A large-volume concrete for tunnels and its preparation method

Abstract

The present invention discloses a large-volume concrete for tunnels. Each component and its weight fraction include: 360 - 380 parts of cement, 720 - 760 parts of quartz sand, 950 - 1150 parts of quartz stone, 20 - 40 parts of admixture, 0.6 - 2.8 parts of composite temperature regulation component, 9 - 18 parts of fiber, 7 - 10 parts of composite admixture, and 160 - 170 parts of water; wherein, the composite temperature regulator is obtained by compounding graphene oxide and cellulose nanocrystals as the main raw materials. The large-volume concrete for tunnels of the present invention can effectively reduce the internal and external temperature difference during the pouring process of large-volume tunnel concrete, make the temperature uniform during the concrete forming process, and take into account good workability, mechanical properties, crack resistance, etc.; and the involved preparation method is relatively simple, without the need to assist other construction control processes, providing a new idea for the preparation of high-performance large-volume concrete for tunnels.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a large-volume concrete for tunnels and a preparation method thereof. Background Art

[0002] With the acceleration of the urbanization process, the demands for urban transportation and infrastructure construction are continuously increasing. As an important means to solve problems such as traffic congestion, underground space utilization, and urban planning, tunnels have been widely applied and developed.

[0003] During the pouring process of large-volume concrete for tunnels, due to the large construction volume, the temperature at the center of the concrete rises relatively fast, resulting in a large temperature gradient after pouring, and it is easy to generate problems such as temperature stress and shrinkage cracks. In addition, the service environment inside the tunnel is complex, and the generation of micro-cracks will accelerate the erosion and damage of the concrete by Cl - , SO4 2- , microorganisms, etc., thereby causing a significant reduction in the service life of the concrete. Controlling the temperature and cracks during the construction of large-volume concrete for tunnels is an urgent problem to be solved at present. Summary of the Invention

[0004] The purpose of the present invention is to provide a large-volume concrete for tunnels in view of the problems and deficiencies existing in the prior art, which can effectively reduce the temperature difference between the inside and outside during the pouring process of large-volume concrete for tunnels, make the temperature uniform during the concrete forming process, and take into account good workability, mechanical properties, crack resistance, etc.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A large-volume concrete for tunnels, the components and their respective weight parts include: 360 - 380 parts of cement, 720 - 760 parts of quartz sand, 950 - 1150 parts of quartz stone, 20 - 40 parts of admixture, 0.6 - 2.8 parts of composite temperature regulation component, 9 - 18 parts of fiber, 7 - 10 parts of composite admixture, 160 - 170 parts of water; wherein, the composite temperature regulator is obtained by compounding graphene oxide and cellulose nanocrystals as the main raw materials.

[0007] In the above solution, the cement is ordinary Portland cement with a grade above P.O 42.5; the fineness modulus of the quartz sand is 2.5 - 2.8, and it is medium sand in Zone II; the quartz stone has a continuous gradation of 5 - 20mm and a crushing value ≤ 6%.

[0008] In the above solution, the mass ratio of graphene oxide to cellulose nanocrystals is 1:1.5 - 2.5; wherein the type of graphene oxide is a sheet-like ultra-thin structure with a thickness of 5 - 20nm and a sheet diameter of 200 - 500nm; the particle size of the cellulose nanocrystals is 10 - 30nm.

[0009] In the above solution, the admixture is Class II fly ash, with a fineness (residue on a 45μm square sieve) not exceeding 20%, a strength activity index greater than 75%, and a free calcium oxide mass fraction not exceeding 0.6%.

[0010] Preferably, the fiber is a copper fiber, with a length of 12 - 20mm, a diameter of 0.8 - 1.3mm, and a spindle shape.

[0011] In the above solution, the composite admixture is a composite of polycarboxylate water reducer and retarder in a mass ratio of 3:2 - 3.

[0012] Furthermore, the water reduction rate of the polycarboxylate water reducer is 20 - 30%.

[0013] Preferably, the retarder can be selected from sodium gluconate, etc.

[0014] The preparation method of the above-mentioned mass concrete for tunnels includes the following steps:

[0015] 1) Weigh the raw materials according to the ratio. Each component and its weight fraction include: 360 - 380 parts of cement, 720 - 760 parts of quartz sand, 950 - 1150 parts of quartz stone, 20 - 40 parts of admixture, 0.6 - 2.8 parts of composite temperature regulating component, 9 - 18 parts of fiber, 7 - 10 parts of composite admixture, and 160 - 170 parts of water;

