Liquid anti-cracking agent for mass concrete

Abstract

The invention discloses a liquid anti-cracking agent for mass concrete. The preparation method comprises the following steps: firstly, preparing a modified ether shrinkage reducing agent which takes methacrylic acid, hydroxypropyl acrylate and ethyl methacrylate as a main chain and takes vinyl diethylene glycol polyoxyethylene ether as a branch chain to be grafted to the main chain; and compounding the modified ether shrinkage reducing agent with a surface tension regulator, an anti-adsorbent, a concrete performance sensitive regulator and water to obtain the liquid anti-cracking agent. The liquid anti-cracking agent provided by the invention solves the problem of shrinkage cracking of mass concrete in an early pouring process, and the anti-cracking agent is sprayed on the surface of the demoulded concrete, so that the cracking of the later concrete is inhibited, the durability of the concrete is improved, and the cracking problem of the concrete is thoroughly solved.

Description

Technical Field

[0001] The invention belongs to the field of construction and relates to a liquid anti-cracking agent for mass concrete. Background Art

[0002] With the development of the construction industry, there are more and more large-scale key projects, and the amount of mass concrete is increasing. Mass concrete refers to a concrete structure with a minimum cross-sectional size of more than 1m. Because of the large amount of cementitious materials used in mass concrete and the high hydration temperature, it has obvious shrinkage cracking characteristics, which can easily cause concrete cracking problems, especially after the freeze-thaw cycle in winter, the concrete cracks will further expand. Concrete cracking has always been an inevitable problem. Cracking leads to structural leakage and reduced concrete strength and durability, thereby shortening the service life of the building, which seriously affects the stability and safety of the building structure. Therefore, the shrinkage cracking problem of mass concrete has attracted the attention of the construction industry, and research on reducing the shrinkage cracking problem of concrete has always been a hot topic in related research.

[0003] At present, there are many ways to reduce concrete cracking. The first solution is to use concrete expansion agent to solve the shrinkage cracking problem of concrete. On the one hand, the raw materials of concrete vary greatly and the environmental conditions are different. The dosage of concrete expansion agent is difficult to control. Excessive dosage causes the expansion agent to expand too much in the concrete, and the cracking is more serious. Small dosage cannot compensate for the shrinkage. On the other hand, the addition of expansion agent requires more maintenance. Under the current construction schedule, it is difficult to achieve timely maintenance and play a role. At the same time, the expansion agent is a powder, and the addition method is difficult to control and fluctuates greatly. The second solution is to change the reinforcement of steel bars, which increases the difficulty of concrete construction and makes it difficult to maintain long-term construction. The third solution is to add hydration temperature rise inhibitor to concrete, which causes the concrete to have a significant reduction in both early and later strength, reducing construction efficiency and affecting the strength of concrete. In short, the shrinkage compensation effect of the above methods requires specific conditions and environment, and has some effect in the early stage, but no obvious effect in the later stage, and the effect of inhibiting cracking is not ideal. Summary of the invention

[0004] In view of the above problems, the present invention provides a liquid anti-cracking agent for large-volume concrete. The present invention first prepares a modified ether shrinkage reducer with methacrylic acid, hydroxypropyl acrylate and ethyl methacrylate as the main chain, and vinyl diethylene glycol polyoxyethylene ether as a branch chain grafted onto the main chain, and then the modified ether shrinkage reducer is compounded with a surface tension regulator, an anti-adsorbent, a concrete performance sensitive regulator and water to obtain a liquid anti-cracking agent. The liquid anti-cracking agent of the present invention solves the shrinkage cracking problem of large-volume concrete during the early pouring process, and the anti-cracking agent is sprayed on the surface of the concrete after demoulding, which inhibits the cracking of the later concrete, improves the durability of the concrete, and completely solves the cracking problem of the concrete, which has great significance and social value.

[0005] The technical scheme of the present invention is: a liquid anti-cracking agent for mass concrete, characterized in that it is composed of the following components in weight ratio: 30-35% of modified ether shrinkage reducer, 0.5-1% of surface tension regulator, 5-8% of anti-adsorbent, 3-5% of concrete performance sensitive regulator, and 51-61.5% of water.

