Multi-source composite expansion super-early-strength concrete and preparation method thereof

Abstract

The invention discloses multi-source composite expansion super-early-strength concrete and a preparation method thereof. The concrete comprises a cementing material, aggregate, a water reducing agent, water and a multi-source composite expansion system. The expansion system is composed of a plastic expansion agent, a calcium sulphoaluminate early expansion source, a magnesium oxide delayed expansion source and an internal curing material. Through precise component design and function time sequence matching, a cooperative compensation network covering the whole life cycle of the concrete is constructed, a plastic expanding agent inhibits plastic shrinkage, calcium sulphoaluminate compensates early-stage self-shrinkage, magnesium oxide resists medium-and-long-term drying shrinkage, an internal curing material provides continuous moisture guarantee for the above process, and the overall performance of the concrete is improved. And the efficiency of each expansion source is excited and coupled. According to the invention, seamless and accurate shrinkage compensation from a plastic stage to a service later stage can be realized on the premise of ensuring the super early strength characteristic of the concrete, the technical problem that the super early strength concrete is easy to crack due to severe shrinkage is fundamentally solved, and the volume stability and durability of the structure are remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building materials, and particularly relates to a multi-source composite expansion super-early-strength concrete and a preparation method thereof. BACKGROUND

[0002] With the rapid development of modern infrastructure construction in China, high requirements are put forward for the early strength of concrete in the fields of prefabricated buildings, expressway bridge repair, emergency rescue and disaster relief, and national defense engineering, and the application of super-early-strength concrete capable of reaching a compressive strength of more than 30 MPa within 2-3 hours is increasingly widespread. In order to achieve this goal, the currently commonly used technical paths include: selecting fast-hardening sulphoaluminate cement, greatly reducing the water-binder ratio, adding high-activity admixtures and high-efficiency water reducing agents, etc.

[0003] However, these technical means which are effective in mechanical properties, while endowing the concrete with super-early-strength characteristics, also bring more severe challenges to the volume stability. First, the extremely low water-binder ratio and the rapid early hydration reaction lead to significant internal self-drying effect of the concrete, causing abnormally severe early self-shrinkage. Second, the high dosage of cementitious materials and the dense microstructure formed thereby make the medium and long-term drying shrinkage of the concrete also not negligible. This continuous shrinkage starting from the early plastic stage and continuing to the later stage is extremely easy to generate accumulated tensile stress in the concrete, which, once exceeding the early tensile strength which is still developing, will cause plastic shrinkage cracks and hardening period shrinkage cracks, seriously damaging the durability, waterproof performance and long-term bearing capacity of the structure.

[0004] In order to control the shrinkage of concrete, an expansion agent is a commonly used technology. However, the traditional single expansion source has obvious limitations in dealing with the complex shrinkage process of super-early-strength concrete. For example, although calcium sulphoaluminate (such as ettringite) expansion agent can provide early expansion, its expansion reaction cannot continue in the environment of the dense microstructure of super-early-strength concrete and the lack of water in the later stage caused by the extremely low water-binder ratio, and it cannot effectively compensate for the medium and late shrinkage. Although magnesium oxide expansion agent has a unique delayed expansion characteristic, its slow expansion process is seriously mismatched in time with the early self-shrinkage of super-early-strength concrete which develops rapidly, and it cannot inhibit the risk of early cracking, and the expansion amount is also uncertain in the dense system lacking of water supply. In addition, internal curing materials (such as superabsorbent resin SAP) can effectively alleviate self-drying by internal water supply, but the expansion driving force provided by themselves is limited, and it is difficult to completely offset the shrinkage when used alone.

[0005] In the prior art, there are also attempts to compound different expansion sources in order to achieve gradient compensation. However, such simple physical compounding often lacks systematic synergistic design, and the action mechanisms of the components may conflict or interfere with each other. For example, the rapid consumption of water by early expansion agents may lead to the failure of internal curing materials, or affect the rapid hydration process dominated by super early strength cement; and the expansion source may produce local stress concentration in the absence of effective guidance and space, thereby damaging the compactness of the matrix. Therefore, the prior art is difficult to provide precise, matched and seamless compensation effects at various key stages (plastic stage, early hardening stage, middle and late stage) of the shrinkage development of super early strength concrete, and there is often a contradiction between shrinkage control and the development of super early strength characteristics.

