Method for evaluating cement hydration promotion effect of iron tailing powder as concrete mineral admixture

Abstract

The invention provides a method for evaluating the hydration promotion effect of iron tailing powder as a concrete mineral admixture on cement and a method for determining the closest packing content of the iron tailing powder in the concrete mineral admixture. On the basis of determining the main action mechanism of the iron tailing powder as the mineral admixture, the method for evaluating the hydration effect of the iron tailing powder on the cement is constructed, and theoretical and experimental basis is provided for wide application of the iron tailing powder as the concrete mineral admixture, so that sustainable development of the environment of mining and green production of concrete are realized.

Description

Technical Field

[0001] This invention belongs to the technical field of concrete mineral admixtures and green production materials, and in particular relates to an evaluation method for the effect of iron tailings powder as a concrete mineral admixture on promoting cement hydration. Background Technology

[0002] After ore beneficiation, the remaining waste is called tailings. With the rapid development of China's steel industry, the amount of iron tailings discharged has been increasing, while the comprehensive utilization rate is low, leading to a large accumulation of tailings. This not only represents a huge waste of resources but also causes serious environmental pollution. In particular, the tailings discharged after secondary beneficiation are too fine, and currently, there are few suitable utilization methods found. Therefore, it is particularly important to solve the problem of iron tailings discharge and accumulation, broaden the utilization methods of iron tailings, and improve the comprehensive utilization rate of iron tailings.

[0003] Domestic and international scholars have conducted extensive research on the application of iron tailings in concrete, achieving numerous research results. However, current resource utilization of iron tailings mainly focuses on using tailings ore and tailings sand as coarse and fine aggregates in concrete, respectively. Many enterprises, in order to extract more iron concentrate, have intensified the grinding of iron ore, resulting in iron tailings with a particle size of less than 0.6 mm accounting for over 90%. Iron tailings in this particle size range are too fine and no longer meet the requirements for manufactured sand. Further grinding of iron tailings for use as a mineral admixture in concrete is a new utilization approach. This not only meets the requirements of comprehensive resource utilization but also alleviates the shortage of traditional mineral admixtures such as fly ash.

[0004] However, current research on the use of finely ground iron tailings powder as a mineral admixture mainly focuses on the mechanical properties of concrete, with limited research on the specific mechanism of action of iron tailings powder and a lack of systematic study. It is necessary to conduct in-depth research on the mechanism of action of iron tailings powder as a mineral admixture in concrete and clarify the influence mechanism of iron tailings powder on cement hydration. Summary of the Invention

[0005] Technical Solution: To address the aforementioned technical problems, this invention specifically provides an evaluation method for the effect of iron tailings powder as a concrete mineral admixture on promoting cement hydration. A hydration-promoting evaluation factor k(t) is defined to determine the degree of influence of iron tailings powder on cement hydration. The formula is as follows:

[0006]

[0007] In Formula 1: t is the age; m0 is the Ca(OH)2 content produced by pure cement hydration; n is the Ca(OH)2 content produced by MITC hydration; and w is the amount of iron tailings powder added.

[0008] As another specific embodiment of the present invention, the present invention provides a method for determining the most compact packing content of iron tailings powder in concrete mineral admixtures, the specific steps of which are as follows:

[0009] Step 1: Pre-treat the iron tailings powder and conduct tests, including XRD mineral composition analysis and pozzolanic property analysis. Mix the powder with reference cement and conduct dry particle size analysis, hydration product analysis, and cement mortar mortar activity analysis. After comprehensive analysis of the test results, the mechanism of action and dosage range of the iron tailings powder are preliminarily determined.

[0010] Step 2: Add the iron tailings powder within the range of addition in Step 1 to the reference cement, calculate the theoretical maximum bulk density of the cement admixture, obtain the theoretical dosage for the best filling effect, and compare it with the micropore structure test of iron tailings powder mortar with different dosages to adjust the addition range of iron tailings powder.

[0011] Step 3: Add the iron tailings powder within the dosage range of Step 2 to the reference cement and conduct iron tailings powder mortar tests with different dosages, including mortar slump, compressive strength and activity index. After comprehensive analysis of the test results, obtain the final dosage range of iron tailings powder.

