Prefabricated composite floor slab and steel bar truss floor deck directly utilizing old slabs, and method

Abstract

Disclosed in the present invention are a prefabricated composite floor slab and steel bar truss floor deck directly utilizing old slabs, and a method. The prefabricated composite floor slab comprises new concrete, old concrete slabs, a slab bottom reinforcing mesh, a slab surface reinforcing mesh, steel bar trusses, steel dowel bars, and post-cast concrete. The steel bar truss floor deck comprises new concrete, old concrete slabs, a steel base plate, a slab surface reinforcing mesh, steel bar trusses, steel dowel bars, and support steel bars. According to the present invention, the old concrete slabs are directly utilized instead of being crushed into recycled blocks or recycled aggregates for reuse, thereby greatly simplifying processing procedures, significantly increasing the recycling rate of old concrete, and significantly reducing the usage amounts of new concrete and corresponding cement, thus achieving a significant carbon emission reduction effect; through holes are vertically drilled in the old concrete slabs, the steel dowel bars are inserted into the through holes, gaps between the steel dowel bars and the through holes are then filled with a high-strength grouting material, and shear resistance members are arranged on the side edges of the old concrete slats to enhance the shear resistance at the interface between the new concrete and the old concrete.

Description

Prefabricated composite floor slab and steel truss floor decking slab directly utilizing old slats and method thereof Technical Field

[0001] The present invention relates to the technical field of recycling waste concrete, and in particular to a prefabricated composite floor slab and a steel bar 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 attracted increasing public attention. The current practice involves crushing old concrete components into small-scale recycled aggregate or blocks, then adding cement and other binders to create recycled aggregate concrete, or mixing it with new concrete to form recycled block concrete. However, crushing old concrete components into recycled aggregate or blocks is a complex process, and the crushing process also produces a large amount of difficult-to-use powder, significantly reducing the recycling rate of the old concrete. Furthermore, preparing recycled aggregate concrete consumes a large amount of cement, and fresh concrete accounts for up to 70% of recycled block concrete, which also consumes a large amount of cement in its production. Because cement production generates significant CO2 emissions, the carbon reduction effect of this current practice needs to be further improved. Therefore, strategies for recycling and reusing old concrete components require further improvement. If simply treated old concrete components could be directly used in the production of new components without crushing, this would undoubtedly greatly alleviate these problems. However, there is currently no precedent for how to simply and efficiently use simply treated old concrete components in the production of new components.

[0003] Precast concrete components are widely used in construction projects due to their rapid construction speed, high degree of industrialization, and minimal environmental pollution. Floor slabs are important horizontal components in building structures. During the production of precast composite floor slabs and reinforced truss floor decks, if the strips formed by cutting old concrete slabs can be directly cast into new concrete slabs, this is undoubtedly an effective way to recycle 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] At present, the existing technology is unable to achieve the component-level recycling and reuse of old concrete slabs. The prefabricated composite floor slabs and steel truss floor decking slabs that directly utilize old concrete slabs and their construction methods are provided by the present invention. It is the first to propose an effective countermeasure for the recycling and reuse of old concrete slabs in prefabricated composite floor slabs and steel truss floor decking slabs, 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, steel trusses, steel bar insertions and post-cast concrete; the new concrete and the post-cast concrete are natural aggregate concrete or recycled aggregate concrete with a maximum coarse aggregate particle size of not more than 20 mm, or recycled aggregate concrete, or recycled aggregate concrete containing recycled sand from engineering waste; 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 vertically drilled in 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, including new concrete, old concrete slabs, a steel base plate, a slab surface steel mesh, steel trusses, steel bar insertions and support steel bars; the new concrete is natural aggregate concrete with a maximum coarse aggregate particle size of not more than 20 mm, or recycled aggregate concrete, or recycled aggregate concrete containing recycled sand from engineering waste; 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 net 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 members are arranged on the sides of the old concrete slabs; a plurality of the steel trusses are fixed on the steel base 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 bar truss floor slab.

[0010] Furthermore, the old concrete slabs 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 compressive strength of the old concrete slabs.

[0012] Furthermore, 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 precast composite floor slab 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 slab.

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

[0015] (1) Tie the steel mesh and steel trusses at the bottom of the slab, and lay protective layer pads between the steel mesh and steel trusses 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 them 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 new concrete layer exceeds the steel mesh at the bottom of the slab, and vibrate it to make it dense.

