A modified aluminate cement, cement product and concrete product

Abstract

The application belongs to the technical field of building materials, and particularly relates to a modified aluminate cement, a cement product and a concrete product. Components of the modified aluminate cement of the application include aluminate cement and carbonized magnesium slag. The modified aluminate cement of the application helps to optimize the composition of hydration products, inhibit the phase transition of calcium aluminate hydrate, and improve the compactness and mechanical properties of the hardened body of the modified aluminate cement. In addition, the application modifies the aluminate cement by using carbonized magnesium slag, which not only helps to realize the resource utilization of carbonized magnesium slag, but also helps to reduce the cost and realize the wide application of the aluminate cement.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a modified aluminate cement, cement products, and concrete products. Background Technology

[0002] As a special type of cement, aluminate cement (CAC) has advantages such as rapid setting and hardening, corrosion resistance, and low permeability. Even at -10℃, CAC can set and harden, making it widely used in applications such as national defense, road repair, and projects in cold winter regions. However, due to cost considerations and issues related to the phase transformation of CAC hydration products (the main clinker CA and CA2 in aluminate cement forms the intermediate hydration product CAH), its application has been limited. 10 A phase transition occurs with C2AH8; when the phase transition occurs, low-density CAH... 10 (C2AH8 will transform into high-density C3AH6, thereby increasing the porosity of the matrix and causing a decrease in mechanical properties), CAC has not been widely used.

[0003] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0004] The purpose of this invention is to provide a modified aluminate cement, cement products, and concrete products to help solve or improve the phase transformation problem of hydration products in aluminate cement.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a modified aluminate cement, wherein the modified aluminate cement comprises aluminate cement and magnesium carbide slag.

[0006] Preferably, the mass percentage of magnesium carbide slag in the modified aluminate cement is ≤40%.

[0007] Preferably, the mass percentage of magnesium carbide slag in the modified aluminate cement is 10%-30%.

[0008] Preferably, the mass percentage of magnesium carbide slag in the modified aluminate cement is 20%-30%.

[0009] Preferably, the magnesium carbide slag is prepared by a method including the following steps: (1) drying and grinding the magnesium slag to obtain magnesium slag dry powder; (2) mixing the magnesium slag dry powder with water evenly to obtain magnesium slag slurry; (3) under constant temperature conditions of 20-30℃, introducing carbon dioxide gas into the magnesium slag slurry, and carbonizing until the pH of the magnesium slag slurry reaches 6.5-7.5, and then separating the solid and liquid to obtain the magnesium carbide slag.

[0010] Preferably, step (2) further includes the step of adding sodium bicarbonate to the magnesium slag dry process; the mass of the sodium bicarbonate is 0.8%-1.2% of the mass of the magnesium slag dry powder.

[0011] The present invention also provides a cement product, which adopts the following technical solution: a cement product, wherein the components of the cement product include the modified aluminate cement as described above.

[0012] The present invention also provides a concrete product, which adopts the following technical solution: a concrete product, wherein the components of the concrete product include the modified aluminate cement as described above.

[0013] Beneficial effects:

[0014] The modified aluminate cement of the present invention helps to optimize the composition of hydration products, inhibit the phase transformation of hydrated calcium aluminate, and improve the density and mechanical properties of the hardened modified aluminate cement body.

[0015] This invention uses magnesium carbide slag to modify aluminate cement, which not only helps to realize the resource utilization of magnesium carbide slag, but also helps to reduce costs and facilitates the widespread application of aluminate cement. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0017] Figure 1 XRD diffraction pattern and particle size distribution of aluminate cement are shown below; (a) is the XRD diffraction pattern and (b) is the particle size distribution.

[0018] Figure 2 XRD diffraction pattern and particle size distribution of magnesium carbide slag are shown; where (a) is the XRD diffraction pattern and (b) is the particle size distribution.

[0019] Figure 3 The graph shows the test results of the effect of magnesium carbide slag on fluidity.

[0020] Figure 4 The graph shows the test results of the effect of magnesium carbide slag on setting time.

[0021] Figure 5 Figure 1 shows the test results of the effect of magnesium carbide slag on compressive strength; where (a) is the test results of compressive strength and (b) is the test results of strength change rate.

[0022] Figure 6Figure 1 shows the test results of the effect of magnesium carbide slag on the heat of hydration; where (a) is the test result of the peak heat of hydration release, and (b) is the test result of the cumulative heat of hydration.

