Method for testing shear strength of new and old concrete interface by considering constraint effect of original structure

Abstract

The invention belongs to the technical field of structure repair and reinforcement, and discloses a new and old concrete interface shear strength testing method considering an original structure constraint effect. The method comprises the following steps that the constraint degree of old concrete of an original structure on new concrete of a reinforcing layer and the inner diameter and the outer diameter of an old concrete ring are determined, and the outer diameter of the new concrete ring is obtained through calculation; pouring to obtain old concrete, and pouring new concrete on the outer side of the old concrete to obtain a circular ring push-out test piece; and performing a push-out test by adopting the circular ring push-out test piece, and calculating the interface shear strength of the new and old concrete. According to the testing method, by changing the thickness of the new concrete ring, the constraint degree is smoothly changed, the shear strength of the new and old concrete interface is conveniently and rapidly tested, then the interface bonding performance of the new and old concrete under the condition of different constraint degrees is evaluated, and scientific guidance is provided for new and old concrete interface treatment in engineering practice.

Description

Technical Field

[0001] The invention relates to the technical field of structural repair and reinforcement, and in particular to a method for testing the shear strength of a new-old concrete interface taking into account the constraint effect of the original structure. Background Art

[0002] As infrastructure service time increases, performance degradation is inevitable, so repair and reinforcement are often required. As a repair and reinforcement method that is easy to construct and simple in principle, the section enlargement method is widely used in the maintenance and reinforcement of concrete slabs, beams, columns and other components. Its core approach is to add a high-performance concrete layer outside the original concrete structure, and achieve structural reinforcement through the synergistic force of the new and old concrete. However, the bonding surface between the new and old concrete is the weak surface of the reinforced structure, and ensuring reliable bonding between the new and old concrete directly determines the success or failure of the reinforcement.

[0003] Interface shear strength is a common way to quantify the bonding effect between new and old concrete. When calculating the shear strength between interfaces, the main factors considered are the impact of factors such as interface roughness, stud implantation, wetness, and maintenance system, and the impact of the degree of constraint on the reinforcement layer is not considered. In fact, the different environments and geometric dimensions of the reinforced objects have great differences in the degree of constraint on the added high-performance concrete layer. When the original structure has strong constraints on the added concrete, it is easy to cause debonding and cracking of the reinforced layer concrete. Therefore, when considering the shear strength of the interface between new and old concrete, the degree of constraint of the original structure on the new concrete should be taken into account.

[0004] However, the current methods for testing interfacial bonding properties have not yet established a correlation between the interfacial shear strength and the degree of constraint of the original structure. For example, double-sided shear tests and single-sided shear tests have not considered the effect of the original structural constraint on the interfacial shear strength. Summary of the invention

[0005] The purpose of the present invention is to provide a testing method for the shear strength of the new-old concrete interface taking into account the constraint effect of the original structure, which can accurately quantify the influence of the constraint degree of the original structure on the interface shear performance.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for testing the shear strength of the interface between new and old concrete taking into account the constraint effect of the original structure, comprising the following steps:

[0008] (1) Determine the degree of constraint of the old concrete of the original structure on the new concrete of the reinforcement layer, and the inner and outer diameters of the old concrete ring;

[0009] The outer diameter of the new concrete ring is calculated based on the degree of constraint, the inner diameter and the outer diameter of the old concrete ring;

[0010] (2) according to the inner diameter and outer diameter of the old concrete ring in step (1), old concrete is poured and naturally cured to obtain an old concrete ring; according to the outer diameter of the new concrete ring in step (1), the new concrete ring is poured outside the old concrete ring and cured to obtain a circular ring push-out specimen;

[0011] (3) Using the circular push-out specimen described in step (2), a push-out test is performed to calculate the interface shear strength between the new and old concrete.

