Prefabricated composite floor slab and steel bar truss floor decking slab and method for directly utilizing old slats

Abstract

The present invention discloses a prefabricated composite floor slab and a steel bar truss floor deck and a method for directly utilizing old slabs. The prefabricated composite floor slab comprises new concrete, old concrete slabs, a steel bar mesh at the bottom of the slab, a steel bar mesh at the surface of the slab, a steel bar truss, a steel bar insert and post-cast concrete. The steel bar truss floor deck comprises new concrete, old concrete slabs, a steel bottom plate, a steel bar mesh at the surface of the slab, a steel bar truss, a steel bar insert and a support steel bar. The present invention directly utilizes old concrete slabs instead of crushing them into recycled blocks or recycled aggregates for reuse, greatly simplifies the processing procedures, significantly improves the recycling rate of old concrete, significantly reduces the amount of new concrete and the corresponding cement, and has a prominent carbon emission reduction effect; through holes are drilled vertically on the old concrete slabs, the steel bar inserts are inserted into the through holes and the gap between the two is filled with high-strength grouting material, and shear members are arranged on the sides of the old concrete slabs to enhance the shear resistance of the interface between the new and old concrete.

Description

Technical Field

[0001] The invention relates to the technical field of recycling waste concrete, and in particular to a prefabricated composite floor slab and a steel truss floor decking slab directly utilizing waste concrete slabs and a construction method thereof. Background Art

[0002] With the rapid development of urban construction, the recycling and reuse of old concrete components has gradually attracted social attention. The current practice is to crush old concrete components into small-scale recycled aggregates or recycled blocks, and then add cement and other cementitious materials to prepare recycled aggregate concrete, or mix with new concrete to form recycled block concrete. However, the process of crushing old concrete components into recycled aggregates or recycled blocks is relatively cumbersome, and a large amount of powder that is difficult to use will be produced during the crushing process, which will significantly reduce the recycling rate of old concrete; at the same time, the preparation of recycled aggregate concrete will consume a lot of cement, and the proportion of fresh concrete in recycled block concrete is as high as 70%, and the production of these fresh concrete will also consume a lot of cement. Since cement production will produce a large amount of CO2 emissions, the carbon emission reduction effect of the above current practices needs to be further improved. For this reason, the recycling and reuse strategy of old concrete components needs to be further improved. If the old concrete components that have been simply treated can be directly used in the production of new components without crushing, it will undoubtedly greatly alleviate the above problems. However, there is currently no precedent for how to simply and efficiently use the old concrete components that have been simply treated in the production of new components.

[0003] Precast concrete components are widely used in engineering construction due to their fast construction speed, high degree of industrialization and low environmental pollution. Floor slabs are important horizontal components in building structures. In the production process of precast composite floor slabs and steel truss floor slabs, if the slats formed by cutting the old concrete slabs can be directly cast inside the new concrete slabs, it is undoubtedly an effective way to recycle the old concrete components.

[0004] In summary, the current existing technology cannot achieve the component-level recycling and reuse of old concrete slabs after simple treatment. Summary of the invention

[0005] The current existing technology is unable to achieve component-level recycling and reuse of old concrete slabs. The present invention provides prefabricated composite slabs and steel truss floor decking that directly utilize old concrete slabs and their construction methods, and is the first to propose an effective strategy for recycling and reuse of old concrete slabs in prefabricated composite slabs and steel truss floor decking, which has a significant carbon emission reduction effect.

