Direct electric curing method for improving early strength of light ultra-high performance concrete

Abstract

The invention provides a direct electric curing method for improving the early strength of light ultra-high performance concrete, which comprises the following steps: mixing and fully stirring a cementing material, adding water and a water reducing agent, then adding pre-wetted coal gangue fine aggregate, finally adding steel fiber, and fully and uniformly stirring to obtain a light ultra-high performance concrete material with an internal curing effect. A concrete material is subjected to pouring forming, pre-curing and electrifying for electric curing, internal curing water serves as a medium for maintaining the electrical conductivity of the concrete, a gradient temperature rise curing method is combined, concrete strength development and temperature rise in the curing process are matched, and concrete expansion damage caused by water vapor pressure at the high temperature is avoided; the early strength of the cast-in-place light ultra-high performance concrete is rapidly improved. The internal curing effect of the aggregate is combined with the direct electric curing technology, the concrete strength is rapidly improved, the engineering construction period is greatly shortened, and the application prospect is wide.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, and particularly relates to a direct electric curing method for improving early strength of lightweight ultra-high performance concrete. BACKGROUND

[0002] Ultra-high performance concrete (UHPC) is a new type of cement-based composite material based on the principle of maximum packing density, which has the characteristics of high strength, high toughness and high durability, and has a wide application prospect in construction. Lightweight UHPC is developed on the basis of UHPC, and has the following characteristics: apparent density ≤2040 kg / m 3 , 28d compressive strength ≥120 MPa, 28d flexural strength ≥18 MPa, and shrinkage rate ≤262 με. In bridge deck paving, the use of lightweight UHPC can effectively reduce the dead load of the bridge and avoid the weakening of the original bridge bearing capacity; similarly, in other flexural members (or other large-span beam members), the self-weight of the material can also be used to further reduce the cross-sectional size and foundation reaction, which has obvious advantages.

[0003] Rapidly improving the early strength of concrete is of great significance to shorten the construction period and speed up the progress of the project. For example, the bridge deck paving concrete needs to be naturally cured for ≥7 days after pouring, and the curing period accounts for a high proportion in the entire construction cycle, which becomes a key link restricting traffic recovery and shortening of the construction period. Existing methods such as early strength agent and accelerator can improve the early strength, but the effect is general when the dosage is low, and the dosage is high, which reduces the later strength and durability of the concrete; although the early strength and fast hardening cement has high early strength and fast hardening, it has problems such as high cost and limited later strength development. The above early strength measures are still affected by weather conditions, and the effect of promoting strength development is poor in low temperature environment. Therefore, there is an urgent need for a simple, convenient and efficient curing technology to rapidly improve the strength of the cast-in-place concrete in the bridge.

[0004] Direct electric curing is a new type of concrete curing method, which only needs to apply an alternating current field to the inside of the concrete, and ohmic heat is generated in the concrete structure under the action of the alternating current field to achieve the curing effect. Compared with conventional steam curing, it does not require complex equipment and special site, has high energy efficiency, uniform temperature field, and will not cause expansion of the concrete surface due to high temperature, and is suitable for rapid curing of concrete in bridge engineering. When the traditional electric curing method is used to cure the concrete, the electrical resistivity of the concrete rapidly increases with hydration, and the heating supply in the later curing is insufficient, so the effect of improving the early strength is limited. Although the addition of conductive materials can reduce the electrical resistivity of the concrete and enhance the curing effect, too much conductive filler will affect the fluidity, and the conductive filler increases the cost of the concrete and requires a complex dispersion process, which limits its application in engineering. SUMMARY

[0005] Therefore, the application provides a direct electric curing method for improving early strength of lightweight ultra-high performance concrete.

[0006] The direct electric curing method for improving early strength of lightweight ultra-high performance concrete provided by the application comprises the following steps: S1, cement, first auxiliary cementitious material, second auxiliary cementitious material, pre-wetted lightweight internal curing aggregate, fiber, water reducing agent and mixing water are stirred and mixed to obtain a lightweight ultra-high performance concrete material with internal curing effect, and the first auxiliary cementitious material is silica fume; S2, electrode sheets are inserted at both ends of the concrete material for pre-curing for 2-3 hours; S3, after pre-curing, electric curing is performed in a step temperature mode, so that the temperature of the concrete material is maintained at a first gradient temperature, a second gradient temperature and a third gradient temperature in sequence, the first gradient temperature ranges from 40 to 60 DEG C, the second gradient temperature ranges from 60 to 80 DEG C, and the third gradient temperature ranges from 80 to 100 DEG C, and the total electric curing time is more than 8 hours.

[0007] Further, the pre-wetting treatment in step S1 is specifically: a certain amount of water is added to the lightweight internal curing aggregate, stirred uniformly, and left to stand for 24 to its saturated water absorption; the amount of water is calculated according to the saturated pre-water absorption rate of the lightweight internal curing aggregate, and the water is only used for pre-wetting treatment and is not included in the amount of mixing water.

[0008] Further, the pre-curing in step S2 is specifically: the concrete material is poured into a mold for molding, and electrode sheets made of copper mesh are inserted at both ends of the concrete, and then placed in a standard curing box for standard curing for 2-3 hours, the standard curing temperature is 20±2 DEG C, and the relative humidity is more than 95%.

[0009] Further, the step of electric curing in a step temperature mode in step S3 is: in the first hour, the temperature is raised from room temperature to the first gradient temperature, and maintained at this temperature for 2 hours; then in the next 0.5 hours, the temperature is raised to the second gradient temperature, and maintained at this temperature for 2 hours; then in the next 0.5 hours, the temperature is raised to the third gradient temperature, and maintained at this temperature for 2 hours.

[0010] Further, the lightweight ultra-high performance concrete comprises the following proportioned raw materials: cement 750-880 kg / m 3 , silica fume 190-220 kg / m 3 , second auxiliary cementitious material 160-200 kg / m 3 , lightweight internal curing aggregate 700-900 kg / m 3 , mixing water 170-240 kg / m 3 , water reducing agent 20-30 kg / m 3 , fiber 160-200 kg / m 3 .

