Micro-expanded steel tube concrete based on gradient expansion, preparation method and application

Abstract

The application belongs to the technical field of building materials, and particularly discloses a micro-expansion steel pipe concrete based on gradient expansion, a preparation method and application. The micro-expansion steel pipe concrete comprises the following components: cementing material 400-600 parts, gradient expansion agent 20-100 parts, gradient internal curing agent 20-200 parts, additive 5-10 parts, fine aggregate 500-800 parts and coarse aggregate 800-1200 parts. The gradient expansion agent comprises aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide, and the gradient internal curing agent comprises ceramic sand, zeolite powder, expanded perlite and superabsorbent resin. The micro-expansion steel pipe concrete can realize gradient continuous expansion, and in the process, water is released under different internal humidity conditions to compensate for the shrinkage effect of the concrete at different hydration stages, and promote the complete reaction of the expansion agent, thereby effectively solving the problems of core concrete and steel pipe wall debonding and debonding, and significantly improving the overall performance of the steel pipe concrete.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology. Specifically, it relates to a micro-expansion steel tube concrete based on gradient expansion, its preparation method and application. More specifically, it relates to a micro-expansion steel tube concrete based on gradient expansion agent and gradient internal curing agent, its preparation method and application. Background Technology

[0002] Currently, the main factor restricting the development of concrete-filled steel tube structures is the debonding and separation between the core concrete and the steel tube wall. This is because concrete undergoes shrinkage behaviors such as autogenous shrinkage and drying shrinkage during hydration, leading to peeling and separation at the steel-concrete interface. Therefore, during the preparation of concrete-filled steel tubes, expansive agents are usually added to counteract these shrinkage effects and reduce separation problems caused by concrete shrinkage. However, numerous experiments and engineering applications have shown that relying solely on expansive agents is not effective in solving the debonding and separation problems of concrete-filled steel tubes. On the one hand, the expansion reaction of the expansive agent requires water, but concrete-filled steel tubes are in a sealed environment and cannot obtain sufficient free water from the external environment, resulting in insufficient reaction of the expansive agent and a weak expansion effect. On the other hand, concrete shrinkage is a continuous and slow process, while the expansive agent usually reacts at a specific moment and cannot continuously compensate for the shrinkage strain of the concrete.

[0003] Based on the aforementioned defects and shortcomings, there is an urgent need in this field to propose a micro-expansion steel-tube concrete based on a gradient expansive agent and a gradient internal curing agent. The gradient expansive agent can achieve continuous expansion of the steel-tube concrete to compensate for the shrinkage effect of concrete at different stages of hydration; the gradient internal curing agent provides the reaction water for the expansive agent to promote complete reaction of the expansive agent and obvious expansion effect, so as to fundamentally solve the problem of debonding and separation of steel-tube concrete caused by insufficient reaction of the expansive agent and insignificant expansion effect. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a micro-expansion steel-tube concrete based on gradient expansion, its preparation method, and its application. Specifically, considering the characteristics of steel-tube concrete itself and its curing process, a micro-expansion steel-tube concrete based on a gradient expansion agent and a gradient internal curing agent is designed. The gradient expansion agent enables continuous expansion of the steel-tube concrete to compensate for the shrinkage effect of concrete at different stages of hydration; the gradient internal curing agent provides the reaction water for the expansion agent to promote complete reaction and significant expansion effect. The micro-expansion steel-tube concrete prepared by this invention effectively solves the problem of debonding and separation between the core concrete and the steel tube wall, significantly improving the overall performance of the steel-tube concrete.

[0005] To achieve the above objectives, according to one aspect of the present invention, a micro-expansion steel-tube concrete based on gradient expansion and curing is proposed, comprising the following components by weight:

[0006] 400-600 parts of cementitious material, 20-100 parts of gradient expansion agent, 20-200 parts of gradient internal curing agent, 5-10 parts of admixture, 500-800 parts of fine aggregate, and 800-1200 parts of coarse aggregate;

[0007] The gradient expansion agent includes aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide, and the gradient internal curing agent includes ceramic sand, zeolite powder, expanded perlite and superabsorbent resin.

[0008] As a further preferred embodiment, the mass ratio of the aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide is 1:(3-8):(2-6):(1-5).

[0009] As a further preferred embodiment, the aluminum powder has a fineness of 100-300 mesh;

[0010] The specific surface area of ​​the calcium oxide is ≥200m². 2 / kg;

[0011] The citric acid value of the M-type magnesium oxide is 130–180s, and the citric acid value of the S-type magnesium oxide is 240–280s.

[0012] As a further preferred embodiment, the mass ratio of the ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin is 1:(0.05-0.5):(0.005-0.05):(0.002-0.03).

[0013] As a further preferred embodiment, the ceramic sand is high-strength shale ceramic sand with a particle size of 0.075–4.75 mm, a 24-hour water absorption rate of 10–30%, and an apparent density of 900–1200 kg / m³. 3 ;

[0014] The zeolite powder is natural zeolite powder with a density of 1600–2000 kg / m³. 3 Porosity ≥ 50%;

[0015] The expanded perlite is made from perlite ore sand through high-temperature roasting, with a density of 40–120 kg / m³. 3 Porosity ≥ 60%;

[0016] The superabsorbent resin includes low-crosslinked sodium polyacrylate with a density of 50–90 kg / m³. 3 The water absorption ratio is 150 to 400 times.

