Early-strength anti-crack joint concrete premix and preparation method thereof

Abstract

The invention relates to an early-strength crack-resistant joint concrete premix and a preparation method thereof, and the early-strength crack-resistant joint concrete premix comprises the following components in parts by mass: 310-370 parts of cement, 130-160 parts of fly ash, 15-35 parts of silica fume, 33-56 parts of an expanding agent, 2.8-16.8 parts of a crystal nucleus early strength agent, 700-800 parts of fine aggregate, 1000-1100 parts of coarse aggregate, 2-12 parts of polyvinyl alcohol modified hybrid fiber, 0.5-2.5 parts of an internal curing material and 0.05-0.3 part of a defoaming agent. Wherein the polyvinyl alcohol modified hybrid fibers comprise modified basalt fibers and modified carbon fibers. The problems that in the related technology, joint concrete cannot meet the construction turnover requirement, the early strength does not reach the standard, the anti-cracking performance and the durability performance are poor, the marine corrosion resistance of steel fibers is weak, and the quality fluctuation in the concrete premix storage process is large can be solved.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and in particular to an early-strength, crack-resistant joint concrete premix and a preparation method thereof. Background Art

[0002] As a key material in simply supported to continuous construction, wet-joint concrete's performance directly impacts the integrity and durability of the bridge's overall structure. The rise of mobile beam-deck concrete mixing plants has overcome the challenges of traditional offshore bridge construction, where concrete must be centrally mixed on land and transported long distances by water to the construction site for pouring. This leads to long transportation times, significant slump loss, and tidal influences on the construction window, which in turn reduces pouring quality. To adapt to the efficient production and construction model of mobile beam-deck concrete mixing plants, reduce construction turnover, and improve construction efficiency, the development of fast-hardening, early-strengthening joint concrete premixes is urgently needed. However, while these fast-hardening, early-strengthening properties can significantly shorten concrete construction cycles, they can also lead to rapid temperature rises and excessive shrinkage deformation, increasing the risk of concrete cracking and compromising joint construction quality and the long-term performance of the structure. Furthermore, the marine environment in which bridge concrete operates presents a complex service environment with numerous corrosion factors, which often occur simultaneously and reinforce each other, placing even more stringent demands on the corrosion resistance of joint concrete structures.

[0003] Due to its high ductility and excellent tensile strength, fiber materials can play a reinforcing role as "micro-rebars" in concrete. Through the bridging effect, they can significantly improve the stress distribution inside the concrete. They can not only effectively inhibit the crack propagation rate, but also significantly control the crack width, thereby improving the crack resistance of the matrix. However, fiber materials are difficult to disperse in practical applications, which greatly reduces their anti-cracking effect and also reduces the flow properties of concrete. At present, steel fibers are mainly used as the anti-cracking reinforcement phase of concrete in engineering practice. However, in marine corrosive environments, steel fibers are easily corroded by chloride ions, causing electrochemical corrosion, resulting in degradation of material performance and reduced structural durability. Therefore, it is necessary to further explore fiber-reinforced materials that can replace steel fibers.

[0004] Furthermore, premixes for joint concrete typically undergo warehousing and transportation from production to construction site application, during which the following quality issues may arise. ① Fiber-reinforced materials are prone to fiber aggregation due to electrostatic adsorption and prolonged static storage, resulting in reduced fiber distribution uniformity in the concrete. ② Premix packaging may be damaged by mechanical impact or environmental erosion, exposing the premix to humid air, causing moisture absorption and agglomeration in the premix and premature hydration of some cementitious materials. These quality issues will directly reduce the performance of the concrete premix, and during the construction phase, problems such as insufficient pouring density and weakened joint interface strength may easily occur. In severe cases, this may lead to the formation of penetration channels or stress concentration defects in the structural joints, which not only affects the overall quality of the project but may also increase subsequent maintenance costs.

[0005] In view of this, how to achieve coordinated regulation of rapid hardening, early strength and crack resistance of joint concrete and improve the quality stability of concrete premix is ​​of great significance to speeding up construction turnover, ensuring construction efficiency, enhancing the durability of bridge structures and extending the life of bridge structures. Summary of the Invention

[0006] The embodiments of the present application provide an early-strength, crack-resistant joint concrete premix and a preparation method thereof, in order to solve the problems in the related art such as the joint concrete failing to meet construction turnover, failing to meet early strength standards, poor crack resistance and durability, weak marine corrosion resistance of steel fibers, and large quality fluctuations during storage of the concrete premix.

