A steel truss-concrete composite beam

Abstract

The present invention relates to the field of structural engineering, and specifically relates to a steel truss-concrete composite beam, comprising a steel truss and a precast concrete slab, wherein the precast concrete slab is integrally cast by concrete and steel bars. The concrete is prepared from the following raw materials, measured by weight: 700-800 parts of cement, 200-400 parts of crushed stone, 600-800 parts of sand, 100-150 parts of fly ash, 80-120 parts of steel fiber, 50-80 parts of an expansion agent, 1-5 parts of an early strength agent, 10-15 parts of a polycarboxylate water reducer, and 180-220 parts of water. The concrete of the present invention has excellent compressive strength and low autogenous shrinkage. Moreover, the volume change during the curing process is small, and the excessive shrinkage and deformation of the concrete itself will not cause abnormal interface bonding between the precast concrete slab and the steel truss and internal steel bars, thereby affecting the bearing capacity.

Description

Technical Field

[0001] The present invention relates to the field of structural engineering, in particular to a steel truss-concrete composite beam. Background Art

[0002] The combination of steel trusses and precast concrete panels to form a composite structure can achieve the advantages of rapid construction and prefabricated assembly. However, after the concrete is poured, the precast concrete panels are in direct contact with the steel trusses. Due to the shrinkage and deformation of the concrete itself (mainly autogenous shrinkage and temperature shrinkage), the interface between the precast concrete panels and the steel trusses and the internal steel bars is poor, which can easily lead to serious voids and debonding problems. This directly affects the bearing capacity of the structure and the composite elastic modulus of concrete, thereby affecting the safety of the structure and whether it can work properly. Although the addition of expansion agents can offset the shrinkage of concrete to a certain extent, the expansion rate of existing expansion agents is often difficult to match the strength development and shrinkage rate of concrete, resulting in unsatisfactory use results. Summary of the Invention

[0003] Purpose of the invention: In order to solve the above technical problems, the present invention proposes a steel truss-concrete composite beam.

[0004] The technical solutions adopted are as follows:

[0005] A steel truss-concrete composite beam comprises a steel truss and a precast concrete panel, wherein the precast concrete panel is integrally cast by concrete and steel bars;

[0006] The concrete is prepared from the following raw materials in parts by weight:

[0007] 700-800 parts of cement, 200-400 parts of crushed stone, 600-800 parts of sand, 100-150 parts of fly ash, 80-120 parts of steel fiber, 50-80 parts of expansion agent, 1-5 parts of early strength agent, 10-15 parts of polycarboxylate water reducer, and 180-220 parts of water;

[0008] The raw materials for preparing the expansion agent include iron tailings sand, calcium carbonate, coal gangue and phosphogypsum.

[0009] Furthermore, the mass ratio of the iron tailings sand, calcium carbonate, coal gangue and phosphogypsum is 15-30:40-60:15-30:5-10.

[0010] Furthermore, the expansion agent is a microcapsule structure, and the wall material of the microcapsule structure is a hydrophobic polyionic liquid.

[0011] Furthermore, the hydrophobic polyionic liquid is any one of poly 1-vinyl-3-ethylimidazole hexafluorophosphate, poly 1-vinyl-3-propylimidazole hexafluorophosphate, poly 1-vinyl-3-butylimidazole hexafluorophosphate, poly 1-vinyl-3-ethylimidazole tetrafluoroborate, poly 1-vinyl-3-propylimidazole tetrafluoroborate, and poly 1-vinyl-3-butylimidazole tetrafluoroborate, or a combination of two or more thereof.

[0012] Furthermore, the preparation method of the expansion agent is as follows:

[0013] The iron tailings, calcium carbonate, coal gangue and phosphogypsum are mixed and ball-milled, dried, passed through a 200-mesh sieve and pressed into sheets, and then sintered at 1200-1400°C for 1-3 hours. The sintered sheets are crushed to obtain core materials, and the core materials are stirred and dispersed in DMF under nitrogen protection. Divinylbenzene, ionic liquid monomer and free radical initiator are then added, stirred evenly, and reacted in a water bath at 50-70°C for 24-48 hours. After the reaction is completed, the product is collected and dried.