[0017] As a further preferred embodiment, the cementing material includes cement, fly ash, mineral powder, and silica fume;

[0018] The mass ratio of the cement, fly ash, mineral powder and silica fume is 1:(0.2-0.4):(0.1-0.3):(0.1-0.2).

[0019] As a further preferred embodiment, the fine aggregate is river sand with a diameter of 0.075–4.75 mm, a fineness modulus of 2.6–3.0, and an apparent density of 2400–2700 kg / m³. 3 ;

[0020] The coarse aggregate is continuously graded crushed stone of 5-20 mm with an apparent density of 2500-2800 kg / m³. 3 .

[0021] As a further preferred embodiment, the water-cement ratio of the micro-expansion steel tube concrete is 0.24 to 0.32.

[0022] Based on any of the above embodiments or combinations of embodiments, according to another aspect of the present invention, a method for preparing micro-expansion steel tube concrete based on gradient expansion and curing is also provided, comprising the following steps:

[0023] Step 1: Mix aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide in proportion to obtain a gradient expansion agent;

[0024] Step 2: Weigh the ceramic sand, zeolite powder, expanded perlite and super absorbent resin according to the proportion, and then dry, refine and mix them in sequence to obtain the gradient internal curing agent. Pre-wet the gradient internal curing agent.

[0025] Step 3: Mix the cementitious material, gradient expansion agent, and fine aggregate evenly according to the proportion to obtain mixture one;

[0026] Step 4: Pour the pre-wetted gradient internal curing agent, additives and water into mixture 1 and continue stirring to obtain mixture 2;

[0027] Step 5: Pour coarse aggregate and water into mixture 2 and continue stirring to obtain micro-expansion steel tube concrete based on gradient expansion and curing.

[0028] As a further preferred option, step two includes the following steps:

[0029] First, weigh out the ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin according to the specified proportions.

[0030] Secondly, the weighed zeolite powder, expanded perlite and superabsorbent resin are dried in an oven at 100±5℃ for 24±2h.

[0031] Then, the dried materials are placed in a ball mill for fine processing at a speed of 400±50 rpm for 15±2 min.

[0032] Finally, the ceramic sand and the refined mixture are placed in a high-speed mixer for homogenization at a speed of 500±50 rpm for 24±2 h to obtain the gradient internal curing agent.

[0033] According to another aspect of the present invention, an application of gradient expansion-based micro-expansion steel pipe concrete in a steel pipe is also provided, as described in any of the above embodiments or combinations thereof. After the micro-expansion steel pipe concrete undergoes gradient continuous expansion in the steel pipe, it comes into close and uniform contact with the inner wall of the steel pipe without any voids or debonding.

[0034] Based on the above embodiments, the gradient and continuous expansion of micro-expansion steel tube concrete in the steel tube includes: the micro-expansion steel tube concrete continuously undergoes an expansion reaction at different hydration stages.

[0035] The first stage involves the reaction of aluminum powder and calcium oxide, primarily occurring in the early stages of cement hydration, to compensate for the autogenous shrinkage of steel-concrete composite.

[0036] The second stage, M-type magnesium oxide, begins to react, mainly in the later stages of cement hydration, and is used to compensate for the drying shrinkage of steel-concrete composite.

[0037] The third stage, S-type magnesium oxide begins to react, mainly after the cement hydration is basically completed, and is used to compensate for carbonation shrinkage in steel-concrete composites.

[0038] Specifically, in the first stage, aluminum powder generates aluminum hydroxide and hydrogen gas in an alkaline environment, resulting in a large number of tiny pores in the concrete. At the same time, calcium oxide hydrates to generate calcium hydroxide, which has twice the volume of calcium oxide. This not only increases the in-situ volume of calcium oxide but also allows calcium hydroxide to fill the pores formed by the aluminum powder, thereby causing the steel-concrete composite to expand in volume.

[0039] In the second stage, within the cement paste, M-type magnesium oxide gradually dissolves, and magnesium ions enter the porous aqueous solution, subsequently forming tiny hexagonal prismatic magnesium hydroxide crystal nuclei. Following this, the M-type magnesium oxide continues to hydrate, while recrystallization occurs. As the magnesium hydroxide crystals continue to grow, they come into contact with each other, exerting growth pressure that compresses the pore walls, resulting in macroscopic volume expansion.

[0040] In the third stage, S-type magnesium oxide, due to its high calcination temperature and high degree of crystallinity, exhibits a low dissolution rate, resulting in slow growth of magnesium hydroxide crystals and a deflection of their growth direction. Ultimately, it forms tetragonal bipyramidal crystals and undergoes volume expansion. The preparation of the gradient expansion agent solves the problems of concentrated expansion reaction, excessively fast reaction rate, and insignificant expansion effect of traditional expansion agents, achieving a long-term, comprehensive compensation shrinkage effect for steel-concrete composite structures.

