A method for determining the additional water quantity of superabsorbent polymers for internal curing of cementitious materials

Abstract

The application relates to a method for determining the additional water amount of super absorbent polymer for internal curing of cement-based materials, belonging to the technical field of concrete preparation. The method comprises the following steps: step one, measuring the final setting time of cement-based materials after super absorbent polymer is added; obtaining a curve of transverse relaxation signal changing with transverse relaxation time T2; calculating the peak area of transverse relaxation time between 10 ms and 10000 ms; testing the transverse relaxation signal of a known mass of copper sulfate solution; calculating the mass of internal curing water in the super absorbent polymer; obtaining the equilibrium water absorption amount of the internal curing water in the super absorbent polymer; and calculating the additional water amount of the super absorbent polymer for internal curing of cement-based materials. The application can accurately obtain the additional water amount of the super absorbent polymer as an internal curing material in low water-cement ratio cement-based materials based on nuclear magnetic resonance technology.

Description

Technical Field

[0001] This invention belongs to the field of concrete preparation technology, specifically relating to a method for determining the additional water content of a superabsorbent polymer used for internal curing of cement-based materials. Background Technology

[0002] In recent years, the increasing complexity of building structures and the gradual deterioration of environmental conditions have driven the development of high-performance, high-strength concrete. A key characteristic of high-performance concrete is its low water-cement ratio, which enhances the concrete's density, thereby improving its mechanical properties and durability. However, cementitious materials with low water-cement ratios often exhibit significant autogenous shrinkage during hydration, which may adversely affect their overall durability.

[0003] A key approach to addressing these issues is to incorporate internal curing agents and additional water into the cementitious material. Internal curing retains the added water within the material. During the curing process, this additional water is released into the matrix to compensate for the water lost during hydration, effectively mitigating autogenous shrinkage. Superabsorbent polymers (SAPs) have gained widespread acceptance as effective internal curing agents. However, the application of SAPs still faces some challenges. Excessive addition of additional water can lead to a significant decrease in strength and durability, while insufficient addition may result in a negligible reduction in autogenous shrinkage. Therefore, determining the appropriate amount of additional water is crucial for achieving a balance between maintaining mechanical properties and mitigating autogenous shrinkage in low water-cement ratio cementitious materials. Summary of the Invention

[0004] To address the problems existing in the application of superabsorbent polymers as internal curing materials, a method for determining the additional water content of superabsorbent polymers for internal curing of cement-based materials is provided. The additional water content determined by this method can ensure that the effect of reducing self-shrinkage is fully utilized, and can also effectively reduce the adverse effects of excessive additional water content on concrete strength.

[0005] The method includes: Step 1, preparing a sample of cement-based material for internal curing, wherein the water-cement ratio of the sample is 0.15-0.45;

[0006] Step 2: Measure the final setting time of the cement-based material after adding the superabsorbent polymer;

[0007] Step 3: Place the cement-based material from Step 1 into a low-field nuclear magnetic resonance spectrometer and scan it using CPMG sequence radio frequency pulses. The results are obtained by inversion, showing the curve of the transverse relaxation signal as a function of the transverse relaxation time T2.

[0008] Step 4: Using the change curve obtained in Step 2, identify the peak with a transverse relaxation time between 10ms and 10000ms and calculate the peak area. This peak area represents the signal amount of internal maintenance water present in the superabsorbent polymer. The calculation formula is as follows:

[0009] S=∑S i (1)

[0010] Where S is the total area (au) of the peak between 10ms and 10000ms, ΣS i It is the peak area (au) corresponding to the transverse relaxation time i;

[0011] Step 5: Test the transverse relaxation signal of a copper sulfate solution of known mass. The total peak area is the signal quantity of an equal volume of water. Calculate the total peak area of ​​copper sulfate solutions of different masses and fit the mass-signal quantity to obtain the following formula:

[0012]

[0013] Where M is the mass of water (g), S is the signal quantity of the low-field NMR measurement (au), and 1 / a is the slope obtained from the fitting.

[0014] Step 6: Substitute the signal quantity of the internal maintenance water in the superabsorbent polymer obtained in Step 4 into Formula 2 in Step 5 to calculate the mass of the internal maintenance water in the superabsorbent polymer.

[0015] Step 7: Compare the mass of the internal curing water in the superabsorbent polymer with the mass of the dried superabsorbent polymer to obtain the equilibrium water absorption of the superabsorbent polymer in the cement-based material, as shown in the following formula:

[0016]

[0017] Where EB is the equilibrium water absorption (g / g), M SAP It is the mass (g) of the internal maintenance water in the superabsorbent polymer, m SAP It is the mass (g) of the dried superabsorbent polymer;

[0018] Step 8: Calculate the additional water content of the superabsorbent polymer used for curing within the cement-based material by multiplying the equilibrium water absorption rate by the superabsorbent polymer dosage. The formula is as follows:

[0019]

[0020] Where EW is the ratio of the additional water volume to the mass of cement in the cement-based material; It is the ratio of the mass of superabsorbent polymer to the mass of cement in the cement-based material.