[0014] Furthermore, the iron tailings sand is activated with organic acid in advance.

[0015] Furthermore, the organic acid is any one of citric acid, oxalic acid, and malic acid, or a combination of two or more thereof.

[0016] Furthermore, the method of organic acid activation is as follows:

[0017] Prepare organic acid into solution, add iron tailings, heat and evaporate the water, collect the solid, put it into an oven and keep it at 40-80℃ for 10-20h, take it out and wash it with clean water until it is neutral, dry it and heat it to 600-800℃ and calcine it for 1-5h.

[0018] Furthermore, the early strength agent is an alcoholamine early strength agent.

[0019] Furthermore, the steel truss includes two upper chords and one lower chord, the two ends of the two upper chords are connected by a cross bar, the upper chord and the lower chord are connected by straight webs at both ends and an inclined web in the middle, and the upper chord is fixed to the concrete precast plate by rivets.

[0020] Beneficial effects of the present invention:

[0021] The present invention provides a steel truss-concrete composite beam, comprising a steel truss and a precast concrete slab. The precast concrete slab is integrally cast from concrete and steel bars. The concrete has excellent compressive strength and a low autogenous shrinkage rate. Furthermore, the volume change during the curing process is small, and the excessive shrinkage and deformation of the concrete itself will not cause abnormal interface bonding between the precast concrete slab, the steel truss, and the internal steel bars, thereby affecting the bearing capacity.

[0022] The chemical composition of iron tailings sand contains Fe2O3, SiO2, SO2, Al2O3, etc., which are commonly used ingredients for preparing expansion agents. The generation of C2(A,F) etc. provides components such as Al, Si, Ca, S, etc., while the addition of calcium carbonate, coal gangue and phosphogypsum can make up for the insufficient content of CaO, Al2O3 and CaSO4, turning waste into treasure and consuming solid waste coal gangue and phosphogypsum. When the expansive agent is mixed with silicate cement and undergoes hydration reaction, it generates ettringite and expands in volume, offsetting the volume shrinkage of concrete, compensating for the shrinkage and cracking of concrete, and improving the mechanical properties.

[0023] Organic acid activation treatment of iron tailings can promote the dissolution of Si and Al in iron tailings, destroy the microstructure of iron tailings, make the mixed sintering reaction with calcium carbonate, coal gangue and phosphogypsum more complete, and promote the The formation of minerals such as C2(A,F) uses hydrophobic polyionic liquid as the wall material and SO4 in concrete 2- 、CO3 2- 、CI - After the anions of the isocyanate are exchanged with the anions of the hydrophobic polyionic liquid, the wall material can be changed from hydrophobic to hydrophilic, and the core material can be gradually released and expanded. The release and expansion process of the core material is controlled by coating the wall material, so that the self-expansion process of the microcapsule structure expansion agent is adapted to the shrinkage process of the concrete, so that the concrete has a smaller self-shrinkage rate and volume change effect, avoiding the premature weakening or even disappearance of the expansion effect of the expansion agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a structural diagram of a steel truss-concrete composite beam in Example 1 of the present invention, where the reference numerals represent:

[0025] 1- Precast concrete slab, 2- Upper chord, 3- Lower chord, 4- Straight web, 5- Inclined web, 6- Cross member. DETAILED DESCRIPTION

[0026] Unless otherwise specified, the following examples and comparative examples were conducted in parallel, using the same processing steps and parameters.

[0027] Cement: Conch P·O 42.5 type Portland cement;

[0028] Gravel: 5-16mm grade gravel;

[0029] Sand: Zone II river sand, fineness modulus 2.8;

[0030] Fly ash: Grade I fly ash

[0031] Steel fiber: hook-end type, diameter 0.75mm, length 40mm, Taian Hongtong New Materials Co., Ltd.

