Constraint shrinkage strain and strain gradient measurement equipment and method for protective layer concrete

Abstract

The invention discloses equipment and a method for measuring constraint shrinkage strain and strain gradient of protective layer concrete. The measuring equipment comprises a concrete pouring container, a fine sand uniform dispenser and monitoring equipment, the concrete pouring container comprises a container A, a container B, a container C and a container D which are used for pouring concrete, fine sand uniform scattering devices and monitoring equipment are arranged above the container A, the container B, the container C and the container D, and fine sand is scattered on the surface of the concrete poured in the container A, the container B, the container C and the container D through the fine sand uniform scattering devices; and the monitoring equipment is arranged facing the surface of concrete poured in the container A, the container B, the container C and the container D. The invention relates to the technical field of constructional engineering, and can be specially used for measuring the constraint shrinkage strain and the constraint shrinkage strain gradient of reinforced concrete protective layer concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of construction engineering, and in particular, to an apparatus and method for measuring the restrained shrinkage strain and strain gradient of cover concrete. Background Art

[0002] After the casting of a concrete member, shrinkage will occur, and the shrinkage occurs from the surface to the interior. The surface layer concrete shrinks the fastest and has the largest shrinkage value. The deeper into the member, the slower the shrinkage occurs and the smaller the shrinkage value. Therefore, the interior concrete will exert a self-restraining effect on the shrinkage of the surface layer concrete, resulting in cracking on the surface of the concrete member. For reinforced concrete, the steel bars are generally arranged at the surface position of the concrete member. There is also a layer of concrete called the steel bar cover outside the steel bars, with a thickness of 2 - 10 cm. The cover concrete is the outermost layer of concrete, with the largest shrinkage and being restricted by the deeper concrete and the steel bars. Therefore, the internal restraint it receives is the strongest, and thus the cracking is the most serious. After the cover cracks, it will cause the rust expansion of the steel bars, further developing the cracks and causing the reinforced concrete member to lose its original designed bearing capacity. In order to quantitatively calculate the cracking of the reinforced concrete cover concrete, it is necessary to accurately measure the magnitude of the restrained shrinkage deformation of the cover concrete and the distribution of the restrained shrinkage along the thickness, that is, the restrained shrinkage strain gradient along the thickness direction.

[0003] Currently, the shrinkage value of a 10*10*50 cm small specimen is usually used as the shrinkage of concrete. However, it is very difficult to specifically measure the restrained shrinkage strain and strain gradient of the reinforced concrete cover concrete, and there are no similar apparatuses and methods. Therefore, there is a need to provide an apparatus and method for measuring the restrained shrinkage strain and strain gradient of cover concrete, which can be specifically used to measure the restrained shrinkage strain and strain gradient of the reinforced concrete cover concrete. Summary of the Invention

[0004] The purpose of the present invention is to provide an apparatus and method for measuring the restrained shrinkage strain and strain gradient of cover concrete, which can be specifically used to measure the restrained shrinkage strain and strain gradient of the reinforced concrete cover concrete.

[0005] The present invention is implemented as follows:

[0006] A measuring device for the restrained shrinkage strain and strain gradient of protective layer concrete, comprising a concrete pouring container, a fine sand evenly spreading device and a monitoring device; the concrete pouring container includes containers A, B, C and D for pouring concrete. Among them, the shape and volume of container A are the same as those of container B, and the shape and volume of container C are the same as those of container D, and the height of containers A and B is greater than the height of containers C and D; above containers A, B, C and D, there are both a fine sand evenly spreading device and a monitoring device, so that the fine sand is scattered on the surface of the concrete poured in containers A, B, C and D through the fine sand evenly spreading device, and the monitoring device is arranged facing the surface of the concrete poured in containers A, B, C and D.

[0007] In the upper part of the said container A, a number of first steel bar installation openings are formed at intervals, and there is a protective layer gap between the plane where the number of first steel bar installation openings are located and the top surface of container A; multiple steel bars are respectively inserted into the first steel bar installation openings correspondingly and are located inside the concrete poured in container A, so that protective layer concrete is poured above the steel bars.

