Comparison of the performance of class-C and class-F fly ash concrete mixtures produced with crushed stone sand

Abstract

The use of fly ash as partial replacement of cement in the production of environmentally-friendly concrete is now an established fact. This study investigated the effects of class-C and class-F fly ash at 20 wt% replacement of Portland cement (PC) on the strength and durability characteristics of concrete mixtures incorporating crushed stone sand as fine aggregate. Experimental investigations were carried to compare the effects of class-C and class-F fly ash as partial replacement of cement on the rheology, compressive strength, moisture sorption, abrasion resistance, and microstructural characteristics of the resulting concrete mixtures at various concrete ages.Test results showed that the use of class-C fly ash lowers the workability (slump value) by 26% and entrained air by 33% of the fresh concrete, while the class-F fly didn’t not affect these characteristics when compared with that of control mixture. On the other hand, the use of class-C and class-F fly ash enhanced the later age compressive strength of the resulting mixtures by 23% and 35%, respectively in comparison to control concrete mixture. At 56 days of concrete age, 20% and 29% reduction in the 8-day cumulative moisture sorption and 14% and 19% reduction in mass loss due to abrasion of class-C and class-F based concrete mixtures, respectively, was recorded as compared to that of control mixture. Scanning electron microscopic (SEM) analyses showed enhancement in the microstructure of the concrete mixtures as results of the inclusion of fly ash as partial replacement of PC. Test results also showed superior performance of class-F fly ash on the strength and durability characteristics of resulting concrete mixture as compared to class-C fly ash at equivalent replacement level. The outcome of this study provides insight into the comparative performance of class-C and class-F fly ash based concrete mixtures in fresh and hardened states.