Method for monitoring concrete hydration process by utilizing near-field microwaves

Abstract

The invention discloses a method for monitoring a concrete hydration process by utilizing near-field microwaves, and relates to the field of concrete forming monitoring. The method comprises the following steps: firstly, making a coagulation degree sample according to a method specified by corresponding concrete, then stretching a probe of a near-field microwave detection device into 0.5-1mm below the surface of the sample, and obtaining curves of resonant frequency fr, quality factor Q, phase P and transmission coefficient S21, corresponding to fr (t), Q (t), P (t) and S21 (t); deriving each curve to correspondingly obtain f '(t), Q' (t), P '(t) and S' (t); zero points in f '(t), Q' (t), P '(t) and S' (t) represent critical points of state change in the coagulation degree hydration process, and respectively determining the zero points in f '(t), Q' (t), P '(t) and S' (t); and determining the critical point of the state change in the concrete hydration process by adopting a mode of averaging one curve or a plurality of curves of f '(t), Q' (t), P '(t) and S' (t). Compared with the prior art, the method has the advantages of simplicity in operation, low cost, adjustable detection precision, high response speed, capability of in-situ detection and high universality.

Description

Technical Field

[0001] The invention relates to the field of concrete forming monitoring, and in particular to a method for monitoring the concrete hydration process by using near-field microwaves. Background Art

[0002] Concrete is a common building material. The main components are cement, sand and water, which are mixed and stirred in appropriate proportions. During the setting process of concrete, a complex chemical reaction occurs inside the concrete, namely a hydration reaction, forming a colloid and releasing a large amount of heat. This hydration reaction has a great influence on the structural strength of concrete, and will cause changes in the compressive strength and pore characteristics of the cement paste. Clarifying the hydration mechanism of ordinary cement is a key scientific issue that needs to be solved urgently.

[0003] Commonly used methods for studying the hydration process include nuclear magnetic resonance (NMR), isothermal calorimetry (TAM air), electrochemical method, thermogravimetric analysis, and X-ray diffraction (XRD). The nuclear magnetic resonance method has a fast response speed and is intuitive to changes in water state, but it is expensive. The isothermal calorimetry method can perform long-term continuous measurements, but there will be a certain delay due to the temperature measurement. The electrochemical method is a non-destructive measurement, but it can only monitor macroscopically, not continuously. Thermogravimetric analysis and X-ray diffraction can quantitatively analyze hydration products, but both will cause damage to the sample, and the former can only measure the content of specific products, while the latter is complicated to operate and difficult to analyze.

[0004] The electromagnetic properties of cement-based materials will change with the hydration products during the hydration process. The near-field microwave method can be used to monitor the changes in the electromagnetic properties of the hydration process, so as to have a clear study of the hydration mechanism. It is an in-situ measurement method with simple operation, fast response and adjustable accuracy. Summary of the invention

[0005] The purpose of the present invention is to provide a method for monitoring the concrete hydration process by using near-field microwaves, which has the advantages of in-situ measurement, simple operation, fast response and adjustable precision.

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

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

[0008] Step 2: Extend the probe of the near-field microwave detection device below the surface of the sample and detect the resonant frequency fr, quality factor Q, phase P and transmission coefficient S of the concrete sample at regular intervals. 21 ;

[0009] Among them, the transmission coefficient S 21 Directly read by the signal generator, the resonant frequency fr is the transmission coefficient S 21 The frequency at the peak, Phase P is the transmission coefficient S 21 The phase of

[0010] Step 3: Obtain the resonant frequency fr, quality factor Q, phase P and transmission coefficient S 21 The curves correspond to fr(t), Q(t), P(t) and S 21 (t); Derivative each curve to obtain f'(t), Q'(t), P'(t) and S'(t);

[0011] Step 4: The zero point in f'(t), Q'(t), P'(t) and S'(t) represents the critical point of the state change during the hydration process of concrete. Determine the zero point in f'(t), Q'(t), P'(t) and S'(t) respectively; use one curve or multiple curves in f'(t), Q'(t), P'(t) and S'(t) to determine the critical point of the state change during the hydration process of concrete.

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

[0013] Furthermore, in step 2, the probe of the near-field microwave detection device is firstly coated with a dielectric or provided with a protective cover.

[0014] Furthermore, in step 4, fr(t), Q(t), P(t) and S are obtained. 21 (t), each curve is firstly smoothed by local weighted scatter plot and then derived.

[0015] Furthermore, the concrete hydration process includes an induction period, an acceleration period, and a stabilization 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, and the second zero point is the critical point between the acceleration period and the stabilization 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. The average value is used as the critical point time value of the coagulation degree sample, thereby determining the duration of each state in the concrete hydration process.

