Preparation method of anti-freezing concrete suitable for high-altitude environment

Abstract

The invention discloses a preparation method of anti-freezing concrete suitable for a high-altitude environment. The preparation method comprises the following steps: firstly, carrying out pre-water absorption treatment on coarse aggregate to obtain pre-treated coarse aggregate, wherein the pre-water absorption rate is 1.5 times of the saturated surface dry water absorption rate; mixing the anti-freezing fiber and the bubble stabilizer; and finally adding the cementing material, the water, the fine aggregate and the additive, and mixing to obtain the concrete. The bubble stabilizer is superfine particles, and the anti-freezing fibers comprise low-elastic-modulus fibers and high-elastic-modulus fibers. By adding the fiber combination, the air entraining agent can be assisted in introducing more beneficial bubbles in the stirring process, a dense network is formed in a concrete mixture and a cement matrix, the bubbles introduced under low air pressure are prevented from overflowing, and meanwhile, the air hole structure of the concrete is optimized through the bubble stabilizer to maintain the air content of the concrete. The fiber composition has a synergistic effect in the hardened concrete, and under the combined action of the fiber composition and the hardened concrete, the anti-freezing durability of the concrete in the high-altitude low-air-pressure environment is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete engineering applications, and specifically relates to a method for preparing frost-resistant concrete applicable to high-altitude environments. Background Art

[0002] Freeze-thaw damage is the main form of damage to concrete in high-altitude areas. Under the characteristic climatic conditions of high altitudes, concrete will undergo frequent freeze-thaw cycles, and concrete is prone to freeze-thaw damage. Once damaged, it will flake off in large areas, accompanied by other diseases such as leakage and carbonation, which will cause the building to fail to perform its due functions and ultimately affect its safe use. Therefore, the frost resistance of concrete in high-altitude areas is an important indicator of the durability of concrete and is also a comprehensive performance indicator. High frost resistance means high durability of concrete.

[0003] Currently, the commonly used method to improve frost-resistant durability is to increase the air content of concrete. However, there are problems in introducing and maintaining bubbles in the low-pressure environment of high-altitude areas. Increasing the dosage of air-entraining agent and adding bubble stabilizers can increase the air content of concrete, but the quality of the introduced pore system will decline, and the proportion of bubbles beneficial to frost resistance is not high, resulting in limited improvement in durability. Summary of the Invention

[0004] In view of the problems existing in the above background art, the present invention provides a method for preparing frost-resistant concrete applicable to high-altitude environments, by pre-treating the coarse aggregate of high-altitude concrete and incorporating a combination of bubble stabilizer and frost-resistant fiber on the basis of air-entrained concrete.

[0005] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0006] A frost-resistant concrete applicable to high-altitude environments is obtained by incorporating frost-resistant fiber and bubble stabilizer into the pre-treated coarse aggregate, and then adding cementitious material, water, fine aggregate and admixture for mixing;

[0007] The water-binder ratio of the high-altitude frost-resistant concrete is less than 0.45, and the air content is greater than 3%; the mix proportion of each component needs to be adjusted according to the properties of the actual aggregate used;

[0008] The method for pre-treating the coarse aggregate includes: pre-absorbing water for the coarse aggregate to reduce the bubble loss caused by the friction between the paste aggregate fiber during the mixing process. The pre-absorption rate of water is 1.5 times the saturated surface dry water absorption rate, that is, the pre-treated coarse aggregate is obtained;

[0009] The bubble stabilizer is an ultra-fine particle. The ultra-fine particle is used as a bubble stabilizer to fill the bubble interface gap and inhibit the merger and escape of bubbles. The diameter of the ultra-fine particle should be less than 150 nm, and its dosage accounts for 1% - 3% of the mass of the cementitious material on the premise of ensuring the workability of the concrete;

[0010] The anti-freezing fiber selected is composed of two types of fibers with complementary high and low elastic moduli, including low elastic modulus fibers and high elastic modulus fibers. Among them, the elastic modulus of the low elastic modulus fibers is less than 20 GPa, and the elastic modulus of the high elastic modulus fibers is greater than 80 GPa. The volume fraction of the anti-freezing fiber is 0.15% - 4% of the total volume of the concrete. The specific dosage is determined by the type of fiber selected to ensure that it does not affect the workability of the concrete. The volume ratio of the high elastic modulus fibers to the low elastic modulus fibers should be controlled within 1 / 4 - 2 / 3. The difference in length and diameter between different types of fibers is relatively large. It is specified that the diameter and length of the low elastic modulus fibers do not exceed those of the high elastic modulus fibers.