[0007] In a first aspect, an early strength and crack resistant joint concrete premix is ​​provided, comprising, by weight: 310-370 parts of cement, 130-160 parts of fly ash, 15-35 parts of silica fume, 33-56 parts of expansion agent, 2.8-16.8 parts of crystal nucleation early strength agent, 700-800 parts of fine aggregate, 1000-1100 parts of coarse aggregate, 2-12 parts of polyvinyl alcohol modified hybrid fiber, 0.5-2.5 parts of internal curing material and 0.05-0.3 parts of defoaming agent; Wherein, the polyvinyl alcohol modified hybrid fiber includes modified basalt fiber and modified carbon fiber.

[0008] In some embodiments, the mass ratio of the modified basalt fiber to the modified carbon fiber is 1:(0.6-0.8).

[0009] In some embodiments, the steps of preparing the polyvinyl alcohol modified hybrid fiber include: performing a dispersion drying process on the hybrid fibers, wherein the hybrid fibers include basalt fibers and carbon fibers; spraying an aqueous solution of polyvinyl alcohol on the surface of the mixed fiber after dispersion and drying, and drying the mixed fiber to obtain a coated fiber; The coated fibers are immersed in a boric acid solution for cross-linking to obtain polyvinyl alcohol-modified hybrid fibers.

[0010] In some embodiments, the mixed fibers are subjected to a dispersion drying process, specifically comprising: Basalt fibers and carbon fibers are added to water and ultrasonic vibration is used to drive the dispersion of the basalt fibers and carbon fibers; The basalt fibers and carbon fibers were removed and dried to remove surface moisture.

[0011] In some embodiments, the mass fraction of the aqueous solution of polyvinyl alcohol is 1.5% to 1.8%; and / or, the mass fraction of the boric acid solution is 2% to 4%; And / or, after spraying, pre-dry at room temperature, then transfer to a drying oven at 40℃~60℃ to dry thoroughly; And / or, before the mixed fibers are dispersed and dried, the preparation step further includes: sandblasting the basalt fibers and carbon fibers, then removing surface impurities with a hydrochloric acid solution, and then rinsing with deionized water.

[0012] In some embodiments, the modified basalt fiber has a diameter of 9 μm to 16 μm and a length of 8 mm to 15 mm; The modified carbon fiber has a diameter of 5 μm to 10 μm and a length of 8 mm to 15 mm.

[0013] In some embodiments, the cement is P.II 52.5 cement; and / or, the fly ash is Class I fly ash; And / or, the silica fume particle size is 150nm to 300nm, and the SiO2 content is ≥95%.

[0014] In some embodiments, the expansion agent includes one or more of a magnesium oxide expansion agent and a calcium-magnesium composite expansion agent; And / or, the crystal nucleus early strength agent comprises one or more of nano-calcium silicate hydrate particles and nano-calcium carbonate particles, and the mortar 12 h compressive strength ratio thereof is ≥200%; And / or, the internal curing material includes a highly absorbent resin; And / or, the defoaming agent includes a silicone defoaming agent.

[0015] In some embodiments, the fine aggregate comprises river sand, and its particle size is 0.1 mm to 0.6 mm; And / or, the coarse aggregate includes small stones with a continuous gradation of 5mm to 16mm and large stones with a continuous gradation of 16mm to 25mm.

[0016] In a second aspect, a method for preparing the early-strength and crack-resistant joint concrete premix as described above is provided, comprising: Cement, fly ash, silica fume and polyvinyl alcohol modified hybrid fiber are uniformly mixed to obtain a dry mixed powder; The expansion agent, the crystal nucleus early strength agent, the internal curing material and the defoaming agent are uniformly mixed to obtain the functional additive material; Fully mix the dry mix powder with the functional additives, add coarse aggregate and fine aggregate, mix well and bag for later use.

