Nano-modified calcareous dry-process manufactured-sand low-carbon high-strength concrete and preparation method thereof

Abstract

This application discloses a low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand and its preparation method, relating to the field of concrete technology. The concrete comprises, by weight, 5-10 parts of modifier, 725-750 parts of calcareous dry-process manufactured sand, 0-40 parts of coal gangue powder, 300-320 parts of cement, 100-120 parts of mineral powder, 60-80 parts of fly ash, 950-1050 parts of crushed stone, 5.5-5.6 parts of admixture, and 155-165 parts of water; the modifier is a compound mixture of nano-calcium carbonate and nano-silica. This application constructs a three-level gradient filling system of "micron-sized stone powder-nano calcium carbonate-nano silica", which reduces the proportion of harmful and multi-harmful pores and increases the proportion of harmless pores. The dual chemical reinforcement mechanism is achieved through the co-admixture of nano calcium carbonate and nano silica, which enables concrete to maintain high strength, good uniformity and workability while reducing the total amount of cementitious materials and cement, and further enhances the mechanical properties and impermeability of concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to a low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand and its preparation method. Background Technology

[0002] Traditional high-strength concrete relies primarily on high-volume cementitious materials to ensure mechanical strength and durability. However, this method is not only costly in terms of materials but also results in high carbon emissions during cement production, leading to a generally high carbon emission level in the concrete industry and hindering its green and low-carbon transformation. Therefore, reducing the amount of cement and cementitious materials and increasing the substitution rate of mineral admixtures, while balancing concrete strength, volume stability, and long-term durability, is the core technological path to achieving low-carbon development of concrete in this field.

[0003] Manufactured sand has become the mainstream raw material for fine aggregate in concrete in my country. Dry-process manufactured sand uses air classification to precisely control the stone powder content, eliminating the need for water washing, thus saving water and being environmentally friendly. It can completely retain the original stone powder particles produced by crushing the parent rock, resulting in a significantly higher resource utilization rate than the wet process, and its engineering application advantages are prominent. The lithology and production process of manufactured sand directly affect its performance in concrete. Among them, calcareous dry-process manufactured sand prepared from limestone has unique technical advantages that siliceous manufactured sand does not possess. Limestone has a dense structure and high strength, and the crushed manufactured sand particles are slightly alkaline with a surface rich in free Ca. 2+ Active sites; the micron-sized limestone powder retained from the dry process can play multiple modifying roles in cement-based systems: First, the micro-aggregate filling effect can fill the voids between cement particles, reduce the porosity of the paste, and improve the density of the matrix; second, the nucleation effect can serve as a nucleation site for the heterogeneous phase of CSH gel, promoting the uniform growth of hydration products and accelerating the early hydration hardening of concrete; third, the chemical activity effect, the calcium carbonate in the stone powder can react with tricalcium aluminate in cement clinker to form a stable Mc phase (C3A·CaCO3·11H2O), inhibiting the conversion of ettringite to monosulfide calcium sulfoaluminate, stabilizing the hydration product system, and ensuring the long-term strength growth and volume stability of concrete.

[0004] Nanomaterials, with their superior size and surface activity, can effectively optimize the microstructure of cement-based materials, making them a research hotspot in the building materials field. Among them, nano-calcium carbonate and nano-silica are readily available, have mature processes, and exhibit excellent modification properties, making them the most widely used nanomaterials for modification. Nano-calcium carbonate has a particle size of only 40–80 nm, much smaller than cement particles (10–100 μm) and fly ash particles (1–100 μm). It can fill micropores such as gel pores and capillaries, achieving multi-level gradient filling from micrometer to nanometer, thus refining the pore structure of the matrix. At the same time, its high specific surface area can provide a large number of hydration active sites, significantly accelerating the early hydration of cement and improving the early mechanical properties of concrete.

[0005] Existing technologies have yielded some research on the modification of calcareous dry-process manufactured sand and the modification of single-component nanomaterials, but significant technical deficiencies remain, and an efficient multi-scale synergistic low-carbon modification system has not yet been formed. Firstly, existing studies mostly employ single-component nano-calcium carbonate or nano-silica modification, with insufficient research on the synergistic modification mechanism and application effects of their combined use. In particular, a "micro-nano" multi-scale synergistic modification system coupling nanomaterials with micron-level CaCO3 stone powder from calcareous dry-process manufactured sand has not been constructed, failing to fully leverage the multi-level powder superposition enhancement effect. Secondly, traditional high-strength concrete mix design methods do not utilize the quasi-cementing activity of calcareous dry-process manufactured sand and still follow the design approach of high cementitious material content, resulting in low stone powder resource utilization and high concrete carbon emission intensity, making it difficult to meet the industry's low-carbon development needs.

