Tunnel muck steel tube concrete applicable to plateau environment and its preparation method

Abstract

The present invention provides a tunnel muck steel tube concrete applicable to plateau environments and a preparation method thereof. The concrete comprises the following raw materials: cement, silica fume, microsphere powder, stone powder, expansion agent, manufactured sand, manufactured gravel, water reducing agent, type I air-entraining agent, type II air-entraining agent, and water. Among them, the manufactured gravel is the second-grade aggregate gravel made from tunnel muck, the manufactured sand is the continuously graded sand made from tunnel muck through dry crushing and screening, and the stone powder is the fine powder with a fineness of <0.075μm in the process of making sand from tunnel muck, which is further ground to a specific surface area ≥2000m 2 / kg. By treating the tunnel muck and combining it with air-entraining agents and other raw materials to make steel tube concrete applicable to plateau environments, the present invention can meet the pumping and jacking construction conditions, and the prepared steel tube concrete can be filled densely without significant debonding and voiding phenomena.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and particularly relates to a tunnel muck steel tube concrete applicable to plateau environments and a preparation method thereof. Background Art

[0002] Plateau regions are characterized by high altitude and low air pressure. The Sichuan-Tibet Railway project under construction in China is in such plateau environments. During the project construction, it is found that the concrete in such regions has difficulties in entraining air and stabilizing air bubbles due to the low air pressure. To achieve the same air content in fresh concrete, the dosage of conventional air-entraining agents when mixing concrete in plateau regions is 2 to 4 times that in plain regions, and the entrained air bubbles are difficult to maintain, resulting in serious air content loss. Therefore, it is necessary to find an air-entraining method applicable to plateau regions. On the other hand, the proportion of bridges and tunnels in the Sichuan-Tibet Railway project is high, and a large amount of tunnel muck is inevitably generated during a large number of tunnel excavations. At the same time, the materials along the Sichuan-Tibet Railway are scarce, the transportation is difficult and the cost is extremely high. It is an inevitable choice to reasonably use tunnel muck as a concrete raw material for in-situ utilization.

[0003] CN115536341A discloses a concrete and a preparation method thereof with all tunnel muck aggregates heated and shaped. It uses tunnel muck to make coarse and fine aggregates for concrete, heats and shapes the manufactured sand, and removes the stone powder and impurities therein. If this concrete is used in high-altitude and low-air-pressure environments, it cannot solve the problem of pipe blockage during the pumping and jacking process caused by difficult air entrainment and air bubble stabilization in this environment. Summary of the Invention

[0004] The purpose of the present invention is to provide a tunnel muck steel tube concrete applicable to plateau environments and a preparation method thereof. By treating tunnel muck and combining with air-entraining agents and other raw materials to make concrete applicable to plateau environments, it can meet the pumping and jacking construction conditions, and the prepared steel tube concrete can be filled densely without significant debonding and void phenomena.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions: A tunnel muck steel tube concrete applicable to plateau environments, comprising the following raw materials: cement, silica fume, microsphere powder, stone powder, expansive agent, manufactured sand, manufactured gravel, water reducer, Type I air-entraining agent, Type II air-entraining agent, and water; wherein the manufactured gravel is a secondary-graded gravel made from tunnel muck, the manufactured sand is a continuously graded sand made from tunnel muck by dry crushing, and the stone powder is made by further grinding the fine powder with a fineness of <0.075μm in the process of making sand from tunnel muck to a specific surface area ≥2000m 2 / kg.

[0006] In a further preferred embodiment, the strength grade of the concrete is C60 - C80. By weight, the mix ratio is 345 - 405 parts of cement, 25 - 45 parts of silica fume, 90 - 120 parts of micro - bead powder, 20 - 35 parts of stone powder, 30 - 45 parts of expansion agent, 799 - 839 parts of manufactured sand, 866 - 909 parts of manufactured gravel, 11 - 15 parts of water - reducing agent, 3 - 6 parts of Type I air - entraining agent, 0.05 - 0.08 parts of Type II air - entraining agent, and 130 - 135 parts of water.

