A method for improving the crack resistance of ultra-high performance concrete structures
By combining composite fiber structures and self-healing microcapsules, the problem of cracking in ultra-high performance concrete during the hardening process has been solved, thereby improving crack resistance and durability, and reducing material costs and construction time.
Patent Information
- Application Number
- CN202610482277.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-13
- Publication Date
- 2026-06-30
AI Technical Summary
Ultra-high performance concrete is prone to temperature stress and shrinkage stress during the hardening process, leading to early and late cracks. Existing methods are difficult to effectively suppress early micro-cracks, and traditional fiber modification has limited effect, affecting the structural load-bearing capacity and durability.
By employing a combination of composite fiber structure and self-healing microcapsules, and through alternating layers of metal fibers and fine slag, combined with the alkali-activated effect of polylactic acid fibers, a three-dimensional support network is formed. This network, along with a gelling system, reduces hydration heat release and shrinkage stress, and allows for rapid healing by releasing repair agents through microcapsules when cracks occur.
It significantly reduces shrinkage cracking, improves tensile and compressive strength, restores mechanical properties, extends durability, and reduces material costs and maintenance cycles.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the field of concrete materials, and more specifically to a method for improving the crack resistance of ultra-high performance concrete structures. Background Technology
[0002] Ultra-high performance concrete (UHPC), a new type of building material with ultra-high strength, excellent durability and good workability, is mainly composed of cement, silica fume, ultrafine quartz sand, steel fiber and other components in an optimized proportion. It has received widespread attention and application in the construction of major infrastructure such as bridges, high-rise buildings and marine engineering. However, during the hardening process, ultra-high performance concrete (UHVPC) is prone to significant temperature stress due to its large cement content and intense hydration reaction. Simultaneously, its high cementitious material content and extremely low water-cement ratio result in substantial drying shrinkage and autogenous shrinkage. The combined effect of these factors makes UHVPC structures highly susceptible to early and late-stage cracking during construction and service. Cracks not only reduce the structure's load-bearing capacity and durability but can also lead to a series of problems such as steel reinforcement corrosion and leakage, severely impacting the safety and service life of the project and limiting the wider application of UHVPC. Currently, there are some research and application methods to improve the crack resistance of ultra-high performance concrete, such as compensating for shrinkage by incorporating expansive agents, reducing heat of hydration by optimizing the mix proportion, and enhancing toughness by using fiber modification. However, existing methods have certain limitations: the expansion effect of some expansive agents is greatly affected by curing conditions, making it difficult to play a stable role in actual engineering; simply optimizing the mix proportion often fails to simultaneously achieve both strength and crack resistance; and traditional fiber modification has limited effect on crack suppression, especially in controlling early-stage fine cracks. Summary of the Invention
[0003] To address the aforementioned shortcomings of existing technologies, this invention provides a method for improving the crack resistance of ultra-high performance concrete structures.
[0004] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for improving the crack resistance of ultra-high performance concrete structures is provided. The ultra-high performance concrete is made from 600-650 parts of silicate cement, 100-110 parts of fly ash, 60-80 parts of fine slag loaded with self-healing microcapsules, 50-70 parts of polylactic acid fiber, 70-80 parts of metal fiber, 10-13 parts of composite admixture and 150-170 parts of water. The specific preparation steps are as follows: S1: Immerse the metal fibers in high-flow polyurethane adhesive, filter out the excess polyurethane adhesive, add polylactic acid fibers and mix evenly to obtain composite fibers. S2: Fine slag loaded with self-healing microcapsules and composite fibers are alternately laid in the mold. The thickness of the fine slag layer is 3~4mm and the thickness of the composite fiber layer is 15~18mm. S3: Prepare a slurry by uniformly mixing silicate cement, fly ash, composite admixture and water; S4: Pour the slurry into the mold with the fine slag layer and composite fiber layer laid, vibrate and cure to obtain ultra-high performance concrete with improved structural crack resistance.
[0005] Furthermore, the preparation method of the fine slag of the self-healing microcapsule is as follows: fine slag of 40~50μm, calcium sulfoaluminate and stannous octoate are mixed evenly in a mass ratio of 100:5~10:3~5, lactide monomer is added, and the mixture is stirred at 200~500rpm / min and 110~150℃ for 2~4h.
