Methods to improve water resistance of gypsum

Methods to improve water resistance of gypsum
Shijiazhuang Jingjin Mechanical Equipment Installation Co., Ltd. --- Zhou Yanhui 13,833,456,715
Methods to improve water resistance of gypsum
The early development of waterproof gypsum products in China was mainly aimed at gypsum blocks and gypsum partition boards, which were used as materials for interior walls, and also referred to foreign research results at the earliest. The following are the ways to improve the water resistance of gypsum. Welcome to read and browse.
Coating impregnation method
Hydrophobic substances that can prevent water from eroding gypsum by coating or dipping are sprayed on the surface of gypsum building materials, such as film-forming hydrophobic lotion. Hydrophobic substances can penetrate below the surface through the pores of gypsum hardening body, and form a dense film after drying, which can effectively block the infiltration of external water and greatly improve the waterproof performance of products. In addition, the surface of gypsum based building materials is sprayed or dipped with H2C2O4 or oxalate aqueous solution to generate water-insoluble CaC2O4 on the surface of the products, thus effectively blocking the erosion of water can also improve the waterproof performance of the materials.
This waterproof treatment method is easy to operate. If it is properly operated, the waterproof and moisture-proof effect of the product is ideal. However, this waterproof approach can not fundamentally overcome the problem of poor waterproof of gypsum. It only temporarily reduces the water absorption rate of the product. If the product surface is damaged and the hydrophobic layer is defective, or the spraying operation is improper, or the hydrophobic layer coated on some surfaces of gypsum products is uneven, the water will seep into the interior of the substrate from the weak hydrophobic area on the surface, causing the film layer to fall off, reducing the waterproof and moisture-proof performance of the product.
In addition, this method also has the problems of poor waterproof ability of the new interface formed after the reprocessing of products, difficulty in overall painting of complex products and high cost. Although this method can only cure the symptoms rather than the root causes, under certain conditions, such as construction, it can be used for temporary moisture-proof and waterproof needs or a part of the building that is not affected by long-term humidity.
Method of adding inorganic non-metallic powder
As early as the 1950s, the relevant research units in China began to add a large amount of water quenched slag to the hemihydrate gypsum, and successfully developed high-strength mixed gypsum products (such as beams, boards, etc.), which were applied to pilot projects and achieved good application results. In recent years, with the enhancement of environmental protection awareness and the extensive utilization of renewable resources such as various industrial waste residues, people have studied ways to introduce various activators to fundamentally change the characteristics of gypsum hardening body. Inorganic non-metallic materials or active industrial waste residues are mixed into gypsum materials to promote chemical reaction with gypsum materials under the action of activators, which not only greatly improves the waterproof performance of gypsum materials, And the strength of gypsum products is effectively improved.
When cement or other admixtures containing active SiO2 and Al2O3 are added into gypsum, gypsum will participate in hydration and hardening reaction together with the above materials to form hydraulic hydration products such as CSH gel and ettringite.
These hydrated products are filled in the pores of CaSO4 · 2H2O crystal or covered on the crystal surface to enhance the compactness of the structure and protect CaSO4 · 2H2O crystal, thereby reducing the solubility of CaSO4 · 2H2O in water and increasing the softening coefficient of the product. The mechanical strength, stability and corrosion resistance of these hydraulically hydrated products are far superior to CaSO4 · 2H2O crystal, which makes the gypsum hardening body both pneumatic and hydraulic, and the water resistance of gypsum products is greatly improved. This waterproof measure is both effective and economical, and can significantly improve the water resistance of gypsum products. However, the addition of pozzolanic materials will reduce the whiteness of gypsum products, which is not suitable for products with high decorative requirements.
Method of adding organic lotion
The method of adding organic lotion can not only maintain the decorative effect of gypsum products, but also achieve the purpose of waterproof. It is a widely used waterproof measure at present. At the beginning of the study, the gypsum material was mainly mixed with organic hydrophobic additives such as silica gel. Later, asphalt, paraffin lotion or additional inorganic non-metallic materials were used to wrap the gypsum particles to prevent water molecules from leaching.
The water resistance of gypsum building materials is modified by paraffin lotion. The modification mechanism is that the paraffin lotion mixed forms a waterproof film and distributes evenly in the continuous phase of gypsum hardening body, blocking the pores between CaSO4 · 2H2O grains, reducing the number of pores in gypsum building materials or partially sealing the reticular capillary, thus improving the hydrophobicity of gypsum. The reason why the silicone waterproof agent can improve the water resistance of gypsum is not to block holes, improve the internal compactness of the matrix, or form a closed film layer, but to soak the pore ports, change their surface energy, so as to improve the water contact angle, enable small water molecules to aggregate into large droplets, block the infiltration of external water, and do not affect the permeability of gypsum itself, so as to achieve waterproof and moisture-proof functions. The silicone waterproof agent will not affect the hydration process of gypsum, nor change the crystal form of gypsum crystal, so it has no adverse effect on the strength of gypsum
Methods to improve the compactness of hardened body
(1) Add superplasticizer
By adding high efficiency water reducing agent into gypsum slurry, it is easy to wrap and adsorb on the surface of gypsum solid particles to form a diffusion double electric layer structure, which prevents gypsum particles from being reunited with each other, so that the adsorbed water in gypsum flocculation structure can be converted into free water, thus increasing the fluidity of gypsum slurry and reducing the water consumption for gypsum standard consistency. The reduction of mixing water can make the crystal structure of hardened body more compact, reduce the number of pores, and improve the water resistance of gypsum products, but this method has limited improvement on the long-term waterproof performance of gypsum.
(2) Add triethanolamine fast nucleating agent
The addition of triethanolamine in gypsum building materials can accelerate the hydration of gypsum, accelerate the formation and growth of crystal nucleus, thus reducing the free water in gypsum slurry, increasing the compactness of products, reducing the amount of capillary pores, thus playing a waterproof role. However, the above effect of triethanolamine makes the slurry thicker, which limits its application range, especially for gypsum products formed by pouring. However, it can be used if appropriate vibration is allowed. When triethanolamine is used for waterproof modification of gypsum building materials, it is usually used with NaCl or nitrite, and its waterproof performance is superior to the former.