High crack resistance mass concrete and preparation method thereof
By using pre-wetted lightweight porous aggregates combined with polypropylene fibers in large-volume concrete, an internal curing and bridging mechanism is formed, which solves the problem of insufficient crack resistance in large-volume concrete and achieves full-process crack control and the homogeneity and strength stability of concrete.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DAZHOU MAOYUAN BUILDING MATERIALS CO LTD
- Filing Date
- 2026-03-18
- Publication Date
- 2026-06-19
Smart Images
Figure CN122233697A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of building materials technology, and more specifically, to a high crack-resistant large-volume cement concrete and its preparation method. Background Technology
[0002] High-crack-resistant mass concrete is a key material for large-volume concrete structures such as hydraulic dams, large foundations, and bridge abutments. During the hardening process, these structures experience significant internal and external temperature differences due to the heat released during cement hydration, leading to temperature stress and shrinkage. If not properly controlled, this can easily result in harmful cracks, severely impacting the structure's integrity, durability, and safety. Therefore, developing mass concrete with excellent crack resistance is crucial for ensuring the long lifespan and safe operation of critical infrastructure.
[0003] To improve the crack resistance of large-volume concrete, existing technologies mainly focus on materials and employ the following strategies: First, adding expansive agents to compensate for concrete shrinkage through the volume expansion of their hydration products; second, incorporating various fibers to inhibit the generation and propagation of microcracks through the bridging effect of the fibers; and third, using lightweight aggregates to partially or completely replace ordinary aggregates to prepare lightweight concrete, thereby reducing the structural self-weight and elastic modulus and thus reducing temperature stress.
[0004] However, the aforementioned existing technologies still have some drawbacks in practical applications: First, the stability of the expansion agent's compensation effect is insufficient: the hydration and expansion effect of the expansion agent are highly dependent on a continuous and sufficient supply of water. Inside large-volume concrete, due to the high temperature and easy loss of water, the expansion agent may not hydrate sufficiently, resulting in an unstable effect in compensating for shrinkage, and even generating unfavorable expansion stress in the later stages. Second, the crack resistance contribution of single fibers has shortcomings: polypropylene fibers are effective in inhibiting early plastic shrinkage cracks, but their inhibitory effect on drying shrinkage and temperature shrinkage cracks after concrete hardening is limited; while steel fibers can improve later crack resistance and toughness, they pose challenges in controlling early cracks and preventing corrosion. Third, it is difficult to achieve a balance in the comprehensive performance of lightweight aggregate concrete: although the introduction of lightweight aggregate can reduce its self-weight, its porous nature usually leads to a decrease in concrete strength, and the interfacial bond between the aggregate and cement paste is weak; during mixing and pouring, lightweight aggregate is prone to floating, resulting in poor homogeneity of concrete, which may introduce new weak points.
[0005] Therefore, there is an urgent need for a high-performance, large-volume concrete that can achieve crack resistance throughout the entire process and in multiple dimensions by synergistically regulating material composition and microstructure. Summary of the Invention
[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a high crack-resistant large-volume cement concrete and its preparation method.
[0007] To achieve the above objectives, the present invention provides the following technical solution: a high crack-resistant large-volume cement concrete, comprising the following components in parts by weight: 260-300 parts cement, 100-150 parts mineral admixtures, 700-750 parts fine aggregate, 1050-1100 parts coarse aggregate, 155-165 parts water, 5.0-8.0 parts polycarboxylate-based high-performance water-reducing agent, and 30-90 parts composite crack-resistant functional material;
[0008] The composite crack-resistant functional material is composed of pre-wetted lightweight porous aggregate and polypropylene fiber; the mass ratio of the lightweight porous aggregate to the polypropylene fiber is 1:(0.15-0.35).
[0009] Preferably, the lightweight porous aggregate is saturated ceramsite.
[0010] Preferably, the particle size of the water-saturated ceramsite is 4.75-9.5 mm.
[0011] Preferably, the length of the polypropylene fiber is 10-20 mm.
[0012] Preferably, the mass ratio of the lightweight porous aggregate to the polypropylene fiber is 1:(0.2-0.3).
[0013] Preferably, the mineral admixture includes fly ash and slag powder.
[0014] Preferably, the pre-wetting treatment controls the volumetric water absorption rate of the lightweight porous aggregate to be within the range of 15%-25%.
