HIGH SHELL POWDER CEMENT

Description

1 HIGH SHELL POWDER CEMENT TECHNICAL FIELD The present invention relates to a high shell powder cement, in particular an environmentally friendly cement with low carbon emission intensity and falls within the field of construction materials. PREVIOUSLY, seashells are an important food source for humanity. Consequently, the amount of shellfish waste in the world is also enormous. In China, the annual production of shellfish waste reached 10 million tons in 2020, and this figure continues to increase year after year. Classified as dry waste, seashells generally have a hard texture and are difficult to recycle. They are usually sent to landfills for disposal. The deposited waste not only occupies land but also pollutes the environment, which has harmful impacts on human health and social life. The shells are composed of inorganic and organic matter.Common shells are composed of 95% (mass fraction) of CaCO3, approximately 5% (mass fraction) of organic matter, and a small amount of inorganic salts containing elements such as K, Na, Mg, Fe, Z, and Se. The structure of a shell consists, from the outside in, of an outer layer of protein, an intermediate layer of calcite, and an inner layer of crystalline calcium carbonate. This unique multi-layered stratified structure gives it advantages such as high hardness, corrosion resistance, and good toughness. Thanks to their chemical composition and unique structure, shell materials find applications in fields such as medicine, corrosion protection and preservation, adsorbent materials, and catalyst supports. However, BE2026 / 7274 2 Most of these developments are still in the experimental research phase and have not yet led to mass production. Moreover, they present disadvantages such as low consumption and a complex manufacturing process.As the most important application materials by volume, construction materials have always attracted particular attention in the field of waste-to-resource recovery. In the cement sector, shells are used in cement manufacturing, replacing aggregates as admixtures for concrete, given their similar composition to that of natural aggregates. Furthermore, shells with a relatively loose structure, large-diameter pores that are widely and uniformly distributed, present promising application prospects in fields such as functional adsorbent construction materials. Currently, numerous studies worldwide focus on the use of shells as construction materials. However, due to the low powder dosage, shell shell and of little effect on performance, their concrete applications15 remain rare and they do not yet benefit from sufficient attention.In ordinary Portland cement, the presence of shells reduces energy consumption during grinding because they have a low hardness and are easy to grind. Furthermore, the high-temperature decomposition of the shells generates highly absorbent CaO, which promotes solid-phase reactions. Moreover, the chloride ions present in the shells improve the reactivity of the raw material, promote the formation of silicate minerals, and reduce the Fe₂O₃ content of the clinker. Therefore, shells can replace limestone in raw materials. However, given that their levels of harmful substances such as K₂O, Na₂O, Cl⁻, and SO₃ in the shells are significantly higher than those in the 25 limestone, they replace limestone in a proportion generally not exceeding 10%. In parallel, in ordinary Portland cement concrete, although limestone powder is widely used as a mixture or as an adjunct in cement concrete works, it is generally inert.Although some BE2026 / 7274 3 study data indicate that limestone can participate in the hydration process of C3A in Portland cement by reacting to form hydrated calcium carbo-aluminate, the C3A content in Portland cement is only about 7 to 10%. Therefore, the reaction of limestone in Portland cement is very limited, which makes a high dosage of limestone powder unrealistic; its dosage generally does not exceed 25%.5 Unlike ordinary Portland cement, the limestone content in sulfo-aluminate cement can be higher, but it generally does not exceed 40%. Moreover, a higher limestone powder content is often accompanied by a degradation of material performance. Cement-based materials will continue to be used as primary construction materials for some time in the future, and their development in a low-carbon and environmentally friendly way is essential. Currently, many countries around the world are actively studying how to reduce carbon emissions while ensuring cement production.One solution is to valorize waste. Sea fruit shells have stable properties15 and some recycling value. Their disposal in landfills or storage constitutes a waste of resources. Therefore, the research and development of low-carbon cements with a high shell powder content offer significant economic and social advantages and contribute to the sustainable development of human society.20 STATEMENT OF THE INVENTION In light of the foregoing, the present invention proposes a high-shell powder cement based on a limestone-ettringite-calcium carbo-aluminate product system. A new cement system whose principal products25 are calcium carbonate, ettringite, and calcium carbo-aluminate by incorporation of shell powder representing a proportion of more than 60% in sulfo-aluminous cements, a green cement containing considerable potential.High-strength shell powder cement is a new green cement with excellent and stable performance, a more environmentally friendly character and a lower cost, with promising application prospects. BE2026 / 7274 4 For the high-content shell powder cement based on a limestone-ettringite-calcium carbo-aluminate product system according to the present invention, said new cement is composed of sulfo-aluminate cement, shell powder, superplasticizer, and sodium gluconate, among which the sulfo-aluminate cement and shell powder constitute the principal materials of the