An intrinsically self-prestressed ECC material and a surface layer structure prepared therefrom and applications thereof

Abstract

The present invention belongs to the technical field of infrastructure structure and materials, and discloses an intrinsic self-prestressed ECC material and a surface layer structure and application prepared therefrom. By utilizing a low-dosage volume expansion component and a construction-maintenance combination strategy, the bottleneck of the incoordination between self-stress and the construction window period is broken through, and the maximum free expansion deformation of the intrinsic self-prestressed ECC material during the temperature and humidity maintenance process is controlled to be between 1500με-10000με, and the free volume deformation in the later service period is kept higher than 55% of the maximum free expansion deformation in the early period, innovatively realizing the dual needs of intrinsic self-prestressing and construction window. The maintenance-free seamless ultra-thin goal of the ECC surface layer structure is achieved through high-performance intrinsic self-prestressing and self-healing. The invention is widely applicable to marine ultra-thin large buoyancy floating bodies, pavements, bridge decks, airport runways, ultra-thin box culverts, concrete panels, pumped storage power station panels, anti-seepage panels, floor panels, channel linings, tunnel linings, and renovation and repair of old structures.

Description

Technical Field

[0001] The present invention relates to the technical field of infrastructure structures and materials, and in particular, to an intrinsically self-prestressed ECC material and a surface layer structure prepared therefrom and applications thereof. Background Art

[0002] To overcome the deficiency of brittle failure of concrete, Professor Victor Li of the University of Michigan in the United States invented Engineered Cementitious Composite (ECC). After being subjected to tension, ECC achieves a tensile ductility higher than 30,000 με through multiple fine cracks and exhibits tensile hardening ability. Due to different perspectives of translation and naming, ECC is also often referred to as High-Ductility Concrete (HDC), Strain-Hardening Cementitious Composite (SHCC), bendable concrete, Ultra-High Toughness Cementitious Composite (UHTCC), etc.

[0003] ECC has been innovatively applied in the field of seamless ultra-thin structures. Due to the excellent mechanical properties of ECC, ECC can reduce the thickness of traditional concrete structures, thereby achieving the purpose of saving materials and costs, such as the ultra-thin ECC pavement load-bearing layer in "Sun Renjuan, Bu Linglai, Guan Yanhua, etc. An ultra-thin pavement structure based on ultra-high toughness cementitious composite and implementation process [P]". In addition, by utilizing the ultra-high tensile deformation ability of ECC, ECC has been applied to seamless bridge decks and pavement structures to improve driving comfort and the durability of road and bridge decks. However, the above seamless road and bridge deck technology transfers the deformations of concrete such as temperature, shrinkage, and load to the ECC surface layer, inducing multiple cracks in ECC. Although the crack resistance and deformation ability of ECC are relatively large, the durability and safety issues of ECC after multiple cracks are still a concern. Therefore, the above is only a structure without construction joints, not a truly seamless and maintenance-free structure.

[0004] During the service process of ECC, the external constraints on its volume deformations such as temperature and shrinkage will generate tensile stresses, resulting in restrained tensile cracks, which affect the durability and service safety of the ECC structure. In particular, the drying shrinkage of ECC can reach 1500 - 3000 με, which is 3 - 6 times that of traditional concrete. To alleviate the above problems, those skilled in the art have obtained ECC with low shrinkage, zero shrinkage, or even expansive deformation through methods such as internal curing, external addition of shrinkage-reducing agents, and expansive agents.

[0005] Here, it is necessary to clearly distinguish two different concepts, that is, "expansive deformation ECC" is not equivalent to "prestressed ECC". High-expansive deformation ECC can be obtained by increasing the dosage of the expansive agent. However, due to the low early elastic modulus and large creep of ECC, the compressive stress generated by the constrained early expansive deformation is limited; the later elastic modulus of ECC is high, the creep is small, and the shrinkage is large, which will generate a relatively high tensile stress. Therefore, "Zhu H, Zhang D, Wang T, et al. Intrinsic self-stressing and low carbon Engineered Cementitious Composites (ECC) for improved sustainability[J]. Cement and Concrete Research, 2021, 149: 106580." points out that expansive deformation ECC may still be subjected to tensile cracking.

[0006] In addition, the ECC with a high dosage of expansive agent has a relatively fast setting speed, which is not conducive to actual construction applications, especially in construction service environments such as high temperature and dryness. In order to ensure that the ECC maintains prestress during service, it is necessary to comprehensively consider the reasonable dosage of the expansive agent, sufficient expansive deformation, controllable later shrinkage, complex service environment, dynamic material properties, etc. The coupling effect of the above complex factors forms a technical bottleneck restricting the intrinsic self-prestressed ECC. Summary of the Invention

[0007] The present invention aims to comprehensively innovate through methods such as materials, structures, and the combination of construction and maintenance, to invent a maintenance-free ultra-thin seamless ECC surface layer structure, and is committed to the development of sustainable high-quality infrastructure. It specifically relates to fields such as road surfaces, bridge decks, airport runways, ultra-thin box culverts, concrete panels, pumped-storage power station panels, anti-seepage panels, ultra-thin large buoyancy floating bodies in the ocean, floor slabs, channel linings, tunnel linings, and the renewal and repair of old structures.

