A method for predicting the time of plastic cracking in concrete
By monitoring the strain data of concrete specimens using DIC technology, a model was established to show the relationship between the half-width and height of micro-strain and the time of macro-crack initiation. This solved the problem of the difficulty in accurately predicting the time of plastic cracking in concrete in existing technologies, and enabled precise prediction of concrete cracking time and crack control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CCCC FOURTH HARBOR ENG INST CO LTD
- Filing Date
- 2023-05-09
- Publication Date
- 2026-05-26
AI Technical Summary
Existing technologies struggle to accurately predict the time of plastic cracking in concrete. Traditional methods primarily focus on the average stress/strain of cement-based materials, failing to effectively evaluate the plastic shrinkage cracking of concrete.
The strain data of concrete specimens were monitored using DIC technology. By establishing a model relating micro-strain half-width and height to macro-crack initiation time, the cracking time of concrete was predicted.
It enables accurate and reliable prediction of concrete cracking time, guiding crack control in the construction of large-volume concrete structures.
Smart Images
Figure CN116819048B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of concrete technology, and in particular relates to a method for predicting the time of plastic cracking in concrete. Background Technology
[0002] Severe early cracking in concrete is a result of the combined effects of plastic settlement, plastic shrinkage, and autogenous shrinkage. It not only negatively impacts aesthetics but also affects the long-term durability of concrete structures. During the drying process, cracks may further propagate and allow corrosive substances such as water and chlorides to penetrate, leading to steel reinforcement corrosion and premature aging of the structure.
[0003] For concrete, its plastic state lasts approximately 3–8 hours after pouring. In this vulnerable state, concrete undergoes volume changes, making it highly susceptible to cracking. The main factors leading to plastic cracking in concrete are the combined and interacting effects of consolidation, hydration, leakage, water evaporation, and capillary pressure. During the plastic stage, the solid particles in concrete first solidify, followed by water evaporation, causing changes in tensile capillary pressure. Both particle consolidation and capillary contraction are related to volume shrinkage. If this shrinkage is uneven, plastic shrinkage strain occurs in the cementitious material. When the accumulated tensile strain exceeds the tensile capacity of the plastic concrete, plastic cracking usually occurs.
[0004] There are many methods for testing the plastic cracking of concrete, such as ring tests, longitudinal tests, plate tests, and substrate-constrained tests. Additionally, ASTM standard C1579 has 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 fresh concrete, the concrete is considered stable for 24 hours after the start of the test. Some researchers have combined different testing methods, such as the plate-constrained test with an electrodeless resistance meter, or the ring-constrained test with an established early hydration model of concrete, 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 or predict the time of plastic cracking. Summary of the Invention
[0005] The purpose of this invention is to provide a method for predicting the time of plastic cracking in concrete, which establishes a relationship between the half-width at half-maximum of micro-strain and the time of macro-crack formation, and predicts the time of concrete cracking from the micro level, resulting in more accurate and reliable prediction results.
[0006] This invention is achieved through the following technical solution:
[0007] A method for predicting the time of plastic cracking in concrete includes the following steps:
[0008] Obtain the concrete mix proportions;
[0009] Based on the concrete mix proportion, the cracking time of the concrete mix proportion is determined according to the pre-established correspondence between the concrete mix proportion and the cracking time.
[0010] The process of establishing the relationship between concrete mix proportions and cracking time includes:
[0011] Based on the concrete mix design, several concrete specimens were prepared and then cured.
[0012] After curing, observation spots were made on the surface of each concrete specimen. DIC technology was used to acquire images of the concrete specimen at multiple preset monitoring times. Based on the acquired images, strain data of the concrete specimen at multiple monitoring times were obtained to obtain several strain data corresponding to each monitoring time.
[0013] Based on strain data, the strain half-width and height are determined, and several strain half-width and heights corresponding to each monitoring time are obtained.
[0014] Based on several strain half-widths and heights corresponding to each monitoring time, a time-strain half-width and height relationship model is fitted.