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

[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 it thoroughly and cure it to form the bottom plate of the precast composite floor slab;

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

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

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

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

[0024] (2) Hoist the steel base plate with welded steel trusses at the construction site, and weld support steel bars at both ends of the steel trusses;

[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) Pour a layer of new concrete into the casting mold, the height of this new concrete layer exceeds the lower chord steel bars of the steel truss (5), and vibrate it to make it dense;

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

[0028] (6) A slab surface reinforcement mesh is laid above the old concrete slab, and the slab surface reinforcement mesh is locally spot-welded to the adjacent reinforcement bars. The upper longitudinal reinforcement inside the old concrete slab is welded to the longitudinal reinforcement of the slab surface reinforcement mesh using pre-bent reinforcement bars. Then, sufficient new concrete is poured into the casting mold, vibrated sufficiently, and maintained.

[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 process, significantly improves the recycling rate of old concrete, and significantly reduces the amount of new concrete and the corresponding fresh cement, with a significant carbon emission reduction effect.

[0031] (2) In the production of the base plate of the precast composite floor, the old concrete slab protrudes from the surface of the new concrete, thereby significantly improving the integrity between the post-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. 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 post-cast concrete and the old concrete slab. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a schematic structural diagram of a prefabricated composite floor slab directly utilizing old concrete slabs provided by an embodiment of the present invention;

[0033] FIG2 is a schematic structural diagram of a steel truss floor deck directly utilizing old concrete slabs provided by an embodiment of the present invention;

[0034] FIG3 is a schematic structural 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] FIG4 is a partial cross-sectional schematic diagram 1-1 of a steel truss floor deck directly utilizing old concrete slabs provided by an embodiment of the present invention;

[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. Modes for Carrying Out the Invention

[0037] The present invention will be further described in detail below with reference to 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, those skilled in the art can implement them with reference to the existing technology.

[0038] As shown in Figures 1 and 3, the present invention provides a prefabricated composite floor slab that directly utilizes old concrete slabs, including new concrete 1, old concrete slabs 2, a bottom steel mesh 3, a 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 waste 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 shorter than that of the prefabricated composite floor slab. The width of the slats 2 is smaller than the clear distance between adjacent steel trusses 5; through holes are drilled vertically on the old concrete slats 2, and the gaps between the through holes and the steel bars 6 are filled with high-strength grouting material; shear members are arranged on the sides of the old concrete slats 2; the old concrete slats 2 are arranged between adjacent steel trusses 5; the old concrete slats 2 are located above the bottom steel mesh 3 of the slab; the slab surface steel mesh 4 is located above the old concrete slats 2; the internal upper longitudinal steel bars of the old concrete slats 2 are connected to the longitudinal steel bars of the slab surface steel mesh 4.

[0039] In some embodiments of the present invention, the prefabricated composite floor slabs directly utilizing old concrete slabs have a width of 1800 mm, a thickness of 120 mm, a concrete cover thickness of 15 mm, and a prefabricated bottom plate thickness of 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 binding steel bars 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 binding steel bars 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 utilizing 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 lay protective layer pads between the steel mesh 3 and steel truss 5 at the bottom of the slab and the bottom formwork;

[0044] (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 shear members on the side of the old concrete slab 2;

[0045] (3) Pour 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 vibrate it to make it dense.

[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 sufficient 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 reinforcement mesh 4 is laid on top of the old concrete slab 2. The slab surface reinforcement mesh 4 is locally spot-welded to the adjacent reinforcement bars 6. The upper longitudinal reinforcement inside the old concrete slab 2 is welded to the longitudinal reinforcement of the slab surface reinforcement mesh 4 using pre-bent reinforcement bars. Then, post-cast concrete 8 is poured on site, fully vibrated, and cured.

[0050] As shown in Figures 2 and 4, a steel truss floor deck that directly utilizes old concrete slabs includes new concrete 1, old concrete slabs 2, a steel base 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 waste soil with a maximum coarse aggregate size of not more than 20 mm; 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 less than the width between adjacent steel trusses 5. The net distance between them; vertical through holes are drilled on the old concrete slabs 2, and the gaps between the through holes and the steel bar insertions 6 are filled with high-strength grouting material; shear members are arranged on the sides of the old concrete slabs 2; a plurality of the steel bar trusses 5 are fixed on the steel bottom plate 7, and the support steel bars 9 are provided at the ends of the steel bar trusses 5; the old concrete slabs 2 are provided between adjacent steel bar trusses 5; the plate surface steel mesh 4 is located above the old concrete slabs 2; the upper internal longitudinal steel bars of the old concrete slabs 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 that directly utilizes old concrete slabs has a width of 600 mm, a thickness of 150 mm, and a concrete cover 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 reinforcement 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 utilizing old concrete slabs comprises the following steps:

