A method for determining the chemical shrinkage of cement paste

Abstract

The present application relates to the technical field of cement performance detection, in particular to a detection method for measuring chemical shrinkage of cement paste, comprising: pouring cement paste with a specified mixing ratio into a flexible transparent cavity wall annular sample cavity and sealing it; horizontally immersing the annular sample cavity in a constant-temperature liquid medium tank; projecting a circular laser spot to the outside of the flexible cavity wall of the annular sample cavity by using a laser emitting device, and continuously collecting image sequences of the spot deformation caused by the deformation of the cavity wall due to the shrinkage of the internal paste by using an image acquisition device; analyzing and calculating the spot deformation parameters based on the image sequences, and then inversely calculating the volume change of the cement paste sample in the annular sample cavity, and calculating the chemical shrinkage value in combination with the initial volume. The present application realizes non-contact, continuous and high-precision measurement of the chemical shrinkage process of the cement paste, is simple to operate, and is less affected by external interference.

Description

Technical Field

[0001] This invention relates to the field of cement performance testing technology, and in particular to a method for determining the chemical shrinkage of cement paste. Background Technology

[0002] Among existing methods for measuring the chemical shrinkage of cement paste, the volumetric drainage method is relatively common. This method indirectly calculates the shrinkage value by measuring the volume of liquid discharged as the cement paste shrinks in a closed container. However, due to the minute amount of chemical shrinkage and the extremely small volume of liquid discharged, traditional drainage devices are prone to introducing significant errors in liquid transfer and reading, and it is difficult to achieve continuous and automatic monitoring of the shrinkage process. Another approach is to use contact displacement sensors to directly measure the length change of a certain dimension of the sample. This type of method requires the sensor probe to be in direct contact with the sample surface or container wall, and the contact force may interfere with the initial structure and development process of the cement paste in a plastic state, leading to measurement distortion. At the same time, to achieve an equivalent conversion from three-dimensional shrinkage to one-dimensional data, complex designs are often required for the sample shape and sensor arrangement, limiting the equipment integration and ease of operation.

[0003] The main drawback of existing technologies lies in the difficulty of achieving continuous, high-precision, non-contact measurement of the true volume changes within the entire sample. Methods based on direct measurement principles are either limited by the accuracy and continuity of capturing minute physical quantities, or interfere with the measured system due to the intervention of the measuring element. These limitations make it difficult to obtain high-precision, full-process chemical shrinkage data. This invention aims to provide a method that can convert the microscopic volume changes within a sample into macroscopic deformation signals easily captured by an optical system through a simple and reliable mechanical structure, and achieve precise quantification of volume changes using non-contact image analysis technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a detection method for determining the chemical shrinkage of cement paste.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a method for determining the chemical shrinkage of cement paste, comprising:

[0006] Prepare cement paste samples with a specified mix ratio, and pour and seal the cement paste samples into an annular sample cavity with a flexible transparent cavity wall.

[0007] The annular sample cavity is placed horizontally in a constant temperature liquid medium tank, so that the liquid in the constant temperature liquid medium tank completely submerges the annular sample cavity.

[0008] A circular laser spot is projected onto the outside of the flexible transparent cavity wall of the annular sample cavity using a laser emitting device.

[0009] Using an image acquisition device, images of the laser spot deformed by the flexible transparent cavity wall are continuously acquired to obtain a sequence of laser spot deformation images;

[0010] Based on the light spot deformation image sequence, the volume change of the cement paste sample inside the annular sample cavity is calculated.

[0011] The chemical shrinkage value of the cement paste is calculated based on the volume change and the initial volume of the cement paste sample.

[0012] As a further aspect of the present invention, the preparation of the cement paste sample with a specified mix ratio involves casting and sealing the cement paste sample within an annular sample cavity with a flexible, transparent wall, specifically as follows:

[0013] According to the standard test method, weigh the cement and mixing water, and use a cement paste mixer to mix the cement and mixing water evenly to obtain the fresh cement paste to be tested.

[0014] Prepare an annular sample cavity consisting of a rigid base, a central column, and an outer flexible transparent membrane. The upper and lower ends of the outer flexible transparent membrane are respectively sealed to the rigid base and the central column to form an annular closed cavity.

[0015] The freshly mixed cement paste to be tested is slowly injected into the annular sealed cavity of the annular sample chamber, avoiding the introduction of air bubbles during the injection process;

[0016] After the freshly mixed cement paste fills the annular sealed cavity, a sealing film is covered on the top of the annular sealed cavity, and a sealing ring is used to press the sealing film onto the rigid base to ensure that the annular sample cavity is completely sealed.

[0017] The sealed annular sample cavity, filled with cement paste sample, is placed on a flat table until the surface of the cement paste sample tends to be horizontal.

[0018] As a further aspect of the present invention, the step of horizontally placing the annular sample cavity in a constant-temperature liquid medium bath, such that the liquid in the constant-temperature liquid medium bath completely submerges the annular sample cavity, specifically involves:

[0019] Prepare a transparent constant temperature liquid medium tank, and inject a low viscosity, high light transmittance liquid medium with a constant temperature into the constant temperature liquid medium tank;

[0020] The constant temperature liquid medium tank is placed on a level adjustment platform and calibrated with a level to ensure that the bottom surface of the constant temperature liquid medium tank is strictly level.

[0021] The sealed annular sample cavity is slowly immersed into the liquid medium in the constant temperature liquid medium tank, ensuring that the rigid base of the annular sample cavity is in parallel contact with the bottom surface of the constant temperature liquid medium tank.

[0022] Continue adding liquid medium until the liquid level completely covers the top of the annular sample cavity and the liquid level height exceeds the upper surface of the sealing ring at the top of the annular sample cavity by at least 15 mm.

[0023] The entire system is placed in a constant temperature environment to ensure that the temperature of the liquid medium in the constant temperature liquid medium tank, the annular sample chamber, and the cement paste sample in the chamber is uniform and constant.

[0024] As a further aspect of the present invention, the use of a laser emitting device to project a circular laser spot onto the outer side of the flexible transparent cavity wall of the annular sample cavity specifically involves:

[0025] Select a laser emitting device with stable wavelength and regular light spot, and fix the laser emitting device on one side of the constant temperature liquid medium tank;

[0026] Adjust the emission angle and position of the laser emitting device so that the laser beam is perpendicularly incident on the flexible transparent membrane on the outside of the annular sample cavity immersed in the liquid medium;

[0027] Adjust the focal length of the laser emitting device so that the laser beam forms a circular spot with clear edges on the outer surface of the outer flexible transparent film;

[0028] The diameter of the circular light spot is smaller than the annular width of the annular sample cavity, and the center of the circular light spot is located at the center of the annular region of the annular sample cavity.