[0011] Preferably, the cement is P·II 52.5 ordinary Portland cement, with an apparent density of 2600-3500 kg / m 3 , and a specific surface area of ≥380 m 2 / kg; the silica fume has a SiO2 mass content of ≥93%, a specific surface area of ≥19100 m 2 / kg, and a bulk density of 250-400 kg / m 3 .

[0012] Preferably, the second auxiliary cementitious material is fly ash microbeads, which do not have internal curing effect, have a loss on ignition of ≤4.5%, a spherical particle volume fraction of ≥91%, a specific surface area of ≥2500 m 2 / kg, and a bulk density of 600-800 kg / m 3 .

[0013] Preferably, the lightweight internal curing aggregate is coal gangue lightweight aggregate, which has a bulk density of 800-1000 kg / m 3 , a saturated pre-absorbed water rate of 6%-12%, a cylinder compressive strength of ≥25 MPa, and a particle size range of 0.15-2.36 mm continuous gradation.

[0014] Preferably, the raw material of the lightweight ultra-high performance concrete further comprises an early strength agent, the dosage of the early strength agent is 1% of the mass of the cement, and the early strength agent is a crystal seed early strength agent, has a water content of ≤3%, and a bulk density of 400-700 kg / m 3 .

[0015] As another preferable solution, the second auxiliary cementitious material is zeolite powder, which has a particle size of 60-80 μm, a specific surface area of ≥20000 m 2 / kg, and a bulk density of 600-800 kg / m 3 ; the zeolite powder is an auxiliary cementitious material with internal curing effect, and the internal curing of the lightweight aggregate can achieve better curing effect; because it has internal curing effect, in the step S1 of directly performing the electric curing method of the present application, the zeolite powder needs to be mixed with mixing water in advance for 24 h to prepare a suspension, and then mixed with other raw materials, and the steps S2 and S3 are the same as the above-mentioned other solutions; the step S1 specifically comprises: The lightweight internal curing aggregate is pre-wetted and placed for 24 h for standby; meanwhile, the zeolite powder and the mixing water in the proportion are mixed and stirred uniformly, and placed for 24 h to prepare a zeolite powder suspension for standby; the cement, the silica fume, the early strength agent, the prepared zeolite powder suspension, the water reducing agent, the pre-wetted lightweight internal curing aggregate, and the fiber are stirred uniformly to obtain the lightweight ultra-high performance concrete material with internal curing effect.

[0016] The direct electric curing method for improving the early strength of lightweight ultra-high performance concrete disclosed in the application has the following beneficial effects compared with the prior art: 1、The direct electric curing technology is applied to the lightweight ultra-high performance concrete in the application, and the early strength of the lightweight ultra-high performance concrete is improved through rapid curing, and the compressive strength within 12 hours can reach 75-87% of the compressive strength requirement of the lightweight ultra-high performance concrete standard curing for 28 days. Compared with conventional steam curing (warm shed method), the direct electric curing does not require complex equipment and special site, and only needs to arrange electrodes and connect external alternating current, and is suitable for cast-in-place curing. Compared with early strength agent or fast hardening early strength cement, the method has good strength improvement effect and small influence on later strength, and is suitable for low temperature construction environment. The application is a physical method for accelerating hydration and strength development to achieve early strength effect, and can be used in combination with a chemical method (such as early strength agent).

[0017] 2、The existing method for enhancing the direct electric curing effect of concrete is to add conductive fillers, and when the percolation threshold is not reached, the effect of improving the electrical conductivity is not obvious. The addition of a large amount of conductive fillers significantly increases the cost of concrete and reduces the fluidity, and brings the problem of dispersion difficulty. The application combines the lightweight ultra-high performance concrete with the direct electric curing method, uses the internal curing characteristics of the porous lightweight aggregate in the lightweight ultra-high performance concrete, supplements the water loss of the slurry hydration, maintains the humidity and resistivity of the UHPC system stable, prolongs the electric curing time, and enhances the curing effect. The medium for reducing the resistivity of the UHPC in the application is internal curing water, and it is not necessary to add conductive fillers, so the cost is low and the fluidity is not reduced.

[0018] 3、The application adopts a stepped temperature curing method, and the principle is that: curing at a lower temperature makes the concrete develop a certain initial strength, and the deformation resistance is enhanced, and at the same time, the concrete pore is refined, and the steam pressure is reduced at high temperature. Then the curing temperature is increased, the hydration of the concrete slurry and the strength development are accelerated without damaging the internal structure of the concrete, compared with single temperature curing, better curing effect can be obtained in a short time, and the influence on the later strength development is smaller.

[0019] 4、Generally, the concrete develops steam curing at an early stage, and the pre-wetting aggregate will increase the free water content in the system, and the steam pressure in the capillary is more likely to increase, which will lead to an increase in the porosity of the concrete or even a volume deformation, that is, internal curing is harmful under high temperature curing [Xiang Y. Swelling deformation mechanism and inhibition technology of steam-cured concrete[D]. Central South University, 2022.] The application solves the contradiction between high temperature curing and internal curing based on the following principles: ①With the hydration of the UHPC slurry, the humidity is gradually decreased, and the internal curing material is released under the driving of the humidity gradient, and the consumption sequence of the internal curing water follows the consumption of water in the coarse pores first and then the consumption of water in the fine pores. Taking the coal gangue aggregate in the application as an example, the pore size distribution curve is as follows: Figure 1As shown, the pore solution is a salt solution, so the initial humidity is considered to be 98% [Lura P, Jensen O M, Van Breugel K. Autogenous shrinkage in high-performance cement paste: An evaluation of basic mechanisms[J]. Cement and concrete research, 2003, 33(2): 223-232.], and the minimum radius change curve of the capillary pores that play an internal curing role can be calculated according to the Kelvin equation (containing salt solution correction), as shown in the figure Figure 1 As can be seen from the figure, in the process of reducing the relative humidity in the paste from 98% to 97.5%, the internal curing water in the pore size range of 100 μm to 160 nm is consumed, and when the humidity drops to 97%, the water in the pore size range of 80 nm and above is consumed. The present application can maintain internal curing at each stage by adding internal curing materials containing different pore sizes, so that the internal curing water is distributed in different size pores; ② the Kelvin equation shows that the smaller the pore size, the greater the curvature, and the lower the water vapor pressure in the pore (containing salt solution correction), as shown in the figure r p Figure 2

