Methods for evaluating the early cement hydration and product crystallization induced by two-component additives

Abstract

This invention provides a method for evaluating the early cement hydration and product crystallization induced by a two-component additive, relating to the field of cement-based material preparation and testing technology. The method includes: step S1, preparing solid hydration products; step S2, detecting the XRD diffraction pattern of the solid hydration products; step S3, reading the intensity of specific diffraction peaks in the XRD pattern; and step S4, calculating the diffraction peak intensity ratio to characterize the early cement hydration and crystallization process. In this invention, the two-component additive promotes the development of early cement strength and effectively inhibits the premature crystallization of Ca(OH)₂ crystals. The peak intensity ratios of C₃S, Ca(OH)₂, and AFt relative to β-C₂S obtained from the sample XRD pattern effectively characterize the variation law of early cement hydration and crystallization.

Description

Technical Field

[0001] This invention relates to the field of cement-based material preparation and testing technology, and in particular to a method for evaluating the early cement hydration and product crystallization induced by two-component additives. Background Technology

[0002] Cement concrete pavement materials used in road engineering are subjected to repeated shearing and compression from traffic loads. Optimizing composition, reducing harmful pores, and improving the bonding strength of each phase are crucial guarantees for improving their durability. Reducing harmful pores and improving bonding strength boils down to improving the material's macroscopic properties, namely, flexural strength. Flexural strength is an important indicator in road concrete design.

[0003] Various measures can be taken to improve the flexural strength of concrete, such as increasing the bond strength between aggregates and cement paste; introducing millimeter-centimeter length fibers into the concrete; forming a polymer network structure in the concrete structure through polymer composites for reinforcement; incorporating micrometer-millimeter scale whiskers into the cement paste for reinforcement; increasing the CSH gel content, optimizing gel distribution, and increasing the density of the hardened paste to improve flexural strength. These measures provide effective solutions for improving the flexural strength and durability of cement concrete pavement materials from different scales and perspectives.

[0004] Existing technologies have found that magnesium carbonate trihydrate has a setting-accelerating effect on silicate cements and can be used to prepare concrete quick-setting agents. However, the effect of magnesium carbonate trihydrate on cement paste is mainly concentrated in a short period of a few hours. For longer periods of 1 to 7 days, other additives are needed to work together. Furthermore, the evaluation of the crystallization of its hydration products requires more parameters for comparison and analysis compared to the existing technology of adding magnesium carbonate trihydrate alone, which only requires calculating the ratio of diffraction peak intensities of the Ca(OH)2(001) crystal plane and the β-C2S(021) crystal plane using the XRD pattern of the crystallized product. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating the early hydration and product crystallization of cement induced by a two-component additive based on magnesium carbonate trihydrate. By using magnesium carbonate trihydrate in combination with another additive, hydration is continuously induced from the start of cement-water mixing, and a positive impact is placed on the crystallization process of the hydration products. Specifically, the evaluation method of this invention is as follows:

[0006] A method for evaluating the early cement hydration and product crystallization induced by two-component additives includes:

[0007] Step S1: Mix magnesium carbonate trihydrate with another additive, cement, and water to obtain a slurry. Mix the slurry at a certain temperature and in the absence of air for a certain period of time. After reaching the specified age, filter the slurry to obtain solid hydration products.

[0008] Step S2: Perform XRD tests on the solid hydration products and obtain the data and diffraction patterns after background removal;

[0009] Step S3: In the background-removed diffraction pattern, select the AFt(100) crystal plane of ettringite, the (001) crystal plane of Ca(OH)2, the (040) crystal plane of C3S (tricalcium silicate), and the (021) crystal plane of β-C2S (dicalcium silicate), and read the corresponding diffraction peak intensities, denoted as I. E(100) I P(001) I A(040) and I L(021) ;

[0010] Step S4: Calculate the ratios I of the peak intensities of AFt, Ca(OH)2, and C3S relative to β-C2S. E(100) / I L(021) I P(001) / I L(021) and I A(040) / I L(021) Values, abbreviated as I E / I L I P / I L and I A / I L To characterize the early hydration and crystallization process of cement;

[0011] At least two samples of different ages should be tested.

