A low-heat and anti-cracking Portland cement with less clinker and a preparation method thereof

Abstract

The application provides a low-heat and low-fuel-silicate cement and a preparation method thereof, and belongs to the technical field of silicate cement. The anti-cracking agent used in the application has a three-layer core-shell structure and a multi-stage release function, and can perfectly solve the contradiction of "early water retention, medium-term anti-shrinkage and late micro-expansion" in a low-fuel system. The superfine calcium carbonate can provide nucleation sites in the early hydration stage of cement, so that the hydration product is changed from coarse plate-shaped crystals to fine needle-shaped or fibrous crystals, which are uniformly distributed in the pores, so as to eliminate the stress concentration points at the micro level and improve the anti-cracking performance of the cement material. The internal curing material can absorb water and store it in the internal pore structure. When the internal curing material is added to the cement, a "micro-reservoir" can be formed in the cement, which can continuously provide hydration water for the unhydrated cementitious material under low humidity conditions, thereby significantly reducing the self-shrinkage.

Description

Technical Field

[0001] This invention relates to the field of silicate cement technology, and in particular to a low-clinker, low-heat, crack-resistant silicate cement and its preparation method. Background Technology

[0002] Fly ash, commonly known as fly ash, is the ash emitted from the flue after the combustion of pulverized coal in thermal power generation. With the development of thermal power generation, a large amount of fly ash is emitted every year. Excess fly ash can only be piled up and stored, which not only occupies valuable land resources but also pollutes the environment. Therefore, it is crucial to realize the resource utilization of fly ash.

[0003] Fly ash mainly consists of silica, alumina, iron oxide, calcium oxide, and unburned carbon. Therefore, it can be used as a cementitious material to replace cement, thereby reducing cement costs and carbon dioxide emissions during cement production, resulting in significant energy conservation and emission reduction. However, while fly ash as a cementitious material can improve workability, reduce heat of hydration, and enhance later-stage strength, its inherent physicochemical properties also lead to engineering challenges such as low early-stage strength, increased autogenous shrinkage, and susceptibility to cracking, severely limiting the application of fly ash cement. Summary of the Invention

[0004] The purpose of this invention is to provide a low-clinker, low-heat, crack-resistant silicate cement and its preparation method. The low-clinker, low-heat, crack-resistant silicate cement provided by this invention has high early strength, low autogenous shrinkage, and is not prone to cracking.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a low-clinker, low-heat, crack-resistant silicate cement, which, by mass parts, comprises 10-20 parts silicate cement clinker, 40-50 parts granulated blast furnace slag powder, 15-30 parts fly ash, 6-10 parts crack-resistant agent, 1-5 parts cement admixture, 3-8 parts ultrafine calcium carbonate, and 2-4 parts internal curing material. The crack-resistant agent has a three-layer core-shell structure; the crack-resistant agent includes a core, an intermediate layer, and an outer shell arranged sequentially from the inside to the outside; the core includes rapid-hardening sulfoaluminate cement, fluorogypsum, and a binder; the intermediate layer includes a calcium oxide powder layer adsorbed on the surface of the core and a coating layer covering the calcium oxide powder layer; the coating layer is ethyl cellulose or cellulose acetate; the outer shell includes polyvinyl alcohol and a water-retaining thickener; The particle size of the ultrafine calcium carbonate is ≤10μm; The internal curing material is diatomaceous earth that has undergone water absorption treatment or porous glass microspheres that have undergone water absorption treatment.

[0006] Preferably, the mass ratio of rapid-hardening sulfoaluminate cement to fluorogypsum in the core of the crack-resistant agent is 1:(0.8~1.2).

[0007] Preferably, the core particle size of the crack-resistant agent is 80~150μm.

[0008] Preferably, the mass ratio of the core and the calcium oxide powder layer in the crack-resistant agent is 1:(0.2~0.6).

[0009] Preferably, the water-retaining thickener in the outer shell of the crack-resistant agent is hydroxypropyl methylcellulose or hydroxyethyl cellulose, and the mass of the water-retaining thickener is 10-30% of the mass of polyvinyl alcohol.

[0010] Preferably, the thickness of the outer shell in the crack-resistant agent is 10~20μm.

[0011] Preferably, the particle size of the anti-cracking agent is 100~200μm.

[0012] Preferably, the method for preparing the crack-resistant agent includes the following steps: (1) After mixing rapid-hardening sulfoaluminate cement, fluorogypsum and binder solution, the mixture is granulated and dried in sequence to obtain the core; (2) Mix the core and calcium oxide powder obtained in step (1) to obtain a mixture, and then mix the mixture with the coating solution and solidify it to obtain a core-calcium oxide-coating layer; (3) Mix the polyvinyl alcohol solution and the water-retaining thickener to obtain a PVA mixture. Mix the core-calcium oxide-coating layer obtained in step (2) with the PVA mixture and then dry it to obtain an anti-crack agent.

[0013] Preferably, the diatomaceous earth has a particle size of 40~200μm; the porous glass microspheres have a particle size of 0.1~2mm; and the water absorption treatment involves mixing diatomaceous earth or porous glass microspheres with saturated lime water for adsorption.

[0014] The present invention provides a method for preparing low-clinker, low-heat, crack-resistant silicate cement as described in the above technical solution, comprising: mixing silicate cement clinker, granulated blast furnace slag powder, fly ash, crack-resistant agent, cement admixture, ultrafine calcium carbonate and internal curing material to obtain low-clinker, low-heat, crack-resistant silicate cement.

