阅读说明：本技术 一种抗裂混凝土及其制备方法 (Anti-crack concrete and preparation method thereof ) 是由 马英英 章贤斌 钟志刚 于 2021-08-09 设计创作，主要内容包括：本申请属于混凝土材料的技术领域,具体公开了一种抗裂混凝土及其制备方法。本申请的一种抗裂混凝土,主要由包括以下重量份的混凝土原料制得：水泥400-500份、粗骨料1200-1300份、细骨料400-460份、水150-250份、膨胀石墨11-13份、改性纳米氧化铝9-10份、月桂酸89-100份、无水乙醇90-100份和减水剂6-10份。本申请中,膨胀石墨能够吸附月桂酸和纳米氧化铝,月桂酸具有较高的相变焓值及热稳定性,可有效控制混凝土的内部温度,防止裂缝的产生,纳米氧化铝能够填充混凝土内部的缝隙,提高混凝土的密实度,提高混凝土的抗裂性能。(The application belongs to the technical field of concrete materials, and particularly discloses anti-crack concrete and a preparation method thereof. The application provides an anti-crack concrete which is mainly prepared from the following concrete raw materials in parts by weight: 500 parts of cement, 1200 parts of coarse aggregate, 1300 parts of fine aggregate, 400 parts of water, 250 parts of water, 11-13 parts of expanded graphite, 9-10 parts of modified nano alumina, 89-100 parts of lauric acid, 90-100 parts of absolute ethyl alcohol and 6-10 parts of water reducing agent. In this application, the expanded graphite can adsorb lauric acid and nanometer aluminium oxide, and lauric acid has higher phase transition enthalpy value and thermal stability, can the internal temperature of effective control concrete, prevents fissured production, and the inside gap of concrete can be filled to nanometer aluminium oxide, improves the closely knit degree of concrete, improves the anti cracking performance of concrete.)

1. The anti-crack concrete is characterized by being mainly prepared from the following concrete raw materials in parts by weight: 500 parts of cement, 1200 parts of coarse aggregate, 1300 parts of fine aggregate, 400 parts of water, 250 parts of water, 11-13 parts of expanded graphite, 9-10 parts of modified nano alumina, 89-100 parts of lauric acid, 90-100 parts of absolute ethyl alcohol and 6-10 parts of water reducing agent.

2. The crack-resistant concrete as claimed in claim 1, wherein the modified nano alumina is prepared by treating a nano alumina powder raw material with 85-95% ethanol solution, a pH regulator and a silane coupling agent, wherein the weight ratio of the nano alumina powder raw material to the silane coupling agent is (20-40) to (1-3).

3. The crack-resistant concrete according to claim 2, wherein the pH regulator is acetic acid.

4. The crack-resistant concrete according to claim 1, wherein: the concrete raw material also comprises 1-4 parts by weight of modified carbon fiber, wherein the modified carbon fiber is mainly prepared by processing the carbon fiber raw material with absolute ethyl alcohol, concentrated nitric acid with the mass fraction of 60-70% and a silane coupling agent, and the weight ratio of the carbon fiber raw material to the silane coupling agent is (12-16) to (3-5).

5. The crack-resistant concrete according to claim 4, wherein the silane coupling agent is a coupling agent Si-69.

6. The crack-resistant concrete according to claim 4, wherein the concrete raw material further comprises 4.8 to 5.8 parts of aluminum dihydrogen phosphate.

7. A method for preparing a crack resistant concrete according to any one of claims 1 to 6, comprising the steps of:

s1, preparation of lauric acid-alumina:

1) placing the modified nano-alumina in absolute ethyl alcohol, and performing ultrasonic treatment to disperse the nano-alumina in the absolute ethyl alcohol to obtain a mixture;

2) heating and melting lauric acid to obtain liquid lauric acid;

3) mixing the mixture prepared in the step 1) with the liquid lauric acid prepared in the step 2), and stirring to obtain liquid lauric acid-aluminum oxide;

s2, preparing a lauric acid-alumina/expanded graphite composite phase-change material: mixing the liquid mixture prepared in the step S1 with expanded graphite, cooling and drying to constant weight;

s3, mixing the cement, the coarse aggregate and the fine aggregate to prepare powder;

s4, adding the powder obtained in the step S3, the lauric acid-alumina/expanded graphite obtained in the step S2, a water reducing agent, modified carbon fibers and aluminum dihydrogen phosphate into water, and stirring to obtain the modified carbon fiber.