[0020] Therefore, the effect of gradient temperature curing is: during the curing process, as the water in the hydration macropores of the paste is consumed first, the relative humidity in the paste decreases, the free water vapor pressure decreases, and the strength of the matrix increases, so the temperature can be further increased. Through the cycle of "temperature rise" → "accelerate paste hydration" → "relative humidity decreases and deformation resistance increases" → "continue to increase the temperature", the contradiction between high temperature curing and internal curing is solved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a coal gangue aggregate pore size distribution and internal curing humidity curve diagram; Figure 2 is a diagram showing the relationship between pore size distribution and saturated water vapor pressure at different temperatures; Figure 3 is a schematic diagram of electrode arrangement for bridge deck pavement construction of the present application; Figure 4 is a graph of the mechanical property test results of Comparative Examples 1-13 and Example 1-4 of the present application; Figure 5 is a graph of the resistance change curve during direct electric curing of Comparative Examples 3, 6 and 10 of the present application; Figure 6 is a graph of the step temperature change curve during direct electric curing of Example 1, 2 and Comparative Example 13 of the present application; ​​​Figure 7 The figure of the power and resistance change curve during the direct electric curing process of the embodiment 1 of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the method will be described clearly, detailedly and completely in combination with some embodiments. Obviously, the listed embodiments are only a small part of the embodiments, and not all the embodiments. Therefore, based on the embodiments in the present application, all the other embodiments proposed by the person skilled in the art without creative labor are within the protection scope of the present application.

[0023] In order to better understand the present application without limiting the scope of the present application, all the numbers and other numerical values used in the present application to express the amount and percentage should be understood as being modified by the word "about" in all cases. Therefore, unless specifically stated otherwise, the numerical parameters set forth in the specification and attached claims are approximations. The numerical parameters set forth in the specification and attached claims are intended to serve as approximations only. In all cases, the numerical parameters set forth in the specification and attached claims should be considered to be open-ended in the sense that they can be extended to approximately a minimum and maximum value defined by the term "about". Each numerical parameter should at least be construed in light of the number of reported significant digits and by applying the rounding techniques.

[0024] Although the present application has been shown and described with respect to several embodiments thereof, it will be apparent that equivalents, substitutes and modifications will occur to others skilled in the art without departing from the spirit and principles of the present application. It is thus intended that the present application not be limited to the particular embodiments disclosed, but that it will include all such embodiments falling within the scope of the appended claims.

[0025] The present application provides a direct electric curing method for improving the early strength of lightweight ultra-high performance concrete, comprising the following steps: S1, cement, first auxiliary cementitious material, second auxiliary cementitious material, pre-wetted lightweight internal curing aggregate, fiber, water reducing agent and mixing water are stirred and mixed to obtain a lightweight ultra-high performance concrete material with internal curing effect, the first auxiliary cementitious material is silica fume; S2, inserting electrode sheets at both ends of the concrete material, and pre-curing for 2-3h; S3, after the pre-curing is completed, electric curing is carried out in a step temperature mode, so that the temperature of the concrete material is maintained at a first gradient temperature, a second gradient temperature and a third gradient temperature in turn, the first gradient temperature ranges from 40 to 60℃, the second gradient temperature ranges from 60 to 80℃, and the third gradient temperature ranges from 80 to 100℃, and the total electric curing time is 8h or more.

[0026] In some embodiments, the pre-wetting treatment in step S1 is specifically: adding a certain amount of water in the lightweight internal curing aggregate, stirring uniformly, and standing for 24 to its saturated water absorption; the amount of water is calculated according to the saturated pre-water absorption rate of the lightweight internal curing aggregate, that is, the amount of water is the dry mass of the lightweight internal curing aggregate multiplied by the saturated pre-water absorption rate, and the water is only used for pre-wetting treatment and is not included in the amount of mixing water.

[0027] In some embodiments, the specific steps of step S2 are: pouring the concrete material into the mold for casting, and in the casting process, when the concrete is in a state of maintaining good fluidity, inserting electrode sheets made of copper mesh at a distance of 1 cm from both ends of the concrete material, and forming a fixed connection between the electrode sheets and the concrete by means of the viscous resistance of the concrete itself and the bonding effect of the subsequent hardening process. Subsequently, the concrete-mold assembly with the electrode sheets is placed in a standard curing box for pre-curing for 2-3 hours, and the standard curing temperature is 20±2℃ and the relative humidity is above 95%.

[0028] In some embodiments, the step S3 is the step of step S3 is the step of: starting from room temperature to the first gradient temperature for 1h, maintaining at this temperature for 2h; then rising to the second gradient temperature for 0.5h, maintaining at this temperature for 2h; then rising to the third gradient temperature for 0.5h, maintaining for 2h.

[0029] In some embodiments, the lightweight ultra-high performance concrete comprises the following proportion of raw materials: cement 750-880 kg / m 3 , silica fume 190-220 kg / m 3 , second auxiliary cementitious material 160-200 kg / m 3 , lightweight internal curing aggregate 700-900 kg / m 3 , mixing water 170-240 kg / m 3 , water reducing agent 20-30 kg / m 3 , fiber 160-200 kg / m 3 .

[0030] In some embodiments, the cement is P·Ⅱ52.5 ordinary portland cement, and the apparent density is 2600-3500 kg / m 3 , and the specific surface area is ≥380 m 2 / kg.

[0031] In some embodiments, the SiO2 content in the silica fume is ≥93%, the specific surface area is ≥19100 m 2 / kg, and the bulk density is 250-400 kg / m 3 .

