A method for monitoring the hydration process of concrete using near-field microwaves

Abstract

This invention discloses a method for monitoring the hydration process of concrete using near-field microwaves, relating to the field of concrete forming monitoring. The invention first prepares concrete samples according to the specified method for the corresponding concrete. Then, the probe of the near-field microwave detection device is inserted 0.5-1 mm below the sample surface to obtain the resonant frequency fr, quality factor Q, phase P, and transmission coefficient S. 21 The curves corresponding to fr(t), Q(t), P(t) and S are... 21 (t); Differentiating each curve yields f'(t), Q'(t), P'(t), and S'(t); Zeros in f'(t), Q'(t), P'(t), and S'(t) represent critical points of state change during concrete hydration. Zeros in f'(t), Q'(t), P'(t), and S'(t) are determined respectively; the critical points of state change during concrete hydration are determined by averaging one or more of the curves f'(t), Q'(t), P'(t), and S'(t). Compared with existing technologies, this invention has the advantages of simple operation, low cost, adjustable detection accuracy, fast response speed, in-situ detection capability, and strong universality.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete forming monitoring, in particular to a method for monitoring the hydration process of concrete by using near-field microwave. BACKGROUND

[0002] Concrete is a common building material. The main components are cement, sand and water, which are mixed and stirred at a proper ratio. During the setting of concrete, complex chemical reactions, i.e. hydration reactions, occur inside the concrete, forming a colloid and releasing a large amount of heat. This hydration reaction has a great influence on the structural strength of concrete and causes changes in the compressive strength and pore characteristics of the cement paste. Clarifying the hydration mechanism of ordinary cement is a key scientific problem that needs to be solved urgently.

[0003] The commonly used methods for studying the hydration process include nuclear magnetic resonance (NMR), isothermal calorimetry (TAM air), electrochemistry, thermogravimetric analysis, and X-ray diffraction (XRD). NMR has a fast response speed and is intuitive in response to water state changes, but it is very expensive. TAM air can perform continuous measurements for a long time, but there is a certain delay due to the measurement of temperature. Electrochemistry is a non-destructive measurement method, but it can only be used for macroscopic monitoring and cannot be used for continuous monitoring. Thermogravimetric analysis and X-ray diffraction can quantitatively analyze hydration products, but they will cause damage to the sample, and the former can only measure the content of specific products, and the latter is complex to operate and difficult to analyze.

[0004] The electromagnetic properties of cement-based materials change with the hydration products during the hydration process. By using near-field microwave, the changes in the electromagnetic properties of the hydration process can be monitored, thereby providing a clear understanding of the hydration mechanism. This is a measurement method that is in-situ, simple to operate, fast in response, and adjustable in precision. SUMMARY

[0005] The purpose of the present application is to provide a method for monitoring the hydration process of concrete by using near-field microwave, which is in-situ, simple to operate, fast in response, and adjustable in precision.

[0006] To achieve the above-mentioned purpose, the present application relates to a method for monitoring the hydration process of concrete by using near-field microwave, and the specific process includes four steps: concrete sample preparation, near-field microwave testing, data processing, and data analysis.

[0007] Step 1: Prepare the concrete sample according to the corresponding method specified for the concrete;

[0008] Step 2: Insert the probe of the near-field microwave detection device below the surface of the sample, and detect the resonance frequency fr, quality factor Q, phase P, and transmission coefficient S of the concrete sample every certain period of time 21 ;

[0009] Wherein, the transmission coefficient S 21 The resonance frequency fr is directly read by the signal generator, and the transmission coefficient S 21 The frequency at the peak, The phase P is the phase of the transmission coefficient S 21 .

[0010] Step 3: Obtain the resonance frequency fr, the quality factor Q, the phase P and the transmission coefficient S 21 of the curves, which correspond to fr(t), Q(t), P(t) and S 21 (t); and the derivatives of the curves are obtained, which correspond to f'(t), Q'(t), P'(t) and S'(t);

[0011] Step 4: The zero points in f'(t), Q'(t), P'(t) and S'(t) represent the critical points of the state changes in the hydration process of the concrete, and the zero points in f'(t), Q'(t), P'(t) and S'(t) are determined respectively; and the critical points of the state changes in the hydration process of the concrete are determined by using one curve or multiple curves of f'(t), Q'(t), P'(t) and S'(t) to determine the average.

[0012] Further, in step 1, the probe of the near-field microwave detection device is inserted below the surface of the sample by 0.5-1 mm.

[0013] Further, in step 2, the probe of the near-field microwave detection device is first coated with a medium or installed with a protective sleeve.

[0014] Further, after obtaining fr(t), Q(t), P(t) and S 21 (t) in step 4, the local weighted scatter plot smoothing processing is first performed on the curves, and then the derivatives are obtained.

[0015] Further, the hydration process of the concrete includes an induction period, an acceleration period and a stable period, the first zero point in f'(t), Q'(t), P'(t) and S'(t) is the critical point between the induction period and the acceleration period, the second zero point is the critical point between the acceleration period and the stable period, the time corresponding to each critical point of f'(t), Q'(t), P'(t) and S'(t) is determined, and then the average value of the time is calculated, which is used as the critical point time value of the consistency sample, so as to determine the time length of each state in the hydration process of the concrete.

[0016] Compared with the prior art, the present application has the advantages of simple operation, low cost, adjustable detection precision, fast response speed, in-situ detection and strong universality. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The method flowchart of the present application.

[0018] Figure 2 Structure diagram of the measuring device involved in step 2.

