Experimental study on the flexural properties of repaired concrete with super early strength under low-velocity impacts

This study delves into the flexural properties and repair effects of unsaturated polyester resin concrete (UPRC) for potential pavement repair applications. Quasi-static flexural test, bonding test, and dynamic flexural test were conducted on UPRC specimens at different curing ages. Results exhibit UPRC's impressive early-age strength, reaching nearly 40% of ultimate strength at 28 days for 1-day curing. UPRC also showcases superior bonding compared to ordinary Portland concrete, rendering it a good choice for pavement repair. SEM analysis provides insights into the bonding mechanism between UPRC and old concrete. Employing digital image correlation, the loading process during impact tests reveals three stages. Accordingly, the calculation methods of strain rate and flexural load were determined. Under low-velocity impacts (≤ 2.0 m/s), extended curing enhances energy dissipation. Besides, the resin and aggregates within the specimen yields a buffering effect. However, under high-velocity impacts, substantial instantaneous strain weakens the energy dissipation capacity. UPRC's peak flexural load displays a significant strain-rate effect. An empirical model correlating dynamic increase factor, strain rate, and curing time was proposed. Consequently, the strain-rate effect diminishes with increasing curing age, stabilizing after 7 days. In summary, UPRC's exceptional early-age strength positions it as an ideal material for emergency repairs.