A method for evaluating the risk of concrete cracking

Abstract

The present application relates to a kind of concrete cracking risk evaluation methods, comprising: obtaining concrete mix proportion;Based on concrete mix proportion, according to the corresponding relationship between the pre-established concrete mix proportion, constraint degree and cracking risk, determine the cracking risk of concrete mix proportion under different constraint degrees;Wherein the establishment process of corresponding relationship includes: according to concrete mix proportion, prepare concrete test piece under different constraint degree conditions and carry out maintenance;For each concrete test piece, the image of concrete test piece is collected at multiple monitoring times using DIC technology, the first principal strain is determined from the image, then the time-damage index relationship formula corresponding to each constraint degree is fitted, the damage index of final setting time under each constraint degree condition is obtained according to each relationship, and the cracking risk of concrete test piece under different constraint degree conditions is determined according to the damage index and the preset damage index limit value, to establish the corresponding relationship between concrete mix proportion, constraint degree and cracking risk.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and in particular relates to a method for assessing the risk of concrete cracking. Background Technology

[0002] Severe early cracking is a result of the combined effects of plastic settlement, plastic shrinkage, and autogenous shrinkage, which not only negatively impacts aesthetics but also affects the long-term durability of concrete structures. In dry environments, cracks may further propagate, accelerating the intrusion of corrosive substances such as chlorides and CO2, leading to steel corrosion and premature structural failure. During the approximately 3 to 8 hours before concrete hardens, it undergoes plastic deformation, including plastic settlement and plastic shrinkage. The main factor leading to plastic cracking in concrete is the accelerated evaporation of surface moisture due to environmental factors such as temperature and wind speed. This creates significant negative pressure in the capillaries, causing the concrete volume to shrink rapidly. At this point, the tensile strength of the concrete is insufficient to resist this shrinkage, resulting in crack formation.

[0003] The main method for evaluating the early plastic cracking performance of concrete is to assess plastic shrinkage cracking under constrained conditions, including ring tests, longitudinal tests, plate tests, and substrate-constrained tests. ASTM-C1579 has also been introduced to compare the plastic shrinkage cracking behavior of concrete mixtures with different types of fibers or admixtures. Considering that traditional crack measurement tools, such as handheld optical microscopes or crack comparators, may interfere with the cracking process of freshly mixed concrete, crack widths are measured in ASTM-C1579 after 24 hours, when the concrete is considered stable. Some researchers have combined different testing methods, such as the plate-constrained test with an electrodeless resistance meter, or the ring-constrained test with their respective established early hydration models, to test and evaluate the effects of concrete composition, test conditions, and curing conditions on concrete cracking. However, these research methods mainly focus on the average stress / strain of cementitious materials and can only provide a qualitative evaluation of the crack resistance of cementitious materials, but cannot accurately evaluate the plastic shrinkage cracking of concrete materials. Summary of the Invention

[0004] The purpose of this invention is to provide a method for assessing the cracking risk of concrete. By changing the degree of constraint and using damage factors at the micro level to assess the cracking risk of concrete, the assessment results are more accurate.

[0005] This invention is achieved through the following technical solution:

[0006] A method for assessing the risk of concrete cracking includes the following steps:

[0007] Obtain the concrete mix proportions;

[0008] Based on the concrete mix proportion, the cracking risk of the concrete mix proportion under different degrees of constraint is determined according to the pre-established correspondence between the concrete mix proportion, the degree of constraint and the cracking risk.

[0009] The process of establishing the correspondence between concrete mix proportions, degree of confinement, and cracking risk includes:

[0010] Based on the concrete mix design, concrete specimens under different constraints were prepared and the concrete specimens were cured.

[0011] After curing, observation spots were made on the surface of concrete specimens under various constraint conditions. DIC technology was used to acquire images of the concrete specimens at multiple preset monitoring times, and the first principal strain of the concrete specimens at multiple monitoring times was obtained based on the acquired images.

[0012] Damage indices are calculated based on the first principal strain, and damage indices corresponding to multiple monitoring times are obtained.

