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

Abstract

The invention belongs to the technical field of building materials, and particularly discloses a micro-expansion concrete filled steel tube based on gradient expansion, a preparation method and application. Comprising the following components in parts by weight: 400-600 parts of a cementing material, 20-100 parts of a gradient expanding agent, 20-200 parts of a gradient internal curing agent, 5-10 parts of an additive, 500-800 parts of fine aggregate and 800-1200 parts of coarse aggregate, wherein the gradient expanding agent comprises aluminum powder, calcium oxide, M type magnesium oxide and S type magnesium oxide, and the gradient internal curing agent comprises pottery sand, zeolite powder, expanded perlite and super absorbent resin. The micro-expansion concrete filled steel tube can realize gradient continuous expansion, and in the process, water is released under different internal humidity conditions to compensate the shrinkage effect of the concrete in different hydration stages and promote complete reaction of an expanding agent, so that the problems of void and debonding of core concrete and the wall of the steel tube are effectively solved; the overall performance of the concrete filled steel tube is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and specifically, relates to a micro-expansive steel tube concrete based on gradient expansion, a preparation method and an application thereof, and more specifically, relates to a micro-expansive steel tube concrete based on a gradient expansion agent and a gradient internal curing agent, a preparation method and an application thereof. Background Art

[0002] At present, the main factor restricting the development of steel tube concrete structure is the debonding and de-bonding between the core concrete and the steel tube wall. This is because the concrete will experience shrinkage behaviors such as autogenous shrinkage and drying shrinkage during the hydration process, which causes the concrete to peel and separate at the steel-concrete interface. For this reason, in the preparation process of steel tube concrete, it is usually necessary to add expansion agents to offset these shrinkage effects in order to reduce the separation problem caused by concrete shrinkage. However, a large number of tests and engineering applications have shown that relying solely on expansion agents is not effective in solving the debonding and de-bonding of steel tube concrete. On the one hand, the expansion reaction of the expansion agent consumes water, and the steel tube concrete is in a sealed environment and cannot obtain enough free water from the external environment, resulting in insufficient reaction of the expansion agent and insignificant expansion effect. On the other hand, concrete shrinkage is a continuous and slow process, and the expansion agent usually reacts at a certain moment and cannot continuously compensate for the shrinkage strain of concrete.

[0003] Based on the above defects and shortcomings, the field urgently needs to propose a micro-expansive steel tube concrete based on gradient expansive agent and gradient internal curing agent. The gradient expansive agent can realize the continuous expansion of steel tube concrete to compensate for the shrinkage effect of concrete at different stages of hydration; the gradient internal curing agent provides reaction water for the expansive agent to promote the complete reaction of the expansive agent and the obvious expansion effect, so as to fundamentally solve the problem of degassing and debonding of steel tube concrete caused by insufficient reaction of the expansive agent and unclear expansion effect. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a micro-expansion steel tube concrete based on gradient expansion, a preparation method and an application thereof, wherein a micro-expansion steel tube concrete based on a gradient expansion agent and a gradient internal curing agent is designed in combination with the characteristics of the steel tube concrete itself and its curing process characteristics, wherein the gradient expansion agent can realize the continuous expansion of the steel tube concrete to compensate for the shrinkage effect of the concrete at different stages of hydration; the gradient internal curing agent provides reaction water for the expansion agent to promote the complete reaction of the expansion agent, and the expansion effect is obvious. The micro-expansion steel tube concrete prepared by the present invention effectively solves the problem of degassing and debonding between the core concrete and the steel tube wall, and significantly improves the overall performance of the steel tube concrete.

[0005] To achieve the above object, according to one aspect of the present invention, a slightly expansive steel tube concrete based on gradient expansion and curing is proposed, which comprises the following components in parts by weight:

[0006] 400-600 parts of cementitious materials, 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, 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 highly absorbent resin.

