A method for preparing a non-autoclaved concrete precast component

Abstract

The present application relates to the technical field of steam-cured concrete prefabricated component, and discloses a preparation method of steam-cured concrete prefabricated component, and the specific steps are as follows: S1. binding the steel bars for concrete components and placing them under the sun for exposure; the steel bars are provided with interconnected steel pipes with a steel bar volume fraction of 10-30%, and the steel pipes are filled with water; S2. cleaning the surface of concrete aggregate and spraying silica sol, sodium silicate solution or saturated calcium hydroxide solution; S3. uniformly stirring cement and water, and then adjusting the pH value of the cement with acid; S4. uniformly stirring cement clinker, mineral admixture, gypsum, the obtained product of S2, the obtained product of S3 and water reducing agent to obtain a mixture, and pouring the mixture into a concrete heat insulation mold; S5. demolding the concrete after curing for 24 hours, and then pouring foam concrete into the steel pipes. The present application solves the problem of high energy consumption in the preparation of prefabricated components by steam curing.

Description

Technical Field

[0001] This invention relates to the field of precast concrete components without autoclaving, and particularly to a method for preparing precast concrete components without autoclaving. Background Technology

[0002] With the continuous improvement of the level of industrialization in the construction industry and the vigorous promotion of prefabricated buildings by the state, precast concrete components are widely used in various engineering constructions along with prefabricated construction methods. Precast components have high production efficiency and stable quality, which can shorten the construction period and reduce construction costs. In the factory production of precast components, in order to shorten curing time, speed up mold turnover and improve production efficiency, PC factories adopt steam curing technology.

[0003] Steam curing can rapidly improve the early strength of concrete, meeting the strength requirements for demolding and lifting precast components, thereby accelerating mold turnover and improving factory efficiency. However, steam curing has the following drawbacks: First, the need for steam curing increases production costs; second, the energy consumption in generating steam is relatively high. According to incomplete statistics, the energy consumption for the thermal curing of precast concrete pipe piles is equivalent to approximately 50 kg / m³ of standard coal. 3 Third, steam curing accelerates the hydration and hardening reaction process of cement-based cementitious materials and improves the early strength of concrete, but it has an adverse effect on the durability and brittleness of concrete.

[0004] Therefore, the precast concrete industry is actively exploring methods for preparing autoclaved concrete precast components, including: selecting superior raw materials, optimizing concrete mix proportions, adopting advanced curing methods, adding water-reducing agents and early-strength agents, and incorporating admixtures such as fly ash microspheres or silica fume. This invention provides a novel method for preparing autoclaved concrete precast components. Summary of the Invention

[0005] Purpose of the invention: This invention provides a method for preparing precast concrete components without steam curing, which solves the problem of high energy consumption when preparing precast concrete components using steam curing.

[0006] Technical solution: This invention provides a method for preparing precast concrete components without autoclaving, comprising the following steps: S1. Reinforcing bars for tying concrete components and exposing them to the sun; the reinforcing bars are provided with interconnected steel pipes containing 10-30% of the reinforcing bar volume, and the steel pipes are filled with water; S2. Clean the concrete aggregate surface and spray it with silica sol, sodium silicate solution, or saturated calcium hydroxide solution; S3. Mix cement and water evenly according to the ratio of cement:water = 5~100:1000, and then adjust its pH value to 7~9 with acid; S4. Mix cement clinker, mineral admixtures, gypsum, the product obtained in S2, the product obtained in S3, and water-reducing agent evenly to obtain a mixture, and pour the mixture into a concrete insulation mold; S5. After the concrete has cured for 24-36 hours, demold it, drain the water from the concrete pipe, and then inject foamed concrete into the pipe.

[0007] Furthermore, in S3, the mass fraction of the acid is 0.5~1.5%.

[0008] Furthermore, the acid is one or both of sulfuric acid and formic acid.

[0009] Furthermore, in S4, the gypsum content does not exceed 6% of the total amount of cementitious material in the mixture.

[0010] Furthermore, in S4, the mineral admixture includes ultrafine mineral powder and ultrafine lithium slag powder.

[0011] Furthermore, the amount of the mineral admixture is less than 25% of the total amount of cementitious material in the mixture.

[0012] Furthermore, in S4, the ratio of the product obtained in S3 to the cementitious material in the mixture is less than 0.5.

[0013] Further, in S2, the concentration of the silica sol is 0.01~1%; the concentration of the sodium silicate solution is 0.01~1%.

[0014] Further, in S2, the amount of silica sol, sodium silicate solution, or saturated calcium hydroxide solution sprayed is 0.5~2kg of silica sol, sodium silicate solution, or saturated calcium hydroxide solution per ton of concrete aggregate.

[0015] Beneficial effects: Compared with the prior art, the beneficial effects of the present invention are specifically as follows: 1. The present invention sets up a water-filled connecting steel pipe in the precast component. By exposing the concrete to sunlight or other means, the temperature of the concrete reinforcement and the water in the connecting steel pipe can be increased, thereby raising the ambient temperature for concrete hydration. The heat released by the concrete during the hydration process can also be stored through the water in the connecting steel pipe and transferred to various parts of the concrete component, ensuring the uniformity of heating of various parts of the concrete.

