Effect of Calcium on Geopolymerization of Aluminosilicate Wastes

The effect of calcium hydroxide on the mechanical and microstructural characteristics of geopolymer produced from alkaline activation of aluminosilicate wastes produced from demolition works were investigated. Demolition wastes are coarse aggregates, including waste concrete and demolished walls with cementing binder, both passing a sieve of 90 mu m. A trial was carried out by making a mix containing demolished walls/waste concrete in the ratio of 60/40 % by weight and other mixes having a hydrated lime content of 0-25% of the dry weight as a partial replacement for demolished walls. Half of the waste concrete was substituted with metakaolin, produced by firing kaolin at 800 degrees C for 3 h. The alkaline activators used were sodium hydroxide and sodium silicate in the ratio of 3: 3 % by weight of the dry weight. Curing of the geopolymer mixes was performed at ambient temperature (23 degrees C) in tap water and under a mild temperature of 40 degrees C [100% relative humidity (RH)]. Drying treatment at 80 degrees C for 24 h was carried out on each specimen mix before subjecting it to compressive strength so as to improve the mechanical properties, and the resulting properties of dried and saturated samples were compared. Addition of the calcium compound improved the mechanical and microstructural properties of the specimens with the increase of hydrated lime up to 10 % by weight for mix specimens that were water-cured under ambient temperature, whereas the properties slightly decreased for those specimens cured in 100% RH at 40 degrees C. DOI: 10.1061/(ASCE)MT.1943-5533.0000352. (C) 2012 American Society of Civil Engineers.