[0006] In order to achieve the purpose of the present invention, the present invention provides a prefabricated composite floor slab that directly utilizes old concrete slabs, including new concrete, old concrete slabs, a bottom steel mesh, a surface steel mesh, a steel truss, a steel bar insertion and post-cast concrete; the new concrete and the post-cast concrete are natural aggregate concrete or recycled aggregate concrete with a maximum particle size of coarse aggregate not greater than 20 mm, or recycled aggregate concrete or recycled aggregate concrete containing recycled sand from engineering slag; the length of the old concrete slab is smaller than the length of the prefabricated composite floor slab, and the width of the old concrete slab is smaller than the clear distance between adjacent steel bar trusses; through holes are drilled vertically on the old concrete slabs, and the gaps between the through holes and the steel bar insertions are filled with high-strength grouting material; shear members are arranged on the sides of the old concrete slabs; the old concrete slabs are arranged between adjacent steel bar trusses; the old concrete slabs are located above the bottom steel mesh; the surface steel mesh is located above the old concrete slabs; the internal upper longitudinal steel bars of the old concrete slabs are connected to the longitudinal steel bars of the surface steel mesh.

[0007] The present invention also provides a steel truss floor deck that directly utilizes old concrete slabs, comprising new concrete, old concrete slabs, a steel bottom plate, a slab surface steel mesh, a steel truss, a steel bar insertion and support steel bars; the new concrete is natural aggregate concrete or recycled aggregate concrete with a maximum particle size of coarse aggregate not greater than 20 mm, or recycled aggregate concrete or recycled aggregate concrete containing recycled sand from engineering slag; the length of the old concrete slab is smaller than the length of the steel truss floor deck, and the width of the old concrete slab is smaller than the clear distance between adjacent steel trusses; through holes are drilled vertically on the old concrete slabs, and the gaps between the through holes and the steel bar insertions are filled with high-strength grouting material; shear-resistant parts are arranged on the sides of the old concrete slabs; a plurality of the steel trusses are fixed on the steel bottom plate, and the support steel bars are arranged at the ends of the steel trusses; the old concrete slabs are arranged between adjacent steel trusses; the slab surface steel mesh is located above the old concrete slabs; the internal upper longitudinal steel bars of the old concrete slabs are connected to the longitudinal steel bars of the slab surface steel mesh.

[0008] Furthermore, the upper and lower surfaces of the old concrete slab are each cut to a thickness of 5-20 mm and roughened.

[0009] Furthermore, the length of the old concrete slab is at least 80 mm smaller than the length of the prefabricated composite floor slab or the steel truss floor slab.

[0010] Furthermore, the old concrete slab strips are strips formed by cutting old concrete slabs obtained by demolishing old buildings or structures.

[0011] Furthermore, the compressive strength of the new concrete is not lower than the concrete compressive strength of the old concrete slabs.

[0012] Further, the compressive strength of the post-cast concrete is not less than the concrete compressive strength of the old concrete slab.

[0013] Furthermore, the length of the steel bar insert is 10-30 mm greater than the original thickness of the old concrete slab and not greater than the total thickness of the prefabricated composite floor after pouring concrete, or the length of the steel bar insert is 10-30 mm greater than the original thickness of the old concrete slab and not greater than the thickness of the steel truss floor deck.

[0014] The construction method of the prefabricated composite floor slab directly using old concrete slabs comprises the following steps:

[0015] (1) Tie the steel mesh and steel truss at the bottom of the slab, and lay protective layer pads between the steel mesh and steel truss at the bottom of the slab and the bottom formwork;

[0016] (2) Drill through holes vertically on the old concrete slabs, insert the steel bars into the through holes and fill the gap between the two with high-strength grouting material; arrange shear members on the sides of the old concrete slabs;

[0017] (3) Pour a layer of new concrete into the casting mold. The height of this layer of new concrete exceeds the steel mesh at the bottom of the slab, and vibrate it to make it dense.

[0018] (4) placing the old concrete slabs that have been fully moistened in advance directly on the layer of new concrete poured in step 1 and between adjacent steel trusses, and applying a vertical downward vibration pressure for a preset time on the upper surface of the old concrete slabs;

[0019] (5) Pour sufficient new concrete around the old concrete slabs in the casting mold until the height of the new concrete is flush with the top of the side of the casting mold, vibrate and cure sufficiently to form the bottom plate of the precast composite floor;

[0020] (6) Hoisting the bottom plate of the prefabricated composite floor at the construction site;

[0021] (7) A slab surface steel mesh is laid on top of the old concrete slab, and the slab surface steel mesh is locally spot welded to the adjacent steel bar insertions. The upper internal longitudinal steel bars of the old concrete slab are welded to the longitudinal steel bars of the slab surface steel mesh using pre-bent steel bars, and then the post-poured concrete is poured on site, fully vibrated and cured.

