Review of fly-ash as a supplementary cementitious material

This paper presents a review of fly-ash as a Supplementary Cementitious Material (SCM) in concrete in terms of its effects on hydration and durability. The climate change agenda has focused the cement and concrete industry on using low embodied CO2 materials and much effort has been made on incorporating industrial by-products into cement as SCMs. With worldwide cement production (circa 4 billion tonnes) currently accounting for approximately 8% of global CO2 emissions and 7% of industry energy use, the use of suitable SCMs to partially replace cement in concrete is extremely important. However, while coal-fired power stations are in the decline, due to the need for more sustainable energy generation, there remains stockpiles of fly-ash for potential use as an SCM. This creates opportunities for ashes not previously used in concrete to be studied both in terms of its behaviour during hydration and durability performance in harsh environments. However, these new fly-ash sources need to be studied carefully due to uncertainties about their physical and chemical constituents, reactivity, long term stability and phase relationships and minor elements distribution due to the variability in the source of coal. The work presented includes a review of fly-ash in terms of its effects during cement hydration and contribution to concretes performance in harsh environments from the literature.