[0023] Figure 7 The XRD test results of the effect of magnesium carbide slag on hydration products are shown in the figure; (a) is the XRD test result of hydration products after 3 days of curing, and (b) is the XRD test result of hydration products after 28 days of curing.

[0024] Figure 8 The graph shows the TG-DTG test results of the effect of magnesium carbide slag on hydration products; where (a) is the TG-DTG curve and (b) is the mass loss rate.

[0025] Figure 9 The image shows the SEM test results of the effect of magnesium carbide slag on the microstructure of aluminate cement.

[0026] Figure 10 The following are the results of the relaxation time test: (a) is the result of the relaxation time test after 1 day of curing, (b) is the result of the relaxation time test after 3 days of curing, (c) is the result of the relaxation time test after 28 days of curing, and (d) is a summary of the test results of the effect of different amounts of magnesium carbide slag replacement and curing age on the porosity of the sample. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0028] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0029] This invention addresses the problem of phase transformation of hydration products in current aluminate cements by providing a modified aluminate cement.

[0030] The modified aluminate cement of this invention comprises aluminate cement and magnesium carbide slag.

[0031] This invention modifies aluminate cement by adding magnesium carbide slag, which helps to optimize the composition of hydration products, inhibit the phase transformation of calcium aluminate hydrate, and improve the density and mechanical properties of the modified aluminate cement hardened body.

[0032] The modified aluminate cement of the present invention not only helps to realize the resource utilization of magnesium carbide slag, but also helps to reduce the cost of aluminate cement and promotes the widespread application of aluminate cement.

[0033] In a preferred embodiment of the modified aluminate cement of the present invention, the mass percentage of magnesium carbide slag in the modified aluminate cement is ≤40%. If the mass percentage of magnesium carbide slag is too high, the dilution effect of magnesium carbide slag will be prominent due to the low content of aluminate cement, resulting in a reduction of hydration products of the modified aluminate cement.

[0034] In a preferred embodiment of the modified aluminate cement of the present invention, the mass percentage of magnesium carbide slag in the modified aluminate cement is 10%-30% (e.g., 10%, 15%, 20%, 25% or 30%).

[0035] In a preferred embodiment of the modified aluminate cement of the present invention, the mass percentage of magnesium carbide slag in the modified aluminate cement is 20%-30% (e.g., 20%, 22%, 24%, 26%, 28% or 30%).

[0036] In a preferred embodiment of the modified aluminate cement of the present invention, magnesium carbide slag is prepared by a method comprising the following steps: (1) drying and grinding magnesium slag to obtain magnesium slag dry powder; (2) mixing magnesium slag dry powder, sodium bicarbonate and water evenly to obtain magnesium slag slurry; (3) under constant temperature conditions of 20-30℃ (e.g. 20℃, 22℃, 24℃, 26℃, 28℃ or 30℃), carbon dioxide gas is introduced into the magnesium slag slurry, and the carbonization reaction is carried out until the pH of the magnesium slag slurry reaches 6.5-7.5 (e.g. 6.5, 6.8, 7, 7.2 or 7.5), and solid-liquid separation is performed to obtain magnesium carbide slag.

[0037] Preferably, the magnesium slag powder in step (1) can pass through a 200-mesh sieve.

[0038] Preferably, step (2) further includes the step of adding sodium bicarbonate to the magnesium slag dry process; the mass of sodium bicarbonate is 0.8%-1.2% of the mass of the magnesium slag dry powder (e.g., 0.8%, 0.9%, 1%, 1.1% and 1.2%).

[0039] More preferably, the mass ratio of magnesium slag powder, sodium bicarbonate and water in the magnesium slag slurry is 1:0.01:(8-12) (e.g., 1:8, 1:9, 1:10, 1:11 or 1:12).

[0040] The present invention also proposes a cement product, wherein the components of the cement product of the present invention include the modified aluminate cement as described above.

[0041] The present invention also proposes a concrete product, wherein the components of the concrete product of the present invention include the modified aluminate cement as described above.

[0042] The modified aluminate cement, cement paste products, and concrete products of the present invention will be described in detail below through specific embodiments.