[0012] Furthermore, in step S1, another additive is selected from one of nano-SiO2, nano-Al2O3, hard calcium silicate (6CaO·6SiO2·H2O, Xon), anhydrous magnesium carbonate (MgCO3), hydromagnesia (4MgCO3·Mg(OH)2·4H2O), and calcium-magnesium carbonate (Mg3Ca(CO3)4). This additive can react with the Ca in the cement slurry after the effect of magnesium carbonate trihydrate disappears. 2+ Ion interaction generates sedimentary phases such as CSH, CaSO4·2H2O, CaCO3, CaMg(CO3)2, Ca(OH)2, AFt(3CaO·Al2O3·3CaSO4·32H2O), and AFm(3CaO·Al2O3·CaSO4·12H2O) that do not adversely affect cement properties, and continuously consumes the Ca in the slurry within 1 to 7 days. 2+ ion.

[0013] Furthermore, in step S1, another additive is preferably calcium silicate (6CaO·6SiO2·H2O, Xon) or nano-SiO2, because it reacts with Ca... 2+ Ionic interactions can generate CSH gels and similar CSH gel-like substances.

[0014] Furthermore, in step S1, the mass of water is more than 10 times the sum of the mass of magnesium carbonate trihydrate, another additive, and cement; the mixing temperature of the slurry is 10-50℃; and the specified age is no more than 7 days.

[0015] Furthermore, the mixing and stirring process of the slurry in step S1 includes:

[0016] Step S11: Pour the mixed slurry into the container, ensuring that the volume of the mixed slurry does not exceed 2 / 3 of the container's capacity, and seal the container opening;

[0017] Step S12: Quickly shake the container, with one cycle consisting of 10 forward shakes followed by 10 reverse shakes. Shake for two cycles each at 10 min, 30 min, and 1 h after adding water; then shake for two cycles every 1 h; after 24 h, shake for two cycles every 3 h; and shake for two cycles again when the specified age is reached.

[0018] In this invention, magnesium carbonate trihydrate is used in combination with another additive to continuously induce hydration from the beginning of cement and water mixing, and has a positive impact on the crystallization process of the hydration products.

[0019] In this invention, the evaluation of early cement hydration and its product crystallization is conducted using peak intensity ratios in XRD diffraction spectra, with the addition of C3S (tricalcium silicate) and AFt (calcium vanadate) indicators. AFt, like Ca(OH)2, is an early cement hydration product. CSH gel is a low-crystallinity hydration product with indistinct diffraction peaks in XRD spectra, making it difficult to process. Cement clinker mineral C3S undergoes early-stage hydration, producing CSH gel and Ca(OH)2 as hydration products. The phase composition of these hydration products may change under the influence of additives; for example, the addition of magnesium carbonate trihydrate may also generate CaCO3. Once C3S hydrates, the diffraction peak intensity of C3S in the hydration sample decreases. β-C2S, with very limited hydration within 7 days, is suitable as a reference phase for the early cement hydration process.

[0020] Select the ettringite (100) crystal plane (2θ=9.091°, JCPDS) respectively. # 41-1451), the (001) crystal plane of Ca(OH)2 (2θ=18.007°, JCPDS) #44-1481), C3S (040) crystal plane (2θ=51.469°, JCPDS) # 49-0442) and the (021) crystal plane of β-C2S (2θ=31.059°, JCPDS) # The diffraction peak intensities of 33-0302 were calculated and compared. Among them, the (100) crystal plane of ettringite is the crystal plane with the strongest diffraction peak of ettringite crystal, the (001) crystal plane of Ca(OH)2 is the crystal plane of the Z-axis direction of the plate-like crystal, that is, the crystal plane of the thickness direction of the plate-like crystal, and the diffraction peaks of the (040) crystal plane of C3S and the (021) crystal plane of β-C2S have no superposition of other phase peaks, which makes it easy to read the data.