[0021] Furthermore, in step two, when testing the equilibrium water absorption of the superabsorbent polymer, the cement mass of the superabsorbent polymer is 0.01%-0.1%.

[0022] Furthermore, in step two, the echo time of the low-field nuclear magnetic resonance spectrometer is selected as 5000-10000 seconds, the number of scans is selected as 64-256, and the waiting time is 1-4 seconds.

[0023] Furthermore, the mass concentration of the copper sulfate solution in step three is 1%.

[0024] The beneficial effect of this invention lies in its ability to accurately obtain the optimal amount of additional water for different types of superabsorbent polymers in low water-cement ratio cementitious materials. This additional water ensures the full realization of the internal curing effect of the superabsorbent polymer while avoiding additional strength loss caused by the extra water. According to this method, simply adjusting the addition of additional water in the mix proportion can greatly improve the effect of superabsorbent polymers in inhibiting self-shrinkage while taking into account the strength of cement-based materials. This can provide a reference for the application of superabsorbent polymers in cement-based materials. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the transverse relaxation signal of a 10g copper sulfate solution obtained by low-field nuclear magnetic resonance and the transverse relaxation signal of the target cement paste containing superabsorbent polymer, as described in a specific implementation.

[0026] Figure 2 This is a schematic diagram showing the comparison of the compressive strength of the example group and each comparative group at 28 days in a specific implementation method.

[0027] Figure 3 This is a schematic diagram comparing the self-shrinkage values ​​of the example group and each comparative group in a specific implementation method.

[0028] Figure 4 This is a schematic diagram comparing the compressive strength of the example group and each comparative group in a specific implementation method. Detailed Implementation

[0029] Specific implementation method one: Step one, using cement paste as a carrier, first mix 0.5% of superabsorbent polymer by weight of cement into cement, and prepare cement paste containing superabsorbent polymer with a water-cement ratio of 0.3. After preparation, test the final setting time of the cement paste according to GB / T1346-2011.

[0030] Step 2: After the final setting of the cement paste was measured, 26g of the cement paste was placed in a low-field NMR spectrometer. The main frequency of the low-field NMR spectrometer was 2MHz, the magnetic field strength was 0.047T, and the echo count was set to 10000, the number of scans to 64, the interval time to 4 seconds, and the repetition time to 60 microseconds. The transverse relaxation signal of the cement paste was acquired using a CPMG pulse sequence. Figure 1 As shown;

[0031] Step 3: Place copper sulfate solutions with masses of 0.5g, 1g, 2g, 3g, 4g, 5g, 6g, 7g, 8g, 9g, 10g, and 20g (1% by mass) into a low-field NMR spectrometer. Use the same parameters and CPMG pulse sequence to acquire the transverse relaxation signals of these solutions. Based on the total peak area of ​​the transverse relaxation signals obtained from different masses of copper sulfate solutions, derive the mass-signal quantity formula. Figure 2 Linear fitting yielded a = 0.8321.

[0032]

[0033] Step 4: Calculate the peak area of ​​the transverse relaxation time T2 in the cement paste transverse relaxation signal between 10ms and 10000ms, and substitute it into the mass-signal formula obtained in Step 3 to calculate the mass of internal curing water in the superabsorbent polymer as 0.54g. Figure 1 The total area of ​​the peak between 10ms and 10000ms is S = 0.3245au, therefore

[0034]

[0035] Step 5: Compare the mass of the internal maintenance water in the superabsorbent polymer with the mass of the dried superabsorbent polymer to obtain the equilibrium water absorption capacity of the internal maintenance water in the superabsorbent polymer as 27 g / g. The calculation formula is as follows:

[0036]

[0037] Step 7: The product of the equilibrium water absorption and the mass of the superabsorbent polymer added yields the additional water content of the superabsorbent polymer cured within the cement-based material (in this study, the superabsorbent polymer dosage was 0.1% of the cement mass, but the calculation method in Step 7 is applicable to any dosage of superabsorbent polymer). The calculation formula is as follows:

[0038] EW = 0.001·27 = 0.027

[0039] Experimental comparison of technical effects: Five groups of cement paste containing superabsorbent polymer with a basic water-cement ratio of 0.3 were prepared.

[0040] Group 1: A control group with a basic water-cement ratio of 0.3, a superabsorbent polymer content of 0.1% of the cement mass, and no additional water.

[0041] Group 2: A lower additional water control group with a basic water-cement ratio of 0.3, a superabsorbent polymer content of 0.1% of the cement mass, and an additional water content of 0.010.

