Method for evaluating early cement hydration and product crystallization induced by two-component additive

Abstract

The invention provides a method for evaluating early cement hydration and product crystallization induced by a two-component additive, and relates to the technical field of cement-based material preparation and inspection, and the method comprises the following steps: S1, preparing a solid hydration product; s2, detecting an XRD (X-Ray Diffraction) spectrogram of the solid hydration product; s3, reading the specific diffraction peak intensity of the XRD spectrogram; and S4, calculating the diffraction peak intensity ratio, and representing the early hydration and crystallization process of the cement. According to the invention, the two-component additive promotes the development of the early strength of the cement and fully inhibits premature crystallization of Ca (OH) 2 crystals; the peak intensity ratio of C3S, Ca (OH) 2 and AFt relative to beta-C2S, which is obtained through a sample XRD spectrum, well represents the change rule of early hydration and crystallization of the cement.

Description

Technical Field

[0001] The invention relates to the technical field of cement-based material preparation and inspection, in particular to a method for evaluating early cement hydration induced by a two-component additive and product crystallization. Background Art

[0002] Cement concrete pavement materials used in road projects are subjected to repeated shearing and extrusion effects of traffic loads. Optimizing composition, reducing harmful pores, and improving the bonding strength of each phase are important guarantees for improving its durability. Reducing harmful pores and improving bonding strength are attributed to the improvement of the macroscopic properties of the material, namely, the flexural (bending) strength. Flexural strength is an important indicator for road concrete design.

[0003] There are many measures that can be taken to improve the flexural strength of concrete: such as increasing the bonding strength between aggregate and cement paste; introducing millimeter-centimeter-long fibers into concrete; forming a polymer network structure in the concrete structure through polymer compounding; compounding micrometer-millimeter-scale whiskers in cement paste to strengthen it; increasing the CSH gel content, optimizing the gel distribution, and increasing the density of the hardened paste to improve the flexural strength. These measures provide effective solutions to improve the flexural strength and durability of cement concrete pavement materials from different scales and aspects.

[0004] The prior art has found that magnesium carbonate trihydrate has a coagulation-promoting effect on silicate cement and can be used to prepare concrete accelerators. However, the effect of magnesium carbonate trihydrate on cement paste is mainly concentrated in a short period of time within a few hours. For a longer period of time of 1 to 7 days, other additives are required to work together. Compared with the prior art in which magnesium carbonate trihydrate is added alone, the evaluation of the crystallization of its hydration product only requires the calculation of the diffraction peak intensity ratio of the Ca(OH)2(001) crystal plane and the β-C2S(021) crystal plane using the XRD spectrum of the product crystal, and more parameters need to be cited for comparative analysis. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the early cement hydration and product crystallization induced by a two-component additive based on magnesium carbonate trihydrate, wherein magnesium carbonate trihydrate is used in combination with another additive to continuously induce cement hydration from the beginning of mixing cement with water, and to have a positive effect on the crystallization process of the hydration product. Specifically, the evaluation method of the present invention is as follows:

[0006] A method for evaluating early cement hydration and product crystallization induced by a two-component additive, comprising:

[0007] Step S1, magnesium carbonate trihydrate, another additive, cement and water are uniformly mixed to obtain a mixed slurry, the mixed slurry is mixed and stirred for a certain period at a certain temperature and in an air-tight condition, and after reaching a specified age, the slurry is filtered to obtain a solid hydration product;

[0008] Step S2, performing XRD test on the solid hydration product, and obtaining data and diffraction spectrum after background removal;

[0009] Step S3, in the diffraction spectrum after background removal, select the (100) crystal plane of ettringite AFt, 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), read the corresponding diffraction peak intensities, and record them as I E(100) ,I P(001) ,I A(040) and I L(021) ;

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

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

[0012] Furthermore, in step S1, another additive is selected from one of nano-SiO2, nano-Al2O3, xonotlite (6CaO·6SiO2·H2O, Xon), anhydrous magnesium carbonate (MgCO3), hydromagnesite (4MgCO3·Mg(OH)2·4H2O), and magnesia (Mg3Ca(CO3)4), and the above additive can react with Ca(CO3) in the cement slurry after the effect of magnesium carbonate trihydrate disappears. 2+ The ions react to form CSH, CaSO4·2H2O, CaCO3, CaMg(CO3)2, Ca(OH)2, AFt(3CaO·Al2O3·3CaSO4·32H2O), AFm(3CaO·Al2O3·CaSO4·12H2O) and other sediment phases which do not have adverse effects on cement properties, and continuously consume Ca in the slurry within 1d to 7d. 2+ ion.

