Dynamic tracking characterization method for water absorption and release process of super absorbent resin in concrete

Abstract

The invention belongs to the technical field of concrete internal curing performance evaluation, and particularly relates to a dynamic tracking characterization method for the water absorption and release process of super absorbent resin in concrete. The dynamic tracking characterization method for the water absorption and release process of the super absorbent resin in the concrete comprises the following steps: (1) putting cement paste or concrete into a sample container as a sample to be detected; (2) placing first super absorbent resin on the surface of the sample to be detected; and (3) monitoring the water absorption and water release of the first super absorbent resin by using a super depth-of-field microscope and / or XRF. The method provided by the invention is helpful for dynamically evaluating the water absorption and water release behaviors of the super absorbent resin in the concrete, revealing the absorption / release path of water, and also helpful for analyzing the promotion effect of the super absorbent resin on the aspects of cement hydration reaction, strength development, crack resistance and the like and the influence of the super absorbent resin on the internal curing performance of the concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete internal curing performance evaluation, and particularly relates to a method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete. Background Art

[0002] Superabsorbent polymer (SAP), a moisture storage and regulation material, has been widely used in concrete curing technology in recent years. Its primary function is to form a three-dimensional network of water storage structures through pre-absorption, continuously releasing water during the critical stage of cement hydration. This effectively compensates for humidity gradients within the concrete, inhibits autogenous and drying shrinkage, and thereby improves the strength and durability of the concrete. The internal curing performance of SAP in concrete depends on its water absorption and release behavior. However, the water absorption and release process of SAP is dynamic, and once SAP is placed in concrete, it cannot be removed and weighed, making it difficult to determine the water absorption or release of SAP in concrete using the traditional tea bag method.

[0003] Therefore, there is an urgent need for a new technical means to dynamically and accurately evaluate the water absorption and release kinetics of superabsorbent resin as an internal curing agent and its internal curing effect.

[0004] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete, so as to help solve or improve the problem that the existing technology is difficult to accurately monitor the water absorption and release process of super absorbent resin in concrete or difficult to evaluate the internal curing performance of super absorbent resin.

[0006] To achieve the above-mentioned object, the present invention provides the following technical solution: a method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete, comprising the following steps: (1) placing cement paste or concrete in a sample container as a sample to be tested; (2) placing a first super absorbent resin on the surface of the sample to be tested; and (3) monitoring the first super absorbent resin using an ultra-depth-of-field microscope and / or XRF.

[0007] Preferably, in step (2), the first super absorbent resin is obtained by soaking the super absorbent resin in a cesium nitrate solution to fully absorb the cesium nitrate solution; or, the first super absorbent resin is obtained by soaking the super absorbent resin in a rubidium nitrate solution to fully absorb the rubidium nitrate solution.

[0008] Preferably, in step (2), the first super absorbent resin is dipped into the first super absorbent resin by a needle and then transferred to the surface of the sample to be tested.

[0009] Preferably, in step (3), the super depth of field microscope is used to obtain an image sequence of the sample, and the indicators detected by the super depth of field microscope include morphological changes of the first super absorbent resin.

[0010] Preferably, XRF is used to detect element changes in the sample to be tested and / or the first super absorbent resin; and the indicators detected by XRF include the distribution of cesium or rubidium.

[0011] Preferably, the distribution of the cesium element or the rubidium element is detected by line scanning and / or area scanning.

[0012] Preferably, the raw materials of the cement paste include cement and mixing water; the raw materials of the concrete include cementitious materials, mixing water and sand and gravel aggregates; during the mixing process of the cement paste or concrete, the step of adding a second super absorbent resin is further included; the second super absorbent resin is an unabsorbed super absorbent resin or a pre-absorbed super absorbent resin; the pre-absorbed super absorbent resin is obtained by allowing the super absorbent resin to fully absorb the mixing water of the cement paste or concrete.

[0013] Preferably, in step (2), after placing the first super absorbent resin on the surface of the sample to be tested, the protective layer further comprises a first protective layer and a second protective layer; the first protective layer is formed by the cement slurry; and the second protective layer is a plastic wrap.

