Rapid test method for sulfate corrosion resistance of magnesium phosphate cement-based material

Abstract

The invention discloses a method for rapidly testing the sulfate corrosion resistance of a magnesium phosphate cement-based material, which comprises the following steps: placing an MPC slurry test piece in a one-dimensional soaking environment of a sulfate solution, and accelerating the diffusion of sulfate ions in the MPC test piece through pulse voltage. Drawing a distribution diagram of the content of the sulfate radicals in the MPC test piece along with the distance from the end surface of the test piece, and fitting to obtain a polynomial mathematical model associated with the two, thereby calculating the surface sulfate concentration and the calculated erosion depth h00 of the sulfate radicals. The sulfate corrosion resistance of the MPC slurry can be quickly judged by calculating the erosion depth h00; and establishing a correlation mathematical model of the corrosion period of the MPC test piece subjected to pulse corrosion and full immersion corrosion when the electric pulse corrosion period is equal to h00, and calculating the corrosion period of the MPC test piece subjected to full immersion corrosion according to the electric pulse corrosion period. According to the method, the sulfate corrosion resistance of the magnesium phosphate cement-based material can be quickly and accurately judged, and the erosion transmission condition of sulfate ions can be intuitively reflected.

Description

Technical Field

[0001] The present invention relates to a method for testing the salt corrosion resistance of cement-based materials, and particularly to a rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials. Background Art

[0002] The hydration products of magnesium phosphate cement (MPC) paste are bonded by strong ionic bonds and have a dense structure similar to ceramics, which can resist the infiltration of corrosive ions. Its main hydration product struvite (or K-struvite) is stable within a pH range of 7-11, and its salt corrosion resistance is significantly better than that of Portland cement. It has been developed and applied in the fields of concrete structure repair and anti-corrosion coatings.

[0003] At present, accelerated test methods are mostly used to evaluate the sulfate erosion resistance of concrete. Due to the small size of the specimens, differences in the production process, erosion environment conditions, test conditions, etc. may all have a significant impact on the test results, resulting in large discreteness of the parallel test results. There are methods that use the combined action of increasing the temperature and concentration of the erosion solution and wet-dry cycling to accelerate the sulfate erosion of concrete, but this will also increase the solubility of various hydration products and cause changes in the composition and structure of the hydration products, thereby changing the sulfate erosion mechanism of concrete and affecting the determination of the sulfate erosion resistance of concrete.

[0004] Currently, there have been studies and evaluations on the sulfate erosion resistance behavior of MPC paste through full immersion in sulfate, sulfate wet-dry cycling, sulfate freeze-thaw, etc. However, these test methods have defects such as long test cycles or large differences from the natural corrosion environment. In these methods, the degree of sulfate erosion is determined by the damage degree (strength loss, deformation, mass loss) of the eroded MPC paste. Not only is the accuracy of the evaluation result poor, but more importantly, it cannot reflect the transport situation of sulfate ions inside the hardened body. For example, Chinese Patent CN101435816A places concrete specimens in a sulfate environment and quickly judges the sulfate corrosion resistance of concrete according to the diffusion and reaction of sulfate ions in the concrete specimens under the action of pulsed voltage. The sulfate corrosion resistance of concrete is judged by the mass change and strength loss value of the concrete. Although this method can obtain the corrosion status of concrete in a sulfate environment in a short time by applying an electric pulse, it still needs to measure the mass change and strength loss value of the concrete to indirectly judge the corrosion resistance of the concrete. Since there are many measured indicators, errors will accumulate during the measurement and calculation process, resulting in relatively low accuracy of the final evaluation result. In addition, the mass change and strength loss value of the concrete cannot intuitively reflect the erosion and transport situation of sulfate ions. Summary of the Invention

[0005] Objective of the Invention: The objective of the present invention is to provide a rapid test method for sulfate corrosion resistance of magnesium phosphate cement-based materials, so as to solve the problems of how to rapidly and accurately evaluate the sulfate corrosion resistance of magnesium phosphate cement-based materials and intuitively reflect the erosion and transmission of sulfate ions.