[0008] The technical solution of the present invention is as follows: An intrinsic self-prestressed ECC material, by mass fraction, consists of 50 - 150 parts of volume expansion components, 100 - 800 parts of cement, 400 - 1200 parts of supplementary cementitious materials, 400 - 800 parts of aggregates, 200 - 400 parts of water, 0 - 30 parts of water reducers, 0 - 50 parts of shrinkage reducing agents, 0 - 10 parts of thickeners, and 10 - 40 parts of fibers.

[0009] The mass fraction of the volume expansion component is 16% - 32% of the total mass fraction of the cement and the volume expansion component; the supplementary cementitious material is 0.8 - 3.6 times the total mass of the cement and the volume expansion component.

[0010] The intrinsic self - prestressed ECC material is composed of 75 - 150 parts by mass of volume expansion components, 100 - 800 parts of cement, 400 - 1200 parts of supplementary cementitious materials, 400 - 800 parts of aggregates, 200 - 400 parts of water, 0 - 30 parts of water - reducing agents, 0 - 50 parts of shrinkage - reducing agents, 0 - 10 parts of thickeners, and 10 - 40 parts of fibers.

[0011] The intrinsic self - prestressed ECC material is composed of 75 - 130 parts by mass of volume expansion components, 100 - 800 parts of cement, 400 - 1200 parts of supplementary cementitious materials, 400 - 800 parts of aggregates, 200 - 400 parts of water, 0 - 30 parts of water - reducing agents, 0 - 50 parts of shrinkage - reducing agents, 0 - 10 parts of thickeners, and 10 - 40 parts of fibers.

[0012] The intrinsic self - prestressed ECC material is composed of 100 - 130 parts by mass of volume expansion components, 100 - 800 parts of cement, 400 - 1200 parts of supplementary cementitious materials, 400 - 800 parts of aggregates, 200 - 400 parts of water, 0 - 30 parts of water - reducing agents, 0 - 50 parts of shrinkage - reducing agents, 0 - 10 parts of thickeners, and 10 - 40 parts of fibers.

[0013] The volume expansion component is an early - stage volume expansion component or a combination of an early - stage volume expansion component and a late - stage volume expansion component.

[0014] The early - stage volume expansion component is one or more of calcium sulfoaluminate cement, aluminate cement, and calcium oxide; the late - stage volume expansion component is one or a combination of magnesia and steel slag.

[0015] The supplementary cementitious materials are one or more of fly ash, ground granulated blast - furnace slag (GGBFS), silica fume, pozzolan, steel slag powder, and metakaolin.

[0016] The aggregates are one or more of manufactured sand, river sand, sea sand, desert sand, steel slag powder, tailings slag, limestone powder, and rubber powder.

[0017] The fibers are one or more of polypropylene (PP) fibers, polyethylene (PE) fibers, polyvinyl alcohol (PVA) fibers, steel fibers, basalt fibers, carbon fibers, glass fibers, and fly ash fibers.

[0018] A maintenance - free ultra - thin seamless ECC surface layer structure is composed of the intrinsic self - prestressed ECC material. The direct tensile deformation ability of the intrinsic self - prestressed ECC material is higher than 30,000 με, the direct - tensile crack width is lower than 100 μm, and the permeability coefficient of the intrinsic self - prestressed ECC material that has experienced a direct tensile deformation of no more than 20,000 με is lower than 10 -8 m / s after contacting water for 14 days; under the external restraint during service, it maintains an intrinsic pre - compression stress of 0.1 MPa - 10 MPa.

[0019] The maintenance-free ultra-thin seamless ECC surface layer structure maintains an intrinsic self-prestressed state throughout its service life and self-heals after cracks occur; the four-point bending flexural strength of the maintenance-free ultra-thin seamless ECC surface layer structure is 8 MPa - 30 MPa, and the thickness of the maintenance-free ultra-thin seamless ECC surface layer structure is 0.5 - 30 cm, which is 60% lower than the thickness of the concrete surface layer with the same compressive strength grade.

[0020] The preparation method of the maintenance-free ultra-thin seamless ECC surface layer structure is as follows:

[0021] Control the volume deformation of the intrinsic self-prestressed ECC material during the temperature and humidity curing process to obtain the maintenance-free ultra-thin seamless ECC surface layer structure; the intrinsic self-prestressed ECC material maintains an intrinsic pre-compressive stress during service; the intrinsic self-prestressed ECC material is a high-ductility material.

[0022] The specific control of the volume deformation of the intrinsic self-prestressed ECC material during the temperature and humidity curing process is: control the maximum free expansion deformation of the intrinsic self-prestressed ECC material to be between 1500 με - 10000 με within 5 days during the temperature and humidity curing process, so that the free volume deformation after the later service is stable is higher than 55% of the early maximum free expansion deformation.

[0023] The temperature and humidity curing method includes spraying water for curing and covering the surface with plastic film, wet cloth, straw curtain, moisture-preserving material, and surface chemical moisture-preserving agent.