[0015] Based on the time-strain half-width-height relationship model and the predetermined strain half-width-height limit, the time corresponding to the strain half-width-height limit is calculated. The strain half-width-height limit is used to indicate the strain half-width-height when the concrete specimen cracks.
[0016] The cracking time of the concrete specimen is obtained by adding the time corresponding to the half-width and height limit of the strain to the curing time of the concrete specimen.
[0017] Based on the cracking time of the obtained concrete specimens, a correspondence between the concrete mix proportion and the cracking time is established.
[0018] Furthermore, the steps for determining the strain half-width and height based on strain data include:
[0019] Based on the strain data, a Gaussian function is used to fit the strain data to obtain the strain half-width and height, where the Gaussian function is shown in formula (1):
[0020]
[0021] In the formula, f(x) is the half-width of the strain, X is the first principal strain and the second principal strain in the strain data, X0 is the expected value, which is the center value of the Gaussian peak, and σ is the standard deviation.
[0022] Furthermore, the steps for curing concrete specimens include:
[0023] The concrete specimens were placed in a curing chamber for curing for 1.5 hours. The temperature of the curing chamber was set to 20±2℃ and the humidity was set to 60±2%RH.
[0024] Furthermore, the steps for creating observation spots on the surface of the concrete specimen include:
[0025] Wipe the surface of the concrete specimen until it is saturated and surface dry;
[0026] 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.
[0027] Black paint was sprayed onto the surface of the concrete specimen, with the spraying direction parallel to the surface of the concrete specimen.
[0028] Furthermore, in the step of acquiring images of concrete specimens using DIC technology at multiple preset monitoring times, the method also includes:
[0029] 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.
[0030] Furthermore, after obtaining the concrete mix proportions, the method also includes:
[0031] Based on the obtained concrete mix proportion, determine whether there is a correspondence between the concrete mix proportion and the cracking time in the preset database.
[0032] If it does not exist, then proceed with the steps of establishing the correspondence between concrete mix proportions and cracking time.
[0033] Furthermore, after establishing the correlation between concrete mix proportions and cracking time, the method also includes:
[0034] The established relationship between concrete mix proportions and cracking time is stored in the database.
[0035] Furthermore, in the step of fitting a time-strain half-width-height relationship model based on several strain half-widths and heights corresponding to each monitoring time, the fitted time-strain half-width-height relationship model is shown in formula (2):
[0036] y = alan(t) + b (2)
[0037] In the formula, y is the strain half-width, t is time, and a and b are constants.
[0038] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention utilizes DIC technology, a microscopic observation technology, to observe the strain data of concrete and calculate the strain half-width and height, thereby obtaining a time-strain half-width and height relationship model. It establishes a relationship between the microscopic strain half-width and height and the time of macroscopic crack initiation, predicting the concrete cracking time from a microscopic level. The prediction results are more accurate and reliable, which is of great significance for clarifying the accurate cracking time of concrete. 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
[0039] Figure 1 This is a flowchart of the steps in the concrete plastic cracking time prediction method of the present invention;
[0040] Figure 2 These are images of concrete specimens collected at multiple monitoring times using DIC technology in the concrete plastic cracking time prediction method of this invention.
[0041] Figure 3 This is a schematic diagram of the strain distribution of a concrete specimen in Example 1;
[0042] Figure 4 This is a schematic diagram showing the change of strain half-width and height over time in Example 1;
[0043] Figure 5 This is a schematic diagram of the strain distribution of a concrete specimen in Example 2;
[0044] Figure 6 This is a schematic diagram showing the change of strain half-width and height over time in Example 2. Detailed Implementation
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] Please see Figure 1 , Figure 1 This is a flowchart illustrating the steps of the concrete plastic cracking time prediction method of the present invention. A concrete plastic cracking time prediction method includes the following steps:
[0051] S1. Obtain the concrete mix proportions;
[0052] S2. Based on the concrete mix proportion, determine the cracking time of the concrete mix proportion according to the pre-established correspondence between the concrete mix proportion and the cracking time.