[0008] As further preferred, 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 further preferred, the fineness of the aluminum powder is 100-300 mesh;

[0010] The specific surface area of ​​the calcium oxide is ≥200m 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 further preferred, the mass ratio of the ceramic sand, zeolite powder, expanded perlite and super absorbent 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 24h water absorption rate of 10-30%, and an apparent density of 900-1200 kg / m 3 ;

[0014] The zeolite powder is natural zeolite powder with a density of 1600-2000 kg / m 3 , porosity ≥ 50%;

[0015] The expanded perlite is made from perlite sand by high temperature roasting, and has a density of 40-120 kg / m 3 , porosity ≥ 60%;

[0016] The highly absorbent resin comprises low cross-linked polyacrylic acid sodium salt, and has a density of 50 to 90 kg / m 3 The water absorption rate is 150 to 400 times.

[0017] As further preferred, the cementitious 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 to 4.75 mm, a fineness modulus of 2.6 to 3.0, and an apparent density of 2400 to 2700 kg / m 3 ;

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

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

[0022] Based on any of the above embodiments or a combination of multiple embodiments, according to another aspect of the present invention, a method for preparing a micro-expansive steel tube concrete based on gradient expansion and curing is 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: weighing pottery sand, zeolite powder, expanded perlite and super absorbent resin in proportion, drying, refining and mixing them in sequence to obtain a gradient internal curing agent, and pre-wetting the gradient internal curing agent;

[0025] Step 3, uniformly mixing the cementitious material, the gradient expansion agent and the fine aggregate according to a proportion to obtain a mixture 1;

[0026] Step 4, pouring the pre-wetted gradient internal curing agent, admixture and water into the mixture 1 and continuing to stir to obtain the mixture 2;

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

[0028] As further preferred, step 2 comprises the following steps:

[0029] First, weigh the ceramic sand, zeolite powder, expanded perlite and super absorbent resin according to the proportion;

[0030] Secondly, the weighed zeolite powder, expanded perlite and super absorbent resin are dried in an oven at a temperature of 100±5°C for 24±2h;

[0031] Then, the dried materials were placed in a ball mill for refining treatment at a speed of 400±50rpm for 15±2min;

[0032] Finally, the ceramic sand and the refined mixture are placed in a high-speed mixer for homogenization treatment 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, there is also provided an application of a micro-expansive steel tube concrete based on gradient expansion in a steel tube as in any embodiment or a combination of multiple embodiments above. After the micro-expansive steel tube concrete undergoes gradient continuous expansion in the steel tube, it is in close and uniform contact with the inner wall of the steel tube without any de-airing or de-bonding phenomenon.

[0034] Based on the above embodiment, the micro-expansive steel tube concrete performs gradient continuous expansion in the steel tube, including: the micro-expansive steel tube concrete performs continuous expansion reaction at different hydration stages:

[0035] In the first stage, aluminum powder and calcium oxide begin to react, mainly in the early stage of cement hydration, to compensate for the shrinkage of steel tube concrete.

[0036] In the second stage, M-type magnesium oxide begins to react, mainly in the later stage of cement hydration, to compensate for the drying shrinkage of steel tube concrete.

[0037] In the third stage, S-type magnesium oxide begins to react, mainly to supplement the carbonization shrinkage of steel tube concrete after the cement hydration is basically completed.

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

[0039] In the second stage, in the cement paste, M-type magnesium oxide gradually dissolves, and magnesium ions enter the pore water solution, subsequently forming tiny hexagonal magnesium hydroxide crystal nuclei. Then, M-type magnesium oxide continues to hydrate and recrystallize. As the magnesium hydroxide crystals continue to grow, the crystals contact each other and exert crystal growth pressure, squeezing the pore walls, thereby producing macroscopic volume expansion.

[0040] In the third stage, the S-type magnesium oxide has a high degree of crystallization due to the high calcination temperature, resulting in a low dissolution rate, slow growth of magnesium hydroxide crystals, and a deflection in the growth direction, eventually forming a tetragonal bipyramidal crystal and producing volume expansion. The preparation of the gradient expansion agent solves the problems of concentrated expansion reaction, too fast reaction rate, and unclear expansion effect of traditional expansion agents, and realizes the long-term and all-round compensation shrinkage effect of steel tube concrete.

