Waterborne polyurethane enhancer, cold-resistant and salt-resistant concrete composition as well as preparation method and application of cold-resistant and salt-resistant concrete composition

Abstract

The invention provides a waterborne polyurethane enhancer, a cold-resistant and salt-resistant concrete composition as well as a preparation method and application of the cold-resistant and salt-resistant concrete composition, and belongs to the technical field of buildings and civil engineering. The waterborne polyurethane enhancer comprises diisocyanate, oligomer polyol, a small molecule chain extender, oxalic acid dihydrazide, oxaloacetic acid and a catalyst, and the cold-resistant and salt-resistant concrete composition comprises cement, aggregate, a water reducing agent, an anti-freezing agent, an air entraining agent, modified straw fibers, the waterborne polyurethane enhancer, calcium silicate and water. Through mutual cooperation of all the components, the obtained concrete has excellent cold resistance, salt resistance, impermeability and compressive strength, and can meet the engineering requirements for concrete durability and use safety under low-temperature and high-salt conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of construction and civil engineering, and specifically relates to a waterborne polyurethane strengthening agent, a cold-resistant and salt-resistant concrete composition, and a preparation method and application thereof. Background Art

[0002] Ordinary concrete is generally made of cement as a gelling material, and is mixed with sand, stone and other aggregates and water in a certain proportion. It has the advantages of easy molding, low energy consumption, good durability, low price, and can be combined with steel to make various load-bearing structures. It is currently the most widely used and largest-volume building material in the world, and plays an irreplaceable role in many fields such as roads, bridges, and tunnels. However, ordinary concrete is highly brittle and has poor durability, and is vulnerable to environmental deterioration and climate change. With the advancement and development of science and technology, more and more concrete is used in high-cold environments and high-salt environments such as saline soil and salt lakes. Concrete is prone to internal microcracks and surface erosion under the combined action of water and freeze-thaw cycles. This freezing damage will eventually cause the concrete structure to expand, crack, erode and collapse after multiple accumulations, and the durability of the concrete structure will decrease. Saline soil and salt lakes contain high concentrations of corrosive ions such as chloride ions and sulfate ions, and concrete is easily corroded, resulting in a decrease in durability. Therefore, it is crucial to improve the cold and salt erosion resistance of concrete.

[0003] At present, the main method for improving the salt corrosion resistance and cold resistance of concrete is to add mineral admixtures and chemical admixtures. For example, Chinese patent CN109608141A discloses a salt corrosion resistant concrete and its preparation method, including cement, gravel, sand, nano clay, water reducer, thickener, defoamer, air entraining agent and water. By adding nano clay, the pore structure inside the concrete is effectively improved, the corrosion of concrete to chloride and sulfate is reduced, and the service life is extended. Chinese patent CN113354368A discloses an antifreeze concrete, including water, sand, stone, cement, fly ash and antifreeze agent, with calcium nitrate, triterpenoid saponin, hexadecyl trimethyl ammonium bromide, carboxymethyl cellulose, hydroxypropyl distarch phosphate as antifreeze agent, which improves the antifreeze performance of concrete in the initial stage of solidification, so that the concrete shows excellent compressive strength after solidification.

[0004] However, there are many types of admixtures, and different types of admixtures have different effects. The way of adding admixtures will also affect the engineering quality of concrete. In addition, many admixtures have poor compatibility with other components in concrete materials and are prone to segregation, thus affecting the performance of concrete. Therefore, it is urgent to better improve the salt erosion resistance and cold resistance of concrete to meet the needs of the project. Summary of the invention

[0005] The purpose of the present invention is to provide a waterborne polyurethane strengthening agent, a concrete composition and a preparation method and application thereof in view of the deficiencies in the prior art. The present invention provides a waterborne polyurethane strengthening agent, a concrete composition and a preparation method and application thereof. Through the mutual coordination of the components, the obtained concrete has excellent cold resistance, salt corrosion resistance, impermeability and high compressive strength, which can meet the engineering needs for concrete durability and safety of use under low temperature and high salt conditions.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A waterborne polyurethane strengthening agent comprises diisocyanate, oligomer polyol, small molecule chain extender, oxalic acid dihydrazide, oxaloacetic acid and a catalyst.

[0008] Furthermore, the mass ratio of oxalic acid dihydrazide to oxaloacetic acid is 0.3-0.5:1, preferably 0.38-0.45:1, and more preferably 0.4:1.

[0009] Further, the diisocyanate is selected from at least one of diphenylmethane diisocyanate, aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate; preferably at least one of 2,6-diisocyanatohexanoic acid, isophorone diisocyanate, methylcyclohexyl diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, tetramethylxylene diisocyanate, and toluene diisocyanate.

[0010] Furthermore, the oligomer polyol is selected from at least one of polyether polyol and polyester polyol; preferably at least one of polypropylene glycol, polytetramethylene glycol, poly(hexylene adipate), poly(butylene adipate), polycarbonate diol and polycaprolactone.