[0021] The original diffraction data were processed using the XRD phase analysis software Jade to remove background values, resulting in background-removed data. After background removal, the diffraction peak intensities of the ettringite (100) crystal plane, Ca(OH)₂ (001) crystal plane, C₃S (040) crystal plane, and β-C₂S (021) crystal plane were recorded as I. E(100) I P(001) I A(040) and I L(021) Calculate I E(100) / I L(021) I P(001) / I L(021) and I A(040) / I L(021) Value. To concisely represent the quotient (relative peak intensity) of the three peak intensities, I E(100) / I L(021) I P(001) / I L(021) and I A(040) / I L(021) Abbreviated as I E / I L I P / I L and I A / I L This invention relates to the peak intensity ratios of C3S, Ca(OH)2, and AFt relative to β-C2S obtained from the XRD spectra of samples, i.e., I... A / I L I P / I L and I E / I L This is used to characterize the early hydration and crystallization process of cement.

[0022] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0023] This invention utilizes magnesium carbonate trihydrate in combination with another additive to continuously induce hydration from the start of cement mixing with water, and positively influences the crystallization process of the hydration products. This allows the clinker minerals to crystallize in a low-Ca environment. 2+ Hydration under high concentration conditions leads to the formation of more and more stable CSH gel. This two-component additive promotes the development of early-age strength in cement and effectively inhibits premature crystallization of Ca(OH)₂ crystals, making it suitable as an additive for cement-based materials in applications requiring rapid hardening and early strength. The peak intensity ratio of C₃S, Ca(OH)₂, and AFt relative to β-C₂S, obtained from the XRD patterns of the samples, is shown in Figure I. A / I L I P / I L and I E / I L This method better characterizes the changes in early-stage cement hydration and crystallization, and can be used as a useful supplement to the study of phases, microstructure and macroscopic properties related to early-stage cement hydration. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 These are the XRD patterns of the 7d sample after background removal in Example 1 of this invention, and the diffraction peak positions corresponding to the four phase crystal planes.

[0026] Figure 2 The images show the SEM morphology of cement hydration products in the samples of this invention, wherein (a) is a morphology image of Ca(OH)2 crystals in the 7-day-old sample of Comparative Example 1; (b) is a morphology image of hydration products AFt and Ca(OH)2 crystals in the 1-day-old sample of Example 1; (c) is a morphology image of hydration products AFt and Ca(OH)2 crystals in the 1-day-old sample of Comparative Example 3; and (d) is a morphology image of AFt crystals in the 1-day-old sample of Comparative Example 1. Detailed Implementation

[0027] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0028] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0029] In this embodiment of the invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent. Similarly, the terms "of," "corresponding," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent.

[0030] In this embodiment of the invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0031] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0032] This invention provides a method for evaluating the early hydration and product crystallization of cement induced by a two-component additive based on magnesium carbonate trihydrate. By combining magnesium carbonate trihydrate with another additive, hydration is continuously induced from the start of cement-water mixing, positively impacting the crystallization process of the hydration products. This method promotes the early hydration of silicate cements and induces product crystallization, improving the mechanical properties and durability of cement materials.

[0033] The aforementioned silicate cements are cement varieties containing clinker minerals C3S and β-C2S. Their strength before 7 days is mainly obtained from the hydration reaction of C3S and a small amount of β-C2S. These include general-purpose silicate cements such as PI and PII type silicate cements, PO ordinary silicate cements, PS slag silicate cements, PF fly ash silicate cements, PP pozzolanic silicate cements, and PC composite silicate cements, as well as PR road silicate cements. When silicate cements are mixed with water, the highly reactive clinker minerals undergo hydration, and the Ca in the slurry increases. 2+ Ions, OH - The ion concentration increases rapidly, and the pH value can reach above 11 within 1 minute. Magnesium carbonate trihydrate dissociates in highly alkaline cement slurry to form CO3. 2- Ions rapidly consume Ca in the slurry 2+ Ions promote the early setting and hardening of silicate cement.

