Early-age strength development in fly ash blended cement composites: investigation through chemical activation

To achieve sustainability in construction, research is currently geared up to utilise more fly ash (FA) in cement. The low early-age strength development of FA–cement composite prevents its broader acceptance and usage in the construction sector. Many attempts have been made by various researchers, including through the use of chemical accelerators, to eliminate this well-known disadvantage of FA–cement composites. This study aims to investigate the influence of various non-chloride chemical accelerators such as calcium formate, calcium nitrate and calcium carbonate in altering the hydration products formed at various replacement levels of FA. The influence of chemical accelerators on two major compounds – tricalcium silicate (C3S) and tricalcium aluminate (C3A) – that are mainly responsible for early-age strength development are discussed in this study. It is found that all the chemical accelerators can be safely used to improve the early-age strength of FA–cement composites at least to the level of 35% of FA replacement prescribed by the existing codes without compromising the long-term strength.