[0011] Furthermore, the molecular weight of the oligomer polyol is 1000-2000, preferably 1000-1500.

[0012] Furthermore, the small molecule chain extender is selected from at least one of alcohol amines, diols, diamines and sulfonic acid group-containing compounds; preferably at least one of propylene glycol, 1,4-butanediol, 1,3-butanediol, diethylene glycol and dipropylene glycol, diethyltoluenediamine, 3,5-dimethylthiotoluenediamine, diethanolamine, triethanolamine and triisopropanolamine.

[0013] Furthermore, the catalyst is selected from at least one of N,N-dimethylcyclohexylamine, dibutyltin laurate, stannous octoate, stannous isooctanoate, tributyltin methoxy, tert-butoxytin, tin phenoxide, tin chloride, tin bromide, acetylated tin, and butyl titanate; preferably at least one of dibutyltin laurate, stannous octoate, and butyl titanate.

[0014] Furthermore, the waterborne polyurethane strengthening agent comprises, by weight:

[0015] 80-150 parts of diisocyanate, 100-200 parts of oligomer polyol, 10-20 parts of small molecule chain extender, 3-6 parts of oxalic acid dihydrazide, 8-12 parts of oxaloacetic acid and 0.5-3 parts of catalyst.

[0016] Furthermore, the waterborne polyurethane strengthening agent comprises, by weight:

[0017] 100-125 parts of diisocyanate, 120-150 parts of oligomer polyol, 14-20 parts of small molecule chain extender, 3-5 parts of oxalic acid dihydrazide, 9-10.5 parts of oxaloacetic acid and 1-2 parts of catalyst.

[0018] Preferably, the waterborne polyurethane strengthening agent comprises, by weight:

[0019] 120 parts of diisocyanate, 140 parts of oligomer polyol, 16 parts of small molecule chain extender, 4 parts of oxalic acid dihydrazide, 10 parts of oxaloacetic acid and 2 parts of catalyst.

[0020] The preparation method of the above-mentioned waterborne polyurethane strengthening agent comprises the following steps:

[0021] (1) diisocyanate and oligomer polyol react under the action of a catalyst to obtain a prepolymer solution;

[0022] (2) After the prepolymer solution is emulsified by adding water, oxaloacetic acid dihydrazide, oxaloacetic acid and a small molecule chain extender are added to react to obtain a waterborne polyurethane strengthening agent.

[0023] Furthermore, in step (1), the reaction temperature is 60-70°C and the reaction time is 40-60 min; preferably, the reaction temperature is 65-70°C and the reaction time is 45-50 min.

[0024] Furthermore, in step (2), the mass ratio of the prepolymer solution to water is 1:1-3, preferably 1-2.

[0025] Furthermore, in step (1), the reaction temperature is 70-85°C, and the reaction time is 1-3h; preferably, the reaction temperature is 75-80°C, and the reaction time is 2-2.5h.

[0026] The application of the above waterborne polyurethane strengthening agent in the preparation of cold-resistant and salt-resistant concrete.

[0027] A cold-resistant and salt-resistant concrete composition comprises cement, aggregate, a water reducing agent, an antifreeze agent, an air entraining agent, modified straw fiber, a water-based polyurethane strengthening agent, calcium silicate and water.

[0028] Furthermore, the aggregate is at least one of sand, gravel, volcanic ash, coal slag and slag, preferably sand and / or gravel.

[0029] Furthermore, the water reducer is selected from at least one of polycarboxylic acid water reducer, naphthalene water reducer, melamine water reducer, lignin sulfonate water reducer, aminosulfonate water reducer and fatty acid water reducer; preferably at least one of melamine, sodium lignin sulfonate and sodium aminosulfonate.

[0030] Furthermore, the antifreeze agent is selected from at least one of calcium nitrate, glycerol, urea, triterpenoid saponin, cetyltrimethylammonium bromide, carboxymethyl cellulose, hydroxypropyl distarch phosphate, epoxy resin and microcrystalline quartz powder, preferably at least one of calcium nitrate, urea, carboxymethyl cellulose and hydroxypropyl distarch phosphate.

[0031] Furthermore, the air entraining agent is selected from at least one of rosin resins, alkyl and alkyl aromatic sulfonates, and dodecyl sulfate saponins; preferably at least one of sodium lignin sulfonate, sodium dodecylbenzene sulfonate, sodium rosin acid, and sodium dodecyl sulfate.

[0032] Furthermore, the preparation method of the modified straw fiber is as follows:

[0033] The straw is boiled in high-temperature water, taken out, dried, crushed, and then activated using an activation solution containing an alkaline substance and isopropanol; then added to dimethyl sulfoxide, itaconic anhydride, acetic acid and a catalyst are added to carry out acetylation reaction, and after the reaction is completed, filtered, washed with water, and dried to obtain modified straw fiber.

