Production of geopolymer mortar system containing high calcium biomass wood ash as a partial substitution to fly ash: An early age evaluation

This paper presents an investigation on the feasibility of inclusion of biomass wood ash (BWA) as a partial replacement material for fly ash (FA) in preparation of blended BWA-FA geopolymer mortars. The blended mortar systems for this study were prepared at three replacement ratios of FA by BWA of 10%, 20% and 30% by binder mass. The engineering properties of the BWA-FA geopolymer mortars were evaluated using compressive strength, flexural strength, water absorption and total porosity measurements. Microstructural and phase composition analysis were also conducted to assess the obtained results and compared with a control mortar mix containing 100% FA at different ages of 3, 7 and 28 days. The results showed the inclusion of BWA up to 20% resulted in higher strength and porosity characteristics than the control mix at age of 3 and 7 days. However, at age of 28 days, the geopolymer contains 10% BWA of the total binder was the only blended mixture that exhibited higher compressive strength and lower total porosity than the control mix. The phase composition results of the blended mixtures at 28 days confirmed the formation of calcium polysialate and calcium silicate hydrate gels coexisted with sodium polysialate phase.