[0053] The process of establishing the relationship between concrete mix proportions and cracking time includes:
[0054] (1) Prepare several concrete specimens according to the concrete mix proportion and cure the concrete specimens;
[0055] (2) After curing, observation spots were made on the surface of each concrete specimen. DIC technology was used to collect images of the concrete specimen at multiple preset monitoring times. Based on the collected images, strain data of the concrete specimen at multiple monitoring times were obtained to obtain several strain data corresponding to each monitoring time.
[0056] (3) Determine the strain half-width and height based on the strain data to obtain several strain half-width and height corresponding to each monitoring time;
[0057] (4) Based on several strain half-widths and heights corresponding to each monitoring time, fit a time-strain half-width and height relationship model;
[0058] (5) Based on the time-strain half-width-height relationship model and the predetermined strain half-width-height limit, the time corresponding to the strain half-width-height limit is calculated, wherein the strain half-width-height limit is used to indicate the strain half-width-height when the concrete specimen cracks.
[0059] (6) Add the time corresponding to the half-width limit of the strain to the curing time of the concrete specimen to obtain the cracking time of the concrete specimen.
[0060] (7) Based on the cracking time of the obtained concrete specimens, establish the correspondence between the concrete mix proportion and the cracking time.
[0061] In step S1 above, the concrete mix proportion obtained is the concrete mix that is practically required in actual engineering. The concrete mix proportion can be determined based on the load-bearing capacity design and durability design of the construction parts of the concrete structure.
[0062] The relationship between concrete mix proportion and cracking time is established before step S2. In step (1) above, experiments are conducted based on the concrete mix proportion obtained in step S1. Concrete specimens are prepared using a conventional forced mixer. Several concrete specimens are prepared for each concrete mix proportion. The number of concrete specimens prepared can be selected according to the actual situation. Preferably, at least 3 concrete specimens are prepared for each concrete mix proportion. The specifications of the concrete specimens can be 200×200×40mm. After the concrete specimens are prepared, they are cured to allow the surface of the concrete specimens to set for a certain period of time, so that observation spots can be made on the surface of the concrete specimens for better observation.
[0063] Furthermore, in step (1), the steps for curing the concrete specimens include:
[0064] (1-1) The concrete specimens were placed in a curing chamber for curing for 1.5 hours. The temperature of the curing chamber was set to 20±2℃ and the humidity was set to 60±2%RH so that the concrete specimens could set for 1.5 hours.
[0065] In step (1-1) above, after preparing the concrete specimen, the molded concrete specimen is moved to the curing chamber for curing for 1.5 hours. The temperature of the curing chamber is set to 20±2℃ and the humidity is set to 60±2%RH.
[0066] In step (2) above, after curing, for each concrete specimen, the surface of the concrete specimen is first treated and observation spots are made on the surface of the concrete specimen 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 specimen.
[0067] Furthermore, in step (2), the step of creating observation spots on the surface of the concrete specimen includes:
[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. A DIC dual-camera system is used to acquire images of the concrete specimen surface at multiple monitoring times. The images of the concrete specimen acquired at multiple monitoring times are shown below. Figure 2 As shown, Figure 2 The image shows images of the concrete specimen surface acquired using a DIC dual-camera system at 0h, 1h, 2h, 3h, 4h, and 5h. The 0h image is the initial image at the time of acquisition. By comparing the images acquired at the other monitoring times with the initial image, the displacement of the observed spots can be obtained. Furthermore, to make the surface phenomena of the concrete specimen more apparent, the method for acquiring images of the concrete specimen at multiple preset monitoring times using DIC technology also includes:
[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, 2h, 3h, 4h, 5h and 6h. The region of interest of the acquired image is selected, such as the area of the concrete specimen forming surface of 200×200mm. The PMLAB analysis software and other analysis software are used for processing and calculation to obtain the strain data of each concrete specimen at multiple monitoring times. Based on the strain data of each concrete specimen at multiple monitoring times, the strain data of several concrete specimens corresponding to each monitoring time are obtained.