[0015] This invention provides a low-clinker, low-heat, crack-resistant silicate cement, comprising, by weight, 10-20 parts silicate cement clinker, 40-50 parts granulated blast furnace slag powder, 15-30 parts fly ash, 6-10 parts crack-resistant agent, 1-5 parts cement admixture, 3-8 parts ultrafine calcium carbonate, and 2-4 parts internal curing material; the crack-resistant agent has a three-layer core-shell structure; the crack-resistant agent includes a core, an intermediate layer, and an outer shell arranged sequentially from the inside out; the core includes rapid-hardening sulfoaluminate cement, fluorogypsum, and a binder; the intermediate layer includes a calcium oxide powder layer adsorbed on the surface of the core and a coating layer covering the calcium oxide powder layer; the coating layer is ethyl cellulose or cellulose acetate; the outer shell includes polyvinyl alcohol and a water-retaining thickener; the particle size of the ultrafine calcium carbonate is ≤10μm; the internal curing material is water-absorbing diatomaceous earth or water-absorbing porous glass microspheres. The crack-resistant agent in this invention has a three-layer core-shell structure and a multi-stage release function, which can perfectly solve the contradiction of "early water retention, mid-term shrinkage resistance, and late-stage micro-expansion" in a low-clinker system. The ultrafine calcium carbonate can provide nucleation sites in the early stage of cement hydration, so that the hydration products are transformed from coarse plate-like crystals into fine needle-like or fibrous crystals, which are evenly distributed in the pores, thereby eliminating stress concentration points at the microscopic level and improving the crack resistance of cement materials. The internal pore structure of the internal curing material stores water, which can form a "micro reservoir" inside the cement, continuously providing hydration water source for unhydrated cementitious materials under low humidity conditions, thereby significantly reducing self-shrinkage. The results of the embodiments show that the low-clinker, low-heat, crack-resistant silicate cement provided by the present invention has a 3-day flexural strength ≥ 5.8 MPa, a 3-day compressive strength > 21.5 MPa, a 28-day flexural strength > 8 MPa, a 28-day compressive strength > 48 MPa, a 3-day heat of hydration < 165 KJ / kg, a 7-day heat of hydration < 195 KJ / kg, a 28-day heat of hydration < 255 KJ / kg, a 1-day shrinkage rate ≤ 0.005%, a 3-day shrinkage rate ≤ 0.010%, a 7-day shrinkage rate ≤ 0.025%, a 14-day shrinkage rate ≤ 0.030%, a 28-day shrinkage rate ≤ 0.005%, and a 90-day shrinkage rate ≤ 0.005%. Detailed Implementation

[0016] This invention provides a low-clinker, low-heat, crack-resistant silicate cement, which, by mass parts, comprises 10-20 parts silicate cement clinker, 40-50 parts granulated blast furnace slag powder, 15-30 parts fly ash, 6-10 parts crack-resistant agent, 1-5 parts cement admixture, 3-8 parts ultrafine calcium carbonate, and 2-4 parts internal curing material. The crack-resistant agent has a three-layer core-shell structure; the crack-resistant agent includes a core, an intermediate layer, and an outer shell arranged sequentially from the inside to the outside; the core includes rapid-hardening sulfoaluminate cement, fluorogypsum, and a binder; the intermediate layer includes a calcium oxide powder layer adsorbed on the surface of the core and a coating layer covering the calcium oxide powder layer; the coating layer is ethyl cellulose or cellulose acetate; the outer shell includes polyvinyl alcohol and a water-retaining thickener; The particle size of the ultrafine calcium carbonate is ≤10μm; The internal curing material is diatomaceous earth that has undergone water absorption treatment or porous glass microspheres that have undergone water absorption treatment.

[0017] The low-clinker, low-heat, crack-resistant silicate cement provided by this invention comprises 10-20 parts by weight of silicate cement clinker. In one embodiment of this invention, the mass fraction of the silicate cement clinker can be 11, 12, 13, 14, 15, 16, 17, 18, or 19 parts. In this invention, the silicate cement clinker is the framework builder of the system, reacting rapidly with water to generate hydrated calcium silicate (CSH) gel and calcium hydroxide (CH), establishing an early (1-3 days) mechanical framework. Simultaneously, the calcium hydroxide (CH) generated during clinker hydration and the resulting high-alkalinity environment can activate granulated blast furnace slag powder and fly ash for secondary hydration reactions, ensuring the system remains stable.

[0018] In one embodiment of the present invention, the silicate cement clinker may be P·O 42.5 or P·O 52.5; the specific surface area of ​​the silicate cement clinker may be 300~350 m². 2 / kg; the particle size D90 of the silicate cement clinker can be ≤45μm; the residue of the silicate cement clinker on a square hole sieve with a fineness of 45μm can be ≤12wt.%; the particle size of the silicate cement clinker can be ≥3μm.

[0019] Based on a mass fraction of 10-20 parts of silicate cement clinker, the low-clinker, low-heat, crack-resistant silicate cement provided by this invention includes 40-50 parts of granulated blast furnace slag powder. In one embodiment of this invention, the mass fraction of the granulated blast furnace slag powder can be 41, 42, 43, 44, 45, 46, 47, 48, or 49 parts. In this invention, granulated blast furnace slag powder is the main component for improving the later-stage strength of the low-clinker, low-heat, crack-resistant silicate cement. Under the CH activation provided by the silicate cement clinker, the granulated blast furnace slag powder undergoes a secondary hydration reaction, generating low-alkalinity CSH gel, significantly improving the strength at 7-28 days and later stages, filling the strength gap caused by insufficient clinker. Furthermore, the generated CSH gel is denser, refining the pore structure and reducing the risk of chloride ion penetration and sulfate attack. Simultaneously, the hydration rate of the granulated blast furnace slag powder is slow and the heat of reaction is low, which can reduce the heat of hydration.

