Development of the Microstructure in LC³ Systems and Its Effect on Concrete Properties

Abstract

In this paper, the difference in the microstructure development of limestone calcined clay cement (LC³) in comparison with the ordinary Portland cement (OPC) and Portland pozzolan cement (represented as FA30) at different water-binder ratios is shown. The results from the studies suggest that a mere adoption of a lower water binder ratio to reduce the capillary pore space for filling by hydrates, ensures only a marginal improvement in the kinetics of microstructural development, as seen from conductivity evolution in OPC and FA30. Highly reactive pozzolans ensure a more rapid drop in conductivity due to low-density hydrates resulting in lower capillary porosity and densification of the hydrate matrix. BSE micrographs also show a more densified binder matrix with LC³, mainly due to high pozzolanicity of calcined clay resulting in CSH with lower C/S ratio with a hybrid hydrated phase assemblage compared to OPC and FA30. The impact of improved kinetics of LC³ binder reflects in better durability parameters at an early age in the different concretes made with LC³ binder. It is seen that the fly ash based systems (FA30) show a marked increase in the concrete resistivity up to an age of 1-year curing. The resultant effect of such microstructural development on the chloride resistance of concretes is also discussed.