Study on the performance degradation of iron ore tailings concrete under microwave irradiation

To fully leverage the microwave-absorbing and heating characteristics of iron ore tailings and achieve high-value utilization of mining solid waste, this study incorporates iron ore tailings as coarse aggregates into concrete. The aim is to investigate the damage mechanisms and the deterioration patterns of mechanical properties under microwave irradiation, thereby laying the foundation for determining microwave-assisted crushing process parameters to meet the demand for green and efficient recycling of construction waste. First, through infrared thermography, ultrasonic testing, and compressive strength experiments, the influence of microwave parameters (power, duration) and iron ore tailings content on the temperature gradient, internal damage, and mechanical properties of concrete was revealed. Subsequently, scanning electron microscopy (SEM) was employed to analyze the microstructural degradation of the concrete before and after microwave exposure. The results indicate that higher iron ore tailings aggregate content leads to higher temperatures in the concrete specimens. The surface temperature rise of the specimens follows a near-linear trend, with an initial rapid increase followed by a slower rate. The ultrasonic pulse velocity (UPV) attenuation rate reaches up to 27.77 %, 11 % higher than that of the limestone control group, while the compressive strength decreases by 31.18 %. Microstructural analysis shows that under microwave irradiation, iron ore tailings rapidly heat up due to their high microwave absorption, creating a significant temperature gradient with the slower-heating mortar. This results in thermal stress cracks (up to 11.28 μm) in the interfacial transition zone. Compared to conventional concrete, iron ore tailings concrete develops more internal defects and microcracks. This study provides theoretical support and process optimization pathways for the microwave-assisted crushing of iron ore tailings concrete, promoting the synergistic development of solid waste recycling and low-carbon construction technologies. • Microwaving iron ore tailings concrete causes significant temperature variation, with the first 3 min decisive. • The UPV attenuation rate of iron ore tailings concrete reaches 27.77 %, which is 11 % higher than that of limestone concrete. • Compressive strength tests showed a 31.18 % reduction in concrete strength under 8kW-5min microwave conditions. • SEM showed that cracks in the ITZ weakened the concrete's internal bond, initiating structural loosening.