Method for testing micro-creep of concrete interface transition zone

Abstract

The present invention provides a method for testing micro-creep in a concrete interface transition zone, which relates to the field of mechanical testing technology. The method comprises using a nanoindenter to perform a nano-indentation test on a polished concrete sample to determine the boundary between the concrete sample aggregate, the interface transition zone, and the cement mortar, thereby obtaining the width of the interface transition zone; using a nano-indentation rectangular grid to assist in locating the coordinates of the indentation center of the micro-creep test; calculating the maximum load of the micro-creep test based on the water-cement ratio of the concrete, the width of the interface transition zone, the average elastic modulus in the interface transition zone, and the average elastic modulus in the cement mortar; and performing a micro-creep test on the micro-creep test area to obtain a contact creep function and a contact creep modulus of the interface transition zone. The present invention can accurately locate the indentation center of the micro-creep test in the concrete interface transition zone, and the test results obtained by the micro-creep test have low discreteness, and can accurately reflect the creep performance of the interface transition zone.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical testing, and in particular to a method for testing micro-creep of a concrete interface transition zone. Background Art

[0002] Concrete is typically a three-phase composite material consisting of aggregate, an interfacial transition zone, and mortar. The interfacial transition zone is referred to as the interface. Accurately measuring micro-creep in this zone is crucial for predicting and actively controlling concrete creep. Instrumented indentation testing offers advantages such as short testing times, high accuracy, and minimal interference. However, the size, viscoelastic properties, and boundary clarity of the interfacial transition zone are significantly affected by aggregate size, surface morphology, initial moisture content, binder mix ratio, and age. This leads to uncertainty in the selection of indentation locations and indentation loads for micro-creep testing.

[0003] Chinese Invention Publication No. CN117571432A discloses a method and system for measuring cement paste creep. This method uses nanoindentation testing to determine the short-term microscopic creep properties of cement paste. However, because the test targets only the cement paste, it does not provide a method for determining the test area in the concrete interface transition zone or a loading method for creep testing in this area. Furthermore, it does not provide a method for locating the composite material interface region. Therefore, a reasonable method for measuring microscopic creep in the concrete interface transition zone is currently lacking. Summary of the Invention

[0004] To address the deficiencies of the aforementioned prior art, the present invention provides a method for testing the micro-creep of a concrete interface transition zone. First, a nanoindentation test is performed to locate the boundaries of the aggregate, interface transition zone, and cement mortar, thereby determining the interface transition zone width. A nanoindentation rectangular grid is then used to assist in locating the center of the micro-creep test indentation based on the interface transition zone width. Finally, the concrete water-cement ratio, interface transition zone width, interface transition zone elastic modulus, and cement mortar elastic modulus are substituted into the equation to determine the maximum load for the micro-creep test. The present method accurately locates the center of the micro-creep test indentation for the interface transition zone, resulting in low discreteness in the test results and accurate reflection of the creep performance of the interface transition zone.

[0005] Specifically, the present invention provides a method for testing the micro-creep of a concrete interface transition zone, the steps of which include:

[0006] S1. Perform nano-indentation test on concrete samples to obtain i groups of indentation points, where i is a positive integer from 1 to N and N is the total number of indentation points. Each time a group is indented, the mean elastic modulus of the current group of indentation points is obtained and recorded as the mean elastic modulus of the i-th group of indentation points E. i , and compare the mean elastic modulus of each two adjacent groups of indentation points until the first When the indentation points of group i-1 are recorded as group a indentation points, the indentation points of group i are recorded as group a+1 indentation points, and the indentation points of group a are used as the boundary between the aggregate and the interface transition zone; the nanoindentation test is continued and the indentation points of group b are used as the boundary between the interface transition zone and the cement mortar, so as to obtain the width of the interface transition zone in the concrete sample. , where D1 is the spacing in the X direction;

[0007] S2, based on S1, calculate the average equivalent indentation radius r of all nanoindentation test indentation points in the interface transition zone of the concrete sample c , get the coordinates (x, y) of the indentation center of the micro creep test;

[0008] S3, the average elastic modulus E of all groups of indentation points in the interface transition zone of the concrete sample ITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar , the maximum load P of the micro creep test is obtained 2,max , the expression is:

[0009] ;

[0010] Where w c is the water-cement ratio of the concrete sample, = E ITZ / E mortar , W is the width of the interface transition zone;

[0011] S4. Perform a micro creep test at the coordinates (x, y) of the center of the micro creep test indentation obtained in S2 to obtain creep data of the interface transition zone in the concrete sample.

