To improve the bonding strength between high-strength repair grouting mortar and the substrate, comprehensive optimization is needed in seven aspects: raw material selection, interface treatment, mortar mix design, construction technology, environmental control, curing management, and performance testing. This ensures synergistic effects across all stages, resulting in a high-strength, durable bonding system.
Raw material quality is fundamental to bonding performance. The core components of high-strength repair grouting mortar include cement, aggregates, admixtures, and mineral additives. High-strength silicate cement or ordinary silicate cement should be selected, as it has high activity and fast hardening, enabling rapid formation of bond strength. Aggregates must have a reasonable gradation and uniform particle size distribution to avoid defects on the bonding surface caused by excessive aggregate porosity. Admixtures such as water-reducing agents, thickeners, and accelerators can significantly improve the workability and hardening performance of mortar. Water-reducing agents reduce water consumption and increase mortar density, while thickeners enhance the water retention of the mortar, preventing excessive moisture loss and a decrease in bond strength. Mineral admixtures such as silica fume and fly ash can fill the voids between cement particles, forming a dense structure and improving the mortar's impermeability and durability.
Interface treatment is a crucial step in improving bond strength. The substrate surface needs to be clean, rough, and moist to increase the contact area and mechanical interlocking force between the mortar and the substrate. Before construction, thoroughly remove oil, dust, loose particles, and other impurities from the substrate surface. If necessary, use a high-pressure water gun for washing or mechanical grinding. For smooth concrete surfaces, increase surface roughness through sandblasting, roughening, or applying an interface agent. The interface agent should be compatible with the mortar system, and its components should be able to penetrate the micropores of the substrate surface to form chemical bonds and enhance interfacial adhesion. Furthermore, the substrate's moisture level is crucial. Excessive dryness will cause the mortar to absorb moisture rapidly, affecting the hydration reaction; excessive wetness may reduce mortar strength. The moisture level needs to be adjusted according to environmental conditions.
The mortar mix ratio must be scientifically sound to balance workability and hardening performance. High-strength repair grouting mortar needs high fluidity to fully fill substrate defects while ensuring sufficient strength and durability after hardening. When designing the mortar mix, the ratio of cementitious materials to aggregates should be adjusted according to the substrate type, repair location, and environmental conditions. Appropriately increasing the amount of cementitious materials can improve mortar adhesion, but excessive amounts should be avoided to prevent shrinkage cracking. The dosage of admixtures needs to be determined through testing to ensure that they improve workability without reducing mortar strength. The proportion of mineral admixtures needs to be controlled; too much may delay early strength development, while too little will not fully exert their filling and reinforcing effects.
Construction techniques directly affect the uniformity and density of the bonding effect. Before grouting, ensure that the defective areas of the substrate are clean and free of water, and pre-embed grouting pipes or vents to ensure sufficient mortar filling. During grouting, layered or pressure grouting should be used to avoid mortar segregation or delamination. For repairs on vertical or top surfaces, grouting should proceed from bottom to top, supplemented by vibration or tapping to remove air bubbles and ensure mortar density. After grouting, the surface should be smoothed promptly to prevent cracking or delamination due to surface shrinkage.
Environmental conditions have a significant impact on the hydration reaction and strength development of mortar. Construction should be avoided during periods of extreme heat, low temperature, or strong winds. High temperatures cause mortar moisture to evaporate too quickly, affecting the hydration reaction; low temperatures may delay strength development or even cause frost damage; strong winds accelerate surface moisture loss, leading to cracking. If construction must be carried out in adverse environments, appropriate measures must be taken, such as erecting sunshades and spraying water for curing in high temperatures, using heating equipment or adding antifreeze for low temperatures, and setting up windbreaks for strong winds.
Curing management is a crucial step in ensuring mortar strength development and bond durability. After grouting, the surface should be covered with plastic film or damp burlap sacks immediately to keep it moist and prevent excessive evaporation. The curing time should be determined based on the mortar type and environmental conditions, generally no less than 7 days, during which time regular water spraying is necessary to maintain moisture. For important projects or special environments, curing agents or steam curing can be used to accelerate strength development and improve bonding performance.
Performance testing is the basis for verifying the bonding effect and guiding construction optimization. After construction is completed, the repaired area should be visually inspected to ensure there are no cracks, delamination or hollow areas. If necessary, core sampling or non-destructive testing (such as ultrasonic testing) can be used to assess the bonding strength between the mortar and the substrate and internal defects. For critical projects, long-term performance monitoring is also required to observe its changes under load and environmental conditions, so as to provide experience for subsequent construction.