[0024] The temperature and humidity curing time is 0.25 - 3 days; the time after the later service is stable is 720 days and above.

[0025] The temperature and humidity curing process time is 0.5 - 2 days.

[0026] The temperature of the temperature and humidity curing is 10 - 40 °C, and the humidity is greater than 95%.

[0027] Through any one method or combination of secondary wet curing, adding steel slag, adding magnesium oxide, and adding stone powder, make the free volume deformation after the later service is stable higher than 55% of the early maximum free expansion deformation.

[0028] The secondary wet curing starts when the maximum expansion deformation retracts to 60 - 80% of the highest free expansion deformation, and the wet curing time is 0.25 - 3 days.

[0029] The temperature of the intrinsic self-prestressed ECC material during mixing and transportation is controlled at 5 - 30 °C.

[0030] The construction method of the maintenance-free ultra-thin seamless ECC surface layer structure is that within 120 minutes from the start of construction, as measured according to "GB / T2419-2020 Determination Method for Fluidity of Cement Mortar", the fluidity of the intrinsically self-stressed ECC material is between 120 mm and 220 mm.

[0031] The construction process is divided into forming the designed thickness in one go or constructing in multiple layers to reach the overall designed thickness.

[0032] The construction method is one or more of spray forming, mold casting, 3D printing, rolling, self-compacting, and smearing.

[0033] An application of a maintenance-free ultra-thin seamless ECC surface layer structure, which is applied to marine floating bodies, road surfaces, bridge decks, airport runways, ultra-thin culverts, concrete panels, impervious panels, pumped storage power station panels, floor slabs, canal linings, tunnel linings, spray repair thin layers, and manual smearing repair layers.

[0034] The beneficial effects of the present invention: Based on the intrinsically self-stressed ECC material with a limited amount of volume expansion components, its volume deformation is controlled so that the maximum free expansion deformation achieved during early temperature and humidity curing is between 1500 με - 10000 με, and the free volume deformation after 720 days and above is higher than 55% of the early maximum free expansion deformation. As a result, the formed maintenance-free ultra-thin seamless ECC surface layer structure maintains an intrinsic pre-compressive stress of 0.1 MPa - 10 MPa, thus ensuring that it can still meet the seamless requirement under the influence of various environmental factors during service, and even if cracks occur, self-healing can be achieved. Description of the Drawings

[0035] Figure 1 It is the evolution law of the fluidity expansion diameter with time under different curing conditions for the C100 scheme.

[0036] Figure 2 It is the evolution law of the fluidity expansion diameter with time under different curing conditions for the C130 scheme.

[0037] Figure 3 It is the evolution law of the fluidity expansion diameter with time under different curing conditions for the C150 scheme.

[0038] Figure 4 It is the evolution law of the fluidity expansion diameter with time under different curing conditions for the C160 scheme.

[0039] Figure 5 It is a schematic diagram of the early free volume deformation of C130-mixed ECC at different curing temperatures.

[0040] Figure 6Schematic diagram of the 180-day free volume deformation of ECC with C130 mix ratio at different curing temperatures.

[0041] Figure 7 Schematic diagram of the early free volume deformation of ECC with C0 mix ratio at different curing temperatures.

[0042] Figure 8 Schematic diagram of the 720-day free volume deformation of ECC with C0 mix ratio at different curing temperatures.

[0043] Figure 9 Free volume deformation of ECC with C130 mix ratio within 3 days.

[0044] Figure 10 Free volume deformation of ECC with C130 mix ratio within 720 days.

[0045] Figure 11 Permeability coefficient during the self-healing process of ECC specimens pre-stretched by 20,000 με.

[0046] Figure 12 Schematic diagram for comparison between maintenance-free ultra-thin seamless ECC pavement and traditional cracked concrete pavement.

[0047] Figure 13 Temperature monitoring results of maintenance-free ultra-thin seamless ECC pavement.

[0048] Figure 14 Deformation monitoring results of maintenance-free ultra-thin seamless ECC pavement.

[0049] Figure 15 Force-displacement curve of the three-sided compression test of ECC and concrete pipe elements.

[0050] Figure 16 Multi-point cracking ductile failure mode diagram of ECC pipe.

[0051] Figure 17 Brittle failure mode diagram of concrete pipe.

[0052] Figure 18 Example of ECC ultra-thin large buoyancy box-shaped floating structure.

[0053] Figure 19 Multi-layer composite structure of ECC ultra-thin large buoyancy box-shaped floating body.

[0054] Figure 20 FRP-reinforced ECC box of ECC ultra-thin large buoyancy box-shaped floating body.

[0055] Figure 21 Schematic diagram of expansion and shrinkage of C50 under different strategies.

[0056] Figure 22Schematic diagram of the expansion and shrinkage of C190 air-cured control ratio under different strategies for C75-magnesium oxide.