[0017] The beneficial effects of the technical solution provided by this application include: This application uses modified basalt fiber and modified carbon fiber. On the one hand, they have the excellent marine corrosion resistance that basalt fiber and carbon fiber originally have. On the other hand, this application uses polyvinyl alcohol to modify basalt fiber and carbon fiber, and forms a water-soluble coating on the surface of basalt fiber and carbon fiber, so that the modified basalt fiber and modified carbon fiber can not only effectively eliminate the electrostatic adsorption of the fiber, and ensure that the concrete premix does not aggregate into agglomerates during storage, but also improve the dispersion, which is conducive to the uniform distribution of the internal components of the premix and enhances the crack resistance. In addition, the water-soluble coating will slowly dissolve during the construction process of the premix, without affecting the function of the fiber, and the coating components have no negative impact on the performance of the concrete. The internal curing material can be used as a desiccant to ensure that the concrete premix does not hydrate prematurely due to excessive humidity in the environment, and maintain stable and reliable quality.

[0018] The nucleus early strength agent component in the joint concrete premix prepared in the present application enables the early strength of the joint concrete to develop rapidly, which can significantly shorten the bridge construction period. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 This is a flow chart for preparing polyvinyl alcohol-modified hybrid fibers provided in an embodiment of the present application. DETAILED DESCRIPTION

[0021] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0022] An embodiment of the present application provides an early-strength and crack-resistant joint concrete premix, which includes, by mass: 310 to 370 parts of cement, 130 to 160 parts of fly ash, 15 to 35 parts of silica fume, 33 to 56 parts of expansion agent, 2.8 to 16.8 parts of crystal nucleation early strength agent, 700 to 800 parts of fine aggregate, 1000 to 1100 parts of coarse aggregate, 2 to 12 parts of polyvinyl alcohol-modified hybrid fibers, 0.5 to 2.5 parts of internal curing material and 0.05 to 0.3 parts of defoaming agent; wherein the polyvinyl alcohol-modified hybrid fibers include modified basalt fibers and modified carbon fibers.

[0023] This application uses modified basalt fiber and modified carbon fiber. On the one hand, they have the excellent marine corrosion resistance that basalt fiber and carbon fiber originally have. On the other hand, this application uses polyvinyl alcohol to modify basalt fiber and carbon fiber, and forms a water-soluble coating on the surface of basalt fiber and carbon fiber, so that the modified basalt fiber and modified carbon fiber can not only effectively eliminate the electrostatic adsorption of the fiber, and ensure that the concrete premix does not aggregate into agglomerates during storage, but also improve the dispersion, which is conducive to the uniform distribution of the internal components of the premix and enhances the crack resistance. In addition, the water-soluble coating will slowly dissolve during the construction process of the premix, without affecting the function of the fiber, and the coating components have no negative impact on the performance of the concrete. The internal curing material can be used as a desiccant to ensure that the concrete premix does not hydrate prematurely due to excessive humidity in the environment, and maintain stable and reliable quality.

[0024] The nucleus early strength agent component in the joint concrete premix prepared in the present application enables the early strength of the joint concrete to develop rapidly, which can significantly shorten the bridge construction period.

[0025] In this application, the modified basalt fiber has a diameter of 9 μm to 16 μm and a length of 8 mm to 15 mm; the modified carbon fiber has a diameter of 5 μm to 10 μm and a length of 8 mm to 15 mm. The two have the same length and are easy to disperse.

[0026] For example, the length is 8 mm, 8 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm or any range thereof.

[0027] The mass ratio of the modified basalt fiber to the modified carbon fiber is 1:(0.6-0.8). For example, the mass ratio of the modified basalt fiber to the modified carbon fiber is 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, or any range thereof.

[0028] This application optimizes the mass ratio of modified basalt fiber to modified carbon fiber to the above-mentioned ratio range. The reason is that when it is higher than 1:0.6, due to the high elastic modulus of the modified carbon fiber and too little dosage, the concrete's ability to inhibit crack propagation will deteriorate, and the synergistic reinforcement effect of the mixed fibers cannot be fully exerted; when it is lower than 1:0.8, the carbon fiber dosage is too high, which will increase costs on the one hand, and increase the conductivity of the concrete and the risk of corrosion on the other hand.

[0029] See also Figure 1 As shown, the preparation steps of the polyvinyl alcohol modified hybrid fiber include: 101: Pre-treating the hybrid fibers, wherein the hybrid fibers include basalt fibers and carbon fibers.

[0030] The pre-treatment specifically includes: sandblasting to enhance the fiber bite force, then using hydrochloric acid solution to remove surface impurities, and rinsing with deionized water after treatment.