[0006] Furthermore, after the fine slag is cleaned and dried, it is impregnated with a 0.5%~1% silane coupling agent solution for 10 minutes.
[0007] Furthermore, the composite admixture is obtained by mixing metakaolin, alkali activator, polycarboxylate superplasticizer, defoamer and retarder in a mass ratio of 3-5 parts: 3-5 parts: 4-5 parts: 0.2-0.3 parts: 0.1-0.2 parts.
[0008] Furthermore, the alkaline activator can be either sodium hydroxide or potassium hydroxide.
[0009] Furthermore, the defoamer is polydimethylsiloxane; the retarder is sodium citrate or sodium gluconate, or a mixture of both in any proportion.
[0010] Furthermore, the metal fibers are copper-plated microfilament steel fibers with a length of 3-4 mm and a diameter of 0.2 mm; the polylactic acid fibers have a length of 10-12 mm and a diameter of 70-90 μm.
[0011] Furthermore, in step S4, the concrete mixture inside the mold is vibrated using a vibrating rod in a grid pattern. Each time the vibrating rod is used, it vibrates up and down 3 to 5 times. After the vibration is completed, a vibrating table is used to vibrate for 25 to 30 seconds.
[0012] Furthermore, in step S4, the maintenance process is as follows: A1: Cured for 24 hours in an environment with room temperature and humidity above 50%; A2: Slowly raise the temperature to 80℃ at a rate of 10℃ / h, and hold at 80℃ for 12h; A3: Slowly cool to room temperature at a rate of 5℃ / h to complete the curing process.
[0013] The beneficial effects of this invention are as follows: This invention utilizes polylactic acid fibers and metal fibers bonded together with polyurethane adhesive to form a composite fiber. After treatment with polyurethane adhesive, the composite fiber forms a three-dimensional support network, which is alternately laid with a fine slag layer to create a gradient structure, effectively inhibiting the initiation and propagation of microcracks. The cementing system, combined with composite additives, reduces the heat of hydration, and the micropores of the fine slag buffer shrinkage stress, significantly reducing shrinkage cracking.
[0014] The self-healing microcapsules loaded with fine slag are uniformly dispersed. When cracks occur, they release a repair agent, rapidly healing the microcracks, significantly restoring mechanical properties and impermeability, and improving durability. Furthermore, under the alkali activation effect during the polylactic acid fiber curing process, the fine slag can bond tightly with the composite fiber, achieving a synergistic effect of "crack prevention and repair." This makes it suitable for the construction of complex components, reducing material costs, shortening the curing cycle, and significantly reducing the total life cycle cost. Detailed Implementation
[0015] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.
[0016] The specifications and sources of the raw materials used in the embodiments of the present invention are shown in Table 1 below; Table 1
[0017] Example 1 Preparation of fine slag for self-healing microcapsules: Fine slag of 40~50μm, calcium sulfoaluminate and stannous octoate are mixed evenly in a mass ratio of 100:5~10:3~5, lactide monomer is added, and the mixture is stirred at 200~500rpm / min and 110~150℃ for 2~4h.
[0018] Example 2 Ultra-high performance concrete was prepared using the following method: S1: Weigh 80 parts of metal fiber and immerse it in high-flow polyurethane adhesive. After filtering out the excess polyurethane adhesive, add 70 parts of polylactic acid fiber and mix evenly to obtain composite fiber. S2: Take 60 parts of the fine slag loaded with self-healing microcapsules prepared in Example 1 and the composite fiber prepared in Example S1, and lay them alternately in a mold, wherein the thickness of the fine slag layer is 3~4mm and the thickness of the composite fiber layer is 15~18mm. S3: Weigh 600 parts silicate cement, 100 parts fly ash, 3 parts metakaolin, 5 parts sodium hydroxide, 4 parts polycarboxylate superplasticizer, 0.2 parts polydimethylsiloxane, 0.2 parts sodium citrate, and 170 parts water, mix them evenly to prepare the slurry; S4: Pour the slurry into the mold with the fine slag layer and composite fiber layer laid. Use a vibrator to vibrate the concrete mixture in the mold in a grid pattern. Each time, the vibrator should vibrate up and down 3 to 5 times. After vibration, use a vibrating table to vibrate for 25 to 30 seconds to remove air bubbles. The mold is cured together with the mold. The curing process is as follows: A1: Cured for 24 hours in an environment with room temperature and humidity above 50%; A2: Slowly raise the temperature to 80℃ at a rate of 10℃ / h, and hold at 80℃ for 12h; A3: Slowly cool to room temperature at a rate of 5℃ / h to complete the curing process.
