Method for predicting long-term creep of cement paste based on dielectric constant

Abstract

The invention discloses a method for predicting long-term creep of cement paste based on dielectric constants, which comprises the following steps of: finding out a relationship between a dielectric constant real part and a long-term creep modulus of the cement paste, firstly measuring the dielectric constant real part and the creep modulus, fitting to construct a corresponding function relational expression, verifying the constructed function expression, and finally predicting the long-term creep of the cement paste based on the dielectric constants. After the accuracy is verified, the method is applied to the long-term creep prediction of the cement paste. According to the method, the function relational expression related to the dielectric constant real part and the long-term creep modulus of the cement paste is established, the function relational expression can accurately predict the long-term creep of the cement paste, the corresponding creep modulus is obtained, and the precision of the prediction result can effectively meet the construction requirement; the whole prediction process is simple and easy to operate, the prediction precision of the long-term creep of the cement paste is greatly improved, the creep deformation of a stressed component of a building structure in a long-term stressed state can be controllably monitored, and then safe operation of an engineering structure is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of cement-based material performance measurement, and in particular to a method for predicting the long-term creep of cement paste based on dielectric constant. Background Art

[0002] Cement-based materials are currently the most widely used materials in construction projects. Their performance encompasses many aspects, including strength, elasticity, plasticity, and long-term deformation behavior. Creep is a key component of long-term deformation behavior in cement-based materials, significantly impacting the safety and durability of structures. Clarifying the long-term creep behavior of cement-based materials is crucial for ensuring the safe and long-term performance of building structures.

[0003] The long-term creep of cement-based materials generally refers to the deformation of the material under load over a period of several months or even years. There are many difficulties in observing this deformation behavior, such as the need to spend a sufficiently long time on actual observation, which will result in a large amount of manpower and material resources. In addition, the creep scale of cement-based materials is generally small, usually at the micro-nano level, which leads to high requirements for test equipment for observing creep and requires high costs. Therefore, conventional long-term creep observation methods have the defects of being time-consuming and costly. At the current stage, there are also many theories and methods for predicting creep, but the prediction accuracy of these long-term creep prediction methods is generally low, and the investment in preliminary experiments is also large. There are also problems such as the poor correspondence between creep at a specific time point and material properties during long-term prediction. The present invention provides a method for predicting the long-term creep of cement slurry based on dielectric constant to solve the above problems. Summary of the Invention

[0004] The present invention provides a method for predicting the long-term creep of cement paste based on dielectric constant, which realizes accurate prediction of the long-term creep of cement paste, and the prediction method is simple, fast and easy to implement.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: A method for predicting long-term creep of cement paste based on dielectric constant comprises the following steps: S1, parameter measurement: perform dielectric constant real part test and creep modulus test on cement paste samples at early age to obtain the above parameters of cement paste samples at different ages in the early age period; S2, constructing a functional formula: grouping the real part of the dielectric constant and the creep modulus of the early-age cement paste samples into corresponding groups, and then constructing the corresponding functional formula; S3, verify the functional formula: predict the creep modulus of cement paste at a long age based on the constructed functional formula, and then measure the creep modulus of cement paste at a long age to verify the accuracy of the functional formula; S4, application of the functional formula: After verifying the accuracy of the functional formula, the functional formula is applied to the long-term creep prediction of cement pastes of different ages.

[0006] Furthermore, in step S2, the constructed functional formula is y=ax+b, where x represents the real part of the dielectric constant of the cement paste, and y represents the creep modulus corresponding to the same cement paste, wherein a and b are constants and are related to the water-cement ratio of the cement paste.

[0007] Furthermore, in step S1, when the real part of the dielectric constant is tested on the cement paste sample at an early age, multiple measurements are performed on the cement paste sample at the same age using different frequencies, and the average is taken.

[0008] Furthermore, when performing the real part test of the dielectric constant, the dielectric constant test frequency band is 3.94 GHz-5.99 GHz.

[0009] Furthermore, in step S1, when performing creep modulus test on cement paste samples at an early age, a micron indentation test is adopted, and the load variation range set in the micron indentation test is 500mN-1.5N according to different water-cement ratios of the cement paste.