[0020] In one embodiment of the present invention, the granulated blast furnace slag powder can be S105 grade slag powder; the specific surface area of ​​the granulated blast furnace slag powder can be 500~550 m². 2 / kg; the 7-day activity of the granulated blast furnace slag powder can be ≥95%; the 28-day activity of the granulated blast furnace slag powder can be ≥105%.

[0021] Based on a clinker mass fraction of 10-20 parts, the low-clinker, low-heat, crack-resistant silicate cement provided by this invention includes 15-30 parts of fly ash. In one embodiment of this invention, the fly ash mass fraction can be 16, 18, 20, 22, 24, 25, 26, or 28 parts. In this invention, the fly ash can optimize the microstructure of the cement through morphological effects (ball effect) and micro-aggregate filling, reducing water demand and improving workability. It can also dilute the clinker concentration, delay the peak hydration heat release, reduce hydration heat, reduce early temperature rise cracks and drying shrinkage, and react with CH to generate CSH in the later stages, contributing to long-term strength, thereby improving the long-term crack resistance of silicate cement.

[0022] In one embodiment of the present invention, the fly ash can be Class I fly ash from a power plant; the residue of the fly ash on a square-hole sieve with a fineness of 0.08 mm can be ≤10 wt.%; and the loss on ignition of the fly ash can be ≤5 wt.%.

[0023] Based on a mass fraction of 10-20 parts of silicate cement clinker, the low-clinker, low-heat, crack-resistant silicate cement provided by this invention includes 6-10 parts of crack-resistant agent. In one embodiment of this invention, the mass fraction of the crack-resistant agent can be 7, 8, or 9 parts. The crack-resistant agent added in this invention has a three-layer core-shell structure and a multi-stage release function, perfectly resolving the contradiction of "early water retention, mid-term shrinkage resistance, and late-stage micro-expansion" in a low-clinker system.

[0024] In this invention, the crack-resistant agent has a three-layer core-shell structure; the crack-resistant agent includes a core, an intermediate layer and an outer shell arranged sequentially from the inside to the outside.

[0025] In this invention, the core of the crack-resistant agent comprises rapid-hardening sulfoaluminate cement, fluorogypsum, and a binder; the preferred mass ratio of the rapid-hardening sulfoaluminate cement to fluorogypsum is 1:(0.8~1.2), more preferably 1:(0.9~1.1), and even more preferably 1:1. This invention does not have a specific limitation on the amount of binder used, as long as it is sufficient to agglomerate the rapid-hardening sulfoaluminate cement and fluorogypsum into granular material. This invention, by adding a binder, can bind calcium sulfoaluminate clinker and fluorogypsum to form granular material; with rapid-hardening sulfoaluminate cement and fluorogypsum as the core, ettringite is continuously generated during the later stages of hydration through ion penetration and solid-phase reaction, achieving micro-expansion in the later stages, thereby preventing cracking.

[0026] In one embodiment of the present invention, the standard designation of the rapid-hardening sulfoaluminate cement may be R·SAC42.5; the fluorogypsum may be a by-product of a hydrofluoric acid plant; the mass percentage of calcium sulfate in the fluorogypsum may be ≥96%; the residue of the fluorogypsum on a square-hole sieve with a fineness of 80μm may be ≤10wt.%; and the specific surface area of ​​the fluorogypsum may be 300~400m². 2 / kg; the binder can be polyethylene glycol or PEG-400.

[0027] In this invention, the particle size of the core is preferably 80-150 μm. As one embodiment of this invention, the particle size of the core can be 90 μm, 100 μm, 110 μm, 120 μm, or 130 μm, 140 μm.

[0028] In this invention, the intermediate layer of the crack-resistant agent comprises a calcium oxide powder layer adsorbed on the core surface and a coating layer covering the calcium oxide powder layer; the mass ratio of the core to the calcium oxide powder layer is preferably 1:(0.2~0.6); the coating layer is preferably ethyl cellulose (EC) or cellulose acetate (CA). In this invention, the calcium oxide powder acts as an expansion source, generating calcium hydroxide during hydration, which increases in volume and causes the concrete paste to expand. This expansion effectively compensates for the shrinkage of the concrete, reducing cracks caused by drying shrinkage and temperature changes; the coating layer formed by EC or CA not only fixes the calcium oxide powder inside but also hydrolyzes in an alkaline environment, thereby releasing the internal calcium oxide expansion source.

[0029] In one embodiment of the present invention, the mass ratio of the core to the calcium oxide powder layer can be 1:(0.4~0.5); the particle size of the calcium oxide powder can be ≤10μm.

[0030] In one embodiment of the present invention, the thickness of the coating layer can be 5~15μm, or 6μm, 8μm, 10μm or 12μm. By controlling the thickness of the coating layer, the present invention can prevent the internal calcium oxide powder from escaping from the coating layer.

[0031] In this invention, the outer shell of the crack-resistant agent comprises polyvinyl alcohol and a water-retaining thickener; the water-retaining thickener is preferably 10-30% of the mass of polyvinyl alcohol. In this invention, the molecular chains of polyvinyl alcohol intertwine to form a continuous, dense solid film, which becomes the main structure of the outer shell, while the water-retaining thickener is fixed in the outer shell during the process of the polyvinyl alcohol molecular chains intertwining.