[0006] In view of this, there is an urgent need in the field to break through the thinking set of the prior art and develop a brand new super early strength concrete material system. The system can achieve seamless, precise and adaptive compensation for the shrinkage of concrete from the plastic stage to the long-term service stage through an internal, multi-component synergistic action mechanism, thereby fundamentally solving the industry problems of poor volume stability and easy cracking of super early strength concrete while ensuring the super early strength characteristics. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a multi-source composite expansion super early strength concrete and a preparation method thereof. By constructing a multi-source synergistic expansion compensation system, seamless shrinkage compensation is achieved from the plastic stage, early hardening stage to the late service stage under the premise of ensuring the super early strength (2 h strength ≥ 30 MPa) of the concrete, thereby fundamentally solving the industry problem of easy cracking of high strength concrete.

[0008] The present application is realized by the following technical solutions:

[0009] A multi-source composite expansion super early strength concrete, comprising cementitious materials, aggregates, water reducing agents, water and a multi-source composite expansion system, wherein the multi-source composite expansion system is composed of a plastic expansion agent, a calcium sulphoaluminate early expansion source, a magnesium oxide delayed expansion source and an internal curing material.

[0010] Preferably, the concrete comprises, by weight:

[0011] Cementitious materials 450-600 parts;

[0012] Coarse aggregates 800-1000 parts;

[0013] Fine aggregates 700-900 parts;

[0014] Water reducing agent is 1.0%-2.5% of the mass of cementitious materials;

[0015] Water is added according to a water-binder ratio of 0.18-0.25;

[0016] The multi-source composite expansion system accounts for 9% to 25% of the mass of the cementitious material.

[0017] Preferably, the percentage of each component in the multi-source composite expansion system relative to the total mass of the cementitious material is:

[0018] Plastic expander 0.01%~0.1%;

[0019] Calcium sulfoaluminate is a 5%–15% early expansion source;

[0020] Magnesium oxide-based delayed expansion sources: 4%–10%;

[0021] Internal maintenance material: 0.2%~0.5%.

[0022] Preferably, the cementitious material is composed of 60% to 80% by mass of rapid-hardening sulfoaluminate cement and 20% to 40% by mass of silicate cement, wherein the strength grade of the rapid-hardening sulfoaluminate cement and the silicate cement is not lower than 52.5.

[0023] Preferably, the plastic expander is aluminum powder or an organic hydrocarbon compound.

[0024] Preferably, the calcium sulfoaluminate early expansion source is prepared by compounding sulfoaluminate cement clinker and gypsum in a mass ratio of (1.5~2.5):1.

[0025] Preferably, the magnesium oxide delayed expansion source is composed of light-burned magnesium oxide and medium-burned magnesium oxide in a mass ratio of 1:(0.8~1.2).

[0026] Preferably, the internal protective material is a superabsorbent polymer with a particle size of 80-120 mesh.

[0027] The above-mentioned method for preparing multi-source composite expansive ultra-early strength concrete includes the following steps:

[0028] Step 1) Pretreatment of key components:

[0029] Step 1-1) Premixing of magnesium oxide delayed expansion source: Lightly calcined magnesium oxide and medium-calcined magnesium oxide are added into a mixer in proportion and mixed evenly to obtain a composite magnesium oxide delayed expansion source;

[0030] Step 1-2) Premixing of calcium sulfoaluminate early expansion source: Add sulfoaluminate cement clinker and gypsum into a mixer in proportion and mix evenly to obtain calcium sulfoaluminate early expansion source premix.

[0031] Steps 1-3) Dispersion treatment of internal curing materials: The superabsorbent polymer is pre-mixed with some dried fine aggregate to form a dispersion;

[0032] Step 2) Concrete mixing and preparation:

[0033] Step 2-1) Initial dry mixing: Put all the coarse aggregate, most of the fine aggregate and some of the cementitious materials into the mixer and dry mix for 30~60 seconds;

[0034] Step 2-2) Secondary dry mixing: Add the remaining cementitious materials, water-reducing agent, composite magnesium oxide delayed expansion source, calcium sulfoaluminate early expansion source premix prepared in step 1), and internal curing material dispersion, and dry mix for 60~90 s until uniform.

