Highly corrosion resistant belite sulfoaluminate cement clinker, method for its production and use

Abstract

This invention discloses a highly corrosion-resistant Belite sulfoaluminate cement clinker, its preparation method, and its applications. The mineral composition of the cement clinker, by mass percentage, includes: C3S 6%–15%, C2S 42%–54%, C4A3 20%–30%, and C4AF 15%–22%. The highly corrosion-resistant Belite sulfoaluminate cement clinker of this invention introduces an appropriate amount of C3S into its phase composition and increases the content of C4AF, forming a four-phase cement clinker dominated by Belite and Yelimite, supplemented by Alite and iron phases. This clinker is used for coordinated strength development at various ages in cement, exhibits good 28-day bond strength, and also possesses excellent resistance to seawater erosion.

Description

Technical Field

[0001] This invention relates to the field of cement technology, specifically to a highly corrosion-resistant belite sulfoaluminate cement clinker, its preparation method, and its applications. Background Technology

[0002] Ordinary Portland cement (OPC), with allit (C3S) as its main mineral phase, is widely used around the world. However, OPC production releases a large amount of CO2 and requires a firing temperature above 1450°C, consuming a significant amount of fuel. Therefore, the total CO2 emissions from cement production remain consistently high. Furthermore, Portland cement contains a large amount of C3S. The hydration products of C3S, especially Ca(OH)2, are more susceptible to sulfate ion attack when used in marine engineering.

[0003] Compared to traditional ordinary silicate cement, high-belite sulfoaluminate cement requires a calcination temperature that is approximately 100–200°C lower, and the amount of limestone needed for clinker calcination is reduced by 20%–30%. Therefore, it can significantly reduce energy consumption and carbon emissions during cement production, offering a substantial advantage in addressing energy conservation and emission reduction issues in the cement industry. Furthermore, high-belite sulfoaluminate cement uses belite (C2S) and calcium sulfoaluminate (Yelmit C4A3$) as its main minerals. C4A3$ exhibits excellent properties such as rapid setting and hardening, high early strength, micro-expansion, low shrinkage, good frost resistance, good impermeability, and good corrosion resistance. High-belite sulfoaluminate cement shows great promise in emergency repairs, rapid construction, seepage prevention and plugging, marine engineering construction, and repair and reinforcement projects.

[0004] However, in high-belite cement, the rapid hydration of C4A3 only benefits early-stage strength, while the slow hydration of C2S mainly contributes to later-stage strength. Overall, this results in high-belite cement exhibiting high early-stage strength, insufficient mid-stage strength growth, and even a decline in later-stage strength. Furthermore, because C4A3 does not produce OH- during hydration... - This results in a lower pH in the pore solution of early and mid-stage hydration products, which is unfavorable for seawater to resist Cl. - Erosion. Ordinary high-belite sulfoaluminate cement, due to its low iron content, cannot cope with the erosion problems of the marine environment. These problems limit the application range of sulfoaluminate cement in marine engineering.

[0005] Currently, regarding the problem of slow or even declining strength growth in high-Belite sulfoaluminate cement, some scholars have proposed adding active admixtures to improve its mechanical properties. Patent CN113880484A proposes an admixture to improve the mechanical strength of high-Belite sulfoaluminate cement. This admixture is mainly composed of aminocarboxylate, polyol amine ester, diol, strong electrolyte, and water. With the addition of 0.1 wt% of the admixture, the strength of high-Belite sulfoaluminate cement at all ages has increased, with a maximum increase of 14.1 MPa at 28 days. Simultaneously, regarding the excessively low early-stage pH of high-Belite sulfoaluminate cement, some scholars have proposed adding alkali to improve its resistance to seawater erosion. (Patent...)