[0012] Preferably, in S1, the direction of the aggregate in the concrete sample toward the cement mortar is set as the X direction, the direction perpendicular to the X direction is set as the Y direction, and N groups of indentation points are set from the origin along the X direction with the same spacing D1, and each group of indentation points includes Q indentation points with a spacing of D2 along the Y direction.

[0013] Preferably, in S1, in the process of determining the boundary line between the interface transition zone and the cement mortar using the bth group of indentation points, the average elastic modulus of each three consecutive groups of indentation points after the ath group is solved, and the two adjacent elastic modulus averages obtained are compared until the difference between the two adjacent elastic modulus averages is greater than or equal to 10% of the first elastic modulus average of the two adjacent elastic modulus averages, then the last group of indentation points corresponding to the second elastic modulus average of the two adjacent elastic modulus averages is recorded as the bth group of indentation points.

[0014] Preferably, in S2, the coordinates (x, y) of the center of the micro creep test indentation are expressed as:

[0015] ;

[0016] .

[0017] Preferably, in S3, the average elastic modulus E of all groups of indentation points in the interface transition zone is ITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar The expressions are:

[0018] ;

[0019] ;

[0020] Among them, E a+1 is the mean elastic modulus of the a+1th group of indentation points, E a+2 is the mean elastic modulus of the a+2 group of indentation points, E b-1 is the mean elastic modulus of the b-1 group of indentation points, E b is the mean elastic modulus of the indentation points in group b, E b+1 is the mean elastic modulus of the b+1th group of indentation points, E b+5 is the average elastic modulus of the b+5th group of indentation points.

[0021] Preferably, in S4, the contact creep function and the contact creep modulus C of the interface transition zone are obtained by processing the creep data.

[0022] Preferably, in S1, the number of N groups of indentation points in the X direction is N=b+5; and in S4, the number of micro creep test areas of each concrete sample is greater than or equal to 5.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention provides a specific method for determining the nanoindentation matrix covering the aggregate, the interface transition zone, and the cement mortar, and based on this, proposes a method for obtaining the number of indentation point groups N in the X direction of the nanoindentation rectangular grid and the width W of the interface transition zone.

[0025] 2. The present invention uses a nanoindentation rectangular grid based on the interface transition zone width W obtained from the test to accurately locate the center of the indentation in the micro-creep test of the interface transition zone, so that the loading point is located at the center of the interface transition zone.

[0026] 3. The present invention proposes a method based on the width of the interface transition zone W and the water-cement ratio of concrete w c , the average elastic modulus E of all groups of indentation points in the interface transition zoneITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar The maximum load P of the micro creep test 2,max The expression can ensure that the indentation radius of the micro-creep test does not exceed the range of the interface transition zone, while making the obtained creep data accurately reflect the creep performance of the interface transition zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of the method for testing micro-creep of concrete interface transition zone according to the present invention;

[0028] Figure 2 This is a graph showing the load (P)-depth (h) curve of the nano-indentation test obtained in a specific embodiment of the method for testing the micro-creep of the concrete interface transition zone of the present invention;

[0029] Figure 3 This is a flow chart of obtaining the width W of the interface transition zone in the method for testing the micro-creep of the concrete interface transition zone of the present invention;

[0030] Figure 4 A coordinate location diagram of the center of the micro-creep test indentation obtained in a specific embodiment of the method for testing the micro-creep of the concrete interface transition zone of the present invention;

[0031] Figure 5 The following is a graph showing several comparisons of creep depth and holding time during the micro creep test with a load of 50 mN.

[0032] Figure 6 3 is a graph showing creep depth and holding time during the loading stage when the micro creep test load is 250 mN according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0034] The present invention proposes a method for testing the micro creep of the concrete interface transition zone, such as Figures 1-6 As shown, the specific implementation steps include:

[0035] S1. The concrete sample is polished and the nanoindentation test is performed on the polished concrete sample using a nanoindenter to obtain the width W of the interface transition zone of the concrete sample, such as Figure 3 As shown, it specifically includes the following sub-steps:

[0036] S11. Select a point in the aggregate of the concrete sample as the origin, set the direction of the aggregate toward the cement mortar as the X direction, set the direction perpendicular to the X direction as the Y direction, set N groups of indentation points at equal intervals D1 along the X direction from the origin, and each group includes Q indentation points at equal intervals D2 along the Y direction.