[0015] This invention also provides a method for preparing the above-mentioned high crack-resistant mass cement concrete, comprising the following steps:
[0016] S1. Premixing: Pre-wetted lightweight porous aggregates are first dry-mixed with some fine aggregates to obtain premixed aggregates;
[0017] S2. Main mixing: Add cement, mineral admixtures, all coarse aggregates and the remaining fine aggregates to the mixer in sequence, dry mix evenly, then add the premixed aggregates and polypropylene fibers, and continue to dry mix until uniform.
[0018] S3. Final mixing: Add water containing admixtures to the uniformly mixed dry materials and perform wet mixing until a uniform concrete mixture is obtained.
[0019] Preferably, in step S2, the dry mixing time after adding polypropylene fiber is controlled at 1-3 minutes.
[0020] Preferably, in the wet mixing process of step S3, the total time for mixing at low speed for 30 seconds and then switching to normal speed is controlled within 2-4 minutes.
[0021] The technical effects and advantages of this invention are as follows:
[0022] 1. Enhanced stability and durability of crack resistance: This invention uses pre-wetted, saturated expanded clay aggregates to replace or supplement traditional expansion agents. These lightweight, porous aggregates form a distributed "micro-reservoir" within the concrete, continuously and slowly releasing moisture during cement hydration, providing uniform and stable internal curing for the cementitious system. This technique effectively overcomes the shortcomings of external curing moisture penetration into large-volume concrete and the dependence of expansion agents on external water supply, ensuring the long-term stability of the shrinkage compensation effect and fundamentally reducing the risk of cracking caused by drying and autogenous shrinkage.
[0023] 2. Achieved Synergistic Crack Resistance Across the Entire Process and at Multiple Scales: This invention creatively combines lightweight porous aggregate with polypropylene fibers in a functional blend. The polypropylene fibers can be uniformly dispersed in concrete, effectively inhibiting the generation and development of microcracks during the early plastic shrinkage stage through bridging. Simultaneously, the introduction of lightweight porous aggregate not only provides internal curing but also helps reduce the overall elastic modulus of the concrete due to its low elastic modulus, thereby alleviating tensile stress caused by temperature gradients. The synergy of these two elements forms a composite crack resistance mechanism combining fiber-based crack inhibition and aggregate water release to relieve stress, achieving full life-cycle crack control of concrete from the early plastic stage to the later hardening and thermal shrinkage stage.
[0024] 3. Improved Comprehensive Performance and Homogeneity of Concrete: Addressing the industry challenge of lightweight aggregates' tendency to float and uneven distribution, this invention employs a unique pre-mixing process. First, pre-wetted lightweight porous aggregates are dry-mixed with a portion of fine aggregates. This crucial step allows fine aggregate particles to adhere to the surface of the lightweight aggregates, significantly increasing their apparent density and friction, thereby effectively suppressing the floating and agglomeration of lightweight aggregates during subsequent mixing and pouring. This technique ensures the uniform distribution of functional materials within the concrete matrix, eliminating weak interfaces caused by material delamination. While improving crack resistance, it also guarantees the stability of concrete strength and the overall homogeneity of the structure. Attached Figure Description
[0025] Figure 1 This is a flowchart of the concrete preparation method of the present invention. Detailed Implementation
[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0027] Example
[0028] Example 1
[0029] Example 1 provides a high crack-resistant mass cement concrete, the preparation method of which is shown below:
[0030] 1. Raw material preparation: Weigh 280 parts by weight of cement, 125 parts by weight of mineral admixtures, 725 parts by weight of fine aggregate, 1075 parts by weight of coarse aggregate, 160 parts by weight of water, and 6.5 parts by weight of polycarboxylate-based high-performance water-reducing agent. Weigh 48 parts by weight of pre-wetted saturated ceramsite as lightweight porous aggregate, with a particle size of 6-9 mm confirmed by sieving; weigh 12 parts by weight of polypropylene fiber, with a length of 15 mm confirmed by measurement; mix the two at a mass ratio of 1:0.25 to prepare 60 parts by weight of composite crack-resistant functional material.
[0031] The mineral admixture is a mixture of Grade II fly ash conforming to GB / T 1596 and Grade S95 slag powder conforming to GB / T 18046 in a mass ratio of 1:1, and its total admixture accounts for about 31% of the total mass of the cementitious materials.
[0032] The fine aggregate is natural river sand with a fineness modulus of 2.7, which meets the requirements for medium sand in GB / T 14684 "Sand for Construction"; the coarse aggregate is crushed stone with a continuous gradation of 5-25mm in particle size, which meets the requirements of GB / T 14685 "Pebbles and Crushed Stone for Construction".