[0006] Technical Solution: A rapid test method for sulfate corrosion resistance of magnesium phosphate cement-based materials according to the present invention includes the following steps:

[0007] (1) Immerse both ends of the magnesium phosphate cement paste specimen into the sulfate aqueous solution respectively, insert electrodes into the sulfate aqueous solution, and apply electric pulses between the two electrodes for accelerated corrosion testing;

[0008] (2) Immerse both ends of another magnesium phosphate cement paste specimen into the sulfate aqueous solution for full immersion corrosion testing;

[0009] (3) At different corrosion time points, take the magnesium phosphate cement paste specimens in the accelerated corrosion testing and full immersion corrosion testing respectively for testing the sulfate content and diffusion depth;

[0010] (4) Plot the distribution points of the sulfate content in the magnesium phosphate cement paste specimen with the distance from the specimen end face at the set corrosion age t, obtain the polynomial related to the sulfate content and the distance from the specimen end face in the magnesium phosphate cement paste specimen by fitting, and solve the calculated erosion depth h of sulfate according to this polynomial. 00 , plot the relationship diagram of different t and h 00 , fit and establish the t~h 00 mathematical model; obtain the t~h 00 mathematical models of the accelerated corrosion testing and full immersion corrosion testing respectively according to this method;

[0011] (5) When h 00 is equal, establish the associated mathematical model of the corrosion age t1 of the accelerated corrosion testing and the corrosion age t2 of the full immersion corrosion testing;

[0012] (6) Calculate the t2 value according to the associated mathematical model of t1~t2 and the t1 value, and evaluate the life cycle of the magnesium phosphate cement paste specimen according to the t2 value and h 00 .

[0013] The present invention utilizes the principle of electric pulse technology to promote the diffusion of sulfate ions into the interior of the MPC paste. By only measuring the sulfate content in the MPC paste specimen to calculate the erosion depth, the sulfate corrosion resistance of the MPC paste can be directly calculated and judged, and its life cycle can be evaluated. According to the set pulse corrosion regime, the pulse power supply is used to accelerate the one-dimensional diffusion of sulfate ions in the MPC specimen, and the sulfate concentration c(x, t) at different distances x from the end face of the MPC specimen at different corrosion ages (t) is measured. By fitting, a polynomial mathematical model of c(x, t) and x is obtained, and according to this model, the surface concentration (cs) of sulfate and the erosion depth h are solved. 00 (trial algorithm). From the calculated h 00 , the sulfate corrosion resistance of the MPC paste can be judged. By comparing the calculated erosion depth h 00 , a correlation mathematical model of the corrosion age of two acceleration corrosion methods (electric pulse accelerated corrosion and full immersion corrosion) can be established. From this mathematical model and the electric pulse corrosion age of the MPC specimen, the corresponding corrosion age of the MPC specimen subjected to full immersion corrosion can be deduced, and its life cycle can be evaluated.

[0014] Preferably, in step (1), the two ends of the magnesium phosphate cement paste specimen are respectively immersed in magnesium sulfate aqueous solution and sodium sulfate aqueous solution; when applying an electric pulse, the electrode inserted into the magnesium sulfate aqueous solution is used as the cathode, and the electrode inserted into the sodium sulfate aqueous solution is used as the anode. The voltage of the electric pulse is 30 - 75V, the pulse period is 30 - 60s, and the total test time is 6 - 30 days.

[0015] Further preferably, the concentration of the magnesium sulfate aqueous solution is 5 - 10wt%, and the concentration of the sodium sulfate aqueous solution is 3 - 7wt%. Preferably, the cathode: 10wt% magnesium sulfate aqueous solution, the anode: 5wt% sodium sulfate aqueous solution.

[0016] Preferably, in steps (1) and (2), the shape of the magnesium phosphate cement paste specimen is one of a cylinder, a cuboid, a cube, and a prism. Before testing, the magnesium phosphate cement paste specimen is placed in a vacuum saturation tank for freshwater saturation; during testing, only the end faces at both ends of the magnesium phosphate cement paste specimen are in contact with the sulfate aqueous solution.

