A coral powder cement, its preparation method and application

Abstract

This invention discloses a coral powder cement, its preparation method, and its application, belonging to the field of cement technology. The coral powder cement's formulation, by mass percentage, includes: 45-62% silicate clinker, 10-25% aluminate clinker, 5-40% coral micropowder, 0-5% calcium nitrite, and 5-9% gypsum. The coral powder cement is prepared by uniformly mixing the silicate clinker, aluminate clinker, coral micropowder, calcium nitrite, and gypsum in a specific ratio. This invention offers advantages such as improved early strength of cement, enhanced mechanical properties of cementitious materials, effective reduction of rapid setting caused by aluminate cement, and corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of cement technology, and relates to a type of cement, particularly a coral powder cement suitable for island and reef structures, its preparation method, and its application. Background Technology

[0002] In recent years, countries around the world have attached great importance to the development of marine resources. my country's marine engineering construction, including ports, seawalls, coastal protection, and airports on distant islands and reefs, has developed particularly rapidly. Island and reef engineering, primarily in the South China Sea, is being vigorously promoted. However, the practical problems of large-scale island and reef construction are: the South China Sea islands and reefs are far from the mainland, lack resources, and have inconvenient transportation. Transporting building materials such as cement from the mainland by ship over long distances would inevitably drive up project costs, and the construction period would be difficult to guarantee due to factors such as wind and waves. Taking the construction of Yongshu Reef as an example, considering the transportation costs of cement and mineral admixtures, the cost of cementitious materials for concrete is as high as 0.07 to 0.12 million yuan / m³. 3 This results in an excessively high cost of 0.8 to 1.0 million yuan per cubic meter of concrete. 3 The cost of such cement far exceeds that of land and near-shore construction. Therefore, there is an urgent need to develop a type of cement suitable for island and reef engineering to solve problems such as raw material shortages, excessively high engineering costs, and excessively long construction periods, thereby significantly accelerating the construction of island and reef projects such as ports, dikes, airports, and roads. Summary of the Invention

[0003] This invention addresses the problems of high demand, difficulty in obtaining, and high transportation costs of building materials for island and reef engineering. It utilizes island and reef coral resources and processes and grinds them to obtain coral powder, which replaces part of the composite materials. This provides a coral powder cement that is locally sourced, low-cost, and highly durable, while reducing transportation costs.

[0004] To achieve the above objectives, the present invention provides a coral powder cement, characterized in that the formulation composition by weight percentage includes: 45-62% silicate clinker, 10-25% aluminate clinker, 5-40% coral powder, 0-5% calcium nitrite, and 5-9% gypsum.

[0005] Furthermore, the silicate clinker includes tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite; the mass ratio of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite is 53-58:22-27:8-12:5-10.

[0006] Furthermore, the aluminate clinker includes monocalcium aluminate, monocalcium dialuminate, and dodecacalcium heptaaluminate; the mass ratio of monocalcium aluminate, monocalcium dialuminate, and dodecacalcium heptaaluminate is 44-51:25-32:7-10.

[0007] Furthermore, the coral micro powder is made from coral reef sand.

[0008] Furthermore, the gypsum is natural gypsum and / or chemical gypsum.

[0009] Furthermore, the specific surface area of ​​the silicate clinker, aluminate clinker, coral powder, calcium nitrite, and gypsum is ≥350m². 2 / kg.

[0010] Furthermore, the specific surface area of ​​the silicate clinker, aluminate clinker, coral powder, calcium nitrite, and gypsum is ≥400m². 2 / kg.

[0011] This invention also provides a method for preparing coral powder cement, characterized by: uniformly mixing the silicate clinker, aluminate clinker, coral micropowder, calcium nitrite, and gypsum in a specified ratio to prepare the coral powder cement. If the calcium nitrite content is 0%, it is mixed with other components at a 0% ratio, i.e., no calcium nitrite is added.

[0012] Furthermore, the preparation method specifically includes the following steps: Step 1: Add calcium nitrite to coral reef sand according to the proportion of ingredients, and mechanically crush and grind it to obtain a mixture of coral micro powder and calcium nitrite; Step 2: Mix and grind the silicate clinker, aluminate clinker, mixture of coral micro powder and calcium nitrite and gypsum according to the proportion to obtain a clinker-gypsum mixture.