[0029] As a further aspect of the present invention, the use of an image acquisition device to continuously acquire images of the laser spot caused by the deformation of the flexible transparent cavity wall, thereby obtaining a sequence of laser spot deformation images, specifically:

[0030] A high-resolution image acquisition device is selected and fixedly installed on the other side of the constant temperature liquid medium tank, and is positioned opposite the laser emitting device along a straight line passing through the central axis of the annular sample cavity.

[0031] Adjust the optical axis of the image acquisition device so that it is perpendicular to the part of the annular sample cavity where the outer flexible transparent film is installed, and directly facing the area where the laser spot is located;

[0032] Set the acquisition parameters of the image acquisition device, including exposure time, frame rate and resolution, to ensure that the shape of the laser spot can be clearly captured;

[0033] At the initial moment when the cement paste sample begins to hydrate, the image acquisition device is activated, and images of the laser spot are continuously acquired at set time intervals.

[0034] The image of the laser spot includes the shape change of the laser spot on the outer flexible transparent membrane caused by the deformation of the membrane wall as the volume of cement paste changes;

[0035] The acquired laser spot images, arranged in chronological order, are stored as a sequence of laser spot deformation images.

[0036] As a further aspect of the present invention, the image of the laser spot includes the shape change of the laser spot on the outer flexible transparent membrane caused by the deformation of the membrane wall due to the change in the volume of cement paste, specifically:

[0037] When the cement paste sample in the annular sample cavity decreases in volume due to chemical shrinkage, the outer flexible transparent membrane deforms inward toward the central axis of the annular sample cavity under the action of pressure changes inside the sample and external liquid static pressure.

[0038] The concave deformation of the outer flexible transparent film causes a change in the curvature of its outer surface, thereby causing the circular laser spot projected onto it to deform.

[0039] The deformation of the circular laser spot is manifested in the change of the spot area and the transformation of the spot edge contour from circular to non-circular;

[0040] In each frame of the image captured by the image acquisition device, the actual shape, size, and intensity distribution of the laser spot at the corresponding moment are recorded.

[0041] As a further aspect of the present invention, the calculation of the volume change of the cement paste sample within the annular sample cavity based on the light spot deformation image sequence specifically involves:

[0042] Extract the initial moment image from the laser spot deformation image sequence, identify the edge contour of the laser spot in the initial moment image, and calculate the reference area and reference shape parameters of the laser spot at the initial moment;

[0043] Each frame of the light spot deformation image sequence is read sequentially, and the same edge contour recognition processing is performed on each frame.

[0044] Calculate the current area and current shape parameters of the laser spot in each frame image, and compare them with the reference area and reference shape parameters to obtain the spot area change rate and shape distortion rate corresponding to each frame image;

[0045] A pre-calibrated relational model is established, which describes the quantitative correspondence between the normal displacement per unit area of ​​the outer flexible transparent film and the rate of change of the area and the rate of shape distortion of the laser spot projected onto it;

[0046] The spot area change rate and shape distortion rate calculated for each frame of image are input into the pre-calibrated relationship model to calculate the average normal displacement of the outer flexible transparent film in the laser spot coverage area.

[0047] Based on the geometric dimensions of the annular sample cavity and the average normal displacement of the outer flexible transparent membrane in the laser spot coverage area, the volume change of the cement paste sample in the annular sample cavity at the corresponding time is calculated through integral calculation.

[0048] As a further aspect of the present invention, the establishment of a pre-calibrated relational model specifically includes:

[0049] Prepare a calibration annular cavity with the same structural dimensions as the annular sample cavity, and inject an incompressible calibration liquid with a fixed volume into the calibration annular cavity;

[0050] The calibration annular cavity for injecting calibration liquid is immersed in the liquid medium of the constant temperature liquid medium tank in the same manner;

[0051] Using a micro-displacement driving device, a small normal displacement of known magnitude is applied to the outer flexible transparent membrane from inside or outside the calibration annular cavity;

[0052] After each small normal displacement is applied, the laser emitting device and the image acquisition device are used to acquire an image of the laser spot at this time, and the spot area change rate and shape distortion rate corresponding to the image are calculated.

[0053] Record a series of different minute normal displacement values ​​and corresponding data pairs of spot area change rate and shape distortion rate;

[0054] The recorded data were analyzed and processed using a curve fitting method to establish a functional relationship between the normal displacement of the outer flexible transparent film and the rate of change of the laser spot area and the shape distortion rate, i.e., the pre-calibrated relationship model.

[0055] As a further aspect of the present invention, based on the geometric dimensions of the annular sample cavity and the average normal displacement of the outer flexible transparent membrane in the laser spot coverage area, the volume change of the cement paste sample in the annular sample cavity at the corresponding time is calculated through integral calculation, specifically as follows:

[0056] Obtain the geometric parameters of the annular sample cavity, including the inner ring radius, outer ring radius, and initial radius of curvature of the outer flexible transparent membrane;

[0057] Assuming that when the outer flexible transparent membrane deforms, its deformation mode is consistent with the mode in the pre-calibration experiment, and the deformation is continuous and smooth within the annular region;

[0058] The annular region covered by the laser spot is discretized into several tiny annular units;

[0059] The average normal displacement of the laser spot coverage area calculated based on the pre-calibrated relational model, combined with the deformation mode assumption, is used to interpolate and estimate the normal displacement of the outer flexible transparent film on each micro-ring unit.

[0060] The increase in cavity volume caused by the deformation of the micro-ring unit is calculated based on the normal displacement of each micro-ring unit and its corresponding ring area.

[0061] The total volume change of the annular sample cavity caused by the overall deformation of the outer flexible transparent membrane is obtained by summing the volume change increments of all the tiny annular units.

[0062] This total volume change is equal to the volume change of the cement paste sample in the annular sample cavity due to chemical shrinkage.

[0063] As a further aspect of the present invention, the calculation of the chemical shrinkage value of the cement paste based on the volume change and the initial volume of the cement paste sample specifically involves:

[0064] Record the initial moment after the cement paste sample is poured into the annular sample cavity;

[0065] The volume of the annular sealed cavity of the annular sample chamber is obtained as the initial volume of the cement paste sample.

[0066] Starting from the initial moment, a series of specific test moments are obtained based on the timestamps of the light spot deformation image sequence;

[0067] Read the volume change of the cement paste sample at each specific test moment, obtained through calculation.