[0008] On the upper part of the said container B, there is a first pouring elevation line, and the first pouring elevation line is at the same horizontal height as a number of first steel bar installation openings on container A.

[0009] In the lower part of the said container C, a number of second steel bar installation openings are formed at intervals, and there is a protective layer gap between the number of second steel bar installation openings and the top surface of container C; multiple steel bars are respectively inserted into the second steel bar installation openings correspondingly and are located inside the concrete poured in container C, so that protective layer concrete is poured above the steel bars.

[0010] On the upper part of the said container D, there is a second pouring elevation line, and the second pouring elevation line is at the same horizontal height as a number of second steel bar installation openings on container C.

[0011] The said fine sand evenly spreading device is a cuboid box-shaped structure with a square bottom surface. The bottom of the fine sand evenly spreading device is provided with a pull-out and detachable bottom plate that extends to the outside of the fine sand evenly spreading device. Partition plates are installed at intervals inside the fine sand evenly spreading device, so that the fine sand is evenly distributed on the concrete surface in an array form.

[0012] The measuring method using the said measuring device for the restrained shrinkage strain and strain gradient of protective layer concrete includes the following steps:

[0013] Step 1: According to the steel bar design requirements, install steel bars in container A through the first steel bar installation openings and install steel bars in container C through the second steel bar installation openings;

[0014] Step 2: Pour concrete into containers A, B, C, and D to the designed height and install concrete strain gauges.

[0015] Step 3: Install monitoring equipment above containers A, B, C, and D through brackets and set it facing the concrete surfaces poured in containers A, B, C, and D.

[0016] Step 4: Evenly spread fine sand on the concrete surfaces poured in containers A, B, C, and D through a fine sand spreader.

[0017] Step 5: Record the readings of each concrete strain gauge according to the strain reading acquisition period. Among them, the reading of the concrete strain gauge in container A is ε 实发砼加钢筋约 , the reading of the concrete strain gauge in container B is ε 实发砼约 , the reading of the concrete strain gauge in container C is ε 实发钢约 , the reading of the concrete strain gauge in container D is ε 实发无约 bundle;

[0018] Step 6: Calculate the restrained shrinkage strain of the concrete in the cover above the steel bars in reinforced concrete. The calculation formula is:

[0019] 1) The actual restrained shrinkage strain of the cover concrete only caused by the restraint of the concrete inside the mass concrete is ε 实际砼约 = ε 实发无约束 - ε 实发砼约 ;

[0020] 2) The actual restrained shrinkage strain of the cover concrete only caused by the restraint of the steel bars is ε 实际钢约 = ε 实发无约束 - εactual steel restraint;

[0021] 3) The actual restrained shrinkage strain of the cover concrete caused by the double restraint of the concrete inside the mass concrete and the steel bars is ε 实际砼加钢筋约 = ε 实发无约束 - ε 实发砼与钢筋约 ;

[0022] Step 7: According to the shooting acquisition period, the monitoring equipment collects photos of the concrete surfaces in containers A, B, C, and D after spreading fine sand and calculates the shrinkage strain of the uppermost surface of the concrete.

[0023] Among them, the shrinkage strain of the uppermost surface of the concrete in container A is δ 实际砼加钢筋约 , the shrinkage strain of the uppermost surface of the concrete in container B is δ 实际砼约 , the shrinkage strain of the uppermost surface of the concrete in container C is δ 实际钢约 , the shrinkage strain of the uppermost surface of the concrete in container D is δ 实发无约束 ;

[0024] Step 8: Calculate the restrained shrinkage strain gradient of the concrete in the cover above the steel bars. The calculation formula is as follows:

[0025] 1) The actual restrained shrinkage strain gradient ζ of the cover concrete only restrained by the concrete inside the mass concrete is 实际砼约 = 2 * (δ 实际砼约 - ε 实际砼约 ) / d 应变计直径 ;

[0026] where d 应变计直径 is the diameter of the concrete strain gauge;

[0027] 2) The actual restrained shrinkage strain gradient ζ of the cover concrete only restrained by the steel bars is 实际钢约 = 2 * (δ 实际钢约 - ε 实际钢约 ) / d 应变计直径 ;

[0028] 3) The actual restrained shrinkage strain gradient ζ of the cover concrete restrained by both the concrete inside the mass concrete and the steel bars is 实际砼加钢筋约 = 2 * (δ 实际砼加钢筋约 - ε 实际砼加钢筋约 ) / d 应变计直径 .