[0057] Figure 23 Schematic diagram of expansion and shrinkage under different strategies for C75-slag. Detailed implementation methods

[0058] 1. Mix ratio and preparation of ECC materials

[0059] Exemplary mixture ratios are listed in Table 1. The cement is Portland cement, and calcium sulfoaluminate cement (CSA) is used as the volume expansion component. The dosages of CSA in the C0, C100, C130, and C160 mix ratios are 0, 100, 130, and 160 kg / m 3 respectively. Machine-made sand with an average particle size of 200 μm and rubber powder with an average particle size of 275 μm are used as ECC aggregates.

[0060] Table 1 (unit: kg / m 3 ).

[0061]

[0062] In this example, a strategy of hybridizing PE fibers and PP fibers is adopted to simultaneously achieve the configuration goals of low-cost and high-performance ECC. In this example, the dosages of both PP fibers and PE fibers are 10 kg / m 3 respectively. In order to utilize the dispersion of PE fibers and PP fibers, a water reducer and a thickener are jointly used to control the viscosity of the slurry between 4–10 Pa•s. Table 2 lists the performance parameters of PE fibers and PP fibers.

[0063] Table 2

[0064]

[0065] The preparation process of intrinsically self-stressing ECC materials (hereinafter referred to as ECC): According to the materials in Table 1, first, dry components such as cement, CSA expansion agent, fly ash, sand, rubber powder, and thickener are stirred in a mixer at a speed of 94 revolutions per minute for 5 minutes; then water and water reducer are added and stirred for another 5 minutes; finally, PP fibers and PE fibers are added and stirred at a speed of 174 revolutions per minute for 5 minutes. The moment of adding water is defined as the 0 moment, representing the starting point of the time for recording fluidity and volume deformation tests.

[0066] During the stirring process, the stirring temperature needs to be strictly controlled at 5 - 30 °C, and the prepared ECC is cured under the environmental conditions shown in Table 3.

[0067] Table 3

[0068]

[0069] 2. Fluidity Test and Construction Opening Time Evaluation

[0070] In this example, the fluidity of ECC was measured according to GB / T 2419-2020 "Determination Method for Fluidity of Cement Mortar", and the results are as Figure 1 shown.

[0071] From the perspective of volume regulation, high-volume CSA can effectively reduce shrinkage and increase expansion deformation; however, excessive CSA has a greater impact on fluidity loss, especially in high-temperature environments such as summer. Figures 1 - 4 It shows that regardless of the dosage of CSA and the curing temperature, the fluidity loss of ECC over time generally presents a bilinear change pattern. In the first stage, the fluidity decreases relatively slowly; after the critical turning point, the fluidity loss accelerates.

[0072] The dosage of CSA has little effect on the initial fluidity of ECC. In this example, the initial expansion diameters of C100, C130, C150, and C160 are all about 175 mm.

[0073] Increasing the dosage of CSA and temperature both accelerate the hardening of ECC and increase the fluidity loss rate. When the curing temperature is below 40 °C, the fluidity loss over time is less affected by temperature; when the curing temperature is increased to 60 °C, the fluidity of ECC decreases significantly over time. According to existing experience, when the fluidity expansion diameter of ECC is below 120 mm, ECC will face challenges in construction and vibration compaction. Therefore, in this example, a fluidity expansion diameter higher than 120 mm is used as the criterion for determining the constructible window period.

[0074] Under the 20-A curing condition, C100, C130, and C150 can still maintain good constructibility at 160 minutes. However, the fluidity expansion diameter of C160 is already below 120 mm at 130 minutes. Under the 40-O curing condition, the constructible window period of C100 is higher than 160 minutes, the constructible window period of C140 is about 140 minutes, and the constructible window period of C150 is about 120 minutes. Due to the limitation of constructibility, the upper limit of the volume expansion component in the intrinsically self-stressing ECC material is determined to be 150 parts; in comparison, the constructible window period of C160 is 110 minutes. It should be noted that in the 60-O curing environment, the constructible window period of C160 is significantly shortened to less than 80 minutes.

[0075] In response to the construction requirements in the high-temperature season of summer, it is necessary to control the temperature of the ECC material during the construction period. For example, cold water mixing or night construction can be used. At the same time, the dosage of CSA should also be strictly controlled; high-volume CSA not only accelerates the fluidity loss of ECC but also increases the heat of hydration.

[0076] In contrast, for the self-stress ECC requirements, the higher the content of CSA, the better. During the material research and application process, it is necessary to comprehensively consider the construction window period and self-stress requirements to select the appropriate CSA content. In this example, C130 is selected as the mix ratio for subsequent volume deformation, mechanical testing, and pavement demonstration applications.

[0077] 3. Free Volume Deformation Measurement

[0078] In this example, according to ASTM C490 / C490M–17, the dry shrinkage deformation of 25mm * 25mm * 300mm ECC specimens is tested. The earliest allowable form removal time is selected as the starting point for volume deformation testing. Table 4 records the maximum expansion deformation of ECC with different mix ratios under different curing environments and the proportion of volume deformation after stabilization.

