Bond deterioration and durability prediction of mortar anchor under NH ₄ Cl-induced leaching

Mortar anchors are widely used in slope and tunnel support systems. However, in groundwater environments containing aggressive ions, the mortar surrounding the mortar anchor is susceptible to chemical leaching, which degrades bond performance and reduces anchorage capacity. In this study, the degradation behaviour of mortar anchors subjected to accelerated NH4Cl-induced leaching was experimentally investigated, and a predictive model for bond strength deterioration was developed. Pull-out and lateral-shear tests were conducted at multiple leaching durations to evaluate the mechanical degradation of the anchorage system, while the evolution of Ca2+ concentration and leaching depth was monitored to characterise the chemical deterioration process. The results show that increasing NH4Cl concentration significantly accelerates calcium dissolution and pore development in mortar, resulting in substantial reductions in pull-out strength and lateral-shear strength. The maximum reductions reached 65.06% and 63.09%, respectively. Incorporation of Class I fly ash effectively mitigated the leaching damage, and an optimal replacement ratio of approximately 14% was identified. Based on calcium diffusion and leaching theory, a degradation prediction model was verified to relate the radial leaching depth to the residual anchorage capacity.