[0068] The volume change at each specific test time is divided by the initial volume of the cement paste sample, and then multiplied by a percentage factor to obtain the chemical shrinkage value of the cement paste at the specific test time.

[0069] The chemical shrinkage values ​​of cement paste at different test times are correlated and recorded to form a chemical shrinkage development curve of the cement paste sample from the initial time over time.

[0070] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0071] Cement slurry is encapsulated in an annular sample cavity with a flexible, transparent wall. The internal chemical shrinkage during cement hydration creates a slight negative pressure within the sealed cavity, driving inward elastic deformation of the entire flexible annular cavity wall surrounding the sample. This structure directly translates the isotropic volume reduction within the sample into a uniform, observable radial displacement of the sealed cavity wall. The annular flexible cavity acts as a monolithic sensing element, exhibiting a definite mechanical response relationship between its deformation and internal volume changes, thus amplifying minute volume shrinkage signals into easily measurable geometric deformation. The sample preparation process involves only pouring and sealing, eliminating the need for complex venting or liquid leveling operations, simplifying the process and reducing human error.

[0072] A circular laser spot is projected onto the deforming flexible cavity wall using a laser emitting device, and an image acquisition device records the image sequence. The deformation of the cavity wall directly changes the shape and size of the laser spot on the imaging plane. By analyzing the continuous changes in features such as the area, contour, or center coordinates of the laser spot in the image sequence, the cavity wall deformation at the corresponding moment can be accurately calculated based on optical geometry. This method requires no contact between any measuring component and the sample or container, eliminating the interference of contact stress on the early cement paste structure. Image-based analysis technology has high spatiotemporal resolution, enabling continuous, real-time monitoring of the shrinkage process. The measurement range and accuracy of the measurement system can be flexibly optimized and calibrated through optical configuration and image algorithms. Attached Figure Description

[0073] Figure 1 This is a flowchart of the detection method for determining the chemical shrinkage of cement paste according to the present invention;

[0074] Figure 2 Flowchart for preparing and sealing cement paste samples;

[0075] Figure 3 A flowchart for placing the annular sample chamber into a constant-temperature liquid medium bath;

[0076] Figure 4 The trend curve of the two parameters of the laser spot during the entire process of cement paste hydration;

[0077] Figure 5 A heatmap showing the correlation between cement paste testing indicators. Detailed Implementation

[0078] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0079] In the description of this invention, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the 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, and therefore should not be construed as a limitation of the invention. Furthermore, in the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0080] See Figure 1 A cement paste sample with a specified mix ratio was prepared. The cement paste sample was poured and sealed within an annular sample cavity with a flexible, transparent wall. The annular sample cavity was placed horizontally in a constant-temperature liquid medium bath, ensuring the liquid completely submerged the cavity. A circular laser spot was projected onto the outside of the flexible, transparent wall of the annular sample cavity using a laser emitting device. An image acquisition device continuously acquired images of the laser spot deformed by the flexible, transparent wall, resulting in a sequence of laser spot deformation images. Based on the laser spot deformation image sequence, the volume change of the cement paste sample within the annular sample cavity was calculated. The chemical shrinkage value of the cement paste was calculated based on this volume change and the initial volume of the cement paste sample.

[0081] In one embodiment of the present invention, see [reference] Figure 2First, moisten the mixing pot and mixing blades. Pour the weighed cement into the mixing pot, fix the mixing pot on the machine base and raise it to the mixing position. Start the mixer and slowly add the mixing water while mixing at low speed. The water addition process should be completed within 20 seconds. Then switch the mixer to high speed and continue mixing for 180 seconds. After stopping the mixing, scrape off the slurry on the blades and the pot wall, and continue mixing at high speed for another 180 seconds. After the mixing program is completed, the fresh cement slurry to be tested is obtained. In some embodiments, an annular sample cavity is prepared. The rigid base of the annular sample cavity is made of polymethyl methacrylate with an outer diameter of 100 mm and a thickness of 10 mm. The central column is made of the same material with an outer diameter of 50 mm and a height of 40 mm, and is fixed to the center of the rigid base. The outer flexible transparent film is a polyethylene terephthalate film with a thickness of 0.2 mm. The lower edge of the outer flexible transparent film is sealed to the outer edge of the rigid base with silicone sealant, and the upper edge of the outer flexible transparent film is sealed to the top of the central column with a detachable sealing clamp. This forms an annular closed cavity between the rigid base, the central column, and the outer flexible transparent film. The inner radius of the annular closed cavity is 25 mm, the outer radius is 40 mm, and the height is 30 mm.

[0082] The rigid base of the annular sample chamber is not a single-plane bottom support, but an integral base with an annular raised outer edge. A central column is vertically fixed to the center of this base. The lower edge of the outer flexible transparent membrane is sealed to the annular raised outer edge of the rigid base with silicone sealant, while its upper edge is sealed to the top of the central column with a detachable sealing clamp. Between the rigid base, the central column, and the outer flexible transparent membrane, an annular cavity with an open top is formed. This open top is the top of the annular sealed cavity to be sealed. The sealing film extends and covers the upper surface of the annular raised outer edge of the rigid base. The inner diameter of the sealing ring is slightly larger than the outer diameter of the central column, and its outer diameter matches the annular raised outer edge of the rigid base. The sealing ring is pressed downwards with bolts or other fasteners, clamping the sealing film together with the annular raised outer edge of the rigid base, thereby achieving an effective seal at the top of the annular sample chamber. After this sealing operation, the outer flexible transparent membrane forms a continuous, deformable annular sensitive surface, which, together with the rigid base, central column, and top sealing structure, constitutes a complete sealed cavity. In practice, the prepared fresh cement paste is transferred to a wide-mouthed beaker. Using a glass rod, the fresh cement paste is slowly poured along the beaker wall into the annular sealed cavity of the annular sample chamber. During the pouring process, the lower end of the glass rod is kept close to the liquid surface, and the pouring speed is controlled to avoid the generation of eddies, until the liquid surface of the fresh cement paste is level with the top of the annular sealed cavity.

[0083] It is understood that after the freshly mixed cement paste fills the annular sealed cavity, a polytetrafluoroethylene film slightly larger than the outer diameter of the annular sealed cavity is immediately taken as a sealing film and placed over the top opening of the annular sealed cavity. A polymethyl methacrylate sealing ring with an outer diameter of 100 mm, an inner diameter of 52 mm, and a thickness of 5 mm is pressed onto the sealing film. The sealing ring is then fastened to the rigid base of the annular sample cavity by four bolts evenly distributed along the circumference, thereby compressing the sealing film to achieve a top seal of the annular sealed cavity. In some embodiments, the annular sample cavity, which has been sealed and is filled with cement paste sample, is placed horizontally on a vibration-free, flat marble table. The static process lasts for 5 minutes. Under the action of gravity, the surface of the cement paste sample gradually tends to be horizontal, and any small number of air bubbles that may exist inside gather upwards below the sealing film.