[0034] Magnesium carbonate trihydrate is used in combination with another additive, which, after the effect of magnesium carbonate trihydrate disappears, reacts with the Ca in the cement slurry. 2+ Ion interaction, continuing to consume Ca 2+ Ions, enabling clinker minerals to be in low Ca content 2+ Under concentrated conditions, continuous hydration forms more and more stable CSH gels. These additives include nano-SiO2, nano-Al2O3, calcium silicate (6CaO·6SiO2·H2O, Xon), anhydrous magnesium carbonate (MgCO3), hydromagnesia (4MgCO3·Mg(OH)2·4H2O), and calcium carbide (Mg3Ca(CO3)4), etc. Among these, the CaO-SiO2 system additives are preferred because they react well with Ca... 2+ Ion interactions generate CSH gels and CSH-like gels.

[0035] The mixture of the above-mentioned two-component additives is thoroughly mixed with silicate cement, and then further mixed with water at least 10 times the weight of the solid powder in a mixing device. The mixture is then placed in a sealed container at a temperature of 10℃ to 50℃ and stirred periodically to prevent the solids from agglomerating and settling. After reaching the specified curing period, the slurry is filtered, and the solid hydration products on the filter are used to stop hydration. The hydrated sample is then dried in an air-isolated environment at a temperature below 50℃ and ground to a fineness of 200 mesh or higher as required for XRD powder diffraction testing.

[0036] The sample powder was subjected to XRD analysis using an X-ray diffractometer. The diffraction angle 2θ ranged from 5° to 70°, and the scan rate was no less than 0.02° / s, obtaining initial diffraction data and spectra. After background removal processing of the initial diffraction spectra, the data after background removal were obtained. Figure 1 The diffraction pattern shown is shown. Figure 1 The diffraction pattern shown is based on the AFt(100) crystal plane of ettringite (2θ = 9.091°, JCPDS). # 41-1451), the (001) crystal plane of Ca(OH)2 (2θ=18.007°, JCPDS) # 44-1481), C3S (040) crystal plane (2θ=51.469°, JCPDS) # 49-0442) and the (021) crystal plane of β-C2S (2θ=31.059°, JCPDS) # 33-0302), read the corresponding diffraction peak intensities, and record them as I. E(100) I P(001) I A(040) and I L(021) , Figure 1 Chinese is abbreviated as I E I PI A and I L Because the hydration degree of cement clinker mineral β-C2S is very limited in a short age of less than 7 days, the peak intensity (IL) in the XRD diffraction spectrum is low. L The value will not change significantly, so it is used as a reference peak intensity. The AFt(100) crystal plane is the strongest crystal plane for diffraction peaks of ettringite crystal. The (001) crystal plane of Ca(OH)2 is the Z-axis crystal plane of the plate-like crystal, that is, the thickness direction crystal plane of the plate-like crystal. The diffraction peaks on the (040) crystal plane of C3S and the (021) crystal plane of β-C2S have no superposition of other phase peaks, which makes it easy to read the data.

[0037] Calculate the ratios I of the peak intensities of AFt, Ca(OH)2, and C3S relative to β-C2S. E(100) / I L(021) I P(001) / I L(021) and I A(040) / I L(021) Values, abbreviated as I E / I L I P / I L and I A / I L This is used to characterize the early hydration and crystallization process of cement.