8. The method for preparing the anti-crack concrete according to claim 7, wherein the modified nano alumina is prepared by the steps of:

s1, mixing the silane coupling agent and the ethanol solution to obtain a mixed solution;

s2, adjusting the pH value of the mixed solution prepared in the step S1 to 4-5 by using a pH adjusting agent, and stirring to obtain an acid solution;

s3, adding the nano-alumina powder raw material into the acidic solution prepared in the step S2, heating to 50-70 ℃, and stirring;

s4, centrifuging, washing and drying.

9. The method for preparing an anti-crack concrete according to claim 8, wherein the modified carbon fiber is prepared by the steps of:

s1, soaking the carbon fiber raw material in absolute ethyl alcohol, ultrasonically cleaning, and drying to constant weight;

s2, soaking the carbon fiber dried in the step S1 in concentrated nitric acid with the mass fraction of 60% -70%, and heating in water bath at 80-90 ℃ for 85-95 min;

s3, washing the carbon fiber heated in the step S2 with water;

s4, soaking the carbon fiber treated in the step S3 in a mixed solution of absolute ethyl alcohol, a Si-69 coupling agent and water at a ratio of 6-8:1.5-2.5:0.7-1.3, stirring at 70-90 ℃, washing with water and drying.

Technical Field

The application relates to the technical field of concrete materials, in particular to anti-crack concrete and a preparation method thereof.

Background

The concrete is usually made by using cement as main cementing material, mixing with water, sand, stone (if necessary, adding chemical additive and mineral admixture) according to a proper proportion, uniformly stirring, compacting, curing and hardening. Concrete is the most used and widely used building material in the world today.

The concrete is used as a heterogeneous brittle material, the shrinkage and cracking phenomena often occur, particularly, in the construction process of reinforced concrete, the concrete shrinks after being solidified and hardened, and the cracking phenomena are generated due to the constraint action of reinforcing steel bars, so that the durability of the concrete is seriously influenced.

In view of the above-mentioned related technologies, people are more and more concerned about how to improve the crack resistance and the safety of use of concrete.

Disclosure of Invention

In order to reduce the generation of concrete cracks, the application provides anti-crack concrete and a preparation method thereof.

In a first aspect, the present application provides an anti-crack concrete, which adopts the following technical scheme:

the anti-crack concrete is mainly prepared from the following concrete raw materials in parts by weight: 500 parts of cement, 1200 parts of coarse aggregate, 1300 parts of fine aggregate, 400 parts of water, 250 parts of water, 11-13 parts of expanded graphite, 9-10 parts of modified nano alumina, 89-100 parts of lauric acid, 90-100 parts of absolute ethyl alcohol and 6-10 parts of water reducing agent.

In conventional concrete, after the internal temperature of the concrete reaches a peak value and then decreases, the concrete generates thermal shrinkage and shrinkage stress, and when the shrinkage stress is greater than tensile stress, the concrete is prone to crack. In the technical scheme, the expanded graphite has high porosity, and can effectively adsorb lauric acid to form the composite phase-change material. Since lauric acid has higher phase transition enthalpy value and thermal stability, the lauric acid is doped into the concrete, so that the internal temperature of the concrete can be effectively controlled, and cracks are prevented from being generated. The nano alumina can fill gaps inside concrete, and the compactness of the concrete is improved, so that the crack resistance of the concrete is improved.

Optionally, the modified nano-alumina is mainly prepared by processing a nano-alumina powder raw material with 85% -95% of ethanol solution, a pH regulator and a silane coupling agent, wherein the weight ratio of the nano-alumina powder raw material to the silane coupling agent is (20-40) to (1-3).