[0029] In the said Step 2, apply butter evenly on the lower surfaces of the inner walls of containers A, B, C, and D, then lay a layer of film, and then pour the concrete.

[0030] In the said Step 2, the concrete strain gauges in containers A and C are installed along the axial directions parallel to and perpendicular to the steel bars respectively. The installation positions and directions of the concrete strain gauges in container B are the same as those in container A, and the installation positions and directions of the concrete strain gauges in container D are the same as those in container C.

[0031] In the said Step 4, the fine sand is black sand grains. The spreading area of the fine sand on the concrete surface is square, and a fine sand array with a spacing of 1 - 2 mm is formed within each square spreading area.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. Since the present invention is provided with container A and container B, it can be used to measure and calculate the actual shrinkage strain occurring in the surface concrete cover under the internal restraint of mass concrete and the horizontal reinforcement, and the actual shrinkage strain occurring in the surface concrete cover only under the internal restraint of concrete. Since the present invention is provided with container C and container D, it can be used to measure and calculate the actual shrinkage strain occurring when the concrete thin plate is only restrained by steel bars under the horizontal reinforcement restraint and the actual shrinkage strain occurring in the concrete thin plate without any restraint, thus solving the problem in the prior art that there is no special equipment to measure the restrained shrinkage strain of the concrete in the steel bar concrete cover, and the measurement and calculation are simple and easy.

[0034] 2. Since the present invention is provided with a fine sand evenly spreading device and a monitoring device, by evenly spreading fine sand on the concrete surface through the fine sand evenly spreading device and periodically collecting photos of the concrete surface with the spread fine sand through the monitoring device, the restrained shrinkage strain gradient of the concrete surface can be calculated by combining a specific program, thus solving the problem in the prior art that there is no special equipment to measure the restrained shrinkage strain gradient of the concrete in the steel bar concrete cover, and the measurement and calculation are simple and easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the front view of the measuring device for the restrained shrinkage strain and strain gradient of the concrete in the cover layer of the present invention;

[0036] Figure 2 is Figure 1 the sectional view of

[0037] Figure 3 is the side view of the measuring device for the restrained shrinkage strain and strain gradient of the concrete in the cover layer of the present invention;

[0038] Figure 4 is Figure 3 the sectional view of

[0039] Figure 5 is the top view of the installation of the monitoring device in the measuring device for the restrained shrinkage strain and strain gradient of the concrete in the cover layer of the present invention;

[0040] Figure 6 is the top view of the measuring device for the restrained shrinkage strain and strain gradient of the concrete in the cover layer of the present invention (without spreading fine sand);

[0041] Figure 7 is the top view of the measuring device for the restrained shrinkage strain and strain gradient of the concrete in the cover layer of the present invention (with spreading fine sand);

[0042] Figure 8 is the sectional view of the surface of the fine sand evenly spreading device in the measuring device for the restrained shrinkage strain and strain gradient of the concrete in the cover layer of the present invention;

[0043] Figure 9 It is a top view of the surface of the fine sand even spreader in the device for measuring the restrained shrinkage strain and strain gradient of the protective layer concrete of the present invention.

[0044] In the figure, 1 is the monitoring device, 2 is the first steel bar installation opening, 3 is the first pouring elevation line, 4 is the second steel bar installation opening, 5 is the second pouring elevation line, 6 is the fine sand, 7 is the support, 8 is the steel bar, 9 is the concrete strain gauge, 10 is the concrete, 11 is the surface of the fine sand even spreader, 12 is the pull-out and detachable bottom plate, and 13 is the partition board. Specific embodiments

[0045] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0046] Please refer to Attachment Figure 1 to Attachment Figure 3 , Attachment Figure 8 and Attachment Figure 9 , a device for measuring the restrained shrinkage strain and strain gradient of the protective layer concrete, including a concrete pouring container, a fine sand even spreader 11 and a monitoring device 1; the concrete pouring container includes containers A, B, C and D for pouring concrete 10, wherein the shape and volume of container A are the same as those of container B, the shape and volume of container C are the same as those of container D, and the height of container A and container B is greater than the height of container C and container D; a fine sand even spreader 11 and a monitoring device 1 are arranged above containers A, B, C and D respectively, so that the fine sand 6 is spread on the surface of the concrete 10 poured in containers A, B, C and D through the fine sand even spreader 11, and the monitoring device 1 is arranged facing the surface of the concrete 10 poured in containers A, B, C and D through the support 7.