[0019] Example 3 Ultra-high performance concrete was prepared using the following method: S1: Weigh 70 parts of metal fiber and immerse it in high-flow polyurethane adhesive. After filtering out the excess polyurethane adhesive, add 50 parts of polylactic acid fiber and mix evenly to obtain composite fiber. S2: Take 80 parts of the fine slag loaded with self-healing microcapsules prepared in Example 1 and the composite fiber prepared in Example S1, and lay them alternately in a mold, wherein the thickness of the fine slag layer is 3~4mm and the thickness of the composite fiber layer is 15~18mm. S3: Weigh 650 parts silicate cement, 110 parts fly ash, 5 parts metakaolin, 3 parts sodium hydroxide, 5 parts polycarboxylate superplasticizer, 0.3 parts polydimethylsiloxane, 0.1 parts sodium citrate, and 160 parts water, mix them evenly to prepare the slurry; S4: Pour the slurry into the mold with the fine slag layer and composite fiber layer laid. Use a vibrator to vibrate the concrete mixture in the mold in a grid pattern. Each time, the vibrator should vibrate up and down 3 to 5 times. After vibration, use a vibrating table to vibrate for 25 to 30 seconds to remove air bubbles. The mold is cured together with the mold. The curing process is as follows: A1: Cured for 24 hours in an environment with room temperature and humidity above 50%; A2: Slowly raise the temperature to 80℃ at a rate of 10℃ / h, and hold at 80℃ for 12h; A3: Slowly cool to room temperature at a rate of 5℃ / h to complete the curing process.
[0020] Example 4 Ultra-high performance concrete was prepared using the following method: S1: Weigh 80 parts of metal fiber and immerse it in high-flow polyurethane adhesive. After filtering out the excess polyurethane adhesive, add 70 parts of polylactic acid fiber and mix evenly to obtain composite fiber. S2: Take 70 parts of the fine slag loaded with self-healing microcapsules prepared in Example 1 and the composite fiber prepared in Example S1, and lay them alternately in a mold, wherein the thickness of the fine slag layer is 3~4mm and the thickness of the composite fiber layer is 15~18mm. S3: Weigh 630 parts silicate cement, 100 parts fly ash, 4 parts metakaolin, 4 parts sodium hydroxide, 5 parts polycarboxylate superplasticizer, 0.2 parts polydimethylsiloxane, 0.2 parts sodium citrate, and 150 parts water, mix them evenly to prepare the slurry; S4: Pour the slurry into the mold with the fine slag layer and composite fiber layer laid. Use a vibrator to vibrate the concrete mixture in the mold in a grid pattern. Each time, the vibrator should vibrate up and down 3 to 5 times. After vibration, use a vibrating table to vibrate for 25 to 30 seconds to remove air bubbles. The mold is cured together with the mold. The curing process is as follows: A1: Cured for 24 hours in an environment with room temperature and humidity above 50%; A2: Slowly raise the temperature to 80℃ at a rate of 10℃ / h, and hold at 80℃ for 12h; A3: Slowly cool to room temperature at a rate of 5℃ / h to complete the curing process.
[0021] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S1, the metal fiber and polylactic acid fiber are directly mixed evenly to form a composite fiber.
[0022] Comparative Example 2 The difference between this comparative example and Example 1 is that the ratio of metakaolin to sodium hydroxide is 3:1.
[0023] Comparative Example 3 The difference between this comparative example and Example 1 is that during mixing, the composite fiber, the fine slag loaded with self-healing microcapsules, and the slurry are stirred together at 60~80 rpm / min for 10~15 min.
[0024] The mechanical properties of the samples from the above embodiments and comparative examples were tested in accordance with the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" GB / T50081-2019.
