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Properties and application technology of special mortar dry mix mortar putty adm
Update time：2017-09-08 00:39:53clicks：2720次Type size：T|T
Dry mixed mortar is the cementation material (cement, fly ash, slag powder, etc.), special graded fine aggregate (quartz sand, emery, etc., sometimes need lightweight aggregate, such as ceramic particles, expanded polystyrene particles, expanded perlite, expanded vermiculite, etc.) and admixtures according to a certain mix ratio after mixing evenly. A building material supplied in dry powder form in bags, drums, or in bulk.
According to the use, there are many varieties of commercial mortar, such as dry mortar for masonry, dry mortar for plastering, dry mortar for ground, special dry mortar for waterproof, heat preservation and other purposes. In summary, dry mixed mortar can be divided into ordinary dry mixed mortar (masonry, plastering and ground dry mixed mortar) and special dry mixed mortar two categories. Special dry mix mortar includes: self-leveling ground mortar, wear-resistant floor material, non-ignition wear-resistant floor, inorganic caulking agent, waterproof mortar, resin coating mortar, concrete surface protection material, color coating mortar and other varieties.
Such a large number of dry mixed mortar, need different varieties, different mechanisms of admixtures with each other, through a large number of tests, in order to prepare. Compared with traditional concrete admixtures, dry mixed mortar admixtures can only use powder products, followed by cold water solubility, or gradually dissolve under alkaline action and play a due effect.
First, thickener, water retaining agent and stabilizer by cement, inert or active mineral admixtures, and fine aggregate preparation of ordinary mortar, its main shortcomings are poor cohesion, poor stability, easy to leak, segregation, settlement, not easy to construction, after construction, the bond strength is low, easy to crack, weak water resistance, poor durability, etc., must be modified by appropriate additives. In terms of improving the cohesibility, water retention and stability of mortar, the additives that can be selected are cellulose ether, modified starch ether, polyvinyl alcohol, polyacrylamide and thickened powder.
1, cellulose ether methyl cellulose (MC), hydroxypropyl methyl cellulose (PMC) and hydroxyethyl methyl cellulose (HEMC) are natural polymer materials (such as cotton, etc.) as raw materials, through a series of chemical processing and production of non-ionic cellulose ether. They have cold water solubility, water retention, thickening, bonding, film forming, lubricity, non-ionic and pH stability. The cold water solubility of such products is greatly improved, and the water retention capacity is enhanced, the thickening is obvious, the diameter of the bubbles introduced is relatively small, and the effect of improving the bond strength of the mortar is greatly enhanced.
Cellulose ether is not only a variety of varieties, the average molecular weight range is wide, the viscosity from 5mPa. s to 200,000 mPa. s, the impact on the new mixing stage and hardening performance of mortar is also different, the specific selection should be carried out a large number of tests, the selection of viscosity and molecular weight range appropriate, small content, no air induction of cellulose varieties, so as to obtain the ideal technical performance, but also has a good economy.
2, starch ether Starch ether is starch glucose molecules on the hydroxyl and chemical reagent reaction of the ether, called starch ether or etherified starch. The main varieties of modified starch ethers are: sodium carboxymethyl starch (CMS), alkylalkyl starch (HES), alkylpropyl ethyl starch (HPS), cyanoethyl starch and so on. They have excellent water solubility, bonding, expansion, flow, covering, depulping, sizing, dispersion and stability, and are widely used in medicine, food, textile, paper, daily chemical and petroleum sectors.
At present, the prospect of starch ether used in dry mortar is also very promising, mainly because: (1) the price of starch ether is relatively cheap, only 1/3 to 1/4 of cellulose ether; (2) The addition of starch ether into mortar can also improve the viscosity, water retention, stability and bonding strength of mortar; (3) Starch ether can be combined with cellulose ether in any proportion, so as to better improve the effect of mortar anti-flow hanging. Some mortar products, such as ceramic wall tile adhesive, interface treatment agent, caulking agent and ordinary commercial mortar, use starch ether as the main thickening water retaining agent and stabilizer. However, throughout China's starch ether manufacturers, many only stay in the supply of primary products, only a few manufacturers produce modified starch ether to meet some of the needs of mortar manufacturers.
