Preparation method of truss type GFRP (glass fiber reinforced plastic) bar seawater and sea sand recycled concrete beam

Abstract

The invention provides a preparation method of a truss type GFRP rib seawater and sea sand recycled concrete beam. The truss type GFRP rib seawater and sea sand recycled concrete beam comprises a truss type FRP rib cage and a seawater and sea sand recycled concrete shell. The invention discloses a preparation method of a truss type GFRP bar seawater and sea sand recycled concrete beam. The preparation method comprises the following steps: 1, preparing seawater and sea sand recycled concrete; 2, a bottom formwork is installed; 3, longitudinal ribs and stirrups are laid; 4, plane inclined ribs are laid, and the plane inclined ribs are placed on the upper layers of the longitudinal ribs; 5, side formworks are installed; step 6, injecting the stirred seawater and sea sand recycled concrete into the mold, and feeding a beam test piece into a curing chamber for standard curing after the concrete is poured to form the beam test piece; and 7, after the maintenance time is up, removing the template, and taking out the test block.

Description

Technical Field

[0001] The invention provides a method for preparing a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam, and relates to the field of prefabricated concrete components. Background Art

[0002] Concrete structures, the most important structures in civil engineering, consume large quantities of natural raw materials during their production. With the current shortage of natural resources such as freshwater and river sand, there is an urgent need to use sustainable building materials to replace traditional freshwater, river sand, and natural coarse aggregate. Using seawater, sea sand, and recycled aggregate as substitutes for these materials is crucial for achieving effective energy conservation and emission reduction in marine engineering structures.

[0003] For marine engineering structures, the use of fiber-reinforced polymer (FRP) bars to reinforce seawater and sea sand recycled concrete components is one of the promising methods. It is of great help in realizing the resource utilization of construction waste and the effective utilization of marine resources. However, the research on FRP bar reinforced seawater and sea sand recycled concrete components has certain limitations. The reinforcement form of FRP bar reinforced seawater and sea sand recycled concrete components is based on rectangular stirrup specimens, and there is a lack of research on truss-type reinforcement specimens. In order to promote the application of FRP bars, it is increasingly urgent to solve the problem of large deformation of FRP bars.

[0004] The massive growth of the construction industry has generated a large amount of construction and demolition waste. Recycling waste concrete as a renewable resource for use in new projects is an effective way to improve the resource utilization of construction solid waste. However, due to the accumulation of internal damage during the crushing process, the aggregate accumulates under external forces, resulting in numerous microcracks and a significant loss of particle size and strength. Furthermore, the loose and porous hardened cement mortar attached to the surface of the recycled aggregate makes the recycled aggregate lower in quality than the same volume of natural aggregate. Salts in seawater and sea sand can strengthen the interface transition zone between recycled coarse aggregate and improve the performance of the recycled aggregate. FRP bars are a fiber-reinforced polymer that is resistant to chloride erosion. Therefore, a novel FRP-reinforced seawater and sea sand recycled concrete structure, composed of seawater, sea sand, recycled aggregate, and FRP bars, holds great promise for future applications. Currently, research and application of seawater and sea sand recycled concrete is limited, and its application in practical engineering is urgently needed.

[0005] Current research indicates that the bearing capacity and stiffness of FRP-reinforced seawater and sand recycled concrete components are generally low, hindering the durability of FRP-reinforced concrete structures. Traditional rectangular stirrups require FRP bars three to four times the area of steel reinforcement to achieve mechanical properties similar to reinforced concrete. This results in excessive material consumption and is uneconomical. Furthermore, the excessive reinforcement area can lead to construction difficulties and difficulties in concrete pouring. Existing FRP bars are also used in longitudinal reinforcement, and the stirrups are still rectangular. This problem remains unresolved. Summary of the Invention

[0006] Due to the shortage of fresh water, river sand and natural coarse aggregate resources, the use of seawater and sea sand concrete can easily cause steel bars to rust and be difficult to restore. Simply using FRP bars instead of steel bars will result in large deformation problems.

[0007] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for preparing truss-type GFRP bar seawater and sea sand recycled concrete beams, which can solve the defect of low stiffness of FRP bar reinforced concrete beams by using truss-type reinforcement.

