A non-destructive monitoring and evaluation method for carbonation degree of concrete

Abstract

The application provides a nondestructive monitoring and evaluation method for the carbonation degree of concrete. First, the accelerated carbonation process of the test piece is monitored by using ultrasonic waves, and the ultrasonic response of different test pieces in the carbonation process is obtained. Then, the characteristics of the slight changes in the ultrasonic response of the test piece in the carbonation process at different accelerated carbonation times are analyzed and extracted, the change relationship between the carbonation time and the ultrasonic response characteristics is established, and then the carbonation degree or carbonation depth of the concrete structure is inversely deduced by using the established relationship. Unlike the commonly used single-point indicators such as sound velocity and amplitude, the interference method realizes the continuous characterization of the overall evolution characteristics of the carbonation process by analyzing the interference waveform changes of the ultrasonic signal in the time interval, overcomes the limitations that the single-point indicators are easily disturbed by local disturbances and have incomplete information, and thus has stronger anti-noise ability and information representation advantage in interval analysis.

Description

Technical Field

[0001] This invention relates to the field of concrete carbonation monitoring technology, specifically to a non-destructive monitoring and evaluation method for the degree of concrete carbonation. Background Technology

[0002] Existing technologies for monitoring concrete carbonation mainly include methods based on ultrasound, electrochemistry, fiber optic sensing, infrared thermography, and image analysis. While electrochemical methods are sensitive to changes in the chemical environment caused by carbonation, they are easily affected by internal humidity, chloride ions, and other ions within the concrete. Long-term embedded sensors suffer from poor durability and baseline drift, making it difficult to achieve stable and continuous monitoring of the carbonation process. Fiber optic sensing technology offers advantages such as resistance to electromagnetic interference and high sensitivity, but its response to subtle strain changes caused by carbonation is limited, and the interface coupling state between the fiber and the concrete matrix changes over time, affecting the reliability and repeatability of long-term monitoring data. Infrared thermography and image analysis methods can be used to qualitatively identify surface carbonization areas, but they are significantly affected by factors such as ambient temperature, light, and surface contamination, making it difficult to quantitatively assess the depth of internal carbonation and failing to meet the needs of long-term automated monitoring.

[0003] In summary, the existing technology system is insufficient to support the need for continuous monitoring and rapid assessment of carbonation status in concrete structures during long-term service. Summary of the Invention

[0004] To address the aforementioned technical shortcomings, the purpose of this invention is to provide a non-destructive monitoring and evaluation method for the degree of concrete carbonation, enabling continuous characterization of the overall evolution of the carbonation process, and exhibiting stronger noise resistance and information representation advantages in interval analysis.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A non-destructive monitoring and evaluation method for the degree of concrete carbonation includes the following steps:

[0007] Step 1: Prepare concrete specimens using the same material as the concrete structure to be monitored;

[0008] Step 2: Install ultrasonic sensors on the surface of the concrete specimen and complete the electrical connection between the ultrasonic sensors and the ultrasonic acquisition equipment;

[0009] Step 3: Conduct accelerated carbonation tests on concrete specimens. During the test, ultrasonic signals of the concrete specimens at different carbonation times are collected simultaneously using an ultrasonic acquisition device.

[0010] Step four: Analyze and calculate the collected ultrasonic signals to extract the relative wave velocity change and decorrelation coefficient of the concrete specimen at each carbonation time.

[0011] Step 5: Perform splitting crack tests on the concrete specimens that have completed the accelerated carbonation test, and measure the actual carbonation depth of each concrete specimen.

[0012] Step 6: Using relative wave velocity change and decorrelation coefficient as input parameters and actual carbonization depth as output parameters, establish quantitative relationship models between relative wave velocity change and carbonization depth, and between decorrelation coefficient and carbonization depth, respectively.

[0013] Step 7: Perform ultrasonic monitoring on the concrete structure to be monitored, collect the ultrasonic response signal of the concrete structure to be monitored, extract the corresponding relative wave velocity change and decorrelation coefficient, substitute them into the quantitative relationship model, and invert to obtain the carbonation depth of the concrete structure to be monitored.

[0014] Preferably, the ultrasonic sensor is installed at the center of the opposite surface of the concrete specimen; before the accelerated carbonation test is started, the initial ultrasonic signal U0 of the concrete specimen is acquired by the ultrasonic acquisition device; during the accelerated carbonation test, a set of ultrasonic signals U corresponding to the carbonation time is acquired at fixed intervals. i .

