Hydroxyethyl methyl cellulose and steel fiber reinforce the interfacial bonding properties of calcium aluminate cement with existing concrete before and after high temperature

The performance of damaged structures after a fire is significantly reduced; however, they can be reused after undergoing proper repair. Hydroxyethyl methyl cellulose (HEMC) can effectively improve the bonding strength of cement-based repair materials. However, it remains unclear whether its water retention can enhance the interfacial bonding performance of high-temperature damaged concrete, as well as its comprehensive performance after synergistic reinforcement with steel fibers (SF). This study proposes using fly ash (FA), HEMC, and SF to enhance the interfacial bonding properties of calcium aluminate cement (CAC). Based on determining the fly ash dosage, the effects of single and combined addition of HEMC and SF on the mechanical strength and interfacial bonding strength of CAC were investigated. Through a preliminary analysis of the Compression-to-flexural ratio and bonding effectiveness, it was determined that the combined addition of the two materials has a positive effect. The modified CAC not only ensures its own strength but also increases the 7-day interface bonding strength by 67.57% and the 28-day interface bonding strength by 58.96%. The optimal ratio was determined by range analysis and analysis of variance (ANOVA). A life cycle assessment was conducted using the cradle-to-site boundary approach. Based on a life cycle assessment, the EE and GWP of H3SF10 decreased by 7.75% and 9.95%, respectively, and the GWP Total decreased by 7.37% compared with the Control. The optimal utilization range of FA is 136 km. By combining the sustainability index with cost analysis, we achieved cost reduction while maintaining stable material performance. A continuous high temperature was used to simulate the fire damage of the concrete matrix, and the interfacial bonding strength was evaluated using a splitting tensile test. After repairing the damage at 400℃, the interfacial bond strength of the specimens at 7 and 28 days remained higher than that of the unmodified CAC at room temperature. The interfacial bond strength of the H and HSF groups at 28 days increased by 1.7% and 18.3%, respectively, compared to the room temperature control group. However, after repairing the damage at 600℃, the interfacial bond strength of the HSF group decreased significantly at both 7 and 28 days, by 35.9% and 31.43%, respectively. Compared with the undamaged matrix, it was found that only the failure mode showed obvious differences. SEM analysis was performed to investigate the effects of FA, HEMC, and SF on the microstructure of CAC, with particular attention paid to interfacial variations between the matrix and CAC before and after thermal exposure. • ·Modification of calcium aluminate cement by fly ash, HEMC and steel fiber. • ·CAC containing 0.3% HEMC and 1.0% SF has better interfacial bond strength • ·The modified CAC altered the failure mode of repaired concrete.