[0010] Furthermore, in step S3, when verifying the functional formula, the specific operation is to measure the real part of the dielectric constant of the cement paste sample at the age of t under the same conditions, and then substitute the mean of the real part of the dielectric constant and the age t into the functional formula to obtain the predicted creep modulus of the cement paste sample at the age of t, and then compare the calculated predicted creep modulus with the measured actual creep modulus of the cement paste sample at the age of t. The accuracy of the functional formula can be verified if the error is within the required range; t represents the curing age of the cement paste sample.

[0011] Furthermore, the cement of the cement paste sample is ordinary Portland cement, the water-cement ratio of the cement paste sample ranges from 0.2 to 0.6, the curing temperature ranges from 10°C to 30°C, and the curing humidity ranges from 50% to 100%.

[0012] The beneficial effects of the present invention are as follows: The relationship between the real part of the dielectric constant and the long-term creep modulus of cement paste was found, and a functional formula was established based on this. The long-term creep of cement paste was predicted according to the functional formula, and an accurate creep modulus was obtained. The accuracy of the prediction results can effectively meet the needs of construction. The entire prediction process is simple and easy to operate, which greatly improves the prediction accuracy of the long-term creep of cement paste, allowing the creep deformation of the load-bearing components of the building structure under long-term stress conditions to be controllably monitored, thereby ensuring the safe operation of the engineering structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the real part of the dielectric constant of the early-age cement paste sample tested in Example 1 of the present invention; Figure 2 Schematic diagram of the mean real part of the dielectric constant of the early-age cement paste sample in Example 1 of the present invention; Figure 3 Schematic diagram of creep modulus of early-age cement paste sample tested in Example 1 of the present invention; Figure 4 Schematic diagram of the relationship curve between the real part of the dielectric constant and the creep modulus in Example 1 of the present invention; Figure 5 Schematic diagram of the real part of the dielectric constant of cement paste samples at 90 days and 120 days of age in Example 1 of the present invention; Figure 6 Schematic diagram of the real part of the dielectric constant of the early-age cement paste sample tested in Example 2 of the present invention; Figure 7 Schematic diagram of the mean real part of the dielectric constant of the early-age cement paste sample in Example 2 of the present invention; Figure 8 Schematic diagram of creep modulus of early-age cement paste sample obtained by testing in Example 2 of the present invention; Figure 9 Schematic diagram of the relationship curve between the real part of the dielectric constant and the creep modulus in Example 2 of the present invention; Figure 10 Schematic diagram of the real part of the dielectric constant of cement paste samples at 60d and 90d in Example 2 of the present invention. DETAILED DESCRIPTION

[0014] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0015] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0016] In Example 1 of the present invention, 42.5-grade ordinary Portland cement was selected as the cementitious material and mixed with water and a water-reducing agent to produce a cement paste sample. The water-cement ratio of the cement paste was 0.24. A method for predicting the long-term creep of a cement paste with a water-cement ratio of 0.24 based on dielectric constant was developed, and the specific steps are as follows.

[0017] S1, parameter measurement: cement paste samples with a water-cement ratio of 0.24 were placed at a temperature of 20°C and a relative humidity of 95% for curing, and cured for 3 days, 7 days, 14 days, 21 days and 28 days respectively. The real part of the dielectric constant of the cement paste samples at the above early ages was then tested in sequence. The electromagnetic wave frequency band used in the test was 3.94 GHz-5.99 GHz. The real part of the dielectric constant obtained by the test is as follows: Figure 1 As shown, the average value of the real part of the dielectric constant of the cement paste sample at each age is calculated to obtain Figure 2 The real part mean of the dielectric constant of the early-age cement paste sample is shown in the figure. Then the creep modulus of the early-age cement paste sample is tested by micron indentation test, and the following is obtained: Figure 3 Creep modulus of early-age cement paste specimens shown.