[0014] Preferably, the thickness of the first protective layer is 1-5 mm; the thickness of the concrete sample is 1-3 cm.

[0015] Beneficial effects:

[0016] The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete of the present invention can achieve:

[0017] (1) High-precision dynamic observation: The present invention provides a dynamic and accurate method for evaluating the internal curing performance of superabsorbent resins by combining ultra-depth-of-field microscopy with X-ray fluorescence technology. This method can reveal the water absorption and release process of superabsorbent resins at the microscopic level, achieve high-precision dynamic observation of the water absorption and release process of superabsorbent resins, and monitor the microscopic morphological changes and water transfer process of superabsorbent resins in real time. The present invention can in-situ test the water release of superabsorbent resins and indirectly reflect the scope and effect of internal curing by observing the amount and distribution of water released.

[0018] (2) Water transfer mechanism revealed: The dynamic tracking and characterization method of the water absorption and release process of the super absorbent resin in concrete of the present invention analyzes the water exchange path between the super absorbent resin and concrete through data fusion, revealing the microscopic dynamics of its water absorption and release process.

[0019] (3) Accurate evaluation of internal curing performance: The method for dynamic tracking and characterization of the water absorption and release process of superabsorbent resin in concrete of the present invention comprehensively evaluates the effect of superabsorbent resin as an internal curing agent by monitoring the water absorption and release behavior, strength development and shrinkage performance changes of superabsorbent resin, providing an accurate basis for engineering application.

[0020] (4) Optimizing internal curing technology: The dynamic tracking and characterization method of the water absorption and release process of super absorbent resin in concrete of the present invention provides a scientific basis for the application and optimization of super absorbent resin in concrete, thereby improving the durability and long-term performance of concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0022] Figure 1 A schematic diagram of a sample to be tested after a first super absorbent resin is placed on the surface of the sample according to an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the super-depth-of-field microscope test results;

[0024] Figure 3 df are the test results of water release of SAP in cement paste; wherein, ac are super depth of field photographs of commercial SAP observed at different times after pre-absorbing cesium nitrate solution and placing it on the surface of the sample to be tested, the measurement results obtained by using the depth up function of the super depth of field microscope to obtain a composite image and perform contour measurement, and the salt resistance test results; df are super depth of field photographs of laboratory-made SAP observed at different times after pre-absorbing cesium nitrate solution and placing it on the surface of the sample to be tested, the measurement results obtained by using the depth up function of the super depth of field microscope to obtain a composite image and perform contour measurement, and the salt resistance test results;

[0025] Figure 4 This is the state diagram (XRF) of laboratory-made SAP pre-absorbed with cesium nitrate solution in cement paste for 7 days;

[0026] Figure 5 This is the state diagram (XRF) of commercial SAP pre-absorbed with cesium nitrate solution in cement paste for 7 days;

[0027] Figure 6 The graphs show the compressive strength and flexural strength test results of cement paste containing commercial SAP and laboratory-made SAP at different ages;

[0028] Figure 7The graph shows the test results of the effects of commercially available SAP and laboratory-made SAP on the shrinkage value of cement paste at different ages;

[0029] Figure 8 This is the XRF line scan of the laboratory-made SAP pre-absorbed with cesium nitrate solution in cement paste for 28 days;

[0030] Figure 9 This is the XRF line scan of commercial SAP pre-absorbed with cesium nitrate solution in cement paste for 28 days;

[0031] Figure 10 This is an XRF surface scan of the surface of the SAP that has pre-absorbed cesium nitrate solution and is covered with a protective layer;

[0032] Figure 11 The XRF line scan image of the surface of the SAP pre-absorbed with cesium nitrate solution is covered with a protective layer;

[0033] Figure 12 This is an XRF surface scan of the surface of the SAP that has been pre-absorbed with cesium nitrate solution and is not covered with a protective layer;

