Efek Variasi Molaritas Natrium Hidroksida terhadap Mikrostruktur dan Kuat Tekan Geopolimer Mortar Berbahan Dasar GGBFS dan Diatomite

Abstract

The modern construction industry demands sustainable material innovations to replace Portland cement, which significantly contributes to CO₂ emissions. This study investigates geopolymer mortar composed of Ground Granulated Blast Furnace Slag (GGBFS) and Diatomite, activated using a combination of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃). The primary objective is to evaluate the influence of NaOH molarity variations (8M, 10M, 12M, and 14M) and GGBFS:Diatomite composition ratios (100:0, 90:10, 80:20, 70:30, 60:40, and 50:50) on the compressive strength and microstructure of geopolymer mortar under ambient curing conditions. Cube specimens measuring 5x5x5 cm were tested at 7, 14, and 28 days. The results showed that the 50:50 GGBFS:Diatomite ratio combined with 8M NaOH produced the highest compressive strength, reaching 28.43 MPa at 28 days. In general, increasing the NaOH molarity beyond 8M did not result in a significant improvement in strength and, in many cases, reduced performance due to unstable gel formation, increased porosity, and a less homogeneous microstructure. Ambient curing facilitated gradual strength development, with 8M molarity proving to be the most effective in supporting optimal geopolymerization and gel network formation. Microstructural analysis using Scanning Electron Microscopy (SEM) revealed that under optimal conditions the geopolymer mortar displayed a dense and cohesive gel structure, although some Diatomite particles remained partially unreacted. These findings highlight the importance of balancing alkali activator concentration and precursor composition under ambient curing conditions to produce strong, stable, and environmentally sustainable geopolymer mortar.