[0038] AFt, like Ca(OH)2, is an early hydration product of cement. CSH gel is a low-crystallinity hydration product with indistinct diffraction peaks in XRD spectra, making it difficult to process. Cement clinker mineral C3S undergoes early-stage hydration, producing CSH gel and Ca(OH)2 as hydration products. Under the influence of additives, the phase composition of the hydration products changes. Once C3S hydrates, the diffraction peak intensity of C3S in the hydration sample decreases, while the hydration degree of β-C2S is very limited in the short age (within 7 days). As the cement clinker mineral C3S continues to hydrate, the amount of Ca(OH)2 precipitated increases, plate-like crystals develop, and the plate surface becomes thicker, increasing the intensity of its (001) plane diffraction peak. P / I L The value increases. Figure 2 (a) The crystal morphology of Ca(OH)₂ in PI-type silicate cement after hydration in 20 times its weight of water for 7 days shows well-developed plate-like crystals. When additives are present, the formation of Ca(OH)₂ is altered, resulting in incomplete crystal development, such as... Figure 2 The dense particles between (b) and (c) cause I P / I L The value decreases. AFt is a reaction product of C3A, C4AF and gypsum in clinker. AFt develops well in the absence of additives, such as... Figure 2(d) Needle-like crystals. However, the addition of additives can also affect the crystallization process of AFt, thus affecting the growth of AFt crystals, such as... Figure 2 (b) and (c) needle-like to columnar crystals.

[0039] The analysis results at different time points were compared, focusing on the influence of magnesium carbonate trihydrate and its synergistic effect with other additives on the early hydration reaction rate and product crystal phase of cement. The inducing effect of different additive combinations on cement hydration was systematically evaluated using quantitative indicators. Based on the experimental data, the optimal addition ratio of magnesium carbonate trihydrate and its optimal combination with other additives were determined. Simultaneously, the influence mechanism of each component on the cement hydration process and product formation was summarized, providing a theoretical basis for further optimization of cement performance.

[0040] This invention relates to a method for evaluating early cement hydration and product crystallization induced by a two-component additive based on magnesium carbonate trihydrate. By combining magnesium carbonate trihydrate with another additive, hydration is continuously induced from the start of cement-water mixing, positively impacting the crystallization process of the hydration products. This allows clinker minerals to crystallize in a low-Ca environment. 2+ Hydration under high concentration conditions leads to the formation of more and more stable CSH gel. The two-component additive in this method promotes the development of early-age strength in cement and effectively inhibits premature crystallization of Ca(OH)₂ crystals. It can be used as an additive in cement-based materials for applications requiring rapid hardening and early strength. The peak intensity ratios of C₃S, Ca(OH)₂, and AFt relative to β-C₂S obtained from the sample XRD spectra better characterize the changes in early-age hydration crystallization in cement. This evaluation method can be a valuable supplement to the study of phases, microstructure, and macroscopic properties related to early-age hydration in cement.

[0041] The following description, in conjunction with specific embodiments, illustrates this point.

[0042] Example 1

[0043] This is a sample co-doped with magnesium carbonate trihydrate and nano-SiO2. 50 parts of PI 42.5 silicate cement and 2.5 parts of magnesium carbonate trihydrate powder with a specific surface area of ​​200 m² were mixed. 2Mix 2.5 parts of nano-SiO2 powder (at a concentration of 1 g / g) and pour the mixture into a suitable, sealable plastic container. Add water, approximately 20 times the total mass of the powder, and stir rapidly until no powder lumps remain in the slurry. Stirring time should be less than 1 minute, and the slurry volume should not exceed 2 / 3 of the container's capacity. Seal the container to prevent further mixing with CO2 from the air. Vigorously shake the container to prevent solid agglomeration and sedimentation. Shake 10 times clockwise, then invert the container and shake 10 times, constituting one cycle. Shake for two cycles each at 10 min, 30 min, and 1 h after adding water, then shake for two cycles every 1 h thereafter. After 24 h, shake for two cycles every 3 h. Upon reaching the designated age, shake for two cycles, filter the slurry, and after stopping the hydration of the solid hydration products on the filter, dry them at 50°C in the absence of air.