[0017] Preferably, in step (3), the test methods for sulfate content and diffusion depth are as follows:

[0018] Clean the two end faces of the magnesium phosphate cement paste specimen and dry it to a constant weight; slice and sample at equal intervals along the end cross-section of the magnesium phosphate cement paste specimen. The sampling part for accelerated corrosion testing is at the cathode end face, and the sampling part for full immersion corrosion testing is at both side end faces. After respectively crushing the sampled solids and sieving them through a sieve (100 - 150 mesh sub-sieve), powder samples are obtained, and the sulfate content in each powder sample is measured.

[0019] Preferably, the preparation method of the magnesium phosphate cement paste specimen is as follows:

[0020] Weigh MgO, KH2PO4, compound retarder, fly ash and water according to the set mix ratio, mix them evenly to obtain MPC paste, pour the MPC paste into a mold, vibrate it densely and level it. After the MPC paste starts to set, cover the specimen with plastic wrap, and then place the specimen with the mold in a curing room at a temperature of 20°C ± 2°C and a relative humidity of 60% ± 5% for curing until 28 days to obtain a magnesium phosphate cement paste specimen with side molds.

[0021] Preferably, in step (4), the correlation coefficient R of the polynomial related to the sulfate content in the magnesium phosphate cement paste specimen and the distance from the specimen surface 2 ≥0.999.

[0022] Preferably, in step (4), the method for calculating the erosion depth h of sulfate according to the polynomial 00 is as follows:

[0023] Taking the measured erosion depth at a single corrosion age as a reference, substitute the measured erosion depth and its adjacent values into the polynomial to calculate the sulfate content at different distances from the end face in the magnesium phosphate cement paste specimen. The calculation result requires the minimum value within the range of 0 - 0.01%. If it exceeds, take the depth of the adjacent layer to recalculate until the requirement is met. Determine the calculated erosion depth h of sulfate with the result meeting the requirement. 00 , when the measured erosion depth ≥ h 00 , it is required that the measured sulfate content at a distance ≥ h 00 from the end face in the magnesium phosphate cement paste specimen < 0.01%.

[0024] Preferably, in step (6), the correlation mathematical model between t1 and t2 is t2 = 17.6t1 - 31.8 or t2 = 23.82t1 + 153.

[0025] Preferably, in step (2), the method for full immersion corrosion test is as follows: Seal the gap between the magnesium phosphate cement paste specimen and the side mold with epoxy resin, only expose the two end faces, completely immerse the sealed magnesium phosphate cement paste specimen in the sodium sulfate aqueous solution, and the liquid level of the sodium sulfate aqueous solution is at least 10 mm higher than the magnesium phosphate cement paste specimen, and replace the sodium sulfate aqueous solution at most once every 15 days.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0027] (1) The present invention places MPC paste specimens in a one-dimensional sulfate immersion environment and accelerates the diffusion of sulfate ions in MPC specimens through pulsed voltage. A distribution diagram of the sulfate content c(x,t) in the MPC specimens with respect to the distance (x) from the specimen end face is plotted, and a polynomial mathematical model relating c(x,t) to x is obtained by fitting, from which the surface sulfate concentration cs and the calculated erosion depth h of sulfate ions are calculated. 00 From the calculated erosion depth h 00 , the sulfate corrosion resistance of MPC paste can be quickly judged; a mathematical model relating the corrosion age of MPC specimens under accelerated corrosion by electric pulse and full immersion corrosion is established (on the premise that h 00 is equal), and the corrosion age of MPC specimens subjected to full immersion corrosion can be deduced from the accelerated corrosion age by electric pulse.