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

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

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

[0016] Step S11, pouring the mixed slurry into a container, wherein the volume of the mixed slurry does not exceed 2 / 3 of the volume of the container, and sealing the container mouth;

[0017] Step S12, quickly oscillate the container, with one cycle being 10 oscillations in the forward direction and then 10 oscillations inverted. Two oscillation cycles are performed each after adding water for 10 minutes, 30 minutes, and 1 hour. Thereafter, two oscillation cycles are performed every 1 hour. After 24 hours, two oscillation cycles are performed every 3 hours. When the specified age is reached, two more oscillation cycles are performed.

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

[0019] In the present invention, the evaluation of early hydration of cement and crystallization of its products is carried out by comparing the peak intensity ratio in the XRD diffraction spectrum, and the indicators of C3S (tricalcium silicate) and AFt (calcium vanadate) are added. AFt, like Ca(OH)2, is an early hydration product of cement. CSH gel is a hydration product with low crystallinity, and its diffraction peak is not obvious in the XRD spectrum, and it is not easy to handle. Cement clinker mineral C3S is hydrated in the early stage, and its hydration products are CSH gel and Ca(OH)2. Under the action of additives, the phase of the hydration product may change. For example, when magnesium carbonate trihydrate is added, CaCO3 is also generated. Once C3S is hydrated, the diffraction peak intensity of C3S in the hydrated sample will decrease. However, the hydration degree of β-C2S is very limited at a short age of less than 7 days, and it is suitable as a reference phase for the early hydration process of cement.

[0020] The ettringite (100) crystal plane (2θ = 9.091°, JCPDS # 41-1451), (001) plane of Ca(OH)2 (2θ=18.007°, JCPDS #44-1481), (040) plane of C3S (2θ=51.469°, JCPDS # 49-0442) and the (021) plane of β-C2S (2θ=31.059°, JCPDS # The diffraction peak intensities of 33-0302) are calculated and compared. Among them, the (100) crystal plane of ettringite is the strongest crystal plane of the diffraction peak of ettringite crystal, the (001) crystal plane of Ca(OH)2 is the crystal plane in the Z-axis direction of the plate crystal, that is, the crystal plane in the thickness direction of the plate crystal, and the diffraction peaks on the (040) crystal plane of C3S and the (021) crystal plane of β-C2S are not superimposed by other phase peaks, which is convenient for reading data.

[0021] The XRD phase analysis software Jade was used to remove the background value of the original diffraction data graph to obtain the data after background removal. After the sample data was processed for background removal, the diffraction peak intensity values ​​of the ettringite (100) crystal plane, Ca(OH)2 (001) crystal plane, C3S (040) crystal plane and β-C2S (021) crystal plane were taken respectively and 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) In order to express the quotient of the three peak intensities (relative peak intensities) concisely, 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 In the present invention, the peak intensity ratio of C3S, Ca(OH)2 and AFt relative to β-C2S obtained by the sample XRD spectrum, that is, I A / I L ,I P / I L and I E / I L , to characterize the early hydration crystallization process of cement.

[0022] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0023] The present invention uses magnesium carbonate trihydrate in combination with another additive to continuously induce hydration of cement from the beginning of mixing cement with water, and has a positive effect on the crystallization process of the hydration product. 2+ The two-component additive of this method promotes the development of early strength of cement and fully inhibits the premature crystallization of Ca(OH)2 crystals. It can be used 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 to β-C2S obtained by the sample XRD spectrum is I A / I L ,I P / I L and I E / I L , which better characterizes the changing law of early hydration crystallization of cement. This evaluation method can be used as a beneficial supplement for the research on physical phase, microstructure and macroscopic properties related to early hydration of cement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is the XRD spectrum of the 7d sample after background removal in Example 1 of the present invention and the diffraction peak positions corresponding to the four phase crystal planes.

[0026] Figure 2 The SEM morphologies of cement hydration products in the samples of the present invention are shown in Figure 1, wherein (a) is the morphology of Ca(OH)2 crystals in the 7d-old sample in Comparative Example 1; (b) is the morphology of hydration products AFt and Ca(OH)2 crystals in the 1d-old sample in Example 1; (c) is the morphology of hydration products AFt and Ca(OH)2 crystals in the 1d-old sample in Comparative Example 3; and (d) is the morphology of AFt crystals in the 1d-old sample in Comparative Example 1. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0028] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0029] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0030] In the embodiments of the present invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are consistent.