[0034] Furthermore, the straw is selected from at least one of rice straw, corn straw, wheat straw, cassava straw and sugarcane straw, preferably rice straw or corn straw.

[0035] Furthermore, the temperature of the high-temperature water boiling is 80-100°C, and the time is 10-30 minutes; preferably, the temperature of the high-temperature water boiling is 90-95°C, and the time is 15-20 minutes.

[0036] Furthermore, the mass ratio of the straw to the activation liquid is 1:8-20, preferably 1:10-12.

[0037] Furthermore, the activation temperature is 50-60°C, and the time is 5-20 min; preferably, the activation temperature is 55-60°C, and the time is 8-15 min.

[0038] Furthermore, in the activation solution, the alkaline substance is at least one of sodium hydroxide, calcium hydroxide, sodium carbonate, calcium oxide, and sodium phosphate, and the organic solvent is ethanol and / or isopropanol; preferably, the alkaline substance is sodium carbonate and / or sodium phosphate, and the organic solvent is ethanol.

[0039] Furthermore, in the activation solution, the mass fraction of the alkaline substance is 2-5%, and the mass fraction of the organic solvent is 10-30%; preferably, the mass fraction of the alkaline substance is 2.5-3%, and the mass fraction of the organic solvent is 12-20%.

[0040] Furthermore, the mass ratio of the straw to dimethyl sulfoxide is 1:10-30, preferably 1:15-20.

[0041] Furthermore, the amount of itaconic anhydride added is 0.2-0.35 times the mass of the straw, and the amount of acetic acid added is 0.1-0.3 times the mass of the straw; preferably, the amount of itaconic anhydride added is 0.25-0.3 times the mass of the straw, and the amount of acetic acid added is 0.12-0.2 times the mass of the straw.

[0042] Furthermore, the catalyst is selected from at least one of sodium bisulfate, hydrofluoric acid and concentrated sulfuric acid, and the added amount is 0.2-2% of the mass of the straw; preferably, the catalyst is concentrated sulfuric acid, and the added amount is 0.5-1% of the mass of the straw.

[0043] Furthermore, the acetylation reaction time is 0.5-4h, preferably the reaction time is 2-2.5h.

[0044] Furthermore, the cold-resistant and salt-resistant concrete composition comprises, by weight percentage:

[0045] Cement 12-20%, aggregate 60-72%, water reducer 0.01-0.5%, antifreeze 0.01-2%, air entraining agent 0.01-0.2%, modified straw fiber 1-5%, water-based polyurethane reinforcing agent 2.5-4%, calcium silicate 0.1-0.3% and balance water.

[0046] Furthermore, the cold-resistant and salt-resistant concrete composition comprises, by weight percentage:

[0047] Cement 15-17%, aggregate 65-70%, water reducer 0.1-0.3%, antifreeze 0.2-0.5%, air entraining agent 0.05-0.1%, modified straw fiber 2-3%, water-based polyurethane strengthener 3-3.4%, calcium silicate 0.2-0.25% and balance water.

[0048] Preferably, the cold-resistant and salt-resistant concrete composition comprises, by weight percentage:

[0049] Cement 16%, aggregate 68%, water reducer 0.2%, antifreeze agent 0.4%, air entraining agent 0.1%, modified straw fiber 2.6%, water-based polyurethane strengthener 3.2%, calcium silicate 0.25% and the balance water.

[0050] The preparation method of the cold-resistant and salt-resistant concrete composition comprises the following steps:

[0051] Cement, aggregate, water reducing agent, antifreeze agent, air entraining agent, modified straw fiber, water-based polyurethane strengthening agent, calcium silicate and water are uniformly mixed, and molding, demoulding and curing treatments are carried out in sequence to obtain cold-resistant and salt-resistant concrete.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The present invention uses cement, aggregate, water reducing agent, antifreeze agent, air entraining agent, modified straw fiber, water-based polyurethane strengthening agent, calcium silicate and water as raw materials to prepare concrete. Through reasonable proportioning, the obtained concrete has excellent cold resistance, salt erosion resistance, impermeability and compressive strength.

[0054] (2) The present invention adds a certain amount of water-based polyurethane strengthener to concrete, which works together with the antifreeze agent to improve the cold resistance of concrete and the compressive strength of concrete; by optimizing the ratio of oxalic acid dihydrazide and oxaloacetic acid in polyurethane, not only the cold resistance and compressive strength of concrete can be further improved, but also the anti-seepage performance can be improved.

