Thermal-induced damage and cohesive fracturing characteristics of concrete using a new generation environmentally sustainable cement

Abstract Concrete applications in heat piles (used in ground source heating systems) and nuclear waste repositories present unique challenges due to the thermal loads imposed on the concrete. These loads significantly affect the mechanical properties and long-term performance of the concrete, ultimately influencing the efficiency of heat piles and the safety of nuclear waste storage. This study investigated the fracture toughness (KIC) and cohesive fracture properties of concrete made with environmentally sustainable cement under high-temperature loading. The fracture toughness (FT) test results showed that FT values decreased by 27.8 % for specimens with a notch crack inclination angle of β = 0°, and by 31.6 % for specimens with β = 30° at 500 °C loading. SEM and 3D image processing analyses revealed a clear exponential relationship with increasing temperature. Microcracks became more extensive and interconnected, forming a network throughout the cement paste at 500 °C. These microcracks initially developed in the interfacial transition zone (ITZ), with significant debonding of the aggregate from the cement paste observed, leading to an overall reduction in ITZ strength. Cohesive zone model (CZM) analysis using NLQ elements with FRANC2D showed that the highest traction opening and traction sliding occurred in the β = 0° specimens at 500 °C loading.