Durable concrete and method for making same

Abstract

The application relates to the field of concrete, in particular to a durable concrete and a preparation method thereof. The durable concrete comprises the following raw materials in parts by weight: cement 400-450 parts, fly ash 45-52 parts, aggregate 1800-2100 parts, additive 4-5 parts and water 120-135 parts; the additive comprises a gradient crosslinking core-shell structure temperature-sensitive polymer composite agent, the gradient crosslinking core-shell structure temperature-sensitive polymer composite agent is prepared by taking N-isopropyl acrylamide as a temperature-sensitive response main monomer, methylene bisacrylamide as a gradient crosslinking agent to prepare a shell layer structure and taking a rigid polymer as a core layer structure. The additive of the application can well solve the aggregate settlement problem in the hardening process of the concrete, so that the concrete can adapt to the field pouring working condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete, in particular to a durable concrete and a preparation method thereof. BACKGROUND

[0002] Concrete is obtained by mixing cement as a gel material, sand and stone as aggregate, and water (which can contain additives and admixtures) in a certain proportion.

[0003] During the hardening process of concrete, aggregate settlement occurs. Aggregate settlement leads to uneven internal structure of concrete, and the porosity of the part where aggregate is concentrated is reduced, while the porosity of the part where cement paste is concentrated is relatively high. In this way, the strength development of different parts of the concrete is inconsistent, and when stressed, the parts with lower strength are prone to crack first, thereby affecting the carrying capacity of the entire structure and reducing the overall strength of the structure. Aggregate settlement causes unevenness in the internal structure of concrete, which reduces the compactness of concrete, and makes it easier for external moisture, oxygen and harmful ions to enter the internal structure of concrete and reach the surface of the steel bar. When the concrete protective layer on the surface of the steel bar cracks or has pores due to aggregate settlement, it will accelerate the corrosion of the steel bar. After the steel bar corrodes, the volume expands, which will further crack the concrete, forming a vicious cycle and seriously shortening the service life of the structure.

[0004] To address the problem of aggregate settlement, technicians have developed many methods to solve it, such as optimizing aggregate gradation, adjusting water-cement ratio, adding thickeners, early strength agents, retarders, air entraining agents and other additives, which have achieved some remarkable results.

[0005] With respect to the above related technology, the applicant found that the above scheme can largely avoid the problem of aggregate settlement, but temperature change is also an important factor affecting aggregate settlement. Aggregate settlement caused by day and night temperature difference in field construction conditions is an important factor affecting engineering quality. SUMMARY

[0006] In order to alleviate the problem of aggregate settlement caused by temperature difference, the present application provides a durable concrete and a preparation method thereof.

[0007] In a first aspect, the present application provides a durable concrete, which adopts the following technical scheme.

[0008] A durable concrete, comprising the following raw materials by weight: cement 400-450 parts, fly ash 45-52 parts, aggregate 1800-2100 parts, additive 4-5 parts, and water 120-135 parts.

[0009] The additive comprises a gradient cross-linking core-shell structure temperature-sensitive polymer composite agent, which is prepared by using N-isopropyl acrylamide as a temperature-sensitive response main monomer, methylene bisacrylamide as a gradient cross-linking agent to form a shell structure, and a rigid polymer as a core structure.

[0010] Further, the preparation method of the gradient cross-linking core-shell structure temperature-sensitive polymer composite agent is as follows:

[0011] 1) Core layer preparation

[0012] Styrene, butyl acrylate and divinylbenzene are dissolved in water to form a homogeneous pre-emulsion by ultrasonic emulsification; then, under nitrogen protection, the temperature is raised to 65-75°C, an initiator is added to initiate polymerization, and the reaction is carried out for 4 hours to obtain core layer microspheres;

[0013] 2) Gradient shell construction

[0014] Gradient cross-linking liquid preparation:

[0015] N-isopropyl acrylamide is mixed with hydroxyethyl acrylate to obtain a mixed liquid, then methylene bisacrylamide is added to the mixed liquid in three stages according to a concentration gradient, a premix liquid is prepared, and the concentration of the concentration gradient is the weight concentration of methylene bisacrylamide;

[0016] Stage-by-stage graft polymerization:

[0017] The core layer microspheres are dispersed to obtain a core layer microsphere dispersion liquid, 0.5% of the premix liquid is added to the core layer microsphere dispersion liquid in stages, and the reaction is carried out to form a shell structure with a decreasing cross-linking degree from the inside to the outside;

[0018] 3) Cross-linking and curing

[0019] The product in 2) is immersed in a glutaraldehyde solution for cross-linking for 12 hours to obtain the gradient cross-linking core-shell structure temperature-sensitive polymer composite agent.

[0020] By using the above technical solution, the gradient cross-linking core-shell structure temperature-sensitive polymer composite agent is used as an additive in concrete, in an environment below 35°C, the shell layer temperature-sensitive material absorbs water and swells, releases water-retaining components, reduces the bleeding rate of concrete, and reduces the driving force for aggregate settlement caused by the upward movement of free water; the swollen shell polymer network adsorbs free water to form a local high-viscosity area, delays water migration, and maintains the uniformity of the paste. At low temperatures, the shell layer swells to fill the capillary pores of the concrete, reducing the bleeding channels and inhibiting the migration of water carrying aggregate particles.

[0021] In an environment above 35℃, the shell layer shrinks to form a dense network, significantly increasing the apparent viscosity of the concrete, enhancing the thixotropy, and inhibiting the sinking rate of the aggregate due to gravity; the gradient cross-linking design, with high internal cross-linking and low external cross-linking, makes the viscosity change smooth, avoiding local rheological imbalance caused by temperature changes. The dense network formed by the shell layer shrinkage at high temperature interweaves with the cement hydration products, enhancing the rigidity of the paste skeleton and further fixing the position of the aggregate.

[0022] The core layer of high cross-linking polystyrene microspheres uniformly disperses in the concrete paste, forming a steric hindrance effect that directly blocks the sinking path of the aggregate. The microsphere particle size and cement particles form a multi-scale filling, optimizing the paste density and reducing the settlement void.

[0023] The core-shell is connected by covalent bonds, balancing the shell shrinkage stress and core rigidity, avoiding internal stress concentration due to temperature changes, and maintaining the structural stability of the composite agent. The stable core-shell structure resists shear damage during mixing and pumping, ensuring that the composite agent continues to play a suspending role.

[0024] The carboxyl or sulfonic groups of the shell layer are adsorbed on the aggregate surface through hydrogen bonding or electrostatic interaction, forming a "polymer-aggregate" anchoring point, enhancing the adhesion between the aggregate and the paste. When the temperature changes, the swelling and shrinking of the shell network dynamically adjusts the anchoring strength, adapting to the rheological requirements at different construction stages.

[0025] Further, the concentration gradient of the methylene bisacrylamide is 0.5%, 0.3%, 0.1%.

[0026] Further, the specific process of the staged graft polymerization is as follows:

[0027] First stage: Add a pre-mixed solution with a concentration of 0.5% to the core layer microsphere dispersion, and react at 50℃ for 2 hours;

[0028] Second stage: Add a pre-mixed solution with a concentration of 0.3% and continue to react for 1.5 hours;

[0029] Third stage: Add a pre-mixed solution with a concentration of 0.1% and react for 1 hour to form a shell structure with decreasing cross-linking degree from inside to outside.

[0030] Further, the weight ratio of N-isopropyl acrylamide to hydroxyethyl acrylate is (55-60):(10-12).

[0031] Further, the weight ratio of styrene, butyl acrylate, and divinylbenzene is (10-13):(5-8):1.

[0032] Further, the core layer further comprises a water reducing agent, the water reducing agent is dissolved in water together with the styrene, and a weight ratio of the water reducing agent to the styrene is (60-65):1.