[0084] Optionally, when weighing the mixing water, the mass of the water can be 0.45 or 0.55 times the mass of the cement. In specific implementation, the material of the outer flexible transparent membrane can be a 0.15 mm thick polyvinyl chloride film. It is understood that the material of the sealing film can also be a polyethylene film. Optionally, during the process of injecting freshly mixed cement paste into the annular sealed cavity, the entire annular sample cavity can be placed on a vibration table, and a short, slight vibration of 5 seconds can be used to help remove introduced air bubbles.

[0085] In one embodiment of the present invention, see [reference] Figure 3 Prepare a transparent thermostatic liquid medium bath, injection molded from polycarbonate material, with internal effective dimensions of 200 mm long, 150 mm wide, and 80 mm high. Pour anhydrous ethanol at 20.0 ± 0.1 degrees Celsius into the bath as the liquid medium, with a pouring volume of 1500 ml. The pouring volume is measured using a glass graduated cylinder with a range of 2000 ml and a graduation of 10 ml. In some embodiments, the thermostatic liquid medium bath is placed on a leveling platform equipped with three adjustable anchor bolts. A bubble level with an accuracy of 0.02 mm / m is placed in the center of the bottom surface of the thermostatic liquid medium bath. The three anchor bolts are adjusted alternately until the bubble of the bubble level is within the center scale ring. At this point, the bottom surface of the thermostatic liquid medium bath is perfectly level, with a levelness error of less than 0.05 degrees.

[0086] In the specific implementation, the sealed annular sample cavity, filled with cement paste sample, is slowly immersed into the anhydrous ethanol liquid medium in the constant temperature liquid medium tank. During immersion, the rigid base plane of the annular sample cavity is kept parallel to the liquid medium surface until the lower surface of the rigid base of the annular sample cavity is in complete contact with the inner bottom surface of the constant temperature liquid medium tank. Anhydrous ethanol liquid medium is then added to the constant temperature liquid medium tank using a glass beaker, avoiding direct scouring of the annular sample cavity during the addition process, until the liquid medium level reaches a height of 5 mm from the upper edge of the constant temperature liquid medium tank. This liquid level completely covers the upper surface of the sealing ring at the top of the annular sample cavity and exceeds the upper surface of the sealing ring at least 15 mm. The entire system is then placed in a constant temperature laboratory environment with an internal air temperature of 20.0 ± 0.5 degrees Celsius and left to stand for 60 minutes to ensure that the temperature of the anhydrous ethanol liquid medium in the constant temperature liquid medium tank, the annular sample cavity, and the cement paste sample in the annular sample cavity is uniform and constant. Temperature monitoring is performed using a calibrated platinum resistance thermometer.

[0087] It is understood that a laser emitting device with stable wavelength and regular beam pattern is selected. The laser emitting device is a semiconductor laser with an output wavelength of 650 nm and an output power of <1 mW. The laser emitting device is fixedly installed on the outer wall of one side of the constant temperature liquid medium tank in the width direction using a three-dimensional adjustable bracket. The center of the laser emitting device's output port is 50 mm away from the outer wall of the constant temperature liquid medium tank, and its height is flush with the center area of ​​the outer flexible transparent film of the annular sample cavity. In some embodiments, the three-dimensional adjustable bracket of the laser emitting device is adjusted to finely adjust the output angle and horizontal position of the laser emitting device so that the red laser beam is perpendicularly incident on the outer surface of the outer flexible transparent film of the annular sample cavity immersed in anhydrous ethanol liquid medium. The incident point is located at the center of the annular area of ​​the outer flexible transparent film, that is, at the midpoint between the outer surface of the central column and the outer edge of the rigid base. The focus adjustment knob at the tail of the laser emitting device is adjusted so that the laser beam forms a well-defined circular spot on the outer surface of the outer flexible transparent film inside the anhydrous ethanol liquid medium. The diameter of the circular spot is measured to be 20 mm.

[0088] Optionally, the diameter setting of the circular light spot must satisfy the following relationship to ensure measurement validity:

[0089]

[0090] in: The measured diameter represents the circular light spot. The annular width represents the diameter of the annular sample cavity, which is the difference between the outer and inner circumferences of the annular sample cavity. In specific implementations, the outer circumference of the annular sample cavity... It is 40 mm, and the inner ring radius is... It is 25 mm in diameter and has a ring width of 25 mm. The calculated diameter is 15 mm, while the actual diameter of the circular light spot obtained through adjustment is... It is 10 mm, which meets the requirements. The relationship is as follows. It can be understood that the center position of the circular light spot is assisted in positioning using the preview screen of the image acquisition device, ensuring that the center point of the circular light spot coincides with the geometric center point of the annular area, and the pixel coordinate deviation between the two in the image does not exceed 5 pixels. Optionally, the fixed installation position of the laser emitting device can also be on one side of the length direction of the constant temperature liquid medium tank.

[0091] In one embodiment of the present invention, a high-resolution image acquisition device is selected. The image acquisition device is a CCD industrial camera with a sensor size of 1 / 1.8 inches and an effective pixel count of 5 million. The image acquisition device is fixedly mounted on the outer wall of the constant temperature liquid medium tank on the other side of the width direction using another three-dimensional adjustable bracket. The front end plane of the lens of the image acquisition device is 100 mm away from the outer wall of the constant temperature liquid medium tank. The optical axis center of the image acquisition device is at the same horizontal height as the beam emission point of the laser emitting device. The image acquisition device and the laser emitting device are aligned along a straight line passing through the central axis of the annular sample cavity. In some embodiments, the three-dimensional adjustable bracket of the image acquisition device is adjusted and the focusing ring on the lens is rotated so that the optical axis of the image acquisition device is perpendicular to the cylindrical surface of the annular sample cavity where the outer flexible transparent film is installed, and is directly facing the area where the laser spot is located. In the preview screen of the computer's camera control software, the laser spot is completely located in the center area of ​​the image and the image is clear.

