Steel bar and steel fiber recycled concrete shear beam and performance verification method
By adding steel fibers and recycled aggregates to recycled concrete, a steel fiber reinforced recycled concrete shear beam was designed, which solved the problem of poor structural stability of recycled concrete in load-bearing components, provided an effective performance verification method, and improved the toughness and load-bearing capacity of the beam.
Patent Information
- Application Number
- CN202510597282.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-09
- Publication Date
- 2025-11-07
AI Technical Summary
Existing recycled concrete exhibits poor structural stability in load-bearing components, and there is a lack of effective performance verification methods.
Design a steel fiber-reinforced recycled concrete shear beam comprising a steel reinforcement skeleton and a concrete composite layer, wherein 0.5%-1.5% steel fiber is added to the concrete, and the recycled fine aggregate and recycled coarse aggregate are replaced by 50%-100% of the steel fiber. The performance is verified through specific test methods.
Reinforced steel fiber recycled concrete beams exhibit a failure mode similar to that of ordinary concrete during shear stress, which improves the toughness and load-bearing capacity of the structure and provides a feasible performance verification method.
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Figure CN120907956A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of building structures, and particularly relates to a steel fiber reinforced recycled concrete shear beam and a performance verification method thereof. BACKGROUND
[0002] The new concrete is formed by mixing the construction waste after cleaning and grading, sand and gravel in a certain proportion and grading, part or all of natural aggregates such as sand and gravel, cement, water and the like.
[0003] At present, there is a lack of concrete shear beams that can be used as load-bearing members and have stable structural performance, and there is also a lack of performance verification methods for the concrete shear beams. SUMMARY
[0004] The present application aims to provide a steel fiber reinforced recycled concrete shear beam and a performance verification method thereof to solve the problems in the background art.
[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions.
[0006] The steel fiber reinforced recycled concrete shear beam comprises a steel reinforcement framework and a concrete mixed layer arranged in and outside the steel reinforcement framework, the concrete mixed layer comprises concrete, steel fibers with a volume rate of 0.5%-1.5%, recycled fine aggregates with a replacement rate of 50%-100% and recycled coarse aggregates with a replacement rate of 50%-100%, the steel reinforcement framework comprises steel bars extending longitudinally and arranged along the edge line of the shear beam and stirrups distributed along the longitudinal direction, and the stirrup spacing is 150mm-250mm.
[0007] The performance verification method of the steel fiber reinforced recycled concrete shear beam comprises the following steps.
[0008] (1) Test specimen design: 13 beams of steel fiber reinforced recycled aggregate concrete were designed for shear test. The concrete compressive strength grade of the steel reinforced concrete beam was C50, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, the stirrup spacing was 200 mm, and the number was C50F0RF0. The different steel fiber volume fractions were 0%, 0.5%, 1.0%, and 1.5%, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, the stirrup spacing was 200 mm, and the numbers of the test beams were C50F0RF100, C50F05RF100, C50F10RF100, and C50F15RF100, respectively. The steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 0% and 50%, the coarse aggregate was natural gravel, the stirrup spacing was 200 mm, and the numbers of the test beams were C50F10RF0 and C50F10RF50, respectively. The steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 100%, the recycled coarse aggregate replacement rate was 50% and 100%, the stirrup spacing was 200 mm, and the numbers of the test beams were C50F10RF100RC50 and C50F10RF100RC100, respectively. The concrete compressive strength grades were C30 and C70, the steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, the stirrup spacing was 200 mm, and the numbers of the test beams were C30F10RF100 and C70F10RF100, respectively. The stirrup spacing was 150 mm and 250 mm, the concrete compressive strength grade was C50, the steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, and the numbers of the test beams were C50F10RF100-1 and C50F10RF100-3, respectively.
[0009] (2) Test specimen production: The test specimens were produced and poured in the laboratory according to the designed mix proportion, and watered for 28 days. Six standard cubic test blocks and six prism test blocks were produced for each test specimen, and the standard test blocks and test specimens were cured under the same conditions for 28 days.