[0006] The modified ether shrinkage reducing agent is prepared by the following method (raw materials are calculated by weight): 350 parts of ethylene diethylene glycol polyoxyethylene ether are dissolved in 300-400 parts of water, 9.5-10.5 parts of polyoxyethylene alcohol (dispersant), 9.5-10.5 parts of 2-acrylamide-2-methylpropane sulfonic acid and 2.0-2.2 parts of hydrogen peroxide are added, and after stirring and melting, A and B materials are added dropwise; wherein A material is a mixed solution of 20 parts of ethyl methacrylate, 14.5-15.5 parts of hydroxypropyl acrylate, 4.5-5.5 parts of methacrylic acid and 25-35 parts of water, and B material is a mixed solution of 8 parts of sodium methacrylate sulfonate, 4.5-5.5 parts of sodium bisulfite and 12-18 parts of water; after the dropwise addition is completed, stirring is continued for 20-50 minutes, and water is added to make up 1000 parts to obtain the modified ether shrinkage reducing agent.

[0007] The surface tension regulator is dibutyl phthalate or tributyl phosphate.

[0008] The anti-adsorption agent is a compound of epichlorohydrin and ethylenediamine, and the molar ratio of the two is 1: (1.1-1.7).

[0009] The concrete performance sensitivity regulator is polypropylene glycol dimethacrylate.

[0010] Application method of liquid anti-cracking agent: Liquid anti-cracking agent is used in ready-mixed concrete, directly mixed in at 0.8-1.2% of the mass of cement; because the concrete surface loses water quickly, in addition to using it in the concrete at 0.8-1.2% of the mass of cement, after the formwork is removed, spray 0.3-0.4 kg / m2 on the concrete surface to reduce the drying shrinkage caused by water loss on the concrete surface and improve the crack resistance of the concrete surface.

[0011] Raw materials and functions:

[0012] The reaction equation of the modified ether shrinkage reducing agent of the present invention is as follows Figure 1 As shown, methacrylic acid, hydroxypropyl acrylate and ethyl methacrylate are used as the main chain, and vinyl diethylene glycol polyoxyethylene ether is grafted onto the main chain as a branch chain. The main chain is wrapped on the surface of cement particles. The steric hindrance of the branch chain repels the cement particles from each other, inhibiting the contact area between cement particles and water and thus affecting the initial hydration. At the same time, the ester group of the main chain slow-release effect reduces the evaporation of water. Therefore, the two effects reduce the autogenous shrinkage, drying shrinkage and plastic shrinkage of concrete, improve the compactness of concrete, and inhibit the early crack formation of concrete. Principle: In the early hardening and molding process of concrete, the water in the capillary pores and gel pores is gradually lost, and a pressure difference will be formed at the gas-liquid interface, causing the liquid surface in the pore to become a concave liquid surface and the surface tension to increase. As the water evaporates continuously, the negative pressure of the capillary pores increases gradually, and the curvature of the concave liquid surface increases continuously, causing the slurry to shrink. Ordinary ether-based shrinkage reducers, such as alcohols and ethers, will not form steric hindrance, resulting in reduced shrinkage in the early stage but no obvious effect in the later stage. The unsaturated double bonds of the branched chains of the modified shrinkage reducer structure are directly connected to the oxygen atoms, and the electron cloud is evenly distributed. There is no resistance to the swing of the branches, and the branches swing evenly, which improves the wrapping and entanglement of the side chains of the shrinkage reducer with the slurry. The wrapping of the concrete is good, and the internal voids are reduced. In addition, when the modified ether-based shrinkage reducer is used in concrete, the surface tension can be reduced by more than 55%, thereby reducing drying shrinkage, while the surface tension of the ordinary shrinkage reducer is reduced by less than 20%, so the shrinkage reduction is limited.

[0013] Surface tension regulator: Use dibutyl phthalate or tributyl phosphate to reduce the surface tension of the liquid phase, reduce the number of pores in the concrete, make the interior of the concrete more compact, reduce the internal shrinkage caused by the hydration of the cementitious material, and reduce the number of modified shrinkage reducers in the pores of the concrete, thereby reducing the shrinkage of the concrete in the early stage.

[0014] Anti-adsorption agent: epichlorohydrin-ethylenediamine is used in combination. For concrete fine aggregates containing mud or with poor gradation, the addition of this material has good anti-mud adaptability, water retention effect, and anti-adsorption effect. It maintains the uniformity of dispersion of various materials in the concrete and reduces the adsorption of modified ethers by fine aggregates in the concrete.