[0013] Based on the damage index corresponding to multiple monitoring times, the time-damage index relationship is fitted to obtain the time-damage index relationship corresponding to each constraint degree.

[0014] The final setting time of the concrete mix proportion is obtained, and the damage index of the final setting time under each constraint degree is obtained based on the time-damage index relationship corresponding to each constraint degree.

[0015] Based on the damage index of the final setting time under various constraint conditions and the preset damage index limit, the cracking risk of concrete specimens under different constraint conditions is determined. The damage index limit is used to indicate the damage index when the concrete specimen cracks.

[0016] Based on the cracking risk of concrete specimens under different constraint conditions, a correspondence between concrete mix proportion, constraint degree, and cracking risk is established.

[0017] Furthermore, the steps for calculating the damage index based on the first principal strain include:

[0018] Based on the first principal strain, the damage index is calculated according to formula (1), where formula (1) is:

[0019]

[0020] In the formula, D is the damage index, and E max The first principal strain at the center of the sub-region, A i |E max >0 represents the area of ​​the region where the first principal strain is positive.

[0021] Furthermore, the steps for creating observation spots on the surface of the concrete specimen include:

[0022] Wipe the surface of the concrete specimen until it is saturated and surface dry;

[0023] White paint was sprayed onto the surface of the concrete specimen, with the spraying direction of the white paint forming an angle with the surface of the concrete specimen.

[0024] Black paint was sprayed onto the surface of the concrete specimen, with the spraying direction parallel to the surface of the concrete specimen.

[0025] Furthermore, in the step of acquiring images of concrete specimens using DIC technology at multiple preset monitoring times, the method also includes:

[0026] The ambient temperature of the concrete specimens was maintained at 20±2℃ and the ambient humidity was maintained at ≥60%, and a fan was used to blow air onto the concrete specimens.

[0027] Furthermore, the steps for curing concrete specimens include:

[0028] The concrete specimens were placed in a curing room for curing for 1.5 hours. The temperature of the curing room was set at 20±2℃ and the humidity at 60±2%RH.

[0029] Furthermore, after obtaining the concrete mix proportions, the method also includes:

[0030] Based on the obtained concrete mix proportions, determine whether there is a correspondence between the concrete mix proportions, constraint degree and cracking risk in the preset database;

[0031] If not, proceed with the steps to establish the correspondence between concrete mix proportions, constraint degree, and cracking risk.

[0032] Furthermore, after establishing the correspondence between concrete mix proportions, restraint, and cracking risk, the method also includes:

[0033] The established correspondence between concrete mix proportions, constraint degree, and cracking risk is stored in the database.

[0034] Compared with existing technologies, the beneficial effects of this invention are as follows: Based on DIC technology, this invention quantitatively monitors the early-stage full-field strain of concrete in real time by changing different degrees of constraint, calculates the damage index, and then obtains the time-damage index relationship corresponding to different degrees of constraint. The damage index obtained by the time-damage index relationship corresponding to different degrees of constraint is used to evaluate the cracking risk of concrete with different degrees of constraint. The evaluation results are more accurate and are of great significance for reducing the risk of cracking in concrete structures during the forming and curing process caused by actual engineering constraints. At the same time, it can also guide the control of cracks during the construction and curing process of large-volume concrete structures. Attached Figure Description

[0035] Figure 1 This is a flowchart of the concrete cracking risk assessment method of the present invention;

[0036] Figure 2 This is a diagram showing the distribution of the first principal strain in concrete according to Embodiment 1 of the present invention;

[0037] Figure 3 This is a diagram showing the distribution of the first principal strain in concrete according to Embodiment 2 of the present invention;

[0038] Figure 4 This is a diagram showing the distribution of the first principal strain in concrete according to Embodiment 3 of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0041] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0042] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0043] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0044] Please see Figure 1 , Figure 1 This is a flowchart illustrating the steps of the concrete cracking risk assessment method of the present invention. A concrete cracking risk assessment method includes the following steps:

[0045] S1. Obtain the concrete mix proportions;

[0046] S2. Based on the concrete mix proportion, determine the cracking risk of the concrete mix proportion under different degrees of constraint according to the pre-established correspondence between the concrete mix proportion, the degree of constraint and the cracking risk.