[0033] The polycarboxylate-based high-performance water-reducing agent is a slow-release polycarboxylate water-reducing agent with a solid content of 40% and a water reduction rate of 28%. Its water reduction performance is determined according to GB / T 8077 "Test Method for Homogeneity of Concrete Admixtures".
[0034] The pre-wetting treatment method is as follows: soak the dried ceramsite in clean water for no less than 24 hours until saturated, remove and drain the surface water, controlling its volumetric water absorption rate within the range of 15%-25%. The method for determining the volumetric water absorption rate is based on GB / T17431.2 "Lightweight aggregates and their test methods Part 2: Lightweight aggregate test methods". In this embodiment, the measured water absorption rate of the ceramsite is 18%.
[0035] 2. Premixing: Take 145 parts by weight of fine aggregate and all 48 parts by weight of saturated ceramsite and put them into a mixer. Dry mix them at normal speed for 60 seconds in a dry state to make the fine aggregate evenly adhere to the surface of the ceramsite, and obtain premixed aggregate for suppressing floating. Discharge and set aside.
[0036] 3. Main mixing: Add all 280 parts by weight of cement, 125 parts by weight of mineral admixtures, 1075 parts by weight of coarse aggregate, and the remaining 580 parts by weight of fine aggregate to the forced mixer in sequence, and dry mix for 60 seconds until uniformly mixed. Then, add all the premixed aggregate prepared above, and at the same time add 12 parts by weight of polypropylene fiber, which together with the water-saturated ceramsite constitutes a composite crack-resistant functional material, and continue to dry mix for 2 minutes until all materials are uniformly dispersed in the dry mix.
[0037] 4. Final Mixing: Dissolve 6.5 parts by weight of polycarboxylate-based high-performance water-reducing agent in all 160 parts by weight of mixing water, and stir until dissolved. Slowly add this solution to the dry mixture in the mixer, first stirring at a low speed of 30 rpm for 30 seconds to initially wet the material, then switch to the normal speed of 60 rpm and continue stirring for 2.5 minutes, with the total wet mixing time controlled at 3 minutes. Discharge the concrete mixture when it is uniform, the paste fully coats the aggregate, and the surface has a noticeable gloss, thus obtaining the high crack-resistant large-volume cement concrete mixture.
[0038] Example 2-3
[0039] Examples 2-3 respectively provide a high crack-resistant large-volume cement concrete.
[0040] The only difference between the above embodiments and Embodiment 1 is that the mass ratio of pre-wetted saturated ceramsite to polypropylene fiber in the composite crack-resistant material is different, as shown below.
[0041] In Example 2: The composite crack-resistant material is prepared by mixing pre-wetting saturated ceramsite and polypropylene fiber at a mass ratio of 1:0.2. That is, 50 parts by weight of saturated ceramsite and 10 parts by weight of polypropylene fiber, totaling 60 parts by weight.
[0042] In Example 3: The composite crack-resistant material is prepared by mixing pre-wetting saturated ceramsite and polypropylene fiber at a mass ratio of 1:0.35. That is, 44.4 parts by weight of saturated ceramsite and 15.6 parts by weight of polypropylene fiber, totaling 60 parts by weight.
[0043] All other process parameters in the above embodiments are the same as those in Embodiment 1.
[0044] Comparative Examples 1-6
[0045] Comparative Examples 1-6 each provide a high crack-resistant, large-volume cement concrete.
[0046] The differences between the above comparative examples and Example 1 are as follows.
[0047] In Comparative Example 1: No composite crack-resistant functional materials or any other crack-resistant components were added.
[0048] In Comparative Example 2: Instead of adding composite crack-resistant materials, 60 parts by weight of UEA-H type concrete expansion agent conforming to GB 23439 standard were added.
[0049] In Comparative Example 3: the composite crack-resistant functional material is only polypropylene fiber, that is, 60 parts by weight of polypropylene fiber is added, and no water-saturated ceramsite is added.
[0050] In Comparative Example 4: the composite crack-resistant functional material consisted only of pre-wetted saturated ceramsite, i.e., 60 parts by weight of saturated ceramsite were added, without the addition of polypropylene fiber.
[0051] In Comparative Example 5: the premixing step was omitted during preparation. All fine aggregates, saturated ceramsite, and polypropylene fibers were added to the mixer along with other dry materials at the start of the main mixing in step S2 for dry mixing.
[0052] In Comparative Example 6: The composite crack-resistant functional material was prepared by mixing saturated ceramsite and polypropylene fiber at a mass ratio of 1:0.1, that is, 54.5 parts by weight of saturated ceramsite and 5.5 parts by weight of polypropylene fiber, totaling 60 parts by weight.
