Internal curing concrete applied to cold and arid regions and preparation method of internal curing concrete

Abstract

The invention discloses internal curing concrete applied to cold and arid regions and a preparation method thereof, and belongs to the technical field of internal curing concrete. The concrete is prepared from the following components in parts by weight: 300 to 340 parts of cement, 65 to 85 parts of fly ash, 700 to 750 parts of fine aggregate, 250 to 300 parts of gravel with the particle size of 5 to 10 mm, 650 to 700 parts of gravel with the particle size of 10 to 20 mm, 145 to 165 parts of water, 5 to 7 parts of high efficiency water reducing agent, 0.3 to 0.6 part of air entraining agent, 16 to 24 parts of micro-expanding agent and 1.2 to 2.0 parts of SAPO (silicoaluminophosphate). According to the technical scheme, the micro-expanding agent composed of 250-400 [mu] m spherical SAP and caustic calcined magnesite and dead calcined magnesite in a specific proportion can sufficiently resist plastic shrinkage in the early stage under the cold and drought curing condition, and expands in the later stage to compensate long-term shrinkage and repair SAP residual pores and air entraining defects in situ, so that the anti-freezing property of the SAP is greatly improved on the premise that the freezing resistance is not sacrificed, and the service life of the SAP is prolonged. And under large-temperature-difference curing, excellent crack resistance and compression resistance can be obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of internal curing concrete, and particularly relates to internal curing concrete applied to cold and arid regions and a preparation method thereof. BACKGROUND

[0003] In recent years, with the highway construction turning from plains to mountainous areas, especially the rapid development of the transportation industry in the northwest region to be further developed, the construction of some major transportation infrastructure projects has attracted close attention from the engineering field. In view of the complex climate environment in the northwest region, such as large temperature difference, dryness, and strong wind, the evaporation of water in the cement concrete is accelerated, which leads to a series of problems such as increased shrinkage deformation of concrete, limited strength development, and external erosion, which seriously affect the service life.

[0004] In order to resist the low temperature and freeze-thaw cycle in winter and at night in the northwest region, the existing concrete must be mixed with air entraining agent. The air entraining agent introduces a large number of small and closed bubbles in the concrete, which serves as a buffer space when water freezes and expands, which is the key to improving the frost resistance and durability of the concrete. However, in order to provide frost resistance, the ability of the concrete to resist early shrinkage cracking is weakened. Therefore, super absorbent polymer (SAP) is introduced as an “internal curing” material. However, SAP with too fine particle size will absorb too much water, causing a decrease in the local water-binder ratio and affecting the establishment of early strength. SAP with too large particle size will leave holes after water release, which will greatly affect the later strength. In order to compensate for the dry shrinkage and self-shrinkage in the middle and later stages, a micro-expanding agent is added. However, due to the early cracking in the northwest cold and arid region, the micro-expanding agent has not started at the time when early cracking needs to be prevented. Therefore, for the northwest cold and arid region, the early cracking of concrete is not caused by a single factor. The conventional technical means of the existing technology will inevitably trigger or exacerbate another contradiction.

[0005] That is, the air entraining agent introduced to resist freeze-thaw risk will weaken the early strength needed for concrete to resist shrinkage stress, greatly increasing the risk of early cracking. In order to prevent shrinkage, an expanding agent is added. However, cracking often occurs in the northwest region before the final setting of the concrete, and at this time the expanding agent has not yet taken effect. Moreover, the hydration reaction of the expanding agent itself needs to consume water. In the cold and arid region where the mixing water is already in short supply due to severe evaporation, the addition of the expanding agent will compete with the cement particles for the limited water, which will further reduce the effective water-binder ratio and inhibit the normal hydration of the cement, thereby affecting the development of early strength. In order to solve the internal drying and promote long-term hydration, the skilled person in the art also thinks of adding superabsorbent resin SAP for internal curing; and the fine SAP needs a large amount of water in the early stage of mixing, which will lead to a decrease in the water necessary for the hydration of cement particles in the early hydration stage, resulting in delayed hydration and reduced early strength; and if the particle size is large, the SAP indeed benefits from the release of water for "internal curing" in the later stage, but after the release of water, a micron-sized hole defect will inevitably be left in situ, which becomes a weak point and a stress concentration source in the structure.