[0010] (3) Test loading device: one end of the test beam support is a fixed hinge support, and the other end is a rolling hinge support, which can move appropriately in the horizontal direction; the test equipment uses a 200t electro-hydraulic servo instrument, which is equipped with a jack and a 1000kN spoke dual-channel load sensor as an auxiliary reaction force device, and the load is applied to the test beam through the distribution beam of the loading device; the formal loading adopts step loading, the loading rate is 0.5mm / min, each load is 20kN, and the holding time of each load is 5 minutes, and after the deflection is stable, the loading continues, and after the loading reaches 80% of the estimated value of the oblique crack, the load difference is reduced, and the load value of each level is changed to 10kN, so as to more accurately observe the appearance of the oblique crack; after the appearance of the oblique crack of the test piece, the normal loading is restored; after 90% of the calculated bearing capacity of the component, continuous slow loading is carried out;
[0011] (4) Deformation measuring point arrangement: a total of 7 strain type displacement sensors are arranged on each test beam, wherein 1 strain type displacement sensor is arranged at each of the two end supports, the mid-span section, the loading point, and the midpoint from the mid-span to the loading point;
[0012] (5) Strain gauge arrangement and pasting: the steel bar strain measuring point is arranged on the stirrup of the section of the line connecting the loading point and the support, and is symmetrically arranged on the left and right, and the size of the resistance strain gauge is 2mm×3mm, and a total of 6 are arranged;
[0013] (6) Crack observation: the crack observation under each load is carried out according to the following method: after the loading is stable, the surface of the test beam is wiped with cotton soaked in acetone, the appearance and development of the crack are observed, and the reading is read through the reading microscope; the newly found crack is numbered, the development of the crack is outlined near the crack, and the load value and the maximum crack width value when the crack appears are recorded on the record table; for the already appeared crack, the maximum crack width value is observed and recorded at each load; the crack width is recorded by drawing the crack development trend on the coordinate paper;
[0014] (7) Test procedure: before the test, the surface of the beam is brushed white, the white paste surface is dried, then a 50mm×100mm grid is popped out on the side of the beam with a ink hopper, then the beam is hoisted to the corresponding position and placed on the support, the positions of the measuring points are determined, then the displacement meter is installed, the wires of the strain gauges are connected to the joints of the DH3816N static strain acquisition instrument, and the resistance is checked; then the geometric centering method is used to install the mechanical jack, the wires of the 200t force sensor are connected to the DH3816N static strain acquisition instrument to measure the size of the force; after checking that all the wires and instruments are working properly, the test begins;
[0015] (8) Shear bearing capacity checking: the shear bearing capacity of the steel fiber recycled aggregate concrete beam is checked.
[0016] Preferably, the natural broken stone in step (1) has a particle size of 5-20 mm.
[0017] Preferably, the standard cube in step (2) has a size of 150 mm x 150 mm x 150 mm.
[0018] Preferably, the standard prism in step (2) has a size of 150 mm x 150 mm x 300 mm.
[0019] Preferably, in step (3), a preloading test is performed before formal loading to ensure that the test piece is in good contact with each part of the equipment and to verify that the measuring instrument is working normally, the preloading load value is set to 40 kN, each level is 10 kN, and the loading rate is 0.5 mm / min.
[0020] Compared with the prior art, the present application has the following beneficial effects:
[0021] The present application provides a reinforced steel fiber recycled concrete shear beam and a performance verification method thereof.
[0022] The following conclusions are drawn through the verification method:
[0023] (1) The shear failure process of the reinforced steel fiber recycled aggregate concrete beam is similar to that of the ordinary reinforced concrete beam, both have an elastic stage and a non-elastic stage, and the application of the reinforced steel fiber recycled aggregate concrete beam to engineering practice is feasible;
[0024] (2) The stirrups at the intersection with the inclined cracks reach the yield strength, the stirrups not intersecting with the inclined cracks do not reach the yield strength, and the shear failure of the reinforced steel fiber recycled aggregate concrete beam belongs to typical shear-compression failure;
[0025] (3) The diagonal section cracking load of the reinforced steel fiber recycled aggregate concrete beam is greater than that of the ordinary reinforced concrete beam, the steel fiber volume fraction of the beam is 1.0%, and the shear bearing capacity of the beam with a recycled coarse aggregate and a recycled fine aggregate replacement rate of 100% is slightly less than that of the ordinary reinforced concrete beam. BRIEF DESCRIPTION OF DRAWINGS
[0026] Figure 1 is a diagonal section beam reinforcement diagram of the present application;
[0027] Figure 2 is a schematic diagram of a diagonal section test beam loading device of the present application;
[0028] Figure 3 is a failure mode of the beam of the present application;
[0029] Figure 4 is a load-stirrup strain curve of the present application;
[0030] Figure 5Load-mid-span deflection curve of the present application. DETAILED DESCRIPTION
[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.
[0032] Embodiment 1
[0033] The steel fiber reinforced recycled concrete shear beam, as shown in Figure 1 , comprises a steel reinforcement framework and a concrete mixed layer 1 arranged inside and outside the steel reinforcement framework, the concrete mixed layer comprises concrete, steel fibers with a volume fraction of 0.5%-1.5%, recycled fine aggregates with a replacement rate of 50%-100%, and recycled coarse aggregates with a replacement rate of 50%-100%, the steel reinforcement framework comprises steel bars 3 extending longitudinally and arranged along the edges of the shear beam, and stirrups 2 distributed along the longitudinal direction, and the stirrup spacing is 150mm-250mm.
[0034] In this embodiment, the concrete can be C30, C50 or C70 concrete according to the requirement, the volume fraction of the steel fibers can be 0.5%, 1.0% or 1.5% according to the requirement, the replacement rate of the recycled fine aggregates can be 50%, 70% or 100% according to the requirement, the replacement rate of the recycled coarse aggregates can be 50%, 70% or 100% according to the requirement, the steel reinforcement framework comprises steel bars extending longitudinally and arranged along the edges of the shear beam, and stirrups distributed along the longitudinal direction, and the stirrup spacing is 150mm, 200mm or 200mm, Figure 1 , and Figure 2 three steel fiber reinforced recycled concrete shear beams in , the stirrup spacing from top to bottom is 150mm, 200mm and 250mm respectively.