[0031] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0032] The present invention provides a method for evaluating early cement hydration and product crystallization induced by a two-component additive based on magnesium carbonate trihydrate. By using magnesium carbonate trihydrate in combination with another additive, cement hydration is continuously induced from the time of mixing cement with water, and the crystallization process of the hydration product is positively affected. The method is used to promote early hydration of silicate cement and induce product crystallization, thereby improving the mechanical properties and durability of cement materials.

[0033] The above-mentioned silicate cement is a type of cement containing clinker minerals C3S and β-C2S. Its strength before 7 days is mainly obtained by hydration reaction of C3S and a small amount of β-C2S. It includes PI, PⅡ type silicate cement, PO ordinary silicate cement, PS slag silicate cement, PF fly ash silicate cement, PP pozzolanic silicate cement and PC composite silicate cement, as well as PR road silicate cement. When silicate cement is mixed with water, the highly active clinker minerals are hydrated, and the Ca in the slurry is 2+ Ion, OH - The ion concentration increases rapidly, and the pH value can reach above 11 within 1 minute. Magnesium carbonate trihydrate dissociates to form CO3 in high alkalinity cement slurry. 2- ions, rapidly depleting Ca in the serum 2+ Ions promote the early setting and hardening of silicate cement.

[0034] Magnesium carbonate trihydrate is mixed with another additive. This additive can react with Ca in cement slurry after the effect of magnesium carbonate trihydrate disappears. 2+ Ion action, continue to consume Ca 2+ ions, making the clinker minerals in low Ca 2+ The additives include nano-SiO2, nano-Al2O3, xonotlite (6CaO·6SiO2·H2O, Xon), anhydrous magnesium carbonate (MgCO3), hydromagnesite (4MgCO3·Mg(OH)2·4H2O), and magnesia (Mg3Ca(CO3)4). The additives of CaO-SiO2 system are the preferred additives because they are compatible with Ca 2+ Ionic action generates CSH gel and CSH gel-like substances.

[0035] After the mixture of the above two-component additives is evenly mixed with silicate cement, it is evenly mixed with water of more than 10 times the mass of the above solid powder in a mixing device. The mixed slurry is mixed and stirred in a closed container at a temperature of 10℃ to 50℃ for a certain period to prevent the solid matter from agglomerating and settling. After reaching the specified age, the slurry is filtered and the solid hydration product is filtered to stop hydration. The sample that has stopped hydration is dried in an air-tight environment at below 50℃, and then ground to a fineness of more than 200 mesh required for XRD powder diffraction test.

[0036] The sample powder was subjected to XRD test on an X-ray diffractometer, with a diffraction angle 2θ ranging from 5° to 70° and a scanning rate of not less than 0.02° / s to obtain initial diffraction data and spectra. The initial diffraction spectra were processed to remove the background value to obtain the data and spectra after removing the background. Figure 1 The diffraction spectrum shown. Figure 1 In the diffraction spectrum shown in the figure, the ettringite AFt(100) crystal plane (2θ=9.091°, JCPDS # 41-1451), (001) plane of Ca(OH)2 (2θ=18.007°, JCPDS # 44-1481), (040) plane of C3S (2θ=51.469°, JCPDS # 49-0442) and the (021) plane of β-C2S (2θ=31.059°, JCPDS # 33-0302), read the corresponding diffraction peak intensity, respectively recorded as I E(100) ,I P(001) ,I A(040) and I L(021) , Figure 1 Abbreviated as I E ,I P,I A and I L Since the hydration degree of cement clinker mineral β-C2S is very limited within a short period of time within 7 days, the peak intensity (I L The (100) crystal plane of AFt is the strongest crystal plane of the diffraction peak of ettringite crystal, the (001) crystal plane of Ca(OH)2 is the crystal plane in the Z-axis direction of the plate crystal, that is, the crystal plane in the thickness direction of the plate crystal, and the diffraction peaks on the (040) crystal plane of C3S and the (021) crystal plane of β-C2S are not superimposed by other phase peaks, which is convenient for reading data.

