Mechanism of action of cement-based permeable crystalline waterproof coating
     The cement-based permeable crystalline waterproof coating is a new type of rigid waterproof coating made of Portland cement or ordinary Portland cement, quartz sand, etc., mixed with active chemical substances. Cement-based permeable crystalline waterproof coatings differ from traditional waterproof coatings in that they do not depend solely on their surface coatings. More importantly, they penetrate into the interior of the substrate to form crystals, which close the water channels, and which are not rigid in the traditional sense. Waterproof coating, which has a certain flexibility and can cover hair-like cracks (
1. Mechanism of action of cement-based permeable crystalline waterproof coating
Different types of cement-based permeable crystalline waterproof coatings have different active substance compositions and different mechanisms of action, but all include dissolution, permeation and crystallization.
1.1 dissolution process
Such active substances form small molecules after being dissolved in water, and then polymerize and grow under certain conditions, and finally form water-insoluble crystals to block cracks and capillary pores. In the powdery and dry state, its hydrophilicity is greater than that of hydrophobicity, soluble in water, and does not undergo polycondensation and crystallization in a dry environment, but undergoes polycondensation and crystallization in a humid environment to form a water-insoluble crystal.
1.2 Infiltration process
When the permeable crystalline waterproof coating is applied to the concrete surface, the active material forms a relatively high concentration region on the surface of the concrete, and in the interior of the concrete due to the lack of these active materials, it is a low concentration region, and at this time the concrete is in the water. The saturated state, that is, the medium water is sufficiently present, as long as the driving force of the chemical potential caused by the concentration difference is greater than the water pressure, diffusion and penetration may occur. Using the concentration osmotic pressure difference, the active ions gradually penetrate into the concrete. This is also the reason why such coatings require sufficient wetting of the concrete base water during construction.
1.3 Crystallization process
It mainly includes precipitation reaction crystallization and complexation-precipitation reaction crystallization.
1.3.1 Precipitation reaction crystallization mechanism
There are a large amount of alkaline substances such as Ca(OH)2 and free Ca2+ in concrete and cement stone. The active material penetrates into the concrete through the water present in the concrete pores, chemically reacts with the free lime and oxide in the capillary pores to form water-insoluble crystals, and seals the capillary network, capillary pores and micro-cracks in the concrete. Water blocking and waterproofing. Once the capillary pores, micro cracks, etc. of the concrete are closed by crystallization, the concrete is in a watertight state.
1.3.2 Complexation-precipitation reaction crystallization mechanism
When the active material entering the concrete is in the high concentration region of Ca(OH)2, it is complexed with the calcium ions ionized in the concrete to form a calcium complex which is easily soluble in water and unstable.
The calcium complex diffuses with the water in the pores of the concrete, and encounters the unreacted cement, cement gel, etc. with higher activity, and the active material is replaced by more stable silicate, aluminate, etc., and crystallization and precipitation reaction occur. Thus, Ca(OH)2 is converted into a crystal composition having a certain strength, filling cracks and capillary pores in the concrete.
2. Application of osmotic crystalline waterproof coating
In recent years, the durability requirements of concrete have become higher and higher, and there is a close relationship between the durability of concrete and its own permeability. It can even be said that permeability plays a decisive role in durability.
2.1 Mechanism of action
The mechanism of action of the permeable crystalline waterproof coating is that after infiltration through the concrete surface, it chemically reacts with the concrete components to form osmotic crystals and close the pores, thereby forming a special protective layer within a certain range from the concrete surface to the interior, so that the concrete The durability is improved.
2.2 Waterproof principle
Mainly to make use of the porosity of the concrete structure. Under the action of water, the active material contained in the waterproof coating is carried into the internal pores of the concrete structure with water as the carrier, and the penetration of water into the pores of the concrete structure and the concrete The ions interact to form water-insoluble crystals. The crystals hydrate and expand in the pores of the concrete structure. From the sparse to dense, the surface layer of the concrete structure gradually forms a dense impermeability zone, which greatly improves the overall resistance of the structure. infiltration capacity.
2.3 Characteristics of osmotic crystalline waterproof coating
(1) Resist high hydrostatic pressure. Since the crystal penetrates into the pores of the substrate, it maintains a strong waterproof structure under high hydrostatic pressure.