[0055] (3) The present invention adds modified straw fiber to concrete. Compared with unmodified straw fiber, the modified straw fiber added to concrete helps to improve the salt corrosion resistance and compression resistance of concrete. DETAILED DESCRIPTION

[0056] The present invention is described below through specific embodiments to make the technical solution of the present invention easier to understand and grasp, but the present invention is not limited thereto, and the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0057] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0058] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should belong to the scope of protection of the present invention. The experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial channels unless otherwise specified. In this embodiment, the cement is silicate cement with a strength grade of 32.5, the aggregate is a continuous grading of 2.36-4.75mm, the moisture content of corn stalks is less than 20%, and the mass fraction of concentrated sulfuric acid is 70%. Unless otherwise specified, the percentages in the embodiments are all mass percentages.

[0059] Example 1

[0060] A cold and salt resistant concrete composition, comprising by weight percentage:

[0061] Cement 16%, aggregate 68%, water reducer 0.2%, antifreeze agent 0.4%, air entraining agent 0.1%, modified straw fiber 2.6%, water-based polyurethane strengthener 3.2%, calcium silicate 0.25% and the balance water.

[0062] The aggregate is gravel and sand in a ratio of 1.5:1.

[0063] The water reducing agent is sodium lignin sulfonate.

[0064] The antifreeze agent is calcium nitrate and urea in a mass ratio of 2:1.

[0065] The air entraining agent is sodium dodecyl sulfate.

[0066] The waterborne polyurethane strengthening agent is prepared by the following method:

[0067] (1) Weighing 120 parts of xylene diisocyanate, 140 parts of polybutylene adipate (molecular weight 1000), 16 parts of diethyltoluenediamine, 4 parts of oxaloacetic acid dihydrazide, 10 parts of oxaloacetic acid and 2 parts of dibutyltin laurate; that is, the mass ratio of oxaloacetic acid dihydrazide to oxaloacetic acid is 0.4:1;

[0068] (2) xylene diisocyanate and polybutylene adipate were reacted under the action of dibutyltin laurate for 50 minutes to obtain a prepolymer solution at a reaction temperature of 65°C;

[0069] (3) After the prepolymer solution is emulsified with 1.5 times the mass of water, oxaloacetic acid dihydrazide, oxaloacetic acid and diethyltoluenediamine are added, and the mixture is reacted at 80° C. for 2 h to obtain a polyurethane.

[0070] The modified straw fiber is prepared by the following method:

[0071] 10 parts of corn stalks were boiled at 90°C for 20 minutes, taken out, dried, crushed, and then immersed in 120 parts of activation solution (containing 2.5% sodium carbonate and 16% isopropanol), and activated at 55°C for 15 minutes; then added to 180 parts of dimethyl sulfoxide, 2.5 parts of itaconic anhydride, 2 parts of acetic acid and 0.1 part of concentrated sulfuric acid to react for 2 hours, filtered, washed with water and dried after the reaction to obtain modified straw fiber.

[0072] After the cold-resistant and salt-resistant concrete composition is mixed, it is molded, demoulded and cured in sequence to obtain the cold-resistant and salt-resistant concrete.

[0073] Example 2

[0074] Another cold and salt resistant concrete composition comprises, by weight percentage:

[0075] Cement 12%, aggregate 72%, water reducer 0.01%, antifreeze 0.01%, air entraining agent 0.01%, modified straw fiber 5%, water-based polyurethane strengthener 4%, calcium silicate 0.1% and water.

[0076] The aggregate is gravel and sand in a ratio of 1.5:1.

[0077] The water reducing agent is sodium aminosulfonate.

[0078] The antifreeze agent is hydroxypropyl distarch phosphate.

[0079] The air entraining agent is sodium rosinate.

[0080] The waterborne polyurethane strengthening agent is prepared by the following method:

[0081] (1) Weighing 80 parts of isophorone diisocyanate, 100 parts of polypropylene glycol (molecular weight 1200), 10 parts of diethanolamine, 3 parts of oxaloacetic acid dihydrazide, 10 parts of oxaloacetic acid and 0.5 parts of stannous octoate; that is, the mass ratio of oxaloacetic acid dihydrazide to oxaloacetic acid is 0.3:1;

[0082] (2) isophorone diisocyanate and polypropylene glycol are reacted under the action of stannous octoate for 50 minutes to obtain a prepolymer solution at a reaction temperature of 65°C;

[0083] (3) After the prepolymer solution is emulsified with 1.5 times the mass of water, oxaloacetic acid dihydrazide, oxaloacetic acid and diethanolamine are added, and the mixture is reacted at 80° C. for 2 h to obtain a polyurethane.

[0084] The modified straw fiber is prepared by the following method:

[0085] 10 parts of rice straw were boiled at 95°C for 15 minutes, taken out, dried, crushed, and then immersed in 120 parts of activation solution (containing 3% sodium phosphate and 20% ethanol) and activated at 60°C for 8 minutes; then added to 200 parts of dimethyl sulfoxide, 3 parts of itaconic anhydride, 2 parts of acetic acid and 0.2 parts of concentrated sulfuric acid to react for 2.5 hours. After the reaction, it was filtered, washed with water and dried to obtain modified straw fiber.