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

[0038] AFt, like Ca(OH)2, is an early hydration product of cement. CSH gel is a hydration product with low crystallinity. Its diffraction peak is not obvious in the XRD spectrum and it is not easy to handle. The cement clinker mineral C3S is hydrated in the early stage, and its hydration products are CSH gel and Ca(OH)2. Under the action of additives, the phase of the hydration product will change. Once C3S is hydrated, the diffraction peak intensity of C3S in the hydrated sample will decrease, while the degree of hydration of β-C2S is very limited at a short age of less than 7 days. As Ca(OH)2 is continuously hydrated with the cement clinker mineral C3S, the amount of precipitation increases, plate-like crystals develop, the plate surface becomes thicker, and the intensity of its (001) plane diffraction peak increases, I P / I L The value becomes larger. Figure 2 (a) is the crystal morphology of Ca(OH)2 after hydration of PI type silicate cement in 20 times the mass of water for 7 days, and its plate-like crystals are developed. When additives are used, the formation of Ca(OH)2 will be changed, causing its crystals to be incompletely developed, such as Figure 2 The dense particles between (b) and (c) cause I P / I L AFt is the reaction product of C3A, C4AF and gypsum in clinker. When there is no additive, AFt develops well, such as Figure 2(d) Needle-shaped crystals. However, the crystallization process of AFt will be affected by additives, which will affect the growth of AFt crystals, such as Figure 2 (b) and (c) Needle-columnar crystals.

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

[0040] The present invention is a two-component additive-based magnesium carbonate trihydrate-based method for inducing early cement hydration and product crystallization evaluation. By using magnesium carbonate trihydrate in combination with another additive, the hydration of cement is continuously induced from the beginning of mixing cement with water, and a positive effect is exerted on the crystallization process of the hydration product. 2+ Hydrate under high concentration environment to form more and more stable CSH gel. The two-component additive of this method promotes the development of early strength of cement and fully inhibits the premature crystallization of Ca(OH)2 crystals. It can be used as an additive for cement-based materials in applications requiring fast hardening and early strength performance. The peak intensity ratio of C3S, Ca(OH)2 and AFt relative to β-C2S obtained by the sample XRD spectrum better characterizes the change law of early hydration crystallization of cement. This evaluation method can be used as a beneficial supplement for the study of physical phase, microstructure and macroscopic properties related to early hydration of cement.

[0041] This will be described below with reference to specific embodiments.

[0042] Example 1

[0043] This is a sample 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 ​​200m 2 / g of nano-SiO2 powder 2.5 parts after mixing, pour into a suitable plastic container with a sealable bottle mouth. Then add 20 times the total mass of the above powder into the container, and stir quickly until there is no powder agglomerate in the slurry. The stirring time is controlled within 1 minute, and the slurry volume does not exceed 2 / 3 of the container volume. Seal the container mouth to prevent further mixing of CO2 in the air. Quickly shake the container to avoid agglomeration and sedimentation of solids in the container. After 10 positive shakes, turn the container upside down and shake it 10 times, which is one cycle. Add water for 10min, 30min, and 1h, and then shake it for two cycles every 1h. After 24h, shake it for two cycles every 3h. When it reaches the specified age, after two cycles of shaking, filter the slurry, and after stopping hydration, isolate it from air and dry it at 50℃.

[0044] The hydration products at 1d and 7d were ground and sent for XRD powder diffraction to obtain two sets of initial diffraction data. After removing the background value of the initial diffraction spectrum, the diffraction peak intensities of the (100) crystal plane of AFt, the (001) crystal plane of Ca(OH)2, the (040) crystal plane of C3S, and the (021) crystal plane of β-C2S were read respectively, that is, I E ,I P ,I A and I L , calculate I E / I L ,I P / I L and I A / I L The values ​​are listed in Table 1. The relative peak intensity ratio of the hydration product AFt and Ca(OH)2 in the 1d-old sample is E / I L ,I P / I L The values ​​are 0.8712 and 0.1299 respectively. The smaller the value, the worse the crystal development and the lower the content. This shows that compared with AFt crystals, the development of Ca(OH)2, the hydration product of the 1d-old sample, is worse. Figure 2 (b) shows the crystal morphology of the hydration products AFt (needle-columnar) and Ca(OH)2 (intermediate dense particles) in the 1-day-old sample. E / I L ,I P / I L The values ​​are 0.5651 and 2.1613, respectively, which indicates that with the progress of the hydration process, the Ca(OH)2 crystals in the sample are further developed, and the degree of change exceeds that of AFt.

[0045] The relative peak intensity ratio of C3S in the 1d and 7d samples isA / I L The values ​​are 1.6050 and 1.4810, respectively, relative to the I A / I L The value of 1d-old sample was 3.9169, which showed a significant decrease, and the value of 1d-old sample decreased by 59.02%. However, the decrease of 7d-old sample was not very large, only 7.73%.