[0092] In the specific implementation, the acquisition parameters of the image acquisition device were set. The exposure time was set to 10 milliseconds, the frame rate was set to 1 frame / minute, the image resolution was set to 1280 pixels × 960 pixels, and the image format was set to lossless compression TIFF format to ensure that the shape and edge details of the laser spot could be clearly captured. At the initial moment when the cement paste sample began to hydrate, that is, when the cement and mixing water were completely mixed, the image acquisition device was started by computer software instructions. The laser spot image was continuously acquired at the set time interval of 1 frame / minute for 48 hours. The laser spot image included the shape change of the laser spot on the outer flexible transparent film due to the deformation of the film wall as the volume of the cement paste changed. The laser spot images, which were acquired in chronological order, were stored in a designated folder on the computer hard drive with the file name format "Timestamp_YYYYMMDD_HHMMSS.tif" to form a laser spot deformation image sequence.

[0093] It is understandable that when the cement paste sample in the annular sample cavity decreases in volume due to chemical shrinkage, the absolute pressure inside the cement paste sample decreases. Under the static pressure of the external anhydrous ethanol liquid medium, the outer flexible transparent membrane deforms inward toward the central axis of the annular sample cavity. In some embodiments, the deformation of the outer flexible transparent membrane causes a change in the local radius of curvature of its outer surface. The spatial distribution of reflected or scattered light from the circular laser spot originally projected onto the flat or initially curved membrane surface changes accordingly, resulting in deformation of the laser spot on the imaging plane of the image acquisition device. The deformation of the circular laser spot manifests as a decrease in the spot area reflected by a reduction in the total number of pixels occupied by the spot, and a transformation of the spot edge contour from a standard circle to an ellipse or a more complex non-circular shape. In specific implementations, each frame of TIFF format image captured by the image acquisition device records the actual shape of the laser spot at the corresponding moment, the spot area size calculated in pixels, and the light intensity distribution information reflected by the image grayscale value.

[0094] Optionally, to quantify the change in laser spot shape, a shape distortion parameter is introduced for description. The shape distortion parameter is defined by the following relationship:

[0095]

[0096] in: The shape distortion parameter represents the laser spot. This represents the length of the major axis of the ellipse obtained by fitting the edge of the deformed light spot to an ellipse. This represents the length of the minor axis of the ellipse obtained by fitting an ellipse to the edge of the deformed laser spot. It can be understood that when the laser spot remains ideally circular, the shape distortion parameter... The theoretical value is 1; when the outer flexible transparent film undergoes uneven depression, the laser spot shape distortion parameter The value will be greater than 1. In specific implementations, the frame rate of the image acquisition device can also be set to 1 frame / 30 seconds or 1 frame / 2 minutes. Optionally, the exposure time of the image acquisition device can be adjusted to 5 milliseconds or 20 milliseconds according to the ambient light intensity.

[0097] In one embodiment of the present invention, the image at the initial moment is extracted from the image sequence of laser spot deformation. The initial moment is defined as the moment when the annular sample cavity is immersed in the constant temperature liquid medium tank after the cement paste mixing is completed. The edge detection algorithm based on the Canny operator is used to identify the edge contour of the laser spot in the image at the initial moment. The reference area and reference shape parameters of the laser spot at the initial moment are calculated. The reference area is represented by the number of pixels, and the reference shape parameter is the product of the minimum circumscribed circle radius of the initial circular spot and the image space calibration coefficient. In some embodiments, each frame of TIFF format image in the laser spot deformation image sequence is read sequentially, and the same edge contour recognition processing is performed on each frame of image. The processing includes image denoising, grayscale binarization, contour finding and ellipse fitting. The current area and current shape parameters of the laser spot in each frame of image are calculated. The current area is obtained by counting the number of pixels inside the contour, and the current shape parameters are obtained by fitting the axis ratio of the ellipse. These are compared with the reference area and reference shape parameters to obtain the spot area change rate and shape distortion rate corresponding to each frame of image. The spot area change rate is defined as the ratio of the difference between the current area and the reference area to the reference area, and the shape distortion rate is defined as the ratio of the difference between the current shape parameter and the reference shape parameter to the reference shape parameter.

[0098] In practice, a pre-calibrated relational model is established, which describes the quantitative correspondence between the normal displacement per unit area of ​​the outer flexible transparent membrane and the rate of change of the area and shape distortion of the laser spot projected onto it. A calibration annular cavity with the same structural dimensions as the annular sample cavity is prepared. The materials and geometric parameters of the rigid base, central column, and outer flexible transparent membrane of the calibration annular cavity are consistent with those of the measured annular sample cavity. Full-scale, incompressible, and fixed-volume deionized water is injected into the calibration annular cavity as the calibration liquid. The calibration annular cavity with the injected calibration liquid is then immersed in the same manner. In an anhydrous ethanol liquid medium in a constant-temperature liquid medium bath, a piezoelectric ceramic micro-displacement driving device with an accuracy of 0.1 micrometers is used to apply a known micro-normal displacement to the outer flexible transparent membrane from inside the central column of the calibration annular cavity through a flat-headed probe that contacts the inner surface of the outer flexible transparent membrane. After each application of the micro-normal displacement, an image of the laser spot is acquired using a laser emitting device and an image acquisition device, and the corresponding spot area change rate and shape distortion rate are calculated. A series of data pairs of different micro-normal displacement values ​​and corresponding spot area change rates and shape distortion rates are recorded, as shown in Table 1.

[0099] Table 1: Correspondence between minute normal displacement and spot parameters in the pre-calibration experiment

[0100]

[0101] It is understandable that the least squares curve fitting method is used to analyze and process the recorded data pairs to establish a functional relationship between the normal displacement of the outer flexible transparent film and the rate of change of the laser spot area and the shape distortion rate.

[0102] The pre-calibrated relational model is a multivariate function model with the laser spot area change rate and shape distortion rate as dual inputs and the normal displacement of the outer flexible transparent membrane as a single output. The least squares method is used to perform bivariate nonlinear curve fitting on the recorded small normal displacement values ​​and the corresponding spot area change rate and shape distortion rate data, establishing the following functional relationship:

[0103]

[0104] in: This represents the normal displacement of the outer flexible transparent membrane. Represents the rate of change of the light spot area. Represents shape distortion rate. Represents a constant term. , , The coefficients represent those obtained from the fitting. In the actual inversion calculation of the normal displacement, the spot area change rate and shape distortion rate calculated for each frame of image are simultaneously substituted into the binary nonlinear function model to directly solve for the unique normal displacement. To address parameter deviations caused by noise or non-ideal deformation during image acquisition and membrane deformation, a moving average filtering algorithm is used to preprocess the area change rate and shape distortion rate obtained from multiple consecutive frames of images before substituting them into the model for calculation, thus reducing the impact of deviations. Simultaneously, based on the moderate positive correlation between the spot area change rate and shape distortion rate, data pairs are normalized during the fitting process to eliminate dimensional differences, prevent ill-conditioned models, and ensure model stability and uniqueness of the solution.

