Shrinkage-compensating concrete as well as preparation method and application thereof

Abstract

The invention relates to shrinkage-compensating concrete as well as a preparation method and application thereof, and relates to the technical field of concrete. The invention provides shrinkage-compensating concrete. The shrinkage-compensating concrete is prepared from the following components: machine-made sand, coarse aggregate, recycled aggregate, a water reducing agent, cement, slag powder, fly ash, an expanding agent and water. According to the shrinkage-compensating concrete disclosed by the invention, a dual composite effect of an expansion effect of the expanding agent in a humid environment and a delayed moisturizing effect of'first absorption and then release 'of the recycled aggregate is utilized, so that the anti-cracking performance of the concrete is improved, the cracking risk is reduced, and meanwhile, good economic benefits and social benefits can be brought.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a shrinkage-compensating concrete, its preparation method, and its application. Background Technology

[0002] Concrete is one of the essential building materials in modern construction. However, structural cracks are a common phenomenon during concrete construction due to various reasons, posing a serious threat to project quality. Although extensive research on concrete shrinkage cracking has been conducted both domestically and internationally, and significant progress has been made, the problem of concrete shrinkage cracking has not yet been completely solved. The root cause of concrete cracking is the influence of shrinkage stress. Counteracting or delaying the shrinkage stress during the concrete hardening process can reduce the risk of cracking. Traditional methods mainly rely on expansive agents to compensate for shrinkage, but the effectiveness of a single expansive agent is limited in complex environments. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a shrinkage-compensating concrete, its preparation method, and its application. This shrinkage-compensating concrete combines an expansive agent to compensate for shrinkage with highly absorbent aggregates. This regulates the rate of water migration, allowing the aggregates to exert a "water absorption-slow release" effect, slowing the surface moisture evaporation rate and reducing capillary pressure. This effectively improves the internal moisture environment of the concrete, achieving a comprehensive aggregate water absorption rate of 1.4%. In this moist environment, the expansive agent continuously generates ettringite to fill micro-cracks, creating a synergistic crack-resistant effect with the aggregate water absorption rate. This fully releases the shrinkage-compensating effect of the concrete, resulting in a denser, more compact concrete after hardening, which improves its durability and reduces the risk of wall cracking. The concrete of this invention is economical and environmentally friendly, aligning with energy conservation, emission reduction, and green low-carbon principles.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: This invention provides a shrinkage-compensating concrete, comprising the following components: manufactured sand, coarse aggregate, water-reducing agent, cement, slag powder, fly ash, expansion agent, and water.

[0005] The beneficial effects of this invention are as follows: This invention utilizes the high water absorption of recycled aggregates to control the overall water absorption rate of concrete aggregates while simultaneously considering the mechanical and durability properties of concrete. The recycled aggregates exert a "water absorption-slow release" effect, slowing down the surface moisture evaporation rate and reducing capillary pressure, effectively improving the internal moisture environment of the concrete. The expansive agent enables the concrete to achieve good compactness, and combined with the water-retaining effect of the pores within the recycled aggregates, it slows down moisture migration, improves the internal moisture environment of the concrete, increases the compensation effect of the concrete, and enhances the impermeability of the concrete.

[0006] Based on the above technical solution, the present invention can be further improved as follows.

[0007] Furthermore, it includes the following components by mass: 700-800 parts manufactured sand, 741-1073 parts coarse aggregate, 0-305 parts recycled aggregate, 5-12 parts water-reducing agent, 250-320 parts cement, 45-60 parts slag powder, 45-60 parts fly ash, 30-40 parts expansion agent, and 150-170 parts water.

[0008] Furthermore, the coarse aggregate comprises 5mm to 20mm of crushed stone.

[0009] Furthermore, the coarse aggregate comprises the following components by weight: 628 to 719 parts of 10 mm to 20 mm mountain crushed stone and 113 to 354 parts of 5 mm to 10 mm mountain crushed stone.

[0010] The beneficial effects of adopting the above-mentioned further scheme are: the coarse aggregate is a compound of natural crushed stone, which controls the overall water absorption rate.

[0011] A second objective of this invention is to provide a method for preparing shrinkage-compensating concrete, comprising the following steps: (1) Pre-treat recycled aggregate, then add manufactured sand and coarse aggregate and mix for the first time, then add water-reducing agent and water and mix for the second time to obtain a mixture; (2) Add cement, slag powder, fly ash and expansion agent to the mixture and stir evenly to obtain slurry; pour the slurry and cure it to obtain shrinkage-compensating concrete.

