scanning-Electron-Microscope (FESEM), Energy-Dispersive-Spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) were conducted in order to study the microstructural properties fly ash based ternary paste cured for 7 days. The compressive strength of hardened fly ash based ternary samples varied between 57.14 and 102.04 MPa. Ternary mixtures were observed to have a homogeneous and denser microstructure, with the development of various gels like CSH, CASH, NASH, and (N, C)-ASH.