[0031] 102: Dispersing and drying the mixed fibers.

[0032] Specifically, basalt and carbon fibers are added to water (e.g., deionized or distilled water) and ultrasonically dispersed. For better dispersion, the fibers can be added in batches. Ultrasonic vibrations are applied at a power of 200-300W for 15 minutes, using the large number of microbubbles generated by microwave oscillation to disperse the fibers.

[0033] After the fibers are dispersed, remove the basalt and carbon fibers and dry them to remove surface moisture. For example, slowly transfer the fibers to a flat plate and dry them in an 80°C oven. Ensure the liquid level is ≤ 1 cm when placing them in the oven. Once the surface moisture evaporates, remove the fibers promptly to prevent them from re-clumping after thorough drying.

[0034] 103: Spraying an aqueous solution of polyvinyl alcohol onto the surface of the mixed fibers after dispersion and drying, and drying the mixed fibers to obtain coated fibers.

[0035] Heat deionized water in a water bath to 80-90°C, slowly add weighed polyvinyl alcohol powder, continue stirring until completely dissolved, control the mass fraction of the polyvinyl alcohol solution between 1.5% and 1.8%, and use a high-pressure sprayer to evenly spray the polyvinyl alcohol solution onto the surface-dried fiber surface. After spraying, pre-dry at room temperature for 10-20 minutes, and then transfer to a 40-60°C oven for thorough drying to avoid cracking of the fiber surface film.

[0036] The present application controls the mass fraction of the polyvinyl alcohol solution to be between 1.5% and 1.8%. The reason for this is that if the mass fraction of the polyvinyl alcohol solution is lower than 1.5%, the film-forming continuity of the polyvinyl alcohol solution is poor and a good film-forming effect cannot be achieved. If the mass fraction is higher than 1.8%, the viscosity of the solution will be too high, making spraying construction difficult, and it will also be difficult for the water to evaporate and dry, thereby reducing production efficiency.

[0037] 104: Immersing the coated fiber in a boric acid solution for cross-linking to obtain polyvinyl alcohol-modified hybrid fiber.

[0038] The coated fibers were immersed in a 2% to 4% mass fraction boric acid solution for crosslinking for 10 s to 30 s to enhance the film strength. The unreacted boric acid was then removed by rinsing with deionized water to obtain modified basalt fibers and modified carbon fibers.

[0039] The fiber coating thickness and cross-linking time can be dynamically adjusted according to the construction mixing time to ensure that the coating remains stable and has sufficient mechanical strength during the concrete mixing process. The presence of the coating can ensure uniform dispersion of fibers and improve crack resistance on the one hand, and significantly improve the fluidity of concrete on the other hand to ensure construction performance.

[0040] In this application, the cement is P.II 52.5 cement with a specific surface area of ​​300-350m 2 / kg, 3d compressive strength ≥30MPa; The fly ash is Class I fly ash, with a 45μm square hole sieve residue of ≤12%, a water requirement ratio of ≤95%, and a loss on ignition of ≤5%; The silica fume particle size is 150nm to 300nm, the SiO2 content is ≥95%, and the ignition loss is ≤3%.

[0041] The expansion agent includes one or more of a magnesium oxide expansion agent and a calcium-magnesium composite expansion agent; The crystal nucleus early strength agent comprises one or more of nano calcium silicate hydrate particles and nano calcium carbonate particles, and the mortar 12 h compressive strength ratio is ≥200%; The internal curing material includes a highly absorbent resin; The defoaming agent includes an organosilicon defoaming agent, such as silicone powder.

[0042] The fine aggregate includes well-mixed river sand and medium sand, with a particle size of 0.1mm to 0.6mm and an apparent density of ≥2550kg / m 3 ; The coarse aggregate includes small stones with continuous grading of 5mm to 16mm and large stones with continuous grading of 16mm to 25mm. The apparent density of the small stones is ≥2650kg / m 3 , the apparent density of large stones is ≥2700kg / m 3 .

[0043] The present application also provides a method for preparing an early-strength, crack-resistant joint concrete premix, which comprises: 201: uniformly mixing cement, fly ash, silica fume and polyvinyl alcohol modified hybrid fiber to obtain a dry mixed powder; 202: Evenly mix the expansion agent, the crystal nucleus early strength agent, the internal curing material, and the defoaming agent to obtain a functional additive material; 203: Mix the dry mix powder and functional additives thoroughly, add coarse aggregate and fine aggregate, mix evenly, and then bag for later use.