[0079] C50-2 days means C50 cured under temperature and humidity for 2 days in Table 1; C50-5 days means C50 cured under temperature and humidity for 5 days in Table 1; C50-stone powder-5 days means C50-stone powder cured under temperature and humidity for 5 days in Table 1; C75-3 days means C75 cured under temperature and humidity for 3 days in Table 1; C75-magnesium oxide and C75-steel slag are both the components shown in Table 1 and cured under temperature and humidity for 3 days; C75-magnesium oxide-secondary curing and C75-steel slag-secondary curing are for the mix ratio in Table 1 after the maximum volume deformation is reduced to 80%, and then secondary wet curing is carried out for 2 days; C100-24 hours means C100 cured under temperature and humidity for 24 hours in Table 1; C190-20-A means C190 in Table 1 cured in air at 20°C.

[0080] Table 4

[0081]

[0082] The curing temperature has a greater impact on both the early expansion and late shrinkage of ECC. As Figure 5 shown, for the three curing conditions of 20-A, 40-O, and 60-O where no temperature and humidity curing scheme is applied in the early stage, C130 all shows the law of first expanding and then shrinking, and finally shrinking. Under high-temperature curing, the time of maximum expansion is advanced. For example, the maximum expansion of C130 under 60-O occurs at 5 hours after measurement, 40-O occurs at 10 hours, and the maximum expansion of 20-A even appears on the second day after testing. Under the 20-A environment, the highest expansion value of C130 is 551 με, slightly higher than that of 40-O (520 με) and 60-O (429 με).

[0083] Figure 6It shows that the late shrinkage magnitudes and development laws of 40-O and 20-A are basically the same, and the shrinkages of both at 180 days are about 900 με. The shrinkage value of 60-O at 180 days is 1625 με, which is 1.8 times that of 20-A and 40-O, and still shows a trend of continuous shrinkage.

[0084] Figures 7 - 8 In the C0 mix ratio, there is no obvious expansion in the early stage, which is completely different from the volume deformation law of C130. High-temperature curing accelerates the early shrinkage but reduces the final shrinkage magnitude. As Figures 7 - 8 shown, under the 20-A curing condition, the shrinkage value of C0 at 180 days is 1550 με; on the contrary, the shrinkage values under the 40-O and 60-O curing conditions are only 900 με.

[0085] Although the CSA content of C130 has reached a relatively high level of 130 kg / m 3 , the dry shrinkage value of C130 at 180 days is still as high as 900 - 1625 με, greatly increasing the cracking risk of ECC during service. If the CSA content is further increased, it is difficult to have sufficient constructible time, especially during construction in high-temperature environments such as summer.

[0086] Figure 9 It shows the early temperature and humidity curing conditions required in this patent application. The temperature and humidity curing humidity is greater than 95%, and the temperature is 10 - 40 °C. The free volume deformation law of C130ECC under the initial temperature and humidity curing for 6 / 12 / 18 hours is shown. The maximum expansion deformation of ECC occurs within the initial 1 - 3 days, and then volume retraction occurs. Prolonging the early temperature and humidity curing time increases the magnitude of the maximum expansion deformation. In this example, the early maximum expansion deformations under the temperature and humidity curing at 20 °C for 6 / 12 / 18 hours are 3560 με, 3800 με, and 4770 με respectively. At 1.5 days, the early maximum expansion deformation is 6125 με; at 3 days, the early maximum expansion deformation is 7800 με.

[0087] The temperature and humidity curing temperature also has a certain influence on the early maximum expansion deformation. 20 °C is the optimal temperature and humidity curing temperature. When the temperature and humidity curing temperature reaches 40 °C, although the material still meets the volume deformation requirements, under the same conditions, the early maximum expansion deformation is less than that under 20 °C.

[0088] After early temperature and humidity curing, C130 can maintain an expanded state at 180 days. The 180-day expansion deformations under the temperature and humidity curing for 6 / 12 / 18 hours are 1803 με, 2472 με, and 3251 με respectively. The present invention unexpectedly finds that different early curing strategies have little influence on the later volume retraction magnitude. In this example, the change amount of volume deformation is about 1333 - 1757 με.

[0089] The total volume deformation of ECC is mostly distributed between 750 - 5000 με, and it is necessary to ensure that the maximum early expansion is more than twice the late retraction to ensure that the ECC maintains the intrinsic self - prestressing effect under external constraints during service.

[0090] Furthermore, control the mass fraction of the volume expansion component to be 16% - 32% of the total mass fraction of cement and the volume expansion component, so that the peak value of the highest free expansion deformation is higher, while meeting the requirements of the construction window.

[0091] Furthermore, when the mass fraction of the volume expansion component is 20% of the total mass fraction of cement and the volume expansion component, the best combination of the peak value of the highest free expansion deformation and the requirements of the construction window is achieved.

[0092] Therefore, in this patent application, a strategy of combining construction and maintenance is proposed. By using the method of combining low - dosage CSA and a reasonable temperature - humidity curing strategy, the bottleneck of the disharmony between self - stress and the construction window period is broken through, and the dual requirements of intrinsic self - prestressing and the construction window are innovatively realized. The highest free expansion deformation during the temperature - humidity curing process of the intrinsic self - prestressing ECC material is between 1500 με - 10000 με, and the free volume deformation during the later service is maintained at more than 55% of the highest free expansion deformation in the early stage. The specific inspirations are as follows: Sufficient early temperature - humidity curing can increase the maximum expansion deformation; Secondly, avoid high - temperature service to prevent exacerbating the later volume retraction; Finally, if high - temperature construction is inevitable, control the temperature of the ECC material below 40 °C, preferably below 30 °C, by adding ice or other means.