[0035] Embodiment 2
[0036] A performance verification method of a steel fiber reinforced recycled concrete shear beam, as shown in Figures 1-5 , comprises the following steps:
[0037] (1) Test piece design: 13 beams of reinforced steel fiber recycled aggregate concrete were designed for shear test, among which the concrete compressive strength grade of the reinforced concrete beam was C50, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, the stirrup spacing was 200mm, and the number was C50F0RF0; the different steel fiber volume fractions were 0%, 0.5%, 1.0% and 1.5%, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, the stirrup spacing was 200mm, and the numbers of the test beams were C50F0RF100, C50F05RF100, C50F10RF100 and C50F15RF100 respectively; the steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 0% and 50%, the coarse aggregate was natural gravel, the stirrup spacing was 200mm, and the numbers of the test beams were C50F10RF0 and C50F10RF50 respectively; the steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 100%, the recycled coarse aggregate replacement rate was 50% and 100%, the stirrup spacing was 200mm, and the numbers of the test beams were C50F10RF100RC50 and C50F10RF100RC100 respectively; the concrete compressive strength grades were C30 and C70, the steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, the stirrup spacing was 200mm, and the numbers of the test beams were C30F10RF100 and C70F10RF100 respectively; the stirrup spacing was 150mm and 250mm, the concrete compressive strength grade was C50, the steel fiber volume fraction was 1.0%, the recycled fine aggregate replacement rate was 100%, the coarse aggregate was natural gravel, and the numbers of the test beams were C50F10RF100-1 and C50F10RF100-3 respectively;
[0038] (2) Test piece production: The test pieces were produced and poured in the laboratory according to the designed mixing proportion, and watered for 28 days, 6 standard cubic test blocks and 6 prism test blocks were produced for each test piece, and the standard test blocks and test pieces were cured under the same conditions for 28 days;
[0039] (3) Test loading device: one end of the test beam support is a fixed hinge support 4, and the other end is a rolling hinge support 6, which can move appropriately in the horizontal direction; the test equipment uses a 200t electro-hydraulic servo instrument, which is equipped with a jack and a 1000kN spoke double-channel load sensor as an auxiliary reaction force device, and the load is applied to the test beam through the distribution beam of the loading device; the formal loading adopts step loading, the loading rate is 0.5mm / min, each load is 20kN, and the holding time of each load is 5 minutes, and after the deflection is stable, the loading continues, and after the loading reaches 80% of the estimated value of the oblique crack, the load difference is reduced, and the loading value is changed to 10kN, so as to more accurately observe the appearance of the oblique crack; after the appearance of the oblique crack of the test piece, the normal loading is restored; after 90% of the calculated bearing capacity of the component, continuous and slow loading is carried out;
[0040] (4) Deformation measuring point arrangement: a total of 7 strain displacement sensors are arranged on each test beam, wherein 1 strain displacement sensor is arranged at each of the two end supports, the mid-span section, the loading point, and the midpoint from the mid-span to the loading point, Figure 1 Figure 2 The middle arrow indicates the loading direction at the loading point, and the strain displacement sensor at the loading point is located at the bottom of the test beam;
[0041] (5) Strain gauge arrangement and pasting: the steel bar strain measuring point is arranged on the stirrup at the section of the connecting line between the loading point and the support, and is symmetrically arranged on the left and right, with a size of 2mm×3mm resistance strain gauge 5, a total of 6;
[0042] (6) Crack observation: the crack observation under each load is carried out according to the following method: after the loading is stable, the test beam side surface concrete surface is wiped with cotton soaked with acetone, the appearance and development of the crack are observed, and the reading is read through the reading microscope; the newly found crack is numbered, the development of the crack is outlined near the crack, and the load value when the crack appears and the maximum crack width value are recorded on the record table; for the already appeared crack, the maximum crack width value is observed and recorded at each load; the crack width is recorded by drawing the crack development trend on the coordinate paper;
[0043] (7) Test procedure: before the test, the beam surface is brushed white, the white paste surface is dried, then a 50mm×100mm grid is popped out on the beam side with a ink hopper, then the beam is hoisted to the corresponding position on the support, the positions of the measuring points are determined, then the displacement meter is installed, the wires of the strain gauges are connected to the joints of the DH3816N static strain acquisition instrument, and the resistance is checked; then the geometric centering method is used to install the mechanical jack, the wires of the 200t force sensor are connected to the DH3816N static strain acquisition instrument to measure the force, and after checking that all the wires and instruments are working properly, the test begins;
[0044] (8) Shear capacity check: The shear capacity of the reinforced steel fiber recycled aggregate concrete beam is checked.
[0045] The natural crushed stone particle size in step (1) is 5-20 mm. The standard cubic size in step (2) is 150 mm x 150 mm x 150 mm. The standard prismatic size in step (2) is 150 mm x 150 mm x 300 mm. Step (3) further includes preloading and formal loading, both of which are loaded according to the pre-established loading system. After each level of loading is completed, the values are collected and recorded, and the development of the crack and the crack width are measured and recorded.
[0046] It should be noted that the other structures of the reinforced steel fiber recycled concrete shear beam shall meet the requirements of the Code for Design of Concrete Structures (GB 50010-2010).