[0105] In practice, the area change rate and shape distortion rate of the light spot calculated for each frame of the image are input into a pre-calibrated relational model to calculate the average normal displacement of the outer flexible transparent film in the laser spot coverage area. Based on the geometric dimensions of the annular sample cavity and the average normal displacement of the outer flexible transparent film in the laser spot coverage area, the volume change of the cement paste sample in the annular sample cavity at the corresponding time is calculated through integral calculation.

[0106] In some embodiments, the geometric parameters of the annular sample cavity are obtained, including the inner ring radius of the annular sample cavity. millimeters, outer ring radius millimeters and the initial radius of curvature of the outer flexible transparent membrane (Considered as a plane); it is assumed that when the outer flexible transparent membrane deforms, its deformation mode is consistent with that in the pre-calibration experiment, and the deformation is continuous and smooth within the annular region; the consistent mode specifically means that the deformation of the outer flexible transparent membrane exhibits radial symmetry, the displacement is uniformly distributed along the circumferential direction, and the normal displacement is linearly distributed radially from the inner ring to the outer ring. In the pre-calibration experiment, when a local point displacement is applied by a flat-headed probe, the deformation of the flexible transparent membrane also follows this radially symmetrical, circumferentially uniform, and radially linear displacement distribution law; the interpolation estimation specifically adopts the radial linear interpolation method. Taking the annular center position of the laser spot coverage area as the reference, combined with the radial coordinates of the inner and outer rings of the spot coverage area and the average normal displacement, the radial linear interpolation function is determined. Based on this function and the radial average coordinates of each micro-annular unit, the normal displacement of the outer flexible transparent membrane corresponding to each micro-annular unit is estimated. During the interpolation process, the constraint condition of continuous and smooth deformation is followed to ensure that there are no abrupt changes in the normal displacement of adjacent micro-annular units. The annular region covered by the laser spot is discretized into A series of tiny concentric ring units. In specific implementation, the average normal displacement of the laser spot coverage area is calculated based on a pre-calibrated relational model. Based on the deformation mode assumption, the normal displacement of the outer flexible transparent membrane on each micro-ring unit is estimated using a bilinear interpolation algorithm. ,in Representing the The average radius of each ring element; based on the normal displacement of each tiny ring element. and its corresponding ring area ( (with radial spacing), calculate the incremental change in cavity volume caused by the deformation of tiny annular units. Volume change increment The approximate calculation formula is:

[0107]

[0108] in: Representing the The volume change increment of a tiny ring-shaped unit, Representing the The area of ​​a tiny ring-shaped unit, Representing the The angle between the surface normal of the flexible transparent membrane on the outer side of the annular unit after deformation and the central axis. Representing the The normal displacement of each ring element; the volume change increment for all tiny ring elements. Summing is performed to obtain the total change in the internal volume of the annular sample cavity caused by the overall deformation of the outer flexible transparent membrane. The total volume change is equal to the volume change of the cement paste sample in the annular sample cavity due to chemical shrinkage.

[0109] Optionally, the geometric parameters of the annular sample cavity can also be an inner ring radius of 20 mm and an outer ring radius of 45 mm. This can be understood as the number of discrete micro-annular units in the laser spot coverage area... It can also be 50 or 200. Optionally, when calculating the incremental change in cavity volume caused by the deformation of the tiny annular unit, it is assumed that the deformation of the outer flexible transparent membrane is a pure normal displacement and tangential strain is ignored; therefore, the included angle... It is approximately zero when the deformation is small. The simplified calculation formula is as follows: In practical implementation, the pre-calibrated relational model can also be established using polynomial fitting or neural network fitting methods. It can be understood that the micro-displacement driving device can also be a combination of a micrometer screw and a lever amplification mechanism.

[0110] See Figure 4 This study visually presents the dynamic evolution of the laser spot area change rate and shape distortion rate during the four hydration stages of cement paste: before initial setting, during initial setting, during final setting, and during the stabilization stage. In the initial hydration stage (before initial setting), the chemical shrinkage effect of the cement paste begins to appear, causing the outer flexible transparent membrane to indent into the cavity, resulting in a negative change in the projected spot area, with the area change rate continuously decreasing from 0. Simultaneously, a slight change in the membrane wall curvature causes the spot edge to deviate from a circular shape, and the shape distortion rate slowly increases from 0. Entering the initial setting stage, the hydration reaction rate accelerates, the chemical shrinkage effect intensifies, and the decrease in the spot area change rate and the increase in the shape distortion rate increase synchronously, reflecting the rapid deepening of the membrane wall indentation. During the final setting stage, the hydration products of the cement paste gradually form a continuous skeleton, the shrinkage rate tends to stabilize, and both the spot area change rate and the shape distortion rate enter a linear change phase. After entering the stable period, the hydration reaction is basically completed, the rate of decrease in the change rate of the light spot area tends to be slow, while the shape distortion rate continues to rise slowly and gradually converges. This characteristic is highly consistent with the long-term development law of chemical shrinkage of cement paste.

[0111] This curve not only verifies the sensitivity of the two parameters of the laser spot (area change rate and shape distortion rate) to the chemical shrinkage of cement paste, but also provides key dynamic response data for subsequent conversion of membrane wall normal displacement and paste volume change through pre-calibrated model.

[0112] In one embodiment of the present invention, the initial time after the cement paste sample is poured into the annular sample cavity is recorded. The initial time is recorded by an electronic timer synchronized with the computer system time. This initial time corresponds to the moment when the cement paste mixing is completed and the sealing operation of pouring into the annular sample cavity is finished. The initial time data is stored in a text-format experimental log file. In some embodiments, the volume of the annular sealed cavity of the annular sample cavity is obtained. The volume of the annular sealed cavity is used as the initial volume of the cement paste sample. The initial volume is obtained by precisely measuring and calculating the geometric dimensions of the annular sample cavity. The measurement is performed using a digital caliper. The inner ring radius of the annular sealed cavity is measured to be 25.00 mm, the outer ring radius is measured to be 40.00 mm, and the annular height is measured to be 30.00 mm. The initial volume is calculated according to the column and shell volume formula.

[0113] Starting from the initial moment, a series of specific test moments are obtained based on the timestamps of the light spot deformation image sequence. The timestamp information is parsed from the image file name "Timestamp_YYYYMMDD_HHMMSS.tif". The selection rule for specific test moments is to extract a corresponding image file name and its timestamp every hour starting from the initial moment. In specific implementation, the volume change of the cement paste sample corresponding to each specific test moment is read and calculated. The volume change data is stored in a structured data file, which contains two columns: "timestamp" and "volume change_cubic millimeters". The specific test moment is associated with the corresponding volume change value through timestamp matching.