The conventional nano alumina particles are easy to absorb hydroxyl due to higher free energy, and the exposed hydroxyl is contacted with each other to form associated hydroxyl under the action of hydrogen bonds, so that an agglomeration phenomenon is generated, and the nano alumina particles are not easy to disperse in concrete. In the technical scheme, the silane coupling agent is used for modifying the nano aluminum oxide, and hydroxyl on the surface of the nano aluminum oxide is reduced due to the substitution of amino, so that the agglomeration phenomenon caused by the association of hydrogen bonds is reduced, and the dispersibility of the nano aluminum oxide in concrete is improved; in addition, the surface of the modified nano-alumina is wrapped with a silane coupling agent, so that a larger steric hindrance is formed, and a certain inhibiting effect on the agglomeration of the nano-alumina is achieved.

Optionally, the pH adjusting agent is acetic acid.

By adopting the technical scheme, acetic acid is used for pH adjustment, and the acetic acid is partially ionized in water to generate hydrogen ions and acetate ions, so that other ions cannot be introduced to influence the reaction.

Optionally, the concrete raw material further comprises 1-4 parts by weight of modified carbon fibers, wherein the modified carbon fibers are mainly prepared by processing the carbon fiber raw material with absolute ethyl alcohol, 60-70% by mass of concentrated nitric acid and a silane coupling agent, and the weight ratio of the carbon fiber raw material to the silane coupling agent is (12-16) to (3-5).

By adopting the technical scheme, the silane coupling agent is used for modifying the carbon fiber, so that the colloid on the surface of the carbon fiber is removed, and the surface roughness and the activity of the carbon fiber are improved. The modified carbon fiber is added into the concrete, so that the modified carbon fiber can be tightly connected with a concrete matrix, the anti-cracking tensile strength of the concrete is improved, and the concrete is prevented from generating cracks.

Optionally, the silane coupling agent is a coupling agent Si-69.

By adopting the technical scheme, the coupling agent Si-69 is used for modifying the carbon fiber, so that the tensile strength and the tear strength of the carbon fiber can be enhanced.

Optionally, the concrete raw material further comprises 4.8-5.8 parts of aluminum dihydrogen phosphate.

By adopting the technical scheme, the modified carbon fibers and the concrete matrix can be more firmly bonded together by adding the aluminum dihydrogen phosphate. In addition, aluminum dihydrogen phosphate and nano-alumina particles form a compact grid structure, and the crack resistance of the concrete is further improved.

In a second aspect, the application provides a preparation method of anti-crack concrete, which adopts the following technical scheme:

a preparation method of anti-crack concrete comprises the following steps:

s1, preparation of lauric acid-alumina:

1) placing the modified nano-alumina in absolute ethyl alcohol, and performing ultrasonic treatment to disperse the nano-alumina in the absolute ethyl alcohol to obtain a mixture;

2) heating and melting lauric acid to obtain liquid lauric acid;

3) mixing the mixture prepared in the step 1) with the liquid lauric acid prepared in the step 2), and stirring to obtain liquid lauric acid-aluminum oxide;

s2, preparing a lauric acid-alumina/expanded graphite composite phase-change material: mixing the liquid mixture prepared in the step S1 with expanded graphite, cooling and drying to constant weight;

s3, mixing the cement, the coarse aggregate and the fine aggregate to prepare powder;

s4, adding the powder obtained in the step S3, the lauric acid-alumina/expanded graphite obtained in the step S2, a water reducing agent, modified carbon fibers and aluminum dihydrogen phosphate into water, and stirring to obtain the modified carbon fiber.

By adopting the technical scheme, on one hand, the lauric acid is introduced into the nano alumina, and then the lauric acid containing the nano alumina is compounded with the expanded graphite to prepare the lauric acid-alumina/expanded graphite composite phase-change material, so that the hydration heat generated in the cement curing process is absorbed, and the concrete is prevented from cracking; on the other hand, the nano-alumina can fill concrete micro-cracks, improve the compactness of the concrete and contribute to preventing the generation of cracks.