[0037] S12. Use a nanoindenter to press indentation points one by one along the X direction from the origin, and record them as the first group of indentation points, the second group of indentation points, ..., the i-1th group of indentation points, the i-th group of indentation points, ..., the Nth group of indentation points. For each group of indentation points, the average elastic modulus of the group of indentation points is obtained, which is recorded as E1, E2, E3, ..., the average elastic modulus of the i-1th group of indentation points E i-1 , the mean elastic modulus E of the i-th group of indentation points i , ..., the mean elastic modulus E of the Nth group of indentation points N .

[0038] In a preferred embodiment of the present invention, the nanoindentation test adopts a quasi-static indentation test method. The nanoindentation test is loaded to a maximum load at a constant rate, and after holding the load for a certain period of time, it is unloaded to zero at a constant rate; a load (P)-indentation depth (h) curve is obtained, and the elastic modulus E of the indentation point is calculated based on the load (P)-indentation depth (h) curve.

[0039] The expression of elastic modulus E at the indentation point of nanoindentation test is:

[0040] ;

[0041] Where M is the indentation modulus of the tested material, ν is the Poisson's ratio of the tested material, and E y is the elastic modulus of the indenter material, ν y is the Poisson's ratio of the indenter material.

[0042] The expression of the indentation modulus M of the tested material is:

[0043] ;

[0044] Where β is the correction coefficient of pressure head, A c is the contact projection area of the indenter, according to A c =24.5h c 2 Calculate, h c is the contact depth at the indentation point, and S is the contact stiffness.

[0045] The contact stiffness S is usually fitted by the elastic segment of the upper half of the unloading curve in the load (P)-compression depth (h) curve. Its expression is:

[0046] .

[0047] Contact depth h at the indentation point c The expression is:

[0048] ;

[0049] Where h max is the maximum displacement of the indentation point, P1 is the maximum load of the nanoindentation test, and ε is a constant related to the indenter shape.

[0050] S13, compare the average elastic modulus of each two adjacent groups of indentation points until the first When the indentation points of group i-1 are recorded as group a indentation points, the indentation points of group i are recorded as group a+1 indentation points, and the indentation points of group a are used as the boundary between the aggregate and the interface transition zone.

[0051] S14. After the boundary line between the aggregate and the interface transition zone is obtained as the ath group of indentation points, continue to indent the indentation points one by one along the X direction and solve the average elastic modulus of each of the next three consecutive groups of indentation points. The expression is:

[0052] .

[0053] S15. Compare the two adjacent average elastic moduli obtained in S14 until the difference between the two adjacent average elastic moduli is greater than or equal to 10% of the first average elastic modulus of the two adjacent average elastic moduli, then record the last group of indentation points corresponding to the second average elastic modulus of the two adjacent average elastic moduli as the bth group of indentation points.

[0054] S16. Based on S15, in order to make the experimental value of the mean elastic modulus of the b-th group of indentation points close to the true value, 5 more groups of indentation points are pressed along the X direction to obtain the total number of indentation point groups in the X direction of the rectangular grid N = b + 5.

[0055] S17. Based on S11 to S16, the width W of the interface transition zone in the concrete sample is obtained, which is expressed as:

[0056] .

[0057] S2. Determine the coordinates (x, y) of the indentation center in the micro-creep test based on the width W of the interface transition zone in the concrete sample to ensure the accuracy of the micro-creep test. This specifically includes the following sub-steps:

[0058] S21. Divide the matrix indentation points obtained in S11 into aggregate, interface transition zone, and cement mortar using the boundary lines of group a and group b in S1. That is, use the indentation points of group a as the boundary line between aggregate and interface transition zone, and use the indentation points of group b as the boundary line between interface transition zone and cement mortar. Calculate the average equivalent indentation radius r of all nanoindentation test indentation points in the interface transition zone of the concrete sample. c .