[0047] The specific verification process is as follows:
[0048] The reinforced steel fiber recycled aggregate concrete beam shear test designs 13 beams, in which the concrete compressive strength grade is C50 reinforced concrete beam as the reference beam, the recycled fine aggregate replacement rate is 100%, the coarse aggregate is natural crushed stone, and the stirrup spacing is 200 mm, numbered as C50F0RF0. Different steel fiber volume fractions are 0%, 0.5%, 1.0%, and 1.5%, the recycled fine aggregate replacement rate is 100%, the coarse aggregate is natural crushed stone, and the stirrup spacing is 200 mm, corresponding to the test beam numbers C50F0RF100, C50F05RF100, C50F10RF100, and C50F15RF100, respectively. The steel fiber volume fraction is 1.0%, the recycled fine aggregate replacement rate is 0% and 50%, the coarse aggregate is natural crushed stone, and the stirrup spacing is 200 mm, corresponding to the test beam numbers C50F10RF0 and C50F10RF50, respectively. The steel fiber volume fraction is 1.0%, the recycled fine aggregate replacement rate is 100%, the recycled coarse aggregate replacement rate is 50% and 100%, and the stirrup spacing is 200 mm, corresponding to the test beam numbers C50F10RF100RC50 and C50F10RF100RC100, respectively. The concrete compressive strength grades are C30 and C70, the steel fiber volume fraction is 1.0%, the recycled fine aggregate replacement rate is 100%, the coarse aggregate is natural crushed stone, and the stirrup spacing is 200 mm, corresponding to the test beam numbers C30F10RF100 and C70F10RF100, respectively. The stirrup spacing is 150 mm and 250 mm, the concrete compressive strength grade is C50, the steel fiber volume fraction is 1.0%, the recycled fine aggregate replacement rate is 100%, and the coarse aggregate is natural crushed stone, corresponding to the test beam numbers C50F10RF100-1 and C50F10RF100-3, respectively.
[0049] The 13 shear beams in the experiment have a cross-sectional size of 150 mm x 300 mm, a length of 3000 mm, a span of 2700 mm, a protective layer thickness of 25 mm, and a shear span ratio of 2. All test beams are configured with 2 HRB400 straight reinforcement bars with a diameter of 8 mm, 4 longitudinal tension reinforcement bars with a diameter of 22 mm in the lower tension zone, and a protective layer thickness of 25 mm for longitudinal tension and compression reinforcement. The stirrups are made of HRB400 grade steel with a diameter of 8 mm, and the stirrup spacing is 150 mm, 200 mm, and 250 mm, respectively. The test parameters are shown in Table 1. The design longitudinal reinforcement diagram and cross-sectional reinforcement diagram of each specimen are shown in Figure 1 .
[0050] Table 1 Test Parameters
[0051]
[0052] Specimen Preparation
[0053] The specimens were cast and cured in the FRP laboratory of the New Building Materials and Structure Research Center of Zhengzhou University according to the designed mix proportion. Six cubic standard test blocks (150 mm x 150 mm x 150 mm) and six prismatic standard test blocks (150 mm x 150 mm x 300 mm) were prepared for each test block, and the standard test blocks were cured under the same conditions as the test blocks for 28 days.
[0054] Test Scheme
[0055] Test Loading Device
[0056] The test beam support is a fixed hinge support at one end and a rolling hinge support at the other end, which can move appropriately in the horizontal direction. The test equipment uses a 200t electro-hydraulic servo instrument, equipped with a jack and a 1000kN spoke dual-channel load sensor as an auxiliary reaction device. The load is applied to the test beam through the distribution beam of the loading device. Before formal loading, a preloading test is conducted to ensure that the test specimen and the equipment parts are in good contact, and to verify the normal operation of the measuring instruments. The preloading load value is set to 40kN, with each level of 10kN and a loading rate of 0.5mm / min. The formal loading uses a step loading method with a loading rate of 0.5mm / min, and each level of load is 20kN. Each level of load is held for 5 minutes, and after the deflection stabilizes, the loading is continued. When the loading reaches 80% of the estimated value of the oblique crack, the loading step difference is reduced, and the loading value is changed to 10kN for each level to more accurately observe the appearance of the oblique crack. After the appearance of the oblique crack in the test specimen, the normal loading is restored. After the calculated bearing capacity of the component reaches 90%, the loading is continuously and slowly applied. The test operation is strictly in accordance with the "Standard for Test Methods of Concrete Structures" (GB 50152-92). Figure 2The loading device for the beam is shown in the figure. The arrangement of the beam is shown in the figure. Figure 3
[0057] Arrangement of deformation measuring points: In order to determine the deflection of the beam during loading, 7 displacement meters are arranged on each test beam, including 1 strain displacement sensor at each end support, mid-span section, loading point, and midpoint between mid-span and loading point. The deflection table is polished smooth with sandpaper, then cleaned with acetone, and then glued with quick-drying glue 502 to ensure smoothness at the measuring point.
[0058] Strain gauge arrangement and adhesion: Steel strain measuring points are arranged on the stirrups at the intersection of the line connecting the loading point and the support, symmetrically arranged on the left and right, with one strain gauge on each steel bar.
