Compacted fly ash, lime, bentonite and water mixtures were cured at 23° and 50°C, for 1, 28, 90 and 180 days. Cementitious products and microstructure were observed by scanning electron microscopy, energy dispersive x-ray spectrometry and x-ray diffractometry. Unconfined compressive strength changes are correlated to the formation of new mineral phases. For bentonite-limefly ash mixtures, strength increased from 1050 kPa (I day) to 2,300 kPa (90 days) and then slightly increased to 2,400 kPa after 180 days at ∼ 230C. Ettringite is the most abundant mineral associated with the increased compressive strength.
New minerals identified in the 23°C mixtures include calcium silicate hydrate - Type 1, afwillite and ettringite. Acicular crystals of these and other minerals were formed by the hydration of lime and fly ash in the montmorillonitic clay. The cementitious phases create a rigid framework joining spheres and clay aggregates. Continued reaction dissolves some of the spheres and slightly reduces the rigidity of the cured samples.