[0047] Since the volume of containers A and B is larger than that of containers C and D, the concrete 10 poured in containers A and B will be hereinafter referred to as mass concrete, and the concrete 10 poured in containers C and D will be hereinafter referred to as concrete thin plates.

[0048] Preferably, containers A and B can adopt stainless steel containers with larger height and open top, which is convenient for the concrete 10 to be poured and formed in the containers. After the concrete 10 is poured in containers A and B, the actual shrinkage strain εactual internal restraint that occurs on the surface concrete protective layer under various possible restraints inside the mass concrete can be measured and calculated.

[0049] Preferably, the containers C and D can be stainless steel containers with a relatively small height (the height is approximately the thickness of the protective layer concrete of the containers A and B) and an open top, which is convenient for the concrete to be poured and formed in the containers. After the concrete is poured into the containers C and D, the actual shrinkage strain that occurs on the surface concrete protective layer under various possible constraints inside the concrete can be measured and calculated.

[0050] Preferably, the bottom surfaces of the containers A, B, C, and D have the same shape and are arranged side by side to form a whole, which is convenient for measurement and use.

[0051] Please refer to the appendix Figure 1 and the appendix Figure 2 , several first steel bar installation holes 2 are formed at intervals in the upper part of the container A, and there is a protective layer gap between the plane where the several first steel bar installation holes 2 are located and the top surface of the container A; multiple steel bars 8 are respectively inserted into the first steel bar installation holes 2 and are located inside the concrete 10 poured in the container A, so that the protective layer concrete is poured above the steel bars 8.

[0052] Preferably, the protective layer gap between the plane where the first steel bar installation hole 2 is located and the top surface of the container A is 10 cm, so that the protective layer concrete with a thickness of 2 - 10 cm can be formed above the steel bars 8. The concrete in this part can be used as the protective layer concrete for research, and is used to measure and calculate the actual shrinkage strain ε that occurs on the surface concrete protective layer under the constraint of the horizontal reinforcement, that is, the steel bars 8, inside the mass concrete. 实发砼与钢筋约 .

[0053] Preferably, the first steel bar installation holes 2 can be formed on the front and rear surfaces of the container A, and the steel bars 8 penetrate through the container A after being inserted into the first steel bar installation holes 2. The aperture, quantity, and spacing of the first steel bar installation holes 2 can be adjusted adaptively according to the diameter, installation quantity, and spacing of the steel bars 8.

[0054] Please refer to the appendix Figure 1 , a first pouring elevation line 3 is provided in the upper part of the container B, and the first pouring elevation line 3 is at the same horizontal height as several first steel bar installation holes 2 on the container A.

[0055] Concrete with the same thickness as the protective layer concrete in the container A can be poured above the first pouring elevation line 3. The concrete in this part can be used as the protective layer concrete for research, and is used to measure and calculate the actual shrinkage strain ε that occurs on the surface concrete protective layer under only the internal constraint of the concrete inside the mass concrete. 实发内砼约 .

[0056] Please refer to the appendix Figure 1 and the appendix Figure 2, a plurality of second steel bar installation openings 4 are formed at intervals in the lower part of the container C, and a protective layer gap is left between the plurality of second steel bar installation openings 4 and the top surface of the container C; a plurality of steel bars 8 are respectively inserted into the second steel bar installation openings 4 and are located inside the concrete 10 poured in the container C, so that protective layer concrete is poured and formed above the steel bars 8.