[0022] The construction method of the steel truss floor deck directly using old concrete slabs comprises the following steps:

[0023] (1) Weld the steel truss to the steel base plate;

[0024] (2) hoisting the steel base plate welded with the steel truss at the construction site, and welding the support steel bars at both ends of the steel truss;

[0025] (3) Drill vertical through holes on the old concrete slabs, insert the steel bars into the through holes and fill the gap between them with high-strength grouting material;

[0026] (4) pouring a layer of new concrete into the casting mold, the height of which exceeds the lower chord steel bars of the steel truss (5), and vibrating and compacting it;

[0027] (5) placing the old concrete slabs that have been fully moistened in advance directly on the layer of new concrete poured in step 1 and between adjacent steel trusses, and applying a vertical downward vibration pressure for a preset time on the upper surface of the old concrete slabs;

[0028] (6) A slab surface steel mesh is laid on top of the old concrete slab, and the slab surface steel mesh is locally spot welded to the adjacent steel bar insertions. The upper internal longitudinal steel bars of the old concrete slab are welded to the longitudinal steel bars of the slab surface steel mesh using pre-bent steel bars. Then, a sufficient amount of new concrete is poured into the casting mold, fully vibrated and cured.

[0029] Compared with the prior art, the present invention has the following advantages and effects:

[0030] (1) Directly utilizing old concrete slabs instead of crushing them into recycled blocks or recycled aggregates for reuse greatly simplifies the processing procedures, significantly improves the recycling rate of old concrete, and significantly reduces the amount of new concrete and the corresponding fresh cement used, with a significant carbon emission reduction effect.

[0031] (2) In the production of the base plate of the prefabricated composite floor, the old concrete slab protrudes from the surface of the new concrete, thereby significantly increasing the integrity between the later-cast concrete and the base plate. At the same time, a number of through holes are drilled vertically on the old concrete slab, steel bars are inserted into the through holes and the gap between the two is filled with high-strength grouting material, and shear members are arranged on the side of the old concrete slab, which can further improve the shear resistance between the new concrete and the old concrete slab, and between the later-cast concrete and the old concrete slab. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of a prefabricated composite floor slab directly utilizing old concrete slabs provided by an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of a steel truss floor deck that directly utilizes old concrete slabs provided by an embodiment of the present invention;

[0034] Figure 3 It is a structural schematic diagram of a bottom plate of a prefabricated composite floor slab directly utilizing old concrete slabs provided by an embodiment of the present invention;

[0035] Figure 4 The partial cross-section diagram of a steel truss floor deck directly using old concrete slabs provided by an embodiment of the present invention is Figure 1-1 ;

[0036] In the figure: 1-new concrete; 2-old concrete slab; 3-slab bottom steel mesh; 4-slab surface steel mesh; 5-steel truss; 6-steel inserts; 7-steel bottom plate; 8-post-poured concrete; 9-support steel bars. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the embodiments and drawings, but the embodiments of the present invention are not limited thereto. It should be pointed out that if there are any processes that are not particularly described in detail below, they can be implemented by those skilled in the art with reference to the prior art.