[0041] Based on the above embodiments, the micro-expansion steel tube concrete releases moisture under different internal humidity conditions. Specifically, the moisture release process is as follows:

[0042] In the first stage, when the internal humidity of the concrete is below 100%, the abundant and large pores of the ceramic sand preferentially release water. This water is mainly used for cement hydration and the reaction of aluminum powder and calcium oxide. In the second stage, when the internal humidity of the concrete is below 90%, the cross-linking structure of the superabsorbent resin weakens its ability to bind water molecules, and water molecules begin to dissociate from the cross-linking structure, continuing to release water. This water is mainly used for the reaction of aluminum powder and calcium oxide, as well as the reaction of M-type magnesium oxide. In the third stage, when the internal humidity of the concrete is below 70%, the resulting humidity difference causes water in the framework-like cavities within the zeolite powder and expanded perlite to begin releasing. This water is mainly used for the reaction of low-activity S-type magnesium oxide. The preparation of the gradient internal curing agent provides the necessary conditions for the reaction of the gradient expansion agent, and also promotes the later degree of cement hydration, refines the pore structure of cement stone, reduces the shrinkage stress of steel-concrete composites, and stabilizes and improves their expansion performance.

[0043] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0044] 1. This invention successfully prepared micro-expansion steel-tube concrete by adding gradient expansion agent and gradient internal curing agent to concrete, effectively solving the problem of voids and debonding of steel-tube concrete caused by insufficient reaction of expansion agent and insignificant expansion effect.

[0045] 2. The gradient expansion agent of this invention is composed of various expansion materials with different activities, including aluminum powder, calcium oxide, M-type magnesium oxide, and S-type magnesium oxide. During the concrete hydration process, aluminum powder and calcium oxide have high activity and begin to react in the early stage of cement hydration, which can compensate for the autogenous shrinkage of concrete; M-type magnesium oxide has moderate activity and mainly undergoes expansion reaction in the later stage of cement hydration, which can compensate for the drying shrinkage of concrete; S-type magnesium oxide has low activity and only begins to react in the late stage of cement hydration, which can compensate for carbonation shrinkage of concrete, etc.

[0046] 3. The gradient internal curing agent of this invention is composed of various porous materials with different water absorption properties, including ceramsite, zeolite powder, expanded perlite, and superabsorbent polymer (SAP). First, as the hydration and expansion reactions proceed, the internal humidity of the concrete begins to decrease. At this point, the pre-wetted water in the ceramsite is released to maintain the reaction. Then, as the cement and the expanding components continue to react, the water in the ceramsite is completely released. At this point, the SAP begins to release water to maintain the reaction. Finally, the zeolite powder and expanded perlite jointly release water, at which point the cement water reaction is essentially complete, primarily providing water for the low-activity S-type magnesium oxide. Attached Figure Description

[0047] Figure 1 The figures show the expansion test results of ordinary steel-concrete composite pipes, steel-concrete composite pipes mixed with conventional expansion agents, steel-concrete composite pipes mixed with the gradient expansion agent of this invention, and steel-concrete composite pipes mixed with the gradient expansion agent and gradient internal curing agent of this invention as the curing age increases. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0049] This invention provides a micro-expansion steel tube concrete based on gradient expansion and curing, which, by weight, comprises the following raw materials:

[0050] 400-600 parts of cementitious material, 20-100 parts of gradient expansion agent, 20-200 parts of gradient internal curing agent, 5-10 parts of admixture, 500-800 parts of fine aggregate, and 800-1200 parts of coarse aggregate;

[0051] The cementing material includes cement, fly ash, mineral powder, and silica fume; the gradient expansion agent includes aluminum powder, calcium oxide, M-type magnesium oxide, and S-type magnesium oxide; and the gradient internal curing agent includes ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin.

[0052] In some embodiments, the mass ratio of the cement, fly ash, mineral powder and silica fume is 1:(0.2-0.4):(0.1-0.3):(0.1-0.2).

[0053] In some embodiments, the cement is ordinary silicate cement or silicate cement, including P·O42.5, P·O52.5, P·Ⅰ42.5, P·Ⅰ52.5, P·Ⅱ42.5, and P·Ⅱ52.5.

[0054] In some embodiments, the fly ash is Class F Grade I fly ash with a water requirement ratio ≤95%.

[0055] In some embodiments, the mineral powder is S95 grade mineral powder.

[0056] In some embodiments, the silica fume contains ≥90% SiO2 and has an activity index ≥105%.

[0057] In some embodiments, the mass ratio of the aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide is 1:(3-8):(2-6):(1-5).

[0058] In some embodiments, the aluminum powder has a purity of 90% and a fineness of 100-300 mesh.

[0059] In some embodiments, the calcium oxide has a purity of 95% or higher and a specific surface area of ​​≥200 m². 2 / kg

[0060] In some embodiments, the citric acid value of the M-type magnesium oxide is 130–180s, and the citric acid value of the S-type magnesium oxide is 240–280s.

[0061] In some embodiments, the mass ratio of the ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin is 1:(0.05-0.5):(0.005-0.05):(0.002-0.03).

[0062] In some embodiments, the ceramic sand is high-strength shale ceramic sand with a particle size of 0.075–4.75 mm, a 24-hour water absorption rate of 10–30%, and an apparent density of 900–1200 kg / m³. 3 .

[0063] In some embodiments, the zeolite powder is natural zeolite powder with a density of 1600–2000 kg / m³. 3 Porosity ≥ 50%.

[0064] In some embodiments, the expanded perlite is made from perlite ore sand that has been roasted at high temperature, and has a density of 40–120 kg / m³. 3 Porosity ≥ 60%.