[0035] Steps 2-3) Wet mixing: Dissolve the plastic expansion agent in all the mixing water beforehand, then add it while stirring, and then wet mix at high speed for 120-180 seconds to obtain a uniform concrete mixture;

[0036] Step 3) Concrete forming and curing:

[0037] Pour the concrete mixture prepared in step 2) into the mold and vibrate it to compact it. For specimens that need to be tested for ultra-early strength, demold and test after curing under standard conditions for 2 hours. For specimens that need to be tested for long-term performance, after sealing and curing, transfer them to standard curing conditions or constant temperature and humidity conditions for curing until the specified age.

[0038] The beneficial effects of this invention are as follows:

[0039] (1) This invention constructs a compensation network covering the entire process of concrete shrinkage through the functional and temporal design of each component. The plastic expansion agent generates microbubbles in the plastic stage, effectively offsetting settlement and plastic shrinkage; the calcium sulfoaluminate expansion source reacts rapidly in the early hardening stage (several hours to 3 days) to generate ettringite (AFt), precisely counteracting the most severe auto-shrinkage in this stage; the magnesium oxide expansion source continues to hydrate in the middle and late stages (after 7 days), stably compensating for drying shrinkage; the internal curing material provides continuous moisture for the above chemical reactions, playing the role of "logistical support" and "efficiency multiplier". This four-component system forms a synergistic effect of "early crack prevention, mid-term compensation, and late-term stabilization", making the expansion curve of the material highly matched with the shrinkage process of ultra-early strength concrete, realizing "seamless" compensation from the start of pouring to long-term service, fundamentally inhibiting the generation of cracks at each stage.

[0040] (2) Sulfoaluminate cement clinker is the source of aluminum and calcium for the formation of ettringite (AFt), an early-expansion product, while gypsum provides the necessary sulfate ions. This invention determined this specific compound ratio through numerous experiments, aiming to optimize the early expansion rate and amount. Too much clinker will lead to excessively rapid and concentrated expansion, potentially damaging the early strength framework; too much gypsum will result in insufficient reaction, and excess gypsum may adversely affect later performance. This invention optimizes the ratio of sulfoaluminate cement clinker to gypsum to ensure that the early expansion rate is coordinated with strength development, avoiding damage to the early strength framework due to excessively rapid and concentrated expansion. This preferred ratio ensures the generation of abundant and smooth expansion stress during the critical window period of ultra-early strength concrete strength development, thereby effectively suppressing early cracking. Experiments have shown that the concrete using this invention can achieve a compressive strength of over 30 MPa in 2 hours, fully meeting the requirements of ultra-early strength technology. At the same time, its early autogenous shrinkage and medium-to-long-term drying shrinkage are significantly suppressed, successfully solving the core contradiction of the difficulty in achieving both high strength and high stability in ultra-early strength concrete.

[0041] (3) Magnesium oxides calcined at different temperatures exhibit different hydration activities. Lightly calcined MgO hydrates faster and can contribute to expansion starting in the middle stage; medium-calcined MgO hydrates slowly and mainly provides for later-stage expansion. By compounding magnesium oxides with different activities, this invention broadens the time domain of delayed expansion. This design avoids the "expansion pulse" or "expansion gap" that may occur with a single expansion source, and instead provides a continuous, mild, and controllable expansion stress, effectively compensating for the long-term drying shrinkage in ultra-early strength concrete, ensuring the long-term stability of the structural volume, and greatly improving crack resistance and durability.

[0042] (4) In ultra-early strength concrete systems with low water-cement ratios, rapid internal moisture consumption is the main factor limiting the effectiveness of expansion agents and causing self-drying shrinkage. This invention preferably uses internal curing materials (SAP) with specific particle sizes, which can pre-absorb moisture during the mixing stage, forming "miniature reservoirs" throughout the system. As the internal humidity of the concrete decreases due to hydration, these SAPs can gradually release the absorbed moisture. This process achieves three benefits: first, it directly alleviates self-drying and reduces self-shrinkage; second, it provides a water source for the continuous hydration of calcium sulfoaluminate, extending and enhancing the early expansion efficiency; and third, it ensures that magnesium oxide can undergo a smooth hydration reaction in the middle and later stages, activating the delayed expansion efficiency. This coupling mechanism of "internal curing" and "multi-source expansion" fully stimulates and guarantees the efficiency of each expansion source, producing a synergistic effect of "1+1>2".

