LAUSR

Abstract Supplementary cementitious materials (SCMs) significantly improve concrete performance. However, the application of SCMs remains limited by their heterogeneity and variability. This study investigated the pozzolanic reaction and curing temperature-dependence of low-calcium fly ash in cement systems over 2 years. The experimental results show that fly ashes have different reactivities and temperature dependencies even though they have similar material properties. A modified tangential method was developed for thermogravimetric analysis of the calcium hydroxide content and chemically bound water of fly ash-blended cement paste. The chemical composition of an aluminium-modified calcium silicate hydrate (C-(A)-S-H) gel of fly ash-blended cement paste was studied by scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS) with image analysis. The experimental results show that as the Ca/Si ratio decreased in fly ash–cement paste, the Al/Si ratio increased. The Al/Si distribution of fly ash-blended cement paste varies widely from 0.05 to 0.50 with no specific maximum. The typical Ca/Si and Al/Si ratios of C-(A)-S-H gel in fly ash cement paste are approximately 1.40 and 0.25.