Leaching behaviour of calcium aluminate cement-based materials in water at 20°C and 60°C

The phase conversion of metastable products in calcium aluminate cement (CAC) at elevated temperatures can significantly affect its durability. This study systematically investigates the degradation and leaching behaviour of CAC-based materials in water environments at 20°C and 60°C. The compressive strength evolution of CAC mortars was tracked over 56 days. The underlying mechanisms were elucidated by analysing the phase composition, microstructure, and pore structure of CAC paste specimens, complemented by monitoring the chemistry of the exposure solution. Crucially, a depth-resolved, layer-by-layer analysis was conducted on larger specimens to reveal the leaching gradient. The results show that at 20°C, the leaching behaviour is not pronounced; instead, ongoing hydration densifies the microstructure, leading to a continuous increase in compressive strength. Conversely, at 60°C, the material undergoes rapid degradation. This is driven by a synergistic process involving the conversion of metastable hydrates to stable C₃AH₆ and gibbsite, and the accelerated dissolution of these products by the water environment, resulting in a porous microstructure and a severe loss of mechanical properties. The depth-resolved analysis provided direct evidence of these mechanisms, confirming that at 60°C, degradation is a progressive process that attacks the material from the exterior.