[0034] Figure 13 This is an XRF line scan of the surface of the SAP that has been pre-absorbed with cesium nitrate solution and is not covered with a protective layer. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0036] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0037] The present invention addresses the current difficulties in accurately monitoring the water absorption and release process of super absorbent resins in concrete or cement paste, or in evaluating the internal curing effect, and provides a method for dynamically tracking and characterizing the water absorption and release process of super absorbent resins in concrete. The method of the present invention comprises the following steps: (1) placing cement paste or concrete in a sample container as a sample to be tested; (2) placing a first super absorbent resin on the surface of the sample to be tested; and (3) monitoring the water absorption and release of the first super absorbent resin using an ultra-depth-of-field microscope and / or XRF.

[0038] The present invention provides a method for dynamically tracking and characterizing the water absorption and release process of a superabsorbent resin in concrete. By using an ultra-depth-of-field microscope for observation, corresponding image sequences can be acquired periodically or irregularly as needed. XRF detection facilitates monitoring of changes in elemental composition. By synchronously collecting and processing XRF and ultra-depth-of-field microscopic image data and combining the images with elemental analysis data, it is possible to analyze changes in the morphology and elemental content of the first superabsorbent resin during its absorption and release processes. This allows for dynamic assessment of the water absorption and release behavior of the superabsorbent resin internal curing agent in concrete, revealing the water absorption / release pathway. Furthermore, by comparing the water absorption / release characteristics of the first superabsorbent resin at different time points, it is also helpful to analyze its promoting effect on cement hydration reactions, strength development, and crack resistance, as well as its impact on the internal curing properties of concrete.

[0039] Preferably, the sample container is an open threaded tube. The sample to be tested (fresh cement paste or concrete) is added to the threaded tube, and then the first super absorbent resin is placed on the sample to be tested. Figure 1 shown.

[0040] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete of the present invention, in step (2), the first super absorbent resin is obtained by immersing the super absorbent resin in a rubidium nitrate solution to fully absorb the pre-absorbed rubidium nitrate solution; or, the first super absorbent resin is obtained by immersing the super absorbent resin in a cesium nitrate solution to fully absorb the cesium nitrate solution. Wherein, since rubidium nitrate or cesium nitrate has good water solubility in a strong alkaline solution and does not react with the super absorbent resin, when the first super absorbent resin releases water, the rubidium or cesium ions can move synchronously with the water; in addition, concrete generally does not contain rubidium or cesium, by immersing the super absorbent resin in a rubidium nitrate or cesium nitrate solution to fully absorb the rubidium nitrate or cesium nitrate solution, and then placing the first super absorbent resin that absorbs the rubidium nitrate or cesium nitrate solution on the surface of concrete or cement paste, it is convenient to observe the behavior of water released by the first super absorbent resin by detecting the distribution of cesium or rubidium elements through XRF.

[0041] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete of the present invention, in step (2), after dipping a needle in the first super absorbent resin, the first super absorbent resin is transferred to the surface of the sample to be tested. The first super absorbent resin, obtained by dipping the needle in a sufficient amount of rubidium nitrate solution or cesium nitrate solution, is transferred to the surface of the sample to be tested, thereby facilitating the first super absorbent resin to be placed on the surface for observation.

[0042] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete of the present invention, in step (3), a super depth of field microscope is used to obtain an image sequence of the sample, and the indicators detected by the super depth of field microscope include the morphological changes of the first super absorbent resin.

[0043] Preferably, the morphological changes of the first super absorbent resin include expansion, contraction and details of the contact interface between the first super absorbent resin and the concrete material.

[0044] More preferably, the indicators detected by the ultra-depth microscope include the height and depth of the first super absorbent resin.

[0045] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete of the present invention, XRF is used to detect element changes in the sample to be tested and / or the first super absorbent resin; the indicators detected by XRF include the distribution of rubidium or cesium elements.

[0046] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of the super absorbent resin in concrete of the present invention, the distribution of the rubidium element or the cesium element is detected by line scanning and / or surface scanning.