[0013] Furthermore, the preparation method specifically includes the following steps: Step 1: Silicate clinker, aluminate clinker and gypsum are mixed and ground in proportion to obtain a clinker-gypsum mixture; calcium nitrite is added to coral reef sand in proportion, and mechanically crushed and ground to obtain a coral micro powder calcium nitrite mixture; Step 2: The clinker-gypsum mixture and the coral micro powder calcium nitrite mixture obtained in Step 1 are added to the mixing system and mixed evenly to obtain coral powder cement.

[0014] The present invention also provides a method for applying coral powder cement, characterized in that: the coral powder cement is mixed with sand or coral reef sand to prepare mortar or concrete, which is then mixed and cured with fresh water and used for the construction of reinforced concrete structures of island and reef buildings.

[0015] The beneficial effects of this invention are as follows:

[0016] I. This invention uses coral micropowder as a blending material, which has a filling effect, forming a good particle size distribution and a densely packed system with fine layers, reducing porosity and thus improving the density of cement-based materials. Furthermore, the use of coral micropowder as a blending material also has a water-reducing effect, reducing the water consumption of the cement clinker-coral micropowder-gypsum slurry system. After the slurry hardens, it forms a relatively dense cement paste, reducing porosity and capillary diameter, thereby improving the mechanical properties of cement-based materials. Finally, the use of coral micropowder as a blending material also has a nucleation effect, acting as a nucleation matrix for hydration products in the cement slurry, lowering the nucleation barrier of hydration products, promoting early hydration of cement, and improving the early strength of cement.

[0017] Second, this invention uses aluminate clinker and silicate clinker as composite cementitious materials, which enables cement materials to have the characteristics of rapid setting, early strength and continuous strength development. At the same time, the addition of coral powder improves the fluidity of cement and effectively reduces the rapid setting phenomenon caused by aluminate cement.

[0018] Third, this invention uses aluminate clinker as one of the components of the cementitious material. The main mineral composition includes monocalcium aluminate, dicalcium aluminate, and dodecacalcium heptahydrate. Its hydration process and products are greatly affected by temperature. When the temperature is below 20°C, the aluminate clinker hydrates to form metastable crystals of calcium aluminate decahydrate and dicalcium aluminate octahydrate, resulting in a sharp drop in structural strength. When the temperature is above 30°C, the metastable crystals of calcium aluminate decahydrate and dicalcium aluminate octahydrate in the hydration products of aluminate clinker will gradually transform into a relatively stable tricalcium aluminate hexahydrate. This is a spontaneous process, which is accelerated by the increase of temperature. The high temperature of the island and reef environment enables the aluminate clinker to hydrate to form a large amount of stable tricalcium aluminate hexahydrate, ensuring the long-term stability of the strength of cement concrete structures.

[0019] IV. This invention uses aluminate clinker and silicate clinker as composite cementitious materials. The hydration products contain a large amount of hydrated calcium aluminate, which allows the cement concrete material to react with chloride ions that diffuse into the concrete protective layer in the island and reef atmosphere containing chloride ion salt spray, generating hydrated calcium chloroaluminate. This enhances the chloride ion binding capacity, reduces the free chloride ion content on the surface of the reinforcing steel, and prevents steel corrosion. Furthermore, the microporous structure of coral micropowder has excellent adsorption capacity, enabling the directional growth and adsorption of hydrated calcium aluminate generated during cement hydration. During structural service, it slowly releases aluminate and calcium ions to maintain the ionic balance of hydrated calcium chloroaluminate in the slurry, further maintaining the long-term chloride ion binding capacity of the cement concrete and ensuring long-term rust prevention.

