This paper investigates the incorporation of sodium hydroxide (NaOH) concentration and CaO-Si component on ground granulated blast furnace slag geopolymers (GGBFS). An optimal mechanical property of GGBFS with various NaOH concentrations had been determined by performing a number of compressive strength tests. It was found that GGBFS with 10M NaOH concentration resulted in high compressive strength at 65.31 MPa after 28 days curing. The microstructure analysis of the GGBFS geopolymers using SEM and FTIR revealed the formation of calcium silicate hydrate (Ca<jats:sub>5</jats:sub>Si<jats:sub>6</jats:sub>O<jats:sub>16</jats:sub>(OH)<jats:sub>2</jats:sub>.4H<jats:sub>2</jats:sub>O) and calcium carbonate (CaCO<jats:sub>3)</jats:sub> phase within the geopolymer backbone chain. The optimum NaOH concentration allows the acceptable formation of CaO-Si bond on the GGBFS geopolymers main structure and thus leads to optimum compressive strength.