[0007] Further, the cement is commercially available P.II 52.5 Portland cement or P.O52.5 ordinary Portland cement; the silica fume is semi - densified or non - densified silica fume, meeting the requirements of the standard GB / T 27690 - 2023 "Silica Fume for Mortars and Concretes"; the micro - bead powder has spherical particles under a high - magnification electron microscope, with a water demand ratio ≤ 95%, a 28 - day activity index ≥ 105%, and a loss on ignition ≤ 1%.

[0008] Further, the expansion agent is a commercially available calcium - magnesium composite expansion agent, with a restricted expansion rate in water at 20°C for 7 days ≥ 0.05%; the water - reducing agent is a high - performance polycarboxylate - based water - reducing agent, with a water - reducing rate of 15% - 20%.

[0009] Further, the fineness modulus of the manufactured sand is 2.7, and the stone powder content below 0.08mm < 3%; and the cumulative sieve residues of < 0.15mm, 0.15 - 0.315mm, 0.315 - 0.63mm, 0.63 - 1.18mm, 1.18 - 2.36mm, 2.36 - 4.75mm are 6 - 9%, 10 - 15%, 15 - 20%, 20 - 30%, 15 - 25%, 10 - 15%, 0 - 5% respectively.

[0010] Further, the mud content of the manufactured gravel < 1%; in the two - stage grading, the particle sizes are 5 - 10mm and 10 - 16mm respectively, and through the calculation of the closest - packing curve, the blending ratio is 25 - 35:65 - 75.

[0011] Further, the Type I air - entraining agent is a high - air - entraining type air - entraining agent, and the Type II air - entraining agent is a low - air - entraining and high - stability foam type air - entraining agent.

[0012] Furthermore, the Type-I air-entraining agent is prepared by mixing rosin powder, polyoxyethylene ether of rosin alcohol, phosphate ester of polyoxyethylene ether of tridecanol, and polyethylene glycol in an effective solid content ratio of 30-40 wt%: 25-35 wt%: 15-30 wt%: 10-15 wt%, stirring and heating to 75-85 °C, stirring and maintaining the temperature for 2-4 h, and then adding deionized water and continuing to stir to prepare a solution with a solid content of 1%; the Type-II air-entraining agent is one or a combination of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium dodecyl polyoxyethylene ether sulfate. When using the Type-II air-entraining agent, 0.05-0.08 parts by mass of the effective solid content is dissolved in part of the mixing water. The method for determining the amount of this part of the mixing water is the product of the mass of the manufactured sand used for mixing and the water absorption rate of the sand, which is 10.63-11.61 parts.

[0013] The present invention also relates to a preparation method of tunnel muck steel pipe concrete applicable to the plateau environment, comprising the following steps:

[0014] Add the Type-II air-entraining agent to part of the water for mixing, and the obtained slurry is atomized and sprayed onto the manufactured sand, then turned and stirred evenly and homogenized for 1-4 h to obtain the pre-treated manufactured sand pre-adsorbed with the Type-II air-entraining agent; then mix it evenly with manufactured gravel, cement, silica fume, microsphere powder, stone powder, and expansion agent, and then add the remaining water, water reducer, and Type-I air-entraining agent, and stir evenly to obtain.

[0015] Furthermore, the amount of water added with the Type-II air-entraining agent is the product of the mass of the manufactured sand and the water absorption rate of the sand, specifically 10.63-11.61 parts.

[0016] In the concrete formula of the present invention, the incorporation of silica fume can exert its "pozzolanic effect" to improve the mechanical properties and durability of the concrete. At the same time, due to the existence of its extremely fine particles, it can displace the water wrapped by cement particles, playing a role in reducing viscosity. The incorporation of microsphere powder can also exert the "pozzolanic effect". At the same time, its low water demand and spherical particles play a "ball bearing" effect, which can produce a physical water reduction effect, reduce the viscosity of the concrete, and improve the pumpability of the steel pipe concrete. After the stone powder is ground fine by a jet mill, on the one hand, it can eliminate the microcracks and micropores in the granodiorite body itself through ultrafine grinding, reducing the water absorption of the granodiorite stone powder. On the other hand, the particle diameter of the stone powder after ultrafine grinding is much smaller than that of the cement particles, and it can fill between the cement particles, playing a role in filling and densifying. Together with the finer silica fume particles, it promotes the system to reach the most closely packed state. The calcium-magnesium composite expansion agent contains two types of expansion components, calcium-based and magnesium-based. The calcium-based expansion component can react rapidly in the early stage of concrete hydration to make up for the initial shrinkage of the concrete. Subsequently, the magnesium-based expansion component can still continue to hydrate in an environment with internal water compensation, generating a continuous compensating shrinkage effect.