[0032] In some embodiments, the second auxiliary cementitious material is fly ash cenospheres, which has no internal curing effect, a loss on ignition of ≤4.5%, a spherical particle volume rate of ≥91%, a specific surface area of ≥2500m 2 / kg, and a bulk density of 600-800kg / m 3 .

[0033] In some embodiments, the lightweight internal curing aggregate includes at least one of coal gangue lightweight aggregate and shale ceramsite.

[0034] In some embodiments, the lightweight internal curing aggregate has a particle size of 0.15-2.36mm.

[0035] In some embodiments, the lightweight internal curing aggregate is preferably coal gangue lightweight aggregate, which has a bulk density of 800-1000kg / m 3 , a saturated pre-absorbed water rate of 6%-12%, a cylinder compressive strength of ≥25MPa, and a particle size range of 0.15-2.36mm continuous gradation.

[0036] In some embodiments, the water reducing agent is a polycarboxylate-based water reducing agent, which has a water reducing rate of ≥30% and a solid content of 40%.

[0037] In some embodiments, the fiber is preferably a copper-plated steel fiber, which has a nominal length of 12-14mm, an equivalent diameter of 0.18mm-0.33mm, and a tensile strength of ≥2000MPa.

[0038] In some embodiments, the raw materials further include an early strength agent, the dosage of the early strength agent is 1% of the mass of the cement, and the early strength agent is a crystal seed early strength agent, which has a water content of ≤3% and a bulk density of 400-700kg / m 3 .

[0039] In some embodiments, the second auxiliary cementitious material is zeolite powder, which is a cementitious material with internal curing effect, and can achieve better curing effect by superimposing the internal curing of lightweight aggregate; since it has internal curing effect, the zeolite powder needs to be mixed with mixing water in advance to prepare a suspension 24h before the step S1 of directly implementing the electric curing method of the application, and then mixed with other raw materials, and the steps S2 and S3 are the same as the above-mentioned other schemes; the step S1 specifically includes: The lightweight internal curing aggregate is pre-wetted and placed for 24h for standby; meanwhile, the zeolite powder and the mixing water in the proportion are mixed and stirred uniformly, and then placed for 24h to prepare a zeolite powder suspension for standby; the cement, silica fume, early strength agent, prepared zeolite powder suspension, water reducing agent, lightweight internal curing aggregate after pre-wetting, and fiber are stirred uniformly to obtain a lightweight ultra-high performance concrete material with internal curing effect.

[0040] Preferably, the zeolite powder has a particle size of 60-80 μm, a specific surface area of ≥20000 m 2 / kg, and a bulk density of 600-800 kg / m 3 .

[0041] In actual engineering, some curing methods for rapidly improving the strength are limited, while direct electric curing does not require complex equipment and special sites (for example, bridge deck paving of lightweight super high performance concrete construction, Figure 3 The direct electric curing scheme has obvious advantages compared with steam curing), which provides the possibility for the application of electric curing. By controlling the temperature for electric curing, the effect of steam curing in actual application can be achieved. High-temperature electric curing quickly consumes the internal water of concrete, while the internal curing material can timely supplement the internal water of concrete. The synergistic effect of internal curing and direct electric curing technology enables the concrete to rapidly improve the strength, shortens the construction period, and has excellent application prospects.

[0042] The following further illustrates the direct electric curing lightweight super high performance concrete of the present application with specific examples. This part further illustrates the content of the present application in combination with specific examples, but should not be understood as a limitation of the present application. If not specifically stated, the technical means used in the examples are conventional means known to those skilled in the art. Unless specifically stated, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the art.

[0043] In the following examples and comparative examples, The cement is produced by Anhui Conch Cement Co., Ltd., and has a strength grade of P·II 52.5; its apparent density is 3100 kg / m 3 , and a specific surface area of 382 m 2 / kg. The silica fume is produced by Sichuan Tianlang Silica Powder Material Co., Ltd., and has a SiO2 mass content of 94%, a specific surface area of 19100 m 2 / kg, and a bulk density of 350 kg / m 3 . The fly ash microbeads are produced by Henan Yixiang New Material Co., Ltd., and have a loss on ignition of 4.5%, a spherical particle volume rate of 92%, a specific surface area of 2500 m 2 / kg, and a bulk density of 700 kg / m 3 . The coal gangue lightweight aggregate is produced by Anhui Huainan East Chen Group Co., Ltd., and has a bulk density of 980 kg / m 3 , a saturated pre-saturation rate of 11.4%, a cylinder compressive strength of 25.6 MPa, and a particle size range of 0.15-2.36 mm continuous gradation; The water is laboratory tap water; Water reducing agent is produced by Jiangsu Suobote, polycarboxylate superplasticizer, water reducing rate is 30%, solid content is 40%; Fiber is copper-plated steel fiber, produced by Wuhan Luqiao Co., Ltd., nominal length is 13 mm, diameter is 0.3 mm, tensile strength is 2850 MPa; Early strength agent is crystal early strength agent, produced by Nanjing Xinyiheng Synthetic Technology Co., Ltd., water content is 3%, bulk density is 650 kg / m 3 ; Zeolite powder is produced by Gongyi Yuanheng Water Purification Material Factory, particle size is 75 μm, specific surface area is 20000 m 2 / kg, bulk density is 750 kg / m 3 ; Quartz sand is produced by Xiamen Aiseo Standard Sand Co., Ltd., particle size range is 0.15~2.36 mm continuous gradation, SiO2content is 96%, and does not have internal curing effect; Polyacrylic acid high water absorption resin (SAP) is produced by Jiangsu Kexing New Material Co., Ltd., particle size is 90~124 μm, internal curing water introduction rate is 11; Copper mesh as electrode is produced by Hengshui Pangdejieshi Energy-saving Technology Co., Ltd., thickness is 0.2 mm; Alternating current power supply is produced by Wuxi Annais Electronic Technology Co., Ltd., upper limit voltage is 80 V, trial voltage is 20 V, experimental power is 2~15 W.