[0028] (2) This test method has low test strength and a short cycle; the entire test process can be completed in only 6 - 30 days, and the test results are also relatively accurate, which can truly reflect the corrosion condition of MPC paste in a sulfate environment and the erosion and transmission of sulfate ions from the surface to the inside. Description of the Drawings

[0029] Figure 1 is a schematic diagram of an MPC specimen, an electric pulse accelerated corrosion test device, and a test principle;

[0030] Figure 2 is a sampling schematic diagram, a sodium sulfate standard solution, and a standard curve graph;

[0031] Figure 3 is the design and screening results of the two-pole corrosion solution and the pulse regime;

[0032] Figure 4 is the polynomial obtained by fitting for the M0 specimen at different corrosion ages under two corrosion methods;

[0033] Figure 5 is the relationship between the erosion age of the M0 specimen and the calculated erosion depth of sulfate ions;

[0034] Figure 6 is the polynomial obtained by fitting for the MF specimen at different corrosion ages under two corrosion methods;

[0035] Figure 7 is the relationship between the erosion age of the MF specimen and the calculated erosion depth of sulfate ions. Detailed Embodiment

[0036] The technical solution of the present invention will be further described below with reference to the drawings.

[0037] Example 1: A rapid test method for the sulfate corrosion resistance of magnesium phosphate cement-based materials, the specific steps are as follows:

[0038] (1) Prepare MPC test specimens. Keep the ambient temperature at 20 °C. Weigh MgO, KH2PO4 (KDP), composite retarder (CR), fly ash (FA) and water according to the mix ratio in Table 1, pour them into the mixing pot of an NJ-160A type cement paste mixer, and stir at a slow speed (62 ± 5 r / min for revolution) and a fast speed (125 ± 10 r / min for revolution) for a certain period of time. After mixing evenly, obtain the MPC paste. Pour the MPC paste into a PVC mold to prepare a Φ50 mm × 100 mm cylindrical specimen, vibrate it densely and level it. After the paste starts to set, cover the specimen with plastic wrap. After 5 h, place the specimen with the PVC mold in a curing room at a temperature of 20 °C ± 2 °C and a relative humidity of 60% ± 5% and cure it for 28 d. Seal the contact area between the MPC specimen and the PVC mold with epoxy resin to meet the requirements of one-dimensional erosion, as Figure 1 shown in Figure (a) below.

[0039] Table 1 Mix ratio of MPC paste (mass ratio)

[0040]

[0041] (2) Before the test, place the specimens in a vacuum saturation tank for freshwater saturation. Then, insert the two ends of the cylindrical specimens into plastic holding boxes respectively, and seal the contact area between the outer mold of the specimens and the holding boxes with epoxy to prevent the solution from leaking out from the joints. Pour 10 wt% MgSO4 aqueous solution and 5 wt% Na2SO4 aqueous solution into the two plastic holding boxes at both ends respectively, and keep the liquid levels of the sulfate aqueous solutions higher than the upper end faces of the test specimens. Select titanium metal mesh as the electrode and insert the electrodes into the sulfate aqueous solutions respectively, as Figure 1 shown in Figure (b) below. Connect the two electrodes to the power supply of a pulse voltage generator ( Figure 1 shown in Figure (c) below). Take the electrode inserted into the magnesium sulfate aqueous solution as the cathode and the electrode inserted into the sodium sulfate aqueous solution as the anode. Design the pulse parameters as a pulse voltage of 75 V and a pulse period of 30 s (on for 15 s, off for 15 s), and turn on the pulse power supply for accelerated corrosion testing; during the test, only the two end faces of the magnesium phosphate cement paste specimens are in contact with the sulfate aqueous solutions to ensure one-dimensional erosion of the end faces.

[0042] (3) At different corrosion time points, take the MPC specimens in the accelerated corrosion test, clean the two end faces of the MPC paste specimens, and dry them at 55 °C to constant weight; slice and sample every 2 mm along the end cross-section of the MPC specimens. The sampling position for the accelerated corrosion test is at the cathode end face, as Figure 2As shown in Figure (a), sampling was carried out until 26 mm from the original end face. The solids obtained by sampling were crushed and passed through a 100-mesh sieve to obtain powder samples. According to GB / T 5750.5-2023 "Standard Test Methods for Drinking Water - Part 5 Inorganic Non-metallic Indicators: Detection Method for Water-soluble Sulfate Radical (Turbidimetry Method)", a sodium sulfate standard solution was prepared and the standard calibration curve of the used ultraviolet spectrophotometer was plotted. As Figure 2 shown in Figures (b) and (c), the sulfate radical content in the powder samples was then measured using the calibrated ultraviolet spectrophotometer.

