Repair of fire-exposed self-consolidating concrete with high-performance fibre-reinforced concretes

Despite the increasing use of high-performance concretes for repair and rehabilitation, the interfacial bond behaviour between the substrate and overlay materials, particularly after exposure to elevated temperatures, remains poorly understood. In this work, the shear and tensile bond strengths of overlay concretes and substrates with different surface preparation (as-cast and grooved) were assessed at ambient temperature and after exposure to elevated temperatures. Different high-performance overlays (engineered cementitious composite (ECC), ultra-high-performance fibre-reinforced concrete (UHPFRC) and a high-strength self-consolidating concrete (HSCC) were cast onto normal-strength self-consolidating concrete (NSCC) substrates. The fire-damaged specimens were exposed to 300°C and 450°C, bearing in mind the spalling sensitivity of UHPFRC, and thermal uniformity was achieved before testing. The experimental results demonstrated that all the overlays effectively repaired and strengthened fire-damaged NSCC substrates, maintaining adequate residual bond strength after elevated-temperature exposure. However, the UHPFRC overlays exhibited the greatest bond performance in both repair and strengthening tests, with up to 134.6% and 53.1% higher residual bond strength than the HSCC and ECC, respectively, after exposure to 300°C. In addition, surface roughening played an important role in significantly enhancing the residual bond strength, with grooved substrates exhibiting markedly less degradation than as-cast ones. Predictive mathematical models were developed and found to be effective for each composite type and test condition.