[0057] Preferably, the protective layer gap between the plane where the second steel bar installation opening 4 is located and the top surface of the container C is 10 cm, so that protective layer concrete with a thickness of 2-10 cm can be formed above the steel bars 8. The height of the container C can be slightly greater than 10 cm, and the second steel bar installation opening 4 is located at the bottom of the concrete thin plate. The concrete in this part can be studied as protective layer concrete, and is used to measure and calculate the actual shrinkage strain ε that occurs when the 2-10 cm surface concrete protective layer is only constrained by the horizontal reinforcement, that is, the steel bars 8. 实发钢筋约 .

[0058] Preferably, the second steel bar installation openings 4 can be formed on the front and rear surfaces of the container C, and the steel bars 8 penetrate through the container C after being inserted into the second steel bar installation openings 4. The aperture, quantity and spacing of the second steel bar installation openings 4 can be adaptively adjusted according to the diameter, installation quantity and spacing of the steel bars 8.

[0059] Please refer to the appendix Figure 1 , the upper part of the container D is provided with a second pouring elevation line 5, and the second pouring elevation line 5 is at the same horizontal height as a plurality of second steel bar installation openings 4 on the container C.

[0060] Concrete with the same thickness as the protective layer concrete in the container C can be poured and formed above the second pouring elevation line 5. The concrete in this part can be studied as protective layer concrete, and is used to measure and calculate the actual shrinkage strain ε that occurs in the 2-10 cm concrete thin plate without any constraint. 实发无约束 .

[0061] Please refer to the appendix Figure 8 and the appendix Figure 9 , the fine sand uniform spreader 11 is a cuboid box structure with a square bottom surface. A pull-out and detachable bottom plate 12 is provided at the bottom of the fine sand uniform spreader 11 and extends to the outside of the fine sand uniform spreader 11. Partition plates 13 are installed at intervals inside the fine sand uniform spreader 11, so that the fine sand 6 is evenly distributed on the concrete surface in an array form.

[0062] Preferably, the fine sand distributor 11 can be a stainless steel rectangular box with a length of 15 cm, a width of 15 cm, and a height of 20 cm. A partition 13 with a height of 1 cm is installed at an interval of 1-2 mm inside the box, and the inner bottom of the stainless steel rectangular box is divided into a sand outlet in an array form. After pouring fine sand 6 into the stainless steel rectangular box and removing the pull-out and detachable bottom plate 12, the fine sand 6 freely falls onto the concrete surface and is distributed in an array.

[0063] Preferably, the fine sand distributor 11 can be set lower than the monitoring device 1 and is located 30 cm above the concrete surface to prevent the fine sand 6 from falling on the monitoring device 1 and affecting the clarity of the photos it collects, while ensuring the uniformity of the fine sand 6 distribution.

[0064] Please refer to Attach Figure 1 to Attach Figure 9 , a method for measuring the restrained shrinkage strain and strain gradient of a protective layer concrete, comprising the following steps:

[0065] Step 1: According to the steel bar design requirements, install steel bars 8 through the first steel bar installation hole 2 in container A and install steel bars 8 through the second steel bar installation hole 4 in container C, as shown in Attach Figure 2 , Attach Figure 4 , Attach Figure 6 and Attach Figure 7 .

[0066] The parameters of the steel bars 8 (including diameter, installation spacing, installation quantity, etc.) are determined according to the steel bar design requirements.

[0067] Step 2: Pour concrete 10 to the designed height in containers A, B, C, and D, and install concrete strain gauges 9, as shown in Attach Figure 4 , Attach Figure 6 and Attach Figure 7 .

[0068] Preferably, the inner bottom surfaces of the containers A, B, C, and D are evenly coated with butter, and then a layer of film is laid before pouring the concrete 10. The strength grade of the concrete 10 is selected according to the design requirements.

[0069] Preferably, the concrete strain gauges 9 in containers A and C are installed along the axial directions parallel to and perpendicular to the steel bars 8 respectively. The installation positions and directions of the concrete strain gauges 9 in container B are the same as those in container A, and the installation positions and directions of the concrete strain gauges 9 in container D are the same as those in container C.

[0070] Reinforced concrete is formed by pouring in containers A and C, and concrete is formed by pouring in containers B and D.