[0059] Crack observation: The crack observation under each load is carried out according to the following method: after loading is stable, wipe the test beam side surface with acetone-soaked cotton, observe the appearance and development of cracks and read the readings through the reading microscope; number the new cracks found, outline the development of the cracks near the cracks, and record the load value and maximum crack width value when the cracks appear; for the cracks that have already appeared, observe the maximum crack width value and record the crack width value under each load; use coordinate paper to depict the crack development trend and record the crack width;
[0060] Test process: The test was conducted in the structure test room of the New Building Materials and Structure Research Center of Zhengzhou University from January 2025 to May 2025, lasting for 4 months.
[0061] Before the test, the surface of the beam was brushed white, and the grid of 50mm x 100mm was popped out on the side of the beam with an ink hopper after the white paste was fully dried. Then the beam was hoisted to the corresponding position on the support, the positions of the measuring points were determined, the displacement meters were installed, the leads of the strain gauges were connected to the connectors of the DH3816N static strain acquisition instrument, and the resistance was checked; then the geometric centering method was used to install the mechanical jack, the leads of the 200-ton force sensor were connected to the DH3816N static strain acquisition instrument to measure the force, and the test was started after checking that all the leads and instruments were working properly.
[0062] Before formal loading, preloading test is carried out to ensure that the test piece and the equipment are in good contact, and to verify the normal operation of the measuring instrument. The preloading load value is set to 40 kN, 10 kN per level, and the loading rate is 0.5 mm / min. Formal loading adopts step loading, the loading rate is 0.5 mm / min, the load of each level is 20 kN, and the holding time of each level is 5 minutes. After the deflection is stable, continue to load. When the load reaches 80% of the estimated value of oblique crack, reduce the loading interval, and change the loading value of each level to 10 kN, so as to more accurately observe the appearance of oblique cracks. After the oblique cracks of the test piece appear, resume normal loading. After 90% of the calculated bearing capacity of the component, continuously and slowly load.
[0063] Main results and analysis of the test:
[0064] Physical and mechanical properties of materials
[0065] The compressive strength, splitting tensile strength, axial compressive strength and elastic modulus of steel fiber recycled aggregate concrete are measured by the reserved 150mmx150mmx150mm cubic test block and 150mmx150mmx300mm prism test block. The tensile test of steel test piece should meet the requirements of the current national standard "Metallic Materials Tensile Test Part 1: Room Temperature Test Method" (GB / T228.1-2010). The test results are shown in Tables 2 and 3.
[0066] Table 2 Test results of main material properties of concrete
[0067]
[0068] Table 3 Mechanical properties of steel
[0069]
[0070] Development of cracks and failure mode
[0071] Figure 3The failure mode of the test beam is shown. Through the analysis of the test, it is found that the failure mode of all test beams is basically similar, which is shear compression failure. The vertical cracks of steel fiber reinforced recycled aggregate concrete beam first appear between the two loading points, and the cracks of the test beam develop rapidly along the height of the beam to the compression zone as the load further increases, and the number of cracks increases rapidly; as the load continues to increase, vertical cracks appear on the beam bottom in the shear span zone; when the load continues to increase, the vertical cracks in the beam bottom of the shear span zone develop obliquely to the loading point, forming a bending shear crack, and then an inclined shear crack is formed at the midpoint of the beam in the shear span zone; when the inclined shear crack appears, the inclined crack continuously extends and expands to the loading point and the support in two directions, accompanied by the appearance of new inclined cracks; when the ultimate load of the test beam is continuously approached, the inclined shear crack extends upward to the lower side of the loading point and downward to the vicinity of the support, and the width of the inclined crack rapidly increases at this time, at which time the hoop reinforcement at the maximum crack first yields, the steel fibers gradually pull out, and the aggregate interlocking force formed by the bonding of the steel fibers and the recycled aggregate concrete material rapidly decreases. Finally, under the combined action of normal stress and shear stress, the steel fiber recycled aggregate concrete at the top of the line connecting the upper end of the inclined crack and the loading point is crushed, and the test beam fails.
[0072] From Figure 3 As can be seen from C50F0RF100 and C50F05RF100 in Table 1, the recycled fine aggregate concrete beam without adding steel fiber is crushed in the compression zone, the crack width is large, and the damage is serious. After adding steel fiber, the recycled fine aggregate concrete beam produces a lot of vertical cracks and inclined cracks, and the crack spacing becomes smaller and smaller with the increase of the steel fiber volume fraction. This is because the steel fiber transfers the higher stress at the crack section to the surrounding concrete matrix, causing more cracks between the existing cracks, or more branch cracks. In addition, the steel fiber reinforced recycled aggregate concrete beam improves the compression deformation resistance of the recycled aggregate concrete due to the bridging effect of the steel fiber, effectively inhibiting the crushing and spalling of the recycled aggregate concrete in the compression zone. In summary, even in the state of shear failure, the incorporation of steel fiber inhibits the cracking of recycled aggregate concrete and increases the toughness of recycled aggregate concrete.