[0041] Based on the above embodiment, 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 humidity inside the concrete is lower than 100%, the pores of the ceramic sand are rich and the pore size is large, and water is released first. This part of water is mainly used for cement hydration and the reaction of aluminum powder and calcium oxide. In the second stage, when the humidity inside the concrete is lower than 90%, the ability of the cross-linked structure of the super absorbent resin to constrain water molecules is weakened, and the water molecules begin to dissociate from the cross-linked structure and continue to release water. This part of 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 humidity inside the concrete is lower than 70%, the humidity difference formed causes the water in the frame-like pore channels inside the zeolite powder and expanded perlite to begin to release. This part of water is mainly used for the reaction of low-activity S-type magnesium oxide. The preparation of the gradient internal curing agent, on the one hand, provides the necessary conditions for the reaction of the gradient expansion agent, and on the other hand, promotes the degree of cement hydration in the later stage, refines the pore structure of cement stone, reduces the shrinkage stress of steel tube concrete, and steadily improves its expansion performance.

[0043] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0044] 1. The present invention successfully prepares micro-expansive steel tube concrete by adding a gradient expansion agent and a gradient internal curing agent into concrete, effectively solving the problem of hollowing and debonding of steel tube concrete caused by insufficient reaction of the expansion agent and unclear expansion effect.

[0045] 2. The gradient expansion agent of the present invention is composed of a plurality of expansion materials with different activities, including aluminum powder, calcium oxide, M-type magnesium oxide and S-type magnesium oxide. In the concrete hydration process, aluminum powder and calcium oxide have higher activity, and start to react in the early stage of cement hydration, which can compensate for the self-shrinkage of concrete; M-type magnesium oxide has moderate activity, and mainly performs expansion reaction in the late stage of cement hydration, which can compensate for the drying shrinkage of concrete; S-type magnesium oxide has lower activity, and starts to react in the late stage of cement hydration, which can compensate for the carbonation shrinkage of concrete, etc.

[0046] 3. The gradient internal curing agent of the present invention is composed of a variety of porous materials with different water absorption properties, including pottery sand, zeolite powder, expanded perlite and super absorbent resin. First, as the hydration and expansion reaction proceed, the humidity inside the concrete begins to decrease, and the pre-wet water in the pottery sand is released to maintain the reaction. Then, as the cement and the expansion component continue to react, the water in the pottery sand is completely released, and the super absorbent resin begins to release water to keep the reaction going. Finally, the zeolite powder and the expanded perlite release water together, and the cement-water reaction is basically completed at this time, mainly to provide water for the low-activity S-type magnesium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The graph is a result of expansion test of ordinary steel tube concrete, steel tube concrete mixed with conventional expansion agent, steel tube concrete mixed with gradient expansion agent of the present invention, and steel tube concrete mixed with gradient expansion agent and gradient internal curing agent of the present invention with the curing age. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0049] An embodiment of the present invention provides a slightly expansive steel tube concrete based on gradient expansion and curing, which comprises the following raw materials in parts by mass:

[0050] 400-600 parts of cementitious materials, 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, 800-1200 parts of coarse aggregate;

[0051] Among them, the cementitious 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; the gradient internal curing agent includes pottery sand, zeolite powder, expanded perlite and highly absorbent resin.

[0052] In some embodiments, 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).

[0053] In some embodiments, the cement is ordinary Portland cement or Portland cement, including P·O42.5, P·052.5, 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, and the water demand ratio is ≤95%.

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

[0056] In some embodiments, the SiO2 content in the silica ash is ≥90%, and the activity index is ≥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 meshes.

[0059] In some embodiments, the purity of the calcium oxide is above 95%, and the specific surface area is ≥ 200m 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 super absorbent 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 / m 3 .

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

[0064] In some embodiments, the expanded perlite is made by high-temperature roasting of perlite sand, and has a density of 40 to 120 kg / m 3 , porosity ≥ 60%.

[0065] In some embodiments, the main chemical component of the super absorbent resin is low cross-linked polyacrylic acid sodium salt, with a density of 50 to 90 kg / m 3 The water absorption rate is 150 to 400 times.

[0066] In some embodiments, the additional water intake of the gradient internal curing agent is 10-40% of its mass.

[0067] In some embodiments, the admixture is a polycarboxylic acid high-efficiency water reducer, and the water reduction rate is ≥25%.

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

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

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

[0071] In a second aspect, the present application provides a method for preparing the above-mentioned micro-expansive steel tube concrete based on 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 according to a certain proportion, at a speed of 200±20 rpm for 24±2 hours 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 into a container together, seal it and let it stand for 24 hours before use.

