Concrete-Repair Mortar Bonding: Effects of Surface Contamination from Steel Corrosion Treatment and Surface Moisture

In practical concrete repair, the use of rust removers and protective agents during steel treatment may contaminate the surrounding concrete substrate, thereby affecting repair performance. This study investigated the effects of such contamination and surface moisture conditions on the bond performance between the concrete substrate and the repair mortar. Three types of concrete substrates were prepared: (a) rust remover treatment, (b) rust remover treatment followed by water rinsing and (c) rust remover treatment followed by water rinsing and the subsequent application of protective agents. The interface bonding strength and microstructure development were evaluated through three-point bending tests and SEM-EDS analysis, respectively. The results showed that the rust remover treatment significantly reduced repair effectiveness to 56.2% at 28 days, whereas water rinsing enhanced it to 84.9%. Applying protective agents can further improve the repair effectiveness to 87.4% at 28 days. SEM-EDS results revealed that rust remover contamination formed a porous interfacial layer between the concrete substrate and repair mortar with higher Ca/Si ratios, whereas protective agents produced a denser interface with lower Ca/Si ratios. In addition, lower surface moisture content can improve repair effectiveness by reducing the w/c ratio at the interface. For practical on-site scheduling, the delayed repair time also affected repair effectiveness, showing a non-linear trend with a critical point at around 60 minutes, beyond which further improvements were minimal. These findings highlight the importance of controlling substrate contamination and moisture conditions to enhance repair performance and construction efficiency.