[0114] It can be understood that the chemical shrinkage value of cement paste at a specific test time is obtained by dividing the volume change at each specific test time by the initial volume of the cement paste sample and then multiplying by a percentage factor. The formula for calculating the chemical shrinkage value of cement paste is as follows:

[0115]

[0116] in: Represents a specific test moment The chemical shrinkage value of cement paste, Represents a specific test moment The volume change of the cement paste sample was calculated. This represents the initial volume of the cement paste sample. In some embodiments, different test times are correlated with their corresponding chemical shrinkage values ​​of the cement paste to form a chemical shrinkage development curve of the cement paste sample over time from the initial time. The correlation record is completed by creating a data table containing two columns: "Time_Hour" and "Chemical Shrinkage Value_Percentage". The data in the "Time_Hour" column is calculated from the difference between the timestamp and the initial time.

[0117] Optionally, the interval between specific test times can be set to 30 minutes or 2 hours. In practice, the initial volume of the cement paste sample can also be obtained by the drainage method. The annular sealed cavity of the annular sample chamber is filled with mercury, the mass of the injected mercury is weighed, and the initial volume is calculated based on the mercury density. The chemical shrinkage development curve is formed by importing the data table into plotting software, creating a scatter plot with "time_hour" on the x-axis and "chemical shrinkage value_percentage" on the y-axis, and then connecting the points to form a line. Optionally, the calculation results of the cement paste chemical shrinkage value can be output as a comprehensive report file including time, volume change, and chemical shrinkage value.

[0118] See Figure 5 The Pearson correlation coefficients of various detection indicators are presented, intuitively revealing the strength and direction of the linear correlation between different physical quantities. Specifically, the correlation coefficient between volume change and chemical shrinkage value is 1.00, indicating a completely positive correlation, which is consistent with the definition of chemical shrinkage value calculated from volume change and initial volume. The correlation coefficient between the spot area change rate and the spot shape distortion rate is 0.41, showing a moderate positive correlation, reflecting the synchronicity of spot area and shape changes when the flexible membrane is deformed. The correlation coefficient between volume change, chemical shrinkage value, and the average normal displacement of the flexible membrane is -0.90, showing a very strong negative correlation. This is because the volume shrinkage of cement paste drives the flexible membrane to indent into the cavity, causing the normal displacement to increase as the volume decreases. In addition, the correlation coefficient between the average normal displacement of the flexible membrane and the hourly shrinkage rate is 0.38, showing a certain positive correlation, indicating that the indentation rate of the membrane is related to the time-varying shrinkage rate of the cement paste.

[0119] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications 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 protection scope of the present invention.

Claims

1. A method for determining the chemical shrinkage of cement paste, characterized in that, Includes the following steps: Prepare cement paste samples with a specified mix ratio, and pour and seal the cement paste samples into an annular sample cavity with a flexible transparent cavity wall. The annular sample cavity is placed horizontally in a constant temperature liquid medium tank, so that the liquid in the constant temperature liquid medium tank completely submerges the annular sample cavity. A circular laser spot is projected onto the outside of the flexible transparent cavity wall of the annular sample cavity using a laser emitting device. Using an image acquisition device, images of the laser spot deformed by the flexible transparent cavity wall are continuously acquired to obtain a sequence of laser spot deformation images; Based on the light spot deformation image sequence, the volume change of the cement paste sample inside the annular sample cavity is calculated. The chemical shrinkage value of the cement paste is calculated based on the volume change and the initial volume of the cement paste sample. The annular sample chamber consists of a rigid base, a central column, and an outer flexible transparent membrane. The upper and lower ends of the outer flexible transparent membrane are respectively sealed to the rigid base and the central column to form an annular closed cavity. The calculation of the volume change of the cement paste sample within the annular sample cavity based on the light spot deformation image sequence is specifically as follows: Extract the initial moment image from the laser spot deformation image sequence, identify the edge contour of the laser spot in the initial moment image, and calculate the reference area and reference shape parameters of the laser spot at the initial moment; Each frame of the light spot deformation image sequence is read sequentially, and the same edge contour recognition processing is performed on each frame. Calculate the current area and current shape parameters of the laser spot in each frame image, and compare them with the reference area and reference shape parameters to obtain the spot area change rate and shape distortion rate corresponding to each frame image; A pre-calibrated relational model is established, which describes the quantitative correspondence between the normal displacement per unit area of ​​the outer flexible transparent film and the rate of change of the area and the rate of shape distortion of the laser spot projected onto it; The spot area change rate and shape distortion rate calculated for each frame of image are input into the pre-calibrated relationship model to calculate the average normal displacement of the outer flexible transparent film in the laser spot coverage area. Based on the geometric dimensions of the annular sample cavity and the average normal displacement of the outer flexible transparent membrane in the laser spot coverage area, the volume change of the cement paste sample in the annular sample cavity at the corresponding time is calculated through integral calculation. The establishment of a pre-calibrated relational model specifically involves: Prepare a calibration annular cavity with the same structural dimensions as the annular sample cavity, and inject an incompressible calibration liquid with a fixed volume into the calibration annular cavity; The calibration annular cavity for injecting calibration liquid is immersed in the liquid medium of the constant temperature liquid medium tank in the same manner; Using a micro-displacement driving device, a small normal displacement of known magnitude is applied to the outer flexible transparent membrane from inside or outside the calibration annular cavity; After each small normal displacement is applied, the laser emitting device and the image acquisition device are used to acquire an image of the laser spot at this time, and the spot area change rate and shape distortion rate corresponding to the image are calculated. Record a series of different minute normal displacement values ​​and corresponding data pairs of spot area change rate and shape distortion rate; The recorded data were analyzed and processed using a curve fitting method to establish a functional relationship between the normal displacement of the outer flexible transparent film and the rate of change of the laser spot area and the shape distortion rate, i.e., the pre-calibrated relationship model.

2. The method for determining the chemical shrinkage of cement paste according to claim 1, characterized in that, The preparation of the cement paste sample with the specified mix proportion involves casting and sealing the cement paste sample within an annular sample cavity with flexible, transparent walls, specifically as follows: According to the standard test method, weigh the cement and mixing water, and use a cement paste mixer to mix the cement and mixing water evenly to obtain the fresh cement paste to be tested. The freshly mixed cement paste to be tested is slowly injected into the annular sealed cavity of the annular sample chamber, avoiding the introduction of air bubbles during the injection process; After the freshly mixed cement paste fills the annular sealed cavity, a sealing film is covered on the top of the annular sealed cavity, and a sealing ring is used to press the sealing film onto the rigid base to ensure that the annular sample cavity is completely sealed. The sealed annular sample cavity, filled with cement paste sample, is placed on a flat table until the surface of the cement paste sample tends to be horizontal.