[0047] The process of establishing the correspondence between concrete mix proportions, degree of confinement, and cracking risk includes:

[0048] (1) Based on the concrete mix proportion, prepare concrete specimens under different constraint conditions and cure the concrete specimens.

[0049] (2) After curing, observation spots were made on the surface of concrete specimens under various constraint conditions. DIC technology was used to collect images of the concrete specimens at multiple preset monitoring times, and the first principal strain of the concrete specimens at multiple monitoring times was obtained based on the collected images.

[0050] (3) The damage index is calculated based on the first principal strain to obtain the damage index corresponding to multiple monitoring times;

[0051] (4) Based on the damage index corresponding to multiple monitoring times, fit the time-damage index relationship to obtain the time-damage index relationship corresponding to each constraint degree.

[0052] (5) Obtain the final setting time of the concrete mix proportion, and based on the time-damage index relationship corresponding to each degree of constraint, obtain the damage index of the final setting time under each degree of constraint.

[0053] (6) Based on the damage index of the final setting time under each constraint condition and the preset damage index limit, determine the cracking risk of concrete specimens under different constraint conditions. The damage index limit is used to indicate the damage index when the concrete specimen cracks.

[0054] (7) Based on the cracking risk of concrete specimens under different constraint conditions, establish the correspondence between concrete mix proportion, constraint degree and cracking risk.

[0055] In step S1 above, the obtained concrete mix proportion is the concrete mix required for practical engineering. It can be determined based on the load-bearing capacity and durability design of the concrete structure construction parts. For example, the obtained concrete mix proportion in a certain project is shown in Table 1.

[0056] Table 1 Concrete Mix Proportions

[0057]

[0058] The correspondence between concrete mix proportion, degree of constraint, and cracking risk is established before step S2. This correspondence includes the concrete mix proportion, the different degrees of constraint corresponding to the concrete mix proportion, and the cracking risk corresponding to the different degrees of constraint. In step (1) above, experiments are conducted based on the concrete mix proportion obtained in step S1. Concrete specimens with different degrees of constraint are prepared using a common forced mixer. The degree of constraint of each concrete specimen is different. The preparation of concrete specimens with different degrees of constraint is mainly achieved by changing the number of constraint bolts in the mold. For example, the number of bolts is set according to the standard JTG3420-2020 for evaluating the early crack resistance of concrete specimens. When the degree of constraint is 60%, the number of constraint bolts is 20; when the degree of constraint is 30%, the number of constraint bolts is 10; when the degree of constraint is 0, the number of constraint bolts is 0, etc. The specifications of the concrete specimens can be 200×200×40mm. After the concrete specimens are made, they are cured to allow them to set for a period of time so that observation spots can be made on them for better observation.

[0059] The following three examples illustrate the point:

[0060] Example 1: Concrete specimens with a degree of constraint of 0 were prepared using the concrete mix proportions shown in Table 1.

[0061] Example 2: Concrete specimens with a constraint degree of 30% were prepared using the concrete mix proportions shown in Table 1.

[0062] Example 3: Concrete specimens with a constraint degree of 60% were prepared using the concrete mix proportions shown in Table 1.

[0063] Furthermore, in step (1), the steps for curing the concrete specimens include:

[0064] (1-1) The concrete specimens were placed in the curing room for curing for 1.5 hours. The temperature of the curing room was set to 20±2℃ and the humidity was set to 60±2%RH.

[0065] In step (1-1) above, after preparing the concrete specimen, the formed concrete specimen is moved to a curing room with a temperature of 20±2℃ and a humidity of 60% for curing for 1.5h, so that the concrete specimen can set for 1.5h.