[0038] like Figure 1 , Figure 3 As shown, the present invention provides a prefabricated composite floor slab that directly utilizes old concrete slabs, comprising new concrete 1, old concrete slabs 2, a slab bottom steel mesh 3, a slab surface steel mesh 4, a steel truss 5, a steel bar 6 and a post-cast concrete 8; the new concrete 1 and the post-cast concrete 8 are both natural aggregate concrete or recycled aggregate concrete or recycled aggregate concrete containing engineering slag recycled sand with a maximum coarse aggregate size of not more than 20 mm; the length of the old concrete slab 2 is shorter than that of the prefabricated composite floor slab, and the old concrete slab 2 is The width is smaller than the clear distance between adjacent steel bar trusses 5; through holes are drilled vertically on the old concrete slab 2, and the gap between the through holes and the steel bar insertion strips 6 is filled with high-strength grouting material; shear members are arranged on the sides of the old concrete slab 2; the old concrete slab 2 is arranged between adjacent steel bar trusses 5; the old concrete slab 2 is located above the bottom steel bar mesh 3; the board surface steel bar mesh 4 is located above the old concrete slab 2; the internal upper longitudinal steel bars of the old concrete slab 2 are connected with the longitudinal steel bars of the board surface steel bar mesh 4.

[0039] In some embodiments of the present invention, the width of the prefabricated composite floor slab directly using old concrete slabs is 1800 mm, the thickness is 120 mm, the thickness of the concrete protective layer is 15 mm, and the thickness of the prefabricated bottom plate is 60 mm.

[0040] In some embodiments of the present invention, the compressive strength of the new concrete 1 is 30 MPa, and the compressive strength of the old concrete slab 2 is 25 MPa.

[0041] In some embodiments of the present invention, the bottom steel mesh 3 is formed by steel bars tied along the span direction and along the width direction, with reinforcement C10@200 along the span direction and reinforcement C8@200 along the width direction; the surface steel mesh 4 is formed by steel bars tied along the span direction and along the width direction, and both are reinforced with C8@250.

[0042] A construction method for prefabricated composite floor slabs directly using old concrete slabs comprises the following steps:

[0043] (1) Tie the steel mesh 3 and steel truss 5 at the bottom of the slab, and arrange protective layer pads between the steel mesh 3 and steel truss 5 at the bottom of the slab and the bottom formwork;

[0044] (2) vertically drilling a through hole on the old concrete slab 2, inserting the steel bar 6 into the through hole and filling the gap between the two with high-strength grouting material; arranging shear members on the side of the old concrete slab 2;

[0045] (3) pouring a layer of new concrete 1 into the casting mold, the height of this layer of new concrete 1 exceeds the steel mesh 3 at the bottom of the slab, and vibrating and compacting it;

[0046] (4) placing the old concrete slab 2 that has been fully moistened in advance directly on the layer of new concrete 1 poured in step (3) and between adjacent steel trusses 5, and applying a vertical downward vibration pressure on the upper surface of the old concrete slab 2 for a preset time (e.g., for not less than 2 minutes);

[0047] (5) Pour a sufficient amount of new concrete 1 around the old concrete slab 2 in the casting mold until the height of the new concrete 1 is flush with the top of the side of the casting mold, vibrate and cure sufficiently to form the bottom plate of the precast composite floor slab;

[0048] (6) Hoisting the bottom plate of the prefabricated composite floor at the construction site;

[0049] (7) A slab surface steel mesh 4 is arranged above the old concrete slab 2, and the slab surface steel mesh 4 is locally spot welded to the adjacent steel bar insertion strips 6. The upper inner longitudinal steel bars of the old concrete slab 2 are welded to the longitudinal steel bars of the slab surface steel mesh 4 using pre-bent steel bars, and then the post-cast concrete 8 is poured on site, fully vibrated and cured.

