Organic silicon waterproofing agents have excellent waterproof, weathering, peeling and chemical corrosion resistance, and are widely used in the protection of various concrete, stone, wood, etc. When applied to the substrate, it can evenly penetrate into the microporous wall and form a very thin hydrophobic film on the surface or inside of the substrate to achieve the purpose of waterproofing. There are many varieties of organic silicon waterproofing agents on the market, and the effects of use are different. They are mainly divided into several categories: methyl silicon alcohol salt, silicone resin, silane, and organic silicon emulsion.
One. Methylsiliconate
Methylsiliconate is the first generation of silicone waterproofing agent. It is a rigid waterproof material. When used, it can react chemically with the surface of the substrate and a large amount of carbon dioxide and water in the air to form a hydrophobic polymethylsiloxane film. This kind of resin with a mesh structure can block the pores inside the cement mortar, enhance the compactness of the mortar, and improve its impermeability, thereby playing an effective waterproofing role. However, it will produce white powdery precipitates on the surface of the substrate, or yellowing due to too strong alkalinity, thus affecting the surface morphology of the building. In addition, methylsiliconate will also generate silanol under strong alkaline conditions and dissolve in water and lose, making its waterproofness automatically invalid under certain conditions.
The waterproofing agent has the advantages of being non-toxic, odorless, non-volatile, non-flammable, excellent weather resistance, and no corrosion to steel bars; it also has a micro-expansion effect, which can compensate for the shrinkage of mortar and concrete; it can be constructed on a damp substrate without affecting the bonding of the waterproof layer to the substrate, and the construction operation is simple and flexible; it is convenient to transport, safe to construct, and low in cost.
Two. Silicone resin
At present, the active component of the common silicone waterproofing agent in the domestic market is methyl silicone resin. In industrial production, it is prepared by hydrolysis and condensation of methyltrichlorosilane in an organic solvent. It can also be prepared from methyltrialkoxysilane. The specific method is to hydrolyze methyltrialkoxysilane in the presence of excess water and trace hydrochloric acid. At the beginning of the reaction, the system is two-phase, and as the reaction proceeds, it is converted into a homogeneous phase. After most of the alcohol and water are evaporated, a colorless and transparent methyl silicone resin soluble in alcohol is obtained.
Silicone resin has excellent high and low temperature resistance, aging resistance, unique hydrophobicity and air permeability, non-toxic and non-corrosive. It is considered to be an ideal waterproof coating and is widely used in waterproof protection of building materials. However, the methyl silicone resin waterproof layer has high gloss and is not resistant to scrubbing, which affects the surface morphology of the building, and the waterproof layer will fail after a few months or 1 to 2 years. Increasing the n(CH3)/n(Si) value of methyl silicone resin is conducive to improving its hydrophobicity and waterproof life. Guo Qingzhong and others found that silicone resin with an n(CH3)/n(si) value of 114 has excellent waterproof and alkali resistance, and is expected to have a more durable waterproof protection function.
Three. Silane
Using silane as a building waterproofing agent has the advantages of simple surface treatment (no water accumulation, dust, oil, etc.), strong penetration, anti-oxidation, UV protection, and surface wear resistance. It is safe and pollution-free to use and is a new type of environmentally friendly product. At present, such products are widely used in foreign countries for waterproofing protection of buildings, but they have not been widely promoted in China due to technical gaps. This type of product has great market potential.
The silane used as a waterproofing agent is mainly long-chain alkyl alkoxy silane, usually referring to straight-chain alkyl alkoxy silane with a carbon number of n8. Long-chain alkyl silane is used as a waterproofing agent for cultural relics and buildings to prevent acid corrosion, freeze-thaw, and weathering from damaging cultural relics (especially outdoor cultural relics) and buildings.
Four. Organic Silicone Emulsion
This type of waterproofing agent is an emulsion formed by linear polyorganosiloxane in water. Compared with methyl siliconate and silicone resin, organic silicone emulsion has the following characteristics: it does not pollute the environment during use, has stronger penetration into bricks, stones, concrete, etc., and has lower cost. This type of waterproofing agent can be added to the formula of the mixture as a waterproofing additive, and can also be used as a surface treatment agent for the surface treatment of bricks, tiles, natural stones, artificial stones, gypsum, cement, ceramics and other inorganic microporous materials, concrete pavements, floors and roofs, bridges, dams, exterior walls, bathroom interior walls, swimming pools, reservoirs, water tanks, water towers, basements, tunnels and other underground projects.
There are mainly the following types of emulsion-type silicone waterproofing agents: one is methyl hydrogen silicone oil emulsion, which has high reactivity due to the hydrogen atoms directly connected to silicon, and is easy to react with active groups such as hydroxyl groups to form a network waterproof film; the second is hydroxy silicone oil emulsion, which can be obtained by direct emulsification or emulsion polymerization of hydroxy silicone oil; the third is alkyl alkoxy silane emulsion, which contains alkoxy groups and is easy to cross-link when encountering the hydroxyl groups of the silicate substrate to produce a network hydrophobic siloxane film.
Different types of silicone waterproofing agents have different performances. In actual operation, several products are usually compounded for use to achieve the best effect. But one thing is worth emphasizing: no waterproofing agent is omnipotent and can be used once and for all. At present, the silicone waterproofing agent on the domestic market is still mainly methylsiliconate. On the one hand, it is because its price is relatively low and the short-term effect is relatively ideal; on the other hand, it is because the country has not yet developed new, high-quality and low-cost alternative products, and relying solely on imports cannot meet and adapt to market demand.
In recent years, China's building waterproofing industry has developed rapidly, and its application scope has expanded from construction to waterproofing projects of infrastructure such as bridges, roads, water conservancy, tunnels, railways, airports, subways, grain depots, and sewage treatment. It is believed that the domestic waterproofing agent market will become more and more extensive, and the demand for new medium and high-end waterproofing materials will increase day by day. Simply relying on imports can no longer meet the demand; accelerating the research and development and marketization of domestic medium and high-end new waterproofing agents has become an urgent problem to be solved.