[0012] Furthermore, the pretreatment of recycled aggregate in step (1) involves pre-wetting the recycled aggregate until it reaches a saturated surface-dry state.

[0013] Furthermore, the first stirring time in step (1) is 4s to 10s.

[0014] Furthermore, the second stirring time in step (1) is 4s to 10s.

[0015] Furthermore, the stirring time in step (2) is 30s~50s.

[0016] A third objective of this invention is to provide an application of shrinkage-compensating concrete, which is used in construction engineering.

[0017] The beneficial effects of this invention are: when the shrinkage-compensating concrete of this invention is used to pour underground exterior walls, the number and width of cracks are greatly reduced, the cracking of the underground walls is significantly improved, and there are no continuous or penetrating cracks. A follow-up visit 28 days after pouring showed no crack growth, and the structural strength met the requirements. Attached Figure Description

[0018] Figure 1The following are concrete shrinkage rate ratio curves for Examples 1-5 of the present invention; Figure 2 The following are concrete shrinkage rate ratio curves for Examples 6-10 of the present invention; Figure 3 This is a graph showing the concrete shrinkage rate ratio of Comparative Examples 1 to 3 of this invention. Figure 4 The graphs show the concrete strength growth curves of Embodiments 6, 10, and Comparative Example 1 of the present invention. Detailed Implementation

[0019] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0020] Example 1: Preparation of Shrinkage Compensating Concrete (1) 719 kg of material with a water absorption rate of 0.2%, a crushing value of 5.1%, a mud content of 0.4%, and an apparent density of 2810 kg / m³ 3 10-20mm mountain gravel (Hebei Laishui Qiumai Building Materials Co., Ltd.) with a water absorption rate of 0.3%, mud content of 0.4%, and apparent density of 2810 kg / m³. 3 5-10mm mountain crushed stone (Hebei Laishui Qiumai Building Materials Co., Ltd.) is mixed to obtain coarse aggregate. The coarse aggregate is mixed with 730kg of manufactured sand (Hebei Laishui Qiumai Building Materials Co., Ltd.) and stirred for 5s. Then, 8.74kg of polycarboxylate high-performance water-reducing agent (Hebei Chang'an Yucai Technology Co., Ltd.) and 166kg of water are added and stirred for 5s to obtain a mixture. (2) Add 297 kg of P•O42.5 ordinary Portland cement (Hebei Baoding Quyang Jinyu Cement Co., Ltd.) and 55 kg of S95 grade slag powder (Tianjin Lanyisheng Environmental Technology Co., Ltd.; specific surface area 433 m²) to the mixture. 2 / kg, flowability ratio 101%, apparent density 2890 kg / m³ 3 7-day activity index 86%, 28-day activity index 105%), 55kg high-quality Class F II fly ash (Tianjin Qishengxiang Building Materials Sales Co., Ltd.; fineness 45μm, sieve residue 20.6%, loss on ignition 1.42%, water requirement ratio 98%, density 2140kg / m³). 3 Mix 30kg of P1 expansion agent (Tianjin Baoming Building Materials Sales Co., Ltd.; water reduction rate 28%, solid content 9.24%) with 30kg of P1 expansion agent for 35s to obtain slurry; after pouring the slurry, you will get shrinkage-compensating concrete.

