Strength and microstructure analysis of bacterial treated cement kiln dust mortar

Cement kiln dust (CKD), a waste by-product material, is generated during manufacturing of cement clinker and possess cementitious characteristics as of cement. CKD represents significant environment concern related to its emission, disposal and reuse due to high alkalinity. In this study, attempts are made in utilizing the bacterial (Bacillus sp.) treated cement kiln dust as partial replacement of Portland cement (10, 20 and 30% w/w) and its effect on the normal consistency, setting times and hydration process of blended cement pastes, and on compressive strength (at 7, 28 and 91 days) of blended cement mortars. Test results show increase in water consistency with CKD concentration where as setting time is decreased up to 10% CKD addition, above which setting time increases due to reduced hydration process. At later curing ages hydration process increases up to 10% bacterial treated CKD–cement paste which later on decreases as CKD content increases. This increase in hydration at later curing ages (91 days) responsible for increase in compressive strength in 10% bacterial treated CKD mortar compared with 0% and 10% untreated CKD mortar, respectively. Scanning electron microscopy (SEM) results exhibits increased calcium silicate hydrate and formation of non-expansive ettringite in pores which dense the mortar structure and increases the compressive strength in bacterial treated 10% CKD mortar.