[0033] By adopting the technical scheme, the water reducing agent is encapsulated in the core layer, and the composite agent can prolong the workability of concrete, shorten the transition time of the slurry from plasticity to hardening, and reduce the time window of aggregate settlement.

[0034] Further, the aggregate comprises coarse aggregate and fine aggregate, the particle size of the fine aggregate is 0.5-2 mm, the particle size of the coarse aggregate is 5-20 mm, and a weight ratio of the fine aggregate to the coarse aggregate is 1:(1.5-2.3).

[0035] In a second aspect, the application provides a method for preparing durable concrete.

[0036] The method for preparing durable concrete comprises uniformly mixing cement, fly ash, aggregate, additive and water to obtain concrete.

[0037] In summary, the application has the following beneficial effects:

[0038] The gradient cross-linking core-shell structure temperature-sensitive polymer composite agent is used as the additive in the concrete, in an environment below 35°C, the shell layer temperature-sensitive material absorbs water to swell, releases the water-retaining component, reduces the water bleeding rate of the concrete, and reduces the driving force of aggregate settlement caused by the rising of free water; the swollen shell layer polymer network absorbs free water to form a local high-viscosity area, delays water migration, and maintains the uniformity of the slurry. The shell layer swells to fill the capillary pores of the concrete at low temperature, reduces the water bleeding channel, and inhibits the migration of water carrying aggregate particles, which well solves the settlement problem of the aggregate in the hardening process of the concrete, maintains the dense and uniform support structure in the concrete, and thus improves the durability of the concrete. DETAILED DESCRIPTION

[0039] The application is further described below in combination with examples.

[0040] Raw materials and intermediate preparation examples

[0041] Raw materials

[0042] The raw materials in the examples of the application can be obtained on the market:

[0043] Cement, Yangchun Haoluo Cement Co., Ltd. P·O42.5;

[0044] Fly ash, I-grade fly ash;

[0045] Coarse aggregate, sand;

[0046] Fine aggregate, gravel;

[0047] Styrene, analytical pure;

[0048] Butyl acrylate, analytical pure;

[0049] Divinylbenzene, analytical pure;

[0050] Initiator, ammonium persulfate initiator;

[0051] N-isopropyl acrylamide, analytical pure;

[0052] Hydroxyethyl acrylate, analytical pure;

[0053] Methylene bisacrylamide, analytical pure;

[0054] Glutaraldehyde solution, concentration 0.5%;

[0055] Water reducing agent, sodium dodecyl sulfate.

[0056] Preparation Example

[0057] Preparation Example 1

[0058] A gradient cross-linked core-shell structure temperature-sensitive polymer complexing agent, the preparation method is:

[0059] 1) Core layer preparation

[0060] Dissolve 60 kg of styrene, 30 kg of butyl acrylate and 5 kg of divinylbenzene into water, ultrasonic emulsification to form a homogeneous pre-emulsion; then under the protection of nitrogen, heat to 70℃, add 1.5 kg of initiator to initiate polymerization, and react for 4 hours to obtain core layer microspheres with a particle size of 150 nm;

[0061] 2) Gradient shell construction

[0062] Gradient cross-linking solution preparation:

[0063] Mix 55 kg of N-isopropyl acrylamide with 12 kg of hydroxyethyl acrylate to obtain a mixed solution, divide the mixed solution into three parts, then add methylene bisacrylamide with a weight concentration gradient of 0.5%, 0.3% and 0.1% respectively into the mixed solution to prepare a premix solution;

[0064] Stage graft polymerization:

[0065] Disperse the core layer microspheres in water to obtain a core layer microsphere dispersion liquid;

[0066] First stage: add the premix solution with a concentration of 0.5% to the core layer microsphere dispersion liquid, and react at 50℃ for 2 hours;

[0067] Second stage: supplement the premix solution with a concentration of 0.3%, and continue to react for 1.5 hours;

[0068] Third stage: add 0.1% of the premix solution, react for 1 hour to form a shell structure with decreasing cross-linking degree from inside to outside;

[0069] Dynamic light scattering (DLS) is used to monitor the change in particle size, and the shell thickness is controlled to be 60 nm;

[0070] 3) Cross-linking and curing

[0071] The product in 2) is immersed in a glutaraldehyde solution for cross-linking for 12 hours to obtain a gradient cross-linking core-shell structure temperature-sensitive polymer complexing agent.