[0043] (5) When concrete is still in a plastic state, surface moisture evaporation and aggregate settlement can easily cause plastic shrinkage cracks. The plastic expansion agent (such as aluminum powder or specific organic matter) selected in this invention can generate uniform, closed micro hydrogen or air bubbles in the slurry within a short time after pouring at extremely low dosage (0.01%~0.1%). The introduction of these bubbles can effectively offset the volume reduction in the plastic stage and lay a good foundation for subsequent compensation.

[0044] (6) The whole system of the present invention has good compatibility with commonly used concrete raw materials, the preparation process is simple, and no special equipment is required. It is very suitable for large-scale application in fields such as prefabrication, rapid repair, and disaster relief where early strength and volume stability are extremely important. Attached Figure Description

[0045] Figure 1 The strength development curves of the concrete prepared in Examples 1-3 and Comparative Examples 1-5 are shown.

[0046] Figure 2 The graph shows a comparison of the shrinkage performance development of concrete prepared in Examples 1-3 and Comparative Examples 1-5. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0048] Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art, and the experimental methods without specific conditions are all conventional methods in the art.

[0049] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0050] In the following embodiments, the raw materials include:

[0051] Cementitious material: P·II 52.5R Portland cement, specific surface area ≥350 m² 2 / kg; Grade 52.5 rapid-hardening sulfoaluminate cement, initial setting time not earlier than 25 min.

[0052] Aggregate: 5~10 mm continuously graded basalt crushed stone, crushing index ≤8%, mud content <0.5%; natural quartz sand with fineness modulus of 2.6 and mud content <1.0%.

[0053] Water-reducing agent: Polycarboxylate-based high-performance water-reducing agent with a solid content of 40% and a water reduction rate of ≥30%.

[0054] Plastic expander: aluminum powder, active aluminum content ≥95%, average particle size 30 μm.

[0055] Early expansion sources of calcium sulfoaluminate: Grade 42.5 sulfoaluminate cement clinker (specific surface area ≥ 400 m²) 2 The gypsum dihydrate (purity ≥90%) was premixed with gypsum dihydrate ( / kg) at a mass ratio of 2:1.

[0056] Magnesium oxide delayed expansion source: It is composed of lightly calcined magnesium oxide (activity value 105±15 s) and medium-calcined magnesium oxide (activity value 280±30 s) in a mass ratio of 1:1.

[0057] Inner curing material: cross-linked sodium polyacrylate superabsorbent polymer (SAP), particle size 100 mesh, water absorption ratio (in deionized water) ≥150 g / g.

[0058] The standard concrete mix proportion is as follows: 550 parts of cementitious materials, of which silicate cement: sulfoaluminate cement = 30:70 (by mass); 950 parts of coarse aggregate; 800 parts of fine aggregate; polycarboxylate superplasticizer at 2.0% of the cementitious materials by mass (based on solid content); and a water-cement ratio of 0.22.

[0059] To systematically verify the synergistic effect of the multi-source composite expansion system of the present invention, the following embodiments and comparative examples were designed. All groups followed the above-mentioned baseline ratios and additional expansion system components as shown in Table 1 were added.

[0060] Table 1 below lists the specific proportions of the expansion system components in preferred embodiments 1-3 and comparative examples 1-5 of the present invention. The concrete preparation methods of each embodiment and comparative example are the same as those in embodiment 1.

[0061] Table 1. Component ratio of the expansion system

[0062]

[0063] Example 1

[0064] A method for preparing multi-source composite expansive ultra-early strength concrete, the specific steps of which are as follows:

[0065] 1. Pretreatment of key components

[0066] (1) Premixing and homogenization of magnesium oxide expansion source

[0067] To ensure the stability of the delayed expansion effect, lightly calcined magnesium oxide (activity value 105 s) and medium-calcined magnesium oxide (activity value 280 s) were physically premixed at a mass ratio of 1:1. A total of 33 parts of the two types of magnesium oxide were added to a V-type mixer and mixed at 30 rpm for 30 min until the color was completely uniform, thus obtaining a composite magnesium oxide delayed expansion source, which was sealed and stored for later use.