[0076] In step (3) above, the strain half-width is one of the characteristic parameters obtained by fitting the strain data to a Gaussian distribution. It is also called the half-width of the Gaussian peak, which reflects the non-uniformity of the concrete strain distribution. The strain data is processed using data processing software such as Origin, Matlab, and Spass. The frequency distribution statistical analysis of the obtained strain values is performed, and a histogram is plotted with the interval center and relative frequency to achieve the fitting of the Gaussian function to the values with the help of the software. Specifically, based on the strain data of several concrete specimens corresponding to each monitoring time, the strain data is fitted with a Gaussian function to obtain the strain half-width, thereby obtaining several strain half-widths corresponding to each monitoring time. The Gaussian function is shown in formula (1):
[0077]
[0078] In the formula, f(x) is the strain half-width, X is the actual value that satisfies the Gaussian distribution parameter, that is, the first principal strain and the second principal strain in the strain data, x0 is the expected value, that is, the center value of the Gaussian peak, which represents the average value of the data; σ is the standard deviation.
[0079] In step (4) above, based on several strain half-widths corresponding to each monitoring time, the least squares method is used to fit the strain half-widths under different monitoring times to obtain the time-strain half-width relationship model of strain half-width changing with time.
[0080] The fitted time-strain half-width-height relationship model is shown in Equation (2):
[0081] y = alan(t) + b (2)
[0082] In the formula, y is the strain half-width, t is time, and a and b are constants.
[0083] In step (5) above, the strain half-width limit is used to indicate the strain half-width at which the concrete specimen cracks. The strain half-width limit is the same for the same concrete mix proportion. The specific process of obtaining the strain half-width limit is as follows: prepare a concrete specimen of the concrete mix proportion, cure the concrete specimen according to the steps in step (1-1), and use DIC technology to capture images of the cracking time point of the concrete specimen. Then, obtain the strain data at the cracking time point based on the captured images. Based on the strain data at the cracking time point, calculate the strain half-width at the cracking time point using formula (1). Use the strain half-width at the cracking time point as the strain half-width limit. Substitute the strain half-width limit into formula (2) as y, and the time corresponding to the strain half-width can be calculated using formula (2).
[0084] In step (6) above, the strain half-width and height is the data measured after the concrete specimen has been cured. Therefore, the time corresponding to the strain half-width and height limit is added to the curing time of the concrete specimen to obtain the cracking time of the concrete specimen. That is, when the concrete specimen is placed for a period of time after pouring and the cracking time is reached, the concrete specimen will crack due to excessive strain value.
[0085] In step (7) above, based on the cracking time of the obtained concrete specimen and the concrete mix ratio used to prepare the concrete specimen, the correspondence between the concrete mix ratio used to prepare the concrete specimen and the cracking time of the concrete specimen can be established, thereby obtaining the correspondence between the concrete mix ratio and the cracking time.
[0086] Furthermore, after obtaining the concrete mix proportions, the method also includes:
[0087] S1a. Based on the obtained concrete mix proportion, determine whether there is a correspondence between the concrete mix proportion and the cracking time in the preset database.
[0088] S1b, if it does not exist, then proceed with the steps of establishing the correspondence between concrete mix proportion and cracking time.
[0089] 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 and cracking time 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 and cracking time has been established. The correspondence between the concrete mix proportion and cracking time stored in the database can be used directly without having to establish the correspondence between the concrete mix proportion and cracking time again, thus saving time. If there is no correspondence between the concrete mix proportion and cracking time in the database, it means that the cracking time of the obtained concrete mix proportion has not been predicted before. Therefore, the step of establishing the correspondence between the concrete mix proportion and cracking time is executed, that is, steps (1) to (7) are executed to establish the correspondence between the concrete mix proportion and cracking time.
