This study focuses on the pre-treatment of paper sludge ash (PSA) as a by-product of paper milling industry that contains high amount of calcium, yet low in silica. The presence of high calcium content in geopolymer system will accelerate the setting time of fresh geopolymer and may disrupt the development of its mechanical strength. Therefore, in this study, the refinement of PSA properties was conducted by treating raw PSA in hydrochloric acid solution with different molarities of 0.5 M, 1.0 M and 2.0 M. The pre-treatment process was mainly purposed to decrease the amount of calcium and other impurities through leaching mechanism.
Based on the experimental results, 2.0 M hydrochloric acid solution (HCl) was determined as the optimum concentration due to its ability in removing higher amount of calcium from the ash, yet still able to increase the amount of silica. Compression test on the hardened properties of geopolymer specimen also showed the deceleration of fresh fly ash based geopolymer and produced a more workable fresh geopolymer.