[0008] The present invention provides a truss-type GFRP reinforced seawater and sea sand recycled concrete beam, comprising a truss-type FRP reinforcement cage and a seawater and sea sand recycled concrete shell; wherein the truss-type FRP reinforcement cage is located inside, and the seawater and sea sand recycled concrete shell is located outside the reinforcement cage;

[0009] Wherein, the truss-type FRP reinforcement cage includes longitudinal reinforcement, stirrups, and plane diagonal reinforcement;

[0010] The longitudinal reinforcement includes longitudinal compression reinforcement and longitudinal tension reinforcement;

[0011] Among them, the stirrups are located at the outermost layer of the truss-type reinforcement cage, the longitudinal reinforcement is located on the inner side of the stirrups, the plane oblique reinforcement is located inside the longitudinal reinforcement, and the plane oblique reinforcement provides support for the longitudinal compression reinforcement and the longitudinal tension reinforcement in the plane.

[0012] A method for preparing a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam, which is used for a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam described in any part of the present invention, wherein the method for preparing a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam comprises the following steps:

[0013] Step 1: Mix recycled aggregate, sea sand, artificial simulated sea water, water reducer and Portland cement to make seawater and sea sand recycled concrete;

[0014] Step 2: Install the bottom template;

[0015] Step 3: Lay longitudinal reinforcement and stirrups; the stirrups are located on the outermost layer, and the longitudinal reinforcement is placed at the four corners inside the stirrups;

[0016] Step 4: Lay the planar oblique reinforcement. The planar oblique reinforcement is placed on the upper layer of the longitudinal reinforcement. In order to connect the planar oblique reinforcement with the longitudinal reinforcement, hooks are formed at both ends of the planar oblique reinforcement. The planar oblique reinforcement and the longitudinal reinforcement are in the same plane. The horizontal section formed by the hooks is connected to the longitudinal reinforcement with wire.

[0017] Step 5: Install side formwork;

[0018] Step 6: Pour the mixed seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a beam specimen, and then send the specimen to the curing room for standard curing;

[0019] Step 7: When the curing time is up, remove the formwork and take out the test block.

[0020] Furthermore, the longitudinal reinforcement, the stirrups, and the planar oblique reinforcement are all made of a type of FRP reinforcement; wherein the type of FRP reinforcement includes one or more of basalt fiber reinforced composite reinforcement, glass fiber reinforced composite reinforcement, and carbon fiber reinforced composite reinforcement.

[0021] Furthermore, the working strength of the FRP bar is designed according to the following formula:

[0022]

[0023] Among them, ξ fb is the height of the relative compression zone; α1 and β1 are the equivalent rectangular stress diagram coefficients; ε cu is the ultimate compressive strain of concrete; f fd is the design strength of FRP reinforcement; E f is the elastic modulus of FRP reinforcement; ρ fb is the limit reinforcement ratio; f c is the axial compressive strength of concrete; is the strain in the compression zone; h is the distance between the edge of the concrete compression zone and the center of the compression steel bar; of is the distance from the center of the tensile reinforcement to the edge of the concrete compression zone; f′ fd is the design strength of FRP bars in the compression zone; is the elastic modulus of FRP reinforcement in the compression zone; ρ fd is the revised reinforcement ratio; is the area of FRP reinforcement in the compression zone; b is the cross-sectional width; f te is the strength of the modified FRP reinforcement; ρ fis the FRP reinforcement ratio; m is the fitting coefficient, which is related to the connection mode of the steel cage and is taken as 1 here; α is the oblique angle between the stirrups and the longitudinal reinforcement; ε fd is the strain coefficient of the FRP reinforcement. x is the height of the equivalent rectangular stress diagram in the concrete compression zone; M is the design value of the bending moment.

[0024] Furthermore, in step 2, the required longitudinal reinforcement, the stirrups, and the planar oblique reinforcement are prefabricated in advance and when making the template, the longitudinal reinforcement, the stirrups, and the planar oblique reinforcement are tied as a whole and placed in the template.

[0025] Furthermore, the water-cement ratio of the seawater and sea sand recycled concrete in step 1 is 0.47; the composition of the seawater and sea sand recycled concrete includes, by weight: 319 parts of Portland cement, 819 parts of sea sand, 1099 parts of coarse aggregate, 150 parts of water, and 3.19 parts of water reducer.

[0026] Furthermore, the production process of the seawater and sea sand recycled concrete includes: mixing by dry mixing, first dry mixing the cement and recycled aggregate for 90 seconds to ensure uniform mixing, then adding 90% of mixing water into the mixer and stirring for about 90 seconds, then adding 10% of mixing water and a water reducer and stirring for 90 seconds before pouring into the mold.

