Properties and microstructure of lime kiln dust activated slag-fly ash mortar

Abstract

Commercially available alkali activators such as sodium hydroxide and water glass are widely used in the formulation of alkali-activated binder (AAB) to activate ground granulated blast furnace slag (GGBS) or fly ash (FA). However, the production of the commercially available alkali activators yields high carbon dioxide (CO 2) emission results in the same environmental impact as cement production. The present study aimed to develop an alternative alkali activator with low embodied CO 2 for the sustainable production of AAB. In this study, the FA/GGBS blend was activated by 5–30% by lime kiln dust (LKD), an industrial by-product from lime production. The resulting binder was used to produce alkali-activated mortar (AAM) to evaluate mechanical, durability and microstructure properties. The increased of LKD replacement level from 5% to 10% was found to improve both the mechanical performance by around 30% and durability performance of alkali-activated mortar (AAM) by 50% as shown by the optimum mix design, L10G36F64. The best ratio of FA to GGBS was for optimal alkali activation was established as 3:2, by binder weight. A further increase in replacement level and GGBS content beyond the stipulated contents reduced the overall performance of the AAM from the optimum level. The main hydration products of LKD activated FA/GGBS were C-A-S-H and C-S-H. The SEM investigation revealed that the best sample with the composition mentioned had dense microstructure and dense foil-like C-S-H gel. LKD was established to be an effective alkali activator for GGBS-FA to yield AAB with the desired mechanical and durability properties due to its inherent quicklime composition.