[0006] CN201910835165.3 discloses an early-strength, seawater-erosion-resistant sulfoaluminate cement. Through the synergistic hydration reaction of clinker, gypsum, and calcium hydroxide, a large amount of ettringite and gel phase are formed, resulting in a dense structure and a high pH in the early pore solution, thus enhancing the cement's early resistance to seawater erosion. The addition of certain mineral admixtures also improves the seawater erosion resistance of high-baley sulfoaluminate cement. However, excessive reliance on alkali activation and admixtures leads to insufficient effectiveness with low addition amounts, while higher addition amounts increase costs. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a highly corrosion-resistant belite sulfoaluminate cement clinker, its preparation method, and its application, thereby solving the technical problem of weak strength and erosion resistance of belite cement in the prior art.

[0008] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0009] In a first aspect, the present invention provides a highly corrosion-resistant Belite sulfoaluminate cement clinker, wherein the mineral composition of the cement clinker, by mass percentage, comprises: C3S 6%–15%, C2S 42%–54%, C4A3S 20%–30%, and C4AF 15%–22%.

[0010] Secondly, the present invention provides a method for preparing highly corrosion-resistant Belite sulfoaluminate cement clinker, comprising the following steps: taking raw materials of cement clinker in proportion, mixing them evenly, pressing them into sheets, then heating them, calcining them, and then rapidly cooling them to obtain cement clinker; wherein, the raw materials include calcium carbonate, silicon dioxide, aluminum oxide, iron oxide, gypsum dihydrate, mineralizer, and activator.

[0011] Thirdly, the present invention provides an application of the above-mentioned cement clinker in the preparation of highly corrosion-resistant Belite sulfoaluminate cement.

[0012] Compared with the prior art, the beneficial effects of the present invention include:

[0013] The high corrosion-resistant Belite sulfoaluminate cement clinker of this invention introduces an appropriate amount of C3S and increases the content of C4AF in its phase composition, forming a four-phase cement clinker dominated by Belite and Yelimite, supplemented by Alite and iron phases. The early hydration of C3S and C4AF solves the problem of low pH and weak resistance to chloride ion attack caused by the lack of Ca(OH)2 in the early hydration products. Simultaneously, the addition of C3S improves the early and mid-stage mechanical properties of the cement and enhances its bonding performance, resolving the problem of inconsistent development of mechanical properties in the mid-stage. The excellent resistance of the iron phase to seawater erosion and scouring is utilized to withstand the harsh environment of seawater. Furthermore, by controlling the content of the iron phase as a liquid phase in the cement, the coexistence of C3S and C4AF is resolved. The high corrosion-resistant Belite sulfoaluminate cement prepared using the cement clinker of this invention exhibits coordinated strength development at all ages, good 28-day bond strength, and suitable alkalinity (12.1–12.5), demonstrating excellent resistance to seawater erosion. Compared to traditional methods of alkali activation and admixtures to improve the performance of high belite sulfoaluminate cement, this invention optimizes the mechanical properties of cement from the cement perspective by simply adjusting the clinker phase composition and adding a small amount of activator and mineralizer, while also achieving good resistance to seawater erosion and scouring. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0015] This invention addresses the requirements for strength and resistance to seawater erosion in marine engineering by proposing a highly corrosion-resistant belite sulfoaluminate cement and its preparation method. This belite sulfoaluminate cement is a high-strength, high-adhesion, and highly corrosion-resistant cement clinker, which can solve the problems encountered by existing high belite sulfoaluminate cement clinker in marine engineering.

[0016] The first aspect of the present invention provides a highly corrosion-resistant belite sulfoaluminate cement clinker, wherein the mineral composition of the cement clinker, by mass percentage, comprises: C3S (alite, tricalcium silicate) 6%–15%, C2S (belite, dicalcium silicate) 42%–54%, C4A3S (yelite, calcium sulfoaluminate) 20%–30%, and C4AF (tetracalcium aluminoferrite, ferrophase) 15%–22%.

[0017] Preferably, by weight, the raw meal of cement clinker includes 64-68 parts calcium carbonate, 12-14.5 parts silicon dioxide, 9.5-13 parts aluminum oxide, 3-13 parts iron oxide, 4-6 parts gypsum dihydrate, 0-0.9 parts mineralizer, and 0-0.5 parts activator.

