Microstructure Analysis of Different NaOH Molarity Towards Fly Ash Geopolymer for Underwater Concreting Material

Geopolymer concrete is a new sustainable and environmentally friendly composite with great potential to replace conventional concrete that is mostly produced by ordinary Portland cement (OPC). Binders used for geopolymer concrete such as fly ash and blast furnaces are mostly industrial wastes or by -products containing high silica and aluminium content that act as stimulants for geopolymerization. Furthermore, geopolymers also exhibit better durability and corrosion resistance than OPCs. However, material subjected to underwater placement method typically exhibit a decrease in properties. While geopolymer has not been widely used as underwater concreting material, this research is purposed to identify the effect of underwater placement method towards geopolymer in terms of microstructure analysis. Using different molarities of sodium hydroxide (NaOH), the optimum compressive strength will be discussed for underwater concrete while correlating with the microstructure result. For alkaline activators, the ratio used is 2.5 and the ratio for solid to liquid is 2.5. The molarities used for alkaline activators were 8 M, 10 M and 12 M. Using the tremie method for underwater concrete, it is possible to measure the leaching loss with respect to the objective of this research. The best compressive strength result is 12 M. The SEM result support with 12 M molarity had less cavities and lowest density.