[0043] (4) Design of the bipolar corrosion solution for MPC paste: Different groups of anodic and cathodic corrosion solutions were designed according to Table 2. At the same voltage (75 V), frequency (30 s), and corrosion time (28 d), the distribution of sulfate radical ion content in the M0 specimens measured under different corrosion solutions at both ends (Table 2) is as Figure 3 shown in Figure (a). When at the same depth from the end face, the order of the sulfate radical ion content is 5 > 3 > 4 > 1 > 2, and the order of the sulfate radical penetration depth after 28 d of accelerated corrosion is 5 = 4 = 3 > 1 > 2. The results show that the diffusion behavior of sulfate radical in MPC paste is significantly affected by the types of solutions at both ends. When the anode is a 5% Na2SO4 aqueous solution, the diffusion degree (content, depth) of sulfate radical corresponding to the cathode is significantly higher than that when the anode is a 5% MgSO4 aqueous solution. When the anode is a 5% Na2SO4 aqueous solution and the cathode end is a 5% MgSO4 aqueous solution, its sulfate radical diffusion degree (content) is significantly higher than that when the cathode end is a 5% Na2SO4 aqueous solution. When the anode is a 5% Na2SO4 aqueous solution and the cathode end is a 10% MgSO4 aqueous solution, its sulfate radical diffusion degree (content) is slightly higher than that when the cathode is a 5% MgSO4 aqueous solution. Therefore, the designed corrosion solution is: 10% MgSO4 aqueous solution at the cathode and 5% Na2SO4 aqueous solution at the anode (No. 5).

[0044] Table 2 Grouping of Different Corrosion Solutions at Both Poles

[0045]

[0046] (5) Design of the pulse regime for MPC paste: The combination No. 5 in Table 2 was taken as the corrosion solution for both poles, and the sulfate radical ion concentration in the MPC paste specimens was measured at voltages of 75 V, 60 V, 45 V, 30 V and frequencies of 60 s, 30 s respectively. There are obvious differences in the sulfate radical erosion depth (in the range of 14 mm - 18 mm) and sulfate radical content (at the same erosion depth) measured under the six pulse regimes, as Figure 3As shown in Figure (b). At the same voltage, the sulfate content measured at a pulse frequency of 30 s (15 s on, 15 s off) is significantly greater than that at 60 s (30 s on, 30 s off); at the same power-on frequency of 30 s (15 s on, 15 s off), the sulfate content measured at 60 V is also significantly higher than that at 30 V, and the sulfate content measured at 75 V is slightly higher than that at 60 V. The results show that the preferred small pulse period and high voltage scheme (30 s - 75 V) has a more obvious erosion effect.

[0047] (6) Full immersion corrosion test: Take a 5wt% sodium sulfate aqueous solution to immerse the MPC specimens sealed with epoxy resin. Only the two end faces of the MPC specimens are exposed to contact with the sodium sulfate aqueous solution. Ensure that the volume of the sodium sulfate aqueous solution is 5 times the volume of the MPC specimens, the distance between the specimens is 20 mm, and the liquid level of the solution is at least 10 mm higher than the specimens. To ensure the effectiveness of erosion, replace the immersion solution every 15 days, and take out the MPC specimens at the set age. Sample and measure the sulfate content in the powder samples in the same method as in step (3). The sampling parts for the full immersion corrosion test are on both end faces, as Figure 2 shown in Figure (a).