[0072] Preparation Example 2

[0073] A gradient cross-linking core-shell structure temperature-sensitive polymer complexing agent is prepared by the following method:

[0074] 1) Core layer preparation

[0075] Dissolve 50 kg of styrene, 40 kg of butyl acrylate, and 5 kg of divinylbenzene into water, and ultrasonically emulsify to form a homogeneous pre-emulsion; then under nitrogen protection, heat to 70°C, and add 1.5 kg of initiator to initiate polymerization, and react for 4 hours to obtain core layer microspheres with a particle size of 150 nm;

[0076] The rest is the same as Preparation Example 1.

[0077] Preparation Example 3

[0078] A gradient cross-linking core-shell structure temperature-sensitive polymer complexing agent is prepared by the following method:

[0079] 1) Core layer preparation

[0080] Dissolve 55 kg of styrene, 25 kg of butyl acrylate, and 5 kg of divinylbenzene into water, and ultrasonically emulsify to form a homogeneous pre-emulsion; then under nitrogen protection, heat to 70°C, and add 1.5 kg of initiator to initiate polymerization, and react for 4 hours to obtain core layer microspheres with a particle size of 150 nm;

[0081] The rest is the same as Preparation Example 1.

[0082] Preparation Example 4

[0083] A gradient cross-linking core-shell structure temperature-sensitive polymer complexing agent is prepared by the following method:

[0084] 1) Core layer preparation

[0085] The same as Preparation Example 1

[0086] 2) Gradient shell construction

[0087] Gradient cross-linking solution preparation:

[0088] Mix 60 kg N-isopropyl acrylamide with 10 kg hydroxyethyl acrylate to obtain a mixed solution, divide the mixed solution into three parts, and then add methylene bisacrylamide into the mixed solution at a weight concentration gradient of 0.5%, 0.3%, and 0.1% respectively to prepare a premix solution;

[0089] The rest is the same as in Preparation Example 1.

[0090] Preparation Example 5

[0091] A gradient crosslinking core-shell structure temperature-sensitive polymer complexing agent, the preparation method is:

[0092] 1) Core layer preparation

[0093] The same as in Preparation Example 1

[0094] 2) Gradient shell construction

[0095] Gradient crosslinking liquid preparation:

[0096] Mix 65 kg N-isopropyl acrylamide with 8 kg hydroxyethyl acrylate to obtain a mixed solution, divide the mixed solution into three parts, and then add methylene bisacrylamide into the mixed solution at a weight concentration gradient of 0.5%, 0.3%, and 0.1% respectively to prepare a premix solution;

[0097] The rest is the same as in Preparation Example 1.

[0098] Preparation Example 6

[0099] A gradient crosslinking core-shell structure temperature-sensitive polymer complexing agent, the preparation method is:

[0100] 1) Core layer preparation

[0101] The same as in Preparation Example 1

[0102] 2) Gradient shell construction

[0103] Gradient crosslinking liquid preparation:

[0104] The same as in Preparation Example 1;

[0105] Staged graft polymerization:

[0106] Disperse the core layer microspheres in water to obtain a core layer microsphere dispersion liquid;

[0107] First stage: add the premix solution with a concentration of 0.1% to the core layer microsphere dispersion liquid, and react at 50°C for 1 hour;

[0108] ‌Second stage: supplement the premix solution with a concentration of 0.3%, and continue to react for 1.5 hours;

[0109] Third stage: 0.5% of the premixed solution was added, and the reaction was carried out for 2 hours to form a shell structure with a decreasing crosslinking degree from inside to outside;

[0110] Dynamic light scattering (DLS) was used to monitor the particle size change, and the shell thickness was controlled to be 60 nm;

[0111] The rest was the same as in Preparation Example 1.