Optionally, the preparation method of the nano aluminum oxide comprises the following steps:

s1, mixing the silane coupling agent and the ethanol solution to obtain a mixed solution;

s2, adjusting the pH value of the mixed solution prepared in the step S1 to 4-5 by using a pH adjusting agent, and stirring to obtain an acid solution;

s3, adding the nano-alumina powder raw material into the acidic solution prepared in the step S2, heating to 50-70 ℃, and stirring;

s4, centrifuging, washing and drying.

By adopting the technical scheme, the silane coupling agent is used for modifying the nano aluminum oxide, the active group amino in the silane coupling agent is grafted to the surface of the nano aluminum oxide, and the hydroxyl adsorbed on the surface of the nano aluminum oxide is replaced and reduced, so that the agglomeration phenomenon caused by hydrogen bond association is reduced, and the modified nano aluminum oxide surface is coated with a layer of organic film to form larger steric hindrance and play a role in inhibiting the agglomeration of the nano aluminum oxide.

Optionally, the preparation method of the carbon fiber comprises the following steps:

s1, soaking the carbon fiber raw material in absolute ethyl alcohol, ultrasonically cleaning, and drying to constant weight;

s2, soaking the carbon fiber dried in the step S1 in concentrated nitric acid with the mass fraction of 60% -70%, and heating in water bath at 80-90 ℃ for 85-95 min;

s3, washing the carbon fiber heated in the step S2 with water;

s4, soaking the carbon fiber treated in the step S3 in a mixed solution of absolute ethyl alcohol, a Si-69 coupling agent and water at a ratio of 6-8:1.5-2.5:0.7-1.3, stirring at 70-90 ℃, washing with water and drying.

By adopting the technical scheme, the carbon fibers are modified, the colloid on the surfaces of the carbon fibers is removed, the roughness and the activity of the surfaces of the carbon fibers are improved, and the carbon fibers are dispersed in concrete more uniformly.

In summary, the present application includes at least one of the following beneficial technical effects:

1. in this application, the expanded graphite can effectively adsorb lauric acid, makes composite phase change material, and lauric acid has higher phase transition enthalpy value and thermal stability, can effectively control the internal temperature of concrete, prevents the production of crack.

2. In this application, the inside gap of concrete can be filled to nanometer aluminium oxide, improves the closely knit degree of concrete, improves the anti cracking performance of concrete.

Detailed Description

Preparation example

Preparation example 1

The raw material of the nano alumina raw material powder adopted in the preparation example is nano alpha-alumina particles with the particle size of 30-60nm and the purity of 99.9 percent; the silane coupling agent is KH-550; the ethanol is 95% ethanol, and is analytically pure; the pH regulator is 5mol/L acetic acid.

The preparation method of the modified nano-alumina of the preparation example comprises the following steps:

s1, dissolving 0.2kg of silane coupling agent KH-550 in 5L of 95% ethanol solution to obtain a mixed solution;

s2, adjusting the pH value of the mixed solution prepared in the step S1 to 5 by using 5mol/L acetic acid, and stirring for 2 hours at 35 ℃ to obtain an acid solution;

s3, weighing 2.0kg of nano alpha-alumina particles, adding the nano alpha-alumina particles into the acidic solution prepared in the step S2, heating to 60 ℃, and continuing stirring for 4 hours;

s4, centrifuging, washing with 95% ethanol solution, and vacuum drying at 70 deg.C for 4 h.

Preparation examples 2 to 3

Preparation of modified nano alumina of preparation examples 2 to 3 referring to preparation example 1, the amounts of the respective raw materials of preparation examples 1 to 3 are shown in table 1.

TABLE 1 amounts of raw materials used in preparation examples 1 to 3

Preparation example	Nano alpha-alumina particles/kg	Silane coupling agent KH-550/kg	Ethanol (volume fraction)
				Preparation example 1	3.0	0.2	95%
Preparation example 2	2.0	0.1	85%
				Preparation example 3	4.0	0.3	90%

Preparation example 4

Preparation example 4 is different from preparation example 1 in that, in step S3, heating was performed to 50 ℃.

