The Effect on Mechanical and Microstructure Properties by Varying GGBS Content and NaOH Solution Concentration in Alkaline Solution of Fly-Ash-Based Self-compacting Geopolymer Concrete

In this research, mechanical and microstructural properties of Fly-ash-based self-compacting geopolymer concrete (SCGC) were investigated for shear strength and impact strength by substituting Fly Ash with Ground Granulated Blast Furnace Slag (GGBS) by 0, 30, 50 and 70% and by using alkali solutions such as sodium hydroxide and sodium silicate in the ratio 1:2.5 for different NaOH solution molarities like 8, 10 and 12 M. An iterative procedure was utilized to arrive at the SCGC design mix by completing workability tests like slump flow in compliance with European Federation of National Associations Representing for Concrete (EFNARC) criteria. After obtaining the requisite flow, the concrete was poured into the moulds and cured for 24 h at 70 °C in the oven, with ambient treatment occurring for the remainder of the test days. A constant binding content of 400 kg/m³ and a fluid to binder ratio of 0.47 by mass have been maintained for all molarities, while the superplasticizer dosage of 3% has remained constant. And by compromising on strength, the extra water content was adjusted to provide the desired flow. With increasing molarity and GGBS, the slump flow was reduced. As GGBS content and molarity increased, engineering properties such as shear and impact strength increased, and this was justified with microstructure analysis. As compared to the other replacement level, the replacement of 70% of the Fly Ash with GGBS at 12 M showed higher structural strength. Hence, fly ash and GGBS in a ratio of 50:50 could be a better CO₂-reducing alternative to traditional OPC concrete in connection to cost and sustainability.