[0048] (7) Plot the distribution points of the sulfate content c(x,t) in the M0 specimens at the set corrosion ages (6 d, 12 d, 18 d, 24 d, 30 d) with respect to the distance (x) from the specimen end face, and obtain the polynomial mathematical model of c(x,t) and x by fitting, as Figure 4 shown in Figure (a). On the premise of satisfying R 2 ≥0.999, they are all third-order polynomials, which is basically consistent with the distribution law of the sulfate content in the M0 specimens at different ages under full immersion in a 5% sodium sulfate solution (reference corrosion environment), as Figure 4 shown in Figure (b). Comparing Figure 4 Figures (a) and (b), it can be seen that the surface sulfate content of the MPC specimens accelerated by electric pulse corrosion for 6 d (0.235%, calculated by substituting x = 0 into the polynomial in Figure 4 (a)) is significantly greater than the surface sulfate content of the MPC specimens under full immersion corrosion for 90 d (0.176%). The results show that the electric pulse can significantly accelerate the diffusion of sulfate in the MPC hardened body and achieve accelerated corrosion.

[0049] (8) According to the Figure 4 polynomial fitted in, the calculated erosion depth h at the set corrosion age can be solved 00(Trial and error method), the method is as follows: When the age of electric pulse corrosion is 6 d, the measured erosion depth h0 is 12 mm. Taking this as a reference, substitute h0 = 11 mm, 12 mm, 13 mm (12 ± 1 mm) into the polynomial to calculate the value of c(h0, 6 d). Considering the error between the fitting curve and the measured results, the calculation result requires the minimum value of c(h0, 6 d) within the range of 0 - 0.01%. If it exceeds, take the adjacent layer depth h0 as 10 mm (10 ± 1 mm) and retest until the requirements are met. After calculation, when h0 = 9 mm, c(9 mm, 6 d) = 0.001%, which is determined as the calculated erosion depth h 00 . When the measured erosion depth h0 ≥ the calculated erosion depth h 00 , it is required that the measured sulfate content in the MPC specimen where x ≥ h 00 < 0.01% ( Figure 4 ). The calculated erosion depths of sulfate in the M0 specimens under different aging periods of electric pulse accelerated corrosion and full immersion corrosion in 5 wt% Na2SO4 aqueous solution calculated by the above method are shown in Table 3.

[0050] Table 3 Calculated erosion depths of M0 specimens obtained by trial calculation using the sulfate ion diffusion fitting model

[0051]

[0052] (9) Draw a relationship diagram between the corrosion age t and the calculated sulfate depth h 00 of the M0 specimen according to Table 3 and perform mathematical fitting. For the M0 specimen subjected to electric pulse corrosion, the relationship between t and h 00 follows an exponential relationship h 00 = 7.2362e 0.0299t , R2 = 0.9915, as shown in Figure (a) of Figure 5 . For the M0 specimen subjected to full immersion corrosion in sulfate aqueous solution, the relationship between t and h 00 follows an exponential relationship h 00 = 7.6378e 0.0017t , R2 = 0.996, as shown in Figure (b) of Figure 5 .

[0053] (10) Based on the mathematical model of t~h Figure 5 in 00 , when the calculated depths h 00 of sulfate diffusion are equal, there is the following relationship between the corrosion ages of the two accelerated corrosion methods (the electric pulse accelerated corrosion age is t1, and the full immersion corrosion age is t2): 7.2362e 0.0299t1 = 7.6378e 0.0017t2 . After arrangement, it can be obtained that: t2 = 17.6t1 - 31.8 (2)

[0054] The sulfate diffusion calculation depth of the M0 specimen after 6 days of electro-pulse accelerated corrosion can be calculated by formula (2), which is equivalent to the sulfate diffusion calculation depth of the M0 specimen after 74 days of full immersion corrosion. The sulfate diffusion calculation depth of the M0 specimen after 30 days of electro-pulse accelerated corrosion is equivalent to the sulfate diffusion calculation depth of the M0 specimen after 496 days of full immersion corrosion. Combining with the diffusion calculation depth h 00 , the life cycle of the M0 paste specimen is evaluated.