[0043] Unless otherwise specified, all raw materials used in the following examples are commercially available; the sources of the main raw materials are as follows:

[0044] The specific surface area of ​​aluminate cement (CA-50) is 373.72 m². 2 / kg, D 50 The particle size is 29.5 μm (see...) Figure 1 (b)); its XRD pattern is as follows Figure 1 As shown in (a), the main mineral compositions include CA, CA2, C2AS and C. 12 A7.

[0045] The specific surface area of ​​the magnesium carbide slag (CMS) in Examples 1-4 is 784.87 m². 2 / kg, D 50 The particle size is 15.4 μm (see...) Figure 2 (b)); The XRD pattern of magnesium carbide slag is as follows: Figure 2 As shown in (a), its main mineral composition is CaCO3.

[0046] Specifically, the magnesium carbide slags of Examples 1-4 were prepared using a method comprising the following steps:

[0047] (1) Raw material pretreatment: a. The magnesium slag (magnesium slag produced by the Pidgeon process (mainly composed of CaO and SiO2), sourced from Yulin City, Shaanxi Province, China) was dried at 105℃ to constant weight to remove moisture; b. The dried magnesium slag was ground using a ball mill and passed through a 200-mesh sieve.

[0048] (2) Solution preparation: Tap water is used directly as the reaction medium; magnesium slag and tap water are mixed in a mass ratio of 1:10.

[0049] (3) Wet carbonization reaction: a. Under constant temperature conditions, magnetic stirring is performed at a rate of 400 r / min for 10 minutes to fully disperse the magnesium slag; b. Under constant temperature conditions of 25℃, CO2 gas with a purity of 99.9% is introduced at a flow rate of 0.1 L / min using a ventilation device (the reaction time is usually about 120 minutes); c. Reaction monitoring: The pH change of the solution is monitored in real time using a digital pH meter (REX PHS-3C type). In the initial stage, the pH drops rapidly to neutral and then tends to stabilize (about 7.0).

[0050] (4) Post-processing of the product: a. After the carbonization reaction, the solid and liquid phases were separated by vacuum filtration; b. The filter cake was washed multiple times with ethanol to remove residual impurities; c. The filter cake was dried in a vacuum drying oven at 50℃ until constant weight; d. The dried product was ground using a planetary ball mill to obtain uniform magnesium carbide slag powder. The particle size distribution was determined by a laser particle size analyzer (Malvern Mastersizer 3000E), with a median particle size (D50) of approximately 15.4 μm and a specific surface area of ​​784.87 m² / kg.

[0051] The chemical compositions of aluminate cement (mainly composed of CaO and Al2O3; abbreviated as CAC) and magnesia carbide slag (mainly composed of CaO and SiO2; abbreviated as CMS) are shown in Table 1 below:

[0052] Table 1. Main chemical components (%) of aluminate cement and magnesium carbide slag

[0053]

[0054] The method for preparing magnesium carbide slag used in Example 5 differs from that in Examples 1-4 only in that sodium bicarbonate (commercially available white granular powder) is added in step (2), and the amount of sodium bicarbonate is 1% of the mass of the magnesium slag dry powder; after CO2 gas is introduced in step (3) for 60 minutes, the pH tends to stabilize (about 7.0).

[0055] Example 1

[0056] The modified cement in this embodiment includes 90% aluminate cement and 10% magnesium carbide slag by mass.

[0057] The modified aluminate cement in this embodiment is abbreviated as M10.

[0058] Example 2

[0059] The modified cement in this embodiment includes 80% aluminate cement and 20% magnesium carbide slag by mass.

[0060] The modified aluminate cement in this embodiment is abbreviated as M20.

[0061] Example 3

[0062] The modified cement in this embodiment includes 70% aluminate cement and 30% magnesium carbide slag by mass.

[0063] The modified aluminate cement in this embodiment is referred to as M30.

[0064] Example 4

[0065] The modified cement in this embodiment includes 60% aluminate cement and 40% magnesium carbide slag by mass.

[0066] The modified aluminate cement in this embodiment is referred to as M40.

[0067] Example 5

[0068] The only difference between the modified cement in this embodiment and that in Example 3 is that the magnesium carbide slag used is different (sodium bicarbonate was added to the magnesium carbide slag in this embodiment during the preparation process; the mass of sodium bicarbonate is 1% of the mass of the magnesium slag dry powder in step (2)), and the rest is consistent with that in Example 3.

[0069] The modified aluminate cement in this embodiment is abbreviated as M30'.

[0070] Comparative Example 1

[0071] This comparative example did not modify the aluminate cement (100% aluminate cement), and is referred to as M0 below.