[0018] More preferably, by weight, the raw meal of cement clinker includes 64-68 parts calcium carbonate, 12-14.5 parts silicon dioxide, 9.5-13 parts aluminum oxide, 4-13 parts iron oxide, 4-6 parts gypsum dihydrate, 0.1-0.9 parts mineralizer, and 0.1-0.5 parts activator.

[0019] Preferably, the activator is copper oxide.

[0020] Preferably, the mineralizing agent is CaF2.

[0021] A second aspect of the present invention provides a method for preparing highly corrosion-resistant belite sulfoaluminate cement clinker, comprising the following steps:

[0022] Calcium carbonate, aluminum oxide, iron oxide, silicon dioxide, gypsum dihydrate, mineralizer, and activator are mixed evenly in a polyurethane mixing tube according to the specified ratio, pressed into tablets, heated in an electric furnace, calcined, and then quickly removed and cooled with a fan to obtain cement clinker.

[0023] Preferably, the calcination temperature is 1300℃~1380℃, and the calcination time is 30min~45min.

[0024] Preferably, during the heating process, the heating rate is 5-15℃ / min; when the temperature reaches 900℃, it is held for 1 hour, and then the temperature is increased and calcined.

[0025] A third aspect of the invention provides the use of the above-mentioned cement clinker in the preparation of highly corrosion-resistant Belite sulfoaluminate cement, which is made by mixing cement clinker and gypsum.

[0026] Preferably, the mass ratio of cement clinker to gypsum is (80-95):(20-5).

[0027] The main mechanisms and advantages of this invention include:

[0028] (1) Compared to ordinary high-belite sulfoaluminate cement, the high-corrosion-resistant belite sulfoaluminate cement of this invention introduces an appropriate amount of C3S into its phase composition and increases the content of C4AF, forming a four-phase cement dominated by belite and yelite, supplemented by allite and iron phases. The early hydration of C3S and C4AF solves the problem of low pH and weak resistance to chloride ion erosion caused by the lack of Ca(OH)2 in the early hydration products. At the same time, due to the addition of C3S, the mechanical properties of the cement in the early and middle stages are also improved, and the bonding properties are also improved, solving the problem of uncoordinated development of mechanical properties in the middle stage. The excellent resistance of the iron phase to seawater erosion and scouring is utilized to resist the harsh environment in seawater.

[0029] (2) Since C3S forms in large quantities at temperatures above 1400℃, while C4A3$ decomposes significantly at this temperature, the coexistence of C3S and C4A3$ needs to be addressed. In this invention, the iron phase serves as the liquid phase in cement, where silicate and aluminate minerals grow. Appropriately increasing the iron phase content can lower the formation temperature of C3S and C4A3$, increasing their coexistence. However, a high iron phase content can lead to sintering and agglomeration, making the cement difficult to grind and causing C4A3$ to decompose at even lower temperatures. Therefore, this invention, through the addition of an appropriate amount of iron phase, improves the coexistence temperature range of C3S and C4A3$, while simultaneously enhancing the cement's resistance to seawater abrasion and erosion, and improving its mechanical properties in the later stages.

[0030] (3) The introduction of mineralizer CaF2 can promote the formation of C3S at lower temperatures. The activator CuO mainly promotes the formation of the iron phase, thus promoting the growth of C3S and C4A3 crystals at lower temperatures. While lowering the firing temperature, the solid solution of copper oxide increases the hydration activity of the iron phase, greatly enhancing the role of the iron phase in marine engineering.

[0031] (4) The process of heat preservation followed by calcination is adopted to ensure the full decomposition of calcium carbonate; rapid cooling is performed after calcination to ensure the high strength of the resulting clinker.

[0032] (5) The cement of the present invention has coordinated strength development at all ages, good 28-day bond strength, and good resistance to seawater erosion.

[0033] The present invention will be further described in detail below through specific embodiments.

[0034] Example 1

[0035] The raw meal for preparing cement clinker, by weight, includes: 66.3 parts calcium carbonate, 13.3 parts silicon dioxide, 11.4 parts aluminum oxide, 4.1 parts iron oxide, and 4.9 parts gypsum dihydrate.