[0047] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete of the present invention, the raw materials of the cement paste in step (1) include cement and mixing water; the raw materials of the concrete include cementitious materials, mixing water and sand and gravel aggregates; during the mixing process of the cement paste or concrete, the step of adding a second super absorbent resin is further included; the second super absorbent resin is an unabsorbed super absorbent resin or a pre-absorbed super absorbent resin; the pre-absorbed super absorbent resin is obtained by allowing the super absorbent resin to fully absorb the mixing water of the cement paste or concrete.

[0048] Preferably, the first super absorbent resin is dry-mixed or pre-absorbed into cement paste or concrete for use as an internal curing agent; specifically, the first super absorbent resin (unabsorbed super absorbent resin or pre-absorbed super absorbent resin) is first mixed evenly with a cementitious material (e.g., cement), and then mixed and stirred evenly with sand and gravel aggregate and mixing water to obtain concrete; alternatively, the first super absorbent resin (unabsorbed super absorbent resin or pre-absorbed super absorbent resin) is mixed evenly with a cementitious material (e.g., cement), and then mixed evenly with mixing water to obtain cement paste.

[0049] More preferably, the components of cement paste or concrete further include admixtures (eg, water reducing agent, etc.).

[0050] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete of the present invention, step (2) further includes providing a protective layer after placing the first super absorbent resin on the surface of the sample to be tested. The protective layer is provided primarily to prevent the first super absorbent resin from directly contacting the air and evaporating and releasing water into the air; further, the provision of the protective layer helps to better restore the water release of the curing agent (SAP) in the concrete.

[0051] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of a super absorbent resin in concrete of the present invention, the protective layer includes a first protective layer and a second protective layer; the first protective layer is formed by cement paste (the mass ratio of cement to water in the cement paste is the same as that in the cement paste in step (1); or, the mass ratio of cementitious material to water in the concrete in step (1) is the same); and the second protective layer is a plastic wrap.

[0052] Preferably, the thickness of the first protective layer is 1-5 mm (for example, 1 mm, 2 mm, 3 mm, 4 mm or 5 mm); if the first protective layer is too thick, SAP deformation is difficult to observe; if the first protective layer is too thin, it is impossible to prevent water in the SAP from evaporating into the air.

[0053] The following detailed description of the present invention's method for dynamically tracking and characterizing the water absorption and release process of a superabsorbent resin in concrete is provided through specific examples. All reagents used in the following experiments, unless otherwise specified, are commercially available; for example, commercial SAP (analytical grade) was purchased from Yixing Credible Chemical Co., Ltd. The laboratory-made SAP was synthesized by copolymerization of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid using the reverse suspension method. The specific steps are as follows: (1) Preparation of the aqueous phase: 10 g of acrylic acid was slowly added dropwise to a sodium hydroxide solution (4.3 g of sodium hydroxide solid dissolved in 20 g of deionized water) using a rubber-tipped dropper to perform a partial neutralization reaction. After the titration was completed, the beaker was sealed with plastic wrap and stirred continuously. After the beaker cooled, AMPS (2-acrylamide-2-methylpropanesulfonic acid), APS (ammonium persulfate), and MBA (methylenebisacrylamide) were added in sequence and stirred thoroughly to dissolve. (2) Preparation of the oil phase: 0.6 g of Span-80 and 100 mL of cyclohexane were added to a three-necked flask equipped with a spherical condenser, a nitrogen gas guide tube, and a mechanical stirring rod (nitrogen was passed through during the experiment to remove oxygen). This was the oil phase. Adjust the mechanical stirring speed to 200 rpm, the water bath temperature to 60°C, use a flow meter to control the nitrogen flow rate to 20 mL / min, and stir for 30 minutes; (3) Synthesis of super absorbent resin: Slowly drip the prepared aqueous phase into the three-necked flask using a constant pressure funnel. After the aqueous phase is completely dripped into the three-necked flask, adjust the water bath to the reaction temperature and react for 2.5 hours. After the reaction is completed, stop heating, remove the three-necked flask from the water bath, and continue stirring until the liquid in the three-necked flask returns to room temperature. Stop stirring, filter the sample in the flask, rinse it with anhydrous ethanol three times to remove the unreacted monomers on the polymer, and use scissors to cut the polymer into small pieces. Then put the sample into an oven, set the oven temperature to 80°C, and bake for 10 hours. Then grind the dried sample into powder with a mortar, rinse it with anhydrous ethanol three times, dry it again, and seal it for use.