[0015] Concrete performance sensitivity regulator: Use polypropylene glycol dimethacrylate to reduce the sensitivity of chemical admixtures, prevent concrete segregation, improve concrete homogeneity, reduce water seepage due to segregation and seepage of modified ether shrinkage reducers, and reduce their effectiveness.

[0016] The technical effects of the present invention are:

[0017] 1. The liquid anti-cracking agent of the present invention solves the shrinkage cracking problem of large-volume concrete during the early pouring process, and the anti-cracking agent is sprayed on the surface of the concrete after demoulding to inhibit the cracking of the later concrete, improve the durability of the concrete, and completely solve the cracking problem of the concrete.

[0018] 2. The liquid anti-cracking agent of the present invention solves the problems of poor uniformity and poor encapsulation in large-volume concrete, improves the workability of concrete, and improves the internal structure of concrete from the concrete state.

[0019] 3. The liquid anti-cracking agent of the present invention can reduce the surface tension of the internal bubbles of the ready-mixed concrete, reduce the capillary pore diameter inside the concrete, and make the internal structure of the concrete more compact.

[0020] 4. The liquid anti-cracking agent of the present invention can self-repair the late concrete micro-cracks and solve the long-term anti-seepage and water leakage problems of concrete.

[0021] 5. Experiments have shown that the liquid anti-cracking agent of the present invention can reduce the hydration temperature rise, improve the homogeneity of concrete, and inhibit the generation of early cracks in large-volume concrete without affecting the early strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the reaction equation for the modified ether shrinkage reducing agent. DETAILED DESCRIPTION

[0023] The effects are described below with reference to embodiments.

[0024] Preparation of modified ether shrinkage reducing agent: dissolve 350g of vinyl diethylene glycol polyoxyethylene ether in 350g of water + 10g of polyoxyethylene alcohol + 10g of 2-acrylamide-2-methylpropane sulfonic acid + 2.1g of hydrogen peroxide, stir and melt for 10 minutes, then add A and B materials dropwise, wherein A material is: 20g of ethyl methacrylate, 15g of hydroxypropyl acrylate, 5g of methacrylic acid and 30g of water, and B material is: 8g of sodium methyl propylene sulfonate, 5g of sodium bisulfite and 15g of water, and the addition time is 70min. After the addition is completed, continue stirring for 30min and add water to 1000g, that is, the modified ether shrinkage reducing agent.

[0025] Example 1: Preparation of liquid anti-cracking agent for large volume concrete

[0026] Mixing ratio (by weight): modified ether shrinkage reducer 32.5%, surface tension regulator (dibutyl phthalate) 0.75%, anti-adsorption agent (epichlorohydrin-ethylenediamine, the molar ratio of the two is 1:1.25) 6.5%, concrete performance sensitive regulator (polypropylene glycol dimethacrylate) 4%, water 56.25%.

[0027] Application method: The amount of liquid anti-cracking agent added during the preparation of ready-mixed concrete is 0.8-1.2% of the cement mass, and 0.3-0.4 kg / m3 is sprayed after demoulding.

[0028] The following is combined with experimental data to illustrate its effect.

[0029] 1. Comparison of the application of liquid anti-cracking agent in cement mortar

[0030] Reference standards JC / T 2608-2021 "Concrete hydration temperature rise inhibitor", JGJ55 "Ordinary concrete mix design code", GB / T 17671-2021 "Cement mortar strength test method (ISO method)"; GB / T50082 "Standard test method for long-term performance and durability of ordinary concrete"; GB / T50081 "Standard test method for physical and mechanical properties of concrete", GB / T50080 "Test method for ordinary concrete mixtures".

[0031] The shrinkage rate, strength and hydration heat index of cement mortar (450g cement + 1350g standard sand + 225g water) of the blank group, the group mixed with the liquid anti-cracking agent of the present invention, and the control group (commercially available expansion agent, commercially available hydration temperature rise inhibitor and ordinary ether shrinkage reducer) were tested at different ages. The amount of the anti-cracking agent of the present invention is 1.0% by weight of cement, and it is sprayed at 0.3 kg / m3 after demoulding. The cement used in the test is PO42.5 cement. The test results are shown in Table 1.