[0093] When controlling the change amount of the free volume deformation of the intrinsic self - prestressing ECC material during later service, the preferred solutions are secondary wet curing, adding steel slag, magnesia or adding stone powder.

[0094] Take Figures 22 - 23 as an example. Divide its volume expansion component into early expansion component and late expansion component. In this embodiment, the early expansion component is CSA, and the late expansion component is steel slag or magnesia; Since the early expansion deformation effect of steel slag / magnesia is limited, its highest free expansion deformation in the early stage is similar to that of C75. During its later service stage, the late expansion component begins to play the role of expansion deformation, causing its volume deformation to increase again, and then slowly decreasing to meet the volume deformation requirements.

[0095] Taking C75 as an example, after its initial temperature - humidity curing, it reaches the peak value of the highest free expansion deformation. Then its free volume deformation begins to gradually decrease. About 10 days after its pouring (when the expansion decreases to about 80%), wet curing is carried out again to make its free volume deformation expand again. After experiencing the second peak value, the free volume deformation changes again, making the free volume deformation during later service higher than 55% of the highest free expansion deformation in the early stage.

[0096] according to Figure 14 The actual monitoring results also confirm the effectiveness of secondary curing. Due to the fact that some volume expansion components did not fully play their role after the initial temperature and humidity curing, when it rained again, some volume expansion components played their role again, increasing the volume expansion deformation again. Based on this finding, the technical solution proposes a secondary wet curing solution, especially starting from the time when the maximum expansion deformation shrinks to 60-80%, which has the best effect of controlling the shrinkage of volume deformation.

[0097] Based on C75, stone powder is added to the intrinsic self-prestressed ECC material to ensure that the materials are fully mixed. Stone powder has a dual role. First, it can prevent the decomposition of ettringite and ensure the stability of the early expansion of ECC; second, it can reduce the shrinkage magnitude of ECC in the later stage. Combined with the strategy of early temperature and humidity curing for 5 days, the required self-stress purpose can still be achieved when the volume expansion component is a low dosage of 50 parts.

[0098] The increase in the proportion of the volume expansion component makes the maximum expansion deformation larger, but the volume deformation after stabilization needs to be controlled to be greater than 55% of the maximum expansion deformation. Figure 22 For example, C190 in 3 Even if the temperature and humidity curing method is not used, its early maximum expansion increases to 3005με. However, since the final expansion deformation at 720 days is only 43% of the early maximum expansion, it does not meet the design requirements of self-stress.

[0099] 4. Mechanical properties test

[0100] Table 5 lists the mechanical properties of ECC cured for 28 days under different conditions. Temperature and humidity curing improves the compressive, bending and direct tensile strength of ECC; the strength of 20-A and 40-O is equivalent; the high temperature of 60℃ (60-O) reduces the strength and deformation capacity of ECC to a certain extent.

[0101] The compressive strength of the C130 ECC in this example is 40.2-44.5MPa, which is equivalent to the C40 strength grade of conventional concrete. Depending on the curing conditions, the four-point bending strength of ECC is 8.5-11.6MPa, and the direct tensile strength is 4.7-5.4MPa, both of which are more than twice that of conventional C40 concrete. The direct tensile strain capacity of ECC is 6.5%-8.4% (65,000-84,000 με), which is 600 times higher than the direct tensile strain capacity of concrete. The average crack width is less than 100μm at tensile failure. Thanks to the above high performance, the thickness of the maintenance-free ultra-thin seamless ECC surface structure can be reduced by 40-60% or even higher than that of concrete with the same compressive strength grade.

[0102] Table 5

[0103]

[0104] 5. Self-healing ability

[0105] For the mixing ratio C130 of this example, a direct tensile test was carried out after 28 days of curing under 20-A. After unloading the dog-bone specimen after stretching 20,000 με, it was then immersed in water for 14 days. In one example, the average crack width before healing was 30 μm, and the crack had completely self-healed after 14 days of immersion in water. Figure 11 It shows that the permeability coefficient of the ECC cracked by stretching 20,000 με can still be maintained at 10 - 7 m / s; the permeability coefficient of the specimen gradually decreases after water curing, and decreases to 10 -9 m / s after 14 days.

[0106] 6. Maintenance-free ultra-thin seamless pavement

[0107] Figure 12 It is a comparison chart of the application of the maintenance-free ultra-thin seamless ECC pavement and the traditional cracked concrete pavement. The thickness of the ECC pavement has no transverse joints and is 100 mm thick. After experiencing the temperature drop and dry shrinkage deformation from summer to winter, no cracks have appeared. On the contrary, even though a transverse joint is set every 3.6 meters for the traditional concrete pavement and the pavement thickness is twice that of the ECC, multiple macroscopic cracks still appear. The existence of cracks seriously affects the service life and driving comfort of the concrete pavement.