[0020] V. This invention uses calcium nitrite as a steel reinforcement corrosion inhibitor, which can delay the electrochemical reaction of the steel reinforcement anode in concrete structures. Specifically, ferrous ions on the steel reinforcement surface react with nitrite ions in an alkaline environment, and the unstable Fe...2+ Oxidized into stable Fe 3+ The rust inhibitor precipitates and adsorbs on the steel surface, forming a passivation film, thereby achieving corrosion protection for the reinforcing steel within the concrete. Furthermore, this invention adds calcium nitrite during the coral reef sand grinding stage, allowing it to fully penetrate the microporous structure of the coral powder. During concrete mixing, the rust inhibitor components adsorbed in the pores on the coral aggregate surface first enter the concrete mixture, providing immediate protection for the reinforcing steel. From the very beginning of pouring, it delays the damage caused by Cl- pitting corrosion. During later service, as the rust inhibitor components in the coral powder micropores are released, diffuse, and migrate to the surface of the reinforcing steel, gradually accumulating to a certain concentration, it can gradually repair or rebuild the passivation film on the pitted reinforcing steel surface, promoting re-passivation and thus improving the later-stage corrosion resistance of the reinforcing steel within the concrete structure. Compared to directly adding calcium nitrite during concrete mixing, the corrosion resistance effect is better when the coral powder adsorbs calcium nitrite before mixing with other components.

[0021] VI. This invention uses island and reef coral sand to replace part of the mixed materials, which effectively reduces transportation costs and realizes the comprehensive utilization of island and reef resources, reducing environmental pollution and resource waste. Attached Figure Description

[0022] Figure 1 This is the XRD pattern of coral micropowder in the coral powder cement of the present invention;

[0023] Figure 2 The XRD patterns are of cement hydration products at different hydration ages for Comparative Examples 1, 2, 3, 6, and 8, where a) represents 3 days and b) represents 28 days.

[0024] Figure 3 This is the strength development curve of coral powder cement mortar at different ages in Example 1;

[0025] Figure 4 The diagram shows the electrochemical test results of Comparative Example 1, Comparative Example 2, Example 4, Example 8, Example 28, and Example 32 (a), and the corrosion current density curves of cement mortar at different hydration ages (b).

[0026] Figure 5 These are SEM images of Comparative Example 1(a), Example 2(b), and Example 6(c) at a 3-day hydration age. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments.

[0028] Example 1

[0029] This embodiment provides a coral powder cement, which is composed of 69.6 parts by weight of silicate clinker, 17.4 parts by weight of aluminate clinker, 7 parts by weight of gypsum dihydrate, and 20 parts by weight of coral powder. The preparation method includes the following steps: Step 1, mixing and grinding the silicate clinker, aluminate clinker, and gypsum dihydrate in a specified ratio to obtain a specific surface area of ​​410 m². 2 / kg of clinker gypsum mixture; coral reef sand was mechanically crushed and ground according to the proportions to obtain a specific surface area of ​​480m². 2 / kg of coral micropowder. Step 2: Add the clinker-gypsum mixture obtained in Step 1 and the coral micropowder to the mixing system and mix evenly to obtain coral powder cement. Mix the coral powder cement with sand or coral reef sand to prepare mortar or concrete, and use fresh water for mixing and curing.

[0030] Example 3

[0031] This embodiment provides a coral powder cement, which, by weight, consists of 62.4 parts silicate clinker, 15.6 parts aluminate clinker, 7 parts dihydrate gypsum, and 15 parts coral micropowder. The preparation method includes the following steps: Step 1, mechanically crushing and grinding coral reef sand to obtain a specific surface area of ​​450 m². 2 / kg of coral micropowder. Step 2: Mix and grind the silicate clinker, aluminate clinker, coral micropowder obtained in Step 1, and gypsum in a certain proportion until the specific surface area is ≥410m². 2 / kg, to obtain coral powder cement. The coral powder cement is mixed with sand or coral reef sand to prepare mortar or concrete, and then mixed and cured with fresh water.

[0032] Examples 2, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24

[0033] This embodiment provides a coral powder cement, whose composition and preparation method are basically the same as those in Example 1, except that the mass fraction and specific surface area of ​​each component are different. Please refer to Table 1 for details.

[0034] Examples 4, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23

[0035] This embodiment provides a coral powder cement, whose composition and preparation method are basically the same as those in Example 1, except that the mass fraction and specific surface area of ​​each component are different. Please refer to Table 1 for details.