[0032] Microcapsule structure expansion agent: homemade;

[0033] Iron tailings sand: comes from an iron ore mining area, and its composition is shown in Table 1 below:

[0034] Table 1: / wt%

[0035]

[0036] Triethanolamine: Jinan Zesheng Chemical Co., Ltd.

[0037] Polycarboxylate water reducer: solid content 40%, Jinan Quanchi New Materials Co., Ltd.

[0038] Water: tap water.

[0039] Example 1:

[0040] This embodiment provides a steel truss-concrete composite beam, comprising a steel truss and a precast concrete panel 1;

[0041] The steel truss includes two upper chords 2 and one lower chord 3. The two ends of the upper chords 2 are connected by a cross bar 6. The upper chord 2 and the lower chord 3 are connected by straight webs 4 at both ends and an inclined web 5 in the middle. The upper chord 2 is fixed to the concrete precast slab 1 by rivets.

[0042] The precast concrete panel 1 is cast integrally with concrete and steel bars. The concrete is prepared from the following raw materials in parts by weight:

[0043] 750 parts of cement, 230 parts of crushed stone, 770 parts of sand, 125 parts of fly ash, 110 parts of steel fiber, 60 parts of microcapsule structure expansion agent, 3 parts of triethanolamine, 12 parts of polycarboxylate water reducer, and 210 parts of water;

[0044] Wherein, the preparation method of microcapsule structure expansion agent is as follows:

[0045] The oxalic acid was prepared into a 0.15 mol / L aqueous solution, and then the iron tailings were added in a solid-liquid mass ratio of 1:5. The mixed solution was heated to 80 ° C and the water was evaporated to dryness, and the solid was collected and placed in an oven at 60 ° C for 15 h. It was taken out and washed thoroughly with clean water until neutral and then dried. It was then placed in a muffle furnace and heated to 800 ° C for calcination for 2 h to obtain activated iron tailings. The activated iron tailings, calcium carbonate, coal gangue and phosphogypsum with a mass ratio of 25:50:18:6 were added to the ball mill, and anhydrous ethanol was used as the ball milling medium. The mixture was ball milled for 10 h and then dried. After passing through a 200-mesh sieve, the mixture was sieved. The product was pressed into tablets and then sintered at 1250 ° C for 2 hours. The sintered sheet was ground to obtain the core material. The core material was stirred and dispersed in DMF according to the solid-liquid mass ratio of 1:10 and protected by nitrogen. Divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN were added. The mass ratio of core material, divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN was 10:0.04:1:0.001. After stirring evenly, the reaction was stirred in a water bath at 60 ° C for 24 hours. After the reaction was completed, the product was collected and dried.

[0046] Example 2:

[0047] This embodiment provides a steel truss-concrete composite beam, comprising a steel truss and a precast concrete panel 1;

[0048] The steel truss includes two upper chords 2 and one lower chord 3. The two ends of the upper chords 2 are connected by a cross bar 6. The upper chord 2 and the lower chord 3 are connected by straight webs 4 at both ends and an inclined web 5 in the middle. The upper chord 2 is fixed to the concrete precast slab 1 by rivets.

[0049] The precast concrete panel 1 is cast integrally with concrete and steel bars. The concrete is prepared from the following raw materials in parts by weight:

[0050] 750 parts of cement, 230 parts of crushed stone, 770 parts of sand, 125 parts of fly ash, 110 parts of steel fiber, 60 parts of microcapsule structure expansion agent, 3 parts of triethanolamine, 12 parts of polycarboxylate water reducer, and 210 parts of water;

[0051] Wherein, the preparation method of microcapsule structure expansion agent is as follows:

[0052] The oxalic acid was prepared into a 0.15 mol / L aqueous solution, and then the iron tailings were added in a solid-liquid mass ratio of 1:5. The mixed solution was heated to 80 ° C and the water was evaporated to dryness, and the solid was collected and placed in an oven at 60 ° C for 15 h. It was taken out and washed thoroughly with clean water until neutral and then dried. It was then placed in a muffle furnace and heated to 800 ° C and calcined for 2 h to obtain activated iron tailings. The activated iron tailings, calcium carbonate, coal gangue and phosphogypsum with a mass ratio of 30:60:30:10 were added to a ball mill, and anhydrous ethanol was used as the ball milling medium. The mixed solution was ball milled for 10 h and then dried and passed through a 200 mesh sieve. The product was tableted and sintered at 1250 °C for 2 hours. The sintered sheet was ground to obtain the core material. The core material was stirred and dispersed in DMF according to a solid-liquid mass ratio of 1:10 and protected by nitrogen. Divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN were added. The mass ratio of core material, divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN was 10:0.04:1:0.001. After stirring evenly, the reaction was stirred in a water bath at 60 °C for 24 hours. After the reaction was completed, the product was collected and dried.

[0053] Example 3:

[0054] This embodiment provides a steel truss-concrete composite beam, comprising a steel truss and a precast concrete panel 1;

[0055] The steel truss includes two upper chords 2 and one lower chord 3. The two ends of the upper chords 2 are connected by a cross bar 6. The upper chord 2 and the lower chord 3 are connected by straight webs 4 at both ends and an inclined web 5 in the middle. The upper chord 2 is fixed to the concrete precast slab 1 by rivets.

[0056] The precast concrete panel 1 is cast integrally with concrete and steel bars. The concrete is prepared from the following raw materials in parts by weight:

[0057] 750 parts of cement, 230 parts of crushed stone, 770 parts of sand, 125 parts of fly ash, 110 parts of steel fiber, 60 parts of microcapsule structure expansion agent, 3 parts of triethanolamine, 12 parts of polycarboxylate water reducer, and 210 parts of water;

[0058] Wherein, the preparation method of microcapsule structure expansion agent is as follows:

[0059] The oxalic acid was prepared into a 0.15 mol / L aqueous solution, and then the iron tailings were added in a solid-liquid mass ratio of 1:5. The mixed solution was heated to 80 ° C and the water was evaporated to dryness, and the solid was collected and placed in an oven at 60 ° C for 15 h. It was taken out and washed thoroughly with clean water until neutral and then dried. It was then placed in a muffle furnace and heated to 800 ° C and calcined for 2 h to obtain activated iron tailings. The activated iron tailings, calcium carbonate, coal gangue and phosphogypsum with a mass ratio of 15:40:15:5 were added to a ball mill, and anhydrous ethanol was used as the ball milling medium. The mixed solution was ball milled for 10 h and then dried. After passing through a 200-mesh sieve, the mixture was sieved. The product was pressed into tablets and then sintered at 1250 ° C for 2 hours. The sintered sheet was ground to obtain the core material. The core material was stirred and dispersed in DMF according to the solid-liquid mass ratio of 1:10 and protected by nitrogen. Divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN were added. The mass ratio of core material, divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN was 10:0.04:1:0.001. After stirring evenly, the reaction was stirred in a water bath at 60 ° C for 24 hours. After the reaction was completed, the product was collected and dried.

[0060] Example 4:

[0061] This embodiment provides a steel truss-concrete composite beam, comprising a steel truss and a precast concrete panel 1;

[0062] The steel truss includes two upper chords 2 and one lower chord 3. The two ends of the upper chords 2 are connected by a cross bar 6. The upper chord 2 and the lower chord 3 are connected by straight webs 4 at both ends and an inclined web 5 in the middle. The upper chord 2 is fixed to the concrete precast slab 1 by rivets.