[0054] Example 1

[0055] In a preferred embodiment of the method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete of the present invention, the method comprises the following steps:

[0056] (1) 0.2 g of cesium nitrate was dissolved in 3.6 g of deionized water. After the cesium nitrate was fully dissolved in the deionized water to obtain a cesium nitrate solution, commercial SAP or laboratory-made SAP (super absorbent resin) was added to the cesium nitrate solution, and the mixture was allowed to stand for 1 hour to allow the SAP to fully absorb water, thereby obtaining a saturated SAP (first super absorbent resin) that had pre-absorbed the cesium nitrate solution;

[0057] (2) 2 g of water reducer was added to 30 g of water and fully dissolved, and then mixed with 100 g of cement and a second super absorbent resin (the amount of SAP was 0.1% of the mass of cement) that had been fully absorbed with water. After stirring until a fluid cement slurry was formed, the cement slurry was added to the threaded tube to form a sample layer (the thickness of the sample layer was 2 cm). A small amount of saturated SAP was dipped into a needle and added to the center of the threaded tube. A protective layer was set: cement slurry was first added (the mass ratio of cement to water was 100:30), and the cement slurry was evenly spread to form a first protective layer (the thickness of the first protective layer was 3 mm). Then, a layer of plastic wrap was attached as a second protective layer.

[0058] (3) Then, a depth up synthesis is performed under a super depth of field 200x lens to obtain the height of SAP; then, XRF is performed to test the distribution of cesium elements.

[0059] Among them, the test results of the ultra-depth of field microscope are as follows: Figure 2-3 As shown:

[0060] I. Figure 2 This is a schematic diagram of the test results of the super depth of field microscope, which indirectly judges the water release of the first super absorbent resin in the cement paste by the changes in the height and diameter of the first super absorbent resin.

[0061] II. Figure 3 Figures a, b, and c show the water release of the first superabsorbent resin obtained by pre-absorbing cesium nitrate solution with commercial SAP in cement paste, while figures d, e, and f show the water release of the first superabsorbent resin obtained by pre-absorbing nitric acid solution with laboratory-made SAP in cement paste.

[0062] Figure II-1a shows super depth-of-field photographs (obtained by direct imaging using the super depth-of-field up function) of the first super absorbent resin obtained by pre-absorbing cesium nitrate solution with commercial SAP, observed after being placed on the surface of the sample layer for different times; Figure d shows super depth-of-field photographs (obtained by direct imaging using the super depth-of-field up function) of the first super absorbent resin obtained by pre-absorbing cesium nitrate solution with laboratory-made SAP, observed after being placed on the surface of the sample layer for different times.

[0063] Figures II-2b and e show the test results obtained by using the Super Depth of Field Microscope's Depth Up function to generate composite images and then perform profile measurements. The changes in the SAP's appearance (determined by the image area) in Figures b and e can be used to determine the amount of water released by the SAP.

[0064] II-3 Test the salt tolerance of laboratory-made SAP and commercial SAP:

[0065] The simulated pore solution test procedure is as follows: SAP, pre-absorbed with 50 times its own volume of deionized water, is placed in a wet tea bag, with an initial mass of W1 g weighed. The bag is then immersed in the simulated pore solution, and the total mass of the tea bag, W2 g, is weighed at intervals of t2 min (t2 = 2, 4, 6, 8, 10, 15, 20, 30, 60). The water retention rate, Q, of the SAP in the simulated pore solution is calculated using the formula:

[0066] Figures c and f are water release diagrams of commercial SAP that has fully absorbed water in deionized water and laboratory-made SAP in the simulated pore solution configured in the laboratory (a mixed solution of NaOH, KOH and Ca(OH)2; obtained by adding a mixed solution of NaOH and KOH to a saturated calcium hydroxide solution and adjusting the pH to 13.5; wherein the mass ratio of NaOH to KOH in the mixed solution of NaOH and KOH is 1:3). They are mainly used to compare the performance of laboratory-made SAP with the salt resistance of commercial SAP (salt resistance is judged based on the difference in the amount of liquid absorbed in the simulated pore solution).