[0059] S22, the average equivalent indentation radius r obtained in S21 c Based on this, the coordinates (x, y) of the indentation center of the micro-creep test are obtained as follows: .

[0060] Specifically, in order to obtain the maximum allowable indentation range of the micro-creep test in the interface transition zone of the concrete sample, the micro-creep test indentation radius a c It should reach half of the width W of the interface transition zone. At the same time, the center of the indentation point should be located at the center of the interface transition zone in the concrete sample along the X direction, that is, the center line of the two indentation points of group a and group b. Considering that the distance between the indentation points in the X direction is D1, the distance between the indentation points of group a and the origin along the X direction is aD1, and the distance between the indentation points of group b and the origin along the X direction is bD1. The distance between the indentation center and the origin along the X direction can be calculated, that is, the x coordinate of the indentation center of the micro creep test is , where a and b are natural numbers.

[0061] At the same time, the interface transition zone in the concrete sample is an irregularly shaped, uniformly width band, requiring a rectangular nanoindentation grid to assist in locating the nearby interface region. Therefore, in the Y direction, the micro-creep test indentation point is placed as close as possible to the rectangular nanoindentation grid. The distance in the Y direction between the micro-creep test indentation point and the origin, i.e., the y-coordinate of the micro-creep test indentation center, is the sum of the following three parts:

[0062] a. Average equivalent indentation radius r of all nanoindentation test indentation points in the interface transition zone of the concrete sample c ;

[0063] b. The indentation radius of the micro creep test shall not exceed half the width of the interface transition zone in the concrete sample. ;

[0064] c. Total width of the nanoindentation grid .

[0065] S3. Calculate the maximum load P for micro creep test 2,max , specifically including the following sub-steps:

[0066] S31. Calculate the average elastic modulus E of all groups of indentation points in the interface transition zone of the concrete sample. ITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar , whose expression is:

[0067] ;

[0068] ;

[0069] Among them, E a+1 is the mean elastic modulus of the a+1th group of indentation points, E a+2 is the mean elastic modulus of the a+2 group of indentation points, E b-1 is the mean elastic modulus of the b-1 group of indentation points, E b is the mean elastic modulus of the indentation points in group b, E b+1 is the mean elastic modulus of the b+1th group of indentation points, E b+5 is the average elastic modulus of the b+5th group of indentation points.

[0070] S32, under the premise of limiting the width of the interface transition zone W obtained in S1, by considering the concrete water-cement ratio w c , the average elastic modulus E of all groups of indentation points in the interface transition zone ITZ , the average elastic modulus E of all groups of indentation points in cement mortar mortar The influence of micro creep test on the maximum load P of micro creep test is obtained. 2,max The expression is:

[0071] ;

[0072] Where w c is the water-cement ratio of the concrete sample, = E ITZ / E mortar , W is the width of the interface transition zone.

[0073] Because the interface transition zone in concrete samples is a heterogeneous composite material composed of hydration products, unhydrated particles, and pores, if the micro-creep test indentation load is too low and the indentation range is too small, the test results will not reflect the overall creep performance of the composite material. At the same time, due to the size limitations of the interface transition zone itself, the indentation load level currently used in ordinary cement mortar is too high, and directly applying it will cause the indentation point to break through the interface transition zone boundary. Taking these two points into consideration, it is necessary to ensure that the micro-creep test indentation radius does not exceed the interface transition zone range while increasing the indentation load level so that the test results of the micro-creep test accurately reflect the creep performance of the interface transition zone.

[0074] Therefore, the maximum load P of the micro creep test2,max The water-cement ratio w of the concrete sample c , the width of the interface transition zone W, the average elastic modulus E of all groups of indentation points in the interface transition zone ITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar The specific process is as follows:

[0075] Firstly, the micro creep test load P2 and the micro creep test indentation radius a of cement mortar under the water-cement ratio of 0.3 are compared. c The test data of the water-cement ratio was fitted to obtain the calculation formula of the micro creep test load of cement mortar under this water-cement ratio: ; Then consider the influence of water-cement ratio, w c / 0.3 is used as a correction factor to make the formula applicable to cement mortars with different water-cement ratios; further, in order to make the formula applicable to the interface transition zone, the ratio of the elastic modulus of the interface transition zone to the elastic modulus of the cement mortar is As another correction factor; taking the micro creep test indentation point not exceeding the interface transition zone as the restriction condition, the micro creep test indentation radius a c The maximum value of is half the width of the interface transition zone, that is, Finally, the maximum load of the micro creep test is obtained .