[0050] like Figure 2 , Figure 4As shown, a steel truss floor deck that directly utilizes old concrete slabs comprises new concrete 1, old concrete slabs 2, a steel bottom plate 7, a slab steel mesh 4, a steel truss 5, steel bar inserts 6 and support steel bars 9; the new concrete 1 is natural aggregate concrete or recycled aggregate concrete or recycled aggregate concrete containing recycled sand from engineering slag with a maximum particle size of coarse aggregate not greater than 20 mm; the length of the old concrete slab 2 is smaller than the length of the steel truss floor deck, and the width of the old concrete slab 2 is smaller than the net width between adjacent steel trusses 5 Distance; through holes are drilled vertically on the old concrete slab 2, and the gap between the through holes and the steel bar insertion strip 6 is filled with high-strength grouting material; shear members are arranged on the side of the old concrete slab 2; a plurality of the steel bar trusses 5 are fixed on the steel bottom plate 7, and the support steel bars 9 are arranged at the ends of the steel bar trusses 5; the old concrete slab 2 is arranged between adjacent steel bar trusses 5; the plate surface steel mesh 4 is located above the old concrete slab 2; the internal upper longitudinal steel bars of the old concrete slab 2 are connected to the longitudinal steel bars of the plate surface steel mesh 4.

[0051] In some embodiments of the present invention, the steel truss floor decking directly utilizing old concrete slabs has a width of 600 mm, a thickness of 150 mm, and a concrete protective layer thickness of 15 mm.

[0052] In some embodiments of the present invention, the steel bottom plate 7 is made of Q235 cold-rolled steel plate with a width of 576 mm and a thickness of 0.5 mm.

[0053] In some embodiments of the present invention, the compressive strength of the new concrete 2 is 30 MPa, and the compressive strength of the old concrete slab 1 is 25 MPa.

[0054] In some embodiments of the present invention, the plate surface steel mesh 4 is formed by binding steel bars along the span direction and along the width direction, and the reinforcement is C8@250.

[0055] The above-mentioned construction method of a steel truss floor deck directly using old concrete slabs comprises the following steps:

[0056] (1) Weld the steel truss 5 to the steel base plate 7;

[0057] (2) hoisting the steel bottom plate 7 welded with the steel truss 5 at the construction site, and welding the support steel bars 9 at both ends of the steel truss 5;

[0058] (3) Drilling a through hole vertically on the old concrete slab 2, inserting the steel bar 6 into the through hole and filling the gap between the two with high-strength grouting material;

[0059] (4) pouring a layer of new concrete 1 into the casting mold, the height of which exceeds the lower chord steel bars of the steel truss 5, and vibrating and compacting it;

[0060] (5) placing the old concrete slab 2 that has been fully moistened in advance directly on the layer of new concrete 1 poured in step (4) and between adjacent steel trusses 5, and applying a vibration pressure vertically downward for a preset time (e.g., for not less than 2 minutes) to the upper surface of the old concrete slab 2;

[0061] (6) A slab surface steel mesh 4 is arranged above the old concrete slab 2, and the slab surface steel mesh 4 is locally spot welded to the adjacent steel bar insertion strips 6. The upper longitudinal steel bars inside the old concrete slab 2 are welded to the longitudinal steel bars of the slab surface steel mesh 4 using pre-bent steel bars, and then a sufficient amount of new concrete 1 is poured into the casting mold, fully vibrated and cured.

[0062] As a traditional practice, the old concrete slabs are often first crushed, the internal steel bars are taken out and sold, and then the large blocks of concrete after crushing are directly used in the form of recycled blocks, or the large blocks of concrete are further crushed for multiple times to be refined into recycled aggregates for use. Whether it is to prepare recycled block concrete using recycled blocks or to prepare recycled aggregate concrete using recycled aggregates, a large amount of fresh cement and other cementitious materials are required, and cement production not only consumes a lot of energy, but also has huge carbon emissions. On the other hand, a large amount of powder that is difficult to use will inevitably be produced during the multiple crushing processes, thereby significantly reducing the recycling rate of the old concrete. In order to solve the above problems, the present invention proposes for the first time the idea of ​​directly recycling the old concrete slabs at the component level, instead of crushing the old concrete slabs into recycled blocks or recycled aggregates. This not only greatly simplifies the processing process, but also avoids the output of powder. More importantly, it can significantly reduce the amount of new concrete and the corresponding fresh cement, and the energy-saving and carbon-reducing effect is significant. Prior to this, there have been no related reports on the direct recycling of old concrete slabs in new components in the world.