[0112] Preparation Example 7

[0113] Different from Preparation Example 1, the concentration gradient of methylene bisacrylamide in Preparation Example 7 was 0.7%, 0.5%, and 0.3%.

[0114] Preparation Example 8

[0115] Different from Preparation Example 1, the concentration of methylene bisacrylamide in Preparation Example 8 was 0.5%.

[0116] Preparation Example 9

[0117] 1) Core layer preparation

[0118] 60 kg of styrene, 30 kg of butyl acrylate, 5 kg of divinylbenzene, and 1 kg of water reducing agent were dissolved in water and ultrasonically emulsified to form a homogeneous pre-emulsion; then under nitrogen protection, the temperature was raised to 70°C, 1.5 kg of initiator was added to initiate polymerization, and the reaction was carried out for 4 hours to obtain core layer microspheres with a particle size of 150 nm;

[0119] The rest was the same as in Preparation Example 1.

[0120] Example

[0121] Examples 1-3

[0122] A durable concrete, the preparation method thereof is:

[0123] The cement, fly ash, aggregate, additive, and water were mixed according to the ratio in Table 1 to obtain the concrete.

[0124] Table 1 Raw material ratio table (kg) of Examples 1-3

[0125]

[0126] The aggregate includes coarse aggregate and fine aggregate, the particle size of the fine aggregate is 0.5-2 mm, the particle size of the coarse aggregate is 5-20 mm, and the weight ratio of the fine aggregate to the coarse aggregate is 1:2; the additive is from Preparation Example 1.

[0127] Examples 4-11

[0128] Different from Example 2, the additive in Examples 4-11 is from Preparation Examples 2-9, respectively.

[0129] Comparative Example 1

[0130] Comparative Example 1

[0131] Different from Example 1, the admixture in Comparative Example 1 is a water reducing agent.

[0132] Comparative Example 2

[0133] Different from Example 1, the admixture in Comparative Example 2 is poly-N-isopropyl acrylamide.

[0134] Performance detection

[0135] The concrete obtained in the examples and comparative examples was mixed and formed into 100mm*100mm*100mm test pieces, and after outdoor curing in Tianjin in July for 56 days, the following tests were performed:

[0136] The anti-chloride ion permeability detection was performed according to the method for the concrete anti-sulfate erosion test in the Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete (GB / T 50082-2009), and the electric flux was recorded. The detection results are shown in Table 2.

[0137] The anti-freeze-thaw cycle test was performed according to the fast freezing method in the Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete (GB / T 50082-2009), and the mass loss rate was calculated. The results are shown in Table 2.

[0138] Table 2 Performance detection results

[0139]

[0140] In combination with Examples 1-11 and Comparative Examples 1-2 and in combination with Table 2, it can be seen that the time resistance and frost resistance of the concrete obtained in Examples 1-11 are better than those of Comparative Examples 1-2, which indicates that the concrete obtained in the application has better durability.

[0141] It can be seen from the combination of Example 1 and Comparative Example 1-2 and Table 2 that the anti-permeability and anti-frost of the concrete time obtained in Example 1 are better than those of Comparative Example 1-2, which shows that the use of the admixture of the application can obtain better concrete durability, which may be because the use of the gradient cross-linked core-shell structure temperature-sensitive polymer composite as an admixture added to the concrete, in an environment below 35℃, the shell temperature-sensitive material absorbs water to swell, releases the water-retaining component, reduces the bleeding rate of the concrete, and reduces the driving force of the aggregate settlement caused by the rising of free water; the swollen shell polymer network adsorbs free water to form a local high-viscosity area, delays water migration, and maintains the uniformity of the slurry. The shell swells to fill the capillary pores of the concrete at low temperature, reduces the bleeding channel, and inhibits the migration of water carrying aggregate particles, which well solves the settlement problem of the aggregate during the hardening process of the concrete, makes the concrete internal support structure keep dense and uniform, and thus improves the durability of the concrete.