[0067] Depend on Figure 3 a and Figure 3 As can be seen in Figure b, when the sample was prepared (t=0h), there was a bulge on the surface of the cement paste observed by ultra-depth-of-field microscopy, indicating that the commercial SAP that had pre-absorbed the cesium nitrate solution was in a swollen state. After 1h of cement hydration (t=1h), the height of the commercial SAP decreased by 20μm, indicating that the commercial SAP had begun to release water. This is because the pre-absorbed commercial SAP enters a multi-ion environment and releases water due to osmotic pressure, such as Figure 3 As shown in Figure c, the pre-absorbed SAP rapidly releases water upon entering the multi-ion environment. As hydration progresses, the increasing ion concentration in the pore solution causes the commercial SAP to rapidly release water. At 2 hours, the cement paste surface begins to dent, forming pores. By 8 hours, the residual pore depth remains unchanged after the SAP releases water, indicating that the commercial SAP has essentially released all its water.

[0068] Unlike commercial SAP, at the initial stage of hydration (t=2h), the height of the homemade SAP not only did not decrease but also increased by about 32μm. Then it decreased slightly at 14d and remained basically unchanged for 28d. This shows that the homemade SAP not only did not release water but also absorbed water again at the initial stage of hydration in cement paste. This may be due to the resistance of homemade SAP to multiple ions (Na + , K + 、Al 3+ , Ca 2+ OH - ) is increased, the saturated liquid absorption rate is greater than the pre-absorption amount, and the phenomenon of competing with the cement paste for water absorption occurs, such as Figure 3 f. After hydration for 14 days, as the relative humidity inside the cement paste decreases, the water inside the homemade SAP is slowly released through the capillaries.

[0069] Among them, the XRF test results are as follows Figure 4-9 As shown:

[0070] Figure 4 This is a diagram of the state of laboratory-made SAP pre-absorbed with cesium nitrate solution in cement paste for 7 days (during the mixing process of the cement paste, SAP that has fully absorbed water is added, and the amount of SAP is 0.1% of the cement mass); Figure 5 This is a diagram of the state of commercial SAP that has pre-absorbed cesium nitrate solution in cement paste for 7 days (SAP that has fully absorbed water is added during the mixing process of the cement paste, and the amount of SAP is 0.1% of the cement mass).

[0071] Figure 4-5 The test results can be used to show the impact area of ​​the self-made SAP on the cement paste at different times of water release. The test results can be used to determine the speed of SAP water release and the impact area of ​​water release. Figure 4 It can be seen that after 7 days of pre-absorbing the cesium nitrate solution, the cesium element is mainly concentrated inside the SAP, indicating that the SAP has a good water retention effect. Because the humidity inside the cement paste is high, a large amount of water release has not yet occurred. The slow water release of the homemade SAP pre-absorbing the cesium nitrate solution can optimize the internal pore structure of the concrete. The small amount of water released can promote secondary hydration, improve shrinkage properties, and increase the compressive strength of the cement paste, resulting in a good internal curing effect.

[0072] Figure 5 This is the state diagram of commercial SAP that has pre-absorbed cesium nitrate solution and is added to cement paste 7 days later; Figure 5 As can be seen from the data, cesium was detected within the test range at 14 days, indicating that the commercial SAP had released water completely and across the entire test range. Rapid water release from the commercial SAP resulted in the formation of numerous pores within the structure, resulting in decreased compressive strength, poor shrinkage control, and poor internal curing.