[0063] The precast concrete panel 1 is cast integrally with concrete and steel bars. The concrete is prepared from the following raw materials in parts by weight:

[0064] 800 parts of cement, 400 parts of crushed stone, 800 parts of sand, 150 parts of fly ash, 120 parts of steel fiber, 80 parts of microcapsule structure expansion agent, 5 parts of triethanolamine, 15 parts of polycarboxylate water reducer, and 220 parts of water;

[0065] Wherein, the preparation method of microcapsule structure expansion agent is as follows:

[0066] The oxalic acid was prepared into a 0.15 mol / L aqueous solution, and then the iron tailings were added according to the solid-liquid mass ratio of 1:5. The mixed solution was heated to 80 ° C and the water was evaporated to dryness, and the solid was collected and placed in an oven at 60 ° C for 15 h. It was taken out and washed with clean water until neutral and then dried. It was then placed in a muffle furnace and heated to 800 ° C for calcination for 2 h to obtain activated iron tailings. The activated iron tailings, calcium carbonate, coal gangue and phosphogypsum with a mass ratio of 15-30:40-60:15-30:5-10 were added to a ball mill, and anhydrous ethanol was used as the ball milling medium. The mixed solution was ball milled for 10 h and then dried. After 2 00 mesh sieve, and then pressed into tablets, and then sintered at 1250℃ for 2h. The sintered sheets were ground and crushed to obtain core materials. The core materials were stirred and dispersed in DMF according to the solid-liquid mass ratio of 1:10 and protected by nitrogen. Divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN were added. The mass ratio of core material, divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN was 10:0.04:1:0.001. After stirring evenly, stir and react in a water bath at 60℃ for 24h. After the reaction is completed, collect the product and dry it.

[0067] Example 5:

[0068] This embodiment provides a steel truss-concrete composite beam, comprising a steel truss and a precast concrete panel 1;

[0069] The steel truss includes two upper chords 2 and one lower chord 3. The two ends of the upper chords 2 are connected by a cross bar 6. The upper chord 2 and the lower chord 3 are connected by straight webs 4 at both ends and an inclined web 5 in the middle. The upper chord 2 is fixed to the concrete precast slab 1 by rivets.

[0070] The precast concrete panel 1 is cast integrally with concrete and steel bars. The concrete is prepared from the following raw materials in parts by weight:

[0071] 700 parts of cement, 200 parts of crushed stone, 600 parts of sand, 100 parts of fly ash, 80 parts of steel fiber, 50 parts of microcapsule structure expansion agent, 1 part of triethanolamine, 10 parts of polycarboxylate water reducer, and 180 parts of water;

[0072] Wherein, the preparation method of microcapsule structure expansion agent is as follows:

[0073] The oxalic acid was prepared into a 0.15 mol / L aqueous solution, and then the iron tailings were added according to the solid-liquid mass ratio of 1:5. The mixed solution was heated to 80 ° C and the water was evaporated to dryness, and the solid was collected and placed in an oven at 60 ° C for 15 h. It was taken out and washed with clean water until neutral and then dried. It was then placed in a muffle furnace and heated to 800 ° C for calcination for 2 h to obtain activated iron tailings. The activated iron tailings, calcium carbonate, coal gangue and phosphogypsum with a mass ratio of 15-30:40-60:15-30:5-10 were added to a ball mill, and anhydrous ethanol was used as the ball milling medium. The mixed solution was ball milled for 10 h and then dried. After 2 00 mesh sieve, and then pressed into tablets, and then sintered at 1250℃ for 2h. The sintered sheets were ground and crushed to obtain core materials. The core materials were stirred and dispersed in DMF according to the solid-liquid mass ratio of 1:10 and protected by nitrogen. Divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN were added. The mass ratio of core material, divinylbenzene, 1-vinyl-3-ethylimidazole hexafluorophosphate and free radical initiator AIBN was 10:0.04:1:0.001. After stirring evenly, stir and react in a water bath at 60℃ for 24h. After the reaction is completed, collect the product and dry it.