[0044] Example 1 The lightweight super high performance concrete provided by the embodiment of the application, raw materials include: Cement 821 kg / m 3 , silica fume 208 kg / m 3 , fly ash microbeads 175 kg / m 3 , coal gangue light aggregate 717.4 kg / m 3 , mixing water 182.4 kg / m 3 , water reducing agent 24.1 kg / m 3 , copper-plated steel fiber 200 kg / m 3 .

[0045] The preparation method of the direct electric curing lightweight super high performance concrete, comprising the following steps: S1, according to the above ratio, the raw materials are weighed; according to the saturated pre-saturation water absorption, 11.4% of water of the coal gangue aggregate is added into the coal gangue aggregate, stirred uniformly, and placed for 24h until it is saturated with water, ready for use (the water is only for pre-wetting treatment, and is not included in the amount of mixing water); the cement, fly ash microbeads and silica fume are added into a mixer and mixed and stirred for 3-5min, then the mixing water and the water reducing agent are added, the pre-wetting treated coal gangue lightweight aggregate is added, and finally the copper-plated steel fiber is added and stirred for 5-8min, to obtain a lightweight super high performance concrete material with internal curing effect; S2, the electrode sheets are inserted into both ends of the concrete material, and pre-curing is performed for 3h; S3, after the pre-curing is completed, an alternating current field is applied, the temperature is controlled by adjusting the power, and the temperature is raised from room temperature 20℃ to the first gradient temperature 45℃ for 1h, maintained at this temperature for 2h; then raised to the second gradient temperature 65℃ for 0.5h, maintained at this temperature for 2h; then raised to the third gradient temperature 85℃ for 0.5h, maintained for 2h, to obtain the lightweight super high performance concrete. This temperature mode is the step temperature 1 in Table 1 and Table 2.

[0046] Example 2 The lightweight super high performance concrete provided by the embodiments of the present application has the same raw materials as Example 1, and the difference between the preparation methods is that: S3, after the pre-curing is completed, an alternating current field is applied, the temperature is controlled by adjusting the power, and the temperature is raised from room temperature 20℃ to the first gradient temperature 40℃ for 1h, maintained at this temperature for 2h; then raised to the second gradient temperature 70℃ for 0.5h, maintained at this temperature for 2h; then raised to the third gradient temperature 100℃ for 0.5h, maintained for 2h, to obtain the lightweight super high performance concrete. This temperature mode is the step temperature 2 in Table 1 and Table 2.

[0047] Example 3 The lightweight super high performance concrete provided by the embodiments of the present application has the following raw materials: Cement 821kg / m 3 Silica fume 208kg / m 3 Fly ash microbeads 175kg / m 3 Early strength agent 8.21kg / m 3 Coal gangue lightweight aggregate 717.4kg / m 3 Mixing water 182.4kg / m 3 Water reducing agent 24.1kg / m 3 Copper-plated steel fiber 200kg / m 3 .

[0048] The preparation method of the above direct electric curing lightweight super high performance concrete comprises the following steps: S1, according to the above ratio, the raw materials are weighed; according to the saturated pre-saturation water absorption rate, 11.4% of water of the mass of the coal gangue aggregate is added to the coal gangue aggregate, and stirred uniformly, and then placed for 24h until it is saturated with water, for standby (the water is only for pre-wetting treatment, and is not included in the amount of mixing water); the cement, fly ash microbeads, silica fume, early strength agent are added into the stirrer and mixed and stirred for 3-5min, then the mixing water and the water reducing agent are added, and the pre-wetting treated coal gangue lightweight aggregate is added, and finally the copper-plated steel fiber is added and stirred for 5-8min, to obtain a lightweight super high performance concrete material with internal curing effect; S2, the electrode sheets are inserted into both ends of the concrete material, and pre-curing is performed for 2h; S3, after the pre-curing is completed, an alternating current field is applied, the temperature is controlled by adjusting the power, and the temperature is raised from room temperature 20℃ to the first gradient temperature 45℃ for 1h, and maintained at this temperature for 2h; then the temperature is raised to the second gradient temperature 65℃ for 0.5h, and maintained at this temperature for 2h; then the temperature is raised to the third gradient temperature 85℃ for 0.5h, and maintained at this temperature for 2h, to obtain the lightweight super high performance concrete. This temperature mode is the step temperature 1 in Tables 1 and 2.

[0049] Example 4 The lightweight super high performance concrete provided by the embodiments of the present application comprises: Cement 821kg / m 3 Silica fume 208kg / m 3 Zeolite powder 175kg / m 3 Early strength agent 8.21kg / m 3 Coal gangue lightweight aggregate 717.4kg / m 3 Mixing water 182.4kg / m 3 Water reducing agent 24.1kg / m 3 Copper-plated steel fiber 200kg / m 3 .

[0050] The preparation method of the above direct electric curing lightweight super high performance concrete comprises the following steps: S1. Weigh the raw materials according to the above proportions; according to the saturated pre-absorption rate, add 11.4% water by weight of the coal gangue aggregate to the coal gangue aggregate, stir evenly, and let stand for 24 hours until it is saturated with water, and set aside (the water mentioned is only for pre-wetting treatment and is not included in the amount of mixing water); at the same time, mix the zeolite powder and mixing water according to the above proportions (i.e., the mass ratio is 175:182.4), stir evenly, and let stand for 24 hours to prepare a zeolite powder suspension, and set aside; add cement, silica fume, and early strength agent to the mixer and mix thoroughly for 3-5 minutes, then add the prepared zeolite powder suspension and water-reducing agent, add the pre-wetted lightweight coal gangue aggregate, and finally add copper-plated steel fiber and stir for 5-8 minutes. After stirring evenly, a lightweight ultra-high performance concrete material with internal curing effect is obtained. S2. Insert electrode plates into both ends of the concrete material and pre-cur it for 2 hours; S3. After pre-curing, an alternating electric field is applied, and the temperature is controlled by adjusting the power. For the first hour, the temperature is increased from room temperature (20℃) to the first gradient temperature (45℃), and maintained at this temperature for 2 hours. Then, after 0.5 hours, the temperature is increased to the second gradient temperature (65℃), and maintained at this temperature for 2 hours. Finally, after another 0.5 hours, the temperature is increased to the third gradient temperature (85℃), and maintained for 2 hours. This process yields lightweight ultra-high performance concrete. This temperature pattern corresponds to step temperature 1 in Tables 1 and 2.