[0044] The present application is described below through examples and comparative examples.

[0045] Example 1 A marine environment early strength and crack resistant joint concrete premix, comprising the following raw materials in parts by mass: 321.6 parts of Portland cement, 160 parts of fly ash, 33.6 parts of silica fume, 44.8 parts of expansion agent, 5.6 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 2.2 parts of polyvinyl alcohol modified hybrid fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent; Among them, the polyvinyl alcohol modified hybrid fiber is composed of modified basalt fiber and modified carbon fiber in a mass ratio of 1:0.8.

[0046] The preparation method is as follows: ①Sandblast the basalt fiber and carbon fiber to enhance the fiber bite force, then use hydrochloric acid solution to remove surface impurities, and rinse with deionized water after treatment; ② Add an appropriate amount of deionized water to a beaker, and add basalt fiber and carbon fiber to the deionized water in batches. During this process, use ultrasonic oscillation at a power of 250W for 15 minutes, and use the large number of microbubbles generated by microwave oscillation to drive the dispersion of the fibers. After the fibers are dispersed, slowly transfer them to a flat plate and place them in an 80℃ oven to dry, ensuring that the liquid level is ≤1cm. After the moisture on the fiber surface evaporates, take them out in time to prevent the fibers from re-aggregating after thorough drying. ③ Heat the deionized water bath to 90°C, slowly add the weighed polyvinyl alcohol powder, and continue stirring until it is completely dissolved. Control the mass fraction of the polyvinyl alcohol solution to 1.6%. Use a high-pressure sprayer to evenly spray the polyvinyl alcohol solution onto the surface-dried fiber surface. After spraying, pre-dry at room temperature for 10 minutes, and then transfer to a 60°C oven to thoroughly dry to avoid cracking of the fiber surface film. ④ The coated fibers were immersed in a 3% mass fraction boric acid solution for cross-linking for 20 s to enhance the film strength, and then rinsed with deionized water to remove the unreacted boric acid to obtain modified basalt fibers and modified carbon fibers; ⑤ Evenly stir cement, fly ash, silica fume and polyvinyl alcohol modified hybrid fiber according to parts by mass to obtain dry mixed powder, weigh expansion agent, crystal nucleation early strength agent, internal curing material and defoaming agent according to parts by mass and mix them evenly to obtain functional additives; ⑥ Further fully mix the dry mix powder and functional additives, add dry coarse aggregate and fine aggregate, mix evenly, and then bag for later use.

[0047] Example 2 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 5.6 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 2.2 parts of polyvinyl alcohol modified mixed fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0048] Example 3 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 370 parts of Portland cement, 130 parts of fly ash, 15.2 parts of silica fume, 44.8 parts of expansion agent, 5.6 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 2.2 parts of polyvinyl alcohol modified mixed fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0049] Example 4 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 5.6 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of polyvinyl alcohol modified mixed fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0050] Example 5 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 5.6 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 11 parts of polyvinyl alcohol modified hybrid fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent; Example 6 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 2.2 parts of polyvinyl alcohol modified mixed fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0051] Example 7 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of polyvinyl alcohol modified mixed fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0052] Example 8 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 11 parts of polyvinyl alcohol modified mixed fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0053] Comparative Example 1 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of polyvinyl alcohol modified mixed fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0054] Comparative Example 2 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of mixed fibers, 1.2 parts of internal curing materials, and 0.1 parts of defoaming agent.

[0055] Among them, the hybrid fiber is composed of basalt fiber and carbon fiber in a mass ratio of 1:0.8.

[0056] Comparative Example 3 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of steel fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent; Comparative Example 4 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of modified basalt fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0057] Comparative Example 5 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of modified carbon fiber, 1.2 parts of internal curing material, and 0.1 part of defoaming agent.

[0058] Comparative Example 6 The only difference from Example 1 is that: Calculated by mass, it includes the following raw materials: 352.8 parts of Portland cement, 140 parts of fly ash, 22.4 parts of silica fume, 44.8 parts of expansion agent, 11.2 parts of crystal nucleation early strength agent, 720 parts of river sand, 216 parts of small stones, 864 parts of large stones, 6.6 parts of polyvinyl alcohol modified mixed fibers, and 0.1 part of defoaming agent.