[0011] Further, the low elastic modulus fibers described in the present invention are selected from any one of cellulose fibers, polypropylene fibers, and polyvinyl alcohol fibers.

[0012] Further, the high elastic modulus fibers described in the present invention are selected from any one of steel fibers, glass fibers, and basalt fibers.

[0013] Further, the low elastic modulus fibers of the present invention are preferably cellulose fibers with an elastic modulus of 7 GPa, an average length of 5 mm, and a diameter of 15 μm; the high elastic modulus fibers are preferably basalt fibers with an elastic modulus of 110 GPa, an average length of 12 mm, and a diameter of 15 μm; and the volume fractions of the two types of fibers are 0.1% for basalt fibers and 0.15% for cellulose fibers, respectively.

[0014] Further, the air bubble stabilizer described in the present invention is selected from any one of nano-clay, carbon nanotubes, and nano-silica; preferably nano-silica with a diameter of 100 nm, and its dosage is 3% of the mass of the cementitious material.

[0015] Further, the present invention provides a method for preparing the above-mentioned anti-freezing concrete applicable to high altitude environments, which includes the following steps:

[0016] (1) Pretreatment of coarse aggregates: Weigh the pretreated coarse aggregates and water and add them to a mixer and stir for 40 - 60 seconds to complete the pretreatment of the coarse aggregates;

[0017] (2) Preparation of high altitude anti-freezing concrete: Add the weighed anti-freezing fiber combination to a mixer and stir for 60 - 90 seconds to fully disperse the fibers; add the weighed cementitious material and fine aggregates, and add the remaining water and admixtures and stir for 120 - 180 seconds for concrete mixing to obtain the high altitude anti-freezing concrete mixture described in the present invention.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) In the present invention, by adding a fiber combination, more beneficial air bubbles can be introduced with the assistance of an air-entraining agent during the mixing process, and a dense network is formed in the concrete mixture and the cement matrix to prevent the air bubbles introduced under low air pressure from overflowing. At the same time, the air void structure of the concrete is optimized by an air bubble stabilizer to maintain the air content of the concrete.

[0020] (2) In the present invention, there is a synergistic effect of the fiber combination in hardened concrete. During the freeze-thaw cycle, the low-modulus fibers reduce the internal freezing stress through the bridging effect and their own fracture to avoid the generation of microcracks. The high-modulus fibers can effectively improve the macroscopic strength and crack resistance of the concrete, inhibit the generation of cracks and the spalling of cement paste. Under the combined action of the two, the frost resistance and durability of the concrete in the high-altitude and low-air-pressure environment are significantly improved. Detailed implementation mode

[0021] To make the content of the present invention easier to understand, the following further illustrates the technical solutions of the present invention in conjunction with specific embodiments, but the present invention is not limited thereto.

[0022] A method for preparing frost-resistant concrete applicable to high-altitude environments includes the following steps:

[0023] (1) Pretreatment of coarse aggregates: Weigh the pretreated coarse aggregates and water, add them to a mixer and stir for 40 - 60 seconds to complete the pretreatment of the coarse aggregates;

[0024] (2) Preparation of high-altitude frost-resistant concrete: Add the weighed frost-resistant fiber combination to the mixer and stir for 60 - 90 seconds to fully disperse the fibers; add the weighed cementitious materials and fine aggregates, and add the remaining water and admixtures and stir for 120 - 180 seconds for concrete mixing to obtain the high-altitude frost-resistant concrete mixture.

[0025] Example

[0026] Prepare F400 frost-resistant designed concrete as shown in Table 1. Pretreat the coarse aggregates, then introduce the fiber combination and air bubble stabilizer, and prepare the high-altitude frost-resistant concrete according to the above method. Table 2 shows the time-dependent change of the air content of the fresh concrete under different frost resistance improvement schemes under normal pressure of 101 kPa and 65 kPa (corresponding to an altitude of 3600 m) with a fixed water-binder ratio.