[0051] Comparative Example 1 The ultra-high performance concrete provided in this application uses quartz sand aggregate, which does not have an internal curing effect, to replace coal gangue lightweight aggregate. The raw materials include: 821 kg / m³ of cement 3 Silica fume 208kg / m 3 175 kg / m³ of fly ash microspheres 3 Quartz sand 1034.6 kg / m³ 3 182.4 kg / m³ of mixing water 3 Water-reducing agent 24.1 kg / m 3 Copper-plated steel fiber 200kg / m 3 .

[0052] Note: In concrete, aggregate replacement is generally done by equal volume. Since quartz sand has a higher density than coal gangue, the mass of quartz sand used per cubic meter is greater.

[0053] The above-mentioned method for preparing ultra-high performance concrete includes the following steps: S1. According to the above raw material ratio, add cement, fly ash microspheres and silica fume into the mixer and mix thoroughly for 3-5 minutes. Then add mixing water and water-reducing agent, add quartz sand aggregate, and finally add copper-plated steel fiber and mix for 5-8 minutes. After mixing evenly, ultra-high performance concrete material is obtained. S2, the concrete material prepared in S1 is poured into a forming mold, and then placed in a standard curing box for curing for 28 days; wherein the standard curing temperature is 20±2℃, and the relative humidity is above 95%.

[0054] Comparative Example 2 The ultra-high performance concrete provided by the comparative example of the present application has raw materials including: cement 821 kg / m 3 , silica fume 208 kg / m 3 , fly ash microbeads 175 kg / m 3 , quartz sand 1034.6 kg / m 3 , mixing water 182.4 kg / m 3 , water reducing agent 24.1 kg / m 3 , copper-plated steel fiber 200 kg / m 3 .

[0055] The preparation method of the direct electric curing ultra-high performance concrete described above includes the following steps: S1, according to the above raw material ratio, the cement, fly ash microbeads, and silica fume are added to the mixer and mixed for 3-5 minutes, then the mixing water and the water reducing agent are added, the quartz sand aggregate is added, and finally the copper-plated steel fiber is added and stirred for 5-8 minutes, and the ultra-high performance concrete material is obtained after uniform stirring; S2, inserting electrode sheets at both ends of the concrete material for pre-curing for 3 hours; S3, after the pre-curing is completed, an alternating current field is applied, the temperature is controlled by adjusting the power, and the concrete material is electrically cured at 45℃ for 8 hours, thereby obtaining the ultra-high performance concrete.

[0056] Comparative Example 3 The ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 2, and the difference between the preparation method of the present application and Comparative Example 2 is that the electric curing temperature of S3 is 65℃.

[0057] Comparative Example 4 The ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 2, and the difference between the preparation method of the present application and Comparative Example 2 is that the electric curing temperature of S3 is 85℃.

[0058] Comparative Example 5 The ultra-high performance concrete provided by the comparative example of the present application has raw materials including: cement 821 kg / m 3 , silica fume 208 kg / m 3 , fly ash microbeads 175 kg / m 3 , quartz sand 1034.6 kg / m 3 , polyacrylic acid-based superabsorbent resin (SAP) 7.57 kg / m 3, mixing water 182.4kg / m 3 , water reducing agent 24.1kg / m 3 , copper plated steel fiber 200kg / m 3 The internal curing water introduction rate of the SAP used is 11.

[0059] The preparation method of the direct electric curing ultra-high performance concrete described above comprises the following steps: S1, according to the above raw material ratio, each raw material is weighed; wherein the SAP needs to be pre-wetted, according to the internal curing water introduction rate of the SAP used, the SAP and water are mixed in a mass ratio of 1:11 (the water is only used for pre-wetting treatment and is not included in the amount of mixing water) to make the SAP fully absorb water, and the mixture is left to stand for 24h for standby; the cement, fly ash microbeads, silica fume, pre-wetted SAP, mixing water and water reducing agent are added to the mixer and fully stirred for 3-5min, then the quartz sand aggregate is added, and finally the copper plated steel fiber is added and stirred for 5-8min, to obtain an ultra-high performance concrete material with internal curing effect; S2, insert electrode sheets at both ends of the concrete material and pre-cure for 3h; S3, after pre-curing, an alternating current field is applied, the temperature is controlled by adjusting the power, and the concrete material is electrically cured at 45℃ for 8h, to obtain an ultra-high performance concrete.

[0060] Comparative Example 6 The ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 5, and the difference between the preparation method of Comparative Example 6 and Comparative Example 5 is that the electric curing temperature of S3 is 65℃.

[0061] Comparative Example 7 The ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 5, and the difference between the preparation method of Comparative Example 7 and Comparative Example 5 is that the electric curing temperature of S3 is 85℃.

[0062] Comparative Example 8 The ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 5, and the difference between the preparation method of Comparative Example 8 and Comparative Example 5 is that Comparative Example 8 uses 28d standard curing and does not perform electric curing, i.e. step S2 is: pouring the concrete material prepared in S1 into a forming mold, and then placing it in a standard curing box for curing for 28d; wherein the standard curing temperature is 20±2℃ and the relative humidity is above 95%, to obtain an ultra-high performance concrete.

[0063] Comparative Example 9 The lightweight ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Example 1, which comprises: Cement 821kg / m 3 Silica fume 208kg / m 3 Fly ash microbeads 175kg / m3 Coal gangue lightweight aggregate 717.4 kg / m 3 Mixing water 182.4 kg / m 3 Water reducing agent 24.1 kg / m 3 Copper-plated steel fiber 200 kg / m 3 .

