Influence of fly ash and silica fume on the compressive strength development of Portland cement concrete

To make concrete more environmentally compatible, this paper investigated the compressive strength development of binary and ternary cement combination concretes containing ordinary Portland cement, fly ash and silica fume at various ages, water/cement ratios and strengths. Due to its higher fineness and improved pozzolanic reactivity, silica fume as binary and ternary cement components resulted in concretes with improved compressive strengths at both early and later ages. While fly ash, at equal water/cement ratios, would reduce compressive strength at early ages, its compressive strength increased progressively with age to contribute to later-age strength development. However, to effectively support long-term strength development, at equal water/cement ratio, a total cement addition content of more than 20% would be required. While the cement combination concretes were generally more environmentally compatible than ordinary Portland cement concrete because of their lower embodied carbon-dioxide contents, 29 (64%) of the 45 cement combination concrete options investigated at equal strengths between 42.5 and 62.5 N/mm2 were cheaper than ordinary Portland cement concrete. At equal strength, fly ash contributed substantially to strength development. Hence, concrete options, majorly fly ash binary cement concretes and some ternary cement concretes at a total replacement level of not more than 35%, are cheaper than ordinary Portland cement concrete.