[0046] The above results show that the dual addition of magnesium carbonate trihydrate and nano-SiO2 promotes the hydration of C3S within 1d, which is helpful for the development of early strength of cement. At the same time, it also inhibits the growth of AFt and Ca(OH)2 crystals, making these two crystals smaller and more evenly distributed in the paste structure. Fine Ca(OH)2 crystals are conducive to the longer-term strength development of mixed silicate cement with mineral powders such as slag and fly ash, so they are also suitable as dual additives for this type of cement.

[0047] Example 2

[0048] The other conditions were the same as those in Example 1, except that the other additive was changed to xonotlite powder. The I E / I L ,I P / I L and I A / I L The relative peak intensity ratios of the hydration product AFt in the samples at 1d and 7d are shown in Table 1. E / I L The values ​​are 0.6952 and 0.3304, respectively, which are slightly lower than the corresponding values ​​of the sample in Example 1. However, the I P / I L The value is only 0.2065, which is slightly larger than the corresponding value of the sample in Example 1. This shows that the two-component doping of magnesium carbonate trihydrate and calcite also inhibits the early crystallization of Ca(OH)2.

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

[0050] The above results show that the dual addition of magnesium carbonate trihydrate and xonotlite not only promotes the hydration of C3S within 1 day, but also maintains a high hydration rate within 7 days, which is conducive to the development of early strength of cement. At the same time, it also inhibits the growth and development of AFt and Ca(OH)2 crystals to a certain extent, making the crystals smaller and more evenly distributed. When magnesium carbonate trihydrate and xonotlite are used as two-component additives for mixed silicate cement, it will also be beneficial to the long-term strength development of this type of cement.

[0051] Comparative Example 1

[0052] The blank control sample was prepared under the same conditions as in Example 1, except that no additives were added, including magnesium carbonate trihydrate. The relative peak intensity ratio of the hydration products AFt and Ca(OH)2 in the 1-day-old sample was E / I L ,I P / I L The values ​​of the 7d-old sample were 1.0560 and 28.7680, respectively, as shown in Table 1. The diffraction peak intensities of AFt crystals and Ca(OH)2 crystals in the blank samples of these two ages exceeded the peak intensity of C2S, indicating that the amount of AFt and Ca(OH)2 generated and the degree of crystal development within 1d exceeded those of the samples of the same age in Example 1, and as the hydration process proceeded, the Ca(OH)2 crystals in the samples were significantly developed. P / I L The value reaches 28.7680. Figure 2 (a) is the morphology of Ca(OH)2 crystals in the 7d-old sample. Ca(OH)2 develops into plate-like crystals with a thickness of 0.5 to 1.5 μm. Figure 2 (d) is the morphology of AFt crystals in the 1d-old sample, showing the development of AFt needle-shaped crystals.

[0053] The relative peak intensity ratio of C3S in the 1d and 7d samples is A / I L The values ​​are 2.9268 and 0.7080, respectively, relative to the I A / I L The value of PI cement is 3.9169, and the decrease of the sample at 1d is 25.28%, which is lower than the decrease of the sample of magnesium carbonate trihydrate and nano-SiO2 in Example 1. However, the decrease of the sample at 7d is significantly larger than that at 1d, reaching 75.81%. It can be seen that the hydration degree of PI cement itself is limited in the short age of 1d, and the hydration degree is significantly improved at 7d, which has a good corresponding relationship with the strength development of the cement.

[0054] The above results show that without the effect of other additives, the hydration degree of C3S is relatively small within 1d, and then the hydration reaction is accelerated. The generated AFt and Ca(OH)2 crystals develop significantly with the extension of 1d to 7d age, and AFt and Ca(OH)2 crystals are distributed in an uneven agglomerate shape in the slurry structure.

[0055] Comparative Example 2

[0056] The other conditions were the same as those in Example 1, except that only magnesium carbonate trihydrate was added, with a total addition amount of 5.0 parts. The relative peak intensity ratio of the hydration product AFt and Ca(OH)2 in the 1-day-old sample was E / I L ,I P / I L The values ​​are 0.5616 and 2.1741 respectively. The two values ​​of the 7-day-old sample are 0.7265 and 6.1541 respectively, as shown in Table 1.