[0012] As an improvement, the pretreatment method for iron tailings powder in step 1 is as follows: the iron tailings are dried at 100-110℃ for 0.5-2 hours, allowed to cool to room temperature, and then mechanically ground to obtain iron tailings powder with a specific surface area of ​​500±20m². 2 / kg.

[0013] As an improvement, in step 1, when the iron tailings powder is subjected to XRD analysis, the average particle size of the powder sample is less than 50 μm, the cross-sectional size of the sample block is (1-2) cm × (0.5-1.5) cm, the thickness is less than 1 cm, the sample is dried at low temperature for 15-30 h before testing, and the scanning step is 0.025°~90°, 4° / min.

[0014] As an improvement, in step 1, when conducting the pozzolanic property analysis test and the cement mortar mortar activity test, the mass ratio of iron tailings powder to reference cement is 7:3.

[0015] As an improvement, the specific steps for calculating the bulk density in step 2 are as follows: First, calculate the volume fraction ψ of the fine powder when the cement-based binary system containing the fine powder reaches its maximum bulk density using a model. p * The model is as follows

[0016]

[0017] In Formula 2, d p For fine powder particles, dc ε represents the cement particle size. o The porosity of cement particles of a single size; Formula 3 is applicable to Formula 4 is applicable

[0018] Then, the mass fractions of different dosages were converted into the corresponding volume fractions; ε o Porosity of cement particles of a single particle size;

[0019] Finally, the theoretical bulk density curves of cement-based binary systems with different amounts or mass fractions of iron tailings powder were determined, and the iron tailings powder content corresponding to the optimal pore filling rate was obtained.

[0020] As an improvement, the amount of hydration products is obtained by testing the hydration products based on the optimal iron tailings powder content in step 1 of the above determination method.

[0021] Beneficial effects: This invention studies the effects of iron tailings powder as a mineral admixture on the mechanical properties and microstructure of concrete through experiments. Based on clarifying the main mechanism of action of iron tailings powder as a mineral admixture, it constructs an evaluation method for the effect of iron tailings powder on cement hydration, providing theoretical and experimental basis for the widespread application of iron tailings powder as a mineral admixture in concrete, so as to achieve the environmentally sustainable development of mining and the green production of concrete. Attached Figure Description

[0022] Figure 1 Comparison of XRD patterns of iron tailings and fly ash in Example 1 of this invention.

[0023] Figure 2 The images shown are powder electron micrographs of iron tailings (a), cement (b), and fly ash (c) in Example 1 of this invention.

[0024] Figure 3 The particle size distribution of iron tailings powder in Example 1 of this invention is shown in the interval (a) and cumulative distribution (b).

[0025] Figure 4 This is a graph showing the pozzolanic properties of activated iron tailings powder in Example 1 of the present invention.

[0026] Figure 5 The microstructure of the MITC, MFAC and SC hardened slurries in Example 1 of this invention is shown.

[0027] Figure 6 This is the EDX spectrum of MITC in Embodiment 1 of the present invention.

[0028] Figure 7 This refers to the mineral composition of the hardened slurry, which consists of MITC, MFAC, and SC, as described in Example 1 of this invention.

[0029] Figure 8 This invention illustrates the effect of iron tailings powder content on the theoretical packing density of cement-based composite materials in Example 2.

[0030] Figure 9 The porosity of iron tailings powder mortar with different dosages is shown in this invention.

[0031] Figure 10 The compressive strength and activity index of iron tailings powder mortar with different dosages are shown in this invention.

[0032] Figure 11 These are the thermal differential-thermal-gravity curves of MITC, MFAC, and SC cement pastes in Example 3 of this invention.

[0033] Figure 12 This refers to the weight loss due to the decomposition of Ca(OH)2 in the MITC, MFAC, and SC cement pastes in Example 3 of this invention. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below, so that those skilled in the art can better understand the advantages and features of the present invention, thereby making a clearer definition of the scope of protection of the present invention. The embodiments described in this invention are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] This invention provides a method for determining the most compacted packing content of iron tailings powder in concrete mineral admixtures, the steps of which are as follows:

[0036] Step 1: Pre-treat the iron tailings powder and conduct tests, including XRD mineral composition analysis and pozzolanic property analysis. Mix the powder with reference cement and conduct dry particle size analysis, hydration product analysis, and cement mortar mortar activity analysis. After comprehensive analysis of the test results, the mechanism of action and dosage range of the iron tailings powder are preliminarily determined.

