Strength development in fly ash and slag mixtures with lime

Abstract

The main objective of this paper is to investigate the effect of the joint activation of fly ash, a by-product of thermal power plants, and ground granulated blast-furnace slag, a by-product of steel manufacture, on the unconfined compressive strength of mixtures of the two materials. Laboratory compaction and strength tests were carried out on ash–slag mixtures at different proportions. The strength was found to increase with slag content. However, the specimens consisting of 30 and 40% of slag and cured for 28 d showed higher strength than the individual materials. Additionally, the effect of different percentages of lime on the strength of the fly ash–slag mixtures was investigated. Tremendous increase in strength was observed with the addition of even 2% of lime. Scanning electron microscopy and X-ray diffraction studies showed the morphological and mineralogical changes that are associated with strength improvement. This study suggests that properly designed combinations of fly ash–slag–lime can be used as construction materials for infrastructure projects such as structural fills or subgrade and sub-base courses in pavements without requiring large quantities of lime.