[0012] Preferably, in the test method, the outer diameter of the new concrete ring in step (1) is based on the

[0013] Formula 1 calculates:

[0014]

[0015] In formula 1, Ψ is the degree of constraint, unit: %; E c1 is the elastic modulus of old concrete, unit: GPa; E c2 is the elastic modulus of new concrete, unit: GPa; υ c1 is the Poisson's ratio of old concrete; c2 is the Poisson's ratio of new concrete; R 1 is the inner ring radius of the old concrete, unit: mm; R 2 is the outer ring radius of the old concrete, unit: mm; R 3 is the outer ring radius of new concrete, unit: mm.

[0016] Preferably, in the test method, the constraint degree in step (1) ranges from 0 to 100%.

[0017] Preferably, in the test method, the temperature of the natural curing in step (2) is 10-30° C., the humidity is 30-80%, and the time is ≥3 months.

[0018] Preferably, in the test method, the curing temperature in step (2) is 18-22° C., the humidity is ≥95%, and the curing time is ≥28 days.

[0019] Preferably, in the test method, the axial length of the new concrete ring in step (2) is equal to the axial length of the old concrete ring.

[0020] Preferably, in the test method, the height difference between the new concrete ring and the old concrete ring in step (2) is ≥ 2 cm.

[0021] Preferably, in the test method, step (2) further comprises treating the outer side of the old concrete ring to enhance the interface roughness before pouring the new concrete ring on the outer side of the old concrete, wherein the treatment comprises one or more of grooving, roughening, reinforcing bars and drilling.

[0022] Preferably, in the test method, the interfacial shear strength of the new and old concrete in step (3) is calculated according to Formula 2:

[0023] T=P / S 公式2 ;

[0024] In formula 2, τ Ψ is the interface shear strength under a certain degree of constraint, unit: MPa; P is the load when the ring pushes out the specimen, unit: N; S is the contact area between the new concrete ring and the old concrete ring, unit: mm 2 .

[0025] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0026] Compared with the existing single-sided shear test or double-sided shear test, the circular ring push-out test method of the present invention has uniform constraints on the new concrete layer in all directions, and can accurately quantify the influence of the original structural constraint degree on the interface shear performance. At the same time, the method changes the thickness of the new concrete ring by adjusting the inner diameter and outer diameter of the old concrete ring, thereby achieving a change in the degree of constraint. It can more conveniently and quickly test the shear strength of the new and old concrete interface considering the constraint effect of the original structure, and then evaluate the interface bonding performance of the new and old concrete under different constraint degrees, providing scientific guidance for the treatment of the new and old concrete interface in engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

[0028] Figure 1 A flow chart of the steps of the new-old concrete interface shear strength test method considering the constraint effect of the original structure;

[0029] Figure 2 It is a three-dimensional schematic diagram of the ring push-out specimen;

[0030] Figure 3 It is a cross-sectional schematic diagram of the ring push-out specimen;

[0031] Figure 2 , Figure 3 In the figure, 1 is the old concrete ring and 2 is the new concrete ring. DETAILED DESCRIPTION

[0032] The present invention provides a method for testing the shear strength of the interface between new and old concrete taking into account the constraint effect of the original structure, comprising the following steps:

[0033] (1) Determine the degree of constraint of the old concrete of the original structure on the new concrete of the reinforcement layer, and the inner and outer diameters of the old concrete ring;

[0034] The outer diameter of the new concrete ring is calculated based on the degree of constraint, the inner diameter and the outer diameter of the old concrete ring;

[0035] (2) according to the inner diameter and outer diameter of the old concrete ring in step (1), old concrete is poured and naturally cured to obtain an old concrete ring; according to the outer diameter of the new concrete ring in step (1), the new concrete ring is poured outside the old concrete ring and cured to obtain a circular ring push-out specimen;

[0036] (3) Using the circular push-out specimen described in step (2), a push-out test is performed to calculate the interface shear strength between the new and old concrete.