[0032] In one embodiment of the present invention, the polyvinyl alcohol can be PVA-1788; the water-retaining thickener can be hydroxypropyl methylcellulose (HPMC) or hydroxyethyl cellulose (HEC). In another embodiment of the present invention, the mass of the water-retaining thickener is preferably 12%, 15%, 18%, 20%, 22%, 25%, or 28% of the mass of polyvinyl alcohol in the polyvinyl alcohol solution. The present invention uses polyvinyl alcohol as a shell, which dissolves within 5-15 minutes after contact with mixing water, releasing water-retaining thickener components and locking in free water, thereby significantly improving the water retention capacity of cement paste while reducing water evaporation channels and decreasing plastic shrinkage and drying shrinkage.

[0033] In one embodiment of the present invention, the thickness of the outer shell can be 10~20μm, or 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm or 19μm. By controlling the thickness of the outer shell, the present invention can improve its stability and avoid cracking.

[0034] In one embodiment of the present invention, the particle size of the anti-cracking agent can be 100~200μm, or 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm or 190μm.

[0035] In this invention, the crack-resistant agent has a three-layer core-shell structure. When the polyvinyl alcohol in the outer shell of the crack-resistant agent comes into contact with water, it undergoes hydrolysis, thereby releasing the water-retaining and thickening components that are fixed due to the entanglement of polyvinyl alcohol, thus improving the water retention performance of the cement slurry. Subsequently, during the curing process, as the hydration reaction proceeds, the pH value of the system rises to an alkaline environment. The coating layer formed by EC or CA will undergo hydrolysis in the alkaline environment, releasing the internal calcium oxide expansion source. Calcium oxide reacts with water to generate calcium hydroxide, achieving volume expansion and reducing the shrinkage of the system. Finally, the rapid-hardening sulfoaluminate cement and fluorogypsum in the core continuously generate ettringite through ion penetration and solid-phase reaction in the middle and late stages of hydration, achieving micro-expansion in the later stage, thereby avoiding cracking in the later stage.

[0036] In this invention, the method for preparing the crack-resistant agent preferably includes the following steps: (1) After mixing rapid-hardening sulfoaluminate cement, fluorogypsum and binder solution, the mixture is granulated and dried in sequence to obtain the core; (2) Mix the core and calcium oxide powder obtained in step (1) to obtain a mixture, and then mix the mixture with the coating solution and solidify it to obtain a core-calcium oxide-coating layer; (3) Mix the polyvinyl alcohol solution and the water-retaining thickener to obtain a PVA mixture. Mix the core-calcium oxide-coating layer obtained in step (2) with the PVA mixture and then dry it to obtain an anti-crack agent.

[0037] In this invention, rapid-hardening sulfoaluminate cement, fluorogypsum, and binder solution are mixed and then granulated and dried sequentially to obtain the core.

[0038] In one embodiment of the present invention, the adhesive solution may be a polyethylene glycol aqueous solution with a mass concentration of 2-5%, or a polyethylene glycol aqueous solution with a mass concentration of 3-4%; the ratio of the total mass of the rapid-hardening sulfoaluminate cement and fluorogypsum to the mass of the adhesive solution may be (5-10):1, or may be 6:1, 7:1, 8:1 or 9:1.

[0039] In this invention, the preferred method for mixing the calcium sulfoaluminate clinker, fluorogypsum, and binder solution is as follows: first, the calcium sulfoaluminate clinker and fluorogypsum are mixed and then ground to obtain a composite powder with a particle size of 5-10 μm. Then, the composite powder is placed in a granulator for rolling, and the binder solution is added via spraying. This invention does not impose any special limitations on the specific grinding operation, as long as the particle size of the composite powder meets the requirements. This invention also does not impose any special limitations on the specific spraying operation; conventional spraying methods are sufficient.

[0040] The present invention does not impose any special limitations on the specific operation of granulation. Based on the technical common sense of those skilled in the art, it is sufficient to ensure that the particle size of the core meets the requirements.

[0041] In one embodiment of the present invention, the drying temperature can be 60-80°C. The present invention does not have a specific limitation on the drying time, as long as it is sufficient to dry to a constant weight. The present invention removes moisture through drying.

[0042] After obtaining the core, the present invention preferably mixes the core and calcium oxide powder to obtain a mixture, and then mixes the mixture with the coating solution and then solidifies it to obtain a core-calcium oxide-coating layer.

[0043] This invention does not impose any particular limitation on the mixing method of the core and calcium oxide powder, as long as they are mixed evenly. As one embodiment of this invention, the core and calcium oxide powder can be mixed by rolling the core in the calcium oxide powder. By mixing the core and calcium oxide powder, this invention can coat the core surface with a layer of calcium oxide powder, facilitating subsequent coating with the coating solution.

[0044] In this invention, the coating layer solution is preferably an ethanol solution of ethyl cellulose or an ethanol solution of cellulose acetate; the mass concentration of the coating layer solution is preferably 3-8%. As one embodiment of this invention, the mass concentration of the coating layer solution can be 4%, 5%, 6%, or 7%. By using the above-mentioned coating layer solution for coating, this invention achieves good adhesion properties, thereby forming a coating layer of the desired thickness on the surface.

[0045] In this invention, the preferred method for mixing the mixture and the coating solution is to spray the coating solution onto the surface of the mixture; the preferred temperature for mixing the mixture and the coating solution is 40~50°C.

[0046] The present invention does not impose any special limitation on the amount relationship between the mixture and the coating solution, as long as the thickness of the coating layer meets the requirements.

[0047] This invention does not impose any special limitations on the curing temperature and time, which can be determined based on the technical common sense of those skilled in the art. In one embodiment of this invention, the curing temperature can be 40~50℃; the curing time can be 1~2 hours.

[0048] After obtaining the core-calcium oxide-coating layer, the present invention preferably mixes a polyvinyl alcohol solution and a water-retaining thickener to obtain a PVA mixture. The core-calcium oxide-coating layer and the PVA mixture are then mixed and dried to obtain a crack-resistant agent.