[0037] Step 2: Add the iron tailings powder within the range of addition in Step 1 to the reference cement, calculate the theoretical maximum bulk density of the cement admixture, obtain the theoretical dosage for the best filling effect, and compare it with the micropore structure test of iron tailings powder mortar with different dosages to adjust the addition range of iron tailings powder.

[0038] Step 3: Add the iron tailings powder within the dosage range of Step 2 to the reference cement and conduct iron tailings powder mortar tests with different dosages, including mortar slump, compressive strength, and activity index. After comprehensive analysis of the test results, the final dosage range of iron tailings powder is obtained. The following examples 1-3 and a comparative example using fly ash will illustrate and introduce the process.

[0039] Example 1

[0040] The iron tailings used in Example 1 came from Qian'an, Hebei Province. The main chemical composition of the finely ground iron tailings powder (ITP) is shown in Table 1. The main chemical components of the iron tailings in Qian'an are SiO2, Fe2O3, MgO, and Al2O3, with SiO2 content exceeding 60%, classifying it as a high-silica iron tailings. The cement used was P·I 42.5 standard cement (PC) produced by China United Cement Group, and the fly ash (FA) was Grade II fly ash (loss on ignition 4.9%) provided by Baoding Thermal Power Plant. The chemical compositions of PC and FA are shown in Table 1.

[0041] Table 1 Chemical composition of iron tailings and fly ash (wt.%)

[0042]

[0043] Pretreatment: Iron tailings were dried at 105℃ for 1 hour and then allowed to cool to room temperature (20℃). Mechanical grinding with a specific surface area of ​​500±20 m² was then performed using an all-around planetary ball mill (MITR-QM-QX). 2 / kg of iron tailings powder.

[0044] 1.1 Test experiment in step 1:

[0045] XRD analysis: Powder samples need to be ground (<50μm); block cross-sectional dimensions are 1cm×1cm, thickness is less than 1cm (at least one flat surface). Low-temperature drying for 24 hours. Equipment model and parameters: Rigaku, Smart Lab-3kw, Japan; scan step size 0.02, 5°~90°, 4° / min.

[0046] Particle size distribution test of iron tailings powder: Dry particle size test was conducted on iron tailings powder, fly ash and cement.

[0047] Volcanic ash characteristic analysis: Iron tailings powder was mixed with reference cement at a 30% internal admixture ratio. 20g of the mixture was quickly poured into a plastic bottle containing 100ml of distilled water (40℃), shaken vigorously for 20s, and then placed in a 40℃ constant temperature incubator. Chemical titration tests were performed at 8d and 15d curing times to determine the CaO content and OH content in the solution. - The concentration of the iron tailings powder was compared with the saturation concentration curve to determine whether the pozzolanic properties of iron tailings powder of different fineness were up to standard.

[0048] Hydration product testing: Thermogravimetric-Differential Scanning Thermal Analysis (TG-DSC) was used. Specifically, the mass ratio of subway tailings powder, fly ash, and cement was 3:7, and the water-cement ratio was 0.4. After thorough mixing, the samples were sealed in centrifuge tubes to minimize the impact of carbonation and cured in a standard curing room to the specified age. After reaching the specified age, the cement stone was removed and soaked in anhydrous ethanol for 24 hours to terminate hydration. The samples were then crushed, ground, and dried at 50℃ for 24 hours. Equipment model: German Netzsch STA449F3 Jupiter; Test conditions for cement hydration product samples: heating rate 10℃ / min, temperature range 30~1000℃; argon atmosphere flow rate 50mL / min; Al crucible.

[0049] Mortar activity testing: 40mm×40mm×160mm prism specimens were prepared, demolded 24 hours after molding, and placed in a standard curing tank at (20±1)℃ for water curing until the specified age. The mass ratio of cement to iron tailings powder was 7:3, and the compressive strength of mortar specimens at different ages was determined by comparison with the same amount of fly ash.