[0072] Comparative Example 2

[0073] The modified aluminate cement in this comparative example comprises 90% aluminate cement and 10% calcium carbonate by mass.

[0074] The modified aluminate cement used in this comparative example is abbreviated as C10.

[0075] Comparative Example 3

[0076] The modified aluminate cement in this comparative example comprises 80% aluminate cement and 20% calcium carbonate by mass.

[0077] The modified aluminate cement used in this comparative example is abbreviated as C20.

[0078] Comparative Example 4

[0079] The modified aluminate cement in this comparative example comprises 70% aluminate cement and 30% calcium carbonate by mass.

[0080] The modified aluminate cement used in this comparative example is abbreviated as C30.

[0081] Experimental Example

[0082] Preparation of cement paste: First, pour aluminate cement and magnesium carbide slag into a mixing pot and mix at low speed for 120 seconds to mix evenly (the step of adding magnesium carbide slag is omitted in Comparative Example 1). Then, pour water (water-cement ratio of 0.4) into the mixing pot, mix at low speed for 120 seconds, stop for 15 seconds, and then mix at high speed for 120 seconds to fully mix evenly.

[0083] Performance testing:

[0084] 1. Setting time and fluidity:

[0085] Test methods: The setting time of cement was tested in accordance with the Chinese standard "Test method for standard consistency water requirement, setting time and soundness" (GB / T 1346-2011); the fluidity was tested in accordance with the national standard "Test method for homogeneity of concrete admixtures" (GB / T8077-2012).

[0086] Test results:

[0087] The effect of CMS (magnesium carbide slag) on ​​the fluidity of aluminate cement is shown in [reference needed]. Figure 3 When the CMS substitution amounts were 0% (Comparative Example 1), 10% (Example 1), 20% (Example 2), 30% (Example 3), and 40% (Example 4), the slurry fluidity was 170 mm, 165 mm, 147 mm, 145 mm, and 135 mm, respectively. Compared to the control group, the fluidity loss rates were 3%, 13.5%, 14.7%, and 20.6%, respectively, indicating that the slurry fluidity gradually decreased with increasing CMS substitution amount. This is mainly attributed to the large specific surface area of ​​CMS; substitution of the same mass reduces the free water content in the slurry, thus decreasing its fluidity.

[0088] The effect of magnesium carbide slag on the setting time of aluminate cement is shown in the figure. Figure 4 The initial setting / final setting times of the slurry were 195 min / 255 min, 162 min / 205 min, 130 min / 180 min, 125 min / 155 min, and 85 min / 135 min for different amounts of magnesium carbide slag replacement, respectively; that is, the greater the amount of magnesium carbide slag replacement, the shorter the initial and final setting times. This is partly because the large water demand of CMS reduces the free water inside the slurry, shortening the thickening time of the slurry; on the other hand, it may be that CMS exerts a nucleation effect or participates in the hydration of CAC (aluminate cement), promoting its early hydration and thus accelerating the setting and hardening of the slurry.

[0089] 2. Compressive strength

[0090] Test method: The compressive strength at 3d and 28d was tested according to the national standard "Test method for strength of cement mortar (ISO method)" (GB / T 17671-2021). The test block size was 40 mm × 40 mm × 40 mm.

[0091] Test results:

[0092] The effect of magnesium carbide slag on the compressive strength of aluminate cement is shown in Figure 5 .from Figure 5It can be seen that the compressive strength first increases and then decreases with the increase of magnesium carbide slag replacement amount. When the magnesium carbide slag replacement amounts are 0%, 10%, 20%, 30%, and 40%, the 3-day compressive strengths are 29.7 MPa, 34 MPa, 38.7 MPa, 40.3 MPa, and 33.3 MPa, respectively. Compared with the blank sample M0, M10, M20, M30, and M40 increase by 14.5%, 30.3%, 35.7%, and 12.1%, respectively, with the highest compressive strength at a replacement amount of 30%. The 28-day compressive strengths of M0, M10, M20, M30, and M40 are 40.6 MPa, 42.7 MPa, 51.4 MPa, 54.2 MPa, and 39.3 MPa, respectively. Compared with the blank sample M0, the compressive strength of M10, M20, and M30 increased by 5.2%, 26.6%, and 33.5%, respectively, while the compressive strength of M40 decreased by 3.2%. Similarly, the highest value was observed at a substitution amount of 30% (i.e., group M30), but it was lower than that of the blank sample (i.e., group M0) at a substitution amount of 40%. Therefore, it can be concluded that when the substitution amount of magnesium carbide slag is 30%, the cementitious material composed of it and aluminate cement exhibits the best mechanical properties, and a substitution amount not exceeding 30% is beneficial for improving mechanical properties.

