Geopolymer concrete is an eco-friendly alternate to conventional concrete that considerably lower green house gases emitting into the atmosphere. Fly ash based geopolymer concrete is reported to become hardened during heat curing process which comes as a major constraint for cast in in-situ applications. In this study, the aluminosilicate materials such as Ground Granulated Blast Furnace Slag (GGBS) with varying percentages such as 0%, 10%, 20%, and 30% replaces the fly ash (FA) in geopolymer concrete was used. Manufactured sand (M-sand) is used as full replacement material for natural sand as fine aggregate owing to its increasing demand. This work aims at investigating the effect of alumino silicate materials on strength properties, characterization and micro structural analysis using Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared spectroscopy (FTIR) and X-ray diffraction (XRD) in geopolymer concrete under ambient curing condition. The SEM and EDX results reveals that, the micro structural properties of fly ash, GGBS materials, CaO, Si/Al ratio, and gel formation have a significant effect on compressive strength and setting time of geopolymer concrete. The FTIR analysis reveals that the stretching vibration of fly ash shifts to low wave number values due to changes in geopolymerization. The X-ray diffraction (XRD) reports show that the C-S-H gel formed around 27–30° 2theta value due to increase of GGBS in geopolymer concrete. © 2020, Springer Nature B.V.