[0027] Furthermore, the cement in step 1 was sampled as 42.5 grade Portland cement.

[0028] Furthermore, the sea sand in step 1 includes one or a mixture of regenerated sand, river sand, and shell sand, and the mixed regenerated aggregate in step 1 includes construction waste that is crushed and recycled from buildings.

[0029] Furthermore, the curing method of the seawater and sea sand recycled concrete beam in step 6 includes: wetting the wooden formwork in advance to prevent the wooden formwork from absorbing moisture in the concrete during pouring, then pouring the seawater and sea sand recycled concrete beam into the wooden formwork, covering the surface of the seawater and sea sand recycled concrete beam with a plastic film to delay moisture evaporation, removing the wooden formwork after 7 to 9 days, covering the surface of the seawater and sea sand recycled concrete beam with a film, and sprinkling water to cure it for 21 to 25 days before use; the temperature is controlled at 20°C ± 2°C, and the relative humidity is 94.5 to 95.5%.

[0030] The present invention has the following advantages:

[0031] The innovative feature of the technical solution of the present invention lies in the use of a truss-type FRP reinforcement cage instead of a traditional rectangular stirrup cage, while maintaining the same total reinforcement ratio. Using a truss-type FRP reinforcement cage instead of a traditional rectangular stirrup cage effectively increases the stiffness and bearing capacity of concrete beams, fully utilizing the corrosion resistance and tensile strength of FRP bars, and is more conducive to the application of FRP bars in concrete beam components. Plane truss FRP bars can inhibit the development of diagonal cracks and provide concrete beams with higher shear resistance. The use of a truss-type reinforcement method can also effectively improve the low elastic modulus of FRP bars, increasing the stiffness and bearing capacity of FRP bars in reinforcing seawater and sea sand recycled concrete beams, giving them excellent durability (corrosion resistance, impermeability, and freeze-thaw cycle resistance) that ordinary concrete does not have. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the reinforcement construction drawing of the stirrup beam referenced by the present invention.

[0033] Figure 2 This invention guarantees Figure 1 Construction drawing of equivalent truss reinforced beam formed under the premise of the same stirrup ratio.

[0034] Figure 3 This is a three-dimensional reinforcement diagram of the truss-type GFRP-reinforced seawater and sea sand recycled concrete beam of the present invention.

[0035] Figure 4 Detailed diagram of the truss FRP reinforcement cage of the truss GFRP reinforced seawater and sea sand recycled concrete beam of the present invention.

[0036] Figure 5 It is a schematic diagram of the theoretical calculation of the present invention.

[0037] Among them, 1-truss-type GFRP reinforced seawater and sea sand recycled concrete beam; 1.1-truss-type FRP reinforcement cage, 1.11-plane inclined reinforcement, 1.12-stirrups, 1.13-longitudinal reinforcement. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this application belongs.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] Figure 1 This is the reinforcement construction drawing of the reference rectangular stirrup beam of the present invention; wherein the stirrups 1.12, the longitudinal reinforcement 1.13, the spacing of the stirrups 1.12 in this reinforcement construction drawing is 60mm, and the diameter of the stirrups 1.12 is 8mm.

[0042] Figure 2 This invention guarantees Figure 1 Construction drawings of an equivalent truss-type reinforced beam with the same stirrup ratio. The planar diagonal bars (1.11) and stirrups (1.12) are spaced 100mm apart and have a diameter of 8mm. The longitudinal bars (1.13) and planar diagonal bars (1.11) are located inboard of the longitudinal bars (1.13) and in the same plane as the upper and lower longitudinal bars (1.13). To facilitate tying during construction, the planar diagonal bars (1.11), stirrups (1.12), and longitudinal bars (1.13) form an integrally loaded reinforcement cage. The ends of the planar diagonal bars (1.11) are bent horizontally for a certain length and tied parallel to the upper and lower longitudinal bars (1.13). Because the bent length of the planar diagonal bars (1.11) is less than the lap length specified in the "GB 50608-2020 Technical Standard for the Engineering Application of Fiber-Reinforced Composite Materials," their contribution to the beam's load is not considered in the actual load calculations. The diameter of the planar diagonal bars (1.11) is 8mm.

