Impact of calcium leaching on mechanical and physical behaviors of high belite cement pastes

•Impact of calcium leaching on mechanical and physical properties of HBC paste is studied.•The calcium leaching evolution of HBC is analyzed by measuring the Ca/Si.•Distribution model of Vickers hardness of leached HBC paste is proposed.•A good linear relevance is found between Equivalent Vickers hardness and compressive strength. Water conservancy engineering such as dams and canals built with high belite cement (HBC) concrete for reducing temperature cracks have been running for many years and are still constantly under construction. However, little research has been conducted on the calcium leaching behaviors of HBC. In this paper, mechanical and physical properties such as mass loss, porosity, leaching depth, compressive strength and hardness of HBC-based pastes (with three w/b ratios and contents of fly ash) exposed to ammonium chloride aqueous solution were measured. In addition, slice specimens of HBC and ordinary Portland cement (OPC) were designed to study their Ca/Si ratio changes in leaching process, XRD, SEM and EDS mapping scanning were also carried out to investigate the variations of composition and microstructures between degraded and intact cement hydrates. Results show that the macro-properties of leached HBC pastes are similar to but slightly worse than those of OPC, while there is a lower calcium leaching rate of HBC in both stages of CH dissolution and C-S-H decomposition. Furthermore, the w/b ratio has an appreciable effect on the physical and mechanical performance of HBC pastes subjected to leaching, and the corrosion damage could be alleviated by adding fly ash. Eventually, a distribution model of Vickers hardness based on Logistic function is proposed to evaluate the degradation of leached pastes with high accuracy, and the axial compressive strength could be quantified by equivalent Vickers hardness with a well linear relationship.