[0071] Step 3: Install the monitoring device 1 above the containers A, B, C, and D through the support 7, and set it facing the surface of the concrete 10 poured in the containers A, B, C, and D.

[0072] At least one monitoring device 1 is set above each container. Preferably, four monitoring devices 1 are symmetrically arranged above each container. As shown in the appendix Figure 5 The monitoring device 1 can be a high-definition camera.

[0073] Step 4: Uniformly spread the fine sand 6 on the surface of the concrete 10 poured in the containers A, B, C, and D through the fine sand uniform spreader 11.

[0074] Preferably, the fine sand 6 is black sand grains. The spreading area of the fine sand 6 on the surface of the concrete 10 is a square, and a fine sand array with a spacing of 1-2 mm is formed within each square spreading area. As shown in the appendix Figure 7 The figure shows.

[0075] Through the matrix spreading of the fine sand 6, it is convenient for the monitoring device 1 to collect the deformation photos of the concrete surface, thereby improving the accuracy of subsequent shrinkage strain calculation.

[0076] Step 5: Record the readings of each concrete strain gauge 9 according to the strain reading acquisition period. Among them, the reading of the concrete strain gauge 9 in container A is ε 实发砼加钢筋约 , the reading of the concrete strain gauge 9 in container B is ε 实发砼约 , the reading of the concrete strain gauge 9 in container C is ε 实发钢约 , and the reading of the concrete strain gauge 9 in container D is ε 实发无约束 .

[0077] Using the concrete strain gauge 9 to collect the readings of the restrained shrinkage strain of the concrete is a conventional operation in the field, which will not be elaborated here.

[0078] Step 6: Calculate the restrained shrinkage strain of the concrete in the cover above the steel bars in the reinforced concrete. The calculation formula is:

[0079] (1) The actual restrained shrinkage strain generated by the concrete in the cover only under the restraint of the concrete inside the mass concrete is ε 实际砼约 = ε 实发无约束 - ε 实发砼约 ;

[0080] (2) The actual restrained shrinkage strain generated by the concrete in the cover only under the restraint of the steel bars is ε 实际钢约 = ε 实发无约 restraint - ε actual steel bar restraint;

[0081] (3) The actual restrained shrinkage strain ε generated by the protective layer concrete under the double constraints of the internal concrete and steel bars in the mass concrete shall be 实际砼加钢筋约 = ε 实发无约束 - ε 实发砼与钢筋约 .

[0082] The restrained shrinkage strain of the protective layer concrete above the steel bars measured and calculated by using the concrete strain gauge 9 in this way is actually the average restrained shrinkage strain of the concrete within the thickness range of the protective layer concrete. Due to the certain thickness of the concrete strain gauge 9 itself, the strain measured by it is the average shrinkage strain within its own thickness range.

[0083] Step 7: According to the shooting and acquisition cycle, the monitoring device 1 acquires the photos of the concrete surface in containers A, B, C, and D after spreading the fine sand 6, and calculates the shrinkage strain of the uppermost surface of the concrete through a specific computer program.

[0084] Among them, the shrinkage strain of the uppermost surface of the concrete in container A is δ 实际砼加钢筋约 , the shrinkage strain of the uppermost surface of the concrete in container B is δ 实际砼约 , the shrinkage strain of the uppermost surface of the concrete in container C is δ 实际钢约 , and the shrinkage strain of the uppermost surface of the concrete in container D is δ 实发无约束 .

[0085] The monitoring device 1 takes photos of the concrete surface at intervals of the shooting and acquisition cycle. Due to the uniform distribution of the fine sand 6, after the concrete surface deforms, the distribution of the fine sand 6 will also change accordingly. The change in the distribution of the fine sand 6 can be analyzed through the image processing technology of the existing technology, so as to obtain the deformation situation of the concrete surface, and then calculate the shrinkage strain of the concrete surface.

[0086] Calculating the shrinkage strain of the concrete surface based on the photos of the concrete surface is a conventional method in the field, and it can be automatically calculated by using a specific computer program, which will not be elaborated here.