[0093] The compressive strength of the modified aluminate cements in Comparative Examples 2-4 and Example 5 were tested and compared with that in Example 3. The test results are shown in Table 2 below:

[0094] Table 2

[0095]

[0096] Table 2 shows that when calcium carbonate is used instead of magnesium carbide slag to modify aluminate cement, the 28-day compressive strength of the modified aluminate cement is the highest (48.2 MPa) when the mass percentage of calcium carbonate in the modified aluminate cement is 10%, but it is still lower than M20 and M30. This indicates that magnesium carbide slag can achieve a better modification effect on aluminate cement than calcium carbonate. This may be because the active silica in magnesium carbide slag can indirectly enhance the performance of modified aluminate cement through auxiliary filling and optimized product composition.

[0097] Example 5 (M30') shows that the magnesium slag prepared by adding sodium bicarbonate to magnesium slag dry powder was used for the modification of aluminate. The 3-day and 28-day compressive strength of the modified aluminate cement M30' was 6.9% and 2.8% higher than that of M30, respectively. This indicates that sodium bicarbonate not only effectively shortens the carbonation time of magnesium slag, but also slightly benefits the compressive strength of the modified aluminate cement.

[0098] 3. Heat of hydration test

[0099] Test method: The heat of hydration was tested using a TAM Air micro calorimeter from TA Instruments Ltd. (USA). Weigh 4g of the required sample, pour the sample into an ampoule and mix well. Then add water and stir for 1-2 minutes. After that, press the cap and ampoule tightly and place them in the corresponding measurement channel. Record the heat flow of the sample.

[0100] Test results: The effect of magnesium carbide slag on the heat of hydration of CAC cement is shown in [reference needed]. Figure 6 .Depend on Figure 6 (a) It can be seen that the induction period gradually shortens with the increase of magnesium carbide slag substitution. When the magnesium carbide slag substitution is 0%, the induction period ends at approximately 4 hours. When the magnesium carbide slag substitution is 10%, 20%, 30%, and 40%, the induction periods of the slurry are 3.2 hours, 2.8 hours, 2.5 hours, and 2.4 hours, respectively. That is, the greater the magnesium carbide slag substitution, the shorter the induction period, which is consistent with the influence on setting time. The exothermic peak of the slurry gradually decreases with the increase of magnesium carbide slag substitution. The exothermic peak is the largest at 0% substitution, which is 17.38 mW / g. When the substitution is 10%, 20%, 30%, and 40%, the peak values ​​are 14.36 mW / g, 12.60 mW / g, 12.10 mW / g, and 9.69 mW / g, respectively, representing decreases of 13%, 22%, 25%, and 43%.

[0101] Depend on Figure 6 (b) It can be seen that as the substitution amount of magnesia carbide slag increases from 0 to 40%, the cumulative heat release is 346.49 J / g, 350.51 J / g, 364.23 J / g, 370.16 J / g, and 306.74 J / g, respectively, that is, it first increases and then decreases. The maximum heat release is found at a substitution amount of 30%, and it is lower than that of the blank sample at 40%. This is consistent with the law of influence on compressive strength, indicating that magnesia carbide slag affects early hydration. When the substitution amount of magnesia carbide slag is no more than 30%, it promotes the hydration of aluminate cement, thereby enhancing its mechanical properties. However, when the substitution amount of magnesia carbide slag further increases to 40%, the aluminate cement clinker is significantly reduced due to its "dilution effect", and the heat release of hydration decreases.

[0102] 4. Microscopic testing

[0103] Test method:

[0104] XRD testing: The collected samples were immersed in ethanol. Before testing, the samples were dried in a vacuum drying oven at 40°C for 48 hours. The phase composition was determined using a SmartLab (9kW) X-ray diffractometer from Rigaku Corporation (Japan), with a scanning range of 5°~65° and a scanning rate of 5° / min.

[0105] Thermogravimetric analysis (TGA): Thermogravimetric analysis was performed using an HCT-3 microcomputer differential thermal balance. The heating range was 30~1000℃, and the heating rate was 10℃ / min.