[0006] In summary, in the northwest cold and arid region, the early cracking of concrete is not caused by a single factor, but by the coupling of multiple physical and chemical factors, and any conventional means in the prior art that attempts to solve a single problem will inevitably fall into the dilemma of pressing down the gourd to float the dipper.

[0007] The prior art has a Chinese invention patent with application number: 201310289190.9, which discloses a hydration heat inhibition type concrete expansion material and its preparation method and application, which comprises an expansion agent, a hydration heat inhibitor and an internal curing agent. When the internal curing agent is internally mixed, it is a mixture of 92wt%-94wt% expansion agent, 2wt%-5wt% hydration heat inhibitor and 1wt%-6wt% internal curing agent; when the internal curing agent is externally mixed, it is a mixture of 95.5wt%-99wt% expansion agent and 1wt%-4.5wt% hydration heat inhibitor, and a separately packaged internal curing agent, and the amount of internal curing agent is 0.05wt%-0.3wt% of the total amount of expansion agent and hydration heat inhibitor mixture.

[0008] The above-mentioned prior art discloses an expansion material composed of an expansion agent, a hydration heat inhibitor and an internal curing agent (SAP); but its core is to pre-mix the three functions, the particle size of SAP is 100-120 mesh, and the water absorption rate is >400mL / g, which belongs to the conventional high water absorption SAP; and the expansion agent contains multiple components (calcium oxide, calcium sulphoaluminate, etc.), which also aims to provide expansion throughout the age; only the components that can solve their own problems are combined, and the cracking and strength problems of internal curing concrete in cold and arid regions cannot be solved.

[0009] There is currently no preparation method for concrete in the northwest cold and arid region under the environment of low temperature, large temperature difference and severe evaporation, therefore, in order to fill the technical gap in the market, the present application provides an internal curing concrete applied in cold and arid regions and a preparation method thereof. SUMMARY

[0010] To solve the defects in the prior art, the present application provides an internal curing concrete for cold and arid regions and a preparation method thereof.The internal curing concrete for cold and arid regions comprises, by weight fraction, cement 300-340 parts, fly ash 65-85 parts, fine aggregate 700-750 parts, 5-10 mm crushed stone 250-300 parts, 10-20 mm crushed stone 650-700 parts, water 145-165 parts, high-efficiency water reducing agent 5-7 parts, air entraining agent 0.3-0.6 parts, micro-expansion agent 16-24 parts, and SAP 1.2-2.0 parts.

[0011] The cement is P·0 42.5 ordinary portland cement. The fly ash is I-class fly ash, and has a fineness of 11%, a loss on ignition of 4.2%, a water requirement of 93%, a free calcium oxide content of 0.9%, and a 28d activity index of 75%. The fine aggregate has a fineness modulus of 2.69, an apparent density of 2642 kg / m, and a clay content of not more than 0.6%.

[0012] The crushed stone is granite crushed stone, and has a clay content of 0.2%, a needle flake content of 2.3%, and a crushing value of 11%.

[0013] The water reducing agent is a polycarboxylic acid high-performance water reducing agent, and has a water-reducing rate of 24%. The micro-expansion agent is composed of light-burned magnesium and heavy-burned magnesium. The light-burned magnesium is prepared by calcining magnesite at 700-1000 DEG C for 3h, and has a MgO content of not less than 92wt%. The heavy-burned magnesium is prepared by calcining magnesite at 1400-1800 DEG C for 3h, and has a MgO content of not less than 92wt%.