[0073] As Figure 3The more branches beside the main crack, as shown in C50F10RF50 and C50F10RF100RC100, the higher the replacement rate of recycled fine aggregate and recycled coarse aggregate. When the replacement rate of recycled fine aggregate is 50%, a part of the branch is separated from the main crack. When the replacement rate of recycled fine aggregate and recycled coarse aggregate is 100%, the branch beside the main crack is very obvious. With the increase of the replacement rate of recycled aggregate, the web shear diagonal cracks in the shear span zone increase, and the branches also increase. This is because, with the increase of the replacement rate of recycled aggregate, there are many micro-cracks and defects in the recycled aggregate concrete. When subjected to external force, stress concentration often occurs at these micro-cracks and defects, which makes these micro-cracks and defects expand through, and ultimately leads to the destruction of the structure.
[0074] Strain of stirrup: The strain gauges of the test beam oblique section stirrup are arranged on the stirrup intersected by the line connecting the loading point to the support. The strain gauge S1 is near the support, S3 is near the loading point, and there are fewer cracks through these two strain gauges. The strain gauge S2 is near the middle position of the loading point to the support. There are more bending shear cracks in the web shear zone through S2. After analyzing the data, it is found that the deformation of S1 and S3 stirrups is not obvious, so the trend of S2 stirrup with load change is depicted, see Figure 4 (a). As can be seen from the figure, the development of load-stirrup strain curve can be roughly divided into three stages, which corresponds to the development of the three stages of load-deflection curve. Point A is the oblique crack cracking point, and point B is the stirrup yield point. After the appearance of the crack, with the increase of the load, the crack expands, the concrete exits the work, and the steel fiber is pulled out, so the strain rate of the steel bar increases faster and faster.
[0075] Figure 4 (b) is the influence of steel fiber volume fraction on the load-stirrup strain curve of the test beam. With the increase of steel fiber volume fraction, the slope of load-stirrup strain curve increases. This is because with the increase of steel fiber volume fraction, the anchoring effect is more obvious, which is similar to the anchoring effect of steel fiber in ordinary reinforced concrete. Figure 4 (c) is the influence of different replacement rates of recycled aggregate on the load-stirrup strain curve. Compared with test beam C50F10RF0, in the second stage, the slope of test beams C50F10RF50 and C50F10RF100 with recycled fine aggregate replacement rates of 50% and 100% respectively decreases by about 20% and 30%. The influence of compressive strength and stirrup spacing of steel fiber recycled aggregate concrete beam on load-stirrup strain curve is similar to that of ordinary reinforced concrete beam, see Figure 4 (d).
[0076] Load-deflection curve
[0077] Figure 5The load-deflection curve of the steel fiber reinforced recycled fine aggregate concrete beam can be divided into three stages, namely, the elastic stage, the elastic-plastic stage and the failure stage. In the elastic stage, the curve still increases linearly after the first crack appears in the bending area of the test beam, until the oblique crack appears in one of the shear span regions of the test beam. Subsequently, with the appearance of the oblique crack, the load-deflection curve shows a nonlinear increase, and as the number and width of the cracks increase, the test beam enters the elastic-plastic stage, and the slope of the load-deflection curve gradually decreases. Finally, after the load reaches the ultimate bearing capacity, the deflection of the test beam develops rapidly, and the load-deflection curve enters the softening stage, and the load begins to gradually decrease.
[0078] Figure 5 (a) The load-deflection curves of the ordinary reinforced concrete beam and the steel fiber reinforced recycled fine aggregate concrete beams with different steel fiber volume fractions. In the elastic-plastic stage, compared with the ordinary reinforced concrete beam C50F0RF0, the stiffness of the steel fiber reinforced recycled fine aggregate concrete beam C50F0RF100 decreases by 14.95%. This is because the recycled fine aggregate is attached with a large number of cement stone particles and dust impurities with low strength on its surface, which has an impact on its cement matrix, reduces the bonding effect between the interfaces of each phase of the concrete, and causes the elastic modulus of the fully recycled fine aggregate concrete to be slightly lower than that of the ordinary concrete. With the increase of the steel fiber volume fraction, the overall slope of the curve and the ultimate load are improved from the beginning of loading to the ultimate load. Compared with the test beam C50F0RF100, when the steel fiber volume fraction is 0.5%, 1.0%, and 1.5%, the slopes of the test beams C50F05RF100, C50F10RF100 and C50F15RF100 in the elastic-plastic stage increase by about 10%, 20% and 30% respectively. This shows that the steel fiber limits the development of cracks, compensates for the weak interface between the recycled fine aggregate and the cement, improves the strength and toughness, improves the overall shear capacity of the concrete, enhances the bonding effect between the steel fiber reinforced recycled fine aggregate concrete and the steel bar, improves the dowel effect of the longitudinal reinforcement and the shear capacity of the stirrup.