[0055] Example 2: The rest is the same as Example 1, except that:

[0056] Prepare MF test specimens according to the mix proportion of the MPC paste in Table 4:

[0057] Table 4 Mix proportion of MPC paste (mass ratio)

[0058]

[0059] Plot the distribution points of the sulfate content c(x, t) in the MF specimen against the distance (x) from the specimen surface at the set corrosion age, and obtain the polynomial mathematical model of c(x, t) and x by fitting (R 2 ≥0.999) as Figure 6 shown.

[0060] According to Figure 6 the fitted polynomial, the calculated erosion depth h of sulfate in the MPC specimen at the set corrosion age can be solved 00 . The calculated erosion depths h of sulfate in the MF specimens at different ages of electro-pulse accelerated corrosion and full immersion corrosion in 5wt% Na2SO4 aqueous solution 00 are shown in Table 5.

[0061] Table 5 Calculated erosion depths of MF specimens obtained by fitting the sulfate ion diffusion model

[0062]

[0063] Plot the relationship diagram of the corrosion age t and the sulfate calculation depth h of the MF specimen according to Table 5 00 and conduct mathematical fitting. For the MF specimen subjected to electro-pulse corrosion, the relationship between t and h 00 obeys an exponential relationship h 00 = 8.6477e 0.0262t , R2 = 0.9978, as shown in Figure 7 Figure (a). For the MF specimen subjected to full immersion corrosion in the solution, the relationship between t and h 00 obeys an exponential relationship h 00 = 7.3077e 0.0011t , R2 = 0.9964, as shown in Figure 7As shown in Figure (b).

[0064] Based on Figure 7 in the range of t to h 00 of the mathematical model, when the calculation depth h of sulfate diffusion 00 is equal, there is the following relationship between the corrosion ages of the two accelerated corrosion methods (the corrosion age of electro-pulse accelerated corrosion is t3, and the corrosion age of full immersion corrosion is t4): 8.6477e 0.0262t3 = 7.3077e 0.0011t4 , after arrangement, it can be obtained: t4 = 23.82t3 + 153 (3)

[0065] From formula (3), the calculation depth of sulfate diffusion of the MF specimen with electro-pulse accelerated corrosion for 6 days can be calculated, which is equivalent to the calculation depth of sulfate diffusion of the M0 specimen with full immersion corrosion for 296 days. The calculation depth of sulfate diffusion of the M0 specimen with electro-pulse accelerated corrosion for 30 days is equivalent to the calculation depth of sulfate diffusion of the M0 specimen with full immersion corrosion for 868 days. Then, combined with the diffusion calculation depth h 00 , evaluate the life cycle of the MF paste specimen.

Claims

1. A rapid test method for the sulfate corrosion resistance of magnesium phosphate cement-based materials, characterized in that: The steps include: (1) The two ends of the magnesium phosphate cement paste specimen are immersed in a sulfate aqueous solution, electrodes are inserted into the sulfate aqueous solution, and an electric pulse is applied between the two electrodes to perform an accelerated corrosion test; (2) Both ends of the magnesium phosphate cement paste specimen were immersed in a sulfate aqueous solution for a full immersion corrosion test; (3) At different corrosion time points, magnesium phosphate cement paste specimens from the accelerated corrosion test and the full immersion corrosion test were taken to test the sulfate content and diffusion depth; (4) Plot the distribution points of sulfate content in magnesium phosphate cement paste specimens as a function of distance from the specimen end face at a set corrosion age t, and obtain a polynomial that relates sulfate content in magnesium phosphate cement paste specimens to the distance from the specimen end face by fitting. The calculated sulfate corrosion depth h is solved based on the polynomial. 00 , plot different t and h 00 The relationship diagram of t~h is established by fitting 00 Mathematical model; According to this method, t~h of accelerated corrosion test and full immersion corrosion test are obtained respectively 00 Mathematical models; (5) In h 00 When they are equal, a correlation mathematical model between the corrosion age t1 of the accelerated corrosion test and the corrosion age t2 of the full immersion corrosion test is established; (6) The t2 value is calculated based on the correlation mathematical model between t1 and t2 and the t1 value. 00 Evaluation of the life cycle of magnesium phosphate cement paste specimens.