[0036] The specific preparation process of high corrosion-resistant belite sulfoaluminate cement is as follows:

[0037] (1) Calcium carbonate, alumina, iron oxide, silicon dioxide, and gypsum dihydrate are mixed evenly in a polyurethane mixing tube according to the specified ratio, pressed into tablets, and then heated in an electric furnace to obtain cement clinker. The heating rate is 10℃ / min. First, the temperature is kept at 900℃ for 1 hour to ensure the full decomposition of calcium carbonate, and then calcined at 1380℃ for 30 minutes.

[0038] (2) After the cement clinker is rapidly cooled, it is ground together with anhydrite at a mass ratio of 90:10 until the particle size is 0.75μm to obtain highly corrosion-resistant Belite sulfoaluminate cement.

[0039] The composition of the cement clinker obtained in this embodiment, determined by the Rietveld standard-free quantitative method, is as follows: C3S: 9.63%, C2S: 47.12%, C4A3S: 25.01%, C4AF: 18.24%.

[0040] Example 2

[0041] The raw meal for preparing cement clinker, by weight, includes: 66.7 parts calcium carbonate, 12.9 parts silicon dioxide, 11.3 parts aluminum oxide, 4.1 parts iron oxide, and 5 parts gypsum dihydrate.

[0042] The specific preparation process of high corrosion-resistant high belite sulfoaluminate cement is as follows:

[0043] (1) Calcium carbonate, aluminum oxide, iron oxide, silicon oxide, and gypsum dihydrate are mixed evenly in a polyurethane mixing tube according to the specified ratio, pressed into sheets, and then heated in an electric furnace to obtain cement clinker. The heating rate is 10℃ / min. First, the temperature is kept at 900℃ for 1h to ensure the full decomposition of calcium carbonate, and then calcined at 1380℃ for 30min.

[0044] (2) After the cement clinker is rapidly cooled, it is ground together with anhydrite at a mass ratio of 90:10 until the particle size is 0.75μm to obtain high corrosion resistant Belite sulfoaluminate cement.

[0045] The composition of the cement clinker obtained in this embodiment, determined by the Rietveld standard-free quantitative method, is as follows: C3S: 13.57%, C2S: 42.11%, C4A3S: 25.79%, C4AF: 18.53%.

[0046] Example 3

[0047] The raw meal for preparing cement clinker, by weight, includes: 66.3 parts calcium carbonate, 13.3 parts silicon dioxide, 11.4 parts aluminum oxide, 4.1 parts iron oxide, 4.9 parts gypsum dihydrate, and 0.5 parts copper oxide.

[0048] The specific preparation process of high corrosion-resistant high belite sulfoaluminate cement is as follows:

[0049] (1) Calcium carbonate, aluminum oxide, iron oxide, silicon oxide, gypsum dihydrate, and copper oxide are mixed evenly in a polyurethane mixing tube according to the specified ratio, pressed into sheets, and then heated in an electric furnace to obtain cement clinker. The heating rate is 10℃ / min. First, the temperature is kept at 900℃ for 1 hour to ensure the full decomposition of calcium carbonate, and then calcined at 1350℃ for 30 minutes.

[0050] (2) After the cement clinker is rapidly cooled, it is ground together with anhydrite at a mass ratio of 90:10 until the particle size is 0.75μm to obtain high corrosion resistant Belite sulfoaluminate cement.

[0051] The composition of the cement clinker obtained in this embodiment, determined by the Rietveld standard-free quantitative method, is as follows: C3S: 8.57%, C2S: 46.33%, C4A3: 23.76%, C4AF: 21.34%.

[0052] Example 4

[0053] The raw meal for preparing cement clinker, by weight, includes: 66.3 parts calcium carbonate, 13.3 parts silicon dioxide, 11.4 parts aluminum oxide, 4.1 parts iron oxide, 4.9 parts gypsum dihydrate, 0.5 parts copper oxide, and 0.9 parts CaF2.

