Influence of crack width on the stiffness recovery and self-healing of reactive magnesia-based binders under CO₂-H₂O conditioning

This study investigated the healing efficiency and phase formations in pre-cracked reactive magnesia-based binders under CO₂/water conditioning. Pre-loaded samples with various crack widths were subjected to a healing regime involving 10% CO₂ and water for 10 cycles. The recovery of samples was assessed by resonance frequency measurements and optical microscopy observations. A relationship between crack width and type of healing phases was established via microstructural analysis and carbonation depth measurements. All samples achieved a complete stiffness recovery after a few healing cycles. The healed cracks revealed a higher stiffness than the surrounding matrix under reloading. The recovery of sample stiffness was associated with the densification of sample microstructure via the formation of hydrated magnesium carbonates (HMCs). Depending on the crack width and depth, two different types of HMCs (nesquehonite and hydromagnesite) were observed within the healed cracks, whose formation was influenced by pH, determined by the diffusion of CO₂.