[0017] More importantly, in order to adapt to the plateau environment, the formula of the present invention adopts two types of air-entraining agents. Among them, Type I air-entraining agent is a high air-entraining type air-entraining agent suitable for the plateau environment, while Type II air-entraining agent is a low air-entraining and high foam-stabilizing air-entraining agent. During the mixing of concrete with dry manufactured sand, due to its high water absorption, part of the mixing water will also be adsorbed, resulting in a decrease in the workability of concrete such as slump. The present invention pre-adsorbs an aqueous solution containing Type II air-entraining agent. On the one hand, it avoids the large adsorption of mixing water by manufactured sand during the concrete mixing process. On the other hand, the water pre-adsorbed in the manufactured sand can be gradually released during the hardening and curing process of the concrete, providing a certain degree of internal curing effect for the airtight environment of the concrete-filled steel tube, promoting the growth of concrete strength, and also providing a guarantee for the hydration reaction of the expansion component. In addition, the Type II air-entraining agent in the aqueous solution will also diffuse in the liquid phase channel of the system during the transportation and jacking construction of the concrete, providing a "secondary air-entraining" effect, compensating for the air-entraining loss caused by the low-pressure environment, and reducing the deterioration of the workability of the concrete and the risk of pipe blockage.

[0018] The present invention has the following beneficial effects:

[0019] Through the multi-level utilization of tunnel muck, manufactured gravel, manufactured sand and stone powder are obtained, and the stone powder is subjected to secondary ultra-fine processing, and combined with cement and admixtures of different fineness grades, the concrete-filled steel tube reaches the most closely packed state, which is more conducive to the stability of the air bubbles introduced into the concrete.

[0020] By optimizing and combining different types of air-entraining agents and using the technical means of graded incorporation and relay effect, first, the high air-entraining Type I air-entraining agent suitable for the plateau environment incorporated during concrete mixing can introduce 3% - 4% air content into the concrete. After the concrete is prepared, in the low-pressure environment, the air content of the concrete first rapidly and then slowly decreases within a certain period of time and finally maintains at a relatively low level (1.5 - 1.7%). After the concrete leaves the mixer, it is transported to the construction site of the concrete-filled steel tube by a concrete mixer truck. During the process, it still flows slowly with the tank. At this time, the air content introduced by the Type I air-entraining agent begins to decrease, while the Type II air-entraining agent pre-adsorbed into the manufactured sand gradually diffuses through the liquid phase in the concrete system and begins to play an air-entraining role, continuously introducing a relatively low and stable air content, maintaining the air content of the concrete-filled steel tube between 2% - 2.5%. Thus, the problems of pumping and jacking pipe blockage caused by the influence of the plateau low-pressure environment on the air content of the concrete are solved. It can also cooperate with the incorporated calcium-magnesium composite expansion agent to provide a certain degree of internal curing and micro-expansion performance, making the concrete fill more densely in the steel tube without significant debonding and dehollowing phenomena. Specific embodiments

[0021] The following will describe the implementation plan of the present invention in detail in combination with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0022] The concrete mix ratios in Examples 1 to 3 are shown in Table 1 below.