[0037] In the present invention, the outer diameter of the new concrete ring in step (1) is calculated according to formula 1:

[0038]

[0039] In formula 1, Ψ is the degree of constraint, unit: %; E c1 is the elastic modulus of old concrete, unit: GPa; E c2 is the elastic modulus of new concrete, unit: GPa; υ c1 is the Poisson's ratio of old concrete; c2 is the Poisson's ratio of new concrete; R 1 is the inner ring radius of the old concrete, unit: mm; R 2 is the outer ring radius of the old concrete, unit: mm; R 3 is the outer ring radius of new concrete, unit: mm.

[0040] In the present invention, the value range of the constraint degree in step (1) is preferably 0 to 100%, more preferably 50 to 100%, and even more preferably 60 to 90%.

[0041] In the present invention, the types of the new concrete and the old concrete in step (1) are not limited, as long as they meet the requirements of the present invention.

[0042] In the present invention, the temperature of the natural curing in step (2) is preferably 10-30°C, more preferably 15-25°C, and more preferably 20°C; the humidity is preferably 30-80%, more preferably 50-75%, and more preferably 60%; the time is preferably ≥3 months, more preferably ≥4 months, and more preferably 4 months.

[0043] In the present invention, the curing temperature in step (2) is preferably 18-22°C, more preferably 19-21°C, and more preferably 20°C; the humidity is preferably ≥95%, more preferably ≥96%, and more preferably 97%; the time is preferably ≥28 days, more preferably ≥35 days, and more preferably 40 days.

[0044] In the present invention, the axial length of the new concrete ring in step (2) is preferably equal to the axial length of the old concrete ring.

[0045] In the present invention, the height difference between the new concrete ring and the old concrete ring in step (2) is preferably ≥2 cm, more preferably ≥3 cm, and even more preferably 4 cm.

[0046] In the present invention, the new concrete ring and the old concrete ring are staggered on the same side plane (such as Figure 2 , Figure 3 The purpose of this (as shown) is to facilitate the smooth introduction of the new concrete ring.

[0047] In the present invention, step (2) preferably further comprises treating the outer side of the old concrete ring to enhance the interface roughness before pouring the new concrete ring on the outer side of the old concrete ring.

[0048] In the present invention, the processing method preferably includes one or more of grooving, roughening, reinforcing bars and drilling, further preferably includes grooving and / or roughening, and more preferably grooving.

[0049] In the present invention, the purpose of treating the outer side of the old concrete ring is to improve the interface bonding performance between the new and old concrete.

[0050] In the present invention, the interfacial shear strength of the new and old concrete in step (3) is calculated according to Formula 2:

[0051] τ ψ =P / S 公式2 ;

[0052] In formula 2, τ Ψ is the interface shear strength under a certain degree of constraint, unit: MPa; P is the load when the ring pushes out the specimen, unit: N; S is the contact area between the new concrete ring and the old concrete ring, unit: mm 2 .

[0053] In the present invention, the method of the push-out test in step (3) is not limited, and a method familiar to those skilled in the art can be used. Specifically, in embodiments 1 to 3 of the present invention, the push-out test in step (3) preferably includes the following steps: (1) placing the push-out specimen on a universal mechanical testing machine, and keeping the push-out specimen flat by placing a layer of fine sand on the top and bottom surfaces of the push-out specimen; (2) starting the universal testing machine, and loading the push-out specimen to failure at a rate of 0.3 kN / s, with a peak load drop of 20% being the standard.

