Macroscopic Performance Evolution and Hydration Mechanism of Limestone Calcined Clay Cement with an Ultra-Low Water/Binder Ratio

To optimise the mix design and elucidate the synergistic mechanisms amongst the constituents of limestone calcined clay cement (LC 3 ), this study systematically examines the evolution of macroscopic performance and microstructure of LC 3 paste prepared at ultra-low water/binder (w/b) ratios. The associated workability, setting time, mechanical properties and drying shrinkage were comprehensively evaluated in LC 3 systems formulated with varying w/b ratios, limestone calcined clay (LC 2 ) contents and silica fume (SF) dosages. The macroscopic performances and microstructural properties of the hydration products were correlated. Results indicate that a 30% LC 2 replacement maximises the compressive strength and considerably reduces the drying shrinkage.Incorporating 5% SF refines the pore structure but excessive SF competes with free water, thus inhibiting hydration. An appropriate combination of LC 2 and SF synergistically promotes the formation of ettringite crystals and highly polymerised calcium–alumino–silicate–hydrate gel. When w/b = 0.16, LC² = 27%, and SF = 10%, it is the optimal mix proportion.This work provides both theoretical foundations and technical support for the subsequent development of low-carbon ultra-high-performance concrete.