[0079] With the increase of the recycled fine aggregate and recycled coarse aggregate replacement rate, the overall slope of the curve and the ultimate load of the test beam decrease, and the stiffness becomes smaller, as shown in Figure 5(b) Compared with the test beam C50F10RF0, the slopes of the test beams C50F10RF50 and C50F10RF100 decrease by about 20% and 30% respectively in the elastic-plastic stage. The trend of the test beams with different recycled coarse aggregate replacement ratios is similar to that of the recycled fine aggregate replacement ratio. This is due to the existence of micro-pores when the mortar is bonded with the recycled aggregate, and continuous cracks appear in the recycled aggregate due to the crushing process. With the increase of the recycled aggregate replacement ratio, this effect leads to the increase of the weakness of the concrete, and accelerates the appearance of bending and shear cracks. As shown in Figs. 6 and 7, the load-deflection curves of the test beams with different recycled fine aggregate replacement ratios are similar to those of the test beams with different recycled coarse aggregate replacement ratios. As shown in Figs. 8 and 9, the load-deflection curves of the test beams with different steel fiber volume ratios are similar to those of the test beams with different recycled coarse aggregate replacement ratios. As shown in Figs. 10 and 11, the load-deflection curves of the test beams with different stirrup spacing are similar to those of the test beams with different recycled coarse aggregate replacement ratios. Figure 5 (c) and (d) show that with the increase of the compressive strength and the decrease of the stirrup spacing, the slope of the load-deflection curve of the test beam increases, and the stiffness improves, which is consistent with the law of ordinary reinforced concrete beams.
[0080] Derivation of the calculation formula:
[0081] The influencing factors studied in this paper are the recycled fine aggregate replacement ratio, the recycled coarse aggregate replacement ratio, the steel fiber volume ratio and the stirrup spacing. In order to study the influence of each parameter on the shear capacity of the steel fiber recycled aggregate concrete beam, the normalization processing is carried out first. That is, the shear capacity produced by the stirrup is subtracted, and then divided by the shear capacity of the test beam without steel fiber and recycled aggregate. The influence of the shear span ratio is analyzed through existing literature. Therefore, considering the influence of the recycled fine aggregate replacement ratio, the recycled coarse aggregate replacement ratio, the steel fiber volume ratio and the shear span ratio on the shear capacity of the steel fiber recycled aggregate concrete beam, four influencing factors are assumed, i.e. k1, k2, k3 and k4.
[0082] According to the test results of this study and the collected test data, the relationship between the recycled fine aggregate replacement ratio, the recycled coarse aggregate replacement ratio, the steel fiber volume ratio and the shear span ratio and the normalized shear capacity. The influence of the recycled fine aggregate replacement ratio, the recycled coarse aggregate replacement ratio, the steel fiber volume ratio and the shear span ratio on the shear capacity is shown in the following expressions:
[0083] k1 = 1 - 0.059r f (1)
[0084] k2 = 1 - 0.064r c (2)
[0085] k3 = 1 + 0.613v f (3)
[0086] k4 = 1 - 0.041(a / d) (4)
[0087] In the formula, k1, k2, k3 and k4 are the influencing factors of the recycled fine aggregate replacement ratio, the recycled coarse aggregate replacement ratio, the steel fiber volume ratio and the shear span ratio, respectively.
[0088] Therefore, the shear capacity of steel fiber reinforced recycled aggregate concrete beams can be calculated by equation (5) considering the influence factors of recycled fine aggregate replacement ratio, recycled coarse aggregate replacement ratio, steel fiber volume fraction and shear span ratio:
[0089]
[0090] wherein: V pro is the predicted shear capacity (kN) ; is the compressive strength of concrete (MPa) ; b is the width of the beam (mm) ; d is the effective depth of the beam (mm) ; V s is the shear strength provided by the stirrups (kN).
[0091] Table 4 Test results to verify the prediction equation
[0092]
[0093]
[0094] To verify the accuracy of the proposed shear capacity equation, the test values of shear capacity of all the beams in this study were compared with the calculated values, as shown in Table 4. It can be seen that the calculated values of the prediction equation are close to the test values.
[0095] It is apparent to those skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments, and that the application can be implemented in other particular forms without departing from the spirit or essential characteristics of the application. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein. It will be apparent to those skilled in the art that various modifications and variations can be made in detail of the present application without departing from the spirit or scope of the application. Thus, it is intended that the present application cover modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.
[0096] In addition, it should be understood that although the present specification describes only one embodiment, each embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be combined appropriately to form other embodiments that those skilled in the art can understand.
Claims
1. A reinforced steel fiber recycled concrete shear beam, characterized in that: The steel reinforced concrete beam includes a steel reinforced framework and a concrete mixed layer arranged in and out of the steel reinforced framework, the concrete mixed layer includes concrete, steel fiber with a volume rate of 0.5%-1.5%, recycled fine aggregate with a replacement rate of 50%-100% and recycled coarse aggregate with a replacement rate of 50%-100%, and the steel reinforced framework includes steel bars extending longitudinally and arranged along the edge line of the shear beam and stirrups distributed along the longitudinal direction with a spacing of 150mm-250mm.