[0106] SEM testing: Morphological observation was performed using a Merlin Compact scanning electron microscope (SEM) from Carl Zeiss NTS GmbH, Germany.

[0107] (1) XRD analysis:

[0108] The XRD test results of the effect of magnesium slag on the hydration products of aluminate cement are shown in the figure. Figure 7 .from Figure 7 It can be seen that, without the addition of magnesium carbide slag, the hydration products are mainly CAH. 10 C2AH8, C3AH6, and AH3 (Al2O3·3H2O), etc., among which the C3AH6 diffraction peak at 28d is stronger than that at 3d, while CAH 10 The C2AH8 diffraction peaks at 3d are stronger than those at 28d, indicating that as hydration continues, the metastable CAH in the hydration products... 10 It continuously transforms from C2AH8 into the stable C3AH6.

[0109] In the sample containing magnesia carbide slag, a characteristic peak (2θ=13°) of C3A·CaCO3·11H2O (single-carbon hydrated aluminocarboxylate) appeared, indicating that the calcium aluminate in the aluminate cement reacted with the calcium carbonate in the magnesia carbide slag, as shown in the reaction equation below. In the 3-day and 28-day XRD patterns of the M10 sample, compared to the M0 and M20-M40 groups, more pronounced characteristic peaks of C3AH6 and AH3 were observed. This indicates that when the magnesia carbide slag substitution amount was 10%, its "nucleation effect" was exerted, thereby promoting the hydration of calcium aluminate cement.

[0110] With the increase in the amount of magnesium carbide slag substitution (M20 and M30 groups), the characteristic peak of C3AH6 decreased, while the characteristic peak of single-carbon hydrated aluminate carboxylate significantly increased. This is because, with the increase in the amount of magnesium carbide slag, the CaCO3 in the magnesium carbide slag can react not only with the main minerals CA and CA2 in aluminate cement, but also with the hydration product CAH of aluminate cement. 10 The reaction with C2AH8 to form C3A·CaCO3·11H2O enhances its characteristic peaks. Correspondingly, due to the partial hydration of CAH... 10 The reaction between C2AH8 and magnesium carbide slag reduced the conversion to C3AH6, thus lowering its characteristic peak. The generated C3A·CaCO3·11H2O interacted with other hydration products to form a framework; the gel-like aluminum hydroxide generated by hydration filled the interior of the framework, increasing the density of the specimen and thus increasing the compressive strength of its hardened body.

[0111] When the replacement amount of magnesium carbide slag reaches 40% (M40 group), due to the reduction of calcium aluminate cement clinker, the "dilution effect" of magnesium carbide slag becomes prominent, the hydration products decrease, the characteristic peaks of the corresponding hydration products all decrease, and the compressive strength also shows a downward trend.

[0112] The reaction formula is as follows:

[0113]

[0114] When sodium bicarbonate is involved:

[0115]

[0116] In the presence of sodium bicarbonate, the silica gel produced by carbonization and the aluminum glue produced by hydration can be converted into sodium aluminosilicate hydrate, thereby further optimizing the composition of the hydration products and slightly improving the compressive strength.

[0117] (2) TG-DTG

[0118] The TG-DTG curves showing the effect of CMS on hydration products are as follows: Figure 8 As shown in (a), the thermogravimetric curves can be divided into three temperature ranges based on the decomposition characteristics of the hydration products. The CAH range is 30-200℃. 10 The thermal decomposition temperatures of hydrated aluminocarbonates are as follows: AH3 and C3AH6 decompose in the 200-400℃ range, while CaCO3 decomposes in the 400-800℃ range. The TG curves show that M30 corresponds to the largest weight loss peak, indicating the potential formation of more hydration products. Furthermore, from... Figure 8 (a) It can be seen that as the amount of CMS substitution increases, the thermal decomposition peak of the sample in the DTG curve gradually increases in the range of 600-800℃, which indicates that the CaCO3 content in the sample gradually increases.