[0053] All other process parameters in the above comparative examples are the same as those in Example 1.
[0054] Performance testing
[0055] 1. Compressive strength and splitting tensile strength tests
[0056] After the specimens were cured to a standard age of 28 days, their compressive strength and splitting tensile strength were tested using standard cubic specimens in accordance with GB / T 50081 "Standard Test Methods for Physical and Mechanical Properties of Concrete". Compressive strength is used to evaluate the basic load-bearing capacity of concrete, while splitting tensile strength directly reflects its ability to resist internal tensile stress and inhibit crack propagation.
[0057] 2. Drying shrinkage rate test
[0058] After the specimens were cured to the specified age according to standard, the drying shrinkage deformation values at 3 days, 7 days, 28 days, 60 days, and 90 days were measured using a horizontal concrete shrinkage meter, in accordance with GB / T 50082 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". This index is used to quantitatively evaluate the long-term volume stability of concrete and directly verify the ability of internal curing to inhibit shrinkage.
[0059] 3. Circular ring constraint crack resistance test
[0060] According to ASTM C1581, "Standard Test Method for Concrete under Constrained Shrinkage Cracking," freshly mixed concrete was poured into a mold with a steel outer ring for confinement and then placed in a constant temperature and humidity environment. The time when the first visible crack appeared on the specimen (initial crack time) was continuously monitored and recorded, and the crack width could be measured later. This test is used to qualitatively and quantitatively evaluate the early crack resistance of concrete under confinement conditions.
[0061] 4. Performance Testing
[0062] According to GB / T 50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the slump and spread of fresh concrete were tested, and its cohesiveness and water retention were observed. This index is used to evaluate the workability of concrete.
[0063] 5. Homogeneity observation
[0064] For Comparative Example 5 and its corresponding embodiments involving lightweight aggregates, the concrete mixture was allowed to stand for a period of time, or the hardened specimens were cut open. By observing the aggregate distribution in the cross-section, it was possible to visually determine whether the pre-wetted lightweight aggregates exhibited floating, stratification, or uneven distribution, thus evaluating the effectiveness of the premixing process in ensuring the homogeneity of the mixture. This observation mainly focused on the distribution of pre-wetted lightweight porous aggregates, namely, saturated expanded clay aggregates.
[0065] The performance test results are shown in Table 1 below.
[0066] Table 1. Concrete performance test results of the examples and comparative examples
[0067]
[0068] Note: “—” in the table indicates that the formula in this group did not contain lightweight aggregate and is not involved in this observation.
[0069] Based on the test results of the examples and comparative examples in Table 1, it can be seen that Comparative Example 1, which did not add any composite crack-resistant functional materials, had a splitting tensile strength of only 3.05 MPa and a 90-day drying shrinkage rate as high as 427 × 10⁻⁶. -6 The initial cracking time in the ring test was only 19.7 hours, indicating significantly insufficient crack resistance. In contrast, the embodiments of this invention, by incorporating a composite crack-resistant functional material made of pre-wetted saturated ceramsite and polypropylene fiber, increased the splitting tensile strength to 4.18 MPa and reduced the drying shrinkage to 283 × 10⁻⁶ MPa. -6 Furthermore, the initial cracking time was extended to 73.8 hours, indicating that the composite material can effectively improve the crack resistance of concrete.
[0070] It should be noted that the 28-day compressive strength of Example 1 decreased slightly from 48.2 MPa in Comparative Example 1 to 45.7 MPa. This is mainly due to the slight increase in internal porosity caused by the introduction of lightweight porous aggregate and the micro-disturbance of the dense matrix structure by the fibers. However, the significant crack resistance gains—a 37% increase in splitting tensile strength, a 34% reduction in drying shrinkage, and a nearly three-fold extension of the initial cracking time—compared to a minor reduction in strength, and the strength of 45.7 MPa fully meets the conventional design requirements for large-volume concrete structures.
[0071] Further comparison of Example 1 with the single-component comparative example shows a significant synergistic effect. Comparative Example 3, which only added polypropylene fibers, achieved a relatively long spring cracking time of 63.9 hours due to fiber bridging, but its 90-day drying shrinkage rate was still as high as 398 × 10⁻⁶. -6 This indicates that its contribution to inhibiting long-term shrinkage is limited; in Comparative Example 4, only pre-wetted ceramsite was added, and although the drying shrinkage rate was effectively reduced to 312×10 through internal curing, it still had limited effect. -6 However, its initial cracking time was only 24.1 hours, indicating weak crack resistance in the early stages under strong constraints. In contrast, Example 1, which combined the two, exhibited both excellent early crack resistance and long-term volume stability, with an initial cracking time of 73.8 hours and a drying shrinkage rate of only 283 × 10⁻⁶. -6 This demonstrates that lightweight porous aggregate and polypropylene fiber exert a synergistic effect in addressing both early and late-stage cracking, jointly achieving crack control throughout the entire process. Furthermore, Comparative Example 5, which omitted the premixing step, exhibited severe stratification and aggregate floating, and its 28-day compressive strength decreased to 40.8 MPa, significantly lower than the 45.7 MPa of Example 1. This indicates that the premixing process employed in this invention plays a crucial role in ensuring the homogeneity and strength stability of the concrete.