[0014] The light-burned magnesium and the heavy-burned magnesium have an average particle size of 100-150 mu m. The SAP is a polyacrylic acid sodium salt type superabsorbent resin. The SAP is prepared by inverse suspension polymerization. The SAP is in a spherical shape, and has a particle size of 250-400 mu m.

[0015] The application relates to a preparation method of internal curing concrete applied in cold and arid regions, which comprises the following steps: firstly, mixing SAP and a micro-expansion agent to prepare a mixture; then, starting a mixer, putting all the gravel and fine aggregates of different particle sizes into the mixer, and dry-mixing for 2-3 minutes to uniformly distribute the aggregates; continuously keeping the mixer, putting the weighed cement and fly ash into the mixer, and continuously dry-mixing for 2-3 minutes; then, keeping the dry-mixing, putting the SAP and the micro-expansion agent into the mixer, and stirring for 1-2 minutes; then, slowly and uniformly adding most of the water and the high-efficiency water reducing agent, continuously wet-mixing for 2 minutes after the addition is completed, and finally mixing the residual water and the air entraining agent, and then adding the mixture into the mixer, and continuously stirring for 1 minute, so that the internal curing concrete applied in the cold and arid regions is prepared.

[0016] The SAP and the micro-expansion agent are put into a double-helix conical mixer during the mixing process, and are dry-mixed at a low speed for 3-5 minutes to be uniformly mixed.

[0017] The application has the following beneficial effects: 1. The application realizes the solution to the internal contradiction among the frost resistance, crack resistance, internal curing and strength development of the internal curing concrete in the cold and arid regions under the curing conditions in the cold and arid regions by optimizing the concrete component formula under the specific component, specific particle size and specific proportion. 2. The hole defects left by the SAP are filled by the dense Mg(OH)2 crystals and the later C-S-H gel generated by the micro-expansion agent, so that the stress concentration source is eliminated, the beneficial micro-prestress is applied to the surrounding matrix by the micro-expansion effect under the cold and arid curing conditions, the early strength loss problem caused by the air entraining and the time mismatching problem possibly existing in the expansion process of the micro-expansion agent are solved, and the components can effectively couple and synergize under the cold and arid curing conditions. 3. The technical scheme of the application can resist the plastic shrinkage in the early stage and compensate the long-term shrinkage and in-situ repair the SAP residual pores and air entraining defects in the later stage under the cold and arid curing conditions, so that the excellent crack resistance and compression resistance can be achieved under the large temperature difference curing without sacrificing the frost resistance. DETAILED DESCRIPTION

[0018] In order to make the objects, technical solutions and advantages of the present application clearer, below, the present application is further described in detail in conjunction with embodiments, the illustrative embodiments and the description thereof are only used to explain the present application, and do not limit the present application. In addition, for the numerical range in the present application, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or stated range and any other stated value or intermediate value in the stated range is also included in the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict between the content of the specification and that of any document incorporated herein by reference, the content of the specification prevails.

[0020] Various modifications and changes can be made to the specific implementation of the present application described in this specification without departing from the scope or spirit of the application. Other implementations of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given herein are exemplary only.

[0021] As used herein, the terms “comprises”, “comprising”, “includes”, “including”, “has”, “having”, and the like are open-ended terms that are intended to denote the inclusion of elements or steps without excluding other elements or steps.

[0022] The “parts” indicated in the following examples are all weight parts.

[0023] Example 1 An internal curing concrete applied in cold and arid regions, the concrete comprises, by weight fraction: cement 300 parts, fly ash 65 parts, fine aggregate 700 parts, 5-10 mm gravel 250 parts, 10-20 mm gravel 650 parts, water 145 parts, high efficiency water reducing agent 5.0 parts, air entraining agent 0.3 parts, micro-expansion agent 15 parts, SAP 1.2 parts; The cement is P·0 42.5 ordinary portland cement; The fly ash is I-class fly ash, the fineness of the fly ash is 11%, the loss on ignition of the fly ash is 4.2%, the water requirement of the fly ash is 93%, the free calcium oxide content of the fly ash is 0.9%, and the 28d activity index of the fly ash is 75%; The fineness modulus of the fine aggregate is 2.69, the apparent density is 2642 kg / m, and the clay content is not more than 0.6%.