[0087] Step 8: Calculate the restrained shrinkage strain gradient of the protective layer concrete above the steel bars. The calculation formula is:

[0088] (1) The actual restrained shrinkage strain gradient ζ generated by the protective layer concrete only under the constraint of the internal concrete in the mass concrete is 实际砼约 = 2 * (δ 实际砼约 - ε 实际砼约 ) / d 应变计直径 ;

[0089] Among them, d 应变计直径 is the diameter of the concrete strain gauge 9, and the same applies hereinafter.

[0090] (2) The actual restrained shrinkage strain gradient ζ generated by the protective layer concrete only under the restraint of steel bars is 实际钢约 = 2 * (δ 实际钢约 - ε 实际钢约 ) / d 应变计直径 ;

[0091] (3) The actual restrained shrinkage strain gradient ζ generated by the protective layer concrete under the double restraint of the internal concrete and steel bars of mass concrete is 实际砼加钢筋约 = 2 * (δ 实际砼加钢筋约 - ε 实际砼加钢筋约 ) / d 应变计直径 .

[0092] The above are only the preferred embodiments of the present invention and are not used to limit the protection scope of the invention. Therefore, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A device for measuring the restrained shrinkage strain and strain gradient of a protective layer of concrete, characterized in that: It includes a concrete pouring container, a fine sand evenly spreading device (11) and a monitoring device (1); the concrete pouring container includes container A, container B, container C and container D for pouring concrete (10). Among them, the shape and volume of container A are the same as those of container B, the shape and volume of container C are the same as those of container D, and the height of container A and container B is greater than that of container C and container D; above container A, container B, container C and container D, there are a fine sand evenly spreading device (11) and a monitoring device (1), so that fine sand (6) is spread on the surface of the concrete (10) poured in container A, container B, container C and container D through the fine sand evenly spreading device (11), and the monitoring device (1) is arranged facing the surface of the concrete (10) poured in container A, container B, container C and container D.

2. The restraint shrinkage strain and strain gradient measuring device for the protective layer concrete according to claim 1, wherein: In the upper part of the said container A, a number of first steel bar installation openings (2) are formed at intervals, and there is a protective layer gap between the plane where the number of first steel bar installation openings (2) are located and the top surface of container A; multiple steel bars (8) are respectively inserted into the first steel bar installation openings (2), and are located inside the concrete (10) poured in container A, so that protective layer concrete is poured above the steel bars (8).

3. The restraint shrinkage strain and strain gradient measuring device for the protective layer concrete according to claim 2, characterized in that: In the upper part of the said container B, there is a first pouring elevation line (3), and the first pouring elevation line (3) is at the same horizontal height as a number of first steel bar installation openings (2) on container A.

4. The restraint shrinkage strain and strain gradient measuring device for the protective layer concrete according to claim 1, wherein: In the lower part of the said container C, a number of second steel bar installation openings (4) are formed at intervals, and there is a protective layer gap between the number of second steel bar installation openings (4) and the top surface of container C; multiple steel bars (8) are respectively inserted into the second steel bar installation openings (4), and are located inside the concrete (10) poured in container C, so that protective layer concrete is poured above the steel bars (8).

5. The restraint shrinkage strain and strain gradient measuring device for the protective layer concrete according to claim 4, characterized in that: In the upper part of the said container D, there is a second pouring elevation line (5), and the second pouring elevation line (5) is at the same horizontal height as a number of second steel bar installation openings (4) on container C.

6. The restraint shrinkage strain and strain gradient measuring device for the protective layer concrete according to claim 1, wherein: The said fine sand evenly spreading device (11) is a cuboid box-shaped structure with a square bottom. The bottom of the fine sand evenly spreading device (11) is provided with a pull-out and detachable bottom plate (12) which extends to the outside of the fine sand evenly spreading device (11). Inside the fine sand evenly spreading device (11), partition plates (13) are installed at intervals, so that the fine sand (6) is evenly distributed on the concrete surface in an array form.