[0072] Compared with Comparative Example 2, which uses a conventional UEA expanding agent, Example 1 shows better performance in terms of drying shrinkage and initial cracking time, proving that the composite crack-resistant material of the present invention is superior to the single expanding agent system in terms of long-term shrinkage inhibition and early crack resistance.
[0073] As shown in Table 1, the slump of the concrete mixtures in all embodiments remained above 170 mm, and the cohesiveness was good. It is noteworthy that Comparative Example 3, which only incorporated a large amount of fiber, had a slump of 162 mm, significantly lower than the control group, verifying the well-known fact that excessive fiber can impair flowability. However, in the composite system of this invention, by compounding and optimizing the ratio of fiber with saturated expanded clay aggregate, this adverse effect was effectively mitigated, enabling the concrete to achieve excellent crack resistance while maintaining good workability and meeting the construction requirements of large-volume concrete.
[0074] Finally, comparing Example 1 with Comparative Example 6, which has a lower fiber ratio, it can be seen that when the mass ratio of saturated ceramsite to polypropylene fiber is 1:0.1, the splitting tensile strength is 3.29 MPa and the initial cracking time is 45.6 h, both of which are lower than those of Example 1 with a mass ratio of 1:0.25. This indicates that controlling the mass ratio of the two in the range of 1:0.15 to 1:0.35, and especially preferably 1:0.2 to 1:0.3, helps to achieve a better crack resistance synergy.
[0075] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A high-crack-resistant, large-volume cement concrete, characterized in that, It includes the following components by weight: 260-300 parts cement, 100-150 parts mineral admixtures, 700-750 parts fine aggregate, 1050-1100 parts coarse aggregate, 155-165 parts water, 5.0-8.0 parts polycarboxylate-based high-performance water-reducing agent, and 30-90 parts composite crack-resistant functional material; The composite crack-resistant material is composed of pre-wetted lightweight porous aggregate and polypropylene fiber. The mass ratio of the lightweight porous aggregate to the polypropylene fiber is 1:(0.15-0.35).
2. The high crack-resistant mass cement concrete according to claim 1, characterized in that, The lightweight porous aggregate is saturated ceramsite.
3. The high crack-resistant mass cement concrete according to claim 2, characterized in that, The saturated ceramsite has a particle size of 4.75-9.5 mm.
4. The high crack-resistant mass cement concrete according to claim 1, characterized in that, The length of the polypropylene fiber is 10-20 mm.
5. The high crack-resistant mass cement concrete according to claim 1, characterized in that, The mass ratio of the lightweight porous aggregate to the polypropylene fiber is 1:(0.2-0.3).
6. The high crack-resistant mass cement concrete according to claim 1, characterized in that, The mineral admixtures include fly ash and slag powder.
7. The high crack-resistant mass cement concrete according to claim 1, characterized in that, The pre-wetting treatment controls the volumetric water absorption rate of the lightweight porous aggregate to be within the range of 15%-25%.
8. A method for preparing high crack-resistant mass cement concrete according to claims 1-7, characterized in that, Includes the following steps: S1. Premixing: Pre-wetted lightweight porous aggregates are first dry-mixed with some fine aggregates to obtain premixed aggregates; S2. Main mixing: Add cement, mineral admixtures, all coarse aggregates and the remaining fine aggregates to the mixer in sequence, dry mix evenly, then add the premixed aggregates and polypropylene fibers, and continue to dry mix until uniform. S3. Final mixing: Add water containing admixtures to the uniformly mixed dry materials and perform wet mixing until a uniform concrete mixture is obtained.
9. The preparation method according to claim 8, characterized in that, In step S2, the dry mixing time after adding polypropylene fiber is controlled at 1-3 minutes.
10. The preparation method according to claim 8, characterized in that, In the wet mixing process of step S3, the total time for mixing at low speed for 30 seconds and then switching to normal speed is controlled to be 2-4 minutes.