cement system, while the superplasticizer and sodium gluconate are used as performance-enhancing ingredients. The mass proportions of the different components are as follows: 30-40 parts sulfo-aluminate cement, 60-70 parts shell powder, 0.3-0.7 parts superplasticizer, and 0.1-0.3 parts sodium gluconate.Advantageously, the said sulfo-aluminous cement is a sulfo-aluminous cement available on the market, with a strength class of 42.5, and a limestone content representing 15 to 20% by mass of the cement; when dosing the components, the fraction of limestone contained in this cement must be deducted from the dose. Advantageously, said shell powder consists of finely ground shells, the average fineness of which is less than that of the sulfoaluminate cement in the composition; when determining the components, the fraction of limestone contained in the sulfoaluminate cement must be included in the dose of this powder. Advantageously, said superplasticizer is a high-performance, powdered water-reducing admixture with a high water reduction rate and good plasticity retention, the water reduction rate of which is at least 25%. Advantageously, said sodium gluconate is of industrial grade, with a purity greater than 98%.25 Advantageously, said high-content shell powder cement based on a system of limestone-ettringite-carbo-aluminated calcium products is applied to a water-binder ratio limited to a value less than 0.25, and preferably to a water-binder ratio limited to a value less than 0.20. The beneficial effects of the present invention reside in the following: 30 BE2026 / 7274 5 Cement production requires significant resource and energy consumption and pollutes the environment. The development of ecological, waste-recycling, energy-efficient, and environmentally friendly cements is the trend for the sustainable development of the cement industry. At the same time, the search for alternative raw materials to replace natural limestone 5 is also an important step in addressing resource depletion in cement production. Shells are a common type of natural limestone raw material.With the expansion of marine aquaculture, their production is increasing year after year, and there are abundant shell resources worldwide. Currently, the use of shells for the manufacture of cement-based materials still presents significant development potential. Replacing cement linker with shell powder derived from the large-scale recycling of shellfish waste will strongly contribute to the evolution towards green cement. The present invention takes advantage of a new green cement system based on 15 sulfo-aluminous cement, whose hydration products are completely different from the ettringite and aluminate gel present in the classic sulfo-aluminous cement, it allows to transform into a new stable multi-component system dominated by limestone, ettringite and tricalcium carboaluminate, in particular the limestone constituting the main material of the final product.This cement system shows that a cement whose products are composed of various naturally occurring rock components could be widely established, thus making the concept of rock-based cement realistic. Shells are organic and inorganic composites formed by the absorption of calcium carbonate during the biological formation process, and exhibit good mechanical properties at the microscopic scale. The shell powder particles are smooth with high skeleton strength. The shell powder present in high concentrations in sulfo-aluminate cement acts from the outset through micro-aggregate effects, mineral water-reducing adjuvant effects, crystalline nucleation effects, and participates in chemical reactions, which makes it possible to solve the key problem of low limestone powder content in existing cements. Furthermore, the performance cement-based materials thus manufactured are better than those of pure sulfo-aluminous cement BE2026 / 7274 6, thus allowing us to overcome the disadvantages inherent in sulfo-aluminous cement.The key to the hydration reaction of the new green cement system based on sulfo-aluminate cement, on which the present invention is based, lies in the fact that: 1) during the hydration process, low-sulfur calcium sulfo-aluminate (AFm) reacts with limestone powder to form calcium carbo-aluminate. This is mainly monocalcium carbo-aluminate when the molar ratio between calcium carbonate and AFm is less than 2:1; and it is mainly tricalcium carbo-aluminate when this ratio is greater than 3:1; 2) For a low water-binder ratio, AFm can be present in large quantities in the hydration products of the sulfo-aluminate cement.The present invention has the following advantages: 1) The application of high-strength shell powder makes it possible to further significantly reduce the consumption of sulfo-aluminate cement clinker used in green cement, considerably decreasing carbon emissions from the cement industry15, avoiding pollution and environmental degradation; 2) It makes it possible to solve the problem of large-scale valorization of shells and to achieve the objective of transforming waste into useful resources; 3) It will contribute to the development of marine concrete structures, for example by enabling the production of more durable concrete, the development20 and research of ecological cementitious products based on shells, as well as their use as artificial marine reefs, etc., thus achieving coordination between the durability of maritime structures and the marine ecosystem; 4) It will lead to the production of low-alkalinity cement, thereby further mitigating the impact of cement-based materials on the natural environment throughout their life cycle. 