[0021] Examples 2-5: The difference between Examples 2-5 and Example 1 lies in the amount of each raw material used; all other conditions are the same as in Example 1. The high-quality Type I expanding agent supplied by Wuhan Sanyuan Building Materials Sales Co., Ltd. is referred to as P1 in the table below; the high-quality Type I expanding agent supplied by Tianjin Baoming Building Materials Sales Co., Ltd. is referred to as P2 in the table below. The amounts of raw materials used in Examples 2-5 are shown in Table 1. Table 1 (Unit: kg) Example 6: Preparation of Shrinkage Compensating Concrete (1) 305 kg of 5-10 mm recycled aggregate (Hebei Xiong'an Rongcheng Construction Waste Processing Plant; water absorption rate 6.0%, mud content 0.4%, apparent density 2410 kg / m³) 3 Pre-wet to saturated surface-dry state; then add 757 kg of manufactured sand (Hebei Laishui Qiumai Building Materials Co., Ltd.), 628 kg of [material name missing] with a water absorption rate of 0.2%, crushing value of 5.1%, mud content of 0.4%, and apparent density of 2810 kg / m³. 3 10-20mm mountain gravel (Hebei Laishui Qiumai Building Materials Co., Ltd.) with a water absorption rate of 0.3%, mud content of 0.4%, and apparent density of 2810 kg / m³. 3 Mix 5-10mm mountain gravel (Hebei Laishui Qiumai Building Materials Co., Ltd.) and stir for 5 seconds, then add 8.74kg of polycarboxylate high-performance water-reducing agent (Hebei Chang'an Yucai Technology Co., Ltd.) and 166kg of water and stir for 5 seconds to obtain a mixture; (2) Add 296 kg of P•O42.5 ordinary Portland cement (Hebei Baoding Quyang Jinyu Cement Co., Ltd.) and 53 kg of S95 grade slag powder (Tianjin Lanyisheng Environmental Technology Co., Ltd.; specific surface area 433 m²) to the mixture. 2 / kg, flowability ratio 101%, apparent density 2890 kg / m³ 3 7-day activity index 86%, 28-day activity index 105%), 53kg of high-quality Class F II fly ash (Tianjin Qishengxiang Building Materials Sales Co., Ltd.; fineness 45μm, sieve residue 20.6%, loss on ignition 1.42%, water requirement ratio 98%, density 2140kg / m³). 3 Mix 35kg of P1 expansion agent (Tianjin Baoming Building Materials Sales Co., Ltd.; water reduction rate 28%, solid content 9.24%) with 35kg of P1 expansion agent for 35s to obtain slurry; after pouring the slurry, you will get shrinkage-compensating concrete.

[0022] Examples 7-10: The difference between Examples 7-10 and Example 1 is that the amounts of each raw material are different, while all other conditions are the same as in Example 1. The high-quality Type I expanding agent supplied by Wuhan Sanyuan Building Materials Sales Co., Ltd. is referred to as P1 in the table below; the high-quality Type I expanding agent supplied by Tianjin Baoming Building Materials Sales Co., Ltd. is referred to as P2 in the table below. The amounts of raw materials used in Examples 7-10 are shown in Table 2. Table 2 (Unit: kg) Comparative Examples 1-3: The difference between Comparative Examples 1-3 and Example 1 is that the amounts of each raw material are different; all other conditions are the same as in Example 1. The amounts of raw materials used in Comparative Examples 1-3 are shown in Table 3. Table 3 (Unit: kg) Experimental example: (1) The concrete shrinkage ratio of Examples 1-10 and Comparative Examples 1-3 was tested using the contact method in GB 50082. When the concrete compressive strength reached 3-5 MPa, the initial length was measured after demolding. The results are shown in Table 4. Figures 1-3 As shown: Table 4 (Unit: %) From Table 1, Figures 1-3 We can obtain: (1) Based on the comprehensive analysis of concrete shrinkage ratio and economy, concrete with about 8% total cementitious materials (cement, fly ash, slag powder) added to the expansion agent, such as the concrete shrinkage performance curve of Example 2, is relatively flat and has a better effect.

[0023] (2) Based on the analysis of the concrete shrinkage ratio results, the concrete in Example 8 has the best shrinkage compensation performance.

[0024] (3) From the analysis of plasticity, the workability of the concrete in each group is good, and the setting time does not change significantly, which can meet the casting requirements. In terms of shrinkage rate, Comparative Example 1 begins to shrink after 1 day, Comparative Example 2 begins to shrink after about 3 days, Comparative Example 3 begins to shrink after about 2 days, and Example 3 has the lowest shrinkage rate at 14 days.

[0025] 2. Properties and mechanical properties of concrete mixtures The performance and standard curing strength of the concrete mixtures in Examples 6-10 and Comparative Example 1 were compared and analyzed. The results are shown in Table 4. Figure 4 As shown.

[0026] Table 4 From Table 4, Figure 4 It can be seen that the 28-day strength of the concrete in Example 8 is 57.8 MPa, which is 11.8% higher than the 28-day strength of 51.7 MPa in Comparative Example 1. This indicates that the coarse aggregate promotes later hydration and slightly improves the mechanical properties, with an improvement of about 5% to 10%. In terms of concrete performance, the setting time is slightly longer, but there is no significant difference in slump expansion.