3. Thickened powder mortar Thickened powder is a new product developed to adapt to the production of ordinary dry powder (ready-mixed) mortar, which is mainly composed of inorganic minerals and organic polymer materials, without lime and entrained air and other components. Its content is about 5% to 20% of the weight of cement. At present, in the production of ordinary commercial mortar in Shanghai, the thickening powder is generally used as the thickening, water retention and stability component, and the effect is remarkable.
Polyvinyl alcohol and polyacrylamide also have a wide viscosity range, but sometimes the gas intake is large, or the water requirement of the mortar is increased too much after incorporation, which should be selected through a large number of tests.
Second, the main function of the redispersible emulsion powder thickener is to improve the water retention and stability of the mortar, although it can prevent the cracking of the mortar to a certain extent (slow down the rate of water evaporation), it is generally not used as a means to improve the toughness, cracking resistance and water resistance of the mortar.
The practice of adding polymer to improve the impermeability, toughness, cracking resistance and impact resistance of mortar and concrete has been recognized. The commonly used polymer emulsions for the modification of cement mortar and cement concrete are: neoprene latex, styrene butadiene rubber emulsion, polyacrylate latex, polyvinyl chloride, chlorinated rubber emulsion, polyvinyl acetate and so on. With the development of scientific research, not only the modification effects of various polymers have been deeply studied, but also the modification mechanism, the interaction mechanism between polymers and cement and cement hydration products have been theoretically analyzed and studied, and a large number of scientific research results have appeared.
Polymer emulsions can be used in the production of ready-mixed mortars, but it is obviously not possible to directly use in the production of dry mortar, so a redispersible emulsion powder is born. At present, the dispersible emulsion powders used in dry mortar mainly include: (1) vinyl acetate-vinyl copolymer (VAC/E); ② Vinyl acetate-tertiary carbonate copolymer (VAC/VeoVa; ③ Acrylate homomers (Acrylate); ④ Vinyl acetate homopolymer (VAC); 4) Styrene-acrylate copolymer (SA), etc. Among them, the use of vinyl acetate - vinyl copolymer is the largest.
The practice has proved that the redispersible emulsion powder has a stable property, and has incomparable effects on improving the bonding strength, toughness, deformation, crack resistance and impermeability of mortar. The addition of hydrophobic emulsion powder made of polyvinyl acetate copolymerized with vinyl chloride, ethylene, vinyl laurate, etc., can also greatly reduce the water absorption of mortar (because of its hydrophobicity), make the mortar breathable and impermeable, enhance its weather resistance, and improve its durability.
Compared with improving the bending strength and bond strength of mortar and reducing its brittleness, the redispersible emulsion powder has limited effect on improving the water retention and enhancing the cohesiveness of mortar. Because the addition of redispersible emulsion powder can play a dispersive role and cause a large amount of air entraining of mortar mix, its water reduction effect is very obvious. Of course, due to the poor structure of the bubbles introduced, this water-reducing effect does not improve the strength of the mortar, on the contrary, the strength of the mortar will gradually decrease with the increase of the content of redispersible emulsion powder. Therefore, in the development of some mortar that needs to consider the compressive and folding strength, it is often necessary to add defoamer at the same time in order to reduce the negative impact of latex powder on the compressive strength and folding strength of mortar.
Third, due to the addition of cellulose, starch ether and polymer materials, defoamer undoubtedly increases the permeability of mortar, which affects the compressive strength, folding strength and bonding strength of mortar, and reduces its elastic modulus; On the other hand, it also has a great impact on the appearance of the mortar, and it is necessary to eliminate the bubbles introduced in the mortar. At present, imported dry powder defoamer is mainly used in China to solve this problem, but it must be noted that due to the large viscosity of commercial mortar, the elimination of bubbles is not a very easy thing.
Fourth, the biggest problem facing the anti-flow hanging agent paste tiles, foam polystyrene board, and the application of rubber powder polystyrene particle insulation mortar is falling. Practice has proved that adding starch ether, sodium bentonite, metakaolin and montmorillonite is an effective measure to solve the problem of mortar falling after construction. The main solution to the problem of falling is to improve the initial shear stress of mortar, that is, to improve its thixotropy. In practical applications, it is not easy to choose a good antiflow agent, because it needs to solve the relationship between thixotropy, constructability, viscosity and water demand.