Preparation example 5

Preparation example 5 differs from preparation example 1 in that, in step S3, heating was performed to 70 ℃.

Preparation example 6

The carbon fiber raw material adopted by the preparation example is the nano carbon fiber, and the purity is 99.9%; the silane coupling agent is a coupling agent Si-69.

The preparation steps of the modified carbon fiber of the preparation example include:

s1, soaking 5kg of carbon nanofibers in 15L of absolute ethyl alcohol, ultrasonically cleaning for 30min, and drying in an oven at 95 ℃ to constant weight;

s2, soaking the carbon fiber dried in the step S1 in 10L of concentrated nitric acid with the mass fraction of 65%, and heating the carbon fiber in a water bath at 85 ℃ for 90 min;

s3, washing the carbon fiber heated in the step S2 with water;

s4, weighing 7kg of absolute ethyl alcohol, 2kg of coupling agent Si-69 and 1kg of water, mixing and stirring at normal temperature for 30min to obtain a mixed solution of the absolute ethyl alcohol, the coupling agent Si-69 and the water;

and S5, soaking the carbon fiber treated in the step S3 in the mixed liquid prepared in the step S4, stirring the mixture for 3 hours at the temperature of 80 ℃, washing the mixture with water and drying the mixture.

Preparation example 7

Preparation of modified carbon fibers of production examples 7 to 8 referring to production example 6, the amounts of the respective raw materials of production examples 6 to 8 used are shown in Table 2.

TABLE 2 amounts of respective raw materials in preparation examples 6 to 8

Preparation example	Absolute ethanol/kg (step S4)	Coupling agent Si-69/kg	Water/kg	Concentrated nitric acid (mass fraction)
					Preparation example 6	7	2	1	65%
Preparation example 7	6	1.5	0.7	60%
					Preparation example 8	8	2.5	1.3	70%

Preparation example 9

Preparation 9 differs from preparation 6 in that in step S2, it was heated in water bath at 80 ℃ for 85 min; in step S5, stirring is carried out at 70 ℃.

Preparation example 10

Preparation example 10 differs from preparation example 6 in that in step S2, it was heated in a water bath at 90 ℃ for 95 min; in step S5, stirring is carried out at 90 ℃.

Examples

The cement used in the following examples was type P042.5R; the expansion temperature of the expanded graphite is 900 ℃, the expansion multiple is 150-400, and the carbon content is 98.02 percent; the purity of lauric acid is 99%; the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent; the fine aggregate is natural fine sand in a III area, the fineness modulus is 2.2, and the mud content is less than 1.0%; the coarse aggregate is crushed stone with 5-20mm grain size and continuous grading.

Example 1

The anti-crack concrete is prepared from the following raw materials in parts by weight: 4.5kg of cement, 12.5kg of coarse aggregate, 4.3kg of fine aggregate, 2.0kg of water, 0.12kg of expanded graphite, 0.095kg of modified alpha-nano alumina, 0.95kg of lauric acid, 0.02kg of modified carbon fiber, 0.053kg of aluminum dihydrogen phosphate, 0.95kg of anhydrous ethanol and 0.08kg of water reducing agent.

Wherein, the modified nano-alumina is prepared from preparation example 1, and the modified carbon fiber is prepared from preparation example 6.

The preparation method of the anti-crack concrete comprises the following steps:

s1, preparation of lauric acid-alumina:

1) soaking 0.095kg of modified alpha-nano alumina in 0.95kg of absolute ethyl alcohol, and performing ultrasonic treatment in an ultrasonic cleaning instrument for 0.5h to disperse the nano alumina in the absolute ethyl alcohol to obtain a mixture;

2) heating and melting 0.95kg of lauric acid to obtain liquid lauric acid;