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

[0075] First, ceramic sand, zeolite powder, expanded perlite and super absorbent resin are weighed in proportion; secondly, the weighed zeolite powder, expanded perlite and super absorbent resin are dried in an oven at a temperature of 100±5°C for 24±2h; then, the dried materials are placed in a ball mill for refinement at a speed of 400±50rpm for 15±2min; finally, the ceramic sand and the refined mixture are placed in a high-speed mixer for homogenization at a speed of 500±50rpm for 24±2h to obtain the gradient internal curing agent.

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

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

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

[0079] According to another aspect of the present invention, there is also provided an application of a micro-expansive steel tube concrete based on gradient expansion in a steel tube as in any embodiment or a combination of multiple embodiments above. After the micro-expansive steel tube concrete undergoes gradient continuous expansion in the steel tube, it is in close and uniform contact with the inner wall of the steel tube without any de-airing or de-bonding phenomenon.

[0080] Based on the above embodiment, the micro-expansive steel tube concrete performs gradient continuous expansion in the steel tube, including: the micro-expansive steel tube concrete performs continuous expansion reaction at different hydration stages:

[0081] In the first stage, aluminum powder and calcium oxide begin to react, mainly in the early stage of cement hydration, to compensate for the shrinkage of steel tube concrete.

[0082] In the second stage, M-type magnesium oxide begins to react, mainly in the later stage of cement hydration, to compensate for the drying shrinkage of steel tube concrete.

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

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

[0085] In the second stage, in the cement paste, M-type magnesium oxide gradually dissolves, and magnesium ions enter the pore water solution, subsequently forming tiny hexagonal magnesium hydroxide crystal nuclei. Then, M-type magnesium oxide continues to hydrate and recrystallize. As the magnesium hydroxide crystals continue to grow, the crystals contact each other and exert crystal growth pressure, squeezing the pore walls, thereby producing macroscopic volume expansion.

[0086] In the third stage, the S-type magnesium oxide has a high degree of crystallization due to the high calcination temperature, resulting in a low dissolution rate, slow growth of magnesium hydroxide crystals, and a deflection in the growth direction, eventually forming a tetragonal bipyramidal crystal and producing volume expansion. The preparation of the gradient expansion agent solves the problems of concentrated expansion reaction, too fast reaction rate, and unclear expansion effect of traditional expansion agents, and realizes the long-term and all-round compensation shrinkage effect of steel tube concrete.

[0087] Based on the above embodiment, 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 humidity inside the concrete is lower than 100%, the pores of the ceramic sand are rich and the pore size is large, and water is released first. This part of water is mainly used for cement hydration and the reaction of aluminum powder and calcium oxide. In the second stage, when the humidity inside the concrete is lower than 90%, the ability of the cross-linked structure of the super absorbent resin to constrain water molecules is weakened, and the water molecules begin to dissociate from the cross-linked structure and continue to release water. This part of 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 humidity inside the concrete is lower than 70%, the humidity difference formed causes the water in the frame-like pore channels inside the zeolite powder and expanded perlite to begin to release. This part of water is mainly used for the reaction of low-activity S-type magnesium oxide. The preparation of the gradient internal curing agent, on the one hand, provides the necessary conditions for the reaction of the gradient expansion agent, and on the other hand, promotes the degree of cement hydration in the later stage, refines the pore structure of cement stone, reduces the shrinkage stress of steel tube concrete, and steadily improves its expansion performance.

[0089] like Figure 1 As shown, the expansion values ​​of ordinary steel tube concrete, steel tube concrete mixed with conventional expansive agent, steel tube concrete mixed with the gradient expansive agent of the present invention, and steel tube concrete mixed with the gradient expansive agent and gradient internal curing agent of the present invention vary with the curing age. It can be clearly seen from the figure that the expansion effect of the steel tube concrete mixed with the gradient expansive agent and gradient internal curing agent of the present invention is obviously superior and stable.

[0090] The present invention is further described below by means of specific examples. Description of raw materials for each example and comparative example:

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

[0092] Example 1

[0093] The present embodiment provides a slightly expansive steel tube concrete based on gradient expansion, which includes the following raw materials by weight:

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

[0095] The 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 according to a certain proportion, with a rotation speed of 200±20 rpm and a time of 24±2 hours to obtain the gradient expansion agent.

