THE USE OF FLY ASH AND BOTTOM ASH IN GEOPOLYMER MORTAR

摘要

This experimental research focused on utilizing fly ash as source material and bottom ash as partial sand (fine aggregates) substitution in geopolymer mortar. Both of these products of combustion were obtained from Sejingkat coal fired power plant in Kuching. The effects of inclusion of bottom ash to partially replaced sand in geopolymer mortar on the mixture water demand and mechanical property were investigated with fixed flow. With 10% of sand substitution by bottom ash, the influences of the following quotients by mass on flow and compressive strength were studied: liquid alkaline to fly ash ratio, extra water to fly ash ratio, extra 12M potassium hydroxide (KOH) to fly ash ratio and the superplasticizer (SP) to fly ash ratio. Besides, the effect of mixing procedures on compressive strength of potassium activated geopolymer mortar was also being studied. Inclusion up to 50% of sand replacement by bottom ash in the geopolymer mixtures with 110± 5% fixed flow decreased the extra water demand of the fresh mortars. Further substitution beyond 50% increased the water requisite to maintain the flow within the addressed range. More bottom ash content has resulted in decreasing maximum sustainable compressive load per unit area of the mortars. Additions of liquid alkaline by mass of fly ash quotient linearly increased the flow of the geopolymer mortars; with duly rise in strength relative to the control sample due to boosted geopolymerisation process. The incorporation of extra water was more efficient than modified polycarboxylate superplasticizer in terms of flow improvement, with similar slight reduction in the strength at 7 days on account of the increased in liquid content. However, the mortar incorporated with the superplasticizer possessed superior compressive strength at 28 days over the mortar added with extra water. Additional extra 12M KOH has been effective in improving the flow of the control sample and inclusion of extra KOH/FA ratio by mass up to 0.06 has increased the maximum stress the specimen mortars can withstand under crush loadings. Incorporation beyond the ratio led to deterioration in the compressive strength. Premixing of fly ash with KOH solution has complimentary effect over the normal mixing sequence on the compressive strength of the geopolymer mortars.