3) placing the mixture prepared in the step 1) in the liquid lauric acid prepared in the step 2), heating and stirring for 4 hours in a water bath at 100 ℃ to volatilize the absolute ethyl alcohol, and uniformly dispersing the nano alpha-alumina particles in the liquid lauric acid to obtain liquid lauric acid-alumina;

s2, preparing a lauric acid-alumina/expanded graphite composite phase-change material:

weighing 0.12kg of expanded graphite, mixing the liquid lauric acid-alumina prepared in the step S1 with the expanded graphite, stirring to fully mix the expanded graphite with the liquid lauric acid-alumina, cooling to room temperature, and then placing in a vacuum drying oven at 50 ℃ to dry to constant weight to obtain the lauric acid-alumina/expanded graphite composite phase-change material;

s3, mixing 4.5kg of cement, 12.5kg of coarse aggregate and 4.3kg of fine aggregate to prepare powder;

s4, adding the powder obtained in the step S3, the lauric acid-alumina/expanded graphite composite phase-change material obtained in the step S2 and 0.053kg of aluminum dihydrogen phosphate into 2.0kg of water, and stirring to obtain the composite phase-change material.

Examples 2 to 12

Preparation of examples 2-12 referring to example 1, the amounts of the respective starting materials of examples 1-12 are shown in table 3.

TABLE 3 amounts of raw materials for examples 1-12

Examples	Water (W) Mud/blood pressure device kg	Coarse bone Material/kg	Slender aggregate kg	Water reducing Dosage/kg	Water/liquor kg	Expansive stone Ink/kg	Modified nano-meter Alumina/kg	Lauric acid is greater or less kg	Modified carbon fiber Vitamin/kg	Phosphoric acid bis (ester) Aluminum hydride/kg	Anhydrous second Alcohol/kg
												Example 1	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0.02	0.053	0.95
Example 2	4	12	4	0.06	1.5	0.12	0.095	0.95	0.02	0.053	0.95
												Example 3	5	13	4.6	0.10	2.5	0.12	0.095	0.95	0.02	0.053	0.95
Example 4	4.5	12.5	4.3	0.08	2	0.11	0.09	0.89	0.02	0.053	0.9
												Example 5	4.5	12.5	4.3	0.08	2	0.13	0.1	1	0.02	0.053	1
Example 6	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0.01	0.053	0.95
												Example 7	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0.04	0.053	0.95
Example 8	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0	0.053	0.95
												Example 9	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0.02	0.048	0.95
Examples 10	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0.02	0.058	0.95
												Examples 11	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0.02	0	0.95
Examples 12	4.5	12.5	4.3	0.08	2	0.12	0.095	0.95	0	0	0.95

Examples 13 to 16

Examples 13-16 differ from example 1 in that examples 13-16 each employ a modified nano alumina prepared by preparation examples 2-5.

Examples 17 to 20

Examples 17 to 20 are different from example 1 in that examples 17 to 20 respectively used modified carbon fibers prepared in production examples 7 to 10.

Comparative example

Comparative example 1

Comparative example 1 is different from example 12 in that comparative example 1 does not add expanded graphite, modified nano alumina, lauric acid, modified carbon fiber and aluminum dihydrogen phosphate.

The crack-resistant concrete of comparative example 1 was prepared from the following raw materials by weight: 4.5kg of cement, 12.5kg of coarse aggregate, 4.3kg of fine aggregate, 2.0kg of water and 0.08kg of water reducing agent.

The preparation method of the crack-resistant concrete of comparative example 1 includes the steps of:

s1, mixing 4.5kg of cement, 12.5kg of coarse aggregate and 4.3kg of fine aggregate to prepare powder;

s2, adding the powder prepared in the step S1 and 0.08kg of water reducing agent into 2.0kg of water, and stirring to obtain the water reducing agent.

Comparative example 2

Comparative example 2 differs from example 12 in that comparative example 2 did not add lauric acid and expanded graphite.

The crack-resistant concrete of comparative example 2 was prepared from the following raw materials by weight: 4.5kg of cement, 12.5kg of coarse aggregate, 4.3kg of fine aggregate, 2.0kg of water, 0.095kg of modified nano alumina and 0.08kg of water reducing agent.

Wherein, the modified nano-alumina is prepared from preparation example 1, and the modified carbon fiber is prepared from preparation example 6.