[0043] Figure 3 This is a three-dimensional reinforcement diagram of the truss-type GFRP reinforced seawater and sea sand recycled concrete beam of the present invention; the beam truss-type FRP reinforcement cage 1.1 of this embodiment includes stirrups 1.12, longitudinal reinforcements 1.13, and flat FRP diagonal reinforcements, wherein the stirrups 1.12 are located at the outermost side, the longitudinal reinforcements 1.13 are located inside the stirrups 1.12, and the flat FRP diagonal reinforcements are located between the upper and lower longitudinal reinforcements 1.13 to form diagonal support.

[0044] Figure 4 This is a detailed diagram of the truss FRP cage of the truss GFRP reinforced seawater and sea sand recycled concrete beam of the present invention; the truss FRP cage 1.1 consists of three parts: plane oblique reinforcement 1.11, stirrups 1.12, and longitudinal reinforcement 1.13. The stirrups 1.12 are located in the outermost layer, the longitudinal reinforcement 1.13 is located above (inside) the stirrups 1.12, and the plane FRP reinforcement is located above the longitudinal reinforcement 1.13.

[0045] Figure 5 is a schematic diagram of the theoretical calculation of the present invention; wherein, ξ fb is the height of the relative compression zone; α1 and β1 are the equivalent rectangular stress diagram coefficients; ε cu is the ultimate compressive strain of concrete; f fd is the design strength of FRP reinforcement; E f is the elastic modulus of FRP reinforcement; ρ fb is the limit reinforcement ratio; f c is the axial compressive strength of concrete; is the strain in the compression zone; h is the distance between the edge of the concrete compression zone and the center of the compression steel bar; of is the distance from the center of the tensile reinforcement to the edge of the concrete compression zone; f′ fd is the design strength of FRP bars in the compression zone; is the elastic modulus of FRP reinforcement in the compression zone; ρ fd is the revised reinforcement ratio; is the area of FRP reinforcement in the compression zone; b is the cross-sectional width; f te is the strength of the modified FRP reinforcement; ρ f is the FRP reinforcement ratio; m is the fitting coefficient, which is related to the connection mode of the steel cage and is taken as 1 here; α is the oblique angle between the stirrup 1.12 and the longitudinal reinforcement 1.13; ε fd is the strain coefficient of the FRP reinforcement. x is the height of the equivalent rectangular stress diagram in the concrete compression zone; M is the design value of the bending moment; and x0 is the distance from the edge of the concrete compression zone to the neutral axis.

[0046] The present invention provides a truss-type GFRP reinforced seawater and sea sand recycled concrete beam, comprising a truss-type FRP reinforcement cage 1.1 and a seawater and sea sand recycled concrete shell; wherein the truss-type FRP reinforcement cage 1.1 is located inside, and the seawater and sea sand recycled concrete shell is located outside the reinforcement cage;

[0047] The truss-type FRP reinforcement cage 1.1 includes longitudinal reinforcement 1.13, stirrups 1.12, and plane diagonal reinforcement 1.11;

[0048] The longitudinal reinforcement 1.13 includes longitudinal compression reinforcement and longitudinal tension reinforcement;

[0049] Among them, the stirrups 1.12 are located at the outermost layer of the truss-type reinforcement cage, the longitudinal reinforcement 1.13 is located inside the stirrups 1.12, and the plane oblique reinforcement 1.11 is located inside the longitudinal reinforcement 1.13. The plane oblique reinforcement 1.11 provides support for the longitudinal compression reinforcement and the longitudinal tension reinforcement in the plane.

[0050] The present invention provides a method for preparing a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam, which is used for a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam described in any part of the present invention, wherein the method for preparing a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam comprises the following steps:

[0051] Step 1: Mix recycled aggregate, sea sand, artificial simulated sea water, water reducer and Portland cement to make seawater and sea sand recycled concrete;

[0052] Step 2: Install the bottom template;

[0053] Step 3: Lay longitudinal reinforcement 1.13 and stirrups 1.12; stirrups 1.12 are located on the outermost layer, and longitudinal reinforcement 1.13 is placed at the four corners inside stirrups 1.12;

[0054] Step 4: Lay the planar oblique reinforcement 1.11. Place the planar oblique reinforcement 1.11 on the upper layer of the longitudinal reinforcement 1.13. To connect the planar oblique reinforcement 1.11 with the longitudinal reinforcement 1.13, form hooks at both ends of the planar oblique reinforcement 1.11. The planar oblique reinforcement 1.11 and the longitudinal reinforcement 1.13 are in the same plane. The horizontal section formed by the hooks is connected to the longitudinal reinforcement 1.13 with wire.

