Limestone calcined clay cement: mechanical properties, crystallography, and microstructure development

Limestone calcined clay cement (LC3) holds promise as a new type of sustainable cement-based material, but the mechanisms underpinning its engineering performance are still poorly understood. Here, a metal intrusion-enhanced imaging approach was employed to quantitatively analyze and link the pore structure development of LC3 to its hydration process, i.e. solid-phase development, and mechanical performance. We found that the early age microstructural development in LC3 is inhomogeneous, with the perimeter of limestone particles displaying higher porosity relative to that surrounding calcined clay and clinker. At later ages, the formation of carboaluminates and calcium-aluminate-silicate-hydrates homogenized the overall microstructure of LC3, thereby delivering improved mechanical performance. Overall, our analysis suggested a more efficient particle packing in LC3 mixes, which decreases the volume/connectivity of micro-pores and can account for LC3's notable flexural strength. These findings can assist the development of improved LC3 binder formulations alongside other ternary binders with possibly higher limestone additions.