[0049] In this invention, the mass concentration of the polyvinyl alcohol solution is preferably 5-10%; the solvent in the polyvinyl alcohol solution is preferably water. As one embodiment of this invention, the mass concentration of the polyvinyl alcohol solution can be 6%, 7%, 8%, or 9%. By controlling the mass concentration of the polyvinyl alcohol solution, this invention can obtain a PVA mixture with excellent adhesion properties after mixing with a water-retaining thickener, thereby forming a shell layer of the required thickness on the surface of the coating layer.

[0050] The present invention does not have any particular limitation on the specific method of mixing the polyvinyl alcohol solution and the water-retaining thickener, as long as they are mixed evenly.

[0051] In this invention, the preferred method for mixing the core-calcium oxide-coating layer and the PVA mixture is to spray the PVA mixture onto the surface of the core-calcium oxide-coating layer.

[0052] The present invention does not impose any special limitations on the dosage relationship between the core-calcium oxide-coating layer and the PVA mixture, as long as the thickness of the outer shell in the crack-resistant agent meets the requirements.

[0053] In this invention, the drying temperature is preferably ≤45°C. There is no particular limitation on the drying time; drying to a constant weight is sufficient. By drying at a lower temperature, this invention avoids excessive cross-linking of PVA or denaturation of the water-retaining thickener.

[0054] Based on a mass fraction of 10-20 parts of silicate cement clinker, the low-clinker, low-heat, crack-resistant silicate cement provided by this invention includes 1-5 parts of cement admixture. In one embodiment of this invention, the mass fraction of the cement admixture can be 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, or 4.5 parts. In this invention, the water-reducing agent releases the encapsulated water through dispersion, reducing the water-cement ratio without decreasing fluidity, thereby significantly improving the density and strength of the material; the early-strength agent accelerates the hydration process of the cementitious materials (clinker, slag), providing a rapidly forming physical skeleton, thereby significantly improving the early strength of cement-based materials.

[0055] As one embodiment of the present invention, the cement admixture may include a water-reducing agent and an early-strength agent; the water-reducing agent may be a polycarboxylate water-reducing agent; the early-strength agent may be sodium sulfate or triethanolamine; the mass ratio of the water-reducing agent to the early-strength agent may be (1~2):(1~2).

[0056] Based on a mass fraction of 10-20 parts of silicate cement clinker, the low-clinker, low-heat, crack-resistant silicate cement provided by this invention comprises 3-8 parts of ultrafine calcium carbonate; the particle size of the ultrafine calcium carbonate is ≤10μm; and the specific surface area of ​​the ultrafine calcium carbonate is preferably ≥15000m². 2 / kg. In one embodiment of the present invention, the mass fraction of the ultrafine calcium carbonate can be 4, 5, 6, or 7 parts. In this invention, the ultrafine calcium carbonate can provide nucleation sites in the early stages of cement hydration, causing the hydration products to transform from coarse plate-like crystals into fine needle-like or fibrous crystals, which are uniformly distributed in the pores, thereby eliminating stress concentration points at the microscopic level and improving the crack resistance of cement materials.

[0057] Based on 10-20 parts by weight of silicate cement clinker, the low-clinker, low-heat, crack-resistant silicate cement provided by this invention includes 2-4 parts of internal curing material; the internal curing material is diatomaceous earth treated with water absorption or porous glass microspheres treated with water absorption; the particle size of the diatomaceous earth is preferably 40-200 μm; the particle size of the porous glass microspheres is preferably 0.1-2 mm; the water absorption treatment is preferably performed by mixing diatomaceous earth or porous glass microspheres with saturated lime water for adsorption. As one embodiment of this invention, the mass fraction of the internal curing material can be 2.5 parts, 3 parts, or 3.5 parts. In this invention, the internal curing material can absorb and store moisture in its internal pore structure. When added to cement, it can form a "micro-reservoir" inside the cement, continuously providing hydration water for unhydrated cementitious materials under low humidity conditions, thereby significantly reducing self-shrinkage.

[0058] In this invention, the crack-resistant agent has a three-layer core-shell structure. The polyvinyl alcohol in the outer shell hydrolyzes upon contact with water, releasing water-retaining and thickening components that were previously fixed due to the entanglement of polyvinyl alcohol, thus improving the water retention performance of the cement slurry. Subsequently, during the curing process, as the hydration reaction proceeds, the pH of the system rises to an alkaline environment. The coating layer formed by EC or CA undergoes hydrolysis in this alkaline environment, releasing the internal calcium oxide expansion source. Calcium oxide reacts with water to generate calcium hydroxide, achieving volume expansion and reducing system shrinkage. Finally, the rapid-hardening sulfoaluminate cement and fluorogypsum in the core undergo ionization during the later stages of hydration. The continuous generation of ettringite through penetration and solid-phase reaction enables micro-expansion in the later stages, thereby preventing cracking. Ultrafine calcium carbonate can provide nucleation sites in the early stages of cement hydration, transforming hydration products from coarse plate-like crystals into fine needle-like or fibrous crystals, which are evenly distributed in the pores. This eliminates stress concentration points at the microscopic level and improves the crack resistance of cement materials. The internal curing material can absorb and store moisture in its internal pore structure. When added to cement, it can form a "miniature reservoir" inside the cement, continuously providing hydration water to unhydrated cementitious materials under low humidity conditions, thereby significantly reducing self-shrinkage.

[0059] The low-clinker, low-heat, crack-resistant silicate cement provided by this invention can achieve the characteristics of reduced consumption, reduced emissions, waste utilization, and reduced costs, and has social, economic, and environmental benefits.

