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.