[0055] Step 5: Install side formwork;

[0056] Step 6: Pour the mixed seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a beam specimen, and then send the specimen to the curing room for standard curing;

[0057] Step 7: When the curing time is up, remove the formwork and take out the test block.

[0058] Furthermore, the longitudinal reinforcement 1.13, the stirrups 1.12, and the planar oblique reinforcement 1.11 are all made of a type of FRP reinforcement; wherein the type of FRP reinforcement includes one or more of basalt fiber reinforced composite reinforcement, glass fiber reinforced composite reinforcement, and carbon fiber reinforced composite reinforcement.

[0059] Furthermore, the working strength of the FRP bar is designed according to the following formula:

[0060]

[0061] Among them, ξ fb is the height of the relative compression zone; α1 and β1 are the equivalent rectangular stress diagram coefficients; ε cu is the ultimate compressive strain of concrete; f fd is the design strength of FRP reinforcement; E f is the elastic modulus of FRP reinforcement; ρ fbis the limit reinforcement ratio; f c is the axial compressive strength of concrete; is the strain in the compression zone; h is the distance between the edge of the concrete compression zone and the center of the compression steel bar; of is the distance from the center of the tensile reinforcement to the edge of the concrete compression zone; f′ fd is the design strength of FRP bars in the compression zone; is the elastic modulus of FRP reinforcement in the compression zone; ρ fd is the revised reinforcement ratio; is the area of FRP reinforcement in the compression zone; b is the cross-sectional width; f te is the strength of the modified FRP reinforcement; ρ f is the FRP reinforcement ratio; m is the fitting coefficient, which is related to the connection mode of the steel cage and is taken as 1 here; α is the angle between the oblique stirrup 1.12 and the longitudinal reinforcement; ε fd is the strain coefficient of the FRP reinforcement. x is the height of the equivalent rectangular stress diagram in the concrete compression zone; M is the design value of the bending moment.

[0062] Furthermore, in step 2, the required longitudinal reinforcement 1.13, the stirrups 1.12, and the planar oblique reinforcement 1.11 are prefabricated in advance and tied together as a whole and placed in the template when making the template.

[0063] Furthermore, the water-cement ratio of the seawater and sea sand recycled concrete in step 1 is 0.47; the composition of the seawater and sea sand recycled concrete includes, by weight: 319 parts of Portland cement, 819 parts of sea sand, 1099 parts of coarse aggregate, 150 parts of water, and 3.19 parts of water reducer.

[0064] Furthermore, the production process of the seawater and sea sand recycled concrete includes: mixing by dry mixing, first dry mixing the cement and recycled aggregate for 90 seconds to ensure uniform mixing, then adding 90% of mixing water into the mixer and stirring for about 90 seconds, then adding 10% of mixing water and a water reducer and stirring for 90 seconds before pouring into the mold.

[0065] Furthermore, the cement in step 1 was sampled as 42.5 grade Portland cement.

[0066] Furthermore, the sea sand in step 1 includes one or a mixture of regenerated sand, river sand, and shell sand, and the mixed regenerated aggregate in step 1 includes construction waste that is crushed and recycled from buildings.

[0067] Furthermore, the curing method of the seawater and sea sand recycled concrete beam in step 6 includes: wetting the wooden formwork in advance to prevent the wooden formwork from absorbing moisture in the concrete during pouring, then pouring the seawater and sea sand recycled concrete beam into the wooden formwork, covering the surface of the seawater and sea sand recycled concrete beam with a plastic film to delay moisture evaporation, removing the wooden formwork after 7 days, covering the surface of the seawater and sea sand recycled concrete beam with a film, and sprinkling water for curing for 21 days before use; the temperature is controlled at 20°C ± 2°C, and the relative humidity is 95%.

[0068] The parameters of the present invention applied to actual engineering products are as follows:

[0069] The sea sand used in the present invention can be replaced by one or more of reclaimed sand, river sand, and shell sand. When sea sand is used as an aggregate for concrete, it should comply with the relevant provisions of the "JGJ 206-2010 Technical Specification for the Application of Sea Sand Concrete". The sea sand used to prepare concrete should be purified, and the particle size distribution of the sea sand should comply with the relevant requirements of the "JGJ 206-2010 Technical Specification for the Application of Sea Sand Concrete".