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

[0098] 3) Pour the admixture and part of the water into the mixture and continue stirring for 60±10s.

[0099] 4) Pour all the coarse aggregate and the remaining water into the mixing pot and continue stirring for 100±20s to obtain the micro-expansion steel tube concrete based on the gradient expansion agent and the 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] The raw materials are as follows, calculated by mass: 423 parts of cementitious materials, 47 parts of gradient expansion agents, 760 parts of fine aggregates, 1050 parts of coarse aggregates, 5.6 parts of admixtures and 136 parts of water; among them, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder and 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 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] The raw materials are as follows:

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

[0107] Among them, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume;

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

[0109] Example 4

[0110] A slightly expansive steel tube concrete based on gradient expansion, comprising the following raw materials by weight:

[0111] 423 parts of cementitious materials, 47 parts of gradient expansion agents, 34 parts of gradient internal curing agents, 675 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixtures, 136 parts of water, and 6.8 parts of additional water; among which, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide; the gradient internal curing agents, calculated by mass percentage, include: 75% pottery sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% super absorbent resin.

[0112] The 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 according to a certain proportion, at a speed of 200±20 rpm for 24±2 hours 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 into a container together, seal it and let it stand for 24 hours before use.

[0115] The step 2) also includes the following steps:

[0116] First, ceramic sand, zeolite powder, expanded perlite and super absorbent resin are weighed in proportion; secondly, the weighed zeolite powder, expanded perlite and super absorbent resin are dried in an oven at a temperature of 100±5°C for 24±2h; then, the dried materials are placed in a ball mill for refinement at a speed of 400±50rpm for 15±2min; finally, the ceramic sand and the refined mixture are placed in a high-speed mixer for homogenization at a speed of 500±50rpm for 24±2h to obtain the gradient internal curing agent.

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

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

[0119] 5) Pour all the coarse aggregate and the remaining water into the mixing pot and continue stirring for 100±20s to obtain the micro-expansion steel tube concrete based on the gradient expansion agent and the 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] The raw materials are as follows:

[0123] 423 parts of cementitious materials, 47 parts of gradient expansion agents, 68 parts of gradient internal curing agents, 590 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixtures, 136 parts of water, and 13.6 parts of pre-wetting water; wherein, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide; the gradient internal curing agents, calculated by mass percentage, include: 75% pottery sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% super absorbent resin.

[0124] Example 6

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

[0126] 423 parts of cementitious materials, 47 parts of gradient expansion agents, 102 parts of gradient internal curing agents, 505 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixtures, 136 parts of water, and 20.4 parts of pre-wetting water; wherein, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide; the gradient internal curing agents, calculated by mass percentage, include: 75% pottery sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% super absorbent resin.

[0127] Example 7

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

[0129] The raw materials are as follows:

[0130] 423 parts of cementitious materials, 47 parts of gradient expansion agents, 68 parts of gradient internal curing agents, 590 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixtures, 136 parts of water, and 13.6 parts of pre-wetting water; wherein, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 8% aluminum powder, 60% calcium oxide, 22% M-type magnesium oxide, and 10% S-type magnesium oxide; the gradient internal curing agents, calculated by mass percentage, include: 75% pottery sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% super absorbent resin.

[0131] Example 8

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

[0133] The raw materials are as follows:

[0134] 423 parts of cementitious materials, 47 parts of gradient expansion agents, 68 parts of gradient internal curing agents, 590 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixtures, 136 parts of water, and 13.6 parts of pre-wetting water; wherein, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 5% aluminum powder, 30% calcium oxide, 35% M-type magnesium oxide, and 30% S-type magnesium oxide; the gradient internal curing agents, calculated by mass percentage, include: 75% pottery sand, 23.7% zeolite powder, 0.8% expanded perlite, and 0.5% super absorbent resin.

[0135] Example 9

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

[0137] The raw materials are as follows:

[0138] 423 parts of cementitious materials, 47 parts of gradient expansion agents, 68 parts of gradient internal curing agents, 590 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixtures, 136 parts of water, and 13.6 parts of pre-wetting water; wherein, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide; the gradient internal curing agents, calculated by mass percentage, include: 60% pottery sand, 36.5% zeolite powder, 2.3% expanded perlite, and 1.2% highly absorbent resin.