[0023] Table 1 Concrete Mix Ratios in Examples 1 to 3 (kg / m 3 )

[0024]

[0025] Among them, P.II 52.5 Portland cement is used. Both silica fume and microbead powder are commercially available products that meet the requirements. The tunnel muck is granodiorite, and the water absorption rate is 1.4%. The stone powder is the stone powder generated during the production of machine-made sand from tunnel muck, and it is ultrafinely ground to a specific surface area of 2100 m 2 / kg; the expansion agent is a commercially available calcium-magnesium composite expansion agent; the machine-made sand is produced from tunnel muck by the dry method, with a fineness modulus of 2.7, the stone powder content below 0.08 mm is 1.3%, and the cumulative sieve residues of <0.15 mm, 0.15 - 0.315 mm, 0.315 - 0.63 mm, 0.63 - 1.18 mm, 1.18 - 2.36 mm, 2.36 - 4.75 mm should be 8.5%, 14.5%, 16.9%, 25.3%, 19.6%, 13.1%, 2.1% respectively, and it is pre-adsorbed with an aqueous solution containing Type II air-entraining agent; the stone is the secondary-graded crushed stone produced by crushing and shaping tunnel muck, and the mixing ratio of 5 - 10 mm and 10 - 16 mm crushed stone is 30:70; the water-reducing agent is a high-performance polycarboxylate water-reducing agent with a water-reducing rate of 18%;

[0026] Preparation of Type I air-entraining agent: Rosin powder, rosin alcohol polyoxyethylene ether, tridecyl alcohol polyoxyethylene ether phosphate, and polyethylene glycol are mixed in an effective solids content ratio of 40 wt%:35 wt%:15%:10 wt%, placed in a reaction vessel, stirred and heated to 80°C, stirred and held for 2 h, then a certain amount of deionized water is added, and stirring continues to prepare a solution with a solids content of 1%, which is the Type I high air-entraining air-entraining agent.

[0027] Type II air-entraining agent is sodium dodecylbenzenesulfonate.

[0028] Previously, the Type II air-entraining agent is dissolved in part of the mixing water (the amount of mixing water is the machine-made sand * water absorption rate, and the water absorption rate of the machine-made sand used in the above case is 1.4%), atomized and sprayed into the dry machine-made sand, mixed evenly and homogenized for 1 h. When mixing the concrete, the machine-made sand pre-adsorbed with Type II air-entraining agent, machine-made stone, cement, silica fume, microbeads, stone powder, and expansion agent are placed in the mixing pot, stirred for 30 s, then the remaining mixing water, water-reducing agent, and Type I air-entraining agent are added, and stirring continues for 2 min to obtain the tunnel muck steel pipe concrete suitable for the plateau environment. The performance of the steel pipe concrete with strength grades C60 - C80 is shown in Table 2.

[0029] Table 2 Concrete Performance in Examples 1 to 3

[0030]

[0031]

[0032] *The test method here is that after the concrete is discharged from the mixer, it enters the concrete mixer truck and the working performance is tested after 2 hours of movement with the truck.

[0033] Thus, through the above raw materials and preparation methods, it is possible to prepare C60 - C80 steel - tube concrete applicable to the plateau environment using tunnel muck. The prepared concrete can maintain the air content within 2.0% - 2.5% after 2 hours of transportation in the concrete mixer truck, with almost no loss in slump and spread, and the free expansion rate in a closed environment is within 0 - 6×10 -4 , and the compressive strength meets the standard. It meets the Technical Code for Steel - Tube Concrete Arch Bridges GB 50923 - 2013, and the concrete can smoothly complete the construction process through pumping and jacking.

[0034] Comparative Example 4

[0035] The concrete mix ratio of Comparative Example 4 is shown in Table 3 below.

[0036] Table 3 Concrete Mix Ratio Table of Comparative Example 4 (kg / m 3 )

[0037]

[0038] Among the raw materials used, except that the stone powder is the stone powder generated during the production of machine - made sand from tunnel muck, with a specific surface area of 420 m 2 / kg, the others are the same as in Example 2. The preparation process is also the same as in Example 2. The steel - tube concrete of Comparative Example 4 is prepared, and its performance is shown in Table 4.

[0039] Table 4 Concrete Performance of Comparative Example 4

[0040]

[0041] *The test method here is that after the concrete is discharged from the mixer, it enters the concrete mixer truck and the working performance is tested after 2 hours of movement with the truck.