[0086] After the cold-resistant and salt-resistant concrete composition is mixed, it is molded, demoulded and cured in sequence to obtain the cold-resistant and salt-resistant concrete.

[0087] Example 3

[0088] Another cold and salt resistant concrete composition comprises, by weight percentage:

[0089] Cement 15%, aggregate 70%, water reducer 0.1%, antifreeze 0.2%, air entraining agent 0.05%, modified straw fiber 3%, water-based polyurethane strengthener 3.4%, calcium silicate 0.3% and the balance water.

[0090] The aggregate is gravel and sand in a ratio of 1.5:1.

[0091] The water reducing agent is sodium lignin sulfonate.

[0092] The antifreeze agent is carboxymethyl cellulose.

[0093] The air entraining agent is sodium rosin acid and sodium dodecyl sulfate in a mass ratio of 1:1.

[0094] The waterborne polyurethane strengthening agent is prepared by the following method:

[0095] (1) Weighing 100 parts of tetramethylxylene diisocyanate, 120 parts of polytetrahydrofuran ether diol (molecular weight 1000), 14 parts of triisopropanolamine, 3.8 parts of oxaloacetic acid dihydrazide, 10 parts of oxaloacetic acid and 1 part of butyl titanate; that is, the mass ratio of oxaloacetic acid dihydrazide to oxaloacetic acid is 0.38:1;

[0096] (2) Tetramethylxylene diisocyanate and polytetrahydrofuran ether diol were reacted with butyl titanate for 50 minutes to obtain a prepolymer solution at a reaction temperature of 65°C;

[0097] (3) After the prepolymer solution is emulsified with 1.5 times the mass of water, oxaloacetic acid dihydrazide, oxaloacetic acid and triisopropanolamine are added, and the mixture is reacted at 80° C. for 2 h to obtain a polyurethane.

[0098] The modified straw fiber is prepared by the following method:

[0099] 10 parts of corn stalks were boiled at 90°C for 20 minutes, taken out, dried, crushed, and then immersed in 120 parts of activation solution (containing 2.5% sodium carbonate and 16% isopropanol), and activated at 55°C for 15 minutes; then added to 180 parts of dimethyl sulfoxide, 2.5 parts of itaconic anhydride, 2 parts of acetic acid and 0.1 part of concentrated sulfuric acid to react for 2 hours, filtered, washed with water and dried after the reaction to obtain modified straw fiber.

[0100] After the cold-resistant and salt-resistant concrete composition is mixed, it is molded, demoulded and cured in sequence to obtain the cold-resistant and salt-resistant concrete.

[0101] Example 4

[0102] Another cold and salt resistant concrete composition comprises, by weight percentage:

[0103] Cement 17%, aggregate 65%, water reducer 0.3%, antifreeze 0.5%, air entraining agent 0.1%, modified straw fiber 2%, water-based polyurethane strengthener 3%, calcium silicate 0.2% and the balance water.

[0104] The aggregate is gravel and sand in a ratio of 1.5:1.

[0105] The water reducing agent is sodium lignin sulfonate.

[0106] The antifreeze agent is calcium nitrate and urea in a mass ratio of 2:1.

[0107] The air entraining agent is sodium dodecyl sulfate.

[0108] The waterborne polyurethane strengthening agent is prepared by the following method:

[0109] (1) Weigh 125 parts of xylylene diisocyanate, 150 parts of polycarbonate diol (molecular weight 1000), 20 parts of diethyltoluenediamine, 4.5 parts of oxaloacetic acid dihydrazide, 10 parts of oxaloacetic acid and 2 parts of dibutyltin laurate; that is, the mass ratio of oxaloacetic acid dihydrazide to oxaloacetic acid is 0.45:1;

[0110] (2) xylene diisocyanate and polycarbonate diol were reacted under the action of dibutyltin laurate for 50 minutes to obtain a prepolymer solution at a reaction temperature of 65°C;

[0111] (3) After the prepolymer solution is emulsified with 1.5 times the mass of water, oxaloacetic acid dihydrazide, oxaloacetic acid and diethyltoluenediamine are added, and the mixture is reacted at 80° C. for 2 h to obtain a polyurethane.

[0112] The modified straw fiber is prepared by the following method:

[0113] 10 parts of corn stalks were boiled at 90°C for 20 minutes, taken out, dried, crushed, and then immersed in 120 parts of activation solution (containing 2.5% sodium carbonate and 16% isopropanol), and activated at 55°C for 15 minutes; then added to 180 parts of dimethyl sulfoxide, 2.5 parts of itaconic anhydride, 2 parts of acetic acid and 0.1 part of concentrated sulfuric acid to react for 2 hours, filtered, washed with water and dried after the reaction to obtain modified straw fiber.

[0114] After the cold-resistant and salt-resistant concrete composition is mixed, it is molded, demoulded and cured in sequence to obtain the cold-resistant and salt-resistant concrete.