[0044] Hydration products aged 1 day and 7 days were ground and then subjected to XRD powder diffraction, yielding two sets of initial diffraction data. After removing background values ​​from the initial diffraction patterns, the diffraction peak intensities of the (100) plane of AFt, the (001) plane of Ca(OH)2, the (040) plane of C3S, and the (021) plane of β-C2S were read, i.e., I E I P I A and I L I was calculated E / I L I P / I L and I A / I L The values ​​are listed in Table 1. The relative peak intensity ratio I of the hydration products AFt and Ca(OH)2 in the 1-day aged samples is... E / I L I P / I L The values ​​were 0.8712 and 0.1299, respectively. The smaller the value, the worse the crystal development and the lower the content. This indicates that the hydration product Ca(OH)2 of the 1-day-old sample was less developed than that of the AFt crystal. Figure 2 (b) shows the crystal morphology of hydration products AFt (acicular-columnar) and Ca(OH)2 (intermediate dense particles) in the 1-day-old sample. Hydration product I in the 7-day-old sample... E / I L I P / I L The values ​​were 0.5651 and 2.1613, respectively, indicating that as the hydration process proceeded, the Ca(OH)2 crystals in the sample were further developed, and the degree of change exceeded that of AFt.

[0045] The relative peak intensity ratio I of C3S in 1d and 7d aged samplesA / I L The values ​​were 1.6050 and 1.4810, respectively, relative to the I values ​​of unhydrated PI 42.5 silicate cement. A / I L The value was 3.9169, showing a significant decrease, with the 1-day-old sample showing a decrease of 59.02%. However, the 7-day-old sample did not show a large decrease compared to the 1-day-old sample, only 7.73%.

[0046] The above results indicate that the co-admixture of magnesium carbonate trihydrate and nano-SiO2 promotes the hydration of C3S within 1 day, which is beneficial to the early strength development of cement. It also inhibits the growth and development of AFt and Ca(OH)2 crystals, resulting in finer crystals and a more uniform distribution in the paste structure. The fine Ca(OH)2 crystals are beneficial for the long-term strength development of mixed silicate cements containing mineral powders such as slag and fly ash, and therefore are suitable as co-admixtures for this type of cement.

[0047] Example 2

[0048] Other conditions were the same as in Example 1, except that another additive was replaced with hard silicate powder. The I values ​​of the 1-day and 7-day aged samples were tested. E / I L I P / I L and I A / I L The values ​​are listed in Table 1. The relative peak intensity ratio I of the hydration product AFt in 1-day and 7-day aged samples is shown. E / I L The values ​​were 0.6952 and 0.3304, respectively, slightly lower than the corresponding values ​​of the sample in Example 1. However, the I value of the hydration product Ca(OH)2 in its 1-day aged sample was higher. P / I L The value was only 0.2065, slightly larger than the corresponding value of the sample in Example 1. This indicates that the dual-component co-doping of magnesium carbonate trihydrate and calcium silicate also inhibited the early crystallization of Ca(OH)2.

[0049] The relative peak intensity ratio I of C3S in 1d and 7d aged samples A / I L The values ​​were 1.7170 and 0.7237, respectively, relative to the I of unhydrated cement. A / I L The values ​​also showed a significant decrease, with the 1-day-old sample value decreasing by 56.16% and the 7-day-old sample value decreasing by 57.85% compared to the 1-day-old sample.

[0050] The above results indicate that the co-admixture of magnesium carbonate trihydrate and calcium silicate not only promotes the hydration of C3S within 1 day but also maintains a high hydration rate within 7 days, which is beneficial to the early strength development of cement. Simultaneously, it also inhibits the growth and development of AFt and Ca(OH)2 crystals to a certain extent, resulting in finer crystals and a more uniform distribution. When magnesium carbonate trihydrate and calcium silicate are used as a two-component additive in mixed silicate cement, it will also be beneficial to the long-term strength development of this type of cement.