[0057] Compared with the blank sample of Comparative Example 1, after adding magnesium carbonate trihydrate, the I E / I L The value becomes smaller, and the I P / I L The value slightly increases, but the I P / I L The value is much smaller than that of the blank sample. This indicates that adding magnesium carbonate trihydrate to PI cement will inhibit the crystallization of AFt crystals at 1d and 7d, and also inhibit the crystallization of Ca(OH)2 at 7d, but will promote the crystallization of Ca(OH)2 at 1d. The relative peak intensity of C3S in the samples at 1d and 7d is higher than that of I A / I L The values ​​are 1.3850 and 0.4992, respectively, which are both smaller than the corresponding values ​​of the blank sample in Comparative Example 1. This indicates that the addition of magnesium carbonate trihydrate alone to PI cement will promote the hydration of C3S. Compared with the sample doped with magnesium carbonate trihydrate and nano-SiO2 in Example 1, the sample doped with magnesium carbonate trihydrate alone has an I value of Ca(OH)2 crystals at 1d and 7d. P / I L The value is relatively larger.

[0058] The above results show that 5% magnesium carbonate trihydrate can also promote the hydration of C3S at 1d and 7d, and still contribute to the development of early strength of cement. However, the higher degree of development of Ca(OH)2 crystals at 1d is not conducive to its uniform distribution in the paste structure, nor is it conducive to using it as an early strength additive for mixed silicate cement, which can still maintain the long-term good strength development of this type of cement.

[0059] Comparative Example 3

[0060] The other conditions were the same as those in Example 1, except that only nano-SiO2 was added, with a total addition amount of 5.0 parts. A / I L ,I E / I L ,I P / I L The values ​​are all smaller than the corresponding values ​​of the blank sample in Comparative Example 1. The specific values ​​are shown in Table 1. This shows that the addition of nano-SiO2 alone 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 doped with magnesium carbonate trihydrate and nano-SiO2 in Example 1, the I value of Ca(OH)2 crystals at 1d age when nano-SiO2 is added alone is P / I L The value is relatively larger.

[0061] The above results show that 5% nano-SiO2 alone greatly promotes the hydration of C3S at 1d and 7d, inhibits the development of Ca(OH)2 crystals, and generates more CSH gel, which helps cement to have excellent strength development in 1d, 7d or even longer. However, when the water-binder ratio of nano-SiO2 is below 0.5 and it is used in actual cement-based materials, due to its excessive specific surface area and high water absorption rate, it seriously affects the working performance of cement mixtures, and its price is too high, which is not conducive to large-scale application.

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

[0063]

[0064] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for evaluating the early cement hydration and product crystallization induced by a two-component additive, characterized in that: include: Step S1, magnesium carbonate trihydrate, another additive, cement and water are uniformly mixed to obtain a mixed slurry, the mixed slurry is mixed and stirred for a certain period at a certain temperature and in an air-tight condition, and after reaching a specified age, the slurry is filtered to obtain a solid hydration product; Step S2, performing XRD test on the solid hydration product, and obtaining data and diffraction spectrum after background removal; Step S3, in the diffraction spectrum after background removal, 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, read the corresponding diffraction peak intensities, and record them as I E(100) ,I P(001) ,I A(040) and I L(021) ; Step S4, respectively calculate the ratios of the three peak intensities of ettringite, Ca(OH)2 and C3S to β-C2S. E(100) / I L(021) ,I P(001) / I L(021) and I A(040) / I L(021) Value, thus characterizing the early hydration crystallization process of cement; At least two samples of different ages were tested.

2. The method according to claim 1, characterized in that In step S1, the other additive is selected from one of nano-SiO2, nano-Al2O3, xonotlite, anhydrous magnesium carbonate, hydromagnesite, and magnesite.

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

4. 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 and stirring temperature of the mixing slurry is 10-50° C.; and the prescribed age is no more than 7 days.

5. The method according to claim 1, characterized in that The mixing and stirring process of the slurry in step S1 includes: Step S11, pouring the mixed slurry into a container, wherein the volume of the mixed slurry does not exceed 2 / 3 of the volume of the container, and sealing the container mouth; Step S12, quickly oscillate the container, with one cycle being 10 oscillations in the forward direction and then 10 oscillations inverted. Two oscillation cycles are performed each after adding water for 10 minutes, 30 minutes, and 1 hour. Thereafter, two oscillation cycles are performed every 1 hour. After 24 hours, two oscillation cycles are performed every 3 hours. When the specified age is reached, two more oscillation cycles are performed.

Images