[0060] The present invention provides a method for preparing low-clinker, low-heat, crack-resistant silicate cement as described in the above technical solution, comprising: mixing silicate cement clinker, granulated blast furnace slag powder, fly ash, crack-resistant agent, cement admixture, ultrafine calcium carbonate and internal curing material to obtain low-clinker, low-heat, crack-resistant silicate cement.

[0061] In this invention, the mixing is preferably carried out in a mixer. This invention does not impose any specific limitations on the model or source of the mixer; any commercially available mixer well-known to those skilled in the art can be used.

[0062] In this invention, the mixing is preferably carried out under stirring conditions. This invention does not impose any particular limitation on the order of addition of the components during mixing; it can be determined based on the technical knowledge of those skilled in the art. This invention also does not impose any particular limitation on the stirring rate; it can be determined based on the technical knowledge of those skilled in the art to ensure uniform mixing of the components. As one embodiment of this invention, the mixing method may involve first mixing silicate cement clinker, granulated blast furnace slag powder, and fly ash, and then sequentially adding cement admixtures, ultrafine calcium carbonate, internal curing materials, and crack-resistant agents; the stirring speed during mixing can be 400~500 r / min.

[0063] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] The specific parameters of each component in the embodiments and comparative examples of this invention are as follows: The silicate cement clinker has a P·O 42.5 content and a specific surface area of ​​320 m². 2 / kg, the particle size D90 of silicate cement clinker is ≤45μm, the residue of silicate cement clinker on a square hole sieve with a fineness of 45μm is ≤12wt.%, and the particle size of silicate cement clinker is ≥3μm.

[0065] The granulated blast furnace slag powder is S105 grade slag powder, and the specific surface area of ​​the granulated blast furnace slag powder is 520 m². 2 / kg, the 7-day activity of granulated blast furnace slag powder is ≥95%, and the 28-day activity of granulated blast furnace slag powder is ≥105%.

[0066] The fly ash is grade I fly ash from power plants, with a sieve residue of ≤10wt.% on a 0.08mm square-hole sieve and a loss on ignition of ≤5wt.%.

[0067] The crack-resistant agent has a three-layer core-shell structure; the crack-resistant agent consists of a core, an intermediate layer, and an outer shell arranged sequentially from the inside to the outside. The core components of the crack-resistant agent are rapid-hardening sulfoaluminate cement, fluorogypsum, and a binder; the mass ratio of the rapid-hardening sulfoaluminate cement to the fluorogypsum is 1:1. The standard designation for the rapid-hardening sulfoaluminate cement is R·SAC 42.5; the fluorogypsum is a byproduct of a hydrofluoric acid plant; the calcium sulfate content in the fluorogypsum is ≥96% by mass; the residue of the fluorogypsum on an 80μm square-hole sieve is ≤10wt.%; the specific surface area of ​​the fluorogypsum is 350m². 2 / kg; the binder is PEG-400; The intermediate layer consists of a calcium oxide powder layer adsorbed on the surface of the core and a coating layer covering the calcium oxide powder layer; the particle size of the calcium oxide powder in the calcium oxide powder layer is ≤10μm; the mass ratio of the core to the calcium oxide powder layer is 1:0.5; the coating layer is EC. The outer shell is composed of polyvinyl alcohol and a water-retaining thickener; the polyvinyl alcohol is PVA-1788, and the water-retaining thickener is HPMC; the mass of the water-retaining thickener is 20% of the mass of the polyvinyl alcohol. The core has a particle size of 80~150μm; the coating layer has a thickness of 10μm; the outer shell has a thickness of 20μm; and the anti-cracking agent has a particle size of 100~200μm. The method for preparing the crack-resistant agent is as follows: (1) First, calcium sulfoaluminate clinker and fluorogypsum are mixed and ground to obtain composite powder with a particle size of 5~10μm. Then, the composite powder is put into a granulator for rolling, and the binder solution is added by spraying. Finally, granulation and drying at 80℃ are carried out to obtain the core. The binder solution is a 5% polyethylene glycol aqueous solution. The ratio of the total mass of the rapid hardening sulfoaluminate cement and fluorogypsum to the mass of the binder solution is 8:1. (2) The core obtained in step (1) is rolled in calcium oxide powder to obtain a mixture. Then, a coating solution is sprayed onto the surface of the mixture at 50°C and cured at 50°C for 2 hours to obtain a core-calcium oxide-coating layer. The coating solution is an ethanol solution of ethyl cellulose. The mass concentration of the coating solution is 5%. (3) Mix a 5% polyvinyl alcohol aqueous solution and a water-retaining thickener to obtain a PVA mixture. Spray the PVA mixture onto the surface of the core-calcium oxide-coating layer obtained in step (2) and then dry it at 40°C to obtain an anti-crack agent.

[0068] The cement admixture is a water-reducing agent and an early-strength agent; the water-reducing agent is a polycarboxylate water-reducing agent; the early-strength agent is sodium sulfate; the mass ratio of the water-reducing agent to the early-strength agent is 1:1.

[0069] The particle size of the ultrafine calcium carbonate is ≤10μm; the specific surface area of ​​the ultrafine calcium carbonate is ≥15000m². 2 / kg.

[0070] The internal curing material is porous glass microspheres that have undergone water absorption treatment in saturated lime water; the particle size of the porous glass microspheres is 0.1~2mm; the specific surface area of ​​the porous glass microspheres is ≥250m². 2 / g.