[0015] Preferably, when analyzing and calculating the acquired ultrasonic signals, the ultrasonic signals are determined. The analysis time window for U i Cross-correlation calculations were performed with U0 to obtain the relative wave velocity change dvi and decorrelation coefficient DCi corresponding to different loads during the carbonization process of the specimen;

[0016] In the formula, U0(t) is the ultrasonic wave field before the disturbance, that is, the ultrasonic wave field when signal U0 is acquired; U i (t) represents the ultrasonic wave field when signal Ui is acquired; ε represents the ultrasonic wave field when signal Ui is acquired. i The scaling factor is ΔT, where ΔT is the length of the time window and T is the center point of the selected time window.

[0017] Preferably, when measuring the actual carbonation depth of a concrete specimen, a phenolphthalein alcohol solution is applied to the cross-section of the split concrete specimen, the carbonation depth of the undiscolored area of ​​the cross-section is measured, and the average carbonation depth of multiple measuring points is taken as the actual carbonation depth of the concrete specimen.

[0018] Preferably, when establishing a quantitative relationship model, an exponential relationship model corresponding to the relative wave velocity change and carbonization depth is constructed, as well as a linear relationship model corresponding to the decorrelation coefficient and carbonization depth.

[0019] In the formula, and The carbonization depth corresponding to the dv / v and DC relationship model; This is the proportionality coefficient; For index; The coefficient of the linear term.

[0020] Preferably, when inverting the carbonation depth of the concrete structure to be monitored, the first carbonation depth value is calculated by an exponential relationship model, and the second carbonation depth value is calculated by a linear relationship model. The average value of the first carbonation depth value and the second carbonation depth value is taken as the final carbonation depth of the concrete structure to be monitored.

[0021] In the formula, D represents the predicted carbonization depth, which is taken as 1. and The average value.

[0022] Preferably, multiple sets of concrete specimens are prepared, each set of concrete specimens corresponding to a different accelerated carbonation time. After each set of concrete specimens completes the accelerated carbonation test for the corresponding time, the ultrasonic signal of the set of concrete specimens is collected and the actual carbonation depth of the set of concrete specimens is measured.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention can inversely deduce the degree of concrete carbonation in a test component or structure by analyzing the relationship between the ultrasonic direct wave response characteristics and carbonation time during the carbonation process, thus enabling the monitoring and evaluation of concrete carbonation. This method eliminates the need for sampling from existing structures, avoids damage to existing structures, and allows for rapid assessment of the structural carbonation status. Furthermore, the method utilizes direct wave interferometry for monitoring, making it convenient to implement. Attached Figure Description

[0025] Figure 1 The graphs show the relationship between dv / v and DC as a function of carbonization time; where (a) is the graph of relative wave velocity variation; and (b) is the graph of decorrelation coefficient variation.

[0026] Figure 2 The figures are splitting test diagrams of concrete specimens; (a) shows the carbonation depth measurement of the specimen after splitting after 3 days of accelerated carbonation; (b) shows the carbonation depth measurement of the specimen after splitting after 28 days of accelerated carbonation.

[0027] Figure 3 This is a graph showing the relationship between carbonation depth and carbonation time in concrete specimens.

[0028] Figure 4 The graphs show the relationship between dv / v and DC and the actual carbonization depth; where (a) is the relationship between relative wave velocity change and carbonization depth; and (b) is the relationship between decorrelation coefficient and carbonization depth. Detailed Implementation

[0029] The invention will now be further described with reference to the accompanying drawings.

[0030] A non-destructive monitoring and evaluation method for the degree of concrete carbonation includes the following steps:

[0031] Step 1. Prepare a batch of concrete specimens made of the same material.

[0032] Step 2. Install an ultrasonic sensor at the center of the opposite side surface of the concrete specimen.

[0033] Step 3. Connect the ultrasound acquisition device.

[0034] Step 4. Conduct accelerated carbonation tests on different concrete specimens, such as... Figure 2 As shown, the accelerated carbonization was divided into groups of 0 days, 3 days, 7 days, 14 days, and 28 days. An ultrasonic signal acquisition device was simultaneously activated, and a set of ultrasonic signals (U) was recorded every 12 hours of accelerated carbonization. i The ultrasound signal acquired at the initial moment after preloading is denoted as U0.