[0090] Furthermore, after establishing the correlation between concrete mix proportions and cracking time, the method also includes:
[0091] S1c. The established relationship between concrete mix proportions and cracking time is stored in the database.
[0092] In step S1c above, the established correspondence between concrete mix proportion and cracking time 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 and cracking time containing that concrete mix proportion in the database can be used directly.
[0093] 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 and cracking time, the cracking time of the concrete mix proportion can be obtained. The cracking time prediction is more accurate and reliable, which is of great significance for clarifying the accurate cracking time of concrete. At the same time, it can also guide the control of cracks during the construction and curing process of large-volume concrete structures. Then, by 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.
[0094] The following two examples briefly illustrate the concrete plastic cracking time prediction method of the present invention:
[0095] Example 1
[0096] A certain highway project uses C30 concrete, and the concrete mix design is shown in Table 1:
[0097] Table 1 Concrete mix proportions (kg / m³) 3 )
[0098] serial number cement fly ash Mineral powder fine aggregate coarse aggregate Water reducing agent 1 215 50 50 613 786 3.5
[0099] According to the concrete mix proportions shown in Table 1, three concrete specimens with dimensions of 200×200×40mm were prepared and each specimen was cured. After curing, strain data of each concrete specimen were collected at multiple monitoring times according to step (2), such as... Figure 3 As shown, Figure 3 The figure shows a schematic diagram of the strain distribution of one of the concrete specimens. The horizontal axis represents the strain data, and the vertical axis represents the probability. Multiple monitoring times were 1h, 2h, 3h, 4h, 5h, and 6h. Then, the three half-widths and heights of the strain corresponding to each monitoring time were calculated according to step (3), as shown in Table 2.
[0100] Table 2
[0101]
[0102] Based on the three strain half-widths and heights corresponding to each monitoring time in Table 2, a time-strain half-width and height relationship model was fitted, and the fitting results are as follows: Figure 4 As shown, the strain half-width and height variation model with time is obtained as shown in formula (3):
[0103] y = 151.31ln(t) + 5284.3 (3)
[0104] According to the concrete mix proportion shown in Table 1, the strain half-width limit is 5500. Substituting 5500 into formula (3), the calculated time is 4.2. Then, 4.2h plus 1.5h equals 5.7h. Therefore, according to the concrete mix proportion shown in Table 1, the concrete will crack due to excessive strain 5.7h after pouring.
[0105] Example 2
[0106] The guardrails for a certain highway project are made of C50 concrete, and the concrete mix design is shown in Table 2.
[0107] Table 3 Concrete mix proportions (kg / m³) 3 )
[0108] serial number cement fly ash Mineral powder fine aggregate coarse aggregate Water reducing agent 1 298 30 30 624 746 5.2
[0109] According to the concrete mix proportions shown in Table 3, three concrete specimens with dimensions of 200×200×40mm were prepared and each specimen was cured. After curing, strain data of each concrete specimen were collected at multiple monitoring times according to step (2), such as... Figure 5 As shown, Figure 5The figure shows a schematic diagram of the strain distribution of one of the concrete specimens. The horizontal axis represents the strain data, and the vertical axis represents the probability. Multiple monitoring times were 1h, 2h, 3h, 4h, 5h, and 6h. Then, the three half-widths and heights of the strain corresponding to each monitoring time were calculated according to step (3), as shown in Table 4.
[0110] Table 4
[0111]
[0112] Based on the three strain half-widths and heights corresponding to each monitoring time in Table 4, a time-strain half-width and height relationship model was fitted, and the fitting results are as follows: Figure 6 As shown, the strain half-width height variation model with time is obtained as shown in formula (4):
[0113] y = 338ln(t) + 5873 (4)
[0114] The strain half-width limit obtained from the concrete mix proportions shown in Table 1 is 6600. Substituting 6600 into formula (4) yields a time of 8.6 hours. Adding 1.5 hours to 8.6 hours gives 10.1 hours. Therefore, according to the concrete mix proportions shown in Table 3, the concrete will crack due to excessive strain 10.1 hours after pouring. Since the final setting time of the concrete does not exceed 10 hours, cracks will not occur during the plastic stage after concrete pouring in this embodiment.