[0064] The preparation method of the directly electrically cured lightweight ultra-high performance concrete described above comprises the following steps: S1, according to the above ratio, the raw materials are weighed; according to the saturated pre-saturation rate, 11.4% of water of the mass of the coal gangue aggregate is added to the coal gangue aggregate, which is stirred uniformly and left to stand for 24 to its saturated water absorption, for standby (the water is only for pre-wetting treatment and is not included in the amount of mixing water); the cement, the fly ash beads and the silica fume are added to the mixer and mixed and stirred for 3-5 min, then the mixing water and the water reducing agent are added, the coal gangue lightweight aggregate after pre-wetting treatment is added, and finally the copper-plated steel fiber is added and stirred for 5-8 min, to obtain a lightweight ultra-high performance concrete material with internal curing effect after uniform stirring; S2, the electrode sheets are inserted at both ends of the concrete material, and pre-curing is performed for 3 h; S3, after the pre-curing is completed, an alternating electric field is applied, the temperature is controlled by adjusting the power, and the concrete material is electrically cured at 45℃ for 8 h, to obtain the lightweight ultra-high performance concrete.

[0065] Comparative Example 10 The lightweight ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 9, and the difference between the preparation method of the present application and Comparative Example 9 is that the electric curing temperature of S3 is 65℃.

[0066] Comparative Example 11 The lightweight ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 9, and the difference between the preparation method of the present application and Comparative Example 9 is that the electric curing temperature of S3 is 85℃.

[0067] Comparative Example 12 The lightweight ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Comparative Example 9; the difference between the preparation method of the present application and Comparative Example 9 is that Comparative Example 12 adopts 28d standard curing without electric curing, i.e. step S2 is: the concrete material prepared in S1 is poured into a forming mold, and then placed in a standard curing box for curing for 28d; wherein the standard curing temperature is 20±2℃, and the relative humidity is above 95%, to obtain the lightweight ultra-high performance concrete.

[0068] Comparative Example 13 The lightweight ultra-high performance concrete provided by the comparative example of the present application has the same raw materials as Example 1, and the difference between the preparation method of the present application and Example 1 is that the step temperature of S3 is different, specifically: S1, according to the above ratio, the raw materials are weighed; according to the saturated pre-saturation water absorption, 11.4% of water of the mass of the coal gangue aggregate is added to the coal gangue aggregate, stirred uniformly, and left for 24 h until it is saturated with water, for standby (the water is only for pre-wetting treatment and is not included in the amount of mixing water); the cement, fly ash microbeads and silica fume are added to the mixer and mixed and stirred for 3-5 min, then the mixing water and the water reducing agent are added, the pre-wetting treated coal gangue lightweight aggregate is added, and finally the copper-plated steel fiber is added and stirred for 5-8 min, to obtain a lightweight super high performance concrete material with internal curing effect; S2, the electrode sheets are inserted at both ends of the concrete material, and pre-curing is performed for 3 h; S3, after the pre-curing is completed, an alternating current field is applied, the temperature is controlled by adjusting the power, the room temperature 20℃ is maintained for 3 h, 20℃ is the first gradient temperature, then the temperature is raised to the second gradient temperature 40℃ for 0.5 h, and maintained at this temperature for 2 h; then the temperature is raised to the third gradient temperature 60℃ for 0.5 h, and maintained for 2 h, to obtain the lightweight super high performance concrete. This temperature mode is the step temperature 3 in Tables 1 and 2.

[0069] For convenience of comparison, the main differences in component mixing ratio and curing method between Examples 1-4 and Comparative Examples 1-13 in the present application are summarized in Table 1.

[0070] Table 1 - mixing ratio and curing method used in Examples 1-4 and Comparative Examples 1-13

[0071] The lightweight super high performance concrete obtained in Examples 1-4 and Comparative Examples 1-13 is subjected to mechanical property test according to GB / T 45594-2025 "Performance test method for non-load bearing components of ultra high performance concrete", and resistivity test is performed using the same TH2811D digital bridge, and the results are shown in Table 2.

[0072] Table 2 is the performance test results of the concrete of Examples 1-4 and Comparative Examples 1-13

[0073] Comparative Examples 2, 5 and 9 show that the effect of promoting hydration is not obvious when direct electric curing is maintained at 45℃, and the early strength of UHPC is not obviously enhanced. Comparative Examples 3, 6 and 10 show that the effect of promoting hydration is obvious when direct electric curing is maintained at 65℃, and the early strength of UHPC can be significantly enhanced. Comparative Examples 4 and 7 and 11 show that the early strength enhancement when direct electric curing is maintained at 85℃ is even not as good as that when direct electric curing is maintained at 65℃, and high temperature 85℃ can increase the porosity of UHPC and even deform the material, and the strength starts to decrease. Therefore, too high or too low temperature is not suitable for the development of early concrete strength, as shown in Table 2. Figure 4 ​

[0074] Comparative Examples 3, 6, and 10 show that the aggregate with internal curing effect has a lower initial resistivity than quartz sand aggregate, is more stable in the resistivity of UHPC, and allows longer direct electric curing. The resistivity change and strength development of coal gangue lightweight aggregate are better than SAP. The resistivity changes of the three groups of samples during curing are shown in Figure 5 .

[0075] Examples 1, 2, and Comparative Examples 9, 10, and 11 show that too high or too low temperature is not conducive to the strength development of UHPC during single temperature curing. Comparative Example 10 shows that although 65℃ curing is suitable for the strength development of UHPC, the strength development of UHPC is still limited due to the limitation of curing time, and the compressive strength after 8h curing is only 61% of the strength of Comparative Example 12 after standard curing for 28d. The use of stepped temperature avoids the poor effect of low temperature curing and the damage to the internal structure of UHPC caused by early high temperature, so that the curing temperature matches the strength development of UHPC. Compared with single curing temperature, stepped temperature can further improve the strength of lightweight UHPC in a short time. The temperature change curves of stepped temperatures 1 and 2 are shown in Figure 6 , and the resistivity and curing power of Example 1 are shown in Figure 7 .

[0076] Example 3 shows that the method of the application can be used in combination with early strength agent. After adding early strength agent, the standing time can be shortened from 3h to 2h, and the curing time can be further shortened without affecting the strength.