[0059] The proportions of each embodiment and comparative example are shown in Table 1.

[0060] Table 1

[0061] Note: In Table 1, “S” stands for “Example”, for example, “S1” stands for “Example 1”, and “D” stands for “Comparative Example”, for example, “D1” stands for “Comparative Example 1”.

[0062] Performance Testing The concrete premixes obtained in Examples 1 to 8 and Comparative Examples 1 to 6 were placed in a standard room at a temperature of 20±2°C and a humidity of 60±5% for 90 days, then taken out and 140 parts of water were added while stirring. The mixture was stirred for 4 minutes to prepare joint concrete, and the following performance tests were performed: (1) Working performance: The slump and expansion tests of fresh concrete were carried out in accordance with GB / T 50080-2016 “Standard for test methods of properties of ordinary concrete mixtures”; (2) Compressive strength: The concrete prepared in Examples 1-8 and Comparative Examples 1-6 was molded into standard specimens of 150 mm × 150 mm × 150 mm. After standard curing for 1 d, 3 d, 7 d, and 28 d, the compressive strength was tested in accordance with GB / T 50081-2019, “Standard for Test Methods for Physical and Mechanical Properties of Concrete”; (3) Electric flux: After the concrete prepared in Examples 1-8 and Comparative Examples 1-6 were cured for 28 days and 56 days, the electric flux method in accordance with GB / T 50082-2009 "Standard for Test Methods of Long-term Properties and Durability of Ordinary Concrete" was used for testing. (4) Slab crack resistance: Test according to GB / T 50082-2009 “Standard for test methods of long-term performance and durability of ordinary concrete”, and fill in the test results in Table 2; Table 2

[0063] According to the data in Table 2, the joint concrete prepared from the premixes obtained in Examples 1 to 8 all have excellent working performance, mechanical properties, crack resistance and durability.

[0064] In Comparative Example 1, compared with Examples 4 and 7, the crystal nucleation early strength agent was omitted. The 1d and 3d compressive strengths of the joint concrete prepared from the obtained premix were reduced by 16.1 MPa, 15.4 MPa and 26 MPa, 19.5 MPa, respectively. This shows that the crystal nucleation early strength agent can provide nucleation sites for hydration products, quickly promote early strength development, accelerate construction turnover, and improve construction efficiency.

[0065] Compared with Example 7, Comparative Examples 2 and 3 use hybrid fibers composited with basalt fiber and carbon fiber and steel fibers to replace the modified hybrid fibers, respectively. This results in difficulty in dispersing the fibers during the mixing process of the concrete premix, poor uniformity, and fiber aggregation during storage. As a result, the crack resistance of the joint concrete prepared therefrom is poor, the tensile strength is reduced, and the total crack area per unit area is increased; the hybrid fibers and steel fibers also cause the flowability of the freshly mixed concrete to decrease, the steel fibers have poor resistance to chloride ion corrosion, and the durability of the concrete to deteriorate.

[0066] Compared with Example 7, Comparative Examples 4 and 5 use modified basalt fiber and modified carbon fiber to replace the modified mixed fiber, respectively. The tensile strength of the joint concrete prepared by the obtained premix is ​​reduced and the crack area is increased. The reason is that the modified basalt fiber has high ductility, which effectively inhibits the early expansion of microcracks in concrete and improves the toughness of concrete. The modified carbon fiber has high tensile strength and prevents the formation of macro cracks in concrete. In addition, both fibers have excellent corrosion resistance. The synergistic effect of the two can achieve multi-scale fiber enhancement and significantly improve the toughness, crack resistance and durability of concrete.

[0067] Compared with Example 7, Comparative Example 6 omitted the internal curing material, which resulted in problems such as moisture absorption and agglomeration of the cementitious material and premature hydration during the storage of the concrete premix in a high humidity environment. As a result, the various properties of the joint concrete prepared therefrom were significantly deteriorated, especially the crack resistance and durability. This shows that the internal curing material can maintain the stability of the quality of the concrete premix and ensure the overall quality of the project.

[0068] The main difference between Comparative Example 1 and Examples 1, 2, 3 and 6 is that Comparative Example 1 does not contain a crystal nucleus early strength agent, which will affect its early strength performance. However, the amount of modified hybrid fiber added in Comparative Example 1 is higher than that in Examples 1, 2, 3 and 6, so its crack resistance is also improved to a certain extent, and the crack area is slightly reduced compared with Example 1.