[0142] It can be seen from the combination of Example 2 and Examples 6-7 and Table 2 that the anti-permeability and anti-frost of the concrete time obtained in Example 2 and Example 6 are better than those of Example 7, which shows that the use of the admixture in Example 2 performs better in improving the durability of the concrete, which may be because N-isopropyl acrylamide and hydroxyethyl acrylate can affect the lower critical solution temperature of the shell of the admixture, and the lower critical solution temperature of the admixture obtained within the ratio range of the application is more suitable for real working conditions.

[0143] The specific embodiments are only an explanation of the application, and are not a limitation of the application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the application, they are protected by the Patent Law.

Claims

1. A durable concrete, characterized by, The raw materials include cement 400-450 parts, fly ash 45-52 parts, aggregate 1800-2100 parts, additive 4-5 parts, and water 120-135 parts by weight; The additive comprises a gradient cross-linking core-shell structure temperature-sensitive polymer composite agent, which is prepared by using N-isopropyl acrylamide as a temperature-sensitive response main monomer, methylene bisacrylamide as a gradient cross-linking agent to form a shell structure, and a rigid polymer as a core structure; The preparation method of the gradient cross-linking core-shell structure temperature-sensitive polymer composite agent is as follows: 1) Core layer preparation Styrene, butyl acrylate and divinylbenzene are dissolved in water to form a homogeneous pre-emulsion by ultrasonic emulsification; then, under nitrogen protection, the temperature is raised to 65-75 DEG C, an initiator is added to initiate polymerization, and the reaction is carried out for 4 hours to obtain core layer microspheres; 2) Gradient shell construction Gradient cross-linking liquid preparation: N-isopropyl acrylamide and hydroxyethyl acrylate are mixed to obtain a mixed liquid, the mixed liquid is divided into several parts, and methylene bisacrylamide is added into the mixed liquid in a concentration gradient, respectively, to prepare a premix liquid, and the concentration gradient is the weight concentration of methylene bisacrylamide; Staged graft polymerization: The core layer microspheres are dispersed to obtain a core layer microsphere dispersion liquid, and the premix liquid is added into the core layer microsphere dispersion liquid in stages: First stage: 0.5% of the premix liquid is added into the core layer microsphere dispersion liquid, and the reaction is carried out at 50 DEG C for 2 hours; Second stage: 0.3% of the premix liquid is added, and the reaction is continued for 1.5 hours; Third stage: 0.1% of the premix liquid is added, and the reaction is carried out for 1 hour to form a shell structure with a decreasing cross-linking degree from inside to outside; 3) Cross-linking and solidification The product in 2) is immersed in a glutaraldehyde solution for cross-linking for 12 hours to obtain the gradient cross-linking core-shell structure temperature-sensitive polymer composite agent.

2. The durable concrete of claim 1, wherein, The weight ratio of N-isopropyl acrylamide to hydroxyethyl acrylate is (55-60):(10-12).

3. The durable concrete of claim 1, wherein, The weight ratio of styrene, butyl acrylate and divinylbenzene is (10-13):(5-8):

1.

4. The durable concrete of claim 1, wherein, The core layer further comprises a water reducing agent, which is dissolved in water together with styrene, and the weight ratio of the water reducing agent to styrene is (60-65):

1.

5. The durable concrete of claim 1, wherein, The aggregate comprises coarse aggregate and fine aggregate, the particle size of the fine aggregate is 0.5-2 mm, the particle size of the coarse aggregate is 5-20 mm, and the weight ratio of the fine aggregate to the coarse aggregate is 1:(1.5-2.3).

6. A durable concrete as claimed in any one of claims 1 to 5, characterised in that, The preparation method is as follows: The cement, fly ash, aggregate, additive and water are uniformly mixed to obtain the concrete.

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