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.