[0024] The crushed stone is granite crushed stone, the clay content is 0.2%, the needle flake content is 2.3%, and the crushing value is 11%.

[0025] The water reducing agent is a polycarboxylic acid high-performance water reducing agent, and the water reducing rate of the water reducing agent is 24%.

[0026] The micro-expansion agent is composed of light-burned magnesium and heavy-burned magnesium.

[0027] The light-burned magnesium is prepared by calcining magnesite at 700-1000℃ for 3h, and the MgO content in the light-burned magnesium is ≥92wt%; The heavy-burned magnesium is prepared by calcining magnesite at 1400-1800℃ for 3h, and the MgO content in the heavy-burned magnesium is ≥92wt%.

[0028] The average particle size of the light-burned magnesium and the heavy-burned magnesium is 100-150μm.

[0029] The SAP is a polyacrylic acid sodium salt type superabsorbent resin; the SAP is polymerized by a reverse-phase suspension polymerization method; The SAP is purchased from Qingdao Shouke New Material Co., Ltd.

[0030] The micro-expansion agent includes light-burned magnesium and heavy-burned magnesium, and the mass ratio of the light-burned magnesium to the heavy-burned magnesium is 1:2. The particle size of the SAP is 250μm.

[0031] A preparation method of an internal curing concrete applied in cold and arid regions: first, the SAP and the micro-expansion agent are put into a double-spiral conical mixer, and dry-mixed at a low speed for 3-5 minutes; after being fully mixed, they are reserved; then, the mixer is started, the crushed stone and the fine aggregate with all particle sizes are put into the mixer, and dry-mixed for 2-3 minutes to make the aggregate uniformly distributed; the mixing is continuously maintained, the cement and the fly ash are put into the mixer, and dry-mixed for 2-3 minutes; then, the dry-mixing is maintained, the SAP and the micro-expansion agent are put into the mixer and stirred for 1-2 minutes; then, most of the water and the high-efficiency water reducing agent are slowly and uniformly added, after the addition is completed, wet-mixing is continuously maintained for 2 minutes, finally, the remaining water and the air entraining agent are mixed and then added into the mixer, and the mixing is continuously maintained for 1 minute, thereby obtaining an internal curing concrete applied in cold and arid regions.

[0032] Example 2 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete includes: Cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts; The micro-expansion agent in the example 2 includes light burned magnesium and heavy burned magnesium, and the mass ratio of the light burned magnesium to the heavy burned magnesium is 1:3.

[0033] Example 3 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: Cement 325 parts, fly ash 80 parts, fine aggregate 740 parts, 5-10mm gravel 285 parts, 10-20mm gravel 685 parts, water 160 parts, high efficiency water reducing agent 6.5 parts, air entraining agent 0.5 parts, micro-expansion agent 20 parts, SAP 1.8 parts; The micro-expansion agent in the example 3 includes light burned magnesium and heavy burned magnesium, and the mass ratio of the light burned magnesium to the heavy burned magnesium is 1:4.

[0034] Example 4 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: Cement 340 parts, fly ash 85 parts, fine aggregate 750 parts, 5-10mm gravel 300 parts, 10-20mm gravel 700 parts, water 165 parts, high efficiency water reducing agent 7 parts, air entraining agent 0.6 parts, micro-expansion agent 25 parts, SAP 2 parts; The micro-expansion agent in the example 4 includes light burned magnesium and heavy burned magnesium, and the mass ratio of the light burned magnesium to the heavy burned magnesium is 1:4.

[0035] Example 5 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: Cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts, SAP 1.5 parts; The particle size of the SAP is 300 microns; The example 5 is based on the example 2, and the difference is that the addition of the micro-expansion agent is omitted.