[0051] Comparative Example 1

[0052] This was a blank control sample, and all other conditions were the same as in Example 1, except that no additives, including magnesium carbonate trihydrate, were added. The relative peak intensity ratio of the hydration products AFt and Ca(OH)2 in the 1-day aged sample was I. E / I L I P / I L The values ​​were both 1.5610. For the 7-day-old samples, these two values ​​were 1.0560 and 28.7680, respectively, as shown in Table 1. In both of these blank samples, the diffraction peak intensities of AFt and Ca(OH)2 crystals exceeded those of C2S, indicating that the amount of AFt and Ca(OH)2 generated and the degree of crystal development within 1 day exceeded those of the samples of the same age in Example 1. Furthermore, with the progress of hydration, the Ca(OH)2 crystals in the samples developed significantly, and the I7 value was 1.5610. P / I L The value reached 28.7680. Figure 2 (a) is a morphology diagram of Ca(OH)2 crystals in a 7-day-old sample. Ca(OH)2 develops into plate-like crystals with a thickness of 0.5–1.5 μm. Figure 2 (d) shows the morphology of AFt crystals in a 1-day-old sample, where AFt needle-like crystals are developed.

[0053] The relative peak intensity ratio I of C3S in 1d and 7d aged samples A / I L The values ​​were 2.9268 and 0.7080, respectively, relative to the I values ​​of unhydrated PI 42.5 silicate cement. A / I L The value was 3.9169, and the decrease in the 1-day sample value was 25.28%, which was less than the decrease in the sample of Example 1 with magnesium carbonate trihydrate and nano-SiO2. However, the decrease in the 7-day sample compared to the 1-day sample was significantly greater, reaching 75.81%. It can be seen that the hydration degree of PI cement is limited in the relatively short period of 1 day, while the hydration degree is significantly improved at 7 days, which corresponds well with the strength development of this cement.

[0054] The above results indicate that, without the effect of other additives, the degree of hydration of C3S is relatively small within the first day of aging, and the hydration reaction accelerates thereafter. The generated AFt and Ca(OH)2 crystals develop significantly with the extension of aging from 1 to 7 days, and the AFt and Ca(OH)2 crystals are distributed in an uneven aggregated manner in the slurry structure.

[0055] Comparative Example 2

[0056] Other conditions were the same as in Example 1, except that only magnesium carbonate trihydrate was added, with a total addition of 5.0 parts. The relative peak intensity ratio of the hydration products AFt and Ca(OH)2 in the 1-day aged sample was I. E / I L I P / I L The values ​​were 0.5616 and 2.1741 for the samples aged 7 days. For the 7-day-old samples, these values ​​were 0.7265 and 6.1541, as shown in Table 1.

[0057] Compared with the blank sample in Comparative Example 1, the addition of magnesium carbonate trihydrate increased the I content of AFt crystals. E / I L The value decreases, and the I of the 1-day aged Ca(OH)2 crystals... P / I L The value increased slightly, but the I value of Ca(OH)2 crystals in the 7-day-old sample increased. P / I L The value is much smaller than that of the blank sample. This indicates that adding magnesium carbonate trihydrate to PI cement inhibits the crystallization of AFt crystals at 1d and 7d, and also inhibits the crystallization of Ca(OH)2 at 7d, but promotes the crystallization of Ca(OH)2 at 1d. The relative peak intensity of C3S in the 1d and 7d aged samples is higher than that of the I sample. A / I L The values ​​were 1.3850 and 0.4992, respectively, both lower than the corresponding values ​​of the blank sample in Comparative Example 1. This indicates that the addition of magnesium carbonate trihydrate to PI cement promotes the hydration of C3S. Compared with the sample doped with magnesium carbonate trihydrate and nano-SiO2 in Example 1, the sample with magnesium carbonate trihydrate alone showed higher I values ​​for Ca(OH)2 crystals at 1d and 7d ages. P / I L The value is relatively larger.