[0119] Quantitative analysis of the thermal decomposition quality of hydration products, such as Figure 8 (b) and Table 3 are shown. From Figure 8 As shown in Table 3, when the magnesia slag substitution rate is 10%, the mass of thermal decomposition products is lowest in the temperature range of 30-200℃, while the mass of thermal decomposition products of group M10 is highest in the temperature range of 200-400℃. This indicates that group M10 contains CAH 10 The amount of hydrated calcium aluminate carbide was the least, while AH3 and C3AH6 were the most abundant; this is consistent with the peak values ​​of XRD; that is, when the amount of magnesium carbide slag substitution is 10%, it accelerates the formation of hydration products AH3 and C3AH6 through the "nucleation effect".

[0120] When the substitution rate of magnesium carbide slag is between 20% and 40%, the mass of thermal decomposition products in the temperature range of 30-200℃ is greater than that of the blank sample, i.e., the CAH content is higher. 10 The amounts of hydrated calcium aluminate carbohydrate and calcium carbohydrate were both greater than those of the blank sample. However, within the 200-400℃ range, the greater the amount of magnesia carbide slag, the less the amount of decomposition products, specifically AH3 and C3AH6. This is mainly because the incorporation of magnesia carbide slag converted some of the hydrated calcium aluminate carbohydrate into hydrated calcium aluminate carbohydrate. This indicates that at CMS substitution levels of 20% and 30%, the formation of hydrated calcium aluminate carbohydrate indirectly inhibited the production of the hydration product CAH. 10 The transformation to the C3AH6 crystal form has a beneficial effect on compressive strength. Furthermore, with the increase in the amount of magnesium carbide slag substitution, the decomposition products in the 400-800℃ temperature range increase accordingly, indicating an increase in the amount of calcium carbonate.

[0121] Table 3 Decomposition rate of samples with different magnesium carbide slag substitution amounts

[0122]

[0123] (3) SEM analysis

[0124] Depend on Figure 9 The SEM images show that, without the addition of magnesium carbide slag, the hydration products at 3 days are mainly needle-like and plate-like CAH. 10 C2AH8 and AH3 are stacked and superimposed, with AH3 adhering to the crystal surface, while the cubic C3AH6 is less abundant. At 28 days, the hydration products of sample M0 show a significant increase in C3AH6, and the crystal structure partially transforms from a lamellar structure to a cubic structure. For sample M10, SEM images at 3 days and 28 days show a greater and more pronounced presence of C3AH6 and AH3. This is due to the "nucleation effect" of the particles in the magnesium carbide slag, which promotes the formation of more hydration products.

[0125] The hydration products of M30 samples at 3d and 28d were mainly hexagonal plate-shaped C3A·CaCO3·11H2O, amorphous AH3, and some CAH. 10 The cubic structure of C3AH6 was significantly reduced, further illustrating that magnesium carbide slag not only promotes the hydration of aluminate cement minerals but also promotes the formation of C3A·CaCO3·11H2O. Hydrated calcium aluminate carbohydrate interlocks with other hydration products, forming the slurry's structural framework. Simultaneously, the generated AH3 gel fills the pores, making the hardened structure more compact. Furthermore, the formation of C3A·CaCO3·11H2O also consumes a certain amount of the main minerals in high-alumina cement, reducing the CAH6 content. 10 The formation of hydration products such as C2AH8 weakens the overall crystal transformation in the system, which helps to make the cement stone structure denser.

[0126] When the replacement amount of magnesium carbide slag was further increased from 30% to 40%, the calcium carbonate particles in the microstructure of the M40 group were found to have increased significantly. The particle surface was covered by a flocculent structure. In addition, some gel-like AH3 could still be observed in the figure. However, the overall microstructure became loose due to the dilution effect, resulting in a decrease in mechanical properties.

[0127] 5. Low-field NMR testing

[0128] Test Method: A low-field nuclear magnetic resonance spectrometer (MesoMR12-060V) manufactured by Suzhou Niumag Analytical Instrument Co., Ltd., China, was used for testing. The operating frequency was 12 MHz, and the magnet and probe temperatures were maintained at 32 ± 0.01 ℃ during the test. The T2 relaxation time distribution was obtained using CPMG pulse sequences, and the transverse relaxation time (T2) was measured in the range of 0.001 ms to 10000 ms. After preparing the slurry, 15 g of sample was quickly placed into a glass bottle (22 mm inner diameter, 50 mm height) and immediately sealed with sealing film to prevent moisture evaporation. The T2 relaxation times were measured at 1 day, 3 days, and 28 days.