[0036] Example 6 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: Cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, superplasticizer 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts; The micro-expansion agent comprises light-burned magnesium and heavy-burned magnesium, wherein the mass ratio of the light-burned magnesium to the heavy-burned magnesium is 1:3. The example 5 is based on the example 2, and the difference is that the addition of the SAP is omitted.

[0037] Example 7 An internal curing concrete applied to cold and arid regions, according to weight parts, the concrete comprises: Cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, superplasticizer 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts; The micro-expansion agent comprises light-burned magnesium and heavy-burned magnesium, wherein the mass ratio of the light-burned magnesium to the heavy-burned magnesium is 1:1. The particle size of the SAP is 300 microns.

[0038] Example 8 An internal curing concrete applied to cold and arid regions, according to weight parts, the concrete comprises: Cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, superplasticizer 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts; The micro-expansion agent comprises light-burned magnesium and heavy-burned magnesium, wherein the mass ratio of the light-burned magnesium to the heavy-burned magnesium is 1:5. The particle size of the SAP is 300 microns.

[0039] Example 9 An internal curing concrete applied to cold and arid regions, according to weight parts, the concrete comprises: Cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, superplasticizer 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts; The micro-expansion agent comprises light-burned magnesium and heavy-burned magnesium, wherein the mass ratio of the light-burned magnesium to the heavy-burned magnesium is 1:9. The particle size of the SAP is 300 microns.

[0040] Comparative example 1 An internal curing concrete applied to cold and arid regions, according to weight parts, the concrete comprises: cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts; The comparative example 1 is based on the example 2, the difference is that the air entraining agent, the micro-expansion agent, and the SAP are omitted.

[0041] Comparative example 2 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts; The comparative example 2 is based on the comparative example 1, and 0.4 parts of the air entraining agent is added on the basis of the comparative example 1.

[0042] Comparative example 3 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts; The comparative example 3 is based on the comparative example 2, and 16 parts of the micro-expansion agent is added on the basis of the comparative example 2. The micro-expansion agent is light burned magnesium: heavy burned magnesium = 1:3.

[0043] Comparative example 4 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10mm gravel 265 parts, 10-20mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts, SAP 1.5 parts; The particle size of the SAP is 150 microns; The comparative example 4 is based on the comparative example 2, and 1.5 parts of the SAP with the particle size of 150 microns is added on the basis of the comparative example 2.

[0044] Comparative example 5 An internal curing concrete applied in cold and arid regions, according to weight parts, the concrete comprises: cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10 mm gravel 265 parts, 10-20 mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts; The particle size of the SAP is 150 microns; The comparative example 5 is based on the comparative example 4, and the micro-expansion agent is added to the comparative example 4; The micro-expansion agent is pure MgO with a single active component, and the average particle size is 100-150 microns.

[0045] Comparative example 6 An internally curing concrete applied to cold and arid regions, according to weight parts, the concrete comprises: cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10 mm gravel 265 parts, 10-20 mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts; The micro-expansion agent comprises light burned magnesium and heavy burned magnesium, and the mass ratio of the light burned magnesium to the heavy burned magnesium is 1:3; The comparative example 6 is based on the comparative example 3, and the irregular powder SAP polymerized by the aqueous solution polymerization method is additionally added, and the SAP can pass through a 250-400 micron sieve.

[0046] Comparative example 7 An internally curing concrete applied to cold and arid regions, according to weight parts, the concrete comprises: cement 315 parts, fly ash 72 parts, fine aggregate 720 parts, 5-10 mm gravel 265 parts, 10-20 mm gravel 670 parts, water 155 parts, high efficiency water reducing agent 6 parts, air entraining agent 0.4 parts, micro-expansion agent 16 parts, SAP 1.5 parts The micro-expansion agent comprises light burned magnesium and heavy burned magnesium, and the mass ratio of the light burned magnesium to the heavy burned magnesium is 1:3; The comparative example 7 is based on the comparative example 3, and the SAP is a fine particle size spherical SAP with a particle size less than 60 microns.