[0074] Comparative Example 1:

[0075] The process is basically the same as Example 1, except that no microcapsule structure expansion agent is added.

[0076] Comparative Example 2:

[0077] The method is basically the same as Example 1, except that the core material is directly used as the expansion agent;

[0078] The preparation method of the expansion agent is as follows:

[0079] Oxalic acid is prepared into a 0.15 mol / L aqueous solution, and then iron tailings are added according to a solid-liquid mass ratio of 1:5. The mixed solution is heated to 80°C to evaporate the water and collect the solid. The solid is placed in an oven and kept warm at 60°C for 15 hours. It is taken out and washed thoroughly with clean water until neutral and then dried. It is then placed in a muffle furnace and heated to 800°C and calcined for 2 hours to obtain activated iron tailings. Activated iron tailings, calcium carbonate, coal gangue and phosphogypsum with a mass ratio of 25:50:18:6 are added to a ball mill, and anhydrous ethanol is used as the ball milling medium. The mixture is ball milled for 10 hours and then dried. The mixture is passed through a 200-mesh sieve and pressed into tablets. The tablets are then sintered at 1250°C for 2 hours, and the fired sheets are ground and crushed.

[0080] Comparative Example 3:

[0081] The process is basically the same as Example 1, except that the commercially available HP-CSA expansion agent is used instead of the microcapsule structure expansion agent.

[0082] Performance testing:

[0083] ① The concrete in Examples 1-5 and Comparative Examples 1-3 were made into test specimens according to GB / T 17671-2021 “Test Method for Strength of Cement Mortar”. Three specimens were prepared in each group. The compressive strength (unit: MPa) of the specimens cured to the standard age of 3d, 7d and 28d was measured using a YAW-300 microcomputer-controlled electro-hydraulic servo pressure testing machine. The average value of the measurement results is shown in Table 2.

[0084] Table 2:

[0085]

[0086]

[0087] As can be seen from Table 2 above, the concrete in the present invention has excellent compressive strength;

[0088] Comparison of the data in Example 1 and Comparative Example 1 shows that the addition of the microcapsule structure expansion agent plays a positive role in improving the compressive strength of concrete. This may be because its self-expansion process is compatible with the shrinkage process of concrete, reducing the formation of cracks in the concrete caused by shrinkage stress, thereby improving the compressive strength.

[0089] From the comparison of the data of Example 1 and Comparative Example 2, it can be seen that since the microcapsule structure has a limiting effect on the expansion of the expansive agent, the expansive agent with a microcapsule structure has a greater improvement in the later compressive strength of concrete compared to directly adding it to the core material;

[0090] From the comparison of the data of Example 1 and Comparative Example 3, it can be seen that the commercially available HP-CSA expansive agent significantly improves the early compressive strength of concrete. It may be that the early expansion effect of the commercially available HP-CSA expansive agent is sufficient to compensate for the shrinkage of the concrete. However, as time goes on, the expansion effect of the commercially available HP-CSA expansive agent weakens or even disappears, and the concrete continues to shrink. The final compressive strength of the concrete is lower than that of Example 1 in which the microcapsule structure expansive agent is added.

[0091] ② The autogenous shrinkage of the concrete in Examples 1-5 and Comparative Examples 1-3 was measured using a contact bellows tester. The inner diameter of the bellows used in the test was 55 mm, the length was 420 ± 5 mm, and the micrometer resolution was 1 μm. Three specimens were prepared for each group, and the average value was taken as the final shrinkage result, and the value was accurate to 1.0 × 10 -6 The autogenous shrinkage test was carried out at a constant temperature of 20±2°C and a constant humidity of 60±5%. The test was carried out in accordance with ASTM C1698-09 "Test method for autogenous shrinkage of cement paste and mortar". The test results are shown in Table 3 below.