[0054] The specific preparation process of high corrosion-resistant high belite sulfoaluminate cement is as follows:

[0055] (1) Calcium carbonate, aluminum oxide, iron oxide, silicon oxide, gypsum dihydrate, copper oxide, and CaF2 are mixed evenly in a polyurethane mixing tube according to the specified ratio, pressed into tablets, and then heated in an electric furnace. Cement clinker is obtained by calcination. The heating rate is 10℃ / min. First, the temperature is kept at 900℃ for 1 hour to ensure the full decomposition of calcium carbonate, and then calcined at 1300℃ for 30 minutes.

[0056] (2) After the cement clinker is rapidly cooled, it is ground together with anhydrite at a mass ratio of 90:10 until the particle size is 0.75μm to obtain high corrosion resistant Belite sulfoaluminate cement.

[0057] The composition of the cement clinker obtained in this embodiment, determined by the Rietveld standard-free quantitative method, is as follows: C3S: 9.85%, C2S: 45.22%, C4A3: 24.69%, C4AF: 20.24%.

[0058] Example 5

[0059] The raw meal for preparing cement clinker, by weight, includes: 66.3 parts calcium carbonate, 13.3 parts silicon dioxide, 11.4 parts aluminum oxide, 4.1 parts iron oxide, 4.9 parts gypsum dihydrate, and 0.9 parts CaF2.

[0060] The specific preparation process of high corrosion-resistant belite sulfoaluminate cement is as follows:

[0061] (1) Calcium carbonate, alumina, iron oxide, silicon dioxide, gypsum dihydrate, and CaF2 are mixed evenly in a polyurethane mixing tube according to the specified ratio, pressed into tablets, and then heated in an electric furnace to obtain cement clinker through calcination. The heating rate is 10℃ / min. First, the temperature is kept at 900℃ for 1 hour to ensure the full decomposition of calcium carbonate, and then calcined at 1300℃ for 30 minutes.

[0062] (2) After the cement clinker is rapidly cooled, it is ground together with anhydrite at a mass ratio of 90:10 until the particle size is 0.75μm to obtain high corrosion resistant Belite sulfoaluminate cement.

[0063] The composition of the cement clinker obtained in this embodiment, determined by the Rietveld standard-free quantitative method, is as follows: C3S: 9.41%, C2S: 48.12%, C4A3S: 24.81%, C4AF: 17.66%.

[0064] Example 6

[0065] The raw meal for preparing cement clinker, by weight, includes: 67.2 parts calcium carbonate, 13.6 parts silicon dioxide, 10.8 parts aluminum oxide, 3.4 parts iron oxide, and 4.8 parts gypsum dihydrate.

[0066] The specific preparation process of high corrosion-resistant belite sulfoaluminate cement is as follows:

[0067] (1) Calcium carbonate, aluminum oxide, iron oxide, silicon oxide, and gypsum dihydrate are mixed evenly in a polyurethane mixing tube according to the specified ratio, pressed into sheets, and then heated in an electric furnace to obtain cement clinker. The heating rate is 10℃ / min. First, the temperature is kept at 900℃ for 1h to ensure the full decomposition of calcium carbonate, and then calcined at 1380℃ for 30min.

[0068] (2) After the cement clinker is rapidly cooled, it is ground together with anhydrite at a mass ratio of 90:10 until the particle size is 0.75μm to obtain high corrosion-resistant Bailey sulfoaluminate cement.

[0069] The composition of the cement clinker obtained in this embodiment, determined by the Rietveld standard-free quantitative method, is as follows: C3S: 6.34%, C2S: 53.43%, C4A3S: 24.51%, C4AF: 15.72%.

[0070] The cements obtained in Examples 1-6 above were subjected to performance tests, and the results are shown in Table 1. Specifically, the free calcium oxide (f-CaO) content was determined using the ethylene glycol method according to GB / T 176-2017 "Cement Chemical Analysis Methods". The compressive strength of the cement was tested according to GB / T 17671-1999. The early pH value of the cement was measured according to GB / T 176-2017. The bond strength was determined using the mortar repair-immersion method according to JC / T 2381-2016. The corrosion resistance coefficient of the cement was tested according to GB / T 749-2008. The impact and abrasion resistance of the cement was tested using the underwater steel ball method according to DL / T 5150-2001.