[0016] 2. Apply alkaline silica sol, sodium silicate solution, or saturated calcium hydroxide solution to the surface of clean concrete aggregate. The sol will deposit on the surface of the concrete aggregate and react with carbon dioxide and other substances in the air to form nano-particle silica, sodium carbonate, calcium carbonate and other products. These products can provide crystal nuclei for concrete hydration and accelerate cement hydration and precipitation of hydration products.

[0017] 3. By utilizing a higher water-cement ratio, cement is thoroughly mixed into water, accelerating cement hydration and ensuring the uniform dispersion of hydration products. Low concentrations of sulfuric acid or formic acid are used to adjust the pH of the solution. On one hand, sulfuric acid and formic acid react with calcium hydroxide, a cement hydration product, producing calcium sulfate and calcium formate, which further accelerate cement hydration. On the other hand, the uniformly dispersed cement hydration products in the aqueous solution can act as crystal nuclei, further accelerating cement hydration. Additionally, both adding cement to water and the neutralization reaction between acid and alkali can increase the temperature of the aqueous solution, which also accelerates the hydration of the cementitious materials.

[0018] 4. Use insulated concrete formwork to reduce the loss of hydration heat inside the concrete, and utilize the hydration heat inside the cement to increase the hydration temperature and hydration rate of precast concrete components.

[0019] 5. By using ultrafine mineral admixtures to adjust the particle size distribution of cementitious materials in concrete, it is helpful to improve the hydration rate and density of cementitious materials. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the embodiments.

[0021] Implementation method 1: This embodiment provides a method for preparing precast concrete components that do not require autoclaving, the specific steps of which are as follows: 1) Reinforcing bars for tying concrete components, wherein the reinforcing bars are provided with interconnected steel pipes comprising 30% of the reinforcing bar volume, the steel pipes are filled with water and exposed to the sun; 2) Clean the surface of the concrete aggregate and spray it with 1% silica sol, with a spraying amount of 2kg per ton of aggregate; 3) Mix cement and water evenly at a ratio of cement:water = 5:1000; then adjust the pH of the solution to 7 using 0.5% sulfuric acid and formic acid. 4) Mix cement clinker, mineral admixtures, gypsum, concrete aggregate from step 2), solution from step 3), and water-reducing agent evenly and pour into a concrete insulation mold; the gypsum content is 6% of the total cementitious materials; the mineral admixtures include ultrafine mineral powder and ultrafine lithium slag powder; the amount of mineral admixtures is 25% of the total cementitious materials; the ratio of solution from step 3) to cementitious materials is 0.38; 5) After the concrete has cured for 24 hours, remove it from the formwork, drain the water from the steel pipe in the concrete, and then inject foamed concrete into the steel pipe.

[0022] Implementation Method 2: This embodiment provides a method for preparing precast concrete components that do not require autoclaving, the specific steps of which are as follows: 1) Reinforcing bars for tying concrete components, wherein the reinforcing bars are provided with interconnected steel pipes comprising 10% of the reinforcing bar volume, the steel pipes are filled with water and exposed to the sun; 2) Clean the surface of the concrete aggregate and spray it with a 0.01% sodium silicate solution. The amount of spraying per ton of aggregate is 2 kg. 3) Mix cement and water evenly according to the ratio of cement:water = 100:1000; then adjust the pH of the solution to 8 using 1.5% formic acid by mass. 4) Mix cement clinker, mineral admixtures, gypsum, concrete aggregate from step 2), solution from step 3), and water-reducing agent evenly and pour into a concrete insulation mold; the gypsum content is 5% of the total cementitious materials; the mineral admixtures include ultrafine mineral powder and ultrafine lithium slag powder; the amount of mineral admixtures is 20% of the total cementitious materials; the ratio of solution from step 3) to cementitious materials is 0.33; 5) After the concrete has cured for 36 hours, remove it from the formwork, drain the water from the steel pipe in the concrete, and then inject foamed concrete into the steel pipe.

[0023] Implementation Method 3: This embodiment provides a method for preparing precast concrete components that do not require autoclaving, the specific steps of which are as follows: 1) Reinforcing bars for tying concrete components, wherein the reinforcing bars are provided with interconnected steel pipes comprising 20% ​​of the reinforcing bar volume, the steel pipes are filled with water and exposed to the sun; 2) Clean the surface of the concrete aggregate and spray it with a saturated calcium hydroxide solution. The amount of solution sprayed per ton of aggregate is 1 kg. 3) Mix cement and water evenly at a ratio of cement:water = 100:1000; then adjust the pH of the solution to 9 using 0.5% formic acid by mass. 4) Mix cement clinker, mineral admixtures, gypsum, concrete aggregate from step 2), solution from step 3), and water-reducing agent evenly and pour into a concrete insulation mold; the gypsum content is 4.5% of the total cementitious materials; the mineral admixtures include ultrafine mineral powder and ultrafine lithium slag powder; the amount of mineral admixtures is 15% of the total cementitious materials; the ratio of solution from step 3) to cementitious materials is 0.36; 5) After the concrete has cured for 24 hours, remove it from the formwork, drain the water from the steel pipe in the concrete, and then inject foamed concrete into the steel pipe.