[0050] 1.2 Experimental Results

[0051] See Figure 1 As shown, quartz exhibits distinct diffraction peaks in iron tailings, indicating long-range order in crystalline SiO2. Quartz in fly ash, however, displays broader diffraction peaks, suggesting a loss of long-range order and the presence of glassy SiO2, indicating higher mineral activity than in iron tailings.

[0052] See Figure 2 As shown, iron tailings powder ( Figure 2 (a) and cement particles ( Figure 2 (b) It exhibits an irregular morphology with numerous sharp edges and a rough surface, containing a large amount of coarse cement particles. Most fly ash particles are spherical with numerous micropores. Figure 2 (c)). Fly ash has a morphological effect that reduces viscosity and friction, while iron tailings powder does not have a morphological effect.

[0053] See Figure 3 As shown, the content of iron tailings powder particles in the 1-5μm range is significantly higher than that of cement and fly ash, while the content of coarse particles is relatively lower. The study indicates that a large number of voids smaller than 5μm exist in the packing structure of cement powder. Iron tailings powder with a particle size smaller than 5μm can effectively fill the voids between cement particles, thereby obtaining a more compact packing structure.

[0054] See Figure 4As shown, the test points for iron tailings powder at different ages (8 days and 15 days) are all above the standard concentration curve, indicating that iron tailings powder of this fineness does not have pozzolanic properties and is an inert admixture. This suggests that the main function of iron tailings powder as a mineral admixture in concrete is the physical filling effect of micro-aggregates. In contrast, the test points for fly ash at 15 days fall below the standard concentration curve, indicating that fly ash has pozzolanic properties.

[0055] See Figure 5 The image shows the microstructure of the hydration products of the MITC and MFAC composite cementitious material. To determine whether the irregularly shaped particles with clear boundaries in MITC are iron tailings powder particles, the microstructure of the hydration products of the MITC and MFAC composite cementitious material is analyzed. Figure 5 Points 1, 2, and 3 in (a) were subjected to EDS energy dispersive spectroscopy analysis. The analysis results are as follows: Figure 6 As shown in the figure. EDX spectrum analysis reveals that the main elements in particles 1 and 2 are Si, O, and Fe. The Au content is due to gold sputtering during electron microscopy preparation and is not an element inherent to the particles themselves. Comparing with the chemical elements of iron tailings powder, it can be determined that these irregular particles are iron tailings powder particles that have not undergone hydration. The main elements at position 3 are Si, O, Ca, and Al, indicating a gel-like substance.

[0056] Depend on Figure 5 (a) It can be observed that the iron tailings powder particles have clear boundaries and show no hydration, consistent with the conclusions of the pozzolanic test. The iron tailings powder particles are surrounded by irregularly shaped CSH gel. Figure 5 (b) A small amount of unhydrated glass microspheres can be observed in the hydration products of MFAC composite cementitious materials. A comparison shows that SC hydration hardening products contain significantly more flocculent cementitious materials than MITC and MFAC. MITC and MFAC have fewer hydration products due to the reduction in cement content, and their microstructure is significantly looser than that of SC hardened paste; while the hardened paste of MITC is looser than that of MFAC.

[0057] The mineral composition of the hardened paste of MITC and MFAC composite cementitious materials is shown in the figure. Figure 7 The hardened pastes were compared with those made from pure cement paste. A comparison of the mineral composition of the hardened pastes revealed that calcium hydroxide was formed in the hardened pastes of MITC, MFAC, and SC, and all contained small amounts of unhydrated cement particles, dicalcium silicate and tricalcium silicate. The comparison showed that the diffraction peaks of dicalcium silicate and tricalcium silicate were weakened in MITC and MFAC, indicating a relatively lower number of unhydrated cement particles. Figure 5 Electron microscopy images show that hydrated calcium silicate gels and other gel-like substances are the main hydration products of MITC, MFAC, and SC. However, these substances belong to the gel-like category and therefore are not visible in the crystal diffraction patterns characterized by XRD.

[0058] The hydration product spectrum of MITC composite cementitious material still shows strong quartz diffraction peaks. Quartz is the main mineral phase of iron tailings powder, further proving that iron tailings powder, as a mineral admixture, basically does not undergo a hydration reaction. The hydration product spectrum of MFAC composite cementitious material shows a small amount of dolomite and mullite diffraction peaks, indicating that FA was not completely hydrated during the hydration process of the composite cementitious material.

