Engineering Properties of Lightweight Geopolymer Synthesized from Coal Bottom Ash and Rice Husk Ash

Geopolymer technology was developed by Joseph Davidovits in 1970s based on reactions among aluminosilicate resources in high alkaline conditions. Geopolymer has been recently gaining attention as an alternative binder for Ordinary Portland cement (OPC) due to its low energy and CO2 burden. The raw materials used for geopolymerization normally contain high SiO2 and Al2O3 in the chemical compositions such as meta-kaoline, rice husk ash, fly ash, bottom ash, blast furnace slag, red mud, and others. Moreover, in this paper, coal bottom ash (CBA) and rice husk ash (RHA), which are industrial and agricultural wastes, respectively, were used as raw materials with high alumino-silicate resources. Both CBA and RHA were mixed with sodium hydroxide (NaOH) solution for 20 minutes to obtain the geopolymer pastes. The pastes were filled in 5-cm cube molds according to ASTM C109/C109M 99, and then cured at room condition for hardening of the geopolymer specimens. After 24 hours, the specimens were removed out of the molds and continuously cured at room condition for 27 days. The geopolymer-based materials were then tested for engineering properties such as compressive strength (MPa), volumetric weight (kg/m(3)), and water absorption (kg/m(3)). Results indicated that the material can be considered lightweight with volumetric weight from 1192 to 1425 kg/m(3); compressive strength at 28 days is in the range of 12.38 to 37.41 MPa; and water absorption is under 189.92 kg/m(3).