How does high-strength repair grouting mortar improve its bond strength and crack resistance with old concrete substrates?
Publish Time: 2025-12-17
Against the backdrop of aging infrastructure, overloaded industrial equipment, and frequent natural disasters, the need for rapid repair and reinforcement of concrete structures is increasingly urgent. Traditional repair materials often fail due to poor bonding with old concrete, shrinkage cracking, or insufficient durability, making them unsuitable for heavy-load, vibration-prone, or emergency repair projects. High-strength repair grouting mortar—a dry powder material composed of polymers, ordinary silicate cement, ultrafine aggregates, expansion agents, and various special admixtures—is becoming a key technology in modern structural repair due to its superior interfacial adhesion and crack resistance. Its excellent performance stems from the microstructure optimization and interfacial strengthening mechanism achieved through the synergistic effect of multiple components.1. Polymer Modification: Constructing a Flexible Transition Layer to Enhance Chemical-Mechanical BondingThe redispersible latex powder added to the mortar is the core component for improving bonding performance. When water is added to the mortar and mixed, polymer particles are uniformly dispersed in the cement paste. As water evaporates and cement hydrates, the polymer forms a continuous, flexible polymer film network within the hardened body and at the interface with the old concrete. This network not only fills micropores and increases density but also creates an "elastic transition layer" between the new and old concrete, effectively mitigating stress concentration caused by differences in elastic modulus. Simultaneously, polymer molecular chains can penetrate microcracks on the surface of the old concrete, forming an "anchoring effect" after curing, achieving dual bonding through chemical adsorption and mechanical interlocking, significantly improving tensile bond strength.2. Ultrafine Aggregate and Admixtures: Optimized Particle Size Distribution, Reduced Interface DefectsThe mortar uses micron-sized ultrafine aggregate to replace part of the coarse sand, significantly reducing the gaps in particle size distribution. This tightly packed structure ensures high fluidity of the paste without segregation, fully wetting the rough surface of the old concrete and penetrating deep into capillaries and microcracks, creating a "micro-injection" effect. At the same time, high-efficiency water-reducing agents and plasticizers ensure that the paste maintains high fluidity for more than 30 minutes, avoiding insufficient interfacial contact due to premature thickening. The dense microstructure not only enhances overall strength but also reduces the channels for moisture and corrosive media to penetrate along the interface, inhibiting bond failure at its source.3. Expansion Compensation Mechanism: Actively Inhibiting Shrinkage CrackingOrdinary cement-based materials are prone to volume shrinkage during hardening due to moisture evaporation and hydration shrinkage, leading to debonding of the repair layer from the substrate or self-cracking. High-strength repair grouting mortar introduces calcium sulfoaluminate or calcium oxide-based expansive agents, generating ettringite or calcium hydroxide crystals in the early stages of hydration, resulting in controllable micro-expansion. This expansion, under constrained conditions, transforms into compressive stress, effectively offsetting drying shrinkage and auto-shrinkage, achieving a "zero shrinkage" or even "micro-expansion" state. The result is a consistently tight bond between the repair layer and the old concrete, without hollow areas or cracks, making it particularly suitable for thin-layer repairs or high-precision grouting applications.4. Multi-component Synergistic Effect: Constructing a Highly Durable Composite SystemThe addition of special crack-resistant fibers further enhances the mortar's resistance to plastic cracking; corrosion inhibitors protect the reinforcing steel at the interface from chloride ion erosion; and active admixtures such as nano-silica accelerate early hydration, improving strength development after 28 days and beyond. These components are not simply added together, but rather scientifically proportioned to form an integrated performance system of "high strength, high viscosity, low shrinkage, and durability."The improvement of the bond strength and crack resistance of old concrete substrates by high-strength repair grouting mortar is a systematic project from macro to micro. It uses polymers as a "bonding bridge," ultrafine materials as a "dense filler," and an expansive agent as a "stress regulator," ultimately constructing a strong, stable, and durable connection between the old and new structures. In critical projects such as bridge bearing replacement, industrial floor repair, and seismic reinforcement, this material not only shortens construction time and ensures safety, but also uses technological power to extend the life and mission of concrete structures.
