Influence of coal ash properties on compressive behaviour of FA- and BA-based GPC

This paper presents the results of an experimental study on the behaviour of fly ash (FA) and bottom ash (BA) based geopolymer concretes (GPCs) cured at ambient temperature. A total of 11 batches of coal-ash-based GPCs were manufactured. Axial compression tests were carried out to determine the compressive behaviour and strength development of hardened GPCs. Test parameters included the type, particle size and chemical composition of coal ash, the alkaline liquid to binder ratio and concentration of sodium hydroxide solution. The results indicate that the chemical composition of BA has a pronounced influence on the compressive behaviour of GPCs, with concretes manufactured with BA with a higher silicon dioxide/aluminium oxide ratio developing higher strengths. The results also indicate that milling of the coal ash and the increased calcium oxide content of the BA both lead to significant improvements in the compressive strength of GPCs. It was also found that strength gain of ambiently cured coal-ash-based GPCs continues beyond a concrete age of 28 d and is significantly influenced by the type, particle size and chemical composition of the coal ash and the concentration of sodium hydroxide solution.