[0042] The main difference between Comparative Example 4 and Example 2 is that the stone powder has not undergone secondary ultra - fine grinding. The coarser stone powder particles cannot form a close packing with other raw materials, and the pores and micro - cracks of the stone powder particles have not been removed by grinding. As a result, the water demand is relatively high, the free water in the concrete system decreases, and further, the slump, spread, and air content of the prepared C70 tunnel - muck steel - tube concrete all decrease, failing to meet the performance requirements for pumping and jacking construction of steel - tube concrete.

[0043] Comparative Example 5

[0044] The concrete mix ratio of Comparative Example 5 is shown in Table 5 below.

[0045] Table 5 Concrete Mix Ratio Table of Comparative Example 5 (kg / m 3 )

[0046]

[0047] Among them, the air-entraining agent used is the commercially available X-max type rosin-based air-entraining agent, which is used according to its recommended dosage. The others are the same as in Example 2.

[0048] During the concrete mixing, the manufactured sand, manufactured stone, cement, silica fume, microbeads, stone powder, and expansive agent in the mixing pot were stirred for 30 s, then the mixing water, water reducer, and commercially available air-entraining agent were added, and stirring was continued for 2 min to obtain the tunnel muck-filled steel tubular concrete of Comparative Example 5. The performance of the steel tubular concrete of Comparative Example 5 is shown in Table 6.

[0049] Table 6 Concrete Performance of Comparative Example 5

[0050]

[0051] *The test method here is that after the concrete is discharged from the machine, it enters the concrete mixer truck and the workability is tested after moving with the truck for 2 h.

[0052] The main difference between Comparative Example 5 and Example 2 is the use of a commercially available air-entraining agent. This commercially available air-entraining agent is a relatively excellent product for air-entraining in the plateau environment after screening. However, in the face of the low-pressure environment, its air-entraining and foam-stabilizing capabilities are still insufficient, resulting in a relatively low air content of the steel tubular concrete of Comparative Example 5 when it is discharged from the machine and a large loss of air content after 2 h. Furthermore, it causes significant problems such as stickiness and slump loss due to insufficient lubrication of the concrete bubbles, and it cannot meet the pumping and jacking construction performance requirements of the steel tubular concrete.

[0053] Comparative Example 6

[0054] The concrete mix ratio of Comparative Example 6 is shown in Table 7 below.

[0055] Table 7 Concrete Mix Ratio Table of Comparative Example 6 (kg / m 3 )

[0056]

[0057] For Comparative Example 6, the raw materials are the same as those in Example 2. During the concrete mixing, the pre-absorbed manufactured sand (not dissolved with Type II air-entraining agent), manufactured stone, cement, silica fume, microbeads, stone powder, and expansive agent in the mixing pot were stirred for 30 s, then the remaining mixing water, water reducer, Type I air-entraining agent, and Type II air-entraining agent were added, and stirring was continued for 2 min to obtain the steel tubular concrete of Comparative Example 6. The performance of the steel tubular concrete of Comparative Example 6 is shown in Table 8.

[0058] Table 8 Concrete Performance of Comparative Example 6

[0059]

[0060]

[0061] *The test method here is that after the concrete is discharged from the mixer and enters the concrete mixer truck, the working performance is tested after 2 hours of movement with the tank.

[0062] The main difference between Comparative Example 6 and Example 2 is that the type II air-entraining agent is not dissolved in water in advance and pre-adsorbed into the manufactured sand, but is incorporated together with the type I air-entraining agent during the concrete mixing process. At this time, although a large air content can still be formed after forced stirring by the mixer, during the subsequent 2-hour transportation process of the concrete mixer truck, the lack of air-entraining component supplementation leads to a sharp decrease in the air content, which in turn causes a decrease in the slump, spread, and air content of the C70 tunnel muck-filled steel tubular concrete prepared, and an increase in the concrete viscosity, making it unable to meet the pumping and jacking construction performance requirements of the steel tubular concrete.