[0139] Example 10

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

[0141] The raw materials are as follows:

[0142] 423 parts of cementitious materials, 47 parts of gradient expansion agents, 68 parts of gradient internal curing agents, 590 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixtures, 136 parts of water, and 13.6 parts of pre-wetting water; wherein, the cementitious materials, calculated by mass percentage, include: 60% cement, 20% fly ash, 12% mineral powder, and 8% silica fume; the gradient expansion agents, calculated by mass percentage, include: 8% aluminum powder, 38% calcium oxide, 32% M-type magnesium oxide, and 22% S-type magnesium oxide; the gradient internal curing agents, calculated by mass percentage, include: 90% pottery sand, 9.1% zeolite powder, 0.6% expanded perlite, and 0.3% super absorbent 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] The raw materials are as follows, calculated by weight: 470 parts of cementitious materials, 760 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixture, and 141 parts of water; among them, the cementitious materials are calculated by weight: 60% of cement, 20% of fly ash, 12% of mineral powder, and 8% of 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] The raw materials include the following by mass: 423 parts of cementitious material, 47 parts of common expansion agent, 760 parts of fine aggregate, 1050 parts of coarse aggregate, 5.6 parts of admixture, and 141 parts of water;

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

[0150] Table 1: Components and their mass fractions in the slightly expansive steel tube concrete of the embodiments and comparative examples

[0151]

[0152]

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

[0154] Performance Testing

[0155] The concrete prepared in all embodiments and comparative examples was subjected to the following performance tests:

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

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

[0158] 1) Test mold preparation: A cylindrical test mold with an inner diameter of 100 mm, a height of 400 mm, and a thickness of 3.2 mm was made from a PVC pipe, and a flat steel plate with a diameter of 100 mm and a thickness of 20 mm was installed into the test mold as a base. The test mold and the base were bonded and sealed as a whole with tape to prevent moisture and slurry from flowing out from the bottom.

[0159] 2) Concrete was prepared for all embodiments and comparative examples, and the prepared concrete was poured into a mold. During the pouring process, the test piece should be vibrated and compacted.

[0160] 3) After the specimen is formed, the surface is smoothed and sealed with plastic wrap. The test mold is moved smoothly into the shrinkage chamber (temperature 20±2℃, humidity 60±5%) and placed vertically on an iron frame with foam board for vibration reduction. A 20mm×20mm glass sheet is placed on the plastic wrap on the top of the specimen. The side head of the micrometer is in contact with the glass sheet and the micrometer is fixed with an iron frame.

[0161] 4) After the micrometer is installed, you can start recording the shrinkage value. After molding, record it every 1 day for the first 7 days. The first measurement value is recorded as L0, and the subsequent measurement values ​​are recorded as L t (t is age), accurate to 0.001mm; record once every 7 days after 7 days and continue until 90 days.

[0162] 5) The calculation formula of expansion value is shown in formula (1)

[0163]

[0164] Where: ε is the volume expansion rate of concrete (unit: 1×10 -6 , the calculation result is positive for expansion and negative for contraction); L0 and L t is the micrometer measurement value of the specimen at the first measurement and age t (mm); 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 of the embodiment and comparative example

[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 slightly decreased, while the expansion values ​​at different ages increased significantly, which indicates that the addition of gradient expansion agent to concrete will weaken the compressive strength, but the expansion effect is obvious.

[0169] Compared with comparative example 2, the compressive strength of Example 2 at different ages is greater, which indicates that the gradient expansion agent has less effect on the compressive strength of concrete than the ordinary expansion agent. At the same time, combined with the expansion values ​​at different ages, it can be seen that the ordinary expansion agent has a larger expansion value in the early stage and a significant contraction in the later stage; while the gradient expansion agent can exert a continuous expansion effect, avoiding the phenomenon of rapid expansion first and then significant contraction, indicating that the actual use effect is better.

[0170] Compared with Comparative Examples 1 and 2, the compressive strength and expansion values ​​of concrete at different ages in Examples 4, 5 and 6 are larger, which shows 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 the compressive strength of concrete when using gradient expansion agent alone, but also make the expansion effect of concrete more significant.