[0036] Comparative Example 1

[0037] This comparative example provides a common cement, composed of 72.8 parts by weight of silicate clinker, 18.2 parts by weight of aluminate clinker, and 9 parts by weight of dihydrate gypsum (0 parts by weight of coral micro powder). The preparation method is as follows: the silicate clinker, aluminate clinker, and dihydrate gypsum are mixed and ground uniformly according to the specified proportions until the specific surface area is 400 m².2 / kg, to obtain cement. The cement is then mixed with sand or coral reef sand to prepare mortar or concrete, which is mixed and cured with fresh water.

[0038] The setting time, compressive strength, flexural strength and strength grade of the cements in Examples 1 to 24 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0039] Table 1. Cement composition and properties of Examples 1-24 and Comparative Example 1

[0040]

[0041]

[0042] Example 25

[0043] This embodiment provides a coral powder cement, which, by weight, consists of 67.5 parts silicate clinker, 16.9 parts aluminate clinker, 8 parts dihydrate gypsum, 5 parts coral powder, and 2.6 parts calcium nitrite. The preparation method includes the following steps: Step 1: The silicate clinker, aluminate clinker, and dihydrate gypsum are mixed and ground according to a specified ratio to obtain a specific surface area of ​​400 m². 2 / kg of clinker gypsum mixture; calcium nitrite was added to coral reef sand according to the proportion, and then mechanically crushed and ground to obtain a specific surface area of ​​480m². 2 / kg of coral micronized calcium nitrite mixture. Step 2: Add the clinker gypsum mixture and coral micronized calcium nitrite mixture obtained in Step 1 to the mixing system and mix evenly to obtain coral powder cement. Mix the coral powder cement with sand or coral reef sand to prepare mortar or concrete, and use fresh water for mixing and curing.

[0044] Example 27

[0045] This embodiment provides a coral powder cement, which, by weight, consists of 59.9 parts silicate clinker, 15 parts aluminate clinker, 7 parts dihydrate gypsum, 15 parts coral micropowder, and 3.1 parts calcium nitrite. The preparation method includes the following steps: Step 1: Add calcium nitrite to coral reef sand according to the proportions, and mechanically crush and grind until the specific surface area is 450 m². 2 / kg, to obtain a mixture of coral micronized calcium nitrite. Step 2: Mix and grind the silicate clinker, aluminate clinker, the coral micronized calcium nitrite mixture obtained in Step 1, and gypsum in a certain proportion until the specific surface area is ≥410m². 2 / kg, to obtain coral powder cement. The coral powder cement is mixed with sand or coral reef sand to prepare mortar or concrete, and then mixed and cured with fresh water.

[0046] Examples 26, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48

[0047] This embodiment provides a coral powder cement, whose composition and preparation method are basically the same as those in Example 25, except that the mass fraction and specific surface area of ​​each component are as detailed in Table 2.

[0048] Examples 28, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49-52

[0049] This embodiment provides a coral powder cement, whose composition and preparation method are basically the same as those in Example 27, except that the mass fraction and specific surface area of ​​each component are different. Please refer to Table 2 for details.

[0050] Comparative Example 2

[0051] This comparative example provides a common cement composed of 71.4 parts by weight of silicate clinker, 17.8 parts by weight of aluminate clinker, 9 parts by weight of gypsum dihydrate, and 1.8 parts by weight of calcium nitrite (0 parts by weight of coral micro powder). The preparation method is as follows: the silicate clinker, aluminate clinker, gypsum dihydrate, and calcium nitrite are mixed and ground uniformly according to the specified proportions until the specific surface area is 400 m². 2 / kg, to obtain cement. The cement is then mixed with sand or coral reef sand to prepare mortar or concrete, which is mixed and cured with fresh water.

[0052] The setting time, compressive strength, flexural strength and strength grade of the cements in Examples 25-52 and Comparative Example 2 were tested, and the results are shown in Table 2.

[0053] Table 2. Cement composition and properties of Examples 25-52 and Comparative Example 2

[0054]

[0055]

[0056] Table 2. Cement composition and properties of Examples 25-52 and Comparative Example 2 (continued)

[0057]

[0058]

[0059] As can be seen from Examples 1-24 and Comparative Example 1, Examples 25-52 and Comparative Example 2, coral micro powder can improve the early strength of cement and the mechanical properties of cement-based materials, while effectively reducing the rapid setting phenomenon caused by aluminate cement.

