Fly Ash and Bottom Ash Utilization as Geopolymer: Correlation on Compressive Strength and Degree of Polymerization Observed using FTIR

Abstract

Concerning on the dependancy of coal on electric generation wordwidely, study on fly ash, thesolid waste of fired coal electricity generation, has been comprehensively conducting, i.e. geopolymer, cenosphere, soil remediation, and adsorbent. However, only few studies dealing with the utilization of bottom ash. Having of about 53% of coal in the 2050 energy mix, Indonesia will be dealing with more than 200 million tonnes of fly ash and bottom ash (FABA). In this study, FABA was mixed in certain proportion of 50:50, 75:25, dan 100:0. The formation of geopolymer was conducted with sodium hydroxide and sodium silicate in certain concentration. Once the mixture had been homogenized, it was casted and cured in varied temperature of 30, 60, dan 90 oC with curing time of 1, 3, 5, 14, 21, dan 28 days. In each curing time, sample was then analyzed using compresive strength apparatus and FTIR in order to observed the geopolimerization of the FABA mixture. It was found that compressive strength representing the macro characteristic of the geopolymer is in line with the CORR analysis of the FTIR results showing that the formation of aluminosilicate is responsible for the mechanical strength of the geopolymer. The higher the bottom ash ratio in the mixture with decrease the strength of the geopolymer in the order of one per second. Higher temperature results higher compresive strength to the value of 42 Mpa (FABA ratio is 75:25 at temperature of 90 oC) above the Indonesian standard for concrete. From this study, kinetics of FABA geopolymerization can be generated in accordance todiffusion model with R2 of 0.9135. Thus the utilization of FABA for geopolymer is going to be a potential solution to overcome the increasing amount of FABA resulted from fired coal electrical generation in Indonesia.