[0018] S2, construct the function: statistically analyze and correspond the real part mean of the dielectric constant and creep modulus of the early-age cement paste samples, and perform fitting to obtain the following: Figure 4 The function of the real part of the dielectric constant and the creep modulus changing with time is shown as y=30.13x-126.61. During the fitting process, the coefficient of determination R 2 The value of is related to the degree of fitting, and the coefficient of determination R 2 The value range of is 0-1. The higher the degree of fit, the higher the determination coefficient R 2 The closer the value is to 1. The coefficient of determination R of the above function 2 The determination coefficient R is 0.976. 2 From the value of , it can be seen that the relationship between the real part of the dielectric constant and the creep modulus is highly consistent with the obtained functional expression.

[0019] S3, verification function: First, continue to cure the cement paste samples of the same batch under the established conditions to 90 days and 120 days, and then test the real part of the dielectric constant of the cement paste samples at 90 days and 120 days, such as Figure 5 As shown, the average values ​​are taken, which are 11.84 and 12.27 respectively, and substituted into the function y=30.13x-126.61. The corresponding curing time is entered, and the creep modulus of the cement paste sample at 90d and 120d of curing are calculated to be 243.08GPa and 249.71GPa respectively. Then, the micron indentation creep modulus test is carried out on the cement paste samples at the ages of 90d and 120d, and the creep moduli obtained are 224.84GPa and 231.76GPa respectively. The errors between the measured creep modulus and the predicted creep modulus are 8.11% and 7.74% respectively. The errors are within the allowable range, indicating that the calculation accuracy of the above function meets the requirements.

[0020] S4, Function Application: After verifying the accuracy of the above function, it can be used to predict the creep modulus of cement paste with a water-cement ratio of 0.24 at longer ages, and the results can be applied to relevant calculations or analyses. In practical applications, the real part of the dielectric constant of the current building structure can be directly measured and substituted into the function to obtain the creep modulus with the required accuracy. This eliminates the need for cumbersome creep modulus measurement methods and makes the operation simpler and more convenient.

[0021] The above method takes advantage of the easy-to-obtain parameters of early-age cement paste samples to construct a functional formula, and then verifies the accuracy of the functional formula. After the accuracy of the functional formula is verified, the above functional formula can be used to predict the creep modulus of cement pastes with longer ages. Since the accuracy of the functional formula has been verified, it means that the accuracy of the creep modulus of cement pastes with longer ages predicted by the functional formula is also within an acceptable range. Then, the creep modulus predicted by the functional formula can be used for qualitative or quantitative analysis without the need for destructive sampling of the building structure, and appropriate maintenance measures can be formulated based on the prediction results to ensure the safety and stability of the building structure.

[0022] In Example 2 of the present invention, 42.5-grade ordinary Portland cement was selected as the cementitious material and mixed with water and a water-reducing agent to produce a cement paste sample. The water-cement ratio of the cement paste was 0.32. A method for predicting the long-term creep of a cement paste with a water-cement ratio of 0.32 based on dielectric constant was developed, and the specific steps are as follows.

[0023] S1, parameter measurement: cement paste samples with a water-cement ratio of 0.32 were placed at a temperature of 22°C and a relative humidity of 85% for curing, and cured for 3 days, 7 days, 14 days, 21 days and 28 days respectively. The real part of the dielectric constant of the cement paste samples at the above early ages was then tested in sequence. The electromagnetic wave frequency band used in the test was 3.94 GHz-5.99 GHz. The real part of the dielectric constant obtained by the test is as follows: Figure 6 As shown, the average value of the real part of the dielectric constant of the cement paste sample at each age is calculated to obtain Figure 7 The real part mean value of the dielectric constant of the early-age cement paste sample is shown in the figure. Then the creep modulus of the early-age cement paste sample is tested by micron indentation test, and the following is obtained: Figure 8 Creep modulus of early-age cement paste specimens shown.

[0024] S2, construct the function: statistically analyze the real part mean of the dielectric constant and creep modulus of the early-age cement paste samples, and fit them to obtain the following equation: Figure 9 The function of the real part of the dielectric constant and the creep modulus changing with time is y=24.87x-117.38, and the determination coefficient R of the above function is 2 It is 0.982.