[0115] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention utilizes DIC technology, a microscopic observation technology, to observe the strain data of concrete and calculate the strain half-width and height, thereby obtaining a time-strain half-width and height relationship model. It establishes a relationship between the microscopic strain half-width and height and the time of macroscopic crack initiation, predicting the concrete cracking time from a microscopic level. The prediction results are more accurate and reliable, which is of great significance for clarifying the accurate cracking time of concrete. At the same time, it can also guide the control of cracks during the construction and curing process of large-volume concrete structures.
[0116] 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 predicting the time of plastic cracking in concrete, characterized in that, Includes the following steps: Obtain the concrete mix proportions; Based on the concrete mix proportion, the cracking time of the concrete mix proportion is determined according to the pre-established correspondence between the concrete mix proportion and the cracking time. The process of establishing the correspondence between the concrete mix proportion and cracking time includes: According to the concrete mix design, several concrete specimens were prepared and the concrete specimens were cured. After curing, observation spots are made on the surface of each concrete specimen. DIC technology is used to acquire images of the concrete specimen at multiple preset monitoring times. Based on the acquired images, strain data of the concrete specimen at multiple monitoring times are obtained to obtain several strain data corresponding to each monitoring time. Based on strain data, the strain half-width and height are determined, and several strain half-width and heights corresponding to each monitoring time are obtained. Based on several strain half-widths and heights corresponding to each monitoring time, a time-strain half-width and height relationship model is fitted, and the fitted time-strain half-width and height relationship model is shown in formula (2): （2） In the formula, For strain half-width and height, For time, and It is a constant; Based on the time-strain half-width-height relationship model and the predetermined strain half-width-height limit, the time corresponding to the strain half-width-height limit is calculated. The strain half-width-height limit is used to indicate the strain half-width-height when the concrete specimen cracks. The cracking time of the concrete specimen is obtained by adding the time corresponding to the half-width and height limit of the strain to the curing time of the concrete specimen. Based on the cracking time of the obtained concrete specimens, a correspondence between the concrete mix proportion and the cracking time is established.
2. The method for predicting the time of plastic cracking in concrete according to claim 1, characterized in that, The steps for determining the strain half-width and height based on strain data include: Based on the strain data, a Gaussian function is used to fit the strain data to obtain the strain half-width and height, where the Gaussian function is shown in formula (1): （1） In the formula, For strain half-width and height, These are the first and second principal strains in the strain data. This is the expected value, which is the center value of the Gaussian peak. The standard deviation is denoted as .
3. The method for predicting the time of plastic cracking in concrete according to claim 1, characterized in that, The steps for curing the concrete specimens include: The concrete specimens were placed in a curing chamber for curing for 1.5 hours. The temperature of the curing chamber was set to 20±2℃ and the humidity was set to 60±2%RH.
4. The method for predicting the time of plastic cracking in concrete according to claim 1, characterized in that, The step of creating observation spots on the surface of the concrete specimen includes: Wipe the surface of the concrete specimen until it is saturated and surface-dry; White paint is 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.
5. The method for predicting the time of plastic cracking in concrete 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 specimen 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 specimen.
6. The method for predicting the time of plastic cracking in concrete 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 and cracking time in the preset database. If it does not exist, then proceed with the steps of establishing the correspondence between the concrete mix proportion and cracking time.
7. The method for predicting the time of plastic cracking in concrete according to claim 6, characterized in that, After the step of establishing the correspondence between the concrete mix proportion and cracking time, the method further includes: The established correspondence between the concrete mix proportions and cracking time is stored in the database.