[0071] Example 1 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 20 parts silicate cement clinker, 50 parts granulated blast furnace slag powder, 20 parts fly ash, 6 parts crack-resistant agent, 2 parts cement admixture, 5 parts ultrafine calcium carbonate, and 4 parts internal curing material. The preparation method of the low-clinker, low-heat, crack-resistant silicate cement is as follows: at a stirring rate of 500 r / min, silicate cement clinker, granulated blast furnace slag powder and fly ash are first mixed in a mixer, and then cement admixture, ultrafine calcium carbonate, internal curing material and crack-resistant agent are added in sequence and mixed evenly to obtain low-clinker, low-heat, crack-resistant silicate cement.

[0072] Example 2 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 18 parts silicate cement clinker, 45 parts granulated blast furnace slag powder, 26 parts fly ash, 8 parts crack-resistant agent, 3 parts cement admixture, 3 parts ultrafine calcium carbonate, and 2 parts internal curing material. Other conditions are the same as in Example 1.

[0073] Example 3 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 17 parts silicate cement clinker, 48 parts granulated blast furnace slag powder, 25 parts fly ash, 7 parts crack-resistant agent, 4 parts cement admixture, 5 parts ultrafine calcium carbonate, and 3 parts internal curing material. Other conditions are the same as in Example 1.

[0074] Example 4 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 15 parts silicate cement clinker, 48 parts granulated blast furnace slag powder, 27 parts fly ash, 8 parts crack-resistant agent, 2 parts cement admixture, 6 parts ultrafine calcium carbonate, and 4 parts internal curing material. Other conditions are the same as in Example 1.

[0075] Example 5 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 10 parts silicate cement clinker, 50 parts granulated blast furnace slag powder, 30 parts fly ash, 8 parts crack-resistant agent, 2 parts cement admixture, 6 parts ultrafine calcium carbonate, and 3 parts internal curing material. Other conditions are the same as in Example 1.

[0076] Example 6 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 17 parts silicate cement clinker, 50 parts granulated blast furnace slag powder, 20 parts fly ash, 8 parts crack-resistant agent, 5 parts cement admixture, 7 parts ultrafine calcium carbonate, and 3 parts internal curing material. Other conditions are the same as in Example 1.

[0077] Comparative Example 1 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 20 parts silicate cement clinker, 50 parts granulated blast furnace slag powder, 20 parts fly ash, 2 parts cement admixture, 5 parts ultrafine calcium carbonate, and 4 parts internal curing material. The preparation method of the low-clinker, low-heat, crack-resistant silicate cement is as follows: at a stirring rate of 500 r / min, silicate cement clinker, granulated blast furnace slag powder and fly ash are first mixed in a mixer, and then cement admixtures, ultrafine calcium carbonate and internal curing materials are added in sequence and mixed evenly to obtain low-clinker, low-heat, crack-resistant silicate cement.

[0078] Comparative Example 2 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 20 parts silicate cement clinker, 50 parts granulated blast furnace slag powder, 20 parts fly ash, 6 parts crack-resistant agent, 2 parts cement admixture, and 4 parts internal curing material. The preparation method of the low-clinker, low-heat, crack-resistant silicate cement is as follows: at a stirring rate of 500 r / min, silicate cement clinker, granulated blast furnace slag powder and fly ash are first mixed in a mixer, and then cement admixtures, internal curing materials and crack-resistant agents are added in sequence and mixed evenly to obtain low-clinker, low-heat, crack-resistant silicate cement.

[0079] Comparative Example 3 A low-clinker, low-heat, crack-resistant silicate cement, by mass parts, consists of 20 parts silicate cement clinker, 50 parts granulated blast furnace slag powder, 20 parts fly ash, 6 parts crack-resistant agent, 2 parts cement admixture and 5 parts ultrafine calcium carbonate. The preparation method of the low-clinker, low-heat, crack-resistant silicate cement is as follows: at a stirring rate of 500 r / min, silicate cement clinker, granulated blast furnace slag powder and fly ash are first mixed in a mixer, and then cement admixture, ultrafine calcium carbonate and crack-resistant agent are added in sequence and mixed evenly to obtain low-clinker, low-heat, crack-resistant silicate cement.

[0080] Comparative Example 4 A low-clinker, low-heat, crack-resistant silicate cement, by weight, comprises 20 parts silicate cement clinker, 50 parts granulated blast furnace slag powder, 20 parts fly ash, 6 parts crack-resistant agent, 2 parts cement admixture, 5 parts ultrafine calcium carbonate, and 4 parts internal curing material; wherein the crack-resistant agent is calcium sulfoaluminate. The preparation method of the low-clinker, low-heat, crack-resistant silicate cement is as follows: at a stirring rate of 500 r / min, silicate cement clinker, granulated blast furnace slag powder and fly ash are first mixed in a mixer, and then cement admixture, ultrafine calcium carbonate, internal curing material and crack-resistant agent are added in sequence and mixed evenly to obtain low-clinker, low-heat, crack-resistant silicate cement.

[0081] The mechanical properties of the low-clinker, low-heat, crack-resistant silicate cements prepared in Examples 1-6 and Comparative Examples 1-4 were tested according to GB 175-2023. The results are shown in Table 1. Table 1. Mechanical properties of low-clinker, low-heat, crack-resistant silicate cements prepared in Examples 1-6 and Comparative Examples 1-4

[0082] As shown in Table 1, when the crack-resistant agent, ultrafine calcium carbonate, and internal curing material are omitted, the early flexural and compressive strengths are less affected. However, without the crack-resistant agent, the compressive and flexural strengths decrease significantly at 28 days, indicating that the addition of the crack-resistant agent can improve the later strength of low-clinker, low-heat crack-resistant silicate cement. The comparison between Example 1 and Comparative Example 4 shows that the crack-resistant agent used in this invention can improve the mechanical properties of clinker in the later stages of hydration compared to existing crack-resistant agents.