[0115] Example 5

[0116] Another cold and salt resistant concrete composition comprises, by weight percentage:

[0117] Cement 20%, aggregate 60%, water reducer 0.5%, antifreeze agent 2%, air entraining agent 0.2%, modified straw fiber 1%, water-based polyurethane reinforcing agent 2.5%, calcium silicate 0.1% and water.

[0118] The aggregate is gravel and sand in a ratio of 1.5:1.

[0119] The water reducing agent is sodium lignin sulfonate.

[0120] The antifreeze agent is calcium nitrate and urea in a mass ratio of 2:1.

[0121] The air entraining agent is sodium dodecyl sulfate.

[0122] The waterborne polyurethane strengthening agent is prepared by the following method:

[0123] (1) Weighing 150 parts of xylene diisocyanate, 200 parts of polybutylene adipate (molecular weight 1000), 20 parts of diethyltoluenediamine, 6 parts of oxaloacetic acid dihydrazide, 12 parts of oxaloacetic acid and 3 parts of dibutyltin laurate; that is, the mass ratio of oxaloacetic acid dihydrazide to oxaloacetic acid is 0.45:1;

[0124] (2) xylene diisocyanate and polybutylene adipate were reacted under the action of dibutyltin laurate for 50 minutes to obtain a prepolymer solution at a reaction temperature of 65°C;

[0125] (3) After the prepolymer solution is emulsified with 1.5 times the mass of water, oxaloacetic acid dihydrazide, oxaloacetic acid and diethyltoluenediamine are added, and the mixture is reacted at 80° C. for 2 h to obtain a polyurethane.

[0126] The modified straw fiber is prepared by the following method:

[0127] 10 parts of corn stalks were boiled at 90°C for 20 minutes, taken out, dried, crushed, and then immersed in 120 parts of activation solution (containing 2.5% sodium carbonate and 16% isopropanol), and activated at 55°C for 15 minutes; then added to 180 parts of dimethyl sulfoxide, 2.5 parts of itaconic anhydride, 2 parts of acetic acid and 0.1 part of concentrated sulfuric acid to react for 2 hours, filtered, washed with water and dried after the reaction to obtain modified straw fiber.

[0128] After the cold-resistant and salt-resistant concrete composition is mixed, it is molded, demoulded and cured in sequence to obtain the cold-resistant and salt-resistant concrete.

[0129] Comparative Example 1

[0130] The difference from Example 1 is that, during the preparation of the waterborne polyurethane strengthening agent, the mass ratio of oxalic acid dihydrazide to oxaloacetic acid is 0.2:1 (the total weight of the two is 14 parts).

[0131] Comparative Example 2

[0132] The difference from Example 1 is that, during the preparation of the waterborne polyurethane strengthening agent, the mass ratio of oxalic acid dihydrazide to oxaloacetic acid is 0.6:1 (the total weight of the two is 14 parts).

[0133] Comparative Example 3

[0134] The difference from Example 1 is that oxalic acid dihydrazide is not added during the preparation of the waterborne polyurethane strengthening agent.

[0135] Comparative Example 4

[0136] The difference from Example 1 is that oxaloacetic acid is not added during the preparation of the waterborne polyurethane strengthening agent.

[0137] Comparative Example 5

[0138] The difference from Example 1 is that no waterborne polyurethane reinforcing agent is added.

[0139] Comparative Example 6

[0140] The difference from Example 1 is that in the process of preparing the modified straw fiber, an equal amount of acetic anhydride is used instead of itaconic anhydride.

[0141] Comparative Example 7

[0142] The difference from Example 1 is that the modified straw fiber is prepared by the following method: 10 parts of corn stalks are boiled in water at 90°C for 20 minutes, taken out and dried, crushed, and then immersed in 120 parts of activation solution (containing 2.5% sodium carbonate and 16% isopropanol) and activated at 55°C for 15 minutes.

[0143] Comparative Example 8

[0144] The difference from Example 1 is that no modified straw fiber is added.

[0145] Experimental Example 1

[0146] Compressive strength

[0147] The compressive strength of concrete was tested with reference to GB / T50081-2002 “Test methods for mechanical properties of ordinary concrete”. The results are shown in Table 1 below.

[0148] Table 1. Compressive strength

[0149]

[0150] As shown in Table 1, the compressive strength of the concrete prepared by the component formula and method of the present invention is high; the compressive strength of the concrete obtained in Comparative Examples 1-5 is lower than that in Example 1, indicating that the compressive strength of the concrete added with the waterborne polyurethane strengthener is higher, and the compressive strength of the concrete obtained in Comparative Examples 1 and 2 is slightly higher than that in Comparative Examples 3-5, which shows that optimizing the ratio of oxalic acid dihydrazide and oxaloacetic acid in the waterborne polyurethane strengthener is helpful to further improve the compressive strength of the concrete; the compressive strength of the concrete obtained in Comparative Examples 6-8 is lower than that in Example 1, indicating that adding the modified straw fiber of the present invention to the concrete can improve the compressive strength; in addition, it can be seen that the difference in the 7d compressive strength between the concrete obtained in Comparative Examples 6-8 and the concrete obtained in the example is more significant, indicating that the modified straw fiber has a more excellent improvement effect on the early compressive strength of the concrete.

