Alkali-activated geopolymer produced by seeded fly ash and rice husk bark ash

In the present work, the flexural strength, percentage of water absorption and pore structure of inorganic polymers (geopolymers) made from a combination of fine and coarse fly ash and rice husk bark ash (seeded mixture) have been investigated. Different specimens were subjected to strength, water absorption and porosimetry tests at 7 and 28 days of curing. The curing regime varied: one set of the specimens was cured at room temperature until 7 and 28 days and the other sets were oven-cured for 36 h at the range of 40 to 90°C and then cured at room temperature until 7 and 28 days. The results indicate that the specimens having a silicon dioxide/aluminium oxide ratio equal to 2·99 and cured at 80°C in both the 7 and 28-day regimes have the best flexural strength and resistance to water absorption and their total specific pore volume is minimum. An empirical relationship was found to correlate the flexural strength to the percentage of water absorption of the specimens at different ages of curing.