The preparation method of the crack-resistant concrete of comparative example 2 includes the steps of:

s1, mixing 4.5kg of cement, 12.5kg of coarse aggregate and 4.3kg of fine aggregate to prepare powder;

s2, adding the modified nano-alumina, the water reducing agent and the powder prepared in the step S1 into 2.0kg of water, and stirring to obtain the water reducing agent.

Comparative example 3

Comparative example 3 is different from example 1 in that the nano alumina used is a general unmodified nano alpha-alumina having a particle size of 30 to 60 nm.

Performance detection

Referring to GB/T50081-2002 Standard test method for mechanical properties of common concrete, concrete products prepared in examples 1-21 and comparative examples 1-2 are made into a plurality of standard test blocks with the side length of 150mm, and after curing, the concrete products are tested for compressive strength and splitting tensile strength.

1. Compressive strength: the concrete prepared in examples 1-21 and comparative examples 1-2 was tested with reference to GB/T50081-2016, Standard test methods for mechanical Properties of general concrete, and the test results are shown in Table 4.

2. Splitting tensile strength: the concrete prepared in examples 1-21 and comparative examples 1-2 was tested with reference to GB/T50081-2016, Standard test methods for mechanical Properties of general concrete, and the test results are shown in Table 4.

3. Temperature stress test: in the test process, the test piece is in a semi-heat-preservation and heat-insulation state, the size of the test piece is 120mm x 1200mm, two ends of the concrete test piece are clamped by two clamping heads, one end of the concrete test piece is fixed, the other end of the concrete test piece is connected with a stepping motor, when the deformation of the test piece exceeds +/-0.5 microns, a displacement control system operates, the deformation of the test piece is always kept within +/-0.5 microns, and the constraint degree in the test process of the test piece is guaranteed to be 100%. During the test, the temperature of the test piece is increased and then decreased, and the test piece is expanded and then contracted. In the shrinkage process, the test piece generates tensile stress due to constraint, and when the tensile stress is greater than the tensile strength of the test piece, the test piece is broken, and the test is finished. The temperature rise during the test was recorded and the test results are shown in Table 5

TABLE 4 test results of compressive strength and tensile strength at cleavage

Sample numbering	Compressive strength (MPa)	Splitting tensile strength (MPa)	Temperature rise (. degree.C.)
				Example 1	45.3	4.68	11.2
Example 2	44.6	4.65	12.1
				Example 3	45.1	4.57	12.3
Example 4	45.3	4.35	13.5
				Example 5	44.8	4.26	13.8
Example 6	45.2	4.18	11.8
				Example 7	44.6	4.23	11.7
Example 8	42.3	3.31	11.9
				Example 9	44.5	3.56	11.8
Example 10	44.7	3.48	11.6
				Example 11	42.6	3.16	11.6
Example 12	41.5	2.97	11.8
				Example 13	44.8	4.51	11.6
Example 14	44.6	4.43	11.7
				Example 15	43.9	4.39	11.8
Example 16	44.2	4.42	11.9
				Example 17	44.7	4.35	11.7
Example 18	45.0	4.39	11.9
				Example 19	44.3	4.29	11.6
Example 20	44.6	4.35	11.8
				Comparative example 1	37.6	1.56	29.5
Comparative example 2	40.3	2.68	20.6
				Comparative example 3	44.1	4.49	12.5

With reference to examples 1 to 20, comparative example 1 and table 4, the compressive strength and the tensile strength at cleavage of the concrete prepared in examples 1 to 20 were superior to those of the concrete prepared in comparative example 1, and the temperature rise of the concrete prepared in examples 1 to 20 was also lower than that of the concrete prepared in comparative example 1. The higher the splitting tensile strength is, the better the anti-cracking performance of the concrete product is; the lower the temperature rise, the better the crack resistance of the concrete product. Therefore, the concrete prepared in examples 1 to 20 has better crack resistance than the concrete prepared in comparative example 1, wherein the concrete prepared in example 1 has the best crack resistance.

Combining examples 1-3 and table 4, the proportions of cement, coarse aggregate, fine aggregate, water reducing agent and water in the concrete raw materials are changed, the changes of the compressive strength and the splitting tensile strength of the prepared concrete are not obvious, and the temperature rise of example 1 is lower than that of examples 2-3, but the changes are not obvious.