3. The method for determining the chemical shrinkage of cement paste according to claim 1, characterized in that, The step of placing the annular sample cavity horizontally in a constant-temperature liquid medium bath, such that the liquid in the constant-temperature liquid medium bath completely submerges the annular sample cavity, specifically involves: Prepare a transparent constant temperature liquid medium tank, and inject a low viscosity, high light transmittance liquid medium with a constant temperature into the constant temperature liquid medium tank; The constant temperature liquid medium tank is placed on a level adjustment platform and calibrated with a level to ensure that the bottom surface of the constant temperature liquid medium tank is strictly level. The sealed annular sample cavity is slowly immersed into the liquid medium in the constant temperature liquid medium tank, ensuring that the rigid base of the annular sample cavity is in parallel contact with the bottom surface of the constant temperature liquid medium tank. Continue adding liquid medium until the liquid level completely covers the top of the annular sample chamber. Furthermore, the liquid level should be at least 15 mm above the upper surface of the sealing ring at the top of the annular sample chamber; The entire system is placed in a constant temperature environment to ensure that the temperature of the liquid medium in the constant temperature liquid medium tank, the annular sample chamber, and the cement paste sample in the chamber is uniform and constant.

4. The method for determining the chemical shrinkage of cement paste according to claim 1, characterized in that, The method of using a laser emitting device to project a circular laser spot onto the outer side of the flexible transparent cavity wall of the annular sample cavity is as follows: Select a laser emitting device with stable wavelength and regular light spot, and fix the laser emitting device on one side of the constant temperature liquid medium tank; Adjust the emission angle and position of the laser emitting device so that the laser beam is perpendicularly incident on the flexible transparent membrane on the outside of the annular sample cavity immersed in the liquid medium; Adjust the focal length of the laser emitting device so that the laser beam forms a circular spot with clear edges on the outer surface of the outer flexible transparent film; The diameter of the circular light spot is smaller than the annular width of the annular sample cavity, and the center of the circular light spot is located at the center of the annular region of the annular sample cavity.

5. The method for determining the chemical shrinkage of cement paste according to claim 1, characterized in that, The process involves using an image acquisition device to continuously acquire images of the laser spot caused by the deformation of the flexible transparent cavity wall, resulting in a sequence of laser spot deformation images. Specifically: A high-resolution image acquisition device is selected and fixedly installed on the other side of the constant temperature liquid medium tank, and is positioned opposite the laser emitting device along a straight line passing through the central axis of the annular sample cavity. Adjust the optical axis of the image acquisition device so that it is perpendicular to the part of the annular sample cavity where the outer flexible transparent film is installed, and directly facing the area where the laser spot is located; Set the acquisition parameters of the image acquisition device, including exposure time, frame rate and resolution, to ensure that the shape of the laser spot can be clearly captured; At the initial moment when the cement paste sample begins to hydrate, the image acquisition device is activated, and images of the laser spot are continuously acquired at set time intervals. The image of the laser spot includes the shape change of the laser spot on the outer flexible transparent membrane caused by the deformation of the membrane wall as the volume of cement paste changes; The acquired laser spot images, arranged in chronological order, are stored as a sequence of laser spot deformation images.

6. The method for determining the chemical shrinkage of cement paste according to claim 5, characterized in that, The image of the laser spot includes the shape change of the laser spot on the outer flexible transparent membrane caused by the deformation of the membrane wall due to the change in the volume of cement paste, specifically: When the cement paste sample in the annular sample cavity decreases in volume due to chemical shrinkage, the outer flexible transparent membrane deforms inward toward the central axis of the annular sample cavity under the action of pressure changes inside the sample and external liquid static pressure. The concave deformation of the outer flexible transparent film causes a change in the curvature of its outer surface, thereby causing the circular laser spot projected onto it to deform. The deformation of the circular laser spot is manifested in the change of the spot area and the transformation of the spot edge contour from circular to non-circular; In each frame of the image captured by the image acquisition device, the actual shape, size, and intensity distribution of the laser spot at the corresponding moment are recorded.

7. The method for determining the chemical shrinkage of cement paste according to claim 6, characterized in that, Based on the geometric dimensions of the annular sample cavity and the average normal displacement of the outer flexible transparent membrane within the laser spot coverage area, the volume change of the cement paste sample within the annular sample cavity at the corresponding time is calculated through integral calculation. Specifically: Obtain the geometric parameters of the annular sample cavity, including the inner ring radius, outer ring radius, and initial radius of curvature of the outer flexible transparent membrane; Assuming that when the outer flexible transparent membrane deforms, its deformation mode is consistent with the mode in the pre-calibration experiment, and the deformation is continuous and smooth within the annular region; The annular region covered by the laser spot is discretized into several tiny annular units; The average normal displacement of the laser spot coverage area calculated based on the pre-calibrated relational model, combined with the deformation mode assumption, is used to interpolate and estimate the normal displacement of the outer flexible transparent film on each micro-ring unit. The increase in cavity volume caused by the deformation of the micro-ring unit is calculated based on the normal displacement of each micro-ring unit and its corresponding ring area. The total volume change of the annular sample cavity caused by the overall deformation of the outer flexible transparent membrane is obtained by summing the volume change increments of all the tiny annular units. This total volume change is equal to the volume change of the cement paste sample in the annular sample cavity due to chemical shrinkage.

8. The method for determining the chemical shrinkage of cement paste according to claim 1, characterized in that, The chemical shrinkage value of the cement paste is calculated based on the volume change and the initial volume of the cement paste sample, specifically as follows: Record the initial moment after the cement paste sample is poured into the annular sample cavity; The volume of the annular sealed cavity of the annular sample chamber is obtained as the initial volume of the cement paste sample. Starting from the initial moment, a series of specific test moments are obtained based on the timestamps of the light spot deformation image sequence; Read the volume change of the cement paste sample at each specific test moment, obtained through calculation. The volume change at each specific test time is divided by the initial volume of the cement paste sample, and then multiplied by a percentage factor to obtain the chemical shrinkage value of the cement paste at the specific test time. The chemical shrinkage values ​​of cement paste at different test times are correlated and recorded to form a chemical shrinkage development curve of the cement paste sample from the initial time over time.

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