Mechanical and Microstructural Characteristics of Manufactured Sand-Based High-Strength Geopolymer Concrete and Its Environmental Impact

Abstract

Geopolymer concrete (GPC) is one of the best alternative options for conventional concrete due to its adequate mechanical and durability properties with the addition of a lower carbon footprint. This research presents the experimental results of using ground granulated blast furnace slag (GGBS), fly ash (FA), and silica fume (SF) as a binder and manufactured sand (MS) as a fine aggregate on fresh and hardened high-strength geopolymer concrete (HSGPC). Initially, 16 mortar mixes were prepared and tested for compressive strength to finalize solution/binder and sodium silicate/sodium hydroxide ratios for HSGPC. The different mix proportions for M70, M80, M90, and M100 were calculated and validated experimentally. The proposed mix design methodology achieved the maximum compressive strength as high as 104 MPa at 28 days, along with coarse aggregate and MS. The promising mechanical properties were observed at 28 days for all grades of concrete. The mechanism of strength increment was appropriately justified by microstructural analysis. The equations of split tensile and flexural strength in terms of compressive strength were compared with the previously proposed equations in the literature. Microstructural analysis of HSGPC revealed that the enhancement in mechanical properties creates a dense microstructure of different gel formations like calcium-silicate-hydrate (C-S-H), calcium-alumino-silicate-hydrate (C-A-S-H), and sodium-alumino-silicate-hydrate (N-A-S-H) gels in HSGPC. Finally, the environmental impact assessment in terms of carbon emission of HSGPC was evaluated. It is found to be 90% lower compared with conventional concrete.