[0092] Table 3:

[0093]

[0094] As can be seen from Table 3 above, the concrete of the present invention has a low autogenous shrinkage rate and a small volume change during the curing process;

[0095] From the comparison of the data of Example 1 and Comparative Example 1, it can be seen that the concrete without the addition of the expansive agent has a larger autogenous shrinkage, while after the addition of the expansive agent, the self-expansion process of the microcapsule structure expansive agent is adapted to the shrinkage process of the concrete, resulting in a lower autogenous shrinkage rate;

[0096] From the comparison of the data of Example 1 with Comparative Examples 2 and 3, it can be seen that when the core material or commercially available HP-CSA expansion agent is directly added, the autogenous shrinkage rate at 3d is better than that of the microcapsule structure expansion agent due to its early expansion effect. However, as the expansion effect weakens or even disappears, the autogenous shrinkage rates at 7d and 28d increase significantly, which makes the volume change of concrete larger, which is not conducive to the interface bonding between the concrete and the steel truss.

[0097] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A steel truss-concrete composite beam, characterized in that: It includes a steel truss and a precast concrete panel, wherein the precast concrete panel is integrally cast by concrete and steel bars; The concrete is prepared from the following raw materials in parts by weight: 700-800 parts of cement, 200-400 parts of crushed stone, 600-800 parts of sand, 100-150 parts of fly ash, 80-120 parts of steel fiber, 50-80 parts of expansion agent, 1-5 parts of early strength agent, 10-15 parts of polycarboxylate water reducer, and 180-220 parts of water; The raw materials for preparing the expansion agent include iron tailings sand, calcium carbonate, coal gangue and phosphogypsum; The mass ratio of the iron ore tailings, calcium carbonate, coal gangue and phosphogypsum is 15-30:40-60:15-30:5-10; The expansion agent is a microcapsule structure, and the wall material of the microcapsule structure is a hydrophobic polyionic liquid; The hydrophobic polyionic liquid is any one of poly 1-vinyl-3-ethylimidazole hexafluorophosphate, poly 1-vinyl-3-propylimidazole hexafluorophosphate, poly 1-vinyl-3-butylimidazole hexafluorophosphate, poly 1-vinyl-3-ethylimidazole tetrafluoroborate, poly 1-vinyl-3-propylimidazole tetrafluoroborate, and poly 1-vinyl-3-butylimidazole tetrafluoroborate, or a combination of two or more thereof; The preparation method of the expansion agent is as follows: The iron tailings, calcium carbonate, coal gangue and phosphogypsum are mixed and ball-milled, dried, passed through a 200-mesh screen and pressed into sheets, and then sintered at 1200-1400°C for 1-3 hours. The sintered sheets are crushed to obtain core materials, and the core materials are stirred and dispersed in DMF under nitrogen protection. Divinylbenzene, ionic liquid monomer and free radical initiator are then added, stirred evenly, and reacted in a water bath at 50-70°C for 24-48 hours. After the reaction is completed, the product is collected and dried. The iron tailings sand is activated with organic acid in advance.

2. The steel truss-concrete composite beam according to claim 1, wherein: The organic acid is any one of citric acid, oxalic acid and malic acid or a combination of two or more thereof.

3. The steel truss-concrete composite beam according to claim 1, wherein: The method of the organic acid activation is as follows: Prepare organic acid into solution, add iron tailings, heat and evaporate the water, collect the solid, put it into an oven and keep it at 40-80℃ for 10-20h, take it out and wash it with clean water until it is neutral, dry it and heat it to 600-800℃ and calcine it for 1-5h.

4. The steel truss-concrete composite beam according to claim 1, wherein: The early strength agent is an alcoholamine early strength agent.

5. The steel truss-concrete composite beam according to claim 1, wherein: The steel truss includes two upper chords and one lower chord, the two ends of the two upper chords are connected by a cross bar, the upper chord and the lower chord are connected by straight webs at both ends and an inclined web in the middle, and the upper chord is fixed to the concrete precast plate by rivets.

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