[0171] It can be seen from Examples 1, 2 and 3 that with the increase of the amount of gradient expansion agent, the compressive strength and expansion value of concrete at different ages first increase and then decrease, which shows that there is an optimal value for the amount of gradient expansion agent, and too much or too little amount cannot make the gradient expansion agent play the maximum effect.

[0172] It can be seen from Examples 2, 4, 5 and 6 that the dosage of the gradient expansion agent is kept unchanged. As the dosage of the 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 values ​​at different ages show a trend of continuous increase. This shows that there is a balance point in the dosage of the gradient expansion agent and the gradient internal curing agent. Only when the balance point is reached can the two be coordinated and interact with each other to exert the maximum expansion effect.

[0173] It can be seen from Examples 5, 7 and 8 that by fine-tuning the proportion of each component in the gradient expansion agent, the compressive strength of the concrete does not change much, but the expansion values ​​at different ages vary greatly, which shows that the proposed gradient expansion agent has good designability and can be adjusted according to specific design requirements to achieve the expected expansion effect.

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

[0175] It will be easily understood by those skilled in the art that the above description is only 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 in the protection scope of the present invention.

Claims

1. A micro-expansion steel tube concrete based on gradient expansion, characterized in that: By weight, it includes the following components: 400-600 parts of cementitious materials, 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, 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 highly absorbent resin.

2. The micro-expansion steel tube concrete based on gradient expansion according to claim 1 is characterized in that: 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).

3. The micro-expansion steel tube concrete based on gradient expansion according to claim 2 is characterized in that: The fineness of the aluminum powder is 100 to 300 meshes; The specific surface area of ​​the calcium oxide is ≥200m 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 super absorbent 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 / m 3 ; The zeolite powder is natural zeolite powder with a density of 1600-2000 kg / m 3 , porosity ≥ 50%; The expanded perlite is made from perlite sand by high temperature roasting, and has a density of 40-120 kg / m 3 , porosity ≥ 60%; The highly absorbent resin comprises low cross-linked polyacrylic acid sodium salt, and has a density of 50 to 90 kg / m 3 The water absorption rate is 150 to 400 times.

6. The micro-expansion steel tube concrete based on gradient expansion according to claim 1, characterized in that: The cementitious materials include cement, fly ash, mineral powder and silica fume; 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).

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 / m 3 ; The coarse aggregate is 5-20 mm continuous graded crushed stone with an apparent density of 2500-2800 kg / m 3 .

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

32.

9. A method for preparing micro-expansion steel tube concrete based on gradient expansion, characterized in that: The following steps are involved: 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: weighing pottery sand, zeolite powder, expanded perlite and super absorbent resin in proportion, drying, refining and mixing them in sequence to obtain a gradient internal curing agent, and pre-wetting the gradient internal curing agent; Step 3, uniformly mixing the cementitious material, the gradient expansion agent and the fine aggregate according to a proportion to obtain a mixture 1; Step 4, pouring the pre-wetted gradient internal curing agent, admixture and water into the mixture 1 and continuing to stir to obtain the mixture 2; Step 5, pouring coarse aggregate and water into the mixture 2 and continuing to stir to obtain a micro-expansion steel tube concrete based on gradient expansion and curing; Preferably, step 2 The following steps are involved: First, weigh the ceramic sand, zeolite powder, expanded perlite and super absorbent resin according to the proportion; Secondly, the weighed zeolite powder, expanded perlite and super absorbent resin are dried in an oven at a temperature of 100±5°C for 24±2h; Then, the dried materials were placed in a ball mill for refining treatment at a speed of 400±50rpm for 15±2min; Finally, the ceramic sand and the refined mixture are placed in a high-speed mixer for homogenization treatment at a speed of 500±50 rpm for 24±2 h to obtain the gradient internal curing agent.

10. An application of a micro-expansive steel tube concrete based on gradient expansion in a steel tube as claimed in any one of claims 1 to 8, characterized in that: The micro-expansive steel tube concrete undergoes gradient continuous expansion in the steel tube and comes into close and uniform contact with the inner wall of the steel tube without any de-airing or de-bonding phenomenon.

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