[0058] The above results indicate that when 5% magnesium carbonate trihydrate is added alone, it can promote the hydration of C3S at 1 day and 7 days, which still contributes to the early strength development of cement. However, the higher degree of Ca(OH)2 crystal development within 1 day is not conducive to its uniform distribution in the paste structure, nor is it conducive to maintaining the long-term good strength development of this type of cement when used as an early strength additive for mixed silicate cement.

[0059] Comparative Example 3

[0060] Other conditions were the same as in Example 1, except that only nano-SiO2 was added, with a total doping amount of 5.0 parts. The I content in the 1-day and 7-day aged samples was... A / I L I E / I L I P / I L The values ​​are all lower than the corresponding values ​​of the blank sample in Comparative Example 1, as shown in Table 1. This indicates that the addition of nano-SiO2 to PI cement not only promotes the hydration of C3S but also inhibits the crystallization of AFt and Ca(OH)2 crystals. However, compared with the sample of magnesium carbonate trihydrate and nano-SiO2 double-doped in Example 1, the I value of Ca(OH)2 crystals at 1 day age when nano-SiO2 is added alone is lower. P / I L The value is relatively larger.

[0061] The above results indicate that 5% nano-SiO2 as a single additive significantly promotes the hydration of C3S at 1d and 7d ages, inhibits the development of Ca(OH)2 crystals, and generates more CSH gel, contributing to superior strength development of cement at 1d, 7d, and even longer. However, when the water-cement ratio is below 0.5 and in practical cementitious material applications, the excessively large specific surface area and high water absorption rate of nano-SiO2 severely affect the workability of cement mixtures, and its high price also hinders large-scale application.

[0062] Table 1 Comparison of the embodiments of the present invention and comparative examples

[0063]

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for evaluating the early cement hydration and product crystallization induced by two-component additives, characterized in that, include: Step S1: Mix magnesium carbonate trihydrate with another additive, cement, and water to obtain a slurry. Mix the slurry at a certain temperature and in the absence of air for a certain period of time. After reaching the specified age, filter the slurry to obtain solid hydration products. Step S2: Perform XRD tests on the solid hydration products and obtain the data and diffraction patterns after background removal; Step S3: In the background-removed diffraction pattern, select the (100) crystal plane of ettringite, the (001) crystal plane of Ca(OH)2, the (040) crystal plane of C3S, and the (021) crystal plane of β-C2S, and read the corresponding diffraction peak intensities, which are denoted as I. E(100) I P(001) I A(040) and I L(021) ; Step S4: Calculate the ratios I of the peak intensities of ettringite, Ca(OH)2, and C3S relative to β-C2S. E(100) / I L(021) I P(001) / I L(021) and I A(040) / I L(021) The value is used to characterize the early hydration and crystallization process of cement; At least two samples of different ages should be tested; In step S1, another additive is selected from one of nano-SiO2, nano-Al2O3, hard silicate calcium stone, anhydrous magnesium carbonate, hydromagnesia, and calcium carbonate magnesium stone.

2. The method according to claim 1, characterized in that, Another additive in step S1 is hard silicate or nano-SiO2.

3. The method according to claim 1, characterized in that, In step S1, the mass of water is more than 10 times the sum of the mass of magnesium carbonate trihydrate, another additive, and cement; the mixing temperature of the slurry is 10-50℃; and the specified age is no more than 7 days.

4. The method according to claim 1, characterized in that, The mixing and stirring process of the slurry in step S1 includes: Step S11: Pour the mixed slurry into the container, ensuring that the volume of the mixed slurry does not exceed 2 / 3 of the container's capacity, and seal the container opening; Step S12: Quickly shake the container, with one cycle consisting of 10 forward shakes followed by 10 reverse shakes. Shake for two cycles each at 10 min, 30 min, and 1 h after adding water; then shake for two cycles every 1 h; after 24 h, shake for two cycles every 3 h; and shake for two cycles again when the specified age is reached.

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