[0076] S4. Perform a micro creep test at the coordinates of the center of the micro creep test indentation obtained in S2, and load at a constant rate to the maximum load P. 2,max After holding the load for a preset constant time, the load is unloaded to zero at a constant rate to obtain creep data; further, the number of micro creep test areas of each concrete sample is greater than or equal to 5.

[0077] The creep data are processed to obtain the contact creep function and contact creep modulus C of the interface transition zone.

[0078] The expression of the contact creep function is:

[0079] ;

[0080] Where Δh(t) is the increment of indentation depth during the loading stage; L(t) and L(0) are the contact creep compliance at loading time t and the beginning of the loading stage, respectively.

[0081] The contact creep modulus C is obtained by fitting the micro-creep test results with a logarithmic function. The expression of the fitting function is:

[0082] ;

[0083] Where: C is the contact creep modulus, τ is the characteristic time of micro creep.

[0084] For lightweight aggregate concrete, as used in this method, it's difficult to clearly capture the boundaries between aggregate and the interface transition zone, and between the interface transition zone and cement paste, using only an optical microscope. This method effectively distinguishes between aggregate, the interface transition zone, and cement mortar, improving the accuracy of micro-creep test results. This method requires repetition for each micro-creep test. For other concretes with sufficiently clear boundaries between aggregate and the interface transition zone, such as conventional aggregate concrete, after obtaining the maximum load for the micro-creep test at S3, a micro-creep test can be performed directly starting from the aggregate boundary and at the W / 2 position along the X-axis.

[0085] The following is a detailed description of a method for testing the micro-creep of a concrete interface transition zone according to the present invention with reference to an example:

[0086] S1. Grind and polish the concrete sample, and measure the roughness of the concrete sample using an atomic force microscope until the roughness is less than a preset value of 100 nm; perform a nanoindentation test on the polished concrete sample using a nanoindenter to obtain the width W of the interface transition zone in the concrete sample, which specifically includes the following sub-steps:

[0087] S11. Select a point inside the aggregate in the concrete sample as the origin, set the direction of the aggregate toward the cement mortar as the X direction, and the direction perpendicular to the X direction as the Y direction. Set N groups of indentation points from the origin along the X direction with a spacing of D1 = 5 μm. Each group contains 5 indentation points with a spacing of D2 = 5 μm along the Y direction.

[0088] S12. Use a nanoindenter to press indentation points from the origin along the X direction in groups, which are respectively recorded as the first group, the second group, ..., the i-th group, ..., the N-th group.

[0089] In this specific embodiment, the nanoindentation test adopts a quasi-static indentation test method. The nanoindentation test is loaded at a rate of 0.2 mN / s to a maximum load of 2 mN. After holding the load for 10 seconds, it is unloaded at a rate of 0.2 mN / s to zero. The load (P)-indentation depth (h) curve is shown in FIG. Figure 2 , Figure 2 Where F1 is loading, F2 is holding load, and F3 is unloading. The elastic modulus E of the indentation point is calculated based on the load (P)-indentation depth (h) curve.

[0090] Each time a group of indentation points is pressed, the average elastic modulus of the group of indentation points is obtained and recorded as E1, E2, E3, ..., E i ,……,E N The calculation results are shown in Table 1.

[0091] Table 1 Nanoindentation test data

[0092]

[0093] S13, compare the average elastic modulus of each two adjacent groups of indentation points. From Table 1, we can see that the first time It appears in Group 6 and Group 7, with Group 6 as the dividing line between the aggregate and interface transition zone, i.e. a=6.

[0094] S14. After obtaining the sixth group of boundary lines between the aggregate and the interface transition zone, continue to press the indentation points one by one along the X direction and calculate the average elastic modulus of each of the next three consecutive groups of indentation points.