[0066] In step (2) above, after curing, the surface of the concrete specimens under each constraint condition is first treated to make observation spots so that the DIC technology can capture the relative displacement of the observation spots, in order to prepare for the later use of software to calculate the overall strain of the concrete specimens.

[0067] Furthermore, the steps for creating observation spots on the surface of the concrete specimen include:

[0068] (2-1) Wipe the surface of the concrete specimen until it is saturated and dry;

[0069] (2-2) Spray white flat paint on the surface of the concrete specimen, with the spraying direction of the white flat paint forming an angle with the surface of the concrete specimen;

[0070] (2-3) Spray black paint onto the surface of the concrete specimen, with the spraying direction of the black paint parallel to the surface of the concrete specimen.

[0071] In steps (2-1) to (2-3) above, the surface of the concrete specimen is first wiped until it is saturated and dry. White flat paint is then sprayed at a 45° angle to the surface of the concrete specimen. After 5 minutes of spraying the white flat paint, black flat paint is sprayed parallel to the surface of the concrete specimen and 30cm away from the surface. This produces a flat black flat paint on the surface of the concrete specimen. Spraying white flat paint can improve the contrast, while spraying black flat paint is to allow the camera in the DIC technology to capture the relative displacement of the black spots.

[0072] In step (2) above, after creating observation spots on the surface of the concrete specimen, each concrete specimen is placed on an observation platform for real-time monitoring. Images of the concrete specimen surface are acquired at multiple monitoring times using a DIC dual-camera system. Furthermore, to make the surface phenomena of the concrete specimen more obvious, the method further includes the following steps in the process of acquiring images of the concrete specimen at multiple preset monitoring times using DIC technology:

[0073] (2-4) Maintain the ambient temperature of the concrete specimen at 20±2℃ and the ambient humidity at ≥60%, and use a fan to blow air onto the concrete specimen.

[0074] In the above steps (2-4), the ambient temperature of the concrete specimen is controlled at 20±2℃ and the ambient humidity is controlled at greater than or equal to 60%. A fan is placed near the concrete specimen, and the wind speed of the fan can be set to 4m / s. The fan accelerates the evaporation of moisture on the molding surface of the concrete specimen, increases its shrinkage, and makes the experimental phenomena on the surface of the concrete specimen more obvious.

[0075] In step (2) above, the monitoring time can be selected according to the actual engineering construction situation. For example, it can be monitored once per hour or once every ten minutes. The more monitoring times and the longer the monitoring time, the more accurate the results will be. In this embodiment, the multiple monitoring times are 1h (hour), 2h, 3h, 4h, 5h and 6h respectively. Select the region of interest of the acquired image, such as the area of ​​the concrete specimen forming surface of 200×200mm, and use analysis software such as PMLAB analysis software to process and calculate, so as to obtain the first principal strain of the concrete specimen in the field at multiple monitoring times. The strain data obtained is statistically processed by Origin to obtain the distribution map of the first principal strain of concrete, so as to facilitate subsequent calculations.

[0076] In Example 1, images of a concrete specimen with zero constraint degree were captured using a DIC dual-camera system at 1h, 2h, 3h, 4h, 5h, and 6h. The resulting first principal strain distribution diagram of the concrete, after analysis and calculation using software and statistical processing via Origin, is shown below. Figure 2 As shown;

[0077] In Example 2, images of concrete specimens with a constraint degree of 30% were captured using a DIC dual-camera system at 1h, 2h, 3h, 4h, 5h, and 6h. The resulting first principal strain distribution diagram of the concrete, after processing and calculation using analysis software and statistical processing via Origin, is shown below. Figure 3 As shown;

[0078] In Example 3, images of concrete specimens with a constraint degree of 60% were captured using a DIC dual-camera system at 1h, 2h, 3h, 4h, 5h, and 6h. The resulting first principal strain distribution diagram of the concrete, after processing and calculation using analysis software and statistical processing via Origin, is shown below. Figure 4 As shown.

