Cooling Treatment of Alkali Solution to Prolong the Setting Time of High Calcium Fly Ash Based Geopolymers

The problem of rapid or short setting time has been reported by many researchers when utilizing high calcium fly ash as an aluminosilicate source material in the synthesis of geopolymers. Meanwhile, there are very few studies carried out to overcome this obstacle. This study was conducted to evaluate the cooling treatment of the alkaline solution to prolong the setting time of the geopolymer. Alkaline solutions with five different temperatures were used to synthesize the geopolymer paste. Each set of fresh geopolymer paste was tested using the Vicat apparatus according to ASTM C191 to measure its setting time. The results showed that a decrease in the temperature of the alkaline solutions prolonged both the initial and the final setting time of the geopolymer paste. An alkaline solution with a temperature of 9°C could double the initial setting time compared to the control mixture (31°C). In the mortar phase, the cooling treatment also increased the compressive strength of the geopolymer mortar besides longer setting time