[0047] Test example 1 The slump test is carried out according to the provisions of GB / T 50080 “Test methods for performance of ordinary concrete mixture”, the initial slump is obtained first, then the concrete is stored under normal temperature and pressure, the corresponding slump is tested at 60 min, and the slump loss rate is calculated, and the calculation method is (initial slump-60 min slump) x 100% / initial slump; Reference GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the performance test of 7-day flexural tensile strength, 28-day flexural tensile strength and 28-day compressive strength is completed; Reference GB / T 50164 "Standard for Quality Control of Concrete", the performance test of 28-day chloride ion migration coefficient is completed. Reference GB / T 50082 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", 28d shrinkage data is tested; Reference GB / T 50082 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", the obtained concrete is subjected to freeze-thaw resistance experiment, and the mass before and after 100 freeze-thaw cycles is weighed to calculate the mass loss rate, wherein the greater the mass loss rate, the worse the freeze-thaw resistance of the concrete; Reference GB / T 50082 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", the crack resistance grade of the concrete is determined, and the evaluation index of the crack resistance grade of the concrete is: L-I (serious early cracking of concrete, high risk), L-II (high risk of early cracking of concrete), L-III (general risk of early cracking of concrete), L-IV (low risk of early cracking of concrete), and L-V (excellent early cracking resistance of concrete, very low risk).

[0048] The preparation methods of the test blocks of Examples 1-9 and Comparative Examples 1-7 all refer to a preparation method of an internal curing concrete applied in cold and arid regions.

[0049] Simulated curing cycle conditions in cold and arid regions: to simulate the diurnal temperature difference change in cold and arid regions, the curing cycle is set to 24 hours, and the specific conditions are as follows: 1. Initial stage: the temperature is kept at 0℃ for 1 hour; 2. Heating stage: the temperature is raised to 20℃ at a rate of 5℃ / h, and then maintained for 3 hours; 3. Cooling stage: the temperature is lowered to -20℃ at a rate of 5℃ / h, and then maintained for 3 hours; 4. Warm-up stage: the temperature is raised to 0℃ at a rate of 5℃ / h, and then maintained for 1 hour.

[0050] During the curing period, the humidity in the environmental chamber is natural humidity, which is not actively controlled.

[0051] The test blocks obtained by curing under the simulated curing cycle conditions in cold and arid regions are tested for their various properties, and the results are shown in Tables 1 and 2; Table 1 Table 2 Performance test analysis: under the simulated maintenance cycle conditions in cold and arid regions, the freeze-thaw cycle mass loss rate of Comparative Example 2 after adding air entraining agent is greatly reduced, which shows that the addition of air entraining agent can significantly improve the freeze-thaw resistance of concrete; although the shrinkage rate of Comparative Example 3 is improved to a certain extent after adding the micro-expanding agent, the anti-cracking grade is still poor, and only the addition of the micro-expanding agent cannot effectively inhibit the plastic and autogenous shrinkage cracking caused by severe temperature difference and evaporation in the early stage of concrete; the 60-minute slump loss rate of Comparative Example 4 after adding the fine-particle SAP is as high as 22.7%, which is much higher than that of Comparative Example 2 (13.1%); and the 7-day flexural strength is as low as 1.9 MPa, which is the worst among all groups; which shows that the selection of conventional fine-particle SAP and the cement matrix have a fierce water competition effect, which affects the workability of the concrete and the establishment of early strength.

[0052] Comparative Example 6 uses irregular powder SAP polymerized by aqueous solution polymerization, which can pass through a 250-400 micron sieve; because its shape is irregular powder, it has a larger specific surface area, and its dispersibility in concrete, local water film thickness and pore morphology after water release are essentially different from spherical SAP; it cannot well produce efficient synergistic effect with the micro-expanding agent; Comparative Example 7 uses ultra-fine particle SAP, and its comprehensive performance is worse than that of Comparative Example 5.