[0065] In some embodiments, the main chemical component of the superabsorbent resin is low-crosslinked sodium polyacrylate, with a density of 50–90 kg / m³. 3 The water absorption ratio is 150 to 400 times.

[0066] In some embodiments, the additional water drawup of the gradient internal maintenance agent is 10 to 40% of its mass.

[0067] In some embodiments, the admixture is a polycarboxylate superplasticizer with a water reduction rate of ≥25%.

[0068] In some embodiments, the fine aggregate is river sand with a diameter of 0.075–4.75 mm, a fineness modulus of 2.6–3.0, and an apparent density of 2400–2700 kg / m³. 3 .

[0069] In some embodiments, the coarse aggregate is continuously graded crushed stone of 5–20 mm with an apparent density of 2500–2800 kg / m³. 3 .

[0070] In some embodiments, the water-cement ratio of the micro-expansion steel tube concrete based on gradient expansion agent and gradient internal curing agent is 0.24 to 0.32.

[0071] Secondly, this application provides a method for preparing the micro-expansion steel tube concrete based on the aforementioned gradient expansion agent and gradient internal curing agent.

[0072] 1) Aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide are mixed in a mixer at a speed of 200±20 rpm for 24±2 h to obtain the gradient expansion agent.

[0073] 2) The gradient internal curing agent needs to be pre-wetted one day in advance. Weigh the gradient internal curing agent and pre-wetting water, pour them together into a container, seal it and let it stand for 24 hours before use.

[0074] In some embodiments, step 2) further includes the following steps:

[0075] First, weigh the ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin according to the specified proportions. Second, dry the weighed zeolite powder, expanded perlite, and superabsorbent resin in an oven at 100±5℃ for 24±2 hours. Then, refine the dried materials in a ball mill at 400±50 rpm for 15±2 minutes. Finally, homogenize the ceramic sand and the refined mixture in a high-speed mixer at 500±50 rpm for 24±2 hours to obtain the gradient internal curing agent.

[0076] 3) Mix the cementitious material, gradient expansion agent and fine aggregate evenly in a mixing pot according to the proportion, and the mixing time is 60±10s.

[0077] 4) Pour the pre-wetted gradient internal curing agent, additives and some water into the mixture and continue stirring for 60±10s.

[0078] 5) Pour all the coarse aggregate and remaining water into the mixing pot and continue mixing for 100±20s to obtain micro-expansion steel pipe concrete based on gradient expansion agent and gradient internal curing agent.

[0079] According to another aspect of the present invention, an application of gradient expansion-based micro-expansion steel pipe concrete in a steel pipe is also provided, as described in any of the above embodiments or combinations thereof. After the micro-expansion steel pipe concrete undergoes gradient continuous expansion in the steel pipe, it comes into close and uniform contact with the inner wall of the steel pipe without any voids or debonding.

[0080] Based on the above embodiments, the gradient and continuous expansion of micro-expansion steel tube concrete in the steel tube includes: the micro-expansion steel tube concrete continuously undergoes an expansion reaction at different hydration stages.

[0081] The first stage involves the reaction of aluminum powder and calcium oxide, primarily occurring in the early stages of cement hydration, to compensate for the autogenous shrinkage of steel-concrete composite.

[0082] The second stage, M-type magnesium oxide, begins to react, mainly in the later stages of cement hydration, and is used to compensate for the drying shrinkage of steel-concrete composite.

[0083] The third stage, S-type magnesium oxide begins to react, mainly after the cement hydration is basically completed, to supplement the carbonation shrinkage and creep shrinkage of steel-concrete composites.

[0084] Specifically, in the first stage, aluminum powder generates aluminum hydroxide and hydrogen gas in an alkaline environment, resulting in a large number of tiny pores in the concrete. At the same time, calcium oxide hydrates to generate calcium hydroxide, which has twice the volume of calcium oxide. This not only increases the in-situ volume of calcium oxide but also allows calcium hydroxide to fill the pores formed by the aluminum powder, thereby causing the steel-concrete composite to expand in volume.

[0085] In the second stage, within the cement paste, M-type magnesium oxide gradually dissolves, and magnesium ions enter the porous aqueous solution, subsequently forming tiny hexagonal prismatic magnesium hydroxide crystal nuclei. Following this, the M-type magnesium oxide continues to hydrate, while recrystallization occurs. As the magnesium hydroxide crystals continue to grow, they come into contact with each other, exerting growth pressure that compresses the pore walls, resulting in macroscopic volume expansion.

[0086] In the third stage, S-type magnesium oxide, due to its high calcination temperature and high degree of crystallinity, exhibits a low dissolution rate, resulting in slow growth of magnesium hydroxide crystals and a deflection of their growth direction. Ultimately, it forms tetragonal bipyramidal crystals and undergoes volume expansion. The preparation of the gradient expansion agent solves the problems of concentrated expansion reaction, excessively fast reaction rate, and insignificant expansion effect of traditional expansion agents, achieving a long-term, comprehensive compensation shrinkage effect for steel-concrete composite structures.