[0032] Table 1 Comparison of shrinkage, strength and hydration heat index

[0033]

[0034] Notes: (1) The commercially available expansion agent is a powder, which is a mixture of calcium oxide, magnesium oxide and calcium sulfoaluminate in a weight ratio of 2:4:4, and the dosage is 10% of the mass of the adhesive; (2) The commercially available hydration temperature rise inhibitor is a powder, which is composed of sodium fluorosilicate, powder slow-release water reducer (acrylic acid and polyoxyethylene ether copolymer, the molar ratio of the two is 3.2:1), citric acid, sodium ethylenediaminetetramethylenephosphonate and cement in a weight ratio of 10:1:4:5:80, and the dosage is 2.0% of the mass of the adhesive; (3) Ordinary ether shrinkage reducer, polyethylene glycol, pentanediol, ethylene diglycol polyoxyethylene ether: water, mass ratio of 2:1:2:5, the dosage is 1% of the mass of cement, and it is sprayed at 0.3 kg / m3 after demoulding.

[0035] It can be seen from Table 1 that for cement mortar at the ages of 7d, 14d and 28d, compared with the blank group, the shrinkage rates of cement mortar mixed with liquid anti-cracking agent of the present invention are reduced by 22.5%, 13.1% and 18.6%, respectively, indicating that the liquid anti-cracking agent can effectively reduce the shrinkage rate of cement mortar; the hydration heat of 3d and 7d is reduced by 33.9% and 20.3%, respectively, reducing the risk of cracking inside the mortar; it can be seen from the strength of the mortar that the 3d strength is not reduced, and the 28d strength is higher than that of the blank group, indicating that the internal structure of the mortar is dense and the strength is improved. Commercially available expansion agents, hydration temperature rise inhibitors and common ether shrinkage reducers have an effect on the 7d shrinkage rate, but have little effect on the shrinkage rates of 14d and 28d mortars, and at the same time reduce the 28d strength of the mortar, affecting the quality of the product itself; commercially available hydration temperature rise inhibitors have an effect on early hydration temperature rise inhibition and reduce the shrinkage rate, but have little effect on the later 28d, and have a greater impact on the 3d strength of cement mortar, affecting the quality of cement; the liquid anti-cracking agent of the present invention improves the strength of cement mortar while reducing the shrinkage rate.

[0036] 2. Test of the performance of liquid anti-cracking agent in C40 concrete

[0037] Concrete mix ratio: cement 280kg / m 3 , mineral powder 80kg / m 3 , fly ash 60kg / m 3 , machine-made sand 750kg / m 3 , crushed stone 980kg / m 3 , water 160kg / m 3 , admixture (water reducing agent) 6.0kg / m 3 The liquid anti-cracking agent is added in an amount of 0.8% of the cement mass and sprayed at 0.3 kg / m3 after demoulding. The cement is PO42.5 ordinary Portland cement (GB175); the fly ash is secondary fly ash (GB / T1596), the mineral powder is S95 grade (GB / T18046), the machine-made sand and gravel meet the standards of GB / T14684 and GB / T14685 respectively, and the water reducer is polycarboxylic acid water reducer with a solid content of 10%, which meets the standard (GB8076).

[0038] The concrete of the blank group, the group mixed with the liquid anti-cracking agent of the present invention, and the control group (commercially available expansion agent, commercially available hydration temperature rise inhibitor and ordinary ether shrinkage reducer) were tested for shrinkage rate, strength, temperature difference, crack area and homogeneity. The results are shown in Table 2.

[0039] Table 2 Comparison of shrinkage, strength, temperature difference, cracking area and homogeneity test results

[0040]

[0041] Note: The formula, application method and dosage of commercial expansion agent, commercial hydration temperature rise inhibitor and common ether shrinkage reducer are the same as those in Table 1.

[0042] It can be seen from Table 2 that:

[0043] (1) For the concrete shrinkage rate at 7d, 14d and 28d, compared with the blank group, the shrinkage rate of the concrete mixed with the liquid anti-cracking agent of the present invention was reduced by 48.1%, 48.4% and 41.8%, respectively, indicating that the liquid anti-cracking agent can effectively reduce the shrinkage rate of concrete; the commercially available expansion agent, hydration temperature rise inhibitor and ordinary ether shrinkage reducer have an effect on the shrinkage rate of concrete at 7d, but have little effect on the shrinkage rate of 14d and 28d.

