Solve the problem of “whitening and frosting” caused by salt precipitation caused by the dosage of early strength agent

Answer: The cause of this phenomenon is:

The internal reason is mainly the presence of soluble salts inside the building materials and alkali substances;

The external reasons can be considered to be due to the certain permeability of the base material. When moisture penetrates from the surface of the material to the interior of the material, The soluble substances inside the material are dissolved. When the material dries, the water migrates from the inside to the outside, and the soluble substances are carried to the surface of the material. As the surface water evaporates, the white soluble substances are left on the surface, which causes whitening. Phenomenon.

The solution is:

1. Reduce the content of soluble salts and alkali inside the building materials

1) At present, sintered clay bricks still occupy a certain position in building materials. Although the country has repeatedly issued orders to restrict their use in order to protect cultivated land, some underdeveloped areas A large amount of farmland is still destroyed, land resources are destroyed, and clay is dug up to bake bricks. For some plain walls, or walls with high decorative requirements, when using clay fired bricks, bricks with good quality and low alkali content should be used as much as possible. You can conduct experiments in advance. After the clay bricks are saturated with water, place them in a cool place and let them dry naturally to see if the surface turns white.

2) When selecting cement, low-alkali cement with low alkali metal oxide content should be used as much as possible.

3) When preparing commercial concrete, aggregates must be selective and their soluble salt content should be strictly controlled.

4) Try not to use additives with high alkali metal content. For commercial concrete with high requirements for surface decoration, the Na2SO4 content is preferably less than 1% of the cement weight; if it is under adverse conditions that are prone to whitening, then it is better not to add Na2SO4.

5) When preparing commercial concrete, add an appropriate amount of active siliceous admixtures. High-quality mineral admixtures have a dual effect in preventing whitening on the surface of mortar or commercial concrete.

2. Improve the impermeability of the base material

1) When preparing commercial concrete or When making mortar, using appropriate admixtures, such as water-reducing agent or high-efficiency water-reducing agent, can reduce the amount of mixing water, thereby reducing the porosity of commercial concrete or mortar, improving the pore structure, and improving the anti-permeability performance. It can be said that any admixture that can enhance the compactness of commercial concrete or mortar, reduce cracking, and contain less alkali metal oxides can be used, such as waterproofing agents, expansion agents, and early strength agents.

2) Pay attention to the construction process. Commercial concrete or mortar should be vibrated and compacted to strengthen the plastering surface. It is best to plaster the surface again before the initial setting, so that the surface Due to the closure of micro-cracks caused by water evaporation, the floating layer of cement slurry becomes dense, thereby improving the impermeability of the surface layer.

3) Strengthen maintenance. In the early stage of hardening of cement-based materials, measures such as covering the surface with plastic film or covering with straw bags for watering and curing are generally required to avoid shrinkage cracks. produce.

4) Spray a layer of transparent paint on the surface of commercial concrete or mortar, which can fill the porosity of the surface of commercial concrete or mortar densely.

3. Hydrophobic treatment on the surface of building materials. Generally speaking, cement-based composite materials such as commercial concrete, mortar and silicate commercial concrete blocks are They are hydrophilic, that is, the contact angle between their surface and water is less than 90 degrees, so they easily absorb water. If the surface of these materials is hydrophobicized and a hydrophobic film is formed on their pore walls, their water absorption will be greatly reduced. </p