5) High-content shell powder cement benefits from a wide range of raw material sources, a simple production process, excellent performance, and low cost, making it easy to generalize and apply.30 BE2026 / 7274 7 SPECIFIC EMBODIMENTS To clarify the objectives, technical solutions, and advantages of the present invention, preferred embodiments of the present invention will be described in detail below: Embodiment 15 High-content shell powder cement based on a limestone-ettringite-calcium carbo-aluminate product system according to this embodiment is composed of sulfo-aluminate cement, shell powder, superplasticizer, and sodium gluconate, among which the superplasticizer and sodium gluconate are used as cement improvement ingredients. The mass proportions of the 10 different components are as follows: 40 parts sulfo-aluminate cement, 60 parts shell powder, 0.7 parts superplasticizer, and 0.2 parts gluconatedesodium.Method of embodiment 2 The high-content shell powder cement based on a 15-product system of limestone-etringite-calcium carbo-aluminate according to this embodiment is composed of sulfo-aluminous cement, shell powder, superplasticizer and sodium gluconate, among which the superplasticizer and sodium gluconate are used as ingredients for improving the cement. The mass proportions of the different components are as follows: 30 parts of sulfo-aluminous cement, 7020 parts of shell powder, 0.5 part of superplasticizer, and 0.1 part of sodium gluconate. Method of embodiment 3 High-content shell powder cement based on a limestone-etringite-calcium carbo-aluminate product system according to this embodiment is 25 composed of sulfo-aluminous cement, shell powder, superplasticizer and sodium gluconate, among which the superplasticizer and sodium gluconate are used as ingredients for improving the cement.The mass proportions of the different components are as follows: 35 parts sulfo-aluminate cement, 65 BE2026 / 7274, 8 parts shell powder, 0.3 part superplasticizer, and 0.3 part sodium gluconate. In embodiments 1 to 3, the quality control parameters of the raw materials of the high-content shell powder cement based on a limestone-etringite-calcium-carbo-aluminate product system are as follows: the cement is a low-alkalinity sulfo-aluminate cement, produced by Sichuan Jiahua Special Cement Co., Ltd.(China), with a resistance class of 42.5 and a limestone content representing 17% of the mass of the material; the shell powder consists of finely ground shells, the average fineness of which is less than that of the sulfo-aluminous material in the composition, i.e. about 600 meshes per inch; the superplasticizer is the water reducing agent SiKa® ViscoCrete®-530P from Switzerland, with a water reduction rate greater than 25%; the sodium gluconate is of industrial grade with a purity greater than 98% and is purchased from Henan Yesheng Environmental Protection Technology Co., Ltd. (China). The manufacturing process of the construction material associated with high-15 shell powder cement based on a system of limestone-ettringite-calcium carbo-aluminate products according to embodiments 1 to 3 includes the steps such as the mixing process, forming and curing, without difference from ordinary Portland cement.High-content shell-powder cement samples based on a 20-product system of limestone-ettringite-calcium carbo-aluminate according to embodiments 1 to 3 were respectively taken and mixed with quartz sand and water at a quartz sand-cement ratio of 0.5:1 and with controlled water consumption according to the principle of fluidity similarity, etc., to form cement mortars, which were poured into molds. One day later, the specimens were 25 demolded and subjected to natural curing in the laboratory. Their compressive strengths were measured in accordance with the Chinese standard JGJ / T70-2019 Standard for Testing the Strength of Cement Mortar, in order to evaluate their strength performance.The test results are shown in the table below: BE2026 / 7274 9 Category Materials / Components of cement / Portions Sand-cement ratio Water-binder ratio Compressive strength (MPa) / day Sulfo-aluminum cement Shell powder Sodium gluconate Superplasticizer 3j7j28 Reference 100—0.20.60.5:10.24:170.378.081.2 Method of implementation 1 40600.20.70.5:10.16:156.472.883.7 Method of implementation 2 30700.10.50.5:10.17:157.161.666 5 Mode of embodiment 3 35650,30,30,5:10,20:1 49, 3 62, 9 74, 8 NB:For the dosage of components in embodiments 1 to 3, the dose of cement does not include the limestone content, the limestone content is included in the shell powder content.It emerges that among the samples of high-shell powder cement based on a calcium carbonate-etringite-carbo-aluminate product system taken for testing, compared to the reference group of pure sulfo-aluminate cement, the cement sample according to embodiment 1 can exhibit a 28-day strength superior to that of the original cement under a low water-binder ratio in the case where the substitution rate of cement by shell powder in the composition reaches 60%; The strengths at different ages of the cement samples according to embodiments 2 to 3 still allow the needs of most real projects to be met, although they are slightly lower than those of the original cement BE2026 / 7274 10 in the case where the rate of substitution of cement by shell powder in the composition is between 60% and 70%.Thus, the optimal substitution rate for high-content shell powder cement is 60%, and it is recommended to use a cement substitution rate not exceeding 70%, in order to avoid altering performance. High-content shell powder cements based on a calcium carbonate-etringite-carbo-aluminate product system according to embodiments 1 to 3 can all be applied in real projects. Finally, it should be noted that the above embodiments are intended only to describe the technical solutions of the present invention and do not in any way constitute a limitation. Although the present invention has been described with reference to its preferred embodiments, a person skilled in the art should understand that it is possible to make various modifications to the form and details without departing from the spirit and scope of the present invention as defined by the accompanying claims. BE2026 / 7274.