Fifth, the coating mortar, tile caulking agent, decorative color mortar and dry mixed mortar for the external wall of the coating system, its waterproof or water-repellent function is indispensable, which requires the addition of powder water-repellent agent, but it should have the following characteristics: (1) make the mortar as a whole hydrophobic, and maintain long-term effect; ② It has no negative effect on the bonding strength of the surface; ③ Some hydrophobic agents commonly used on the market, such as calcium stearate, are not suitable hydrophobic additives for dry mixed mortar, especially for plasters used in mechanical construction, because they are difficult to mix evenly with cement mortar quickly.
Recently, a silyl powder hydrophobic agent has been developed, which is a silyl powder product obtained by spray drying silane coated with water-soluble protective colloid and anti-caking agent. When the mortar is mixed with water, the protective colloidal shell of the hydrophobic agent quickly dissolves in the water, and releases the wrapped silane to disperse it into the mixing water. In the highly alkaline environment after cement hydration, the hydrophilic organic functional groups in silane hydrolyze to form highly reactive silanol groups, and the silanol groups continue to react irreversely with the hydroxyl groups in the cement hydration products to form chemical bonds, so that the silanes connected by crosslinking are firmly fixed on the surface of the pore wall in the cement mortar. Since the hydrophobic organic functional group is oriented to the outer side of the pore wall, the surface of the pore is hydrophobic, which brings the overall hydrophobic effect to the mortar.
Caustic soda inhibitor caustic soda will affect the beauty of cement-based decorative mortar, which is a universal problem that needs to be solved. It is reported that a resin-based anti-pantothenic additive has been developed recently, which is a dispersible powder with good stirring performance. This product is particularly suitable for use in relief coating, putty, caulk or finishing mortar formulations, and has good compatibility with other additives.
Adding an appropriate amount of fiber into the mortar can increase the tensile strength, enhance toughness, and improve the cracking resistance. At present, chemical synthetic fiber and wood fiber are commonly used in dry mixed mortar. Chemical synthetic fibers, such as polypropylene staple fiber, polypropylene staple fiber, etc., such fibers after surface modification, not only good dispersion, but also low content, can effectively improve the mortar anti-plasticity, cracking, at the same time, the mechanical properties of hardened mortar have little impact. The diameter of wood fiber is smaller, and the addition of wood fiber should pay attention to its increase in water demand for mortar.
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According to the use, there are many varieties of commercial mortar, such as dry mortar for masonry, dry mortar for plastering, dry mortar for ground, special dry mortar for waterproof, heat preservation and other purposes. In summary, dry mixed mortar can be divided into ordinary dry mixed mortar (masonry, plastering and ground dry mixed mortar) and special dry mixed mortar two categories. Special dry mix mortar includes: self-leveling ground mortar, wear-resistant floor material, non-ignition wear-resistant floor, inorganic caulking agent, waterproof mortar, resin coating mortar, concrete surface protection material, color coating mortar and other varieties.
Such a large number of dry mixed mortar, need different varieties, different mechanisms of admixtures with each other, through a large number of tests, in order to prepare. Compared with traditional concrete admixtures, dry mixed mortar admixtures can only use powder products, followed by cold water solubility, or gradually dissolve under alkaline action and play a due effect.
First, thickener, water retaining agent and stabilizer by cement, inert or active mineral admixtures, and fine aggregate preparation of ordinary mortar, its main shortcomings are poor cohesion, poor stability, easy to leak, segregation, settlement, not easy to construction, after construction, the bond strength is low, easy to crack, weak water resistance, poor durability, etc., must be modified by appropriate additives. In terms of improving the cohesibility, water retention and stability of mortar, the additives that can be selected are cellulose ether, modified starch ether, polyvinyl alcohol, polyacrylamide and thickened powder.
1, cellulose ether methyl cellulose (MC), hydroxypropyl methyl cellulose (PMC) and hydroxyethyl methyl cellulose (HEMC) are natural polymer materials (such as cotton, etc.) as raw materials, through a series of chemical processing and production of non-ionic cellulose ether. They have cold water solubility, water retention, thickening, bonding, film forming, lubricity, non-ionic and pH stability. The cold water solubility of such products is greatly improved, and the water retention capacity is enhanced, the thickening is obvious, the diameter of the bubbles introduced is relatively small, and the effect of improving the bond strength of the mortar is greatly enhanced.
