Setting time and microstructure of Portland cement-bottom ash–sugarcane bagasse ash pastes

Abstract

Bottom ash (BA) and sugarcane bagasse ash (SCBA) are by-products from power plants and the sugar industry and they have a great potential to be used in green-concrete structure applications. This study reports the effects of BA and SCBA on the properties of Portland cement (PC) pastes and mortars as cement replacement, by up to 20 percent by weight. All mortars had a water to binder ratio (w/PC + BA, w/PC + SCBA, and w/PC + BA + SCBA) of 0.5. Normal consistency, setting time, compressive strength, and microstructure (using scanning electron microscope, SEM) were systematically investigated. The results showed that the water requirement for a normal consistency was decreased with increasing BA content. The addition of SCBA, on the other hand, caused the water requirement to increase. The initial and final setting times of all pozzolan mixes were longer when compared to that of PC mix. The compressive strengths of all mixtures with BA were similar to that of the PC mix at 90 days. In addition, the SEM micrograph of pastes confirmed a good pozzolanic reaction between ash particles and Portland cement, resulting in an increase in the compressive strength of the mortars, especially after a period of time (more than 28 days).