[0025] The results are shown in Table 1 below; Table 1
[0026] As shown in Examples 2-4 of Table 1, the technical solution of this invention can produce concrete with better tensile and compressive strength, and also with better crack resistance. As shown in Comparative Example 1, when metal fibers and polylactic acid fibers are directly mixed to form composite fibers, the tensile and compressive strength of the prepared concrete samples are reduced. In actual preparation, it was found that after the composite fiber slurry was poured into the mold, some polylactic acid fibers would float to the surface, and vibration and compaction would exacerbate this, resulting in uneven fiber distribution within the concrete sample. This led to a decrease in both tensile and compressive strength, but a slight decrease in shrinkage. As shown in Comparative Example 2, when the amount of alkali activator was reduced, almost all of the alkali activator reacted with the metakaolin, without decomposing the polylactic acid fibers. The polylactic acid fibers did not hydrolyze, preventing the formation of more porous structures in the concrete. This resulted in the 28-day compressive and flexural strength of the concrete samples being significantly lower than in Example 1, and a significant increase in shrinkage. As shown in Comparative Example 3, after replacing vibration with stirring, the tensile strength of the concrete sample decreased, but the compressive strength and shrinkage did not change significantly. This may be because stirring caused the polylactic acid fibers to agglomerate.
Claims
1. A method for improving the crack resistance of ultra-high performance concrete structures, characterized in that, Ultra-high performance concrete is made from 600-650 parts of silicate cement, 100-110 parts of fly ash, 60-80 parts of fine slag loaded with self-healing microcapsules, 50-70 parts of polylactic acid fiber, 70-80 parts of metal fiber, 10-13 parts of composite admixture and 150-170 parts of water. The specific preparation steps are as follows: S1: Immerse the metal fibers in high-flow polyurethane adhesive, filter out the excess polyurethane adhesive, add polylactic acid fibers and mix evenly to obtain composite fibers. S2: Fine slag loaded with self-healing microcapsules and composite fibers are alternately laid in the mold. The thickness of the fine slag layer is 3~4mm and the thickness of the composite fiber layer is 15~18mm. S3: Prepare a slurry by uniformly mixing silicate cement, fly ash, composite admixture and water; S4: Pour the slurry into the mold with the fine slag layer and composite fiber layer laid, vibrate and cure to obtain ultra-high performance concrete with improved structural crack resistance.
2. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 1, characterized in that, The preparation method of the fine slag of the self-healing microcapsule is as follows: fine slag of 40~50μm, calcium sulfoaluminate and stannous octoate are mixed evenly in a mass ratio of 100:5~10:3~5, lactide monomer is added, and the mixture is stirred at 200~500rpm / min and 110~150℃ for 2~4h.
3. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 2, characterized in that, After the fine slag is cleaned and dried, it is also soaked in a 0.5%~1% silane coupling agent solution for 10 minutes.
4. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 1, characterized in that, The composite admixture is obtained by mixing metakaolin, alkali activator, polycarboxylate superplasticizer, defoamer and retarder in a mass ratio of 3-5 parts: 3-5 parts: 4-5 parts: 0.2-0.3 parts: 0.1-0.2 parts.
5. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 4, characterized in that, The alkaline activator is either sodium hydroxide or potassium hydroxide.
6. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 4, characterized in that, The defoamer is polydimethylsiloxane; the retarder is sodium citrate or sodium gluconate, or a mixture of both in any proportion.
7. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 1, characterized in that, The metal fiber is copper-plated microfiber steel fiber with a length of 3-4 mm and a diameter of 0.2 mm; the polylactic acid fiber has a length of 10-12 mm and a diameter of 70-90 μm.
8. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 1, characterized in that, In step S4, the concrete mixture in the mold is vibrated using a vibrating rod in a grid pattern. Each time the vibrating rod is vibrated up and down 3 to 5 times, the mixture is vibrated for 25 to 30 seconds after the vibration is completed.
9. The method for improving the crack resistance of ultra-high performance concrete structures according to claim 1, characterized in that, In step S4, the maintenance process specifically includes: A1: Cured for 24 hours in an environment with room temperature and humidity above 50%; A2: Slowly raise the temperature to 80℃ at a rate of 10℃ / h, and hold at 80℃ for 12h; A3: Slowly cool to room temperature at a rate of 5℃ / h to complete the curing process.