[0063] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A steel tube concrete filled with tunnel muck applicable to plateau environment, characterized in that, It includes the following raw materials: cement, silica fume, microbead powder, stone powder, expansive agent, manufactured sand, manufactured gravel, water reducer, Type I air-entraining agent, Type II air-entraining agent and water; among which, the manufactured gravel is the second-grade aggregate gravel made from tunnel muck, the manufactured sand is the continuously graded sand made from tunnel muck through dry crushing and screening, and the stone powder is made by further grinding the fine powder with a fineness of <0.075μm in the process of making sand from tunnel muck to a specific surface area ≥2000m 2 / kg. The Type I air-entraining agent is a high air-entraining type air-entraining agent, which is prepared by mixing rosin powder, rosin alcohol polyoxyethylene ether, tridecyl alcohol polyoxyethylene ether phosphate, and polyethylene glycol in an effective solid content ratio of 30-40 wt%: 25-35 wt%: 15-30 wt%: 10-15 wt%, stirring and heating to 75-85 °C, stirring and keeping warm for 2-4 h, and then adding deionized water and continuing to stir to prepare a solution; The Type II air-entraining agent is a low air-entraining and high foam-stabilizing type air-entraining agent, specifically one or a combination of several of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium dodecyl polyoxyethylene ether sulfate.

2. The concrete according to claim 1, characterized in that: The strength grade of the concrete is C60-C80. By weight, the mix ratio is 345-405 parts of cement, 25-45 parts of silica fume, 90-120 parts of microbead powder, 20-35 parts of stone powder, 30-45 parts of expansive agent, 799-839 parts of manufactured sand, 866-909 parts of manufactured gravel, 11-15 parts of water-reducing agent, 3-6 parts of Type I air-entraining agent, 0.05-0.08 parts of Type II air-entraining agent, and 130-135 parts of water.

3. The concrete according to claim 1, wherein: The cement is commercially available P.II 52.5 Portland cement or P.O52.5 ordinary Portland cement; the silica fume is semi-dense or non-dense silica fume, meeting the specification requirements of GB / T 27690-2023 "Silica Fume for Mortar and Concrete"; the microbead powder has spherical particles under a high-power electron microscope, with a water demand ratio ≤ 95%, a 28-day activity index ≥ 105%, and a loss on ignition ≤ 1%.

4. The concrete according to claim 1, characterized in that: The expansive agent is a commercially available calcium-magnesium composite expansive agent, with a restricted expansion rate in water at 20 °C for 7 days ≥ 0.05%; the water-reducing agent is a high-performance polycarboxylate-based water-reducing agent, with a water reduction rate of 15%-20%.

5. The concrete according to claim 1, wherein: The fineness modulus of the manufactured sand is 2.7, and the stone powder content below 0.08 mm < 3%; and the cumulative sieve residues of < 0.15 mm, 0.15-0.315 mm, 0.315-0.63 mm, 0.63-1.18 mm, 1.18-2.36 mm, 2.36-4.75 mm, and > 4.75 mm are 6-9%, 10-15%, 15-20%, 20-30%, 15-25%, 10-15%, and 0-5% respectively.

6. The concrete according to claim 1, wherein: The mud content of the manufactured gravel < 1%; in the two-stage grading, the particle sizes are 5-10 mm and 10-16 mm respectively, and through the calculation of the closest packing curve, the blending ratio is 25-35: 65-75.

7. The preparation method of the tunnel muck-filled steel tube concrete applicable to the plateau environment according to any one of claims 1 to 6, characterized in that, It includes the following steps: Add the Type II air-entraining agent to part of the water for mixing, and the obtained slurry is atomized and sprayed onto the manufactured sand and stirred evenly and homogenized for 1-4 h to obtain the pretreated manufactured sand pre-adsorbed with the Type II air-entraining agent; then mix it evenly with the manufactured gravel, cement, silica fume, microbead powder, stone powder, and expansive agent, and then add the remaining water, water-reducing agent, and Type I air-entraining agent and stir evenly to obtain.

8. The preparation method according to claim 7, wherein: The amount of water added with the Type II air-entraining agent is the product of the mass of the manufactured sand and the water absorption rate of the sand.

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