[0073] Figure 8 This is the XRF line scan of the laboratory-made SAP that pre-absorbed cesium nitrate solution in cement paste after 28 days (during the mixing process of the cement paste, the pre-absorbed SAP was added, and the amount of SAP was 0.1% of the cement mass); Figure 9 This is the XRF line scan of commercial SAP that has pre-absorbed cesium nitrate solution in cement paste for 28 days (during the mixing process of cement paste, SAP that has been fully absorbed is added, and the amount of SAP is 0.1% of the cement mass). Figure 8 It can be seen that the line scanning results of the 28d self-made SAP show that the cesium element is located inside and around the self-made SAP. The self-made SAP releases a small amount of water into the concrete. The water release range is within an area with a radius of about 150μm with the center of the SAP as the center. Figure 9 It can be seen that the cesium element in the 28d commercial SAP is relatively evenly distributed in the scanning area, indicating that the moisture has been completely released and can migrate to an area with a radius of about 300μm centered on the center of the SAP.

[0074] Depend on Figure 3-5 and Figure 8-9 It can be seen that the method of the present invention can observe and compare the water release (or water retention) rate and water release range of SAP in cement paste, as well as the morphological changes and salt resistance of SAP, and can be used to predict the effect of SAP internal curing.

[0075] Figure 6 The graph shows the compressive strength and flexural strength test results of cement paste containing commercial SAP and laboratory-made SAP (the water-cement ratio is 0.3; during the mixing process of the cement paste, SAP is added to fully absorb the mixing water, and the amount of SAP is 0.1% of the cement mass) at different ages.

[0076] Depend on Figure 6 The left figure shows that after adding SAP, the compressive strength of the cement paste also increased to varying degrees, but this increase was not obvious in the early stage. At 28 days, the compressive strength of the paste with the homemade SAP in the laboratory was the highest, increasing by 7.6% compared to the blank group and 5% compared to the commercial SAP group. Figure 6 As shown in the right figure, the flexural strength of the blank group at 3, 7, and 28 days was 9 MPa, 9.5 MPa, and 10.6 MPa, respectively. The addition of SAP improved the flexural strength of all cement pastes compared to the control group, but the magnitude of this improvement gradually decreased over time. Furthermore, at 28 days, the flexural strength of the cement pastes incorporating commercial SAP and the lab-made SAP increased by 1.75% and 7%, respectively, compared to the blank group.

[0077] The compressive strength of the laboratory-made SAP was much higher than that of the commercial SAP group and the blank group at different curing times (3d, 7d, and 28d). This may be because the laboratory-made SAP slowly released water, which promoted the hydration of the cement slurry and filled the pores created by the SAP after the water was released.

[0078] Figure 7 The figure shows the test results of the effects of commercially available SAP and laboratory-made SAP on the shrinkage value of cement paste (water-cement ratio 0.3; during the mixing process of the cement paste, pre-absorbed SAP is added, and the amount of SAP is 0.1% of the cement mass) at different ages.

[0079] Depend on Figure 7 As can be seen, the shrinkage of all cement pastes continued to increase with age, with a slower increase after 28 days. Furthermore, throughout the curing period, the shrinkage of the cement pastes in the samples with SAP (both laboratory-prepared and commercial SAP) was less than that of the blank. Compared with the blank at 56 days (4582 με), the shrinkage strains of the laboratory-prepared and commercial SAP groups decreased by 6% (4315 με) and 12% (4012 με), respectively. These results indicate that the introduction of SAP can mitigate concrete shrinkage. The shrinkage of cement paste is primarily influenced by internal moisture content, pore structure, and capillary effects. In this experiment, all specimens had the same water-cement ratio (0.3), and the water pre-absorbed by the SAP served as mixing water for the cement paste. When pre-absorbed SAP is added to the cement paste, it releases or reabsorbs some water depending on its salt tolerance, thereby varying the content and distribution of free water in the cement paste. The salt resistance of the laboratory-made SAP is improved compared to the commercial SAP, which allows the pre-absorbed water to be slowly released into the capillaries, compensating for the decrease in relative humidity in the cement slurry and reducing the negative pressure on the concave liquid surface of the capillary pores, thereby effectively counteracting the shrinkage of the cement.