(2) Construction in wet areas is required. Since the paint must penetrate the inside of the substrate by the action of water, it is necessary to work in a wet area. If the concrete is dry, it must be wetted with water before application.
(3) Waterproof function with rehydrating surface. The crystal formed by the waterproof coating is integrated with the substrate to prevent the passage of water in all directions, and is effective for waterproofing the water surface and the back surface.
(4) The waterproof layer has good wear resistance. After the waterproof layer is completely dried, the pedestrian area, the basement, the original soil backfill, the waterproof layer, the concrete, and the concrete are generally not damaged, so that no special protection is required.
(5) It is flexible. It can cover cracks of less than 0.4mm and resists slight vibrations.
(6) Based on cement-based products, tiles, plasters or paints can be directly laid on the waterproof layer.
(7) Such waterproof coatings are generally non-toxic and harmless, and can be directly used in drinking water tanks and fish ponds. At the same time, the coating has the function of inhibiting mold growth, and can prevent moisture and salt from contaminating the finish.
(8) Concrete can still maintain gas permeability. The crystal formed by the waterproof coating in the pores of the concrete still retains the gas permeability, the water cannot pass through the pores, and the air and water vapor can still be unblocked. Therefore, the concrete can still be normally cured and dried after use, and the water vapor is prevented. build up.
(9) Appearance with different colors, can be used for different levels, through the overlapping of different colors, easy to construct and check whether the coating is intact, and also can be used as a joint material for exterior wall paint or exterior wall tile. Appearance and color will not cause light, reflection and other phenomena.
3. Construction of osmotic crystalline waterproof coating
3.1 Basic requirements and treatment
(1) The substrate must be strong and flat; the surface must be clean and free of dust, greasy, detached, release agents and other debris.
(2) All small pores and sand holes can be mixed with a little water or cement glue to form a wet dough, which is smoothed.
(3) The sharp outer corner edge should be removed, and the inner and outer corners can be smeared with a cement mortar to form a circular arc angle of 120°.
(4) The slurry is preferably applied to the surface of the concrete, and may also be applied to the bottom of the cement. However, the cement foundation must have a thickness of 10 mm or more and be permanently bonded to the concrete.
(5) Before the coating is applied, the substrate should be fully wetted, but there should be no water. Keeping the substrate moist helps the coating penetrate the substrate and makes the construction easier and faster.
3.2 Construction methods
(1) Use a brush or a sprayer to fully wet the substrate, but ensure that there is no clear water at the construction site.
(2) The concentrated paint and the purified water are blended in proportion to prepare a thick paste. When mixing, the liquid must first be poured into the container, then the powder is poured into the liquid and stirred thoroughly to a latex-free form. The slurry and powder should be kept intermittently agitated during use to prevent precipitation.
(3) Apply the mixed slurry to the cement substrate, and the direction of brushing is consistent. Carefully inspect the cement substrate for flaws and loopholes, and allow the slurry to fill the pores and tiny pores on the cement to ensure uniform and compact coating. Brush the first coat should not be too thick to facilitate curing.
(4) After the first coating is not completely dried after brushing, but the hand touch will not fall off, start to apply the second coating, so that there will be the best adhesion between the two layers. If the surface of the first coating film is already dry, spray a small amount of water to wet it before applying. It is usually cured and cured for 24 hours after the first coating.
(5) When the second coating is applied, the brush should be oriented perpendicular to the first coating to achieve the best coverage. After the completion of construction, it is forbidden to step on within 24 hours, and all the waterproof layers can be completely dried before proceeding to the next process.
(6) High temperature should be avoided during hot weather construction to prevent premature drying of the coating film, causing surface cracking and affecting the penetration effect, and must not be applied in the rain.
Conclusion:
(1) The osmotic crystalline waterproof coating on the one hand seals the pores by crystals grown by itself or crystals formed by reacting with ions in the pores of the concrete, and on the other hand promotes hydration of cement in the concrete to form hydrated calcium silicate. CSH gel or crystal body increases the compactness of concrete and acts as a waterproof and impervious.
(2) Concrete penetration has external causes and internal causes: external causes include water pressure and ion diffusion; internal causes are mainly caused by defects in concrete structure. The permeable crystalline waterproof coating improves the impermeability of the concrete and improves the durability of the concrete. 