[0068] (2) Premixing of calcium sulfoaluminate early expansion source

[0069] 35 parts of sulfoaluminate cement clinker and 20 parts of dihydrate gypsum were put into the same mixer and mixed evenly using the same process to obtain calcium sulfoaluminate early expansion source premix.

[0070] (3) Anti-caking treatment of internal curing material (SAP)

[0071] To prevent the superabsorbent polymer (SAP) from clumping instantly upon contact with water during stirring, it is initially mixed manually in a bag with 10 times its weight of dry silica sand (taken from the fine aggregate portion) to form SAP-quartz sand dispersion.

[0072] 2. Concrete mixing and preparation

[0073] The preparation process was carried out at room temperature (20±5℃).

[0074] (1) Initial dry mixing

[0075] All coarse aggregate (950 parts), all fine aggregate (790 parts, minus 10 parts used for SAP dispersion), and half of the cementitious material (i.e., 82.5 parts silicate cement and 192.5 parts sulfoaluminate cement) were added to a forced twin-shaft mixer. The mixture was dry-mixed at low speed (60 rpm) for 30 seconds to allow the aggregate surface to be initially coated with the cementitious material.

[0076] (2) Secondary dry mixing

[0077] Add the remaining cementitious materials, polycarboxylate superplasticizer powder (11 parts, based on solid content), the premixed calcium sulfoaluminate early expansion source (55 parts), the composite magnesium oxide delayed expansion source (33 parts), and SAP-quartz sand dispersion to the mixer. Increase the mixer speed to medium speed (90 rpm) and continue dry mixing for 60 seconds until all powders are visually observed to be uniformly mixed and without color difference.

[0078] (3) Wet mixing

[0079] Pre-disperse the plasticizing agent (0.275 parts) in a small amount of mixing water (approximately 5 parts) to prepare a plasticizing agent suspension. Keep the mixer running at medium speed (90 rpm), and add the remaining 115 parts of mixing water and the plasticizing agent suspension to the mixing vessel at a uniform rate over 1 minute. After all the water has been added, increase the mixer speed to high speed (120 rpm) and continue mixing for 120 seconds. At this point, the mixture should become viscous and moist, the SAP particles should be uniformly dispersed with water, and there should be no obvious dry material or lumps. The entire mixture should exhibit a highly uniform state.

[0080] 3. Specimen molding and segmented curing

[0081] (1) Molding

[0082] The freshly mixed concrete was quickly poured into 150 mm × 150 mm × 150 mm molds and compacted on a vibrating table until the surface was covered with cement paste. At the same time, samples were taken to measure the slump flow of the concrete.

[0083] (2) Ultra-early curing and performance testing (for 2-hour strength)

[0084] To test the 2-hour early strength performance, the mold was immediately moved into a standard curing room (temperature 20±2℃, relative humidity ≥95%). Two hours after casting, the mold was removed and its compressive strength was immediately tested using a pressure testing machine.

[0085] (3) Standard maintenance (for routine performance)

[0086] ①Self-shrinking specimens: Another batch of specimens were sealed with aluminum foil tape immediately after final setting (determined by the penetration resistance method), and a contact sensor was installed. They were placed in a constant temperature environment of 20±2℃ to automatically record the length changes.

[0087] ② Drying shrinkage and long-term strength specimens: After another batch of specimens were molded and sealed for 3 days, they were immediately moved into a constant temperature and humidity chamber at 20±2℃ and 60±5% humidity, and cured for 1 day, 3 days, 7 days, 28 days and 56 days respectively, and their drying shrinkage value and compressive strength were tested.

[0088] Test Example 1

[0089] 1. Experimental Design

[0090] The specimens prepared in Examples 1-3 and Comparative Examples 1-5 were tested according to national standards. The workability was in accordance with standard GB / T 50080, the mechanical properties were in accordance with standard GB / T 50081, and the shrinkage properties were in accordance with standard GB / T 50082.

