Evaluation of alternative sources of SCMs for concrete materials

This study investigated the use of alternative sources of supplementary cementitious materials (SCMs), namely landfilled reclaimed fly ash (RFA) and reclaimed ground bottom ash (GBA), for its beneficial use in concrete. The study characterized RFA and GBA along with conventional Class F fly ash (FA), as control. Furthermore, the influence of the three ashes on the fresh and hardened properties of concrete was investigated (when used to replace 10% of cement by mass). Experimental results revealed that all the ashes were classified as class F fly ash according to ASTM C618. Yet, in contrast to FA, RFA and GBA presented an increased water requirement, which was attributed to the differences in micro-morphology. Furthermore, RFA exhibited a lower strength activity index (SAI), while GBA presented a higher SAI, in contrast to FA. This was attributed to the CaO contents of the ashes, which was lowest for RFA and highest for GBA. RFA admixed concrete exhibited a slight decrease in workability, while GBA admixed concrete exhibited a significant decrease. This was attributed to the irregular shape of GBA particles. The control concrete mixture (with no ashes) exhibited the highest air content among all concrete mixtures, while GBA admixed concrete exhibited the lowest air content. Notably, while RFA exhibited the highest loss on ignition (LOI), RFA admixed concrete presented the highest amount of air from all concrete mixtures implementing ashes, including FA. In terms of hardened properties, all coal ashes had a minimal influence on the compressive strength of concrete, producing marginal decrements in strength. Furthermore, all concrete mixtures with ashes exhibited a slight increase in surface resistivity compared to control