[0025] S3, verification function: First, continue to cure the cement paste samples of the same batch under the established conditions to 60 days and 90 days, and then test the real part of the dielectric constant of the cement paste samples at 60 days and 90 days, such as Figure 10 As shown, the average values ​​are taken, which are 12.98 and 13.39 respectively, and substituted into the function y=24.87x-117.38. The corresponding curing time is entered, and the creep modulus of the cement paste sample at 60d and 90d of curing are calculated to be 205.43GPa and 215.62GPa respectively. Then, the micron indentation creep modulus test is carried out on the cement paste samples at the age of 60d and 90d, and the creep moduli obtained are 198.71GPa and 205.48GPa respectively. The errors between the measured creep modulus and the predicted creep modulus are 3.38% and 4.93% respectively. The error range is small, indicating that the calculation accuracy of the above function meets the requirements.

[0026] S4, Application of the Function: After verifying the accuracy of the above function, it can be used to predict the creep modulus of cement paste with a water-cement ratio of 0.32 at a longer age, and the obtained results can be applied to related calculations and analyses.

[0027] Furthermore, the cement used in the present invention is ordinary Portland cement, the water-cement ratio of the cement paste sample ranges from 0.2 to 0.6, the curing temperature ranges from 10°C to 30°C, and the curing humidity ranges from 50% to 100%.

[0028] Furthermore, when conducting creep modulus tests on cement paste samples, a micron indentation test is used, and the load variation range set during the micron indentation test is 500 mN-1.5 N according to different water-cement ratios of the cement paste.

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description. It is intended that all variations within the meaning and range of equivalents of the claims be embraced herein, and any reference signs in the claims should not be construed as limiting the claims to which they relate.

Claims

1. A method for predicting long-term creep of cement paste based on dielectric constant, characterized by: The following steps are included: S1, parameter measurement: the real part of the dielectric constant and the creep modulus test are performed on the cement paste samples in the early age curing period to obtain the above parameters of the cement paste samples at different ages in the early age period; S2, constructing a functional formula: grouping the real part of the dielectric constant and the creep modulus of the early-age cement paste samples into corresponding groups, and then constructing the corresponding functional formula; S3, verify the functional formula: predict the creep modulus of cement paste at a long age based on the constructed functional formula, and then measure the creep modulus of cement paste at a long age to verify the accuracy of the functional formula; S4, application of the functional formula: After verifying the accuracy of the functional formula, the functional formula is applied to the long-term creep prediction of cement pastes of different ages.

2. The method for predicting long-term creep of cement paste based on dielectric constant according to claim 1, characterized in that: In step S2, the constructed functional formula is y=ax+b, where a and b are constants and are related to the water-cement ratio of the cement paste.

3. The method for predicting long-term creep of cement paste based on dielectric constant according to claim 1, characterized in that: In S1, when the real part of the dielectric constant is tested on cement paste samples at an early age, multiple measurements are performed on cement paste samples of the same age using different frequencies and the average is taken.

4. The method for predicting long-term creep of cement paste based on dielectric constant according to claim 3, wherein: When performing the real part test of the dielectric constant, the dielectric constant test frequency band is 3.94 GHz-5.99 GHz.

5. The method for predicting long-term creep of cement paste based on dielectric constant according to claim 1, wherein: In step S1, when performing a creep modulus test on a cement paste sample at an early age, a micron indentation test is used. During the micron indentation test, a load variation range is set to 500 mN-1.5 N according to different water-cement ratios of the cement paste.

6. The method for predicting long-term creep of cement paste based on dielectric constant according to claim 1, characterized in that: In step S3, when verifying the functional formula, the specific operation is to measure the real part of the dielectric constant of the cement paste sample at age t under the same conditions, and then substitute the mean of the real part of the dielectric constant and the age t into the functional relationship to obtain the predicted creep modulus of the cement paste sample at age t, and then compare the calculated predicted creep modulus with the measured actual creep modulus of the cement paste sample at age t. If the error is within the required range, the accuracy of the functional formula can be verified.

7. The method for predicting long-term creep of cement paste based on dielectric constant according to claim 1, characterized in that: The cement of the cement paste sample is ordinary Portland cement, the water-cement ratio of the cement paste sample ranges from 0.2 to 0.6, the curing temperature ranges from 10°C to 30°C, and the curing humidity ranges from 50% to 100%.

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