[0091] 2. Experimental Results and Analysis

[0092] Table 2 Results of concrete material properties and strength development for each group

[0093]

[0094] Table 3. Results of shrinkage performance development of concrete materials in each group (unit: µε)

[0095]

[0096] Tables 2 and 3 show a comparison of the workability, strength, and shrinkage properties of the concrete prepared in Examples 1-3 and Comparative Examples 1-5. The strength development curves of each group of concrete are shown in the figures. Figure 1 As shown, the early autogenous shrinkage and medium-to-long-term drying shrinkage development curves of each group of concrete are as follows: Figure 2As shown. The specific analysis is as follows:

[0097] (1) From Table 2 and Figure 1 As can be seen, all groups maintained good workability. With the increase of the total dosage of the multi-source composite expansion system (Example 1 → Example 2), the expansion decreased slightly, but was still far above the lower limit of the construction requirements (e.g., 600 mm). In terms of strength, the 2-hour compressive strength of Examples 1-3 all exceeded 30 MPa, meeting the core index of ultra-early strength. Compared with Comparative Example 1 (baseline group), the early strength of Examples 1-3 was slightly reduced due to the introduction of a large amount of expansion components, but this is a reasonable price to pay for achieving excellent volume stability. A key finding is that all groups containing internal curing material (SAP) (Examples 1-3, Comparative Example 5) had 28-day strengths that were higher than or close to the baseline group, and significantly higher than Comparative Example 4 without SAP. This demonstrates that internal curing not only does not impair later strength, but also improves the final strength of the material by promoting full hydration of the cementitious material, optimizing the microstructure.

[0098] (2) From Table 3 and Figure 2 It can be seen that the shrinkage values ​​of Examples 1-3 were consistently lower than those of Comparative Examples 1-5 throughout all test periods from 3 days to 56 days. This fully demonstrates the comprehensive advantages and reliability of the "quaternary composite system" provided by this invention in shrinkage control.

[0099] (3) The key role of internal curing materials (SAP)

[0100] Compared with Comparative Example 4 (without SAP) and Example 1 (with SAP), the shrinkage value of Example 1 was significantly lower than that of Comparative Example 4 at all ages. This directly proves that SAP is a "bridge" connecting early expansion and delayed expansion, and the internal moisture it provides is a necessary condition for activating and maintaining the expansion efficiency of both, achieving a good synergistic effect.

[0101] (4) Contribution of plastic expansion agent

[0102] Comparing Comparative Example 5 (without plastic expansion) and Example 1, it can be seen that Example 1 has a significant advantage in 3-day auto-shrinkage performance. This indicates that the plastic expansion agent effectively fills the "shrinkage compensation window" between pouring and early hardening, laying a solid foundation for the entire shrinkage control system.

[0103] (5) Effectiveness of the ratio range

[0104] Examples 1-3 represent three typical formulations of the present invention: high, medium, and low. Their shrinkage data exhibit a regular variation: Example 2, with the highest content of the expanding component, shows the best shrinkage control effect, while Example 3, with the lowest content, shows a slightly weaker effect. However, all three are significantly better than any comparative example. This proves that the formulation range of the present invention is scientific and effective, and significantly superior effects to existing technologies can be obtained within this range.

[0105] (6) Synergistic effect of the four-component system

[0106] The above test data fully demonstrates that the quaternary system of "plastic expansion agent + calcium sulfoaluminate early expansion source + magnesium oxide delayed expansion source + internal curing material (SAP)" provided by this invention is not a simple superposition of functions, but rather produces a profound positive synergistic effect:

[0107] Synergistic effect: The four components play their roles in the plastic phase, early hardening phase and mid-to-late hardening phase, respectively, covering the entire cycle of shrinkage development.

[0108] Hydration Synergy: The internal maintenance material (SAP) is the "hub" of the synergistic effect. Through internal water supply, it simultaneously ensures the durability of early expansion and activates the reliability of delayed expansion, thereby tightly coupling the other three "expansion power sources" together.

[0109] Ultimately, this invention, while ensuring the ultra-high early strength of ultra-early strength concrete, achieves precise and efficient control over its shrinkage deformation throughout the entire process, with technical effects far exceeding expectations and solving a long-standing technical bottleneck in this field.