[0060] XRD tests were performed on the coral micropowder from Example 1, and the results are as follows: Figure 1As shown. XRD tests were performed on the cement hydration products at different hydration ages of Comparative Example 1, Example 2, Example 3, Example 6, and Example 8. The results are as follows. Figure 2 As shown in Example 1, the strength development pattern of coral powder cement mortar at different ages is as follows. Figure 3 As shown in the figure. Corrosion current density tests were performed on the cement mortar of Comparative Example 1, Comparative Example 2, Example 4, Example 8, Example 28, and Example 32. The results are as follows. Figure 4 As shown in (b). From Figure 4 (b) It can be seen that both coral micropowder and calcium nitrite have rust-inhibiting effects, and the two can synergistically inhibit rust. SEM images of the cement from Comparative Example 1, Example 2, and Example 6 at 3 days of hydration age are shown below. Figure 5 As shown.

[0061] This invention addresses the problems of raw material shortages, high construction costs, and long construction periods in island and reef engineering projects. It significantly reduces the amount of cementitious materials needed for transporting materials to remote islands and reefs, offering substantial convenience and economic benefits. Furthermore, the product's manufacturing process is simple, making it suitable for island and reef engineering projects such as dikes, ports, roads, and airport runways. It has broad application prospects in the construction and repair of concrete structures for island and reef projects, as well as in military protection engineering.

[0062] In this invention, unless otherwise stated, scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, the reagents, materials, and procedures used herein are all widely used in the relevant fields.

[0063] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a coral powder cement, characterized in that: the raw materials of the coral powder cement are composed of the following formula in terms of mass percentage: 45-62% of silicate clinker, 10-25% of aluminate clinker, 5-40% of coral micro powder, 1.8-5% of calcium nitrite, and 5-9% of gypsum; the sum of the mass percentages of the above components meets 100%; the method comprises the following steps: step one, adding calcium nitrite to coral reef sand according to the proportion of ingredients, and performing mechanical crushing and grinding to obtain a coral micro powder calcium nitrite mixture; step two, mixing and grinding the silicate clinker, aluminate clinker, coral micro powder calcium nitrite mixture, and gypsum according to the proportion of ingredients to obtain a clinker gypsum mixture; alternatively, the method comprises the following steps: step one, mixing and grinding the silicate clinker, aluminate clinker, and gypsum according to the proportion of ingredients to obtain a clinker gypsum mixture; adding calcium nitrite to coral reef sand according to the proportion of ingredients, and performing mechanical crushing and grinding to obtain a coral micro powder calcium nitrite mixture; step two, adding the clinker gypsum mixture and the coral micro powder calcium nitrite mixture obtained in step one to a mixing system, and mixing uniformly to obtain the coral powder cement; the coral powder cement is mixed with sand or coral reef sand to prepare mortar or concrete, and is mixed and maintained with fresh water, and is used for the construction of reinforced concrete structures of island reef buildings.

2. The method for preparing a coral powder cement according to claim 1, characterized in that: the silicate clinker comprises tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite; the mass ratio of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite is 53-58:22-27:8-12:5-10.

3. The method for preparing a coral powder cement according to claim 1, characterized in that: the aluminate clinker comprises monocalcium aluminate, dialuminate, and dodecacerium aluminate; the mass ratio of monocalcium aluminate, dialuminate, and dodecacerium aluminate is 44-51:25-32:7-10.

4. The method for preparing a coral powder cement according to claim 1, characterized in that: the coral micro powder is ground from coral reef sand.

5. The method for preparing a coral powder cement according to claim 1, characterized in that: the gypsum is natural gypsum or / and chemical gypsum.

6. The method for preparing a coral powder cement according to claim 1, characterized in that: wherein ​ ​ wherein ​ ​ wherein ​ ​ wherein ​ ​ wherein The specific surface area of the silicate clinker, aluminate clinker, coral micro powder, calcium nitrite and gypsum is ≥ 350 m 2 / kg.

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