[0063] According to the scheme of the present invention, the steel bars inside the old concrete slabs are no longer taken out and sold, which seems to reduce a certain amount of economic income. This is also the main reason why predecessors found it difficult to think of directly recycling the old concrete slabs. However, considering that the equipment and labor costs related to the crushing of the old concrete slabs and the removal of the steel bars are saved, the expenses of transporting and dumping a large amount of powder are avoided, and the cost savings caused by the new concrete brought about by the direct recycling of the old concrete slabs in the new components and the corresponding fresh cement consumption are significantly reduced, the present invention still has good overall comprehensive economic benefits. At the same time, the internal steel bars of the old concrete slabs can also provide a certain amount of assistance during the service of the new components, thereby reducing the reinforcement requirements of the new components, which undoubtedly makes the present invention have greater advantages.

[0064] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Prefabricated composite floor slabs directly using old concrete slabs, characterized in that: It includes new concrete (1), old concrete slab (2), slab bottom steel mesh (3), slab surface steel mesh (4), steel truss (5), steel bar inserts (6) and post-cast concrete (8); The new concrete (1) and the post-cast concrete (8) are natural aggregate concrete or recycled aggregate concrete with a maximum coarse aggregate size of not more than 20 mm, or recycled aggregate concrete containing recycled sand from construction waste soil; The length of the old concrete slab (2) is shorter than the length of the prefabricated composite floor slab, and the width of the old concrete slab (2) is smaller than the clear distance between adjacent steel trusses (5); through holes are drilled vertically on the old concrete slab (2), and the gap between the through holes and the steel bar inserts (6) is filled with high-strength grouting material; and shear-resistant parts are arranged on the sides of the old concrete slab (2); The old concrete slabs (2) are arranged between adjacent steel bar trusses (5); the old concrete slabs (2) are located above the slab bottom steel bar mesh (3); the slab surface steel bar mesh (4) is located above the old concrete slabs (2); and the internal upper longitudinal steel bars of the old concrete slabs (2) are connected to the longitudinal steel bars of the slab surface steel bar mesh (4).

2. Directly utilize the steel truss floor deck of the old concrete slab, characterized in that: It includes new concrete (1), old concrete slab (2), steel base plate (7), slab surface steel mesh (4), steel truss (5), steel bar inserts (6) and support steel bars (9); New concrete (1) refers to natural aggregate concrete or recycled aggregate concrete with a maximum coarse aggregate size of not more than 20 mm, or recycled aggregate concrete containing recycled sand from construction waste; The length of the old concrete slab (2) is shorter than the length of the steel truss floor deck, and the width of the old concrete slab (2) is smaller than the clear distance between adjacent steel trusses (5); through holes are drilled vertically on the old concrete slab (2), and the gap between the through holes and the steel bar inserts (6) is filled with high-strength grouting material; and shear-resistant parts are arranged on the sides of the old concrete slab (2); A plurality of the steel bar trusses (5) are fixed on the steel bottom plate (7), and the support steel bars (9) are arranged at the ends of the steel bar trusses (5); the old concrete slabs (2) are arranged between adjacent steel bar trusses (5); the slab surface steel bar mesh (4) is located above the old concrete slabs (2); and the internal upper layer longitudinal steel bars of the old concrete slabs (2) are connected to the longitudinal steel bars of the slab surface steel bar mesh (4).

3. The prefabricated composite floor slab or steel truss floor slab according to claim 1 or 2, characterized in that: The upper and lower surfaces of the old concrete slab (2) are cut to a thickness of 5-20 mm and roughened.

4. The prefabricated composite floor slab or steel truss floor slab according to claim 1 or 2, characterized in that: The length of the old concrete slab (2) is at least 80 mm shorter than the length of the prefabricated composite floor slab or the steel bar truss floor slab.

5. The prefabricated composite floor slab or steel truss floor slab according to claim 1 or 2, characterized in that: The old concrete slab strips (2) are strips formed by cutting old concrete slabs obtained by demolishing old buildings or structures.