2. The rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: In step (1), both ends of the magnesium phosphate cement slurry specimen are immersed in a magnesium sulfate aqueous solution and a sodium sulfate aqueous solution respectively; when an electric pulse is applied, the electrode inserted into the magnesium sulfate aqueous solution is used as the cathode, and the electrode inserted into the sodium sulfate aqueous solution is used as the anode. The voltage of the electric pulse is 30-75V, the pulse period is 30-60s, and the total test time is 6-30 days.

3. The rapid test method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 2, characterized in that: The concentration of the magnesium sulfate aqueous solution is 5-10 wt %, and the concentration of the sodium sulfate aqueous solution is 3-7 wt %.

4. The rapid test method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: In steps (1) and (2), the shape of the magnesium phosphate cement slurry specimen is one of a cylinder, a cuboid, a cube, and a prism. Before testing, the magnesium phosphate cement slurry specimen is placed in a vacuum saturation tank for saturation with fresh water. During the test, only the end faces of both ends of the magnesium phosphate cement slurry specimen are in contact with the sulfate aqueous solution.

5. The rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: In step (3), the test method for sulfate content and diffusion depth is: The two end faces of the magnesium phosphate cement slurry specimen were cleaned and dried to constant weight; samples were taken by equidistantly sliced ​​sections along the end cross section of the magnesium phosphate cement slurry specimen. The sampling position of the accelerated corrosion specimen was at the cathode end face, and the sampling position of the full immersion corrosion specimen was at the end faces on both sides. The solid samples were crushed and sieved to obtain powder samples, and the sulfate content in each powder sample was determined.

6. The rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: The preparation method of the magnesium phosphate cement slurry specimen is: MgO, KH2PO4, composite retarder, fly ash and water were weighed according to the set mix ratio, and mixed to obtain MPC slurry. The MPC slurry was poured into the mold, vibrated to compact and scraped flat. After the MPC slurry initially set, the specimen was covered with plastic wrap, and then the specimen with the mold was placed in a curing room with a temperature of 20℃±2℃ and a relative humidity of 60%±5% and cured for 28 days to obtain a magnesium phosphate cement slurry specimen with a side mold.

7. The rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: In step (4), the correlation coefficient R of the polynomial related to the sulfate content in the magnesium phosphate cement paste specimen and the distance from the specimen surface is 2 ≥0.

999.

8. The rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: In step (4), the calculation depth of sulfate erosion h is obtained by solving the polynomial equation 00 The method is: Taking the measured erosion depth under a single corrosion age as a reference, the measured erosion depth and its adjacent values ​​are substituted into the polynomial to calculate the sulfate content at different distances from the end face of the magnesium phosphate cement paste specimen. The calculation result is required to be within the minimum value within the range of 0-0.01%. If it exceeds, the adjacent layer depth is taken and recalculated until the requirement is met. The calculation result that meets the requirement is determined as the calculated erosion depth of sulfate h. 00 , when the measured erosion depth ≥ h 00 When the distance from the end surface of the magnesium phosphate cement paste specimen is required to be ≥h 00 The measured sulfate content is less than 0.01%.

9. The rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: In step (6), the associated mathematical model of t1 to t2 is t2 = 17.6t1-31.8 or t2 = 23.82t1+153.

10. The rapid testing method for the sulfate corrosion resistance of magnesium phosphate cement-based materials according to claim 1, characterized in that: In step (2), the method of the full immersion corrosion test is: the gap between the magnesium phosphate cement slurry specimen and the side mold is sealed with epoxy resin, only the two end faces are exposed, and the sealed magnesium phosphate cement slurry specimen is completely immersed in a sodium sulfate aqueous solution, the liquid level of the sodium sulfate aqueous solution is at least 10 mm higher than the magnesium phosphate cement slurry specimen, and the sodium sulfate aqueous solution is replaced at most every 15 days.

Images