[0016] 2) Stir the weighed quartz sand, quartz stone, admixture, cement, and fiber evenly to obtain a solid mixture; dissolve the composite temperature regulating component in the weighed water and disperse it evenly to obtain a mixed solution; add the mixed solution and the composite admixture to the solid mixture and stir evenly to obtain the mass concrete for tunnels.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1) The present invention uses graphene oxide and cellulose nanocrystals in combination, which can effectively reduce the heat at the interface during the forming process of concrete structures, and can promote the formation of a uniform network structure in concrete, which is beneficial to the dispersion of heat during the setting and hardening process of concrete and improves mechanical properties, etc.: 1) The present invention combines the heat dissipation channels of graphene oxide and the heat dissipation ability of cellulose nanocrystals, which is beneficial to the dispersion of heat during the setting and hardening process of concrete; graphene oxide can form heat conduction channels during the formation of the structure of concrete hydration products, promoting the rapid conduction and dispersion of heat, and improving the internal heat conduction ability of concrete. Cellulose nanocrystals can also increase the specific surface area and porosity of concrete, enhancing the ability of the structure to absorb moisture and dissipate heat; 2) The mutual cooperation of cellulose nanocrystals and graphene oxide forms a more compact and stable network structure; cellulose nanocrystals can provide longitudinal connection and fiber-reinforcing effects, and graphene oxide has a high specific surface area and good dispersibility, which can fill the pore structure in concrete, increase the compactness of concrete and improve the porosity. The combined action of the two can effectively improve the homogeneity and crack resistance of the internal structure of concrete; in addition, the introduced cellulose nanocrystals can fill the microvoids and cracks in tunnel concrete, reduce water penetration and the erosion of harmful substances, and at the same time have good resistance to chloride ion and sulfate erosion, improving the durability and corrosion resistance of concrete, etc.

[0019] 2) The addition of copper fibers can effectively improve problems such as the cracking and shrinkage performance of concrete, reduce the formation and expansion of cracks, and has good antibacterial properties, having a good inhibitory effect on the growth of microorganisms, which is more conducive to its application in tunnel engineering; in addition, copper fibers also have excellent heat transfer performance. The uniformly dispersed copper fibers during the forming process of concrete can evenly conduct the hydration heat generated by the uneven hydration inside the concrete, thereby reducing the temperature difference between the inside and outside of the concrete and reducing the generation of temperature cracks in the concrete.

[0020] 3) The combined use of a retarder and a water reducer can delay the hydration reaction rate of cement, extend the setting time of concrete, enabling better flow and filling between the hydration products and raw materials; it is beneficial to improving the workability of concrete and helps to reduce problems caused by temperature rise and volume shrinkage during construction. Detailed implementation manners

[0021] To further understand the present invention, the following describes the preferred implementation schemes of the present invention in combination with embodiments. These descriptions are only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention.

[0022] In the following examples, the Portland cement used is Huaxin P.O42.5 ordinary Portland cement with a 28-day strength of 52.7 MPa; the fly ash comes from Ezhou Power Plant, Grade II, with a 28-day strength activity index of 78%, a residue on a 45um square hole sieve of 16.1%, and a free calcium oxide mass fraction of 0.4%; the graphene oxide has a flaky ultra-thin structure with an average thickness of 5 - 16 nm and a sheet diameter of 230 - 400 nm; the cellulose nanocrystals come from Kaiyi New Materials Technology Co., Ltd., with a density of 1.05 - 1.19 g / cm 3 , and the average particle size is between 15 - 20 mm; the polycarboxylate superplasticizer used is from China State Construction Western Region Construction New Materials Technology Co., Ltd., with a model of PC-12%, a solid content of 11.4%, and a concrete water reduction rate of 29%. The retarding agent used is sodium gluconate provided by Yuxing in Xingtai, Hebei, and its retarding effect can reach 30 minutes; the copper fiber comes from Xinyuan Friction Materials Co., Ltd., with a diameter of 1 - 1.2 mm, a length of 15 - 20 mm, and a spindle shape; the fineness modulus of the quartz sand is 2.5, medium sand in Zone II; the quartz stone has a continuous gradation of 5 - 16 mm, a crushing value ≤ 6%, a mud content ≤ 0.5%, a needle and flake content of 0.6%, and the water is from the tap water in Wuhan.

[0023] Examples 1 - 10

[0024] The preparation method of the mass concrete for tunnels described in Examples 1 - 10 includes the following steps:

[0025] 1) Weigh each raw material according to the formula system described in Table 1. Among them, the composite temperature regulation component used is obtained by compounding graphene oxide and cellulose nanocrystals in a mass ratio of 1:2, and the composite admixture is obtained by compounding polycarboxylate superplasticizer and retarding agent in a mass ratio of 3:2;

[0026] 2) Put the weighed quartz sand, quartz stone, admixture, cement, and fiber into a mixer and pre-stir for 1 minute. Then dissolve the composite temperature regulation in the weighed water and disperse it evenly to obtain a mixed solution. While adding the evenly dispersed mixed solution to the mixer, slowly add the composite admixture on the other side, and the stirring time is 3 minutes to obtain the mass concrete for tunnels.