[0016] Compared with the prior art, the present invention has the advantages of simple operation, low cost, adjustable detection accuracy, fast response speed, ability to detect in situ, and strong universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a flow chart of the method of the present invention.

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

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

[0020] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, may be combined in any manner and, unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes, that is, unless otherwise stated, each feature is merely an embodiment of a series of equivalent or similar features.

[0021] See also Figure 1 Among the numerous embodiments of the present invention, a method for monitoring the concrete hydration process using near-field microwaves includes four steps: concrete sample preparation, near-field microwave testing, data processing, and data analysis. The specific implementation method is described by taking cement hydration process monitoring as an example. The specific operation steps are as follows:

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

[0023] Step 2 (Near Field Microwave Test): See Figure 2 In this embodiment, the resonant cavity is a 1 / 4 wavelength resonant cavity, and the probe tip is coated with 502 glue in advance to prevent direct contact with the slurry; a culture dish containing cement slurry is placed on the stage, and by observing the distance between the sample and the needle tip, the translation stage is moved longitudinally so that the probe is inserted into the test area selected by the cement slurry, and the depth d is 0.5 mm; the resonant frequency fr, quality factor Q, phase P and transmission coefficient S measured by the vector network analyzer are read by a computer every 6 seconds. 21 ;

[0024] Step 3 (data processing): The resonant frequency fr, quality factor Q, phase P and S obtained in step 2 are 21 Using the python algorithm for Loess smoothing, we get f = fr(t), Q = Q(t), P = P(t) and S = S 21 (t) and its derivative image.

[0025] Step 4 (data analysis): The electromagnetic properties of cement are constantly changing during the hydration process. The various stages of the hydration process can be obtained based on the trend changes of the obtained curve image and the turning points obtained from the derivative diagram combined with the analysis of the electromagnetic properties. Figure 3 , which is a schematic diagram of the change of the quality factor Q within 8 hours obtained in step 2 with time. The arrow is the turning point. The Q value remains basically stable within 0-2.963 hours, which is the hydration induction period; the Q value changes greatly within 2.963-5.467 hours, and reaches a peak value near 6 hours, indicating that the cement begins to solidify at 3 hours, the hydration products continue to increase, the water continues to decrease, and the cement changes from slurry to solid. At around 6 hours, the cement solidification is basically completed, and the acceleration period ends, that is, 2.963-5.467 hours is the hydration acceleration period; during the hydration deceleration period, the hydration products increase slowly, and the dielectric constant of tricalcium silicate is smaller than its hydration products, so the Q value will decrease, and after 5.467 hours, it is the hydration deceleration period. Due to the measurement time, other processes are not analyzed for the time being.

[0026] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent changes made to the above embodiment based on the technical essence of the present invention are included in the protection scope of the present invention.

Claims

1. A method for monitoring concrete hydration process using near-field microwaves, the method comprising: Step 1: Prepare a concrete sample according to the method specified for the corresponding concrete; Step 2: Extend the probe of the near-field microwave detection device below the surface of the sample and detect the resonant frequency fr, quality factor Q, phase P and transmission coefficient S of the concrete sample at regular intervals. 21 ; Among them, the transmission coefficient S 21 Directly read by the signal generator, the resonant frequency fr is the transmission coefficient S 21 The frequency at the peak, Phase P is the transmission coefficient S 21 The phase of Step 3: Obtain the resonant frequency fr, quality factor Q, phase P and transmission coefficient S 21 The curves correspond to fr(t), Q(t), P(t) and S 21 (t); Derivative each curve to obtain f'(t), Q'(t), P'(t) and S'(t); Step 4: The zero point in f'(t), Q'(t), P'(t) and S'(t) represents the critical point of the state change during the hydration process of concrete. Determine the zero point in f'(t), Q'(t), P'(t) and S'(t) respectively; use one curve or multiple curves in f'(t), Q'(t), P'(t) and S'(t) to determine the critical point of the state change during the hydration process of concrete.

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

3. The method for monitoring concrete hydration process using near-field microwaves according to claim 1, characterized in that: In the step 2, the probe of the near-field microwave detection device is firstly coated with a dielectric or provided with a protective cover.

4. The method for monitoring the hydration process of concrete using near-field microwaves according to claim 1, characterized in that: In step 4, fr(t), Q(t), P(t) and S are obtained. 21 (t), each curve is firstly smoothed by local weighted scatter plot and then derived.

5. The method for monitoring concrete hydration process using near-field microwaves according to claim 1, characterized in that: The concrete hydration process includes an induction period, an acceleration period, and a stabilization 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, and the second zero point is the critical point between the acceleration period and the stabilization 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. The average value is used as the critical point time value of the coagulation degree sample, thereby determining the duration of each state in the concrete hydration process.

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