[0054] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Example 1

[0056] This embodiment provides a test method for the shear strength of the new and old concrete interface taking into account the constraints of the original structure (the test process is as follows Figure 1 As shown), comprising the following steps:

[0057] (1) Determine the degree of restraint of the original structure's old concrete on the new concrete of the reinforcement layer Ψ = 60.5%, and the size of the old concrete ring R 1 =70mm, R 2 =100mm; old concrete is C30, E c1 =30GPa,υ c1 =0.2; new concrete is C50, E c2 =34.5GPa,υ c2 =0.22; Based on the degree of constraint of the original structure's old concrete on the new concrete of the reinforcement layer and the size of the old concrete ring, the size of the new concrete ring R is calculated by referring to Formula 1 3 =125mm;

[0058] (2) pouring C30 concrete according to the size of the old concrete ring obtained in step (1), and curing for 3 months under natural conditions of 25° C. and 75% humidity to obtain an old concrete ring;

[0059] (3) According to the size of the new concrete ring obtained in step (1), C50 concrete is poured on the outside of the old concrete ring, the axial length of the new concrete ring and the old concrete ring is 150 mm, and the height difference between the new concrete ring and the old concrete ring is 4 cm. The ring is cured at 20° C. and 95% humidity for 28 days to obtain a circular ring push-out specimen;

[0060] (4) The push-out test was carried out using the circular push-out specimen of step (2). The load P of the circular push-out specimen when pushed out was recorded as 172000N and the contact area S between the new and old concrete was 69080mm. 2 According to formula 2, the interface shear strength τ between new and old concrete at 60.5% constraint degree is calculated. Ψ =2.5MPa.

[0061] Example 2

[0062] This embodiment provides a method for testing the shear strength of the new-old concrete interface taking into account the constraint effect of the original structure, comprising the following steps:

[0063] (1) Determine the degree of restraint of the original structure's old concrete on the new concrete of the reinforcement layer Ψ = 74.2%, and the size of the old concrete ring R 1 =0mm, R 2 =100mm; old concrete is C30, E c1 =30GPa,υ c1 =0.2; new concrete is C50, E c2 =34.5GPa,υ c2 =0.22; Based on the degree of constraint of the original structure's old concrete on the new concrete of the reinforcement layer and the size of the old concrete ring, the size of the new concrete ring R is calculated by referring to Formula 1 3 =155mm;

[0064] (2) pouring C30 concrete according to the size of the old concrete ring obtained in step (1), and curing for 3 months under natural conditions of 25° C. and 75% humidity to obtain an old concrete ring;

[0065] (3) According to the size of the new concrete ring obtained in step (1), C50 concrete is poured on the outside of the old concrete ring, the axial length of the new concrete ring and the old concrete ring is 150 mm, and the height difference between the new concrete ring and the old concrete ring is 4 cm. The ring is cured at 20° C. and 95% humidity for 28 days to obtain a circular ring push-out specimen;

[0066] (4) The push-out test was carried out using the circular ring push-out specimen of step (2). The load P of the circular ring push-out specimen when pushed out was recorded as 214000N, and the contact area S between the new and old concrete was 69080mm. 2 According to formula 2, the interface shear strength τ between new and old concrete at 74.2% constraint degree is calculated. Ψ =3.1MPa.

[0067] Example 3

[0068] This embodiment provides a method for testing the shear strength of the new-old concrete interface taking into account the constraint effect of the original structure, comprising the following steps:

[0069] (1) Determine the degree of restraint of the original structure's old concrete on the reinforced layer's new concrete: Ψ = 83.8% and the size of the old concrete ring: R 1 =0mm, R 2 =100mm; old concrete is C30, E c1 =30GPa,υ c1 =0.2; new concrete is C50, E c2 =34.5GPa,υ c2 =0.22; Based on the degree of constraint of the original structure's old concrete on the new concrete of the reinforcement layer and the size of the old concrete ring, the size of the new concrete ring R is calculated by referring to Formula 1 3 =125mm;

[0070] (2) pouring C30 concrete according to the size of the old concrete ring obtained in step (1), and curing for 3 months under natural conditions of 25° C. and 75% humidity to obtain an old concrete ring;

[0071] (3) According to the size of the new concrete ring obtained in step (1), C50 concrete is poured on the outside of the old concrete ring, the axial length of the new concrete ring and the old concrete ring is 150 mm, and the height difference between the new concrete ring and the old concrete ring is 4 cm. The ring is cured at 20° C. and 95% humidity for 28 days to obtain a circular ring push-out specimen;

[0072] (4) The push-out test was carried out using the circular push-out specimen of step (2). The load P of the circular push-out specimen when pushed out was recorded as 242000N and the contact area S between the new and old concrete was 69080mm. 2 According to formula 2, the interface shear strength τ between new and old concrete at 83.8% constraint degree is calculated. Ψ =3.5MPa.

