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 ~40 wt%. 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 lm spatial resolution (voxel size 0.32 lm), were 16.6, 10.0 and
2.4 vol% at 7, 8 and 60 days 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 days. The reactions filling the pores were investigated by
Rietveld quantitative phase analysis and 27Al MAS-NMR.