[0024] Implementation Method 4: This embodiment provides a method for preparing precast concrete components that do not require autoclaving, the specific steps of which are as follows: 1) Reinforcing bars for tying concrete components, wherein the reinforcing bars are provided with interconnected steel pipes comprising 20% ​​of the reinforcing bar volume, the steel pipes are filled with water and exposed to the sun; 2) Clean the surface of the concrete aggregate and spray it with 0.06% silica sol, with a spraying amount of 1 kg per ton of aggregate; 3) Mix the cement and water evenly at a ratio of 50:1000; then adjust the pH of the solution to 8 using 0.5% sulfuric acid. 4) Mix cement clinker, mineral admixtures, gypsum, concrete aggregate from step 1), solution from step 2), and water-reducing agent evenly and pour into a concrete insulation mold; the gypsum content shall not exceed 5% of the total amount of cementitious materials; the mineral admixtures include ultrafine mineral powder and ultrafine lithium slag powder; the amount of mineral admixtures shall be 10% of the total amount of cementitious materials; the ratio of solution from step 2) to cementitious materials shall be 0.36; 5) After the concrete has cured for 24 hours, remove it from the formwork, drain the water from the steel pipe in the concrete, and then inject foamed concrete into the steel pipe.

[0025] Performance testing:

[0026] Table 1 shows the performance evaluation indicators of this invention. The mechanical properties of the concrete were tested in accordance with GB / T50081—2002 standard. The concrete mix proportions of the comparative examples are as follows: 320 kg of P·O 42.5 cement, 50 kg of mineral powder, 50 kg of fly ash, 800 kg of sand, and 1100 kg of stone. In comparative example 1, water is 160 kg and polycarboxylate superplasticizer is 5 kg, maintaining the same water-cement ratio as in embodiment 1. In comparative example 2, water is 140 kg and polycarboxylate superplasticizer is 6 kg, maintaining the same water-cement ratio as in embodiment 2. In comparative example 3, water is 150 kg and polycarboxylate superplasticizer is 5.5 kg, maintaining the same water-cement ratio as in embodiments 3 and 4. Comparative examples 1 to 3 are steam-cured at 80℃ for 7 hours, and then water-cured at 20±2℃ after demolding.

[0027] The concrete in this embodiment was prepared using the method of the present invention. After demolding, the concrete was also water-cured at a temperature of 20±2℃.

[0028]

[0029] As shown in Table 2, the early 3-day mechanical properties of the precast components prepared by the present invention are similar to those of the steam-cured components, but the 28-day strength is higher than that of the comparative components with the same water-cement ratio, and the 60-day strength is basically one strength grade higher than that of the comparative components. Moreover, the slow strength growth or even strength reduction phenomenon in the later stage, as seen in the comparative components, does not occur.

[0030] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing precast concrete components without autoclaving, characterized in that, Includes the following steps: S1. Reinforcing bars for tying concrete components and exposing them to the sun; the reinforcing bars are provided with interconnected steel pipes containing 10-30% of the reinforcing bar volume, and the steel pipes are filled with water; S2. Clean the concrete aggregate surface and spray it with silica sol, sodium silicate solution, or saturated calcium hydroxide solution; S3. Mix cement and water evenly according to the ratio of cement:water = 5~100:1000, and then adjust its pH value to 7~9 with acid; S4. Mix cement clinker, mineral admixtures, gypsum, the product obtained in S2, the product obtained in S3, and water-reducing agent evenly to obtain a mixture, and pour the mixture into a concrete insulation mold; S5. After the concrete has cured for 24-36 hours, demold it, drain the water from the concrete pipe, and then inject foamed concrete into the pipe.

2. The method for preparing precast concrete components without autoclaving according to claim 1, characterized in that: In S3, the mass fraction of the acid is 0.5~1.5%.

3. The method for preparing precast concrete components without autoclaving according to claim 2, characterized in that: The acid is one or both of sulfuric acid and formic acid.

4. The method for preparing precast concrete components without autoclaving according to claim 1, characterized in that: In S4, the mineral admixture includes ultrafine mineral powder and ultrafine lithium slag powder.

5. The method for preparing precast concrete components without autoclaving according to claim 1, characterized in that: In S2, the concentration of the silica sol is 0.01~1%; the concentration of the sodium silicate solution is 0.01~1%.

6. The method for preparing precast concrete components without autoclaving according to any one of claims 1-5, characterized in that: In S2, the amount of silica sol, sodium silicate solution, or saturated calcium hydroxide solution sprayed is 0.5~2kg of silica sol, sodium silicate solution, or saturated calcium hydroxide solution per ton of concrete aggregate.

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