[0044] (2) After adding the liquid anti-cracking agent to concrete, the temperature difference between the inside and outside of the concrete was reduced by 32% and the early cracking area was reduced by 60.5% compared with the blank concrete. The early cracking of concrete was significantly inhibited, which was better than the commercially available products.

[0045] (3) Compared with blank concrete, the homogeneity of the concrete added with the liquid anti-cracking agent of the present invention is reduced by 5s, and the later strength of the concrete is improved. The commercially available expansive agent and the common shrinkage reducing agent reduce the later strength of the concrete and have no effect on the homogeneity of the concrete. The liquid anti-cracking agent of the present invention is used in concrete, and is significantly superior to the commercially available expansive agent, the hydration temperature rise inhibitor and the common shrinkage reducing agent in terms of shrinkage rate, temperature difference and cracking area, and has an effect of improving the strength of the concrete.

[0046] Example 2: Preparation of liquid anti-cracking agent for large volume concrete

[0047] Mixing ratio (by weight): modified ether shrinkage reducer 35%, surface tension regulator (dibutyl phthalate) 1%, anti-adsorption agent (epichlorohydrin-ethylenediamine, the molar ratio of the two is 1:1.4) 8%, concrete performance sensitive regulator (polypropylene glycol dimethacrylate) 5%, water 51%.

[0048] Application method: The amount of liquid anti-cracking agent added during the preparation of ready-mixed concrete is 0.8-1.2% of the cement mass, and 0.3-0.4 kg / m3 is sprayed after demoulding.

[0049] Example 3: Preparation of liquid anti-cracking agent for large volume concrete

[0050] Mixing ratio (by weight): modified ether shrinkage reducer 30%, surface tension regulator (tributyl phosphate) 0.5%, anti-adsorption agent (epichlorohydrin-ethylenediamine, the molar ratio of the two is 1:1.2) 5%, concrete performance sensitive regulator (polypropylene glycol dimethacrylate) 3%, water 61.5%.

[0051] Application method: The amount of liquid anti-cracking agent added during the preparation of ready-mixed concrete is 0.8-1.2% of the cement mass, and 0.3-0.4 kg / m3 is sprayed after demoulding.

Claims

1. A liquid anti-cracking agent for mass concrete, characterized in that: The invention is composed of the following components in weight ratio: 30-35% of modified ether shrinkage reducing agent, 0.5-1% of surface tension adjusting agent, 5-8% of anti-adsorption agent, 3-5% of concrete performance sensitive adjusting agent and 51-61.5% of water.

2. The liquid anti-cracking agent for mass concrete as claimed in claim 1, characterized in that: The modified ether shrinkage reducing agent is prepared by the following method: dissolving 350 parts of ethylene diethylene glycol polyoxyethylene ether in 300-400 parts of water, adding 9.5-10.5 parts of polyoxyethylene alcohol, 9.5-10.5 parts of 2-acrylamide-2-methylpropane sulfonic acid and 2.0-2.2 parts of hydrogen peroxide, stirring and melting, and then dropping materials A and B; wherein material A is a mixture of 20 parts of ethyl methacrylate, 14.5-15.5 parts of hydroxypropyl acrylate, 4.5-5.5 parts of methacrylic acid and 25-35 parts of water, and material B is a mixture of 8 parts of sodium methacrylate sulfonate, 4.5-5.5 parts of sodium bisulfite and 12-18 parts of water; after the dropwise addition is completed, stirring is continued for 20-50 minutes, and water is added to make up 1000 parts, so as to obtain the modified ether shrinkage reducing agent, and the above parts are all parts by weight.

3. A liquid anti-cracking agent for mass concrete as claimed in claim 1 or 2, characterized in that: The surface tension regulator is dibutyl phthalate or tributyl phosphate.

4. A liquid anti-cracking agent for mass concrete as claimed in claim 1 or 2, characterized in that: The anti-adsorption agent is a compound of epichlorohydrin and ethylenediamine, and the molar ratio of the two is 1: (1.1-1.7).

5. A liquid anti-cracking agent for mass concrete as claimed in claim 1 or 2, characterized in that: The concrete performance sensitivity regulator is polypropylene glycol dimethacrylate.

6. The method for applying the liquid anti-cracking agent for mass concrete according to claim 1 or 2, characterized in that: The liquid anti-cracking agent is added in an amount of 0.8-1.2% of the cement mass during the preparation of ready-mixed concrete, and is sprayed at 0.3-0.4 kg / m3 after demoulding.

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