[0035] Step 5. Conduct signal analysis and select... To analyze the time window, cross-correlation calculations were performed on Ui and U0 to obtain the relative wave velocity change dvi and decorrelation coefficient DCi corresponding to different loads during the specimen carbonization process. (wherein...) For the arrival time of the direct wave, select 1.5. This is based on a comprehensive consideration that the ratio of P-wave to S-wave velocity in concrete is approximately 1.6, thus excluding the influence of S-wave.

[0036]

[0037]

[0038] In the formula, U0(t) is the ultrasonic wave field before the disturbance, that is, the ultrasonic wave field when the signal U0 is acquired. i (t) is the signal U i The ultrasonic wave field during acquisition, where ε is the signal U i The scaling factor is ΔT, where ΔT is the length of the time window and T is the center point of the selected time window.

[0039] Step 6. Summarize the dv / v and DC data calculated in Step 5 to obtain the relationship between carbonization time and relative wave velocity change and decorrelation coefficient, as shown below. Figure 1 As shown, they all exhibit a clear exponential relationship.

[0040] Step 7. Use a microcomputer-controlled electro-hydraulic servo universal testing machine to perform splitting crack tests on concrete specimens. The splitting specimens are shown below. Figure 2 As shown.

[0041] Step 8. After cleaning the residue from the specimen surface, apply phenolphthalein alcohol solution and measure the depth of the uncolored carbonized area. Count the carbonization depth of the four sides of the two halves of each specimen after splitting, and take the average of the eight data points as the actual carbonization depth of the specimen. Figure 3 As shown, the carbonization depth also exhibits an exponential trend with carbonization time.

[0042] Step 9. Using the relative wave velocity change dv / v and decorrelation coefficient DC of the concrete specimen obtained in Step 6 as the abscissa and the actual carbonation depth of the specimen obtained in Step 8 as the ordinate, calculate and plot the relationship between dv / v and DC and the actual carbonation depth, as shown below. Figure 4 As shown.

[0043] Establish a quantitative relationship model between indicators (relative wave velocity change and decorrelation coefficient) and carbonization depth.

[0044] In the formula, and The carbonization depth corresponding to the dv / v and DC relationship model. This is the proportionality coefficient. For index, Here, is the coefficient of the first-order term, and D is the predicted carbonization depth, taken as . and The average value.

[0045] in, , , .

[0046] Step 10. In actual testing, only ultrasonic monitoring of the concrete structure under test is required. The ultrasonic response signal is collected, and the corresponding relative wave velocity change (dv / v) and decorrelation coefficient (DC) are extracted. These are then substituted into the established quantitative relationship model to quickly infer the carbonation depth of the structure. This method is simple to operate, has a sensitive response, does not require structural damage, and is suitable for long-term monitoring of the carbonation status of concrete structures.

[0047] Other concrete specimens from the same batch were predicted and verified. The actual carbonation depth was 20 mm, and the predicted carbonation depths were 21.3 mm, 20.9 mm and 21.1 mm, respectively. The results were similar and the prediction effect was good.

[0048] Application example: If the dv / v value measured at the center of the structural symmetry plane is 0.0005, the carbonation depth of the corresponding model mentioned above is approximately 3mm; the DC value is 0.03, and the carbonation depth of the corresponding model mentioned above is approximately 2.5mm. The predicted carbonation depth is (3+2.5) / 2=2.75mm, indicating that the structural concrete is in the early stage of carbonation development, the carbonation depth has not exceeded the thickness of the protective layer, and the performance is basically unaffected.

[0049] If the dv / v value measured at the center of the structural symmetry plane is 0.015, the corresponding carbonation depth of the model is 18mm; if the DC value is 0.24, the corresponding carbonation depth of the model is 20mm, and the predicted carbonation depth is (18+20) / 2=19mm, it indicates that the structural concrete is in the late stage of carbonation development, and the carbonation depth exceeds the thickness of the protective layer (the actual thickness needs to be determined according to the structural design, and here we assume the protective layer thickness is 20mm). It is close to or exceeds the design service limit, and the risk of steel corrosion is high. It is necessary to take protective or reinforcement measures quickly.