[0069] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. An early strength and crack resistant joint concrete premix, characterized in that: Calculated by mass, it includes: 310-370 parts of cement, 130-160 parts of fly ash, 15-35 parts of silica fume, 33-56 parts of expansion agent, 2.8-16.8 parts of crystal nucleation early strength agent, 700-800 parts of fine aggregate, 1000-1100 parts of coarse aggregate, 2-12 parts of polyvinyl alcohol modified hybrid fiber, 0.5-2.5 parts of internal curing material and 0.05-0.3 parts of defoaming agent; Wherein, the polyvinyl alcohol modified hybrid fiber includes modified basalt fiber and modified carbon fiber.

2. The early strength and crack resistant joint concrete premix according to claim 1, characterized in that: The mass ratio of the modified basalt fiber to the modified carbon fiber is 1:(0.6-0.8).

3. The early strength and crack resistant joint concrete premix according to claim 1, characterized in that: The preparation steps of the polyvinyl alcohol modified hybrid fiber include: performing a dispersion drying process on the hybrid fibers, wherein the hybrid fibers include basalt fibers and carbon fibers; spraying an aqueous solution of polyvinyl alcohol on the surface of the mixed fiber after dispersion and drying, and drying the mixed fiber to obtain a coated fiber; The coated fibers are immersed in a boric acid solution for cross-linking to obtain polyvinyl alcohol-modified hybrid fibers.

4. The early strength and crack resistant joint concrete premix according to claim 3, characterized in that: Dispersion and drying of mixed fibers, including: Basalt fibers and carbon fibers are added to water and ultrasonic vibration is used to drive the dispersion of the basalt fibers and carbon fibers; The basalt fibers and carbon fibers were removed and dried to remove surface moisture.

5. The early strength and crack resistant joint concrete premix according to claim 3, characterized in that: The mass fraction of the aqueous solution of polyvinyl alcohol is 1.5% to 1.8%; and / or, the mass fraction of the boric acid solution is 2% to 4%; And / or, after spraying, pre-dry at room temperature, then transfer to a drying oven at 40℃~60℃ to dry thoroughly; And / or, before the mixed fibers are dispersed and dried, the preparation step further includes: sandblasting the basalt fibers and carbon fibers, then removing surface impurities with a hydrochloric acid solution, and then rinsing with deionized water.

6. The early strength and crack resistant joint concrete premix according to claim 1, characterized in that: The modified basalt fiber has a diameter of 9 μm to 16 μm and a length of 8 mm to 15 mm; The modified carbon fiber has a diameter of 5 μm to 10 μm and a length of 8 mm to 15 mm.

7. The early strength and crack resistant joint concrete premix according to claim 1, characterized in that: The cement is P.II 52.5 cement; and / or, the fly ash is Class I fly ash; And / or, the silica fume particle size is 150nm to 300nm, and the SiO2 content is ≥95%.

8. The early strength and crack resistant joint concrete premix according to claim 1, characterized in that: The expansion agent includes one or more of a magnesium oxide expansion agent and a calcium-magnesium composite expansion agent; And / or, the crystal nucleus early strength agent comprises one or more of nano-calcium silicate hydrate particles and nano-calcium carbonate particles, and the mortar 12 h compressive strength ratio thereof is ≥200%; And / or, the internal curing material includes a highly absorbent resin; And / or, the defoaming agent includes a silicone defoaming agent.

9. The early strength and crack resistant joint concrete premix according to claim 1, characterized in that: The fine aggregate includes river sand, and its particle size is 0.1mm to 0.6mm; And / or, the coarse aggregate includes small stones with a continuous gradation of 5mm to 16mm and large stones with a continuous gradation of 16mm to 25mm.

10. A method for preparing the early strength and crack resistant joint concrete premix according to any one of claims 1 to 9, characterized in that: It includes: Cement, fly ash, silica fume and polyvinyl alcohol modified hybrid fiber are uniformly mixed to obtain a dry mixed powder; The expansion agent, the crystal nucleus early strength agent, the internal curing material and the defoaming agent are uniformly mixed to obtain the functional additive material; Fully mix the dry mix powder with the functional additives, add coarse aggregate and fine aggregate, mix well and bag for later use.

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