Enhancement of strength of coal fly ash–carbide lime blends through chemical and mechanical activation

Abstract

Compacted coal fly ash–carbide lime blends have vast prospects for being used as building materials, such as walls, foundations and floors of habitations, also as base and sub-base of pavements. The residues used on the present research (coal fly ash and carbide lime) offer an advantageous replacement to natural soils or Portland cement due to the pozzolanic reactions arising from SiO2 and Al2O3 (from coal fly ash) and Ca++ (from carbide lime), which strengthen and stiffen the blends. Nevertheless, these reactions could be time-consuming at ambient temperatures, demanding lengthy curing periods to reach a minimum unconfined compressive strength – qu≥1.3MPa and 2.1MPa, to be employed in constructing walls of habitations and base/sub-base of pavements, respectively. Therefore, this investigation aspires to estimate the impact of NaCl and ash grinding on the compressive strength of compacted ash-lime mixtures. Adding 1.0% NaCl or grinding coal fly ash (increasing particles specific surface area in 50%) triplicates strength (regarding analogous specimens deprived of NaCl or grinding). Combining NaCl and ash grinding doubled strength gain on top of the increase of using only one of the techniques. Besides, the strength of the specimens moulded was normalised in order to obtain a single framework quantifying its chemical and mechanical impacts. The established normalisation was efficaciously stretched to other fly ashes treated with carbide lime available from literature, with distinctive curing times and temperatures.