Claims

1. A non-destructive monitoring and evaluation method for the degree of carbonation in concrete, characterized in that, Includes the following steps: Step 1: Prepare concrete specimens using the same material as the concrete structure to be monitored; Step 2: Install ultrasonic sensors on the surface of the concrete specimen and complete the electrical connection between the ultrasonic sensors and the ultrasonic acquisition equipment; Step 3: Conduct accelerated carbonation tests on concrete specimens. During the test, ultrasonic signals of the concrete specimens at different carbonation times are collected simultaneously using an ultrasonic acquisition device. Step four: Analyze and calculate the collected ultrasonic signals to extract the relative wave velocity change and decorrelation coefficient of the concrete specimen at each carbonation time. Step 5: Perform splitting crack tests on the concrete specimens that have completed the accelerated carbonation test, and measure the actual carbonation depth of each concrete specimen. Step 6: Using relative wave velocity change and decorrelation coefficient as input parameters and actual carbonization depth as output parameters, establish quantitative relationship models between relative wave velocity change and carbonization depth, and between decorrelation coefficient and carbonization depth, respectively. Step 7: Perform ultrasonic monitoring on the concrete structure to be monitored, collect the ultrasonic response signal of the concrete structure to be monitored, extract the corresponding relative wave velocity change and decorrelation coefficient, substitute them into the quantitative relationship model, and invert to obtain the carbonation depth of the concrete structure to be monitored.

2. The method for non-destructive monitoring and evaluation of concrete carbonation degree as described in claim 1, characterized in that, The ultrasonic sensor is installed at the center of the opposite surface of the concrete specimen. Before the accelerated carbonation test is started, the initial ultrasonic signal U0 of the concrete specimen is acquired by the ultrasonic acquisition device. During the accelerated carbonation test, a set of ultrasonic signals U corresponding to the carbonation time is acquired at fixed intervals. i .

3. The method for non-destructive monitoring and evaluation of concrete carbonation degree as described in claim 2, characterized in that, When analyzing and calculating the acquired ultrasound signals, the ultrasound signal is determined. The analysis time window for U i Cross-correlation calculations were performed with U0 to obtain the relative wave velocity change dvi and decorrelation coefficient DCi corresponding to different loads during the carbonization process of the specimen; In the formula, U0(t) is the ultrasonic wave field before the disturbance, that is, the ultrasonic wave field when signal U0 is acquired; U i (t) represents the ultrasonic wave field when signal Ui is acquired; ε represents the ultrasonic wave field when signal Ui is acquired. i The scaling factor is ΔT, where ΔT is the length of the time window and T is the center point of the selected time window.

4. The method for non-destructive monitoring and evaluation of concrete carbonation degree as described in claim 1, characterized in that, When measuring the actual carbonation depth of a concrete specimen, a phenolphthalein alcohol solution is applied to the cross-section of the split concrete specimen, and the carbonation depth of the undiscolored area of ​​the cross-section is measured. The average carbonation depth of multiple measuring points is taken as the actual carbonation depth of the concrete specimen.

5. The method for non-destructive monitoring and evaluation of concrete carbonation degree as described in claim 1, characterized in that, When establishing a quantitative relationship model, an exponential relationship model corresponding to the relative wave velocity change and carbonization depth is constructed, as well as a linear relationship model corresponding to the decorrelation coefficient and carbonization depth. In the formula, and The carbonization depth corresponding to the dv / v and DC relationship model; This is the proportionality coefficient; For index; The coefficient of the linear term.

6. The method for non-destructive monitoring and evaluation of concrete carbonation degree as described in claim 5, characterized in that, When inverting the carbonation depth of the concrete structure to be monitored, the first carbonation depth value is calculated by the exponential relationship model and the second carbonation depth value is calculated by the linear relationship model. The average value of the first carbonation depth value and the second carbonation depth value is taken as the final carbonation depth of the concrete structure to be monitored. In the formula, D represents the predicted carbonization depth, which is taken as 1. and The average value.

7. The method for non-destructive monitoring and evaluation of concrete carbonation degree as described in claim 1, characterized in that, Multiple sets of concrete specimens were prepared, each set corresponding to a different accelerated carbonation time. After each set of concrete specimens completed the accelerated carbonation test for the corresponding time, the ultrasonic signal of the set of concrete specimens was collected and the actual carbonation depth of the set of concrete specimens was measured.

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