[0108] Figure 13 The results of the sensors buried in the ECC pavement show that the ECC pavement is constructed in summer, the initial pouring temperature of the material is controlled at about 25 °C, and then the highest temperature rises to 34.5 °C; after turning to winter, the lowest temperature is -8 °C; the overall maximum temperature difference is 42.5 °C, which is equivalent to a temperature deformation of 425 με. Unexpectedly, no temperature cracks and volume shrinkage cracks have appeared in the ECC pavement.

[0109] The pavement deformation monitoring data shows that the ECC pavement structure is always in a state of expansion and compression, that is, it serves under intrinsic self-prestressing. Coupled with the fact that the intrinsic self-prestressing ECC material has the ability of crack self-healing. Therefore, the ECC pavement in this example has achieved an innovative breakthrough in maintenance-free ultra-thin seamless. At the same time, it also has application inspiration for the maintenance-free ultra-thin seamless ECC surface layer structures in fields such as bridge decks, airport runways, ultra-thin box culverts, ultra-thin large buoyancy floating bodies in the ocean, floor slabs, concrete panels, pumped storage power station panels, impervious panels, channel linings, tunnel linings, and renewal and repair of old structures.

[0110] 7. Ultra-thin box / floating body

[0111] A circular pipe unit is made of ECC and C40 strength grade concrete in this example. The height of the pipe unit is 1 m, and the inner diameter is 300 mm; the thickness of the ECC pipe is 50 mm, and the thickness of the C40 concrete pipe is 75 mm. Figure 15 The force-displacement curves of the ECC pipe and the concrete pipe according to the ASTM C407-19 three-sided compression test. The results show that even though the thickness of the ECC pipe unit is only 2 / 3 of that of the concrete pipe unit, its load-bearing capacity is increased by 20%, and the ultimate displacement is increased by more than 300%.

[0112] Based on the improvement of the load-bearing and deformation capacities, the failure mode of the ECC pipe unit has also been fundamentally improved. As Figures 16 - 17 shown, the concrete pipe undergoes brittle failure after reaching the peak load. The ECC pipe unit, however, exhibits a ductile failure mode with multiple cracking. Figure 16 The failure mode diagram shows that the cracks on the ECC pipe unit extend from the inner / outer edge along the thickness direction of the pipe wall, and then are captured in the ECC pipe wall and stop expanding. Therefore, the ECC pipe unit has the unique cracking advantage of "cracking without penetrating", and can achieve the technical breakthrough of "cracking without leaking" during the water service process, especially suitable for engineering applications such as water pipelines, marine / canal floating bodies, etc.

[0113] The corrosion resistance of ECC is much higher than that of concrete materials and steel, so it has the advantage of long-term service in complex service environments such as the ocean. In addition to Figures 16 - 17 the circular pipe unit shape in, the maintenance-free ultra-thin seamless ECC surface layer structure in this example can also be used to make box-shaped floating bodies ( Figure 18 ), multi-layer composite structures ( Figure 19 ), and used in combination with reinforcing materials such as FRP ( Figure 20 ). At the same time, the box-shaped structure can also be combined with internal rib partitions, etc. Due to its ultra-thin layer structure and high durability, it can play a unique advantage in lightweight, high-strength, maintenance-free, and high-buoyancy-efficiency marine floating bodies.

Claims

1. An intrinsic self-prestressed ECC material, characterized in that: The intrinsic self-prestressed ECC material is composed of 75-130 parts of volume expansion components, 100-800 parts of cement, 400-1200 parts of supplementary cementitious materials, 400-800 parts of aggregates, 200-400 parts of water, 0-30 parts of water reducers, 0-50 parts of shrinkage reducers, 0-10 parts of thickeners, and 10-40 parts of fibers in terms of mass fraction; Control the volume deformation of the intrinsic self-prestressed ECC material during the temperature and humidity curing process: Control the intrinsic self-prestressed ECC material to reach the maximum free expansion deformation between 1500με-10000με within 5 days during the temperature and humidity curing process, so that the free volume deformation after the later service stability is higher than 55% of the maximum free expansion deformation in the early stage; maintain 0.1MPa-10MPa intrinsic prestress under the external constraints during the service process; The temperature and humidity maintenance time is 0.25-3 days; the time after later service stability is 720 days or more.

2. The intrinsic self-prestressed ECC material according to claim 1, characterized in that: The mass fraction of the volume expansion component is 16%-32% of the total mass fraction of cement and the volume expansion component; the mass of the supplementary cementitious material is 0.8-3.6 times of the total mass of cement and the volume expansion component.

3. The intrinsic self-prestressed ECC material according to claim 2, characterized in that: The intrinsic self-prestressed ECC material is composed of 100-130 parts of volume expansion components, 100-800 parts of cement, 400-1200 parts of supplementary cementitious materials, 400-800 parts of aggregates, 200-400 parts of water, 0-30 parts of water reducers, 0-50 parts of shrinkage reducers, 0-10 parts of thickeners, and 10-40 parts of fibers by mass fraction.

