1. Optimize material formula
To control the shrinkage performance of quick repair mortar, we must first start with the material formula. It is crucial to select the appropriate cement variety. For example, low-heat cement generates relatively low heat of hydration during the hydration process, which can reduce volume shrinkage caused by temperature changes. At the same time, mineral admixtures such as fly ash, slag powder, etc. should be properly matched. Fly ash has pozzolanic activity and can fill the pores inside the mortar during the later reaction to reduce shrinkage. In terms of aggregates, choose hard and well-graded aggregates, which can provide a stable skeleton structure for the mortar and restrain the shrinkage and deformation of the mortar. For example, the use of continuously graded gravel and sand can reduce the internal porosity of the mortar and increase the density, thereby effectively controlling shrinkage. In addition, adding an appropriate amount of expansion agent is also a common method. The expansion agent produces volume expansion during the hydration process to compensate for the shrinkage of the mortar. For example, ettringite expansion agents can produce moderate expansion in the early stage, offset part of the shrinkage stress, and reduce the risk of cracking. .
2. Control the construction technology
The construction process also has a significant impact on the shrinkage and cracking of quick repair mortar. During the mixing process, the amount of water added should be strictly controlled to avoid increased shrinkage of the mortar due to excessive water-cement ratio. Follow the prescribed mixing time and sequence to ensure that the components are evenly mixed. When pouring or applying mortar, it should be done in layers. The thickness of each layer should not be too thick, generally controlled at 2-3 cm. This can make the heat and moisture inside the mortar more easily dissipated and reduce shrinkage caused by the difference in temperature and humidity between inside and outside. Evenly. Vibration or compaction operations must be moderate to ensure the density of the mortar without excessive vibration leading to mortar segregation. After construction is completed, timely maintenance is performed. Maintenance is a key link to control shrinkage and prevent cracking. In the early stage, spray curing can be used to keep the surface moist and prevent water from evaporating too quickly. In the later stage, methods such as covering with moisturizing materials can be used. The curing time is generally not less than 7 days to ensure that the mortar has sufficient water supply during the hardening process and reduce the risk of drying out. Cracks caused by shrinkage.
3. Introduction of fiber reinforcement
Incorporating fiber into quick repair mortar is an effective anti-cracking measure. Fibers can form a three-dimensional randomly distributed support system inside the mortar. When the mortar shrinks, the fibers can bear part of the tensile stress and prevent the expansion of cracks. Commonly used fibers include polypropylene fiber, steel fiber, etc. Polypropylene fiber has the advantages of light weight, corrosion resistance, and good dispersion. Its diameter is usually thin, and a large amount is evenly distributed in the mortar, which can effectively improve the toughness and crack resistance of the mortar. Steel fibers have higher strength and elastic modulus, which can significantly enhance the tensile strength of mortar. The amount of fiber is generally determined based on the usage requirements and performance characteristics of the mortar, usually between 0.1% and 2%. For example, in some repair projects that require higher strength and crack resistance, the content of steel fibers can be appropriately increased to obtain better anti-cracking effects.
4. Regulation of environmental factors
Environmental factors have a non-negligible impact on the shrinkage and cracking of quick repair mortar, so they need to be regulated. In terms of temperature, try to avoid construction in high or low temperature environments. A high-temperature environment will accelerate the hydration reaction and water evaporation of the mortar, resulting in increased shrinkage; a low-temperature environment will cause the mortar to harden slowly, increasing the possibility of shrinkage and cracking. If it cannot be avoided, corresponding temperature control measures should be taken, such as shading and cooling when the temperature is high, and heating and insulation measures when the temperature is low. In terms of humidity, keep the relative humidity of the construction environment and the surrounding environment of the repaired mortar stable to avoid sudden changes in humidity. For example, in a dry environment, you can increase the air humidity by setting up a humidifier or using a moisturizing covering to reduce shrinkage cracks caused by water loss in the mortar due to drying. At the same time, care should be taken to prevent the mortar from being disturbed by external factors such as wind and rain, so as to provide a relatively stable environment for the hardening of the mortar, thereby effectively controlling its shrinkage performance and preventing the occurrence of cracking.