[0079] In step (3) above, based on the first principal strain at multiple monitoring times, the damage index is calculated according to formula (1) to obtain the damage index at multiple monitoring times, where formula (1) is:

[0080]

[0081] In the formula, D is the damage index, and E max The first principal strain at the center of the sub-region, A i |E max >0 represents the area of ​​the region where the first principal strain is positive.

[0082] In Example 1, the damage index for multiple monitoring times was calculated using the first principal strain data obtained in Example 1, as shown in Table 2.

[0083] Table 2

[0084]

[0085] In Example 2, the damage index for multiple monitoring times was calculated using the first principal strain data obtained in Example 2, as shown in Table 3.

[0086] Table 3

[0087]

[0088]

[0089] In Example 3, the damage index for multiple monitoring times was calculated using the first principal strain data obtained in Example 3, as shown in Table 3.

[0090] Table 4

[0091]

[0092] In step (4) above, based on the damage index corresponding to multiple monitoring times, a second-order polynomial mathematical model can be used to fit the time-damage index relationship, thus obtaining the time-damage index relationship corresponding to each constraint degree: A = at 2 +bt+c; where A is the damage index after drying time t, t is the drying time, i.e. the monitoring time, and a, b, and c are fitting constants.

[0093] In Example 1, using the damage indices from multiple monitoring times obtained in Example 1, a time-damage index relationship with a constraint degree of 0 was fitted as follows: A = 0.321t 2 +2.293t +17.6;

[0094] In Example 2, using the damage indices from multiple monitoring times obtained in Example 2, a time-damage index relationship with a constraint degree of 30% was fitted as follows: A = -2.41t 2 +28.189t+98.9;

[0095] In Example 3, using the damage indices from multiple monitoring times obtained in Example 3, a time-damage index relationship with a constraint degree of 30% was fitted as follows: A = -0.393t 2 +11.03t +160;

[0096] In step (5) above, the final setting time is determined by the concrete mix proportion. Concrete specimens with the same mix proportion have the same final setting time, which can be determined by testing. For example, the concrete specimens prepared with the concrete mix proportions shown in Table 1 have a final setting time of 6 hours after curing. Thus, the final setting time of the concrete mix proportions shown in Table 1 is 6 hours. Based on the time-damage index relationship corresponding to each degree of constraint, the damage index of the final setting time under each degree of constraint is obtained.

[0097] In Example 1, the time-damage exponent relationship with a constraint degree of 0 is: A = 0.321t 2 +2.293t+17.6 The damage index obtained by calculating the final setting time of 6h is 42.914;

[0098] In Example 2, the time-damage index relationship with a constraint degree of 30% is: A = -2.41t 2 The damage index calculated using +28.189t+98.9 and a final setting time of 6 hours is 181.274.

[0099] In Example 3, the time-damage index relationship with a constraint degree of 60% is: A = -0.393t 2 The damage index obtained by calculating the final setting time of 6 hours (+11.03t+160) is 212.032.

[0100] In step (6) above, the damage index limit is used to indicate the damage index of the concrete specimen when it cracks. The damage index limit is the same for the same concrete mix proportion. The specific process of obtaining the damage index limit is to prepare concrete specimens of the concrete mix proportion. The degree of constraint of the concrete specimen can be higher, so that the concrete specimen is more likely to crack. After curing the concrete specimen according to step (1a), the DIC technology is used to capture the image of the cracking time point of the concrete specimen. Then, the first principal strain at the cracking time point is obtained according to the image. Based on the first principal strain at the cracking time point, the damage index at the cracking time point is calculated by formula (1). The damage index at the cracking time point is used as the damage index limit. Specifically, the damage index limit obtained by the above experiment using the concrete mix proportion shown in Table 1 is 142. Then, the damage index of the final setting time under each constraint condition is compared with the preset damage index limit. If the damage index of the final setting time is less than the damage index limit, it indicates that the risk of cracking is small. If the damage index of the final setting time is greater than the damage index limit, it indicates that the risk of cracking is large. Thus, the cracking risk of concrete specimens under different constraint conditions is determined.