[0077] Example 4 shows that different pore size internal curing water can further supplement the water loss of the slurry hydration, maintain the humidity and resistivity stability of the UHPC system, and further promote the strength development of UHPC. After curing for only 10h, the strength can reach about 87% of the strength of Comparative Example 12 after standard curing for 28d.

[0078] Comparative Example 13 and Example 1 show that stepped temperature curing needs a suitable temperature system to match the curing temperature of UHPC with its strength. If the overall temperature is too low (the stepped temperature curve of Comparative Example 13 is shown in Figure 6 ), the curing effect cannot be achieved due to insufficient hydration rate. Similarly, too high overall temperature will also cause damage to the microstructure of UHPC due to high temperature, resulting in reduced strength.

[0079] It can be understood that the technical features of the above-described examples can be combined in any way. In order to make the description simple, all possible combinations of the technical features in the above-described examples are not described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the description.

[0080] The above merely describes preferred embodiments of the present application, and only specifically describes the technical principles of the present application, and these descriptions are only for explaining the principles of the present application, and cannot be explained as limitations on the protection scope of the present application in any way. Based on the explanations here, any modifications, equivalent replacements and improvements made within the spirit and principles of the present application, and other specific embodiments of the present application that can be thought of by those skilled in the art without creative labor, should be included in the protection scope of the present application.

Claims

1. A direct electrical curing method for improving the early strength of lightweight ultra-high performance concrete, comprising the following steps: S1. Cement, first auxiliary cementitious material, second auxiliary cementitious material, pre-wetted lightweight internal curing aggregate, fiber, water-reducing agent and mixing water are mixed to obtain lightweight ultra-high performance concrete material with internal curing effect. The first auxiliary cementitious material is silica fume. S2. Insert electrode plates into both ends of the concrete material and pre-cur it for 2-3 hours; S3. After the pre-curing is completed, the electric curing is carried out in a stepped temperature mode, so that the temperature of the concrete material is maintained successively at the first gradient temperature, the second gradient temperature, and the third gradient temperature. The first gradient temperature range is 40~60℃, the second gradient temperature range is 60~80℃, and the third gradient temperature range is 80~100℃. The total electric curing time is more than 8 hours.

2. The direct electrical curing method as described in claim 1, characterized in that, The pre-wetting treatment in step S1 specifically involves adding a certain amount of water to the lightweight internal curing aggregate, stirring it evenly, and letting it stand for 24 hours until it is saturated with water; the amount of water added is calculated based on the saturated pre-absorption rate of the lightweight internal curing aggregate.

3. The direct electrical curing method as described in claim 1, characterized in that, The pre-curing process described in step S2 is as follows: concrete material is poured into a mold and shaped, and copper mesh electrode plates are inserted into both ends of the concrete. Then, it is placed in a standard curing box for standard curing for 2-3 hours. The standard curing temperature is 20±2℃ and the relative humidity is above 95%.

4. The direct electrical curing method as described in claim 1, characterized in that, The stepped temperature mode electrical curing steps described in step S3 are as follows: First, the temperature is increased from room temperature to the first gradient temperature in the first hour, and maintained at this temperature for 2 hours; then, the temperature is increased to the second gradient temperature in the next 0.5 hours, and maintained at this temperature for 2 hours; then, the temperature is increased to the third gradient temperature in the next 0.5 hours, and maintained for 2 hours.

5. The direct electrical curing method as described in claim 1, characterized in that, The lightweight ultra-high performance concrete comprises the following raw materials in the following proportions: cement 750~880kg / m³ 3 Silica fume 190~220kg / m³ 3 Second auxiliary cementitious material: 160~200 kg / m 3 Lightweight internal curing aggregate 700~900kg / m³ 3 Mixing water 170~240kg / m 3 Water-reducing agent 20~30kg / m 3 Fiber 160~200kg / m 3 .

6. The direct electrical curing method as described in claim 5, characterized in that, The cement is P·Ⅱ 52.5 ordinary Portland cement, with an apparent density of 2600~3500 kg / m³. 3 Specific surface area ≥380m² 2 / kg; the silica fume has a SiO2 mass content ≥93% and a specific surface area ≥19100m². 2 / kg, with a bulk density of 250~400kg / m³ 3 .

7. The direct electrical curing method as described in claim 5, characterized in that, The second auxiliary cementitious material is fly ash microspheres, with a loss on ignition ≤4.5%, spherical particle volume fraction ≥91%, and specific surface area ≥2500 m². 2 / kg, with a bulk density of 600~800kg / m³ 3 .

8. The direct electrical curing method as described in claim 5, characterized in that, The lightweight internal curing aggregate is coal gangue lightweight aggregate with a bulk density of 800~1000 kg / m³. 3 The saturated pre-absorption rate is 6%~12%, the cylinder compressive strength is ≥25MPa, and the particle size range is 0.15~2.36mm with continuous gradation.

9. The direct electrical curing method as described in claim 5, characterized in that, The raw materials also include an early-strength agent, the dosage of which is 1% of the cement mass. The early-strength agent is a seed crystal early-strength agent with a moisture content ≤3% and a bulk density of 400~700 kg / m³. 3 .

10. The direct electrical curing method as described in claim 9, characterized in that, The second auxiliary cementitious material is zeolite powder with a particle size of 60~80μm and a specific surface area ≥20000m². 2 / kg, with a bulk density of 600~800kg / m³ 3 ; Step S1 of the direct electro-curing method is as follows: the lightweight internal curing aggregate is pre-wetted and left to stand for 24 hours for later use; at the same time, the zeolite powder and mixing water of the specified ratio are mixed, stirred evenly, and left to stand for 24 hours to prepare a zeolite powder suspension for later use; cement, silica fume, early strength agent, the prepared zeolite powder suspension, water-reducing agent, the pre-wetted lightweight internal curing aggregate, and fiber are stirred evenly to obtain a lightweight ultra-high performance concrete material with internal curing effect.

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