[0053] The inventors surprisingly found that when the core scheme of the present application is adopted, that is, the specific coarse particle size 250-400 μm spherical SAP and the specific ratio of micro-expanding agent (light burned magnesium: heavy burned magnesium mass ratio of 1:2 to 1:4) are compounded and added to MgO, and under the cold and arid maintenance conditions, the performance of the concrete has a qualitative leap and unexpected technical effect.

[0054] As in Example 2 of the present application, the 60-minute slump loss rate is only 8.8%, the 7-day flexural strength is as high as 4.2 MPa, the 28-day compressive strength reaches 54.2 MPa, the 28-day shrinkage rate is as low as 0.012%, the freeze-thaw mass loss rate is only 1.3%, and the anti-cracking grade reaches L-V performance, and all performance indicators are significantly excellent.

[0055] Examples 1-4 of the present application show excellent comprehensive performance under the simulated maintenance cycle conditions in cold and arid regions, the anti-cracking grade reaches L-V, the freeze-thaw mass loss rate is controlled within 1.8%, and the 28-day compressive strength exceeds 51 MPa.

[0056] Test Example 2 The test block obtained by adopting the standard maintenance cycle condition maintenance is maintained at 20℃ and 95% humidity, and each performance is tested, and the performance test results are shown in Tables 3 and 4. Table 3 Table 4 Performance test analysis: after the standard maintenance condition, the moisture and temperature conditions are good, and the comparative example 5 exhibits high compressive strength, bending tensile strength and good crack resistance; after the standard maintenance, the compressive strength of the application example 2 is even reduced by 3.4%, and the compressive strength of the comparative example 5 is increased by 25.4% after the standard maintenance; under the standard maintenance condition, the optimal micro-expansion agent ratio is example 7, and the compressive strength reaches 53.4 MPa, and the optimal compressive strength of example 2 under the simulation maintenance cycle condition in the non-cold and arid region is 52.4 MPa; this shows that the ratio selected by the application is not the optimal solution in the general case, but the result of precise regulation and control for the specific contradictions in the cold and arid region.

[0057] The conventional anti-freezing scheme in the prior art, such as the comparative example 2, exhibits a freeze-thaw cycle quality loss rate of 1.5% under the standard maintenance, but under the simulation cold and arid maintenance, the formation of early micro-cracks cannot be inhibited, and the cumulative damage leads to a sharp deterioration of the final anti-freezing performance.

[0058] In sharp contrast, the unique formula of the application example 2 can effectively inhibit early damage, so that it can still maintain excellent crack resistance and freeze-thaw resistance after experiencing severe cold and arid maintenance; and this ability to maintain performance stability in extreme environments is not achieved by the prior art, directly proving that the application solves the long-term technical problem in the field. Through a large number of creative experimental researches, a synergistic enhancement mechanism between a specific physical form and particle size of SAP and a specific micro-expansion agent formula under cold and arid maintenance conditions is utilized.

[0059] The application scheme is not the optimal choice of each performance under the conventional maintenance environment, but when placed under the simulation maintenance cycle condition in the cold and arid region, the synergistic mechanism of the application is fully activated, and an unexpected technical effect is produced; it is not a simple combination and optimization of the prior art, but it systematically solves the internal contradictions in the prior art. And the performance exhibited by examples 7, 8 and 9 shows that there is a narrow and unconventional optimal ratio window in the ratio of SAP particle size and micro-expansion agent, which fully proves that the technical scheme of the application cannot be predicted by any conventional screening or simple combination, and it is completed by the inventors' great creative labor.

[0060] In summary, the inventiveness of the present application lies in that the inventors do not simply make a routine optimization on the components of the concrete, but deeply understand and first solve the contradictory problems existing among the frost resistance, strength and crack resistance of the concrete material in the northwest cold and arid region.