2. A method of verifying the performance of a reinforced steel fiber recycled concrete shear beam according to claim 1, characterized in that The method comprises the following steps: (1) specimen design: 13 beams are designed for the shear test of the steel reinforced steel fiber recycled aggregate concrete beam, wherein the concrete compressive strength grade of a steel reinforced concrete beam is C50, the recycled fine aggregate replacement rate is 100%, the coarse aggregate is natural gravel, and the stirrup spacing is 200mm, and the beam is numbered as C50F0RF0; the steel fiber volume rate is 0%, 0.5%, 1.0% and 1.5% respectively, the recycled fine aggregate replacement rate is 100%, the coarse aggregate is natural gravel, and the stirrup spacing is 200mm, and the test beams are numbered as C50F0RF100, C50F05RF100, C50F10RF100 and C50F15RF100 respectively; the steel fiber volume rate is 1.0%, the recycled fine aggregate replacement rate is 0% and 50% respectively, the coarse aggregate is natural gravel, and the stirrup spacing is 200mm, and the test beams are numbered as C50F10RF0 and C50F10RF50 respectively; the steel fiber volume rate is 1.0%, the recycled fine aggregate replacement rate is 100%, the recycled coarse aggregate replacement rate is 50% and 100% respectively, and the stirrup spacing is 200mm, and the test beams are numbered as C50F10RF100RC50 and C50F10RF100RC100 respectively; the concrete compressive strength grade is C30 and C70 respectively, the steel fiber volume rate is 1.0%, the recycled fine aggregate replacement rate is 100%, the coarse aggregate is natural gravel, and the stirrup spacing is 200mm, and the test beams are numbered as C30F10RF100 and C70F10RF100 respectively; the stirrup spacing is 150mm and 250mm respectively, the concrete compressive strength grade is C50, the steel fiber volume rate is 1.0%, the recycled fine aggregate replacement rate is 100%, and the coarse aggregate is natural gravel, and the test beams are numbered as C50F10RF100-1 and C50F10RF100-3 respectively; (2) specimen production: the specimens are produced and poured in the laboratory according to the designed mixing ratio, and water is poured for curing for 28 days, 6 standard cubic test blocks and 6 prism test blocks are produced for each specimen from the same batch of concrete, and the standard test blocks and the specimens are cured under the same conditions for 28 days; (3) Test loading device: one end of the test beam support is a fixed hinge support, and the other end is a rolling hinge support, which can move appropriately in the horizontal direction; the test equipment uses a 200t electro-hydraulic servo instrument, which is equipped with a jack and a 1000kN spoke dual-channel load sensor as an auxiliary reaction force device, and the load is applied to the test beam through the distribution beam of the loading device; the formal loading uses step loading, the loading rate is 0.5mm / min, each load is 20kN, and each load holding time is 5 minutes, and after the deflection is stable, the loading continues, after the loading reaches 80% of the estimated value of the oblique crack, the loading interval is reduced, and each loading value is changed to 10kN, so as to more accurately observe the appearance of the oblique crack; after the appearance of the oblique crack of the test piece, the normal loading is restored; After 90% of the calculated bearing capacity of the component, continuously and slowly load; (4) Deformation measuring point arrangement: a total of 7 strain displacement sensors are arranged on each test beam, wherein 1 strain displacement sensor is arranged at each of the two end supports, the mid-span section, the loading point, and the midpoint from the mid-span to the loading point; (5) Strain gauge arrangement and pasting: the steel bar strain measuring point is arranged on the stirrup of the section of the connecting line between the loading point and the support, and is symmetrically arranged on the left and right, and the size of the resistance strain gauge is 2mm×3mm, and a total of 6 are arranged; (6) Crack observation: the crack observation under each load is carried out according to the following method: after the loading is stable, the test beam side surface concrete surface is wiped with cotton soaked with acetone, the appearance and development of the crack are observed, and the reading is read through the reading microscope; the newly found crack is numbered, the development of the crack is outlined near the crack, and the load value and the maximum crack width value when the crack appears are recorded on the record table; for the already appeared crack, the maximum crack width value is observed and recorded at each load; the crack width is recorded and the crack development trend is depicted on the coordinate paper; (7) Test procedure: before the test, the beam surface is brushed white, the white paste surface is dried, then a 50mm×100mm grid is popped out on the beam side surface with a ink hopper, then the beam is hoisted to the corresponding position and placed on the support, the positions of the measuring points are determined, then the displacement meter is installed, the wires of the strain gauges are connected to the joints of the DH3816N static strain acquisition instrument, and the resistance is checked; then the geometric centering method is used to install the mechanical jack, the wires of the 200t force sensor are connected to the DH3816N static strain acquisition instrument to measure the size of the force; after checking that all the wires and instruments are working normally, the test begins; (8) Shear bearing capacity checking: the shear bearing capacity of the steel fiber recycled aggregate concrete beam is checked.
3. The method for verifying the performance of a reinforced steel fiber recycled concrete shear beam according to claim 2, characterized in that, In step (1), the particle size of the natural crushed stone is 5-20mm.
4. The method for verifying the performance of a steel fiber reinforced recycled concrete shear beam according to claim 2, characterized in that, In step (2), the size of the standard cube is 150mm×150mm×150mm.
5. The method for verifying the performance of a reinforced steel fiber recycled concrete shear beam according to claim 2, characterized in that, In step (2), the size of the standard prism is 150mm×150mm×300mm.
6. The method for verifying the performance of a steel fiber reinforced recycled concrete shear beam according to claim 2, wherein In step (3), before formal loading, a preloading test is carried out to ensure that the test piece and the equipment are in good contact, and to verify that the measuring instruments are working normally, the preloading load value is set to 40kN, each level is 10kN, and the loading rate is 0.5mm / min.