[0059] Example 2

[0060] The volume fraction ψ of the fine powder was calculated using a model to determine the maximum bulk density of a cement-based binary system containing fine powder. p * The model is as follows

[0061]

[0062] In formula (2), d p For fine powder particles, d c ε represents the cement particle size. o The porosity of cement particles of a single size; Formula (3) is applicable to Formula (4) is applicable

[0063] Then, the mass fractions of different dosages were converted into the corresponding volume fractions; ε o Porosity of cement particles of a single particle size;

[0064] Finally, the theoretical bulk density curves of cement-based binary systems with different amounts or mass fractions of iron tailings powder were determined, and the iron tailings content corresponding to the optimal pore filling rate was obtained. Table 2 shows the numerical values ​​of the flowability of the mortar with different amounts of iron tailings powder according to this invention.

[0065] Table 2. Mortar mix proportions and flowability for different iron tailings powder admixtures

[0066]

[0067] Table 2 shows that when the iron tailings powder content is below 30%, the flowability ratio of MITC mortar to SC mortar does not change significantly, both remaining within 3%. However, when the iron tailings powder content reaches 40%, the flowability decreases by 4.5%. Using formula 2-4 and Table 2, the theoretical packing density of the cement-based binary system with different iron tailings powder contents (mass fraction) is calculated. Figure 8 As shown. Wherein: the particle size d of the fine particles p The particle size of cement particles is μm; d c The thickness is μm; the density of the iron tailings powder is 2.78 g / cm³. 3 The density of cement is 3.15 g / cm³. 3 The mass fractions of different dosages are converted into corresponding volume fractions; εo The porosity of cement particles of a single size is taken as 0.52.

[0068] With the increase of iron tailings powder content, the theoretical packing density of the cement-based binary system first increases and then decreases. When the iron tailings powder content is 20% (mass fraction), the theoretical packing density of the cement-based binary system reaches its maximum value of 0.63. When the iron tailings powder content exceeds 20%, the theoretical packing density of the cement-based binary system decreases rapidly. Theoretically, this indicates that the iron tailings powder content should not be too high, otherwise it will cause a decrease in packing density, thereby affecting the pore structure of the system and its strength and durability. When the iron tailings powder content is 20%, the total porosity and the amount of harmful pores (…) Figure 9 The pore size was lower than that of pure cement mortar specimens, and at the same time, the number of harmful pores was the least in the pore distribution.

[0069] This is because iron tailings powder is finer than cement particles, and its particle size distribution provides excellent filling effect, making the concrete structure denser. This aligns with the conclusion that a 20% iron tailings powder content results in the highest theoretical bulk density. Therefore, a 20% iron tailings powder content provides the optimal filling effect.

[0070] The compressive strength and activity index of mortar specimens with different iron tailings powder contents were measured after standard curing to different ages. Figure 10 As the amount of iron tailings powder added increases, the compressive strength of the mortar specimens continuously decreases, especially when the addition exceeds 30%, where the compressive strength decreases significantly. The compressive strength of mortar specimens with different iron tailings powder additions at 28 days was compared with that of pure cement mortar specimens at the same age. The relative compressive activity index of different iron tailings powder additions is shown in the figure. Figure 10 (b)

[0071] When the ITP content exceeds 36%, the activity index will be lower than 60%. In accordance with the industry standard requirements for iron tailings powder, the optimal content of iron tailings powder is adjusted to 30%.

[0072] Example 3

[0073] In this embodiment, thermogravimetric analysis (TG-DSC) was used to test the thermogravimetric curves (W / B = 0.4) of the hydration products of MITC composite cementitious materials and MFAC composite cementitious materials at 1d, 3d, 7d, 28d, and 56d of hydration. Figure 11 As shown, the hydration products of pure cementitious materials with the same water-cement ratio are compared.

