Cooling-induced thermal stress evolution in exothermic-curing anchoring adhesives: Experimental characterization and numerical simulation

Anchorage adhesive materials are a key constituent of anchorage systems and directly affect stability and safety in mining and geotechnical engineering. To cope with complex service environments, diverse materials have been developed; however, their mechanical performance varies considerably and thermally induced stresses during curing are often overlooked. Three commercial anchorage adhesive products were investigated: an MGJ resin anchoring agent, an RBA 380 pumping-type thixotropic anchoring agent, and a ZJJ rebar anchorage adhesive. The full temperature history during fixed-volume curing was recorded to determine the peak temperature and high-temperature duration. Post-curing damage was examined by SEM, and tensile, compressive, and shear strengths were obtained from macroscopic tests. Thermophysical properties (density, specific heat, thermal conductivity, and linear expansion coefficient) were measured and incorporated into finite-element simulations to quantify thermal-stress distribution and concentration. All materials exhibited exothermic curing, with peak temperatures ranked as ZJJ (122°C) > RBA 380 (103.5°C) > MGJ (64.6°C). High-temperature duration followed RBA 380 (8 h) > ZJJ (>6 h) > MGJ (>5 h). ZJJ showed higher overall strength than MGJ and RBA 380. Key information was obtained from the fitting of simulation data: temperature decays exponentially with distance, indicating the presence of a temperature gradient driving heat flow, which in turn leads to the existence of a strain gradient. At the same time, thermal strain increases exponentially with time, whilst thermal stress decays exponentially with time, indicating the occurrence of stress relaxation. Thermally induced stresses degraded microstructural integrity and promoted cracks in closed, partially open, and fully open states. Thermal-stress-driven interfacial mismatch may impair anchorage reliability, indicating a need for construction optimization.