[0027] Table 1 Mix proportion of F400 frost-resistant designed concrete

[0028]

[0029]

[0030] Table 2 Time-dependent change of the air content of F400 frost-resistant designed concrete

[0031]

[0032]

[0033] As can be seen from the experiments in Table 1, under normal pressure conditions, using fiber in combination with air-entraining stabilizer is effective in maintaining the air content of fresh concrete, and under low-pressure conditions, the effect of increasing and maintaining the air content is significant.

[0034] The rapid freezing and thawing cycle test of concrete was carried out in a low-pressure test chamber, and the mass loss rate and dynamic elastic modulus were measured every 100 times. The test results are shown in Table 3.

[0035] Table 3 Test Results of Freezing and Thawing Cycles of F400 Frost-Resistant Design Concrete

[0036]

[0037] The test results in Table 3 show that the frost resistance of concrete mixed with fiber and air-entraining stabilizer has been significantly improved. After 400 freezing and thawing cycles, there is still a certain margin of frost resistance. Considering the comprehensive frost resistance and workability of concrete, the performance improvement effect is the best when 0.1% basalt fiber, 0.15% cellulose fiber, and 3% nano-silica are used.

Claims

1. An anti-freezing concrete applicable to high altitude environments, characterized in that: It is obtained by adding antifreeze fibers and bubble stabilizers to the pretreated coarse aggregate, and then adding cementitious materials, water, fine aggregate and admixtures for mixing. The water-binder ratio of the high-altitude antifreeze concrete is less than 0.45, and the air content is greater than 3%. The pretreatment method of the coarse aggregate includes: performing pre-absorption treatment on the coarse aggregate, and the pre-absorption rate is 1.5 times the saturated surface dry absorption rate, that is, the pretreated coarse aggregate is obtained. The bubble stabilizer is an ultra-fine particle with a diameter less than 150 nm, and the dosage accounts for 1% - 3% of the mass of the cementitious material. The antifreeze fibers include low elastic modulus fibers and high elastic modulus fibers. Among them, the elastic modulus of the low elastic modulus fibers is less than 20 GPa, and the elastic modulus of the high elastic modulus fibers is greater than 80 GPa; the volume fraction of the antifreeze fibers is 0.15% - 4% of the total volume of the concrete, and the volume ratio of the high elastic modulus fibers to the low elastic modulus fibers should be controlled at 1 / 4 - 2 / 3, and the diameter and length of the low elastic modulus fibers do not exceed those of the high elastic modulus fibers.

2. The anti-freezing concrete applicable to high-altitude environments according to claim 1, wherein The low elastic modulus fibers are selected from any one of cellulose fibers, polypropylene fibers, and polyvinyl alcohol fibers.

3. A frost-resistant concrete applicable to high-altitude environments according to claim 1, characterized in that, The high elastic modulus fibers are selected from any one of steel fibers, glass fibers, and basalt fibers.

4. The anti-freezing concrete applicable to high altitude environment according to claim 1, characterized in that The low elastic modulus fiber is a cellulose fiber with an elastic modulus of 7 GPa, an average length of 5 mm, and a diameter of 15 μm. The high elastic modulus fiber is a basalt fiber with an elastic modulus of 110 GPa, an average length of 12 mm, and a diameter of 15 μm. And the dosages of the above two fibers in terms of volume fraction are 0.1% for basalt fiber and 0.15% for cellulose fiber respectively.

5. A frost-resistant concrete applicable to high-altitude environments according to claim 1, characterized in that, The bubble stabilizer is selected from any one of nano-clay, carbon nanotubes, and nano-silica.

6. An anti-freezing concrete applicable to high altitude environments according to claim 5, characterized in that, The bubble stabilizer selects nano-silica with a diameter of 100 nm, and its dosage is 3% of the mass of the cementitious material.

7. A method for preparing the frost-resistant concrete applicable to high-altitude environments according to any one of claims 1 to 6, characterized in that, It includes the following steps: (1) Pretreatment of coarse aggregate: Weigh the pretreated coarse aggregate and water and add them to a mixer and stir for 40 - 60 seconds to complete the pretreatment of the coarse aggregate. (2) Preparation of high-altitude antifreeze concrete: Add the weighed combination of antifreeze fibers to the mixer and stir for 60 - 90 seconds to fully disperse the fibers; add the weighed cementitious materials and fine aggregate, and add the remaining water and admixtures and stir for 120 - 180 seconds for concrete mixing to obtain the high-altitude antifreeze concrete mixture.

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