[0071] Table 1. Cement performance test results obtained in Examples 1-6

[0072]

[0073]

[0074] As shown in Table 1, the cement obtained in the embodiments of the present invention all exhibit good compressive strength at various ages: 1-day compressive strength of 25.1–31.7 MPa, 3-day compressive strength of 32.8–40.9 MPa, 7-day compressive strength of 45.8–53.4 MPa, and 28-day compressive strength of 57.8–75.4 MPa; and excellent abrasion resistance (0.62–0.67 × 10⁻⁶ MPa). 3 h·cm 2 g -1 It possesses suitable alkalinity (12.1–12.5) and corrosion resistance (corrosion resistance coefficient between 0.90 and 1.09). Suitable for concrete engineering projects in marine environments.

[0075] A comparison of Examples 2 and 6 with Example 1 shows that increasing the C3S content in cement can improve the cement's compressive strength, bond strength, and pH value. However, increasing the C3S content requires more liquid phase. When the C4AF content is low, the amount of liquid phase is insufficient to fully calcine the C3S at 1380℃, leading to an increase in f-CaO content. Simultaneously, a low C4AF content also reduces the cement paste's resistance to erosion and abrasion.

[0076] A comparison of Examples 3, 4, and 5 with Example 1 shows that the mineralizer calcium fluoride and the activator copper oxide have a significant impact on the performance of cement, and both can reduce the firing temperature. However, the performance of Example 5 (with calcium fluoride) is even lower than that of Example 1 (without calcium fluoride and copper oxide), indicating that the addition of calcium fluoride alone will reduce various properties and have an inhibitory effect. The performance of Example 4 is better than that of Examples 1 and 3 (with only copper oxide). Therefore, the present invention combines calcium fluoride with an appropriate amount of copper oxide, which can not only reduce the firing temperature, but also effectively improve the overall performance, producing a synergistic effect.

[0077] Compared with existing technologies, this invention provides a highly corrosion-resistant belite sulfoaluminate cement clinker, its preparation method, and its applications. The clinker mineral composition by mass percentage is: C3S 6%–15%, C2S 42%–54%, C4A3S 20%–30%, and C4AF 15%–22%. The highly corrosion-resistant belite sulfoaluminate cement is prepared by mixing the highly corrosion-resistant belite sulfoaluminate cement clinker with gypsum. This invention's alite-modified high-belite sulfoaluminate cement has advantages such as high strength, stable development, excellent bonding performance, good erosion resistance, and good impact and abrasion resistance, making it suitable for repair projects in marine environments. In addition to its high strength and impact and abrasion resistance, this invention's sulfoaluminate cement has a low firing temperature and low carbon emissions, conforming to the green development concept of the cement industry.

[0078] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A highly corrosion-resistant belite sulfoaluminate cement clinker, characterized in that, The mineral composition of the cement clinker, by mass percentage, is: C3S 9.85%, C2S 45.22%, C4A3S 24.69%, and C4AF 20.24%. By weight, the raw meal of the cement clinker is 66.3 parts calcium carbonate, 13.3 parts silicon dioxide, 11.4 parts aluminum oxide, 4.1 parts iron oxide, 4.9 parts gypsum dihydrate, 0.5 parts copper oxide, and 0.9 parts CaF2. The preparation method of the highly corrosion-resistant Belite sulfoaluminate cement clinker consists of the following steps: taking raw cement clinker in proportion, mixing it evenly, pressing it into sheets, then heating it, calcining it, and then rapidly cooling it to obtain cement clinker. The calcination temperature is 1300℃, and the calcination time is 30 minutes; During the heating process, the heating rate is 10℃ / min; when the temperature reaches 900℃, it is held for 1 hour, and then the temperature is increased again for calcination.

2. The application of the cement clinker as described in claim 1 in the preparation of highly corrosion-resistant Belite sulfoaluminate cement.

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