[0061] The above detailed description further explains the purpose, technical scheme and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An internally cured concrete for use in cold and arid regions, characterized in that, By weight, the internally cured concrete comprises: 300-340 parts cement, 65-85 parts fly ash, 700-750 parts fine aggregate, 250-300 parts 5-10mm crushed stone, 650-700 parts 10-20mm crushed stone, 145-165 parts water, 5-7 parts high-efficiency water-reducing agent, 0.3-0.6 parts air-entraining agent, 16-24 parts micro-expansion agent, and 1.2-2.0 parts SAP.

2. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The micro-expansion agent includes lightly calcined magnesium and heavily calcined magnesium, wherein the mass ratio of lightly calcined magnesium to heavily calcined magnesium is 1:2-1:

4.

3. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The SAP is a sodium polyacrylate superabsorbent resin.

4. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The SAP is polymerized using reverse suspension polymerization.

5. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The SAP is spherical with a particle size of 250-400 μm.

6. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The internally cured concrete comprises: 315 parts cement, 72 parts fly ash, 720 parts fine aggregate, 265 parts 5-10mm crushed stone, 670 parts 10-20mm crushed stone, 155 parts water, 6 parts high-efficiency water-reducing agent, 0.4 parts air-entraining agent, 16 parts micro-expansion agent, and 1.5 parts SAP.

7. The internally cured concrete for use in cold and arid regions according to claim 6, characterized in that, The micro-expanding agent comprises lightly calcined magnesium and heavily calcined magnesium, wherein the mass ratio of lightly calcined magnesium to heavily calcined magnesium is 1:3; the particle size of the SAP is 300 μm.

8. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The fly ash is Grade I fly ash, with a fineness of 11%, a loss on ignition of 4.2%, a water requirement of 93%, a free calcium oxide content of 0.9%, and a 28-day activity index of 75%.

9. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The fine aggregate has a fineness modulus of 2.69, an apparent density of 2642 kg / m³, and a mud content of no more than 0.6%.

10. The internally cured concrete for use in cold and arid regions according to claim 1, characterized in that, The crushed stone is granite crushed stone with a mud content of 0.2%, a needle-like and flaky content of 2.3%, and a crushing value of 11%.

11. The internally cured concrete for use in cold and arid regions according to claim 2, characterized in that, The lightly calcined magnesium is prepared by calcining magnesite at 700-1000℃ for 3 hours, and the MgO content in the lightly calcined magnesium is ≥92wt%.

12. The internally cured concrete for use in cold and arid regions according to claim 2, characterized in that, The recalcined magnesium is prepared by calcining magnesite at 1400-1800℃ for 3 hours, and the MgO content in the recalcined magnesium is ≥92wt%.

13. The internally cured concrete for use in cold and arid regions according to claim 2, characterized in that, The average particle size of the lightly calcined magnesium and the heavily calcined magnesium is 100-150 μm.

14. The method for preparing internally cured concrete for use in cold and arid regions according to any one of claims 1-13, characterized in that, Includes the following steps: First, thoroughly mix SAP and micro-expansion agent and set aside. Then, start the mixer and add the weighed crushed stone and fine aggregate of all sizes into the mixer. Dry mix for 2-3 minutes to ensure uniform aggregate distribution. Continue mixing and add the weighed cement and fly ash into the mixer. Continue dry mixing for 2-3 minutes. Then, while maintaining dry mixing, add SAP and micro-expansion agent and mix for 1-2 minutes. Next, slowly and evenly add most of the water and high-efficiency water-reducing agent. After adding all the water, continue wet mixing for 2 minutes. Finally, mix the remaining water and air-entraining agent and add them back into the mixer. Continue mixing for 1 minute to prepare an internally cured concrete suitable for cold and arid regions.

15. The method for preparing internally cured concrete for use in cold and arid regions according to claim 14, characterized in that, During the mixing process, the SAP and micro-expanding agent are added to a double-helix conical mixer and dry-mixed at low speed for 3-5 minutes to ensure thorough mixing.

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