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

[0057] (2) hoisting and welding the steel base plate 7 of 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) Drill a through hole vertically on the old concrete slab 2, insert the steel bar 6 into the through hole and fill the gap between the two with high-strength grouting material;

[0059] (4) Pour a layer of new concrete 1 into the casting mold, the height of this layer of new concrete 1 exceeds the lower chord steel bars of the steel truss 5, and vibrate it to make it dense;

[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 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);

[0061] (6) A slab surface reinforcement mesh 4 is laid above the old concrete slab 2. The slab surface reinforcement mesh 4 is locally spot-welded to the adjacent reinforcement bars 6. The upper longitudinal reinforcement inside the old concrete slab 2 is welded to the longitudinal reinforcement of the slab surface reinforcement mesh 4 using pre-bent reinforcement bars. Then, sufficient new concrete 1 is poured into the casting mold, vibrated sufficiently, and cured.

[0062] Traditionally, old concrete slabs are first crushed, their internal steel bars removed and sold. The crushed large concrete blocks are then directly recycled as blocks, or the blocks are further crushed multiple times to be refined into recycled aggregate for reuse. Whether using recycled blocks to produce recycled block concrete or recycled aggregate concrete to produce recycled aggregate concrete, large amounts of fresh cement and other cementitious materials are required. Cement production is not only energy-intensive but also emits significant carbon emissions. Furthermore, the multiple crushing processes inevitably produce a large amount of difficult-to-use powder, significantly reducing the recycling rate of the old concrete. To address this issue, the present invention proposes for the first time the direct recycling of old concrete slabs at the component level, rather than crushing them into recycled blocks or recycled aggregate. This not only greatly simplifies the processing process and avoids the production of powder, but more importantly, significantly reduces the amount of new concrete and the corresponding fresh cement used, resulting in significant energy savings and carbon reduction. Previously, there were no international reports on the direct recycling of old concrete slabs in new components.

[0063] According to the present invention, the rebar within the old concrete slabs is no longer removed and sold, which appears to reduce economic income to a certain extent. This is also the main reason why previous researchers had difficulty conceiving of directly recycling old concrete slabs. However, considering the savings in equipment and labor associated with crushing the old concrete slabs and removing the rebar, the avoidance of large amounts of waste material transportation and dumping expenses, and the significant reduction in new concrete and corresponding fresh cement consumption resulting from the direct recycling of old concrete slabs in new components, the present invention still has good overall economic benefits. At the same time, the internal rebar of the old concrete slabs can also provide some support during the service life of the new component, thereby reducing the reinforcement requirements of the new component, which undoubtedly makes the present invention more advantageous.

[0064] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Prefabricated composite floor slabs that directly utilize 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 trusses (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 or recycled aggregate concrete containing recycled sand from construction waste soil, with the maximum coarse aggregate size not exceeding 20 mm; The length of the old concrete slab (2) is smaller 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; shear members 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 old concrete slabs, characterized by: It includes new concrete (1), old concrete slab (2), steel base plate (7), slab surface reinforcement mesh (4), reinforcement trusses (5), reinforcement bars (6) and support bars (9); New concrete (1) is 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 smaller 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 members 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 each 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 precast composite floor slab or the steel 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 less than the compressive strength of the concrete 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 10-30 mm greater than the original thickness of the old concrete slab (2) 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 10-30 mm greater than the original thickness of the old concrete slab (2) 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) Tie the bottom steel mesh (3) and the steel truss (5) of the slab, and arrange protective layer pads between the 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 shear members on the side of the old concrete slab (2); (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; (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 predetermined period of time; (5) pouring sufficient 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 it 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 reinforcement mesh (4) is arranged above the old concrete slab (2), the slab surface reinforcement mesh (4) is locally spot-welded to the adjacent reinforcement bars (6), and the upper longitudinal reinforcement of the old concrete slab (2) and the longitudinal reinforcement of the slab surface reinforcement mesh (4) are welded together using pre-bent reinforcement bars, and then post-cast concrete (8) is poured on site, fully vibrated, and cured.

10. A construction method for steel truss floor decking that directly utilizes old concrete slabs is characterized by: The following steps are involved: (1) Welding the steel truss (5) to the steel base plate (7); (2) hoisting the steel base 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); (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 predetermined period of time; (6) A slab surface reinforcement mesh (4) is arranged above the old concrete slab (2), the slab surface reinforcement mesh (4) is locally spot-welded to the adjacent reinforcement bars (6), and the upper longitudinal reinforcement of the old concrete slab (2) is welded to the longitudinal reinforcement of the slab surface reinforcement mesh (4) using pre-bent reinforcement bars, and then sufficient new concrete (1) is poured into the casting mold, fully vibrated and cured.

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