[0027] Table 1 Raw material dosage (weight parts) of the mass concrete for tunnels described in Examples 1 - 10

[0028]

[0029] Comparative Examples 1 - 5

[0030] The preparation method of the mass concrete in Comparative Examples 1 - 5 is generally the same as that in Examples 1 - 10, except that the raw material dosages used are shown in Table 2.

[0031] Table 2 Raw material dosages (parts by weight) of the mass concrete for tunnels described in Comparative Examples 1-5

[0032]

[0033] The above examples and comparative examples were molded according to the weight ratio, and the initial workability of the concrete was tested. Subsequently, they were molded in concrete molds of 150 mm×150 mm×150 mm and 150 mm×150 mm×600 mm. The 150 mm×150 mm×150 mm specimens were used to test the impermeability and strength of the concrete. Temperature sensors were installed inside and outside the 150 mm×150 mm×600 mm concrete synchronously, and the temperature changes were detected and recorded in real time through a data acquisition system to measure the maximum value of the internal and external temperature difference. The mass loss rate of the 28-day specimens was measured to characterize the durability of the concrete. The performance of the mass concrete for tunnels in all aspects was characterized by the above test methods, and the specific test data are shown in Table 3 below.

[0034] Table 3 Performance test results of the concrete obtained from Examples 1-10 and Comparative Examples 1-5

[0035]

[0036]

[0037] Comparing Examples 3 and 4 with Comparative Example 1, the results show that adding an appropriate amount of composite temperature regulating component can effectively reduce the maximum value of the internal and external temperature difference of the concrete by more than 50% within 24 hours, and its mechanical properties, durability, and crack resistance are all significantly improved.

[0038] Comparing Examples 3 and 4 with Comparative Examples 2-5, the results show that when using a single graphene oxide or cellulose nanocrystal as the temperature regulating component, the effect on improving the crack resistance, durability of the concrete and reducing the internal and external temperature difference is relatively limited.

[0039] The present invention is not limited to the above embodiments. For those of ordinary skill in the art in the technical field, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches are also regarded as within the protection scope of the present invention. The content not described in detail in this specification belongs to the prior art well-known to those of ordinary skill in the art.

Claims

1. A large-volume concrete for tunnels, characterized in that, The components and their weight portions include: 360-380 portions of cement, 720-760 portions of quartz sand, 950-1150 portions of quartz stone, 20-40 portions of admixture, 0.6-2.8 portions of composite temperature regulating component, 9-18 portions of fiber, 7-10 portions of composite admixture, and 160-170 portions of water; among them, the composite temperature regulator is obtained by compounding graphene oxide and cellulose nanocrystals as the main raw materials; The graphene oxide has a flaky ultra-thin structure with a thickness of 5-20 nm and a sheet diameter of 200-500 nm; the particle size of the cellulose nanocrystals is 10-30 nm.

2. The mass concrete for tunnels according to claim 1, characterized in that, The mass ratio of the graphene oxide to the cellulose nanocrystals is 1:1.5-2.

5.

3. The mass concrete for tunnel according to claim 1, characterized in that, The cement is ordinary Portland cement with a grade above P.O 42.

5.

4. The mass concrete for tunnels according to claim 1, wherein The fineness modulus of the quartz sand is 2.5-2.8, medium sand in Zone II; the quartz stone has a continuous gradation of 5-20 mm and a crushing value ≤ 6%.

5. The mass concrete for tunnel according to claim 1, characterized in that, The admixture is Class II fly ash, the residue on a 45um square hole sieve does not exceed 20%, the strength activity index is greater than 75%, and the mass fraction of free calcium oxide does not exceed 0.6%.

6. The mass concrete for tunnels according to claim 1, wherein The fiber is copper fiber with a length of 12-20 mm, a diameter of 0.8-1.3 mm, and a spindle shape.

7. The mass concrete for tunnel according to claim 1, wherein, The composite admixture is a composite of polycarboxylate water reducer and retarder in a mass ratio of 3:2-3.

8. The mass concrete for tunnel according to claim 7, characterized in that, The water reducing rate of the polycarboxylate water reducer is 20-30%.

9. The preparation method of the mass concrete for tunnels according to any one of claims 1 to 8, characterized in that, It includes the following steps: 1) Weigh the raw materials according to the ratio. The components and their weight portions include: 360-380 portions of cement, 720-760 portions of quartz sand, 950-1150 portions of quartz stone, 20-40 portions of admixture, 0.6-2.8 portions of composite temperature regulating component, 9-18 portions of fiber, 7-10 portions of composite admixture, and 160-170 portions of water; 2) Stir the weighed quartz sand, quartz stone, admixture, cement, and fiber evenly to obtain a solid mixture; dissolve the composite temperature regulating component in the weighed water and disperse it evenly to obtain a mixed solution; add the mixed solution and the composite admixture to the solid mixture and stir evenly to obtain the mass concrete for tunnels.

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