Construction and Building Materials | 2021
Phase and microstructure evolutions in LC3 binders by multi-technique approach including synchrotron microtomography
Abstract
Abstract Limestone Calcined Clay Cements, LC3, are attracting a lot of attention as it is possible to reduce the clinker factor by 50%, which means a cement CO2 footprint reduction of 40%. This is compatible with maintaining the mechanical strength performances after one week, if the kaolinite contents of the raw clays are above\xa0~40\xa0wt%. Durability properties are also maintained or even enhanced. Here, it is used a multi-technique approach to understand the phase and microstructure developments. From the thermal analysis, partial limestone reactivity is proven. Chiefly, high-resolution synchrotron microtomography has been employed, for the first time in these systems, to characterize their microstructures. The measured total porosities, within our 1\xa0μm spatial resolution (voxel size 0.32 μm), were 16.6, 10.0 and 2.4\xa0vol% at 7, 8 and 60\xa0days of hydration, respectively. Pore connectivity strongly decreases with hydration time due to the chemical reactions producing new phases filling the pores. The 6-connected porosity fractions were 92, 78, and 9% at 7, 8 and 60\xa0days. The reactions filling the pores were investigated by Rietveld quantitative phase analysis and 27Al MAS-NMR.