[0083] The heat of hydration of the low-clinker, low-heat, crack-resistant silicate cements prepared in Examples 1-6 and Comparative Examples 1-4 was tested according to GB / T 200-2017. The results are shown in Table 2. Table 2 shows the heat of hydration of low-clinker, low-heat, crack-resistant silicate cements prepared in Examples 1-6 and Comparative Examples 1-4.

[0084] As can be seen from Table 2, the low-clinker, low-heat, crack-resistant silicate cement provided by the present invention can significantly reduce its heat of hydration by adding crack-resistant agent, ultrafine calcium carbonate and internal curing material; the comparison between Example 1 and Comparative Example 4 shows that the crack-resistant agent used in the present invention can reduce the heat of hydration of cement compared with existing crack-resistant agents.

[0085] The shrinkage rates of the low-clinker, low-heat, crack-resistant silicate cements prepared in Examples 1-6 and Comparative Examples 1-4 were tested according to GB / T 749-2008. The results are shown in Table 3. Table 3. Shrinkage rates of low-clinker, low-heat, crack-resistant silicate cements prepared in Examples 1-6 and Comparative Examples 1-4

[0086] As can be seen from Table 3, the present invention can significantly reduce the shrinkage rate of low-clinker, low-heat, crack-resistant silicate cement by adding crack-resistant agent, ultrafine calcium carbonate and internal curing material, thereby improving its crack resistance performance. The comparison between Example 1 and Comparative Example 4 shows that the crack-resistant agent used in the present invention can significantly reduce the shrinkage of cement compared with existing crack-resistant agents.

[0087] In summary, the preparation method of the low-clinker, low-heat, crack-resistant silicate cement provided by this invention is simple, low-cost, uses readily available raw materials, and is green and low-carbon. At the same time, the strength, heat of hydration, and drying shrinkage of the cement mortar fully meet the national standards for cement, and have significant economic and environmental benefits.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-clinker, low-heat, crack-resistant silicate cement, comprising, by weight parts, 10-20 parts silicate cement clinker, 40-50 parts granulated blast furnace slag powder, 15-30 parts fly ash, 6-10 parts crack-resistant agent, 1-5 parts cement admixture, 3-8 parts ultrafine calcium carbonate, and 2-4 parts internal curing material; The crack-resistant agent has a three-layer core-shell structure; the crack-resistant agent includes a core, an intermediate layer, and an outer shell arranged sequentially from the inside to the outside; the core includes rapid-hardening sulfoaluminate cement, fluorogypsum, and a binder; the intermediate layer includes a calcium oxide powder layer adsorbed on the surface of the core and a coating layer covering the calcium oxide powder layer; the coating layer is ethyl cellulose or cellulose acetate; the outer shell includes polyvinyl alcohol and a water-retaining thickener; The particle size of the ultrafine calcium carbonate is ≤10μm; The internal curing material is diatomaceous earth that has undergone water absorption treatment or porous glass microspheres that have undergone water absorption treatment.

2. The low-clinker, low-heat, crack-resistant silicate cement according to claim 1, characterized in that, The mass ratio of rapid-hardening sulfoaluminate cement and fluorogypsum in the core of the crack-resistant agent is 1:(0.8~1.2).

3. The low-clinker, low-heat, crack-resistant silicate cement according to claim 1, characterized in that, The core particle size of the anti-cracking agent is 80~150μm.

4. The low-clinker, low-heat, crack-resistant silicate cement according to claim 1, characterized in that, The mass ratio of the core and the calcium oxide powder layer in the anti-cracking agent is 1:(0.2~0.6).

5. The low-clinker, low-heat, crack-resistant silicate cement according to claim 1, characterized in that, The water-retaining thickener in the outer shell of the anti-cracking agent is hydroxypropyl methylcellulose or hydroxyethyl cellulose, and the mass of the water-retaining thickener is 10-30% of the mass of polyvinyl alcohol.

6. The low-clinker, low-heat, crack-resistant silicate cement according to claim 1, characterized in that, The thickness of the outer shell in the anti-cracking agent is 10~20μm.

7. The low-clinker, low-heat, crack-resistant silicate cement according to claim 1, characterized in that, The particle size of the crack-resistant agent is 100~200μm.

8. The low-clinker, low-heat, crack-resistant silicate cement according to any one of claims 1 to 7, characterized in that, The method for preparing the crack-resistant agent includes the following steps: (1) After mixing rapid-hardening sulfoaluminate cement, fluorogypsum and binder solution, the mixture is granulated and dried in sequence to obtain the core; (2) Mix the core and calcium oxide powder obtained in step (1) to obtain a mixture, and then mix the mixture with the coating solution and solidify it to obtain a core-calcium oxide-coating layer; (3) Mix the polyvinyl alcohol solution and the water-retaining thickener to obtain a PVA mixture. Mix the core-calcium oxide-coating layer obtained in step (2) with the PVA mixture and then dry it to obtain an anti-crack agent.

9. The low-clinker, low-heat, crack-resistant silicate cement according to claim 1, characterized in that, The diatomaceous earth has a particle size of 40~200μm; the porous glass microspheres have a particle size of 0.1~2mm; the water absorption treatment involves mixing diatomaceous earth or porous glass microspheres with saturated lime water for adsorption.

10. A method for preparing the low-clinker, low-heat, crack-resistant silicate cement according to any one of claims 1 to 9, comprising: Silicate cement clinker, granulated blast furnace slag powder, fly ash, crack-resistant agent, cement admixture, ultrafine calcium carbonate, and internal curing material are mixed to obtain low-clinker, low-heat, crack-resistant silicate cement.

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