[0074] Comparison of the TG curves of the hydration products of iron tailings powder cementitious composite (MITC), fly ash cement-based composite cementitious material (MFAC), and cement hydration products revealed three main endothermic peaks: 40-200℃, 400-550℃, and 600-800℃. This indicates a similarity in the types of hydration products of iron tailings powder cementitious composite, fly ash cement-based composite cementitious material, and cement.

[0075] Ca(OH)2 decomposes and dehydrates at around 400–500℃. Its weight loss range usually does not overlap with any other thermal weight loss effect, so the Ca(OH)2 content results obtained are reliable. The percentage content of Ca(OH)2 in the hydrated sample can be calculated based on the weight loss within this range.

[0076] Furthermore, the Ca(OH)2 content in the MITC and MFAC composite cement paste was characterized using a semi-quantitative weight loss method at 425–525℃. Within this range, the weight loss was as follows: Figure 12 As shown.

[0077] Depend on Figure 12 It can be seen that the weight loss of Ca(OH)2 in iron tailings powder cement-based composite cementitious slurry and pure cement slurry generally increases with age, which is a result of the continuous increase in Ca(OH)2 generated by cement hydration. However, in fly ash cement-based composite cementitious slurry, during the early stage of hydration (1-7 days), the weight loss of Ca(OH)2 increases with age. This is mainly because the degree of fly ash hydration reaction is low at this stage, and the consumption of Ca(OH)2 by fly ash hydration reaction is much lower than the amount generated by cement hydration reaction.

[0078] At 28 days, the weight loss of Ca(OH)2 in the fly ash cement-based composite cementitious material slurry showed a significant decrease, indicating an increased degree of fly ash hydration reaction at this stage. At 56 days, the weight loss increased, indicating an increase in Ca(OH)2, but the increase was lower than in the early hydration stage. This suggests that the consumption of Ca(OH)2 by the fly ash hydration reaction at this stage was lower than the amount of cement generated, indicating that fly ash improves the hydration environment and has a certain promoting effect on cement hydration.

[0079] It was also observed that, except for the 1-day curing period, the Ca(OH)₂ content in both MITC and MFAC composite cement pastes was lower than that in SC cement paste. This is mainly because the addition of admixtures reduced the amount of cement, decreasing the degree of hydration reaction of the composite cementitious materials and thus reducing the amount of Ca(OH)₂ produced. The Ca(OH)₂ content in MITC composite cement pastes at all curing ages was higher than that in MFAC. This is because fly ash has pozzolanic properties, and the secondary hydration of fly ash consumes some of the Ca(OH)₂, resulting in a decrease in the remaining Ca(OH)₂ in the MFAC composite paste.

[0080] This result confirms that the pozzolanic properties of iron tailings powder are far lower than those of fly ash. In the microstructure of concrete, Ca(OH)2 is mostly enriched in the transition zone between aggregates and cement paste as platy crystals, which is an important reason why the transition zone becomes the weakest area in concrete. Fly ash can consume some calcium hydroxide and generate CSH gel, which can enhance the microstructure of the transition zone, thus improving the later strength of hardened concrete, reducing its later permeability, and improving its durability.

[0081] The Ca(OH)2 content of MITC and MFAC was compared with the Ca(OH)2 loss of pure cement paste and normalized. The relative Ca(OH)2 content in MITC and MFAC composite cement paste is shown in Table 3.

[0082] Table 3. Relative Ca(OH)2 content in MITC and MFAC composite cement pastes

[0083]

[0084] Table 3 shows that the relative Ca(OH)2 content of MITC paste was greater than 70% at all ages. Since the cement content in MITC composites was 70%, and iron tailings powder did not participate in the hydration reaction, it did not affect the Ca(OH)2 content. This further indicates that the incorporation of iron tailings powder promoted cement hydration. Simultaneously, it can be observed that the Ca(OH)2 content of MFAC at all ages was lower than that of MITC, and the relative content was generally around 70%. The Ca(OH)2 content in the hydration products of MFAC depends on the consumption of fly ash in the hydration reaction and the amount of cement hydration generated. Fly ash also has a certain promoting effect on cement hydration.