[0070] Among them, the test methods for quality inspection of sea sand and recycled coarse aggregate should comply with the provisions of the current industry standard "Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete" JGJ 52.

[0071] The water-cement ratio of the seawater and sea sand recycled concrete sampled in the present invention is 0.47; wherein, the composition of the seawater and sea sand recycled concrete includes the following contents in parts by weight:

[0072] 319 parts of Portland cement, 819 parts of sea sand, 1099 parts of coarse aggregate, 150 parts of water, and 3.19 parts of water reducer.

[0073] Among them, the specific parameters of seawater and sea sand recycled concrete are shown in Table 1:

[0074]

[0075] Table 1 SSRAC concrete mix proportion

[0076] The present invention provides a method for assembling a truss-type FRP reinforcement cage 1.1, comprising: longitudinal reinforcement 1.13, stirrups 1.12, and planar diagonal reinforcement 1.11. The rectangular stirrups 1.12 are positioned on the outermost sides, the longitudinal reinforcement 1.13 is positioned inwardly of the stirrups 1.12, and the planar diagonal reinforcement 1.11 is positioned between the upper and lower longitudinal reinforcements 1.13. The ends of the planar diagonal reinforcements 1.11 are formed into straight hooks to facilitate binding with the longitudinal reinforcements 1.13. Thus, the longitudinal reinforcements 1.13, stirrups 1.12, and planar diagonal reinforcements form an integrally loaded truss-type FRP reinforcement cage 1.1. The longitudinal reinforcements 1.13 have a diameter of 14 mm, while the stirrups 1.12 and planar diagonal reinforcements 1.11 have diameters of 8 mm. The tensile strength of the 8mm GFRP bar is 1281MPa, the elastic modulus is 56.2GPa, and the ultimate strain is 0.0228; the tensile strength of the 14mm GFRP bar is 978MPa, the elastic modulus is 52.9GPa, and the ultimate strain is 0.0185.

[0077] The basic parameters of a truss-type FRP reinforcement cage 1.1 in the embodiment of the present invention are set as follows:

[0078] ε cu =0.0044,f fd =1176MPa, E f =84500MPa,f c =20.7MPa,ε fd =0.014, stirrup 1.12 diameter is 8mm, longitudinal reinforcement diameter is 2D12mm, ρ f =0.084, the cross-sectional dimensions are 150×300mm. Substitute the above parameters into the formula for calculation:

[0079]

[0080] The designed beam reinforcement ratio is greater than 1.5 times the limit reinforcement ratio, which is over-reinforced.

[0081]

[0082]

[0083] Where a is the lever arm, which corresponds to the distance from the support to the loading point; V is the bending moment M and the force corresponding to the lever arm a.

[0084] The bearing capacities under other working conditions can be obtained in the same way, and are summarized in Table 2.

[0085]

[0086]

[0087] Table 2 Summary of theoretical calculation values of four-point bending bearing capacity of truss-type GFRP reinforced seawater and sea sand recycled concrete beams

[0088] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A truss-type GFRP reinforced seawater and sea sand recycled concrete beam, characterized in that: It includes a truss-type FRP reinforcement cage and a seawater and sea sand recycled concrete shell; wherein the truss-type FRP reinforcement cage is located inside, and the seawater and sea sand recycled concrete shell is located outside the reinforcement cage; The truss-type FRP reinforcement cage includes longitudinal reinforcement, stirrups, and plane diagonal reinforcement; wherein the longitudinal reinforcement includes longitudinal compression reinforcement and longitudinal tension reinforcement; Among them, the stirrups are located at the outermost layer of the truss-type reinforcement cage, the longitudinal reinforcement is located inside the stirrups, the plane oblique reinforcement is located inside the longitudinal reinforcement, and the plane oblique reinforcement provides support for the longitudinal reinforcement in the plane.