Cellulose ether is not only a variety of varieties, the average molecular weight range is wide, the viscosity from 5mPa. s to 200,000 mPa. s, the impact on the new mixing stage and hardening performance of mortar is also different, the specific selection should be carried out a large number of tests, the selection of viscosity and molecular weight range appropriate, small content, no air induction of cellulose varieties, so as to obtain the ideal technical performance, but also has a good economy.
2, starch ether Starch ether is starch glucose molecules on the hydroxyl and chemical reagent reaction of the ether, called starch ether or etherified starch. The main varieties of modified starch ethers are: sodium carboxymethyl starch (CMS), alkylalkyl starch (HES), alkylpropyl ethyl starch (HPS), cyanoethyl starch and so on. They have excellent water solubility, bonding, expansion, flow, covering, depulping, sizing, dispersion and stability, and are widely used in medicine, food, textile, paper, daily chemical and petroleum sectors.
At present, the prospect of starch ether used in dry mortar is also very promising, mainly because: (1) the price of starch ether is relatively cheap, only 1/3 to 1/4 of cellulose ether; (2) The addition of starch ether into mortar can also improve the viscosity, water retention, stability and bonding strength of mortar; (3) Starch ether can be combined with cellulose ether in any proportion, so as to better improve the effect of mortar anti-flow hanging. Some mortar products, such as ceramic wall tile adhesive, interface treatment agent, caulking agent and ordinary commercial mortar, use starch ether as the main thickening water retaining agent and stabilizer. However, throughout China's starch ether manufacturers, many only stay in the supply of primary products, only a few manufacturers produce modified starch ether to meet some of the needs of mortar manufacturers.
3. Thickened powder mortar Thickened powder is a new product developed to adapt to the production of ordinary dry powder (ready-mixed) mortar, which is mainly composed of inorganic minerals and organic polymer materials, without lime and entrained air and other components. Its content is about 5% to 20% of the weight of cement. At present, in the production of ordinary commercial mortar in Shanghai, the thickening powder is generally used as the thickening, water retention and stability component, and the effect is remarkable.
Polyvinyl alcohol and polyacrylamide also have a wide viscosity range, but sometimes the gas intake is large, or the water requirement of the mortar is increased too much after incorporation, which should be selected through a large number of tests.
Second, the main function of the redispersible emulsion powder thickener is to improve the water retention and stability of the mortar, although it can prevent the cracking of the mortar to a certain extent (slow down the rate of water evaporation), it is generally not used as a means to improve the toughness, cracking resistance and water resistance of the mortar.
The practice of adding polymer to improve the impermeability, toughness, cracking resistance and impact resistance of mortar and concrete has been recognized. The commonly used polymer emulsions for the modification of cement mortar and cement concrete are: neoprene latex, styrene butadiene rubber emulsion, polyacrylate latex, polyvinyl chloride, chlorinated rubber emulsion, polyvinyl acetate and so on. With the development of scientific research, not only the modification effects of various polymers have been deeply studied, but also the modification mechanism, the interaction mechanism between polymers and cement and cement hydration products have been theoretically analyzed and studied, and a large number of scientific research results have appeared.
Polymer emulsions can be used in the production of ready-mixed mortars, but it is obviously not possible to directly use in the production of dry mortar, so a redispersible emulsion powder is born. At present, the dispersible emulsion powders used in dry mortar mainly include: (1) vinyl acetate-vinyl copolymer (VAC/E); ② Vinyl acetate-tertiary carbonate copolymer (VAC/VeoVa; ③ Acrylate homomers (Acrylate); ④ Vinyl acetate homopolymer (VAC); 4) Styrene-acrylate copolymer (SA), etc. Among them, the use of vinyl acetate - vinyl copolymer is the largest.
The practice has proved that the redispersible emulsion powder has a stable property, and has incomparable effects on improving the bonding strength, toughness, deformation, crack resistance and impermeability of mortar. The addition of hydrophobic emulsion powder made of polyvinyl acetate copolymerized with vinyl chloride, ethylene, vinyl laurate, etc., can also greatly reduce the water absorption of mortar (because of its hydrophobicity), make the mortar breathable and impermeable, enhance its weather resistance, and improve its durability.