[0110] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. The scope of protection of the present invention is determined by the scope claimed in the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A multi-source composite expansive ultra-high early strength concrete, characterized in that, The concrete comprises cementitious material, aggregate, water reducing agent, water and multi-source composite expansion system, wherein the multi-source composite expansion system is composed of plastic expansion agent, calcium sulphoaluminate early expansion source, magnesium oxide delayed expansion source and internal curing material.

2. The multi-source composite expansive ultra-high early-strength concrete according to claim 1, characterized in that, The concrete comprises, in parts by weight: Cementitious material 450-600 parts; Coarse aggregate 800-1000 parts; Fine aggregate 700-900 parts; Water reducing agent is 1.0%-2.5% of the mass of cementitious material; Water is added according to water-binder ratio of 0.18-0.25; Multi-source composite expansion system is 9%-25% of the mass of cementitious material.

3. The multi-source composite expansive ultra-high early strength concrete according to claim 2, characterized in that, The percentage of each component in the multi-source composite expansion system in the total mass of cementitious material is: Plastic expansion agent 0.01%-0.1%; Calcium sulphoaluminate early expansion source 5%-15%; Magnesium oxide delayed expansion source 4%-10%; Internal curing material 0.2%-0.5%.

4. The multi-source composite expansive ultra-high early strength concrete according to claim 1, characterized in that, The cementitious material is composed of 60%-80% of fast-hardening sulphoaluminate cement and 20%-40% of Portland cement, and the strength grade of the fast-hardening sulphoaluminate cement and the Portland cement is not less than 52.

5.

5. The multi-source composite expansive ultra-high early strength concrete according to claim 1, characterized in that, The plastic expansion agent is aluminum powder or organic hydrocarbon compound.

6. The multi-source composite expansive ultra-high early strength concrete according to claim 1, characterized in that, The calcium sulphoaluminate early expansion source is compounded by sulphoaluminate cement clinker and gypsum according to mass ratio (1.5-2.5):

1.

7. The multi-source composite expansive ultra-high early strength concrete according to claim 1, characterized in that, The magnesium oxide delayed expansion source is compounded by light-burned magnesium oxide and medium-burned magnesium oxide according to mass ratio 1:(0.8-1.2).

8. The multi-source composite expansive ultra-high early strength concrete according to claim 1, characterized in that, The internal curing material is superabsorbent polymer with particle size of 80-120 mesh.

9. A method of producing a multi-source composite expansive super-early-strength concrete according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: Step 1) pretreatment of key components: Step 1-1) premixing of magnesium oxide delayed expansion source: light-burned magnesium oxide and medium-burned magnesium oxide are put into a mixer in proportion and mixed uniformly to obtain composite magnesium oxide delayed expansion source; Step 1-2) premixing of calcium sulphoaluminate early expansion source: sulphoaluminate cement clinker and gypsum are put into a mixer in proportion and mixed uniformly to obtain calcium sulphoaluminate early expansion source premix; Step 1-3) dispersion treatment of internal curing material: superabsorbent polymer is pre-mixed with part of dry fine aggregate to form dispersion material; Step 2) mixing and preparation of concrete: Step 2-1) initial dry mixing: all coarse aggregate, most of fine aggregate and part of cementitious material are put into a mixer and dry mixed for 30-60 s; Step 2-2) secondary dry mixing: the remaining cementitious material, water reducing agent, composite magnesium oxide delayed expansion source prepared in step 1, calcium sulphoaluminate early expansion source premix and internal curing material dispersion material are put in and dry mixed for 60-90 s until uniform; Step 2-3) wet mixing: plastic expansion agent is pre-dissolved in all mixing water, then added in the mixing state, and high-speed wet mixing is carried out for 120-180 s to obtain uniform concrete mixture; Step 3) molding and curing of concrete: The concrete mixture prepared in step 2 is poured into a mold and vibrated to be compacted; the test piece for testing ultra-early strength is demolded and tested after curing for 2 h under standard conditions; the test piece for testing long-term performance is cured after sealing, and then transferred to standard curing conditions or constant temperature and humidity conditions for curing until the specified age.

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