7. The measuring method of the restrained shrinkage strain and strain gradient of the protective layer concrete using the measuring device as claimed in claim 1, characterized in that: It includes the following steps: Step 1: According to the steel bar design requirements, install steel bars (8) through the first steel bar installation openings (2) in container A, and install steel bars (8) through the second steel bar installation openings (4) in container C; Step 2: Pour concrete (10) in container A, container B, container C and container D to the designed height, and install concrete strain gauges (9); Step 3: Install the monitoring device (1) above container A, container B, container C and container D through the bracket (7), and arrange it facing the surface of the concrete (10) poured in container A, container B, container C and container D. Step 4: Uniformly spread fine sand (6) on the surface of the concrete (10) poured in containers A, B, C, and D through a fine sand uniform spreader (11); Step 5: Record the readings of each concrete strain gauge (9) according to the strain reading acquisition period, where the reading of the concrete strain gauge (9) in container A is ε 实发砼加钢筋约 , the reading of the concrete strain gauge (9) in container B is ε 实发砼约 , the reading of the concrete strain gauge (9) in container C is ε 实发钢约 , the reading of the concrete strain gauge (9) in container D is ε 实发无约束 ; Step 6: Calculate the restrained shrinkage strain of the concrete in the cover above the steel bars in the reinforced concrete. The calculation formula is: 1) The actual restrained shrinkage strain ε generated by the internal concrete restraint of the mass concrete on the protective layer concrete shall be 实际砼约 = ε 实发无约束 - ε 实发砼约 ; 2) The actual restrained shrinkage strain ε generated by the protective layer concrete only under the restraint of steel bars 实际钢约 = ε 实发无约束 - εactual steel restraint; 3) The actual restrained shrinkage strain ε generated by the double restraint of the concrete in the protective layer by the internal concrete and steel bars of the mass concrete shall be 实际砼加钢筋约 = ε 实发无约束 - ε 实发砼与钢筋约 ; Step 7: According to the shooting and acquisition cycle, the monitoring device (1) acquires photos of the concrete surface in containers A, B, C, and D after spreading fine sand (6), and calculates the shrinkage strain of the uppermost surface of the concrete; Among them, the shrinkage strain of the uppermost surface of the concrete in container A is δ 实际砼加钢筋约 , the shrinkage strain of the uppermost surface of the concrete in container B is δ 实际砼约 , the shrinkage strain of the uppermost surface of the concrete in container C is δ 实际钢约 , the shrinkage strain of the uppermost surface of the concrete in container D is δ 实发无约束 ; Step 8: Calculate the restrained shrinkage strain gradient of the concrete in the cover above the steel bars. The calculation formula is: 1) The actual restraint shrinkage strain gradient ζ generated by the concrete in the protective layer only under the restraint of the internal concrete of the mass concrete is 实际砼约 = 2 * (δ 实际砼约 - ε 实际砼约 ) / d 应变计直径 ; where d 应变计直径 is the diameter of the concrete strain gauge (9); 2) The actual restrained shrinkage strain gradient ζ generated by the protective layer concrete only under the restraint of steel bars is 实际钢约 = 2*(δ 实际钢约 - ε 实际钢约 ) / d 应变计直径 ; 3) The actual restraint shrinkage strain gradient ζ generated by the double restraint of the concrete in the protective layer by the internal concrete and steel bars of the mass concrete is 实际砼加钢筋约 = 2*(δ 实际砼加钢筋约 - ε 实际砼加钢筋约 ) / d 应变计直径 .

8. The measurement method according to claim 7, characterized in that: In step 2, apply butter evenly on the lower surfaces of the inner walls of containers A, B, C, and D, and then lay a layer of film before pouring the concrete (10).

9. The measuring method according to claim 7, characterized in that: In step 2, the concrete strain gauges (9) in containers A and C are installed along the axial directions parallel to and perpendicular to the steel bars (8) respectively. The installation position and direction of the concrete strain gauge (9) in container B are the same as those of the concrete strain gauge (9) in container A, and the installation position and direction of the concrete strain gauge (9) in container D are the same as those of the concrete strain gauge (9) in container C.

10. The measurement method according to claim 7, characterized in that: In step 4, the fine sand (6) is black sand grains. The spreading area of the fine sand (6) on the concrete (10) surface is square, and a fine sand array with a spacing of 1 - 2 mm is formed within each square spreading area.

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