Compared with improving the bending strength and bond strength of mortar and reducing its brittleness, the redispersible emulsion powder has limited effect on improving the water retention and enhancing the cohesiveness of mortar. Because the addition of redispersible emulsion powder can play a dispersive role and cause a large amount of air entraining of mortar mix, its water reduction effect is very obvious. Of course, due to the poor structure of the bubbles introduced, this water-reducing effect does not improve the strength of the mortar, on the contrary, the strength of the mortar will gradually decrease with the increase of the content of redispersible emulsion powder. Therefore, in the development of some mortar that needs to consider the compressive and folding strength, it is often necessary to add defoamer at the same time in order to reduce the negative impact of latex powder on the compressive strength and folding strength of mortar.
Third, due to the addition of cellulose, starch ether and polymer materials, defoamer undoubtedly increases the permeability of mortar, which affects the compressive strength, folding strength and bonding strength of mortar, and reduces its elastic modulus; On the other hand, it also has a great impact on the appearance of the mortar, and it is necessary to eliminate the bubbles introduced in the mortar. At present, imported dry powder defoamer is mainly used in China to solve this problem, but it must be noted that due to the large viscosity of commercial mortar, the elimination of bubbles is not a very easy thing.
Fourth, the biggest problem facing the anti-flow hanging agent paste tiles, foam polystyrene board, and the application of rubber powder polystyrene particle insulation mortar is falling. Practice has proved that adding starch ether, sodium bentonite, metakaolin and montmorillonite is an effective measure to solve the problem of mortar falling after construction. The main solution to the problem of falling is to improve the initial shear stress of mortar, that is, to improve its thixotropy. In practical applications, it is not easy to choose a good antiflow agent, because it needs to solve the relationship between thixotropy, constructability, viscosity and water demand.
Fifth, the coating mortar, tile caulking agent, decorative color mortar and dry mixed mortar for the external wall of the coating system, its waterproof or water-repellent function is indispensable, which requires the addition of powder water-repellent agent, but it should have the following characteristics: (1) make the mortar as a whole hydrophobic, and maintain long-term effect; ② It has no negative effect on the bonding strength of the surface; ③ Some hydrophobic agents commonly used on the market, such as calcium stearate, are not suitable hydrophobic additives for dry mixed mortar, especially for plasters used in mechanical construction, because they are difficult to mix evenly with cement mortar quickly.
Recently, a silyl powder hydrophobic agent has been developed, which is a silyl powder product obtained by spray drying silane coated with water-soluble protective colloid and anti-caking agent. When the mortar is mixed with water, the protective colloidal shell of the hydrophobic agent quickly dissolves in the water, and releases the wrapped silane to disperse it into the mixing water. In the highly alkaline environment after cement hydration, the hydrophilic organic functional groups in silane hydrolyze to form highly reactive silanol groups, and the silanol groups continue to react irreversely with the hydroxyl groups in the cement hydration products to form chemical bonds, so that the silanes connected by crosslinking are firmly fixed on the surface of the pore wall in the cement mortar. Since the hydrophobic organic functional group is oriented to the outer side of the pore wall, the surface of the pore is hydrophobic, which brings the overall hydrophobic effect to the mortar.
Caustic soda inhibitor caustic soda will affect the beauty of cement-based decorative mortar, which is a universal problem that needs to be solved. It is reported that a resin-based anti-pantothenic additive has been developed recently, which is a dispersible powder with good stirring performance. This product is particularly suitable for use in relief coating, putty, caulk or finishing mortar formulations, and has good compatibility with other additives.
Adding an appropriate amount of fiber into the mortar can increase the tensile strength, enhance toughness, and improve the cracking resistance. At present, chemical synthetic fiber and wood fiber are commonly used in dry mixed mortar. Chemical synthetic fibers, such as polypropylene staple fiber, polypropylene staple fiber, etc., such fibers after surface modification, not only good dispersion, but also low content, can effectively improve the mortar anti-plasticity, cracking, at the same time, the mechanical properties of hardened mortar have little impact. The diameter of wood fiber is smaller, and the addition of wood fiber should pay attention to its increase in water demand for mortar.
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