[0087] Based on the above embodiments, the micro-expansion steel tube concrete releases moisture under different internal humidity conditions. Specifically, the moisture release process is as follows:

[0088] In the first stage, when the internal humidity of the concrete is below 100%, the abundant and large pores of the ceramic sand preferentially release water. This water is mainly used for cement hydration and the reaction of aluminum powder and calcium oxide. In the second stage, when the internal humidity of the concrete is below 90%, the cross-linking structure of the superabsorbent resin weakens its ability to bind water molecules, and water molecules begin to dissociate from the cross-linking structure, continuing to release water. This water is mainly used for the reaction of aluminum powder and calcium oxide, as well as the reaction of M-type magnesium oxide. In the third stage, when the internal humidity of the concrete is below 70%, the resulting humidity difference causes water in the framework-like cavities within the zeolite powder and expanded perlite to begin releasing. This water is mainly used for the reaction of low-activity S-type magnesium oxide. The preparation of the gradient internal curing agent provides the necessary conditions for the reaction of the gradient expansion agent, and also promotes the later degree of cement hydration, refines the pore structure of cement stone, reduces the shrinkage stress of steel-concrete composites, and stabilizes and improves their expansion performance.

[0089] like Figure 1 As shown in the figure, the expansion values ​​of ordinary steel-concrete composite, steel-concrete composite with conventional expansive agent, steel-concrete composite with gradient expansive agent of the present invention, and steel-concrete composite with gradient expansive agent and gradient internal curing agent of the present invention are as follows with the curing age. It can be clearly seen from the figure that the expansion effect of steel-concrete composite with gradient expansive agent and gradient internal curing agent of the present invention is significantly superior and stable.

[0090] The present invention will be further described below through specific embodiments. Description of raw materials for each embodiment and comparative example:

[0091] The cement is P·Ⅱ52.5 Portland cement, with a specific surface area and density of 380 m² / m³. 2 / kg and 3150kg / m 3 The fly ash is Class I fly ash, with a specific surface area and density of 510 m² / m³. 2 / kg and 2710kg / m 3 The water requirement ratio is 91%. The mineral powder is S95 grade, with a density of not less than 2.9 g / cm3, and a specific surface area and density of 480 m². 2 / kg and 2930kg / m 3 The specific surface area and density of silica fume are 26 m². 2 / kg and 2100kg / m 3 The activity index is 110%. The aluminum powder has a purity of 95% and a fineness of 220 mesh. The calcium oxide has a purity of 98% and a specific surface area of ​​230 m². 2 / kg. M-type magnesium oxide has a citric acid value of 150s and a median particle size of 15.76μm. S-type magnesium oxide has a citric acid value of 250s and a median particle size of 19.51μm. The ceramic sand is high-strength porous shale ceramic aggregate with a 24-hour water absorption rate of 22% and an apparent density of 1080 kg / m³. 3 The zeolite powder is natural zeolite powder with a density of 1900 kg / m³. 3 The porosity is 54%. The density of expanded perlite is 70 kg / m³. 3 The porosity is 67%. The density of the superabsorbent resin is 65 kg / m³. 3 The water absorption ratio is 300 times. The conventional expanding agent is a calcium oxide-based expanding agent, with a calcium oxide content of 78% and a median particle size of 16.25 μm. The fine aggregate is well-aggregated river sand with a particle size of 0.075–4.75 mm, a fineness modulus of 2.8, and an apparent density of 2550 kg / m³. 3 The coarse aggregate is continuously graded crushed stone with a particle size of 5–20 mm and an apparent density of 2700 kg / m³. 3 The admixture is a polycarboxylate superplasticizer with a water reduction rate of 30%. The water used is ordinary domestic water. The water-to-binder ratio is 0.29. Additional water is added at 20% of the gradient expansion agent's mass.

[0092] Example 1

[0093] This embodiment provides a micro-expansion steel tube concrete based on gradient expansion, which, by mass fraction, comprises the following raw materials:

[0094] The composition includes 437 parts cementitious materials, 33 parts gradient expansion agent, 760 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, and 136 parts water. The cementitious materials, by mass percentage, comprise: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by mass percentage, comprises: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide.

[0095] Its preparation method is as follows:

[0096] 1) Aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide are mixed in a mixer at a speed of 200±20 rpm for 24±2 h to obtain the gradient expansion agent.

[0097] 2) Mix the cementitious material, gradient expansion agent and fine aggregate evenly in a mixing pot according to the proportion, and the mixing time is 60±10s.

[0098] 3) Pour the additive and some water into the mixture and continue stirring for 60±10s.

[0099] 4) Pour all the coarse aggregate and remaining water into the mixing pot and continue mixing for 100±20s to obtain micro-expansion steel pipe concrete based on gradient expansion agent and gradient internal curing agent.

[0100] Example 2

[0101] The operation steps of this embodiment are basically the same as those of Embodiment 1, except that:

[0102] By weight, the raw materials include: 423 parts cementitious materials, 47 parts gradient expansion agent, 760 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, and 136 parts water; wherein, the cementitious materials, by weight percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume; the gradient expansion agent, by weight percentage, includes: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide.

[0103] Example 3

[0104] The operation steps of this embodiment are basically the same as those of Embodiment 1, except that:

[0105] By weight, it includes the following raw materials:

[0106] 409 parts cementitious material, 61 parts gradient expansion agent, 760 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, and 136 parts water;

[0107] The cementitious materials, by weight percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume.

[0108] The gradient expansion agent, by mass percentage, comprises: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide.