[0042] Group 3: The basic water-cement ratio is 0.3, the superabsorbent polymer content is 0.1% of the cement mass, and the additional water content is 0.027% of the additional water content determined by this method.

[0043] Group 4: A control group with an excessively high additional water content, consisting of a basic water-cement ratio of 0.3, a superabsorbent polymer content of 0.1% of the cement mass, and an additional water content of 0.054.

[0044] Group 5: The baseline group with a basic water-cement ratio of 0.3 and no superabsorbent polymers.

[0045] To observe the effect of different amounts of additional water on the compressive strength and autogenous shrinkage of cement paste with the same water-cement ratio. Specific experimental comparison results are presented. Figure 3 As shown. Figure 3 As shown, the autogenous shrinkage of the baseline group was 1283 με. The autogenous shrinkage of the cement paste decreased to varying degrees after the addition of the superabsorbent polymer. The autogenous shrinkage of the control group without additional water was 1236 με, a decrease of 3.7% compared to the baseline group. The autogenous shrinkage of the control group with lower additional water was 849 με, a decrease of 33.8% compared to the baseline group. The autogenous shrinkage of the example group was 584 με, a decrease of 54.5% compared to the baseline group. The autogenous shrinkage of the control group with excessively high additional water was 520 με, a decrease of 59.5% compared to the baseline group. The addition of additional water can significantly reduce the autogenous shrinkage of the cement paste, but once the additional water exceeds the equilibrium water absorption calculated by this method, the autogenous shrinkage does not decrease significantly further.

[0046] like Figure 4 As shown, the compressive strength of the groups with no additional water, low additional water, and the example groups was basically the same as that of the baseline group with the same water-cement ratio, all of which could well guarantee the compressive strength of the material. However, the compressive strength of the control group with excessively high additional water content decreased significantly, by 16.5%.

[0047] The example group significantly reduced autogenous shrinkage while ensuring that the compressive strength of the cement paste was not significantly damaged by controlling the amount of additional water.

Claims

1. A method for determining the additional water content of a superabsorbent polymer used for internal curing of cement-based materials, characterized in that: The method includes: Step 1, preparing a sample of cement-based material for internal curing, wherein the water-cement ratio of the sample is 0.15 - 0.45; Step 2: Measure the final setting time of the cement-based material after adding the superabsorbent polymer; Step 3: Place the cement-based material from Step 1 into a low-field nuclear magnetic resonance spectrometer and scan it using CPMG sequence radio frequency pulses. The results are obtained by inversion, showing the curve of the transverse relaxation signal as a function of the transverse relaxation time T2. Step 4: Using the change curve obtained in Step 3, identify the peak with a transverse relaxation time between 10ms and 10000ms and calculate the peak area. This peak area represents the signal amount of internal maintenance water present in the superabsorbent polymer. The calculation formula is as follows: (1)； Where S is the total area (au) of the peak between 10ms and 10000ms. It is the peak area (au) corresponding to the transverse relaxation time i; Step 5: Test the transverse relaxation signal of a copper sulfate solution of known mass. The total peak area is the signal quantity of an equal volume of water. Calculate the total peak area of ​​copper sulfate solutions of different masses and fit the mass-signal quantity to obtain the following formula: (2)； Where M is the mass of water (g), S is the signal quantity of the low-field NMR measurement (au), and 1 / a is the slope obtained from the fitting. Step 6: Substitute the signal quantity of the internal maintenance water in the superabsorbent polymer obtained in Step 4 into Formula 2 in Step 5 to calculate the mass of the internal maintenance water in the superabsorbent polymer. Step 7: Compare the mass of the internal curing water in the superabsorbent polymer with the mass of the dried superabsorbent polymer to obtain the equilibrium water absorption of the superabsorbent polymer in the cement-based material, as shown in the following formula: (3)； Where EB is the equilibrium water absorption (g / g), M SAP It is the mass (g) of the internal maintenance water in the superabsorbent polymer, m SAP It is the mass (g) of the dried superabsorbent polymer; Step 8: Calculate the additional water content of the superabsorbent polymer used for curing within the cement-based material by multiplying the equilibrium water absorption rate by the superabsorbent polymer dosage. The formula is as follows: （4）； Where EW is the ratio of the additional water volume to the mass of cement in the cement-based material; φ SAP It is the ratio of the mass of superabsorbent polymer to the mass of cement in the cement-based material.

2. The method according to claim 1, characterized in that: In step two, when testing the equilibrium water absorption of the superabsorbent polymer, the cement mass of the superabsorbent polymer is 0.01%-0.1%.

3. The method according to claim 1 or 2, characterized in that: In step two, the echo time of the low-field nuclear magnetic resonance spectrometer is selected as 5000-10000 microseconds, the number of scans is selected as 64-256, and the waiting time is 1-4 seconds.

4. The method according to claim 3, characterized in that: The mass concentration of the copper sulfate solution in step three is 1%.

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