By combining the embodiment 1, the embodiments 4 to 5 and the table 4, the mixture ratio of the expanded graphite, the modified nano alumina and the lauric acid in the concrete raw materials is changed, and when 0.12kg of the expanded graphite, 0.095kg of the modified nano alumina and 0.95kg of the lauric acid are used, the prepared concrete has the best compressive strength and the best splitting tensile strength, the temperature rise change is the lowest, and the effect of reducing the hydration heat of the concrete is the best.

By combining the embodiment 1, the embodiments 6 to 8 and the table 4, the amount of the modified carbon fibers in the concrete raw material is changed, the compressive strength and the splitting tensile strength of the concrete prepared by adding the modified carbon fibers are superior to those of the concrete prepared by not adding the modified carbon fibers, the temperature rise is not obviously changed, and the compressive strength and the splitting tensile strength of the prepared concrete are optimal when 0.02kg of the modified carbon fibers are used.

With reference to example 1, examples 9 to 11 and table 4, the amount of aluminum dihydrogen phosphate in the concrete raw materials was changed, and the compressive strength and the cleavage tensile strength of the concrete prepared by adding aluminum dihydrogen phosphate were superior to those of the concrete prepared without adding aluminum dihydrogen phosphate, and the compressive strength and the cleavage tensile strength of the prepared concrete were the best when 0.053kg of aluminum dihydrogen phosphate was used.

With reference to example 1, example 8, examples 11 to 12 and table 4, the concrete prepared in example 12 (without the addition of the modified carbon fiber and aluminum dihydrogen phosphate) had the lowest compressive strength and tensile strength at cleavage, and the concrete prepared in example 1, example 8 and examples 11 to 12 showed no significant change in temperature rise.

The compressive strength and the split tensile strength of the concrete prepared by using the modified nano alumina prepared in preparation example 1 and the modified carbon fiber prepared in preparation example 6 were both optimal without significant change in temperature rise, in combination with example 1, examples 13 to 20 and table 4.

With reference to example 1, comparative example 3 and table 4, the concrete prepared in example 1 (using modified nano alumina) has better compressive strength and tensile strength at cleavage than the concrete prepared in comparative example 3 (using unmodified nano alumina), and the concrete prepared in example 1 (using modified nano alumina) has lower temperature rise than the concrete prepared in comparative example 3 (using unmodified nano alumina), which indicates that the modified nano alumina has a certain effect of reducing the hydration heat of the concrete and a significant effect of enhancing the compressive strength and tensile strength at cleavage of the concrete.

By combining the example 12 with the comparative examples 1-2 and table 4, the temperature rise of the concrete prepared in the example 12 (adding the expanded graphite, the modified nano alumina and the lauric acid) is obviously lower than that of the concrete prepared in the comparative example 2 (adding the modified nano alumina, the non-added expanded graphite and the lauric acid) and the comparative example 1 (not adding the expanded graphite, the modified nano alumina and the lauric acid), and the temperature rise of the concrete prepared in the comparative example 2 is lower than that of the concrete prepared in the comparative example 1, which shows that the composite phase change material prepared from the lauric acid and the expanded graphite has a remarkable effect on reducing the hydration heat of the concrete, and the introduced modified nano alumina also plays a certain role in reducing the hydration heat of the concrete, so that the generation of concrete cracks is reduced;

the compression strength and the splitting tensile strength of the concrete prepared in the example 12 are not obviously changed from those of the concrete prepared in the comparative example 2, the compression strength and the splitting tensile strength of the concrete prepared in the comparative example 2 are better than those of the concrete prepared in the comparative example 1, and the modified nano alumina is favorable for improving the compression strength and the splitting tensile strength of the concrete to a certain extent.

The above embodiments are preferred embodiments of the present application, and the protection scope of the present application is not limited by the above embodiments, so: all equivalent changes made according to the structure, shape and principle of the present application shall be covered by the protection scope of the present application.