[0109] Example 4

[0110] A type of micro-expansion steel-tube concrete based on gradient expansion, comprising the following raw materials by mass parts:

[0111] The composition includes 423 parts cementitious material, 47 parts gradient expansion agent, 34 parts gradient internal curing agent, 675 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, 136 parts water, and 6.8 parts additional water. The cementitious material, by weight percentage, comprises: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by weight percentage, comprises: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide. The gradient internal curing agent, by weight percentage, comprises: 75% ceramsite sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% superabsorbent resin.

[0112] Its preparation method is as follows:

[0113] 1) Aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide are mixed in a mixer at a speed of 200±20 rpm for 24±2 h to obtain the gradient expansion agent.

[0114] 2) The gradient internal curing agent needs to be pre-wetted one day in advance. Weigh the gradient internal curing agent and pre-wetting water, pour them together into a container, seal it and let it stand for 24 hours before use.

[0115] Step 2) further includes the following steps:

[0116] First, weigh the ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin according to the specified proportions. Second, dry the weighed zeolite powder, expanded perlite, and superabsorbent resin in an oven at 100±5℃ for 24±2 hours. Then, refine the dried materials in a ball mill at 400±50 rpm for 15±2 minutes. Finally, homogenize the ceramic sand and the refined mixture in a high-speed mixer at 500±50 rpm for 24±2 hours to obtain the gradient internal curing agent.

[0117] 3) Mix the cementitious material, gradient expansion agent and fine aggregate evenly in a mixing pot according to the proportion, and the mixing time is 60±10s.

[0118] 4) Pour the pre-wetted gradient internal curing agent, additives and some water into the mixture and continue stirring for 60±10s.

[0119] 5) Pour all the coarse aggregate and remaining water into the mixing pot and continue mixing for 100±20s to obtain micro-expansion steel pipe concrete based on gradient expansion agent and gradient internal curing agent.

[0120] Example 5

[0121] The operation steps of this embodiment are basically the same as those of embodiment 4, except that:

[0122] By weight, it includes the following raw materials:

[0123] The composition includes 423 parts cementitious material, 47 parts gradient expansion agent, 68 parts gradient internal curing agent, 590 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, 136 parts water, and 13.6 parts pre-wetting water. The cementitious material, by weight percentage, comprises: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by weight percentage, comprises: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide. The gradient internal curing agent, by weight percentage, comprises: 75% ceramsite sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% superabsorbent resin.

[0124] Example 6

[0125] The operation steps of this embodiment are basically the same as those of embodiment 4, except that:

[0126] The composition includes 423 parts cementitious material, 47 parts gradient expansion agent, 102 parts gradient internal curing agent, 505 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, 136 parts water, and 20.4 parts pre-wetting water. The cementitious material, by weight percentage, comprises: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by weight percentage, comprises: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide. The gradient internal curing agent, by weight percentage, comprises: 75% ceramsite sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% superabsorbent resin.

[0127] Example 7

[0128] The operation steps of this embodiment are basically the same as those of embodiment 4, except that:

[0129] By weight, it includes the following raw materials:

[0130] The composition includes 423 parts cementitious material, 47 parts gradient expansion agent, 68 parts gradient internal curing agent, 590 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, 136 parts water, and 13.6 parts pre-wetting water. The cementitious material, by weight percentage, comprises: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by weight percentage, comprises: 8% aluminum powder, 60% calcium oxide, 22% M-type magnesium oxide, and 10% S-type magnesium oxide. The gradient internal curing agent, by weight percentage, comprises: 75% ceramsite sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% superabsorbent resin.

[0131] Example 8

[0132] The operation steps of this embodiment are basically the same as those of embodiment 4, except that:

[0133] By weight, it includes the following raw materials:

[0134] The composition includes 423 parts cementitious material, 47 parts gradient expansion agent, 68 parts gradient internal curing agent, 590 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, 136 parts water, and 13.6 parts pre-wetting water. The cementitious material, by weight percentage, comprises: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by weight percentage, comprises: 5% aluminum powder, 30% calcium oxide, 35% M-type magnesium oxide, and 30% S-type magnesium oxide. The gradient internal curing agent, by weight percentage, comprises: 75% ceramsite sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% superabsorbent resin.

[0135] Example 9

[0136] The operation steps of this embodiment are basically the same as those of embodiment 4, except that:

[0137] By weight, it includes the following raw materials:

[0138] The composition includes 423 parts cementitious material, 47 parts gradient expansion agent, 68 parts gradient internal curing agent, 590 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, 136 parts water, and 13.6 parts pre-wetting water. The cementitious material, by weight percentage, comprises: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by weight percentage, comprises: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide. The gradient internal curing agent, by weight percentage, comprises: 60% ceramsite sand, 36.5% zeolite powder, 2.3% expanded perlite, and 1.2% superabsorbent resin.

[0139] Example 10

[0140] The operation steps of this embodiment are basically the same as those of embodiment 4, except that:

[0141] By weight, it includes the following raw materials:

[0142] The composition includes 423 parts cementitious material, 47 parts gradient expansion agent, 68 parts gradient internal curing agent, 590 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, 136 parts water, and 13.6 parts pre-wetting water. The cementitious material, by weight percentage, comprises: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume. The gradient expansion agent, by weight percentage, comprises: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide. The gradient internal curing agent, by weight percentage, comprises: 90% ceramsite sand, 9.1% zeolite powder, 0.6% expanded perlite, and 0.3% superabsorbent resin.

