The bond interface is the weakest part of the repair system, and its performance is a key factor impacting the repair effectiveness of damaged concrete constructions. However, the research on the damage law and the mechanism of repair of the bonded interface in the cold region marine environment is not in-depth. In this study, the influence of polyvinyl alcohol (PVA) fibers and crystalline admixtures (CAs) on the mechanical properties and volumetric deformation performance of cementitious repair materials was researched. Furthermore, the deterioration patterns of the bond strength and chloride ion diffusion characteristics of the repair interface under the coupling of seawater-freeze-thaw cycles were investigated. Combined with the composition, micro-morphology, and micro-hardness of hydration products before and after erosion, the damage mechanism of the repaired bonding interface was revealed. The results indicate that the synergistic use of PVA fibers and CAs can significantly improve the compressive strength, bond strength and volume stability of the repair materials. The compressive strength and 40° shear strength of S0.6CA at 28 d were 101.7 MPa and 45.95 MPa, respectively. Under the seawater-freeze-thaw cycle action, the relationship between the contents of free and bound chloride ions in the bonded interface can be better fitted by the Langmuir equation. The deterioration process of the bonding interface and the penetration rate of chloride ions can be effectively delayed by PVA fiber and CAs. After 700 seawater-freeze-thaw cycles, the loss rates of bond strength and chloride diffusion coefficient of S0.6CA were reduced by 26.34% and 52.5%, respectively, compared with S0.

The bonding interface between repair materials and concrete substrate is the weakest link in the entire repair structure. If the interface bonding performance is insufficient, the repair material is prone to cracking or falling off, leading to repair failure. The shrinkage of repair materials is one of the primary factors affecting the bonding performance of these interfaces. In this study, sulphoaluminate cement (SAC) was used to improve the repair performance of ordinary Portland cement (OPC)–granulated blast furnace slag (GGBS) composite repair materials. The influence of SAC on the mechanical properties, bonding performance, expansion behavior, impermeability, and hydration heat of OPC-GGBS-SAC composite repair materials was investigated. The results demonstrate that the rapid hydration of SAC significantly improved the early strength and mechanical properties of the composite system at negative temperatures. The hydration products filled the pores within the concrete matrix, thereby enhancing the mechanical meshing effect at the interface. The early expansion effect of SAC formed a pre-stressor at the interface, which not only strengthened the bonding force between repair materials and the substrate, but also effectively inhibited the shrinkage of the composite system and prevented crack formation, thus significantly promoting the long-term reliability of the bonding interface. An appropriate amount of SAC can accelerate the hydration process of OPC-GGBS system, advance the exothermic peak, and promote the development of early strength. However, excessive incorporation will inhibit the later hydration of the composite system due to the way in which the hydration products wrap the cement particles. When the content of SAC was 5–10%, optimal comprehensive properties of the OPC-GGBS-SAC composite system were attained.

Corrosion of reinforcing steel and degradation of concrete caused by chloride penetration are the most critical forms of durability failure in marine environments. This requires that repair materials possess both high impermeability and stable chemical binding capacity. In this study, the impact patterns of sulfoaluminate cement (SAC) dosage on the chloride erosion durability of an OPC-GGBS-SAC ternary repair system were systematically evaluated. Through chloride ion binding capacity tests, electrical flux experiments, and microscopic analytical techniques including XRD, DTG and SEM-EDS, the synergistic regulation mechanisms of the dual functions of ‘physical barrier’ and ‘chemical binding’ in the composite material were elucidated. The findings show that the performance of the composite material was optimal at an SAC content of 10%. The electrical flux of composite materials at 28 d was 28.9% lower than that of the OPC system, whilst the chloride ion binding rate increased by 3.92%. Microstructural analysis indicates that an appropriate amount of SAC promoted the generation of ettringite (AFt) to optimize the early-age pore structure and stimulated the production of more C-S-H gel and AFm phases, thus synergistically enhancing impermeability and chemical binding capacity. When the SAC content exceeded 10%, excess gypsum inhibited the formation of AFm. Moreover, the concentration of early-stage hydration led to microdefects, resulting in a decline in durability. This study identifies the optimal dosage of SAC in the ternary system and clarifies the underlying mechanism, thereby providing a scientific basis for designing high-durability repair materials suitable for harsh ocean conditions.

In response to the issues of concentrated early-stage hydration heat and significant self-shrinkage in high-strength cementitious grouting materials at low water-to-binder ratios, improvements were achieved by co-blending granulated blast furnace slag (GGBS) with calcium sulphatoaluminate (UEA) and magnesium oxide (MEA) expansive agents. The workability, mechanical properties, volumetric stability and hydration heat characteristics of the composite system were systematically investigated, and the underlying mechanisms were elucidated through microscopic analysis methods such as XRD, TG and SEM. The results indicate that GGBS improved the fluidity of the pastes and promoted the development of later-stage strength. At the same time, GGBS delayed the peak of hydration heat release and reduced total heat release. In terms of volume deformation, UEA expanded rapidly and exhibited significant compensatory shrinkage in the early stages. MEA expanded slowly in the early stages and displayed more sustained expansion under wet-curing conditions, but experienced significant shrinkage rebound in the later stages under dry environments. Further research revealed that GGBS inhibited the expansion performance of both types of expansive agents. This is primarily attributed to the consumption of Ca(OH)₂ within the system, which reduced the alkalinity of the liquid phase. GGBS physically restricted the formation and development of expansion products by promoting the densification of the C–S–H gel.