4. The intrinsic self-prestressed ECC material according to claim 3, characterized in that: The volume expansion component is an early volume expansion component or a combination of an early volume expansion component and a late volume expansion component.

5. The intrinsic self-prestressed ECC material according to claim 4, characterized in that: The early volume expansion component is one or more of sulphoaluminate cement, aluminate cement and calcium oxide; the late volume expansion component is one or a combination of magnesium oxide and steel slag.

6. The intrinsic self-prestressed ECC material according to claim 3, characterized in that: The supplementary cementitious material is one or more of fly ash, granulated blast furnace slag powder GGBFS, silica ash, volcanic ash, steel slag powder and metakaolin.

7. The intrinsic self-prestressed ECC material according to claim 3, characterized in that: The aggregate is one or more of machine-made sand, river sand, sea sand, desert sand, steel slag powder, tailings slag, limestone powder and rubber powder.

8. The intrinsic self-prestressed ECC material according to claim 3, characterized in that: The fiber is one or more of polypropylene PP fiber, polyethylene PE fiber, polyvinyl alcohol PVA fiber, steel fiber, basalt fiber, carbon fiber, glass fiber, and fly ash fiber.

9. A maintenance-free ultra-thin seamless ECC surface structure, characterized in that: The intrinsic self-stressed ECC material is composed of any one of claims 1 to 8, wherein the direct tensile deformation capacity of the intrinsic self-stressed ECC material is higher than 30,000 με, the width of the straight tension crack is lower than 100 μm, and the permeability coefficient of the intrinsic self-stressed ECC material that has undergone a direct tensile deformation of no more than 20,000 με and is in contact with water for 14 days is lower than 10 -8 m / s.

10. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 9, characterized in that: The maintenance-free ultra-thin seamless ECC surface layer structure maintains an intrinsic self-prestressed state throughout the service process and self-heals after cracks appear; the four-point bending flexural strength of the maintenance-free ultra-thin seamless ECC surface layer structure is 8MPa-30MPa, and the thickness of the maintenance-free ultra-thin seamless ECC surface layer structure is 0.5-30cm, which is 60% lower than the thickness of the concrete surface layer with the same compressive strength grade.

11. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 9 or 10, characterized in that: The preparation method of the maintenance-free ultra-thin seamless ECC surface layer structure is as follows: The volume deformation of the intrinsic self-prestressed ECC material during temperature and humidity curing is controlled to obtain a maintenance-free ultra-thin seamless ECC surface layer structure; the intrinsic self-prestressed ECC material maintains the intrinsic pre-compressive stress during service; the intrinsic self-prestressed ECC material is a high-ductility material.

12. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 11, characterized in that: The control of the volume deformation of the intrinsic self-prestressed ECC material during the temperature and humidity curing process is specifically: controlling the intrinsic self-prestressed ECC material to reach a maximum free expansion deformation between 1500με-10000με within 5 days during the temperature and humidity curing process, so that the free volume deformation after the later service stability is higher than 55% of the early maximum free expansion deformation.

13. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 11, characterized in that: The method of warm and wet curing includes water spraying curing and surface covering with plastic film, wet cloth, straw mat, moisturizing material and surface chemical moisturizing agent.

14. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 13, characterized in that: The temperature and humidity curing process lasts for 0.5-2 days.

15. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 11, characterized in that: The temperature of the temperature and humidity curing is 10-40° C., and the humidity is greater than 95%.

16. The maintenance-free ultra-thin seamless ECC surface structure according to claim 10, characterized in that: Through any one or combination of secondary wet curing, adding steel slag, adding magnesium oxide, adding stone powder, the free volume deformation after later service stabilization is made higher than 55% of the early maximum free expansion deformation.

17. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 16, characterized in that: The secondary wet curing begins when the maximum expansion deformation shrinks to 60-80% of the maximum free expansion deformation, and the wet curing time is 0.25-3 days.

18. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 11, characterized in that: The temperature of the intrinsic self-prestressed ECC material is controlled at 5-30°C during mixing and transportation.

19. The maintenance-free ultra-thin seamless ECC surface structure according to claim 9 or 10, characterized in that: The construction method of the maintenance-free ultra-thin seamless ECC surface layer structure is that within 120 minutes from the start of construction, according to "GB / T2419-2020 "Determination Method for Fluidity of Cement Mortar", the fluidity of the intrinsic self-prestressed ECC material is between 120 mm and 220 mm.

20. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 19, characterized in that: The construction process is divided into one-time forming to achieve the designed thickness or into multiple layers of construction to achieve the overall designed thickness.

21. The maintenance-free ultra-thin seamless ECC surface layer structure according to claim 20, characterized in that: The construction method is one or more of injection molding, mold casting molding, 3D printing molding, rolling molding, self-compacting molding, and smearing molding.

22. An application of the maintenance-free ultra-thin seamless ECC surface structure according to claim 9 or 10, characterized in that: It is used for marine floating bodies, pavements, bridge decks, airport runways, ultra-thin box culverts, concrete panels, anti-seepage panels, pumped storage power station panels, floor panels, channel linings, tunnel linings, spray repair thin layers, and hand-applied repair layers.

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