Influence of temperature on hydration and microstructure properties of limestone-calcined clay blended cement

Abstract

In this article, the strength and microstructure development of two low clinker blended cements; limestone calcined clay cement (LC3) and slag-fly ash composite cement (CC) cured at 27 °C and 50 °C are analysed and compared to those of ordinary Portland cement (OPC). A significant difference in the 28 days strength was observed between 27 and 50 °C cured specimens in low clinker blends. The results show that the quantities of ettringite and carbo-aluminate phases significantly reduce when LC3 is cured at 50 °C. EDX analysis shows that significant quantities of aluminate are taken up in C–A–S–H, when curing is done at a higher temperature. It was seen from BSE image analysis that the C–A–S–H formed from the hydration of LC3 is much more heterogenous than the other cements due to non-uniformity in C–A–S–H density as well as intermixing of hydration products. It was also seen that although an increase in the temperature leads to a measurable increase in the density of C–S–H in OPC and CC, the influence on LC3 is not clear, the heterogeneity of the product appears to reduce. In the case of both LC3 and CC, the hydration of clinker is slowed down, especially after the first day, when cured at 50 °C. All these factors lead to a coarsening of the pore-structure and a reduction in the compressive strength of both low clinker cements, when cured at the higher temperature.