[0080] Figure 6-7 The experimental results and Figure 3-5 and Figure 8-9 The experimental phenomena observed and based on Figure 3-5 and Figure 8-9 The inferred internal curing effect is consistent with that of the conventional method; thus, the effectiveness of the method of the present invention can be further demonstrated.

[0081] Figure 10 and 11 These are the XRF surface scan and line scan images of a commercial SAP pre-absorbed with cesium nitrate solution placed on a cement paste surface for 1 hour, with a protective layer provided on its surface. (During the mixing process of the cement paste, the commercial SAP, which had fully absorbed the mixing water, was added at a concentration of 0.1% of the cement mass.)

[0082] Figure 12-13 The following are XRF surface scans and line scans of commercial SAP pre-absorbed with cesium nitrate solution placed on the surface of cement paste for 1 hour, without a protective layer (commercial SAP that has fully absorbed mixing water was added during the mixing process of the cement paste, and the amount of commercial SAP used was 0.1% of the cement mass);

[0083] Comparing the XRF surface scan and line scan of the same sample with and without protective layer, we can see that the XRF surface scan without protective layer ( Figure 12 ) and line scans ( Figure 13 ) releases water to a significantly greater extent into the surrounding environment. This is primarily because, when the protective layer is not applied, the water in the SAP readily evaporates into the air, or the influence of air humidity causes water redistribution on the surface, affecting the detection of the SAP release effect within the concrete. By providing a protective layer, the present invention effectively reduces or avoids errors caused by the influence of air on the first superabsorbent resin on the surface of the sample being tested, thereby helping to ensure the accuracy of the characterization results of the present method for dynamically tracking the water absorption and release process of superabsorbent resin in concrete.

[0084] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete, characterized in that: The steps include: (1) Place cement paste or concrete in a sample container as the sample to be tested; (2) placing a first super absorbent resin on the surface of the sample to be tested; (3) Using an ultra-depth-of-field microscope and / or XRF to monitor the first super absorbent resin.

2. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 1, wherein: In step (2), the first super absorbent resin is obtained by soaking the super absorbent resin in a cesium nitrate solution to fully absorb the cesium nitrate solution; or, The first super absorbent resin is obtained by soaking the super absorbent resin in a rubidium nitrate solution and fully absorbing the rubidium nitrate solution.

3. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 1, wherein: In step (2), the first super absorbent resin is dipped into the first super absorbent resin by a needle, and then the first super absorbent resin is transferred to the surface of the sample to be tested.

4. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 1, wherein: In step (3), the super depth of field microscope is used to obtain an image sequence of the sample, and the indicators detected by the super depth of field microscope include the morphological changes of the first super absorbent resin.

5. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 2, wherein: XRF is used to detect element changes in the sample to be tested and / or the first super absorbent resin; The indicators detected by XRF include the distribution of cesium or rubidium elements.

6. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 5, characterized in that: The distribution of cesium or rubidium elements is detected by line scanning and / or area scanning.

7. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 1, wherein: The raw materials of the cement paste include cement and mixing water; the raw materials of the concrete include cementitious materials, mixing water and sand and gravel aggregates; During the mixing process of the cement paste or concrete, the method further comprises adding a second super absorbent resin; The second super absorbent resin is an unabsorbed super absorbent resin or a pre-absorbed super absorbent resin; The pre-absorbent super absorbent resin is obtained by allowing the super absorbent resin to fully absorb the mixing water of cement paste or concrete.

8. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to any one of claims 1 to 7, characterized in that: In step (2), after placing the first super absorbent resin on the surface of the sample to be tested, the method further includes providing a protective layer.

9. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 8, wherein: The protective layer includes a first protective layer and a second protective layer; The first protective layer is formed by the cement paste; The second protective layer is a fresh-keeping film.

10. The method for dynamically tracking and characterizing the water absorption and release process of super absorbent resin in concrete according to claim 9, characterized in that: The thickness of the first protective layer is 1-5 mm; The thickness of the concrete sample is 1-3 cm.

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