[0151] Experimental Example 2

[0152] Cold resistance

[0153] According to the slow freezing method in GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", the concrete was subjected to 300 freeze-thaw cycles. After the freeze-thaw cycles, the mass loss rate (%) and compressive strength loss rate (%) of the concrete were tested. The results are shown in Table 2 below.

[0154] Table 2. Cold resistance performance

[0155] Group Mass loss rate (%) Compressive strength loss rate (%) Example 1 0.37 8.75 Example 2 0.38 9.48 Example 3 0.40 9.17 Example 4 0.42 10.05 Example 5 0.36 8.62 Comparative Example 1 2.51 16.30 Comparative Example 2 2.85 15.25 Comparative Example 3 5.22 19.81 Comparative Example 4 5.81 22.54 Comparative Example 5 6.85 24.51 Comparative Example 6 1.04 9.87 Comparative Example 7 0.98 10.24 Comparative Example 8 1.68 10.09

[0156] As shown in the table, the concrete prepared by the component formula and method of the present invention has excellent cold and frost resistance, and its mass loss rate and compressive strength loss rate are low after 300 freeze-thaw treatments; the mass loss rate and compressive strength loss rate of the concrete obtained in Comparative Examples 1-5 are significantly higher than those in Example 1, which shows that the addition of the water-based polyurethane strengthener helps to improve the cold and frost resistance of the concrete; the mass loss rate and compressive strength loss rate of the concrete obtained in Comparative Examples 1-5 also have certain differences, indicating that there is a certain synergistic effect between oxalic acid dihydrazide and oxaloacetic acid in the water-based polyurethane strengthener, and optimizing the ratio of the two can further improve the cold and frost resistance of the concrete.

[0157] Experimental Example 3

[0158] Salt corrosion resistance

[0159] Referring to the method in GB / T50082-2009 "Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete", the chloride ion diffusion coefficient of concrete at 28 days under standard curing and the compressive strength corrosion resistance coefficient after 120 cycles were tested. The results are shown in Table 3 below.

[0160] Table 3. Salt corrosion resistance

[0161] Group <![CDATA[28d Chloride ion diffusion coefficient (10 -12 m 2 / s)]]> Compressive strength corrosion resistance coefficient (%) Example 1 1.32 98.7 Comparative Example 6 8.41 91.8 Comparative Example 7 8.82 92.5 Comparative Example 8 10.73 89.4

[0162] As shown in the table, the concrete prepared by the component formula and method of the present invention has a low chloride ion diffusion coefficient, a high compressive strength and corrosion resistance coefficient, and a strong resistance to chloride and sulfate corrosion; the chloride ion diffusion coefficient of comparative examples 6-7 is low, and the compressive strength and corrosion resistance coefficient are significantly different from those of Example 1. It can be seen that the addition of the modified straw fiber of the present invention to the concrete improves its resistance to salt corrosion.

[0163] Experimental Example 4

[0164] Anti-seepage performance

[0165] The anti-permeability of concrete was tested with reference to GB / T50082-2009 "Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete". The sample was in the shape of a truncated cone with a top diameter of 70 mm, a ground diameter of 80 mm, and a height of 30 mm. The penetration pressure of the sample was 3.5 MPa and the pressurization time was 48 h. The results are shown in Table 4 below.

[0166] Table 4. Impermeability grades

[0167] Group Example 1 Example 2 Example 3 Example 4 Example 5 Impermeability grade ＞P12 P12 ＞P12 ＞P12 P12 Group Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Impermeability grade P8 P8 P8 P6 P6

[0168] As shown in the table, the impermeability grade of the concrete obtained in Examples 1-5 reaches P12 or above, and the impermeability performance is excellent, while the impermeability grade of the concrete obtained in Comparative Examples 1-5 is significantly lower than that in Example 1, and the difference in the impermeability grade between Comparative Examples 1-5 is relatively small. It can be seen that there is a certain synergistic effect between oxaloacetic acid dihydrazide and oxaloacetic acid in the waterborne polyurethane strengthener, and optimizing the ratio of the two is helpful to improve the impermeability performance of the concrete.

[0169] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A waterborne polyurethane strengthening agent, characterized in that: The invention comprises diisocyanate, oligomer polyol, small molecule chain extender, oxalic acid dihydrazide, oxaloacetic acid and a catalyst.

2. The waterborne polyurethane strengthening agent according to claim 1, characterized in that: The mass ratio of oxalic acid dihydrazide to oxaloacetic acid is 0.3-0.5:

1.