[0129] Test results: LF-NMR enabled non-destructive monitoring of the pore structure of cement-based materials. The relaxation time distribution of samples with different CMS substitution amounts and curing ages is shown in the figure. Figure 10 .Depend on Figure 10 It can be seen that the T2 relaxation times of the samples are mostly between 0.01 ms and 1-10 ms. The most significant signal intensity peaks are mainly distributed between 0.01 ms and 1 ms, corresponding to the gel pores in the structure, while the range of 1-10 ms corresponds to the capillary pores. The T2 relaxation time and area are related to the porosity of the samples; the shorter the T2 relaxation time and the smaller the area, the lower the porosity of the samples.

[0130] from Figure 10 As shown in (a) and 10(b), at 1d and 3d ages, the peak intensity of the T2 relaxation time signal decreases with increasing CMS substitution, while the relaxation time increases. This indicates that the addition of CMS alters the pore structure ratio of the hardened body. The reduction in gel pores may be due to two factors: firstly, the finer CMS fills the pores of the hardened body; secondly, the formation of aluminate carbonates also fills the gel pores, leading to a decrease in peak signal intensity within 0.01–10 ms. However, with increasing CMS substitution, the dilution effect caused by CMS replacing cement reduces hydration products and increases the number of capillary pores. At ages 3d to 28d (from... Figure 10 (b) to Figure 10(c) The peak signal intensity of group M10 increases. Combined with TG analysis, it can be seen that the low-density CAH in group M10... 10 The conversion generated more high-density C3AH6, thus increasing porosity and peak signal.

[0131] In addition, the effects of different CMS substitution amounts and curing ages on the porosity of the samples are summarized, see [link to relevant documentation]. Figure 10 (d) It can be clearly seen that from 1 day to 3 days, the characteristic peak signal value decreases rapidly with the change in curing age. This is because the hydration reaction proceeds, and the pores inside the sample are gradually filled by hydration products, reducing the porosity. However, from 3 days to 28 days, the characteristic peak signal value does not decrease significantly, indicating that the formation rate of hydration products has slowed down. This also corresponds to the fast early hydration rate of aluminate cement and the fact that the 3-day strength can reach about 80% of the complete hydration level. During the 1-10 ms relaxation time, the characteristic peak gradually shifts to the left, corresponding to the gradual reduction and refinement of pores. This indicates that the generated hydration products have a filling effect on the capillaries, which is one of the reasons why the 28-day strength is greater than the 3-day strength.

[0132] In summary, the XRD and TG-DTG analyses show that magnesium carbide slag not only optimizes the composition of hydration products but also promotes the formation of C3A·CaCO3·11H2O, effectively inhibiting the phase transformation of hydrated calcium aluminate. Low-field NMR and SEM tests indicate that magnesium carbide slag optimizes the pore structure ratio of the hardened body, fills the gel pores, thereby improving the density of the hardened body and having a corresponding impact on compressive strength.

[0133] This invention uses magnesium carbide slag to modify aluminate cement, which achieves better modification results compared to using calcium carbonate. It not only helps to realize the resource utilization of magnesium slag, but also helps to reduce the mining and utilization of non-renewable limestone resources, significantly reducing the cost of modified aluminate cement and facilitating the widespread use of aluminate cement.

[0134] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified aluminate cement, characterized in that, The modified aluminate cement comprises aluminate cement and magnesium carbide slag. The mass percentage of magnesium carbide slag in the modified aluminate cement is 20%-30%.

2. The modified aluminate cement as described in claim 1, characterized in that, The magnesium carbide slag is prepared by a method comprising the following steps: (1) The magnesium slag is dried and ground to obtain magnesium slag powder; (2) Mix the magnesium slag powder with water evenly to obtain magnesium slag slurry; (3) Under constant temperature conditions of 20-30℃, carbon dioxide gas is introduced into the magnesium slag slurry, and the carbonization reaction is carried out until the pH of the magnesium slag slurry reaches 6.5-7.

5. The solid and liquid are separated to obtain the carbonized magnesium slag.

3. The modified aluminate cement as described in claim 2, characterized in that, Step (2) also includes the step of adding sodium bicarbonate to the magnesium slag dry powder; The mass of sodium bicarbonate is 0.8%-1.2% of the mass of the magnesium slag dry powder.

4. A cement product, characterized in that, The cement product comprises the modified aluminate cement as described in any one of claims 1-3.

5. A concrete product, characterized in that, The components of the concrete product include the modified aluminate cement as described in any one of claims 1-3.

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