Fracture behavior of SAP concrete under the interaction of fatigue load and extreme environments based on acoustic emission

Superabsorbent polymers (SAPs) enhance concrete durability by mitigating early cracks and promoting secondary hydration; however, their enhancement effect may be influenced by extreme environments (e.g., high/low temperature, and freeze–thaw cycles) and varying fatigue load levels (0.4, 0.55, and 0.7). A four-point bending fracture test combined with acoustic emission (AE) technology was used to assess the fracture behavior of SAP concrete under the interaction of environmental and dynamic fatigue loading. Additionally, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were used to examine crack evolution mechanisms. The results demonstrated that SAPs slow the rate of decline in flexural tensile strength, peak load, and fracture energy under varying fatigue load durations and temperature fields. Specifically, under 0.55 stress-level fatigue load and temperature environments, the fracture energies of the control group decreased by 42.86 %–87.75 %, while those of SAP concrete decreased by only 35.96 %–85.51 %. The impact of environmental factors on concrete can be ranked in the following order: freeze–thaw cycles, high temperature, and low temperature. Moreover, the anti-cracking performance of SAP concrete is more pronounced at low temperatures than at high temperatures. Mechanistically, SAPs optimized the pore structure and enhanced concrete compactness through internal curing, reducing the average pore diameter of the concrete by 12.25 %. This also decreased crack length, width, and density, as the incorporation of SAPs increased the initial damage threshold and inhibited crack propagation. This research provides a theoretical foundation and technical support for the application of SAP concrete in highway engineering.