[0095] S15. Compare the two adjacent average elastic moduli obtained in S14. The calculation results are shown in Table 1. It can be seen from Table 1 that the difference between the average elastic moduli of the 21st group and the 20th group is greater than or equal to 10% of the average elastic modulus of the 20th group, that is, the first average elastic modulus. Then, the three groups of indentation points corresponding to the average elastic modulus of the 21st group, that is, the 21st group of indentation points, the 22nd group of indentation points and the 23rd group of indentation points are used as the last group of indentation points (the 23rd group of indentation points) as the boundary line between the interface transition zone and the cement mortar, that is, b=23.

[0096] S16. Continue to press 5 groups of indentation points along the X direction. The total number of indentation point groups in the X direction of the rectangular grid is N=28.

[0097] S17. Based on S11 to S16, the width of the interface transition zone in the concrete sample is obtained as W = 85 μm.

[0098] S2. Determine the coordinates (x, y) of the center of the micro-creep test indentation based on the width W of the interface transition zone in the concrete sample. This specifically includes the following sub-steps:

[0099] S21, through the boundary line between the 6th and 23rd groups in S1, the matrix indentation points obtained in S11 are divided into aggregate, interface transition zone and cement mortar. The average equivalent indentation radius r of all indentation points in the interface transition zone is calculated from Table 1. c =1.304μm.

[0100] S22, according to the parameters a, b, D1, D2, Q obtained from S1 and the parameter r obtained from S21 c , the coordinates of the indentation center in the micro-creep test are obtained as (72.5, 83.8).

[0101] S3. Calculate the maximum load P for micro creep test 2,max , specifically including the following sub-steps:

[0102] S31. Calculate the average elastic modulus E of all groups of indentation points in the interface transition zone of the concrete sample. ITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar, E is calculated from Table 1 ITZ =17.98GPa, E mortar =24.33GPa.

[0103] S32, under the premise of limiting the width of the interface transition zone W obtained in S1, consider the concrete water-cement ratio w c The average elastic modulus E of all groups of indentation points in the interface transition zone is 0.3. ITZ , the average elastic modulus E of all groups of indentation points in cement mortar mortar The influence of micro creep test on the maximum load P of micro creep test is obtained. 2,max =251.87mN, and the actual loading is taken as 250mN.

[0104] S4. Perform a micro creep test at the center coordinate of the indentation obtained in S2. In this specific embodiment, the micro creep test adopts a quasi-static test method. The loading phase takes 10 seconds and is loaded at a rate of 25 mN / s to a maximum load P. 2,max After holding the load for 180 seconds, the material was unloaded at a rate of 25 mN / s to zero, and creep data was recorded. By processing the creep data, the contact creep function and contact creep modulus C of the micro-creep test indentation point were obtained, which more accurately reflects the creep performance of the concrete interface transition zone.

[0105] In order to prove the accuracy of the method of the present invention, a commonly used interface transition zone micro creep test load value of 50mN was used for comparison. Figure 5 Several comparative curves of creep depth and holding time during the loading phase are given when the micro-creep test load is 50mN. This traditional method only uses a nanoindenter in high-power mode to capture the aggregate boundary without distinguishing between aggregate, interface transition zone and cement mortar, and selects 5 areas near the aggregate boundary for micro-creep testing. First, this traditional method cannot ensure that the indentation point in the micro-creep test is accurately pressed within the interface transition zone; second, 50mN is too low as the micro-creep test load level. Table 2 gives the results based on Figure 5 The contact creep modulus values calculated from the data have a mean of 205.24 GPa and a variance of 3927.31. The results are highly discrete and cannot accurately reflect the creep performance of the interface transition zone.

[0106] Table 2 Contact creep modulus at the indentation point of 50 mN and 250 mN micro-creep tests

[0107]

[0108] The method of the present invention is to first determine the center coordinates of the indentation in the micro creep test after distinguishing the aggregate, the interface transition zone and the slurry, so that the indentation point of the micro creep test is at the center of the interface transition zone, and then calculate the maximum load P of the micro creep test based on this method. 2,max =250mN. Figure 6 The creep depth and holding time curve of the micro creep test load of 250mN obtained by the method of the present invention are given in Table 2. Figure 6 The contact creep modulus values calculated from the data have a mean of 184.02 GPa and a variance of 41.58. Compared with the micro-creep test results using a maximum load of 50 mN, the test results obtained based on this method have less discreteness and can more accurately reflect the creep performance of the interface transition zone.