[0143] Comparative Example 1

[0144] The operation steps of this comparative example are basically the same as those of Example 1, except that:

[0145] By weight, the raw materials include: 470 parts cementitious materials, 760 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, and 141 parts water; wherein, by weight percentage, the cementitious materials include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume.

[0146] Comparative Example 2

[0147] The operation steps of this comparative example are basically the same as those of Example 1, except that:

[0148] By weight, the raw materials include: 423 parts cementitious material, 47 parts ordinary expanding agent, 760 parts fine aggregate, 1050 parts coarse aggregate, 5.6 parts admixture, and 141 parts water.

[0149] The cementitious materials, by weight percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume.

[0150] Table 1: Components and their mass fractions in micro-expansion steel tube concrete of the examples and comparative examples

[0151]

[0152]

[0153] Note: In Table 1, "S" represents "Example", for example, "S1" represents "Example 1", and "D" represents "Comparative Example", for example, "D1" represents "Comparative Example 1".

[0154] Performance testing

[0155] The following performance tests were performed on the concrete prepared in all examples and comparative examples:

[0156] (1) Compressive strength: The prepared concrete was hardened for 7 days, 28 days and 56 days, and tested according to the 150mm×150mm×150mm standard specimen of GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0157] (2) Expansion value: Considering that the steel-concrete composite pipe is in a sealed environment, its expansion value is determined using the following method:

[0158] 1) Mold preparation: A cylindrical mold with an inner diameter of 100mm, a height of 400mm, and a thickness of 3.2mm is made from PVC pipe. A flat steel plate with a diameter of 100mm and a thickness of 20mm is placed in the mold as a base. The mold and the base are bonded and sealed together with tape to prevent moisture and slurry from flowing out from the bottom.

[0159] 2) Concrete was prepared for all examples and comparative examples, and the prepared concrete was poured into molds. During the pouring process, the specimens were vibrated to ensure compaction.

[0160] 3) After the specimen is formed, smooth the surface, seal it with plastic wrap, and move the specimen mold smoothly into the shrinkage chamber (temperature 20±2℃, humidity 60±5%). Place it vertically on the iron frame with foam board for vibration damping. Place a 20mm×20mm glass plate on the top of the specimen with plastic wrap, and make the side of the dial indicator contact the glass plate. Fix the dial indicator with the iron frame.

[0161] 4) After the dial indicator is installed, shrinkage values ​​can be recorded. After molding, records should be taken every day for the first 7 days. The first measurement is recorded as L0, and subsequent measurements are recorded as L... t (t is age), accurate to 0.001 mm; record once every 7 days after 7 days, until 90 days.

[0162] 5) The formula for calculating the expansion value is shown in equation (1).

[0163]

[0164] Where: ε is the volumetric expansion rate of concrete (unit: 1×10⁻⁶). -6 (Positive values ​​in the calculation result represent expansion, and negative values ​​represent contraction); L0 and L t The values ​​(mm) are the dial gauge measurements of the specimen at the first measurement and at age t; 400 is the original length of the sample.

[0165] The test results are shown in Table 2.

[0166] Table 2: Test results of micro-expansion steel tube concrete in the examples and comparative examples

[0167]

[0168] According to the data in Table 2, compared with Comparative Example 1, the compressive strength of concrete at different ages in Examples 1, 2, and 3 decreased slightly, while the expansion value at different ages increased significantly. This indicates that adding a gradient expansion agent to concrete will weaken the compressive strength, but the expansion effect is obvious.

[0169] Compared to Comparative Example 2, Example 2 showed higher compressive strength at different ages, indicating that the gradient expansive agent has a smaller impact on the compressive strength of concrete compared to ordinary expansive agents. Furthermore, considering the expansion values ​​at different ages, it can be seen that ordinary expansive agents have a larger early expansion value but significant shrinkage in the later stages; while the gradient expansive agent can exert a continuous expansion effect, avoiding the phenomenon of rapid expansion followed by significant shrinkage, indicating better practical performance.

[0170] Compared with Comparative Examples 1 and 2, Examples 4, 5, and 6 show larger compressive strength and expansion values ​​of concrete at different ages. This indicates that the combined use of gradient expansion agent and gradient internal curing agent can not only offset the deterioration effect of gradient expansion agent on concrete compressive strength when used alone, but also make the concrete expansion effect more significant.

[0171] As can be seen from Examples 1, 2 and 3, with the increase of the gradient expansion agent dosage, the compressive strength and expansion value of concrete at different ages all increase first and then decrease. This indicates that there is an optimal value for the dosage of gradient expansion agent, and too much or too little dosage will not allow the gradient expansion agent to exert its maximum effect.

[0172] As can be seen from Examples 2, 4, 5 and 6, keeping the dosage of gradient expansive agent constant, as the dosage of gradient internal curing agent increases, the compressive strength of concrete at different ages shows a trend of first increasing and then decreasing, while the expansion value at different ages shows a trend of continuous increase. This indicates that there is a balance point between the dosage of gradient expansive agent and gradient internal curing agent. Only when the balance point is reached can the two coordinate and interact to achieve the maximum expansion effect.

