Effects of clay type and component fineness on the hydration and properties of limestone calcined clay cement

Abstract

Limestone calcined clay cement (LC³) is emerging as an alternative to Portland cement, offering economic advantages, reduced CO₂ emissions, and mechanical properties on par with Portland cement. Central to the effective utilization of LC³ is understanding how the fineness of its components affects its performance. The current study investigates limestone calcined clay cement mixtures composed of kaolinite, illite, and montmorillonite calcined clays and limestone at two levels of fineness. Strengths of mortar cubes were tested at 1, 3, 7, and 28 d and statistical analysis was performed with a 95% confidence level. Additionally, LC³ pastes were analyzed using x-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy, and isothermal calorimetry. The fineness of the calcined clay along with the fineness of limestone is found to be statistically significant for 28-d strength in LC³ mortars made with kaolinitic and montmorillonite calcined clays. All hydrated blends had a hemicarboaluminate phase, whose intensity was related to the fineness of the calcined clay, and the monocarboaluminate phase formation was found to be dependent on both the fineness and type of calcined clay. Porosimetry revealed that LC³ pastes with illite clay have larger threshold pore diameters than those with kaolinite clay. LC³ pastes containing kaolinite have denser microstructures due to C–S–H and hemicarboaluminate formation. Pastes produced with coarse calcined clay and coarse limestone led to a broader, weaker heat development peak and lower normalized cumulative heat. LC³ with kaolinitic clay has the highest normalized cumulative heat, while that with montmorillonite calcined clay has the lowest.

Graphical abstract