[0109] The present invention provides a method for testing micro-creep in a concrete interface transition zone. The method includes obtaining the width of the concrete interface transition zone, locating the center coordinates of a micro-creep test indentation, selecting and applying a micro-creep load, and ultimately obtaining creep performance indicators for the interface transition zone. The test results accurately and quantitatively describe the creep characteristics of the concrete interface transition zone, providing essential empirical parameters for multi-scale modeling of concrete creep and having practical significance for the reasonable prediction of concrete creep behavior.

[0110] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for testing the micro creep of the concrete interface transition zone, characterized in that: The steps include: S1. Perform nano-indentation test on concrete samples to obtain i groups of indentation points, where i is a positive integer from 1 to N and N is the total number of indentation points. Each time a group is indented, the mean elastic modulus of the current group of indentation points is obtained and recorded as the mean elastic modulus of the i-th group of indentation points E. i , and compare the mean elastic modulus of each two adjacent groups of indentation points until the first When the indentation points of group i-1 are recorded as group a indentation points, the indentation points of group i are recorded as group a+1 indentation points, and the indentation points of group a are used as the boundary between the aggregate and the interface transition zone; the nanoindentation test is continued and the indentation points of group b are used as the boundary between the interface transition zone and the cement mortar, so as to obtain the width of the interface transition zone in the concrete sample. , where D1 is the distance between adjacent groups of indentation points in the X direction, and the X direction is the direction of aggregate toward cement mortar in the concrete sample; In the process of determining the boundary between the interface transition zone and the cement mortar using the bth group of indentation points, the average elastic modulus of each of three consecutive groups of indentation points after the ath group is calculated, and the two adjacent average elastic moduli obtained are compared until the difference between the two adjacent average elastic moduli is greater than or equal to 10% of the first average elastic modulus of the two adjacent average elastic moduli. Then, the last group of indentation points corresponding to the second average elastic modulus of the two adjacent average elastic moduli is recorded as the bth group of indentation points; S2, based on S1, calculate the average equivalent indentation radius r of all nanoindentation test indentation points in the interface transition zone of the concrete sample c , get the coordinates (x, y) of the indentation center of the micro creep test; S3, the average elastic modulus E of all groups of indentation points in the interface transition zone of the concrete sample ITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar , the maximum load P of the micro creep test is obtained 2,max , the expression is: ； Where w c is the water-cement ratio of the concrete sample, = E ITZ / E mortar , W is the width of the interface transition zone; S4. Perform a micro creep test at the coordinates (x, y) of the center of the micro creep test indentation obtained in S2 to obtain creep data of the interface transition zone in the concrete sample.

2. The method for testing micro-creep of a concrete interface transition zone according to claim 1, characterized in that: In S1, the direction of the aggregate in the concrete sample toward the cement mortar is set as the X direction, and the direction perpendicular to the X direction is set as the Y direction. N groups of indentation points are set from the origin along the X direction with the same spacing D1. Each group of indentation points includes Q indentation points with a spacing of D2 along the Y direction.

3. The method for testing micro-creep of concrete interface transition zone according to claim 2, characterized in that: In S2, the coordinates (x, y) of the indentation center in the micro-creep test are expressed as: ； 。 4. The method for testing micro-creep of a concrete interface transition zone according to claim 1, characterized in that: In S3, the average elastic modulus E of all groups of indentation points in the interface transition zone is ITZ and the average elastic modulus E of all groups of indentation points in cement mortar mortar The expressions are: ； ； Among them, E a+1 is the mean elastic modulus of the a+1th group of indentation points, E a+2 is the mean elastic modulus of the a+2 group of indentation points, E b-1 is the mean elastic modulus of the b-1 group of indentation points, E b is the mean elastic modulus of the indentation points in group b, E b+1 is the mean elastic modulus of the b+1th group of indentation points, E b+5 is the average elastic modulus of the b+5th group of indentation points.

5. The method for testing micro-creep of concrete interface transition zone according to claim 1, characterized in that: In S4, the contact creep function and contact creep modulus C of the interface transition zone are obtained by processing the creep data.

6. The method for testing micro-creep of a concrete interface transition zone according to claim 2, characterized in that: In S1, the number of N groups of indentation points in the X direction is N=b+5; in S4, the number of micro creep test areas of each concrete sample is greater than or equal to 5.

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