[0173] As can be seen from Examples 5, 7 and 8, by finely adjusting the proportion of each component in the gradient expansion agent, the compressive strength of concrete does not change much, but the expansion value at different ages changes significantly. This indicates that the proposed gradient expansion agent has good designability and the components can be adjusted according to specific design requirements to achieve the expected expansion effect.

[0174] As can be seen from Examples 5, 9, and 10, by adjusting the proportion of each component in the gradient internal curing agent, the compressive strength and expansion value of the concrete changed significantly. This indicates that the gradient internal curing agent plays a significant role in the concrete. However, to achieve the best effect, it is necessary to ensure that the reaction of the gradient expansion agent and the release of water by the gradient internal curing agent occur simultaneously.

[0175] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A micro-expansion steel-tube concrete based on gradient expansion, characterized in that, By weight, it comprises the following components: 400-600 parts of cementitious material, 20-100 parts of gradient expansion agent, 20-200 parts of gradient internal curing agent, 5-10 parts of admixture, 500-800 parts of fine aggregate, and 800-1200 parts of coarse aggregate; The gradient expansion agent includes aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide, and the gradient internal curing agent includes ceramic sand, zeolite powder, expanded perlite and superabsorbent resin. The additive is a polycarboxylate superplasticizer.

2. The micro-expansion steel-tube concrete based on gradient expansion according to claim 1, characterized in that, The mass ratio of aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide is 1:(3-8):(2-6):(1-5).

3. The micro-expansion steel-tube concrete based on gradient expansion according to claim 2, characterized in that, The fineness of the aluminum powder is 100-300 mesh; The specific surface area of ​​the calcium oxide is ≥200m². 2 / kg; The citric acid value of the M-type magnesium oxide is 130–180s, and the citric acid value of the S-type magnesium oxide is 240–280s.

4. The micro-expansion steel-tube concrete based on gradient expansion according to claim 1, characterized in that, The mass ratio of the ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin is 1:(0.05~0.5):(0.005~0.05):(0.002~0.03).

5. The micro-expansion steel-tube concrete based on gradient expansion according to claim 1, characterized in that, The ceramic sand is high-strength shale ceramic sand with a particle size of 0.075–4.75 mm, a 24-hour water absorption rate of 10–30%, and an apparent density of 900–1200 kg / m³. 3 ; The zeolite powder is natural zeolite powder with a density of 1600–2000 kg / m³. 3 Porosity ≥ 50%; The expanded perlite is made from perlite ore sand through high-temperature roasting, with a density of 40–120 kg / m³. 3 Porosity ≥ 60%; The superabsorbent resin includes low-crosslinked sodium polyacrylate with a density of 50–90 kg / m³. 3 The water absorption ratio is 150 to 400 times.

6. The micro-expansion steel-tube concrete based on gradient expansion according to claim 1, characterized in that, The cementing materials include cement, fly ash, mineral powder, and silica fume; The mass ratio of cement, fly ash, mineral powder and silica fume is 1:(0.2-0.4):(0.1-0.3):(0.1-0.2).

7. The micro-expansion steel-tube concrete based on gradient expansion according to claim 1, characterized in that, The fine aggregate is river sand with a diameter of 0.075–4.75 mm, a fineness modulus of 2.6–3.0, and an apparent density of 2400–2700 kg / m³. 3 ; The coarse aggregate is continuously graded crushed stone of 5-20 mm with an apparent density of 2500-2800 kg / m³. 3 .

8. The micro-expansion steel-tube concrete based on gradient expansion according to claim 1, characterized in that, The water-cement ratio of the micro-expansion steel tube concrete is 0.24 to 0.

32.

9. A method for preparing micro-expansion steel-tube concrete based on gradient expansion as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Mix aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide in proportion to obtain a gradient expansion agent; Step 2: Weigh the ceramic sand, zeolite powder, expanded perlite and super absorbent resin according to the proportion, and then dry, refine and mix them in sequence to obtain the gradient internal curing agent. Pre-wet the gradient internal curing agent. Step 3: Mix the cementitious material, gradient expansion agent, and fine aggregate evenly according to the proportion to obtain mixture one; Step 4: Pour the pre-wetted gradient internal curing agent, additives, and some water into mixture 1 and continue stirring to obtain mixture 2; Step 5: Pour all the coarse aggregate and remaining water into Mixture 2 and continue stirring to obtain micro-expansion steel tube concrete based on gradient expansion.

10. The method for preparing micro-expansion steel-tube concrete based on gradient expansion according to claim 9, characterized in that, Step two includes the following steps: First, weigh out the ceramic sand, zeolite powder, expanded perlite, and superabsorbent resin according to the specified proportions. Secondly, the weighed zeolite powder, expanded perlite and superabsorbent resin are dried in an oven at 100±5℃ for 24±2h. Then, the dried materials are placed in a ball mill for fine processing at a speed of 400±50 rpm for 15±2 min. Finally, the ceramic sand and the refined mixture are placed in a high-speed mixer for homogenization at a speed of 500±50 rpm for 24±2 hours to obtain the gradient internal curing agent.

11. An application of micro-expansion steel-tube concrete based on gradient expansion as described in any one of claims 1 to 8 in a steel tube, characterized in that, After undergoing gradient and continuous expansion within the steel pipe, the micro-expansion steel-concrete composite material comes into close and uniform contact with the inner wall of the steel pipe, without any voids or debonding.

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