6. The prefabricated composite floor slab or steel truss floor slab according to claim 1 or 2, characterized in that: The compressive strength of the new concrete (1) is not lower than the concrete compressive strength of the old concrete slab (2).

7. The prefabricated composite floor slab or steel truss floor slab according to claim 1 or 2, characterized in that: The compressive strength of the post-cast concrete (8) is not lower than the concrete compressive strength of the old concrete slab (2).

8. The prefabricated composite floor slab or steel truss floor slab according to claim 1 or 2, characterized in that: The length of the steel bar insert (6) is greater than the original thickness of the old concrete slab (2) by 10-30 mm and is not greater than the total thickness of the prefabricated composite floor slab after pouring the post-cast concrete (8), or the length of the steel bar insert (6) is greater than the original thickness of the old concrete slab (2) by 10-30 mm and is not greater than the thickness of the steel truss floor slab.

9. A construction method for prefabricated composite floor slabs directly using old concrete slabs, characterized in that: The following steps are involved: (1) tying the slab bottom steel mesh (3) and the steel truss (5), and arranging protective layer pads between the slab bottom steel mesh (3) and the steel truss (5) and the bottom formwork; (2) drilling a through hole vertically on the old concrete slab (2), inserting the steel bar (6) into the through hole and filling the gap between the two with high-strength grouting material; arranging a shear member on the side of the old concrete slab (2); (3) pouring a layer of new concrete (1) into the casting mold, wherein the height of the new concrete (1) exceeds the steel mesh (3) at the bottom of the slab, and vibrating and compacting the concrete; (4) placing the old concrete slab (2) that has been fully moistened in advance directly on the layer of new concrete (1) poured in step (3) and between adjacent steel trusses (5), and applying a vertical downward vibration pressure on the upper surface of the old concrete slab (2) for a preset period of time; (5) pouring a sufficient amount of new concrete (1) around the old concrete slab (2) in the casting mold until the height of the new concrete (1) is flush with the top of the side of the casting mold, vibrating and curing sufficiently to form the bottom plate of the precast composite floor; (6) Hoisting the bottom plate of the prefabricated composite floor at the construction site; (7) A slab surface steel mesh (4) is arranged above the old concrete slab (2), the slab surface steel mesh (4) and the adjacent steel bar insertion strips (6) are locally spot welded, and the upper internal longitudinal steel bars of the old concrete slab (2) and the longitudinal steel bars of the slab surface steel mesh (4) are welded and connected using pre-bent steel bars, and then post-cast concrete (8) is poured on site, fully vibrated and cured.

10. A construction method for a steel truss floor deck directly using old concrete slabs, characterized in that: The following steps are involved: (1) Welding the steel truss (5) to the steel base plate (7); (2) hoisting a steel bottom plate (7) welded with a steel truss (5) at the construction site, and welding support steel bars (9) at both ends of the steel truss (5); (3) drilling a through hole vertically on the old concrete slab (2), inserting the steel bar (6) into the through hole and filling the gap between the two with high-strength grouting material; (4) pouring a layer of new concrete (1) into the casting mold, wherein the height of the new concrete (1) exceeds the lower chord steel bars of the steel truss (5), and vibrating and compacting the concrete; (5) placing the old concrete slab (2) that has been fully moistened in advance directly on the layer of new concrete (1) poured in step (4) and between adjacent steel trusses (5), and applying a vertical downward vibration pressure on the upper surface of the old concrete slab (2) for a preset time; (6) A slab surface steel mesh (4) is arranged above the old concrete slab (2), the slab surface steel mesh (4) and the adjacent steel bar insertion strips (6) are locally spot welded, and the upper internal longitudinal steel bars of the old concrete slab (2) and the longitudinal steel bars of the slab surface steel mesh (4) are welded and connected using pre-bent steel bars, and then a sufficient amount of new concrete (1) is poured into the casting mold, fully vibrated and cured.

Images