[0019] Figure 3 Schematic diagram of the quality factor Q changing with time involved in step 3. DETAILED DESCRIPTION

[0020] All features disclosed in this specification, and / or all steps of any methods or processes disclosed, may be combined in any combination, except where such a combination is not technically in the art, or would have been impossible, unless the specification indicates that a combination of certain features, steps or materials cannot be applied, or is inadvisable, or is technically impossible. In particular, no individual feature is essential to the working of the application, unless the specification states otherwise.

[0021] Referring to Figure 1 , the specific process of the method for monitoring the hydration process of concrete using near-field microwaves in one of the many embodiments of the application includes four steps: concrete sample preparation, near-field microwave testing, data processing, and data analysis. The specific implementation is illustrated by taking the monitoring of the cement hydration process as an example, and the specific operation steps are as follows:

[0022] Step 1 (sample preparation): weigh 20 g of P·O42.5R grade ordinary Portland cement into a paper cup, then weigh 10 g of deionized water into the paper cup, and quickly stir with a stirring rod for 120 s until uniform. Then weigh 25 g of cement paste into a petri dish.

[0023] Step 2 (near-field microwave testing): referring to Figure 2 , the resonant cavity in this embodiment is a 1 / 4 wavelength resonant cavity, and the probe tip is coated with 502 glue in advance to prevent direct contact with the paste. Place the petri dish containing the cement paste on the sample stage. By observing the distance between the sample and the tip, move the displacement stage vertically so that the probe is inserted into the selected measurement area of the cement paste with a depth d of 0.5 mm. Use a computer to read the resonant frequency fr, quality factor Q, phase P, and transmission coefficient S 21 measured by the vector network analyzer every 6 s.

[0024] Step 3 (data processing): the resonant frequency fr, quality factor Q, phase P, and S 21 of step 2 are processed using a python algorithm for Loess smoothing to obtain the curve images of f = fr(t), Q = Q(t), P = P(t), and S = S 21 (t) and their derivative images.

[0025] Step 4 (data analysis): the electromagnetic properties of cement also change during hydration process, according to the trend of the obtained curve image and the turning point of the derivative graph, the analysis of electromagnetic properties can obtain each stage of the hydration process. See Figure 3 Fig. 8 is a schematic diagram of the quality factor Q of the cement obtained in step 2 changing with time within 8h. The arrow is the turning point. The Q value remains stable within 0-2.963h, which is the induction period of hydration; the Q value changes greatly within 2.963-5.467h, and reaches a peak near 6h, indicating that the cement begins to set at 3h, the hydration products increase and the water decreases, the cement changes from slurry to solid, and the setting of the cement is basically completed near 6h, which is the end of the acceleration period, i.e. 2.963-5.467h is the acceleration period of hydration; the hydration products increase slowly in the deceleration period, the dielectric constant of tricalcium silicate is smaller than that of its hydration products, so the Q value decreases, and after 5.467h it is the deceleration period of hydration. Due to the measurement time, the other processes are not analyzed.

[0026] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Any simple modification or equivalent change of the above embodiment according to the technical essence of the present application is also included in the protection scope of the present application.

Claims

1. A method for monitoring the hydration process of concrete by using near-field microwave, the method comprising: Step 1: preparing a concrete sample according to the method prescribed for the concrete; Step 2: The probe of the near-field microwave detection device is extended below the surface of the sample, and the resonance frequency fr, the quality factor Q, the phase P, and the transmission coefficient S of the concrete sample are detected every certain period of time 21 ; wherein the transmission coefficient S 21 read directly by the signal generator, the resonance frequency fr is the transmission coefficient S 21 the frequency at the peak, the phase P is the phase of the transmission coefficient S 21 ; Step 3: Obtain the resonant frequency fr, quality factor Q, phase P, and transmission coefficient S. 21 The curves corresponding to fr(t), Q(t), P(t) and S are... 21 (t); Differentiating each curve yields f'(t), Q'(t), P'(t), and S'(t); Step 4: the zero points in f'(t), Q'(t), P'(t) and S'(t) represent the critical points of state change in the hydration process of the concrete, the zero points in f'(t), Q'(t), P'(t) and S'(t) are determined respectively, and the critical points of state change in the hydration process of the concrete are determined by using one curve or the average of multiple curves of f'(t), Q'(t), P'(t) and S'(t).

2. A method for monitoring the hydration process of concrete using near field microwaves as claimed in claim 1, wherein, In the step 1, the probe of the near-field microwave detection device is inserted into the sample surface below 0.5-1 mm.

3. A method for monitoring the hydration process of concrete using near field microwaves as claimed in claim 1, wherein, In the step 2, the probe of the near-field microwave detection device is first coated with a medium or installed with a protective sleeve.

4. A method for monitoring the hydration process of concrete using near field microwaves as claimed in claim 1, wherein, fr(t), Q(t), P(t) and S 21 After the derivation of the curves, the local weighted scatterplot smoothing is first applied to each curve, and then the derivative is calculated.

5. A method for monitoring the hydration process of concrete using near field microwaves as claimed in claim 1, wherein, The hydration process of the concrete includes an induction period, an acceleration period and a stable period, the first zero point in f'(t), Q'(t), P'(t) and S'(t) is the critical point between the induction period and the acceleration period, the second zero point is the critical point between the acceleration period and the stable period, the time corresponding to each critical point of f'(t), Q'(t), P'(t) and S'(t) is determined, then the average value of the time is calculated, the average value is taken as the critical point time value of the concrete sample, and thus the time length of each state in the hydration process of the concrete is determined.

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