[0101] For example, in Example 1, the concrete specimen with a constraint degree of 0 prepared using the concrete mix proportions shown in Table 1 has a damage index of 42.914 at a final setting time of 6 hours, which is less than the damage index limit of 142. This indicates that the concrete specimen with a constraint degree of 0 prepared using the concrete mix proportions shown in Table 1 has a low risk of cracking.

[0102] For example, in Example 2, the concrete specimen with a restraint of 30% prepared using the concrete mix proportions shown in Table 1 had a damage index of 181.274 at a final setting time of 6 hours, which is greater than the damage index limit of 142. This indicates that the concrete specimen with a restraint of 30% prepared using the concrete mix proportions shown in Table 1 has a high risk of cracking.

[0103] For example, in Example 3, the concrete specimen with a restraint of 60% prepared using the concrete mix proportions shown in Table 1 had a damage index of 212.032 at a final setting time of 6 hours, which is greater than the damage index limit of 142. This indicates that the concrete specimen with a restraint of 60% prepared using the concrete mix proportions shown in Table 1 has a high risk of cracking.

[0104] In step (7) above, based on the cracking risk of concrete specimens under different constraint conditions determined in step (6), a correspondence is established between concrete mix proportions, different constraint degrees corresponding to concrete mix proportions, and cracking risks corresponding to different constraint degrees. As shown in Table 1, the cracking risk is low for concrete mix proportions with 0% constraint degree, high for 30% constraint degree, and high for 60% constraint degree.

[0105] Furthermore, after obtaining the concrete mix proportions, the method also includes:

[0106] S1a. Based on the obtained concrete mix proportion, determine whether there is a correspondence between the concrete mix proportion, constraint degree and cracking risk in the preset database.

[0107] S1b If it does not exist, then proceed with the steps to establish the correspondence between concrete mix proportions, constraint degree and cracking risk.

[0108] In steps S1a and S1b above, when obtaining the concrete mix proportion, it is first determined whether there is a correspondence between the concrete mix proportion, constraint degree, and cracking risk in the preset database. If the database contains the concrete mix proportion, it means that the concrete mix proportion has been used in a previous project, and the correspondence between the concrete mix proportion, constraint degree, and cracking risk has been established. The correspondence between the concrete mix proportion, constraint degree, and cracking risk stored in the database can be used directly without having to establish the correspondence again, thus saving time. If there is no correspondence between the concrete mix proportion, constraint degree, and cracking risk in the database, it means that the obtained concrete mix proportion has not been evaluated before. Therefore, the step of establishing the correspondence between the concrete mix proportion, constraint degree, and cracking risk is executed, that is, steps (1) to (7) are executed to establish the correspondence between the concrete mix proportion, constraint degree, and cracking risk.

[0109] Furthermore, after establishing the correspondence between concrete mix proportions, restraint, and cracking risk, the method also includes:

[0110] S1c. The established relationship between concrete mix proportions, constraint degree, and cracking risk is stored in the database.

[0111] In step S1c above, the established correspondence between concrete mix proportion, constraint degree and cracking risk is stored in the database. If the concrete mix proportion used in other projects is the same as that used in this project, the correspondence between concrete mix proportion, constraint degree and cracking risk containing that concrete mix proportion can be used directly in the database.

[0112] In step S2 above, based on the concrete mix proportion obtained in step S1, and according to the pre-established correspondence between the concrete mix proportion, constraint degree, and cracking risk, the cracking risk of the concrete mix proportion under different constraint degrees can be obtained. The evaluation results are more accurate and are of great significance for reducing the risk of cracking in the concrete structure during the forming and curing process caused by actual engineering constraints. At the same time, by predicting the cracking risk of concrete in advance and calculating the initial cracking time of concrete, and then continuously optimizing the concrete mix proportion, the effect of controlling early cracks in concrete structures can be achieved, so as to guide the control of cracks during the construction and curing process of large-volume concrete structures.

