EFFECT OF SODIUM HYDROXIDE CONCENTRATION AND SODIUM SILICATE TO SODIUM HYDROXIDE RATIO ON PROPERTIES OF CALCINED KAOLIN-WHITE PORTLAND CEMENT GEOPOLYMER

This study presents the effects of sodium hydroxide concentration (NH) and sodium silicate to sodium hydroxide ratio (NS/NH) on the mechanical properties and microstructure of geopolymer pastes prepared from calcined kaolin (CK) and white Portland cement (WPC). Different curing conditions viz., ambient curing, temperature curing, and moist curing were used. The results indicated the increasing NH concentration and NS/NH ratio increased the compressive strength of CK-WPC geopolymers and gave the highest compressive strength at NH concentration of 15 molar and NS/NH ratio of 1.0. Furthermore, the use of 50% WPC increased the compressive strength of geopolymer paste. The samples with ambient temperature curing showed high early compressive strength equal to that with temperature curing. For moist curing, the compressive strengths of WPC samples at the later age were continuously developed and were higher than those with ambient and temperature curings. The microstructures of geopolymer paste were tested using SEM images and pattern of XRD (X-ray diffractometer) which showed the denser paste and higher calcium compound in the CK-WPC samples than those in CK samples.