3. The waterborne polyurethane strengthening agent according to claim 2, characterized in that: The mass ratio of oxaloacetic acid dihydrazide to oxaloacetic acid is 0.38-0.45:

1.

4. The waterborne polyurethane strengthening agent according to claim 2, characterized in that: The mass ratio of oxaloacetic acid dihydrazide to oxaloacetic acid is 0.4:

1.

5. The waterborne polyurethane strengthening agent according to any one of claims 1 to 4, characterized in that: Contains by weight: 80-150 parts of diisocyanate, 100-200 parts of oligomer polyol, 10-20 parts of small molecule chain extender, 3-6 parts of oxalic acid dihydrazide, 8-12 parts of oxaloacetic acid and 0.5-3 parts of catalyst.

6. The waterborne polyurethane strengthening agent according to claim 5, characterized in that: Contains by weight: 100-125 parts of diisocyanate, 120-150 parts of oligomer polyol, 14-20 parts of small molecule chain extender, 3-5 parts of oxalic acid dihydrazide, 9-10.5 parts of oxaloacetic acid and 1-2 parts of catalyst.

7. The method for preparing the waterborne polyurethane strengthening agent according to any one of claims 1 to 6, characterized in that: The steps include: (1) diisocyanate and oligomer polyol react under the action of a catalyst to obtain a prepolymer solution; (2) After the prepolymer solution is emulsified by adding water, oxaloacetic acid dihydrazide, oxaloacetic acid and a small molecule chain extender are added to react to obtain a waterborne polyurethane strengthening agent.

8. Application of waterborne polyurethane strengthening agent in preparing cold-resistant and salt-resistant concrete, characterized in that: The waterborne polyurethane strengthening agent is the waterborne polyurethane strengthening agent according to any one of claims 1 to 6 or the waterborne polyurethane strengthening agent prepared by the method according to claim 7.

9. A cold and salt resistant concrete composition, characterized in that: The invention comprises cement, aggregate, water reducing agent, antifreeze agent, air entraining agent, modified straw fiber, water-based polyurethane strengthening agent, calcium silicate and water; the water-based polyurethane strengthening agent is the water-based polyurethane strengthening agent according to any one of claims 1 to 6 or the water-based polyurethane strengthening agent prepared by the method according to claim 7.

10. The cold-resistant and salt-resistant concrete composition according to claim 9, characterized in that: The preparation method of the modified straw fiber is as follows: The straw is boiled in high-temperature water, taken out, dried, crushed, and then activated using an activation solution containing an alkaline substance and isopropanol; then added to dimethyl sulfoxide, itaconic anhydride, acetic acid and a catalyst are added to carry out acetylation reaction, and after the reaction is completed, filtered, washed with water, and dried to obtain modified straw fiber.

11. The cold-resistant and salt-resistant concrete composition according to claim 10, characterized in that: In the activation solution, the alkaline substance is at least one of sodium hydroxide, calcium hydroxide, sodium carbonate, calcium oxide, and sodium phosphate, and the organic solvent is ethanol and / or isopropanol.

12. The cold-resistant and salt-resistant concrete composition according to claim 10, characterized in that: The amount of itaconic anhydride added is 0.2-0.35 times the mass of the straw, and the amount of acetic acid added is 0.1-0.3 times the mass of the straw.

13. The cold and salt resistant concrete composition according to any one of claims 9 to 12, characterized in that: Contains by weight percentage: Cement 12-20%, aggregate 60-72%, water reducer 0.01-0.5%, antifreeze 0.01-2%, air entraining agent 0.01-0.2%, modified straw fiber 1-5%, water-based polyurethane reinforcing agent 2.5-4%, calcium silicate 0.1-0.3% and balance water.

14. The cold-resistant and salt-resistant concrete composition according to claim 13, characterized in that: Contains by weight percentage: Cement 15-17%, aggregate 65-70%, water reducer 0.1-0.3%, antifreeze 0.2-0.5%, air entraining agent 0.05-0.1%, modified straw fiber 2-3%, water-based polyurethane strengthener 3-3.4%, calcium silicate 0.2-0.25% and balance water.

15. The cold and salt resistant concrete composition according to claim 14, characterized in that: Contains by weight percentage: Cement 16%, aggregate 68%, water reducer 0.2%, antifreeze agent 0.4%, air entraining agent 0.1%, modified straw fiber 2.6%, water-based polyurethane strengthener 3.2%, calcium silicate 0.25% and the balance water.

16. The method for preparing the cold-resistant and salt-resistant concrete composition according to any one of claims 9 to 15, characterized in that: The steps include: Cement, aggregate, water reducing agent, antifreeze agent, air entraining agent, modified straw fiber, water-based polyurethane strengthening agent, calcium silicate and water are uniformly mixed, and molding, demoulding and curing treatments are carried out in sequence to obtain cold-resistant and salt-resistant concrete.

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