[0113] Compared with existing technologies, the beneficial effects of this invention are as follows: Based on DIC technology, this invention quantitatively monitors the early-stage full-field strain of concrete in real time by changing different degrees of constraint, calculates the damage index, and then obtains the time-damage index relationship corresponding to different degrees of constraint. The damage index obtained by the time-damage index relationship corresponding to different degrees of constraint is used to evaluate the cracking risk of concrete with different degrees of constraint. The evaluation results are more accurate and are of great significance for reducing the risk of cracking in concrete structures during the forming and curing process caused by actual engineering constraints. At the same time, it can also guide the control of cracks during the construction and curing process of large-volume concrete structures.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for assessing the risk of concrete cracking, characterized in that, Includes the following steps: Obtain the concrete mix proportions; Based on the concrete mix design, the cracking risk of the concrete mix design under different degrees of constraint is determined according to the pre-established correspondence between the concrete mix design, degree of constraint and cracking risk. The process of establishing the correspondence between concrete mix proportions, confinement degree, and cracking risk includes: Based on the concrete mix design, concrete specimens under different constraint conditions were prepared and the concrete specimens were cured. After curing, observation spots were made on the surface of concrete specimens under various constraint conditions. DIC technology was used to acquire images of the concrete specimens at multiple preset monitoring times, and the first principal strain of the concrete specimens at multiple monitoring times was obtained based on the acquired images. Damage indices are calculated based on the first principal strain, and damage indices corresponding to multiple monitoring times are obtained. Based on the damage index corresponding to multiple monitoring times, the time-damage index relationship is fitted to obtain the time-damage index relationship corresponding to each constraint degree. The final setting time of the concrete mix proportion is obtained, and the damage index of the final setting time under each constraint degree is obtained based on the time-damage index relationship corresponding to each constraint degree. Based on the damage index of the final setting time under various constraint conditions and the preset damage index limit, the cracking risk of concrete specimens under different constraint conditions is determined. The damage index limit is used to indicate the damage index when the concrete specimen cracks. Based on the cracking risk of concrete specimens under different confinement conditions, establish the correspondence between concrete mix proportion, confinement degree and cracking risk; The step of calculating the damage index based on the first principal strain includes: Based on the first principal strain, the damage index is calculated according to formula (1), where formula (1) is: （1） In the formula, D is the damage index. The first principal strain at the center of the sub-region It is the area of ​​the region where the first principal strain is positive.

2. The method for assessing the risk of concrete cracking according to claim 1, characterized in that, The steps for creating observation spots on the surface of the concrete specimen include: Wipe the surface of the concrete specimen until it is saturated and surface dry; White paint was sprayed onto the surface of the concrete specimen, with the spraying direction of the white paint forming an angle with the surface of the concrete specimen. Black paint was sprayed onto the surface of the concrete specimen, with the spraying direction parallel to the surface of the concrete specimen.

3. The method for assessing the risk of concrete cracking according to claim 1, characterized in that, The method further includes the following steps in the step of acquiring images of concrete specimens using DIC technology at multiple preset monitoring times: The ambient temperature of the concrete specimens was maintained at 20±2℃ and the ambient humidity was maintained at greater than or equal to 60%, and a fan was used to blow air onto the concrete specimens.

4. The method for assessing the risk of concrete cracking according to claim 1, characterized in that, The steps for curing the concrete specimens include: The concrete specimens were placed in a curing room for curing for 1.5 hours. The temperature of the curing room was set to 20±2℃ and the humidity was set to 60±2%RH.

5. The method for assessing the risk of concrete cracking according to claim 1, characterized in that, After the step of obtaining the concrete mix proportion, the method further includes: Based on the obtained concrete mix proportion, determine whether there is a correspondence between the concrete mix proportion, constraint degree and cracking risk in the preset database; If not, proceed with the step of establishing the correspondence between the concrete mix proportion, constraint degree, and cracking risk.

6. The method for assessing the risk of concrete cracking according to claim 5, characterized in that, After the step of establishing the correspondence between the concrete mix proportion, constraint degree, and cracking risk, the method further includes: The established correspondence between the concrete mix proportions, constraint degree, and cracking risk is stored in the database.

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