2. A method for preparing a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam, used to prepare the truss-type GFRP-reinforced seawater and sea sand recycled concrete beam according to claim 1, characterized in that: The method for preparing a truss-type GFRP-reinforced seawater and sea sand recycled concrete beam comprises the following steps: Step 1: Mix recycled aggregate, sea sand, artificial simulated sea water, water reducer and Portland cement to make seawater and sea sand recycled concrete; Step 2: Install the bottom template; Step 3: Lay longitudinal reinforcement and stirrups; the stirrups are located on the outermost layer of longitudinal reinforcement and are placed on the four corners inside the stirrups; Step 4: Lay the planar oblique reinforcement. The planar oblique reinforcement is placed on the upper layer of the longitudinal reinforcement. In order to connect the planar oblique reinforcement with the longitudinal reinforcement, hooks are formed at both ends of the planar oblique reinforcement. The planar oblique reinforcement and the longitudinal reinforcement are in the same plane. The horizontal section formed by the hooks is connected to the longitudinal reinforcement with wire. Step 5: Install side formwork; Step 6: Pour the mixed seawater and sea sand recycled concrete into the mold, wait until the concrete pouring is completed to form a beam specimen, and then send the specimen to the curing room for standard curing; Step 7: When the curing time is up, remove the formwork and take out the test block.

3. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 2, characterized in that: The longitudinal reinforcement, the stirrups and the plane oblique reinforcement are all made of a kind of FRP reinforcement; wherein the kind of FRP reinforcement includes one or more of basalt fiber reinforced composite reinforcement, glass fiber reinforced composite reinforcement and carbon fiber reinforced composite reinforcement.

4. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 3, characterized in that: The working strength of the FRP reinforcement is designed according to the following formula: Among them, ξ fb is the height of the relative compression zone; α1 and β1 are the equivalent rectangular stress diagram coefficients; ε cu is the ultimate compressive strain of concrete; f fd is the design strength of FRP reinforcement; E f is the elastic modulus of FRP reinforcement; ρ fb is the limit reinforcement ratio; f c is the axial compressive strength of concrete; is the strain in the compression zone; h is the distance between the edge of the concrete compression zone and the center of the compression steel bar; of is the distance from the center of the tensile reinforcement to the edge of the concrete compression zone; is the design strength of FRP bars in the compression zone; is the elastic modulus of FRP reinforcement in the compression zone; ρ fd is the revised reinforcement ratio; is the area of FRP reinforcement in the compression zone; b is the cross-sectional width; f te is the strength of the modified FRP reinforcement; ρ f is the FRP reinforcement ratio; m is the fitting coefficient, which is taken as 1 here; α is the oblique angle between the stirrups and the longitudinal reinforcement; ε fd is the strain coefficient of the FRP tendon; x is the height of the equivalent rectangular stress diagram in the concrete compression zone; M is the design value of the bending moment.

5. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 2, characterized in that: In step 2, the required longitudinal reinforcement, stirrups, and planar oblique reinforcement are prefabricated in advance and when making the template, the longitudinal reinforcement, stirrups, and planar oblique reinforcement are tied as a whole and placed in the template.

6. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 2, characterized in that: The water-cement ratio of the seawater and sea sand recycled concrete in step 1 is 0.47; the composition of the seawater and sea sand recycled concrete includes, by weight: 319 parts of Portland cement, 819 parts of sea sand, 1099 parts of coarse aggregate, 150 parts of water, and 3.19 parts of water reducer.

7. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 6, characterized in that: The production process of the seawater and sea sand recycled concrete includes: mixing by dry mixing, first dry mixing cement and recycled aggregate for 90 seconds to ensure uniform mixing, then adding 90% mixing water into the mixer and stirring for about 90 seconds, then adding 10% mixing water and water reducing agent and stirring for 90 seconds before pouring into the mold.

8. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 6, characterized in that: The cement in step 1 was sampled from 42.5 grade Portland cement.

9. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 6, characterized in that: The sea sand in step 1 includes one or a mixture of regenerated sand, river sand, and shell sand, and the mixed regenerated aggregate in step 1 includes construction waste that is crushed and recycled from buildings.

10. The method for preparing a truss-type GFRP reinforced seawater and sea sand recycled concrete beam according to claim 2, characterized in that: The curing method of the seawater and sea sand recycled concrete beam in step 6 includes: wetting the wooden formwork in advance to prevent the wooden formwork from absorbing moisture in the concrete during pouring, then pouring the seawater and sea sand recycled concrete beam into the wooden formwork, covering the surface of the seawater and sea sand recycled concrete beam with a plastic film to delay moisture evaporation, removing the wooden formwork after 7 to 9 days, covering the surface of the seawater and sea sand recycled concrete beam with a film, and sprinkling water to cure it for 21 to 25 days before use; the temperature is controlled at 20°C ± 2°C, and the relative humidity is 94.5 to 95.5%.

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