Cracking behaviour of concrete with superabsorbent polymer (SAP) under rolling fatigue load and temperature coupling

To explore the long-term crack resistance of pavement concrete containing superabsorbent polymer (SAP), a fatigue test was designed with the consideration of rolling fatigue load and temperature coupling. The four-point fracture and acoustic emission tests were combined to evaluate the evolution of crack resistance. Additionally, the enhancement mechanism was revealed through scanning electron microscopy and mercury intrusion porosimetry experiments. The results indicate that the coupling effects of rolling fatigue load and temperature accelerate the deterioration of the fracture performance of concrete, particularly the freeze–thaw conditions. The concrete with SAP had greater fracture toughness, with improvements of 9.3%, 11.9%, and 58.1% under the coupling rolling fatigue loading and high temperatures, low temperatures, and freeze‒thaw cycles, respectively. The fracture process of concrete with SAP includes fluctuation, fatigue accumulation, and fatigue failure periods, and the SAP delays the arrival time of cumulative ring count and energy, significantly reducing the rate of concrete damage. More fibrous C-S-H and ettringite were generated at the interface microcracks in the concrete containing SAP, confirming the greater degree of hydration. Moreover, the SAP reduced the porosity and average pore size, which enabled the concrete to better resist the impact of rolling fatigue loading and adverse environmental temperatures.