[0073] From the results of Examples 1 to 3, it can be seen that the different degrees of constraint of the original structure lead to significant differences in the interface shear strength, which in turn leads to significant differences in the interface bonding degree. It can be seen that the ring push-out test set by the present invention is more uniform in the degree of constraint of the old concrete on the new concrete in all directions than the single-sided shear test and the double-sided shear test, which effectively associates the degree of constraint with the interface bonding performance of the new and old concrete, and accurately quantifies the influence of the degree of constraint of the original structure on the interface bonding performance.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for testing the shear strength of the interface between new and old concrete taking into account the constraints of the original structure, characterized in that: The following steps are involved: (1) Determine the degree of constraint of the old concrete of the original structure on the new concrete of the reinforcement layer, and the inner and outer diameters of the old concrete ring; The outer diameter of the new concrete ring is calculated based on the degree of constraint, the inner diameter and the outer diameter of the old concrete ring; (2) according to the inner diameter and outer diameter of the old concrete ring in step (1), old concrete is poured and naturally cured to obtain an old concrete ring; according to the outer diameter of the new concrete ring in step (1), the new concrete ring is poured outside the old concrete ring and cured to obtain a circular ring push-out specimen; (3) A push-out test is performed using the circular push-out specimen described in step (2) to calculate the interfacial shear strength between the new and old concrete.

2. The testing method according to claim 1, characterized in that: The outer diameter of the new concrete ring in step (1) is calculated according to formula 1: In formula 1, Ψ is the degree of constraint, unit: %; E c1 is the elastic modulus of old concrete, unit: GPa; E c2 is the elastic modulus of new concrete, unit: GPa; υ c1 is the Poisson's ratio of old concrete; c2 is the Poisson's ratio of the new concrete; R1 is the inner ring radius of the old concrete, unit: mm; R2 is the outer ring radius of the old concrete, unit: mm; R3 is the outer ring radius of the new concrete, unit: mm.

3. The testing method according to claim 1 or 2, characterized in that: The value range of the constraint degree in step (1) is 0 to 100%.

4. The testing method according to claim 1, characterized in that: The temperature of the natural curing in step (2) is 10-30° C., the humidity is 30-80%, and the time is ≥3 months.

5. The testing method according to claim 1 or 4, characterized in that: The curing temperature in step (2) is 18-22° C., the humidity is ≥95%, and the curing time is ≥28 days.

6. The testing method according to claim 1, characterized in that: In step (2), the axial length of the new concrete ring is equal to the axial length of the old concrete ring.

7. The testing method according to claim 6, characterized in that: In step (2), the height difference between the new concrete ring and the old concrete ring is ≥ 2 cm.

8. The testing method according to claim 1, characterized in that: Step (2) also includes treating the outer side of the old concrete ring to enhance the interface roughness before pouring the new concrete ring on the outer side of the old concrete ring, wherein the treatment method includes one or more of grooving, roughening, embedding reinforcement and drilling.

9. The testing method according to claim 1, characterized in that: The interfacial shear strength of the new and old concrete in step (3) is calculated according to formula 2: τ ψ = P / S formula 2; In formula 2, τ Ψ is the interface shear strength under a certain degree of constraint, unit: MPa; P is the load when the ring pushes out the specimen, unit: N; S is the contact area between the new concrete ring and the old concrete ring, unit: mm 2 .

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