[0027] 3. Impermeability: According to GB / T 50082-2024, an impermeability test was conducted on the optimal mix proportion (Example 8, aggregate water absorption rate 1.40%), and the results are shown in Table 5: Table 5 As shown in Table 5, the expansion agent enables the concrete to achieve good compactness and bonding. The water storage function of the pores inside the recycled aggregate slows down the migration of moisture, improves the internal humid environment of the concrete, increases the compensation effect of the concrete, and improves the impermeability.

[0028] 4. Freeze resistance: According to GB / T 50082-2024, the optimal mix proportion (Example 8, aggregate water absorption rate 1.40%) was tested using the rapid freezing method (100 cycles). The results are shown in Table 6. Table 6 Table 6 shows that adding recycled aggregate increases the overall water absorption rate of concrete aggregate, but has no significant effect on the frost resistance of concrete.

[0029] Based on preliminary tests, on April 19, 2025, concrete of Example 1 was used to pour the exterior wall of the basement of Building 8-5# in Plot E04-07-02 (Plot 08) of the Phase I Supporting Project of the University Town in the Fifth Cluster of the Xiong'an New Area Start-up Zone. The concrete strength grade was Example 7, and the construction unit was China Metallurgical Construction Group. Seven days after pouring, two minor cracks, approximately 30 cm long and less than 0.1 mm wide, were observed on the inner wall surface of the 20-meter section between the pouring strips. Compared with previous underground exterior wall pours, the number and width of cracks were significantly reduced, and the cracking of the underground wall was significantly improved. There were no continuous or penetrating cracks. A follow-up visit to the project 28 days after pouring revealed no crack growth and a rebound value of 38.6 MPa, which is equivalent to 41.3 MPa after conversion. The structural strength met the requirements.

[0030] In summary, the preparation method of this invention combines recycled aggregate with crushed stone, achieving a comprehensive water absorption rate of 1.4%. This effectively improves the internal moisture environment of the concrete, allowing the shrinkage compensation effect of the concrete to be fully released, thereby reducing the risk of wall cracking. The high water absorption of the recycled aggregate allows the expansion performance of the expanding agent to be fully utilized, resulting in denser concrete after hardening and improved durability. Compared with conventional aggregates such as dolomite, recycled aggregate has a price advantage, reducing the unit cost of concrete by more than 2 yuan / cubic meter, bringing certain economic benefits. Furthermore, the application of recycled aggregate realizes the reuse of construction waste resources, aligning with energy conservation, emission reduction, and green low-carbon initiatives.

[0031] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A shrinkage-compensating concrete, characterized in that, It includes the following components: manufactured sand, coarse aggregate, recycled aggregate, water-reducing agent, cement, slag powder, fly ash, expanding agent, and water.

2. The shrinkage-compensating concrete according to claim 1, characterized in that, Includes the following components by weight: 700-800 parts manufactured sand, 741-1073 parts coarse aggregate, 0-305 parts recycled aggregate, 5-12 parts water-reducing agent, 250-320 parts cement, 45-60 parts slag powder, 45-60 parts fly ash, 30-40 parts expansion agent, and 150-170 parts water.

3. The shrinkage-compensating concrete according to claim 2, characterized in that, The coarse aggregate consists of 5mm to 20mm of crushed stone.

4. The shrinkage-compensating concrete according to claim 3, characterized in that, The coarse aggregate comprises the following components by weight: 628 to 719 parts of 10 mm to 20 mm mountain gravel and 113 to 354 parts of 5 mm to 10 mm mountain gravel.

5. A method for preparing shrinkage-compensating concrete according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Pre-treat the recycled aggregate, then add the manufactured sand and coarse aggregate and mix them for the first time, then add the water-reducing agent and water for the second time to obtain the mixture; (2) Add cement, slag powder, fly ash and expansion agent to the mixture and stir evenly to obtain slurry; after pouring the slurry, shrinkage-compensating concrete is obtained.

6. The method for preparing shrinkage-compensating concrete according to claim 5, characterized in that, The pretreatment of coarse aggregate in step (1) specifically involves pre-wetting the coarse aggregate until it reaches a saturated surface-dry state.

7. The method for preparing shrinkage-compensating concrete according to claim 5, characterized in that, The first stirring time in step (1) is 4s to 10s.

8. The method for preparing shrinkage-compensating concrete according to claim 5, characterized in that, The second stirring time in step (1) is 4s to 10s.

9. A method for preparing shrinkage-compensating concrete according to claim 5, characterized in that, The stirring time in step (2) is 30s~50s.

10. An application of shrinkage-compensating concrete, characterized in that, The shrinkage-compensating concrete of claim 9 is used in building construction.

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