[0085] In this invention, the optimal dosage of iron tailings powder was used in the hydration product testing experiment. A promoting factor was defined as a characterizing parameter for the promoting effect of iron tailings powder on cement hydration. The hydration promotion evaluation factor k(t) was defined as follows:

[0086]

[0087] In Formula 1: t is the age; m0 is the Ca(OH)2 content produced by pure cement hydration, n is the Ca(OH)2 content produced by MITC hydration, and w is the amount of iron tailings powder added; the promoting factor is used as a characterization parameter to represent the promoting effect of iron tailings powder on cement hydration. The increase rate of Ca(OH)2 content generated by cement hydration is used to characterize the promoting effect of admixture on cement hydration. It should be noted that Formula (1) is based on the mechanism of action of iron tailings powder as a concrete mineral admixture. Through the analysis of mineral composition, pozzolanic effect and micromorphology of iron tailings powder, it can be determined that iron tailings powder itself does not participate in the hydration reaction.

[0088] In this invention, as summarized above, the final result is that when the iron tailings powder content is 30%, the hydration promotion factor of iron tailings powder on cement hydration for 28 days is 22.62%.

[0089] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for evaluating the effect of iron tailings powder as a mineral admixture in concrete on promoting cement hydration, characterized in that: Define a hydration-promoting evaluation factor k(t) to determine the degree of influence of iron tailings powder on cement hydration, as follows: In Formula 1: t is the age; m0 is the Ca(OH)2 content produced by pure cement hydration; n is the Ca(OH)2 content produced by MITC hydration; and w is the amount of iron tailings powder added.

2. A method for determining the most compacted packing content of iron tailings powder in concrete mineral admixtures, characterized by the following specific steps: Step 1: Pre-treat the iron tailings powder and conduct tests, including XRD mineral composition analysis and pozzolanic property analysis. Mix the powder with reference cement and conduct dry particle size analysis, hydration product analysis, and cement mortar mortar activity analysis. After comprehensive analysis of the test results, the mechanism of action and dosage range of the iron tailings powder are preliminarily determined. Step 2: Add the iron tailings powder within the range of addition in Step 1 to the reference cement, calculate the theoretical maximum bulk density of the cement admixture, obtain the theoretical dosage for the best filling effect, and compare it with the micropore structure test of iron tailings powder mortar with different dosages to adjust the addition range of iron tailings powder. Step 3: Add the iron tailings powder within the dosage range of Step 2 to the reference cement and conduct iron tailings powder mortar tests with different dosages, including mortar slump, compressive strength and activity index. After comprehensive analysis of the test results, obtain the final dosage range of iron tailings powder.

3. The determination method according to claim 2, characterized in that: The specific method for pretreating iron tailings powder in step 1 is as follows: drying the iron tailings at 100-110℃ for 0.5-2 hours, allowing the dried tailings to cool to room temperature, and then mechanically grinding them to obtain iron tailings powder with a specific surface area of ​​500±20m². 2 / kg.

4. The determination method according to claim 2, characterized in that: In step 1, when the iron tailings powder was subjected to XRD analysis, the average particle size of the powder sample was less than 50 μm, the cross-sectional size of the sample block was (1-2) cm × (0.5-1.5) cm, and the thickness was less than 1 cm. Before the test, the sample was dried at low temperature for 15-30 h, and the scanning step was 0.025°~90°, 4° / min.

5. The determination method according to claim 2, characterized in that: In step 1, when conducting the mortar activity test of the cement mortar, the mass ratio of iron tailings powder to the reference cement is 7:

3.

6. The determination method according to claim 2, characterized in that: The specific steps for calculating the bulk density in step 2 are as follows: First, the volume fraction ψ of the fine powder is calculated using a model to determine the maximum bulk density of the cement-based binary system containing the fine powder. p * The model is as follows In Formula 2, d p For fine powder particles, d c ε represents the cement particle size. o The porosity of cement particles of a single size; Formula 3 is applicable to Formula 4 is applicable Then, the mass fractions of different dosages were converted into the corresponding volume fractions; ε o Porosity of cement particles of a single particle size; Finally, the theoretical bulk density curves of cement-based binary systems with different amounts or mass fractions of iron tailings powder were determined, and the iron tailings content corresponding to the optimal pore filling rate was obtained.

7. The determination method according to claim 2, characterized in that: The amount of hydration products was obtained by testing the hydration products based on the optimal iron tailings powder content in step 1.

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