[0006] Typical existing technologies, such as the early-strength high-performance concrete technology disclosed in patent CN103979886B, only use nano-silica modification, which has obvious technical shortcomings: the cement consumption of this scheme is as high as 550kg / m³, the amount of cementitious materials is large, and the carbon emissions are high; moreover, the fine aggregate is only river sand, without taking advantage of the filling and active modification advantages of dry-process manufactured sand and gravel powder, and without adopting a nano-compound synergistic modification scheme, it is impossible to ensure the high performance of concrete while reducing the amount of cementitious materials. It has problems such as low resource utilization, poor low carbon content, and single modification effect. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this application provides a nano-modified calcareous dry-process manufactured sand low-carbon high-strength concrete and its preparation method, in order to solve the technical problems of existing high-strength concrete, such as the need for a large amount of cementitious materials to ensure high performance, low resource utilization, poor low-carbon properties, and limited modification effects.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A nano-modified calcareous dry-process manufactured sand low-carbon high-strength concrete, comprising, by weight: The mixture comprises 5-10 parts modifier, 725-750 parts calcareous dry-process manufactured sand, 0-40 parts coal gangue powder, 300-320 parts cement, 100-120 parts mineral powder, 60-80 parts fly ash, 950-1050 parts crushed stone, 5.5-5.6 parts admixture, and 155-165 parts water; wherein the modifier is a compound mixture of nano-calcium carbonate and nano-silica, and the mass ratio of nano-calcium carbonate to nano-silica is 1:0.5. The nano-calcium carbonate is a white powder, existing in the calcite crystal form, with a particle size of 40-80 nm, a specific surface area of ​​not less than 24 m² / g, a calcium carbonate weight content of not less than 95%, and a pH value of 9.5-10.0.

[0009] The nano-silica is fumed silica, an amorphous white powder with a primary particle size of 7-40 nm, a BET specific surface area of ​​150-380 m² / g, a silica content of not less than 99.8%, and a surface rich in silanol groups with a density of 3-4.5 OH / nm².

[0010] The calcareous dry-process manufactured sand is manufactured sand prepared from limestone through a series of dry crushing, screening and air classification processes. The parent rock is limestone, the stone powder content is 8%-12%, the fineness modulus is 2.5-3.0, the MB value is not greater than 1.0, and the crushing index is not greater than 16%.

[0011] In one embodiment, the coal gangue powder is prepared by grinding coal gangue, calcining it at high temperature, and then activating it.

[0012] In one embodiment, the cement is P·O 52.5 grade ordinary Portland cement with a specific surface area of ​​not less than 350 m² / kg; the mineral powder is S95 grade granulated blast furnace slag powder with a density of not less than 2.8 g / cm³, a specific surface area of ​​not less than 400 m² / kg, and a 28-day activity index of not less than 95%; the fly ash is Grade I fly ash with a fineness of not more than 2.5% residue on a 45 μm square-hole sieve.

[0013] In one embodiment, the crushed stone is 5-25mm continuously graded limestone crushed stone, with a crushing index of no more than 15%, a needle-like and flaky particle content of no more than 8%, and a mud content of no more than 0.5%; the admixture is a polycarboxylate-based high-performance water-reducing agent with a water reduction rate of no less than 25%; and the water is deionized water or clean tap water that meets the standards for concrete mixing water.

[0014] This application also provides a method for preparing high-strength concrete, wherein the concrete is the above-mentioned nano-modified calcareous dry-process manufactured sand low-carbon high-strength concrete, comprising the following steps: S1, add 5-10 parts of modifier to 55 parts of water, and disperse by high-speed shear for 5 minutes to fully disperse the nanoparticles and obtain nano-dispersion suspension A; S2: Weigh 725-750 parts of calcareous dry-process manufactured sand, 0-40 parts of coal gangue powder, 300-320 parts of cement, 100-120 parts of mineral powder, 60-80 parts of fly ash, 950-1050 parts of crushed stone, 5.5-5.6 parts of admixture and 155-165 parts of water, and mechanically mix them evenly to obtain slurry B; S3, add the nano-dispersed suspension A obtained in step S1 to the slurry B in step S2, and mechanically stir until the slurry is uniform and the workability meets the design requirements, thus obtaining the nano-modified calcium dry-process manufactured sand low-carbon high-strength concrete mixture.

[0015] Compared with the prior art, this application has at least the following beneficial effects: 1. This invention utilizes naturally occurring micron-sized limestone powder (1-10 μm) in calcareous dry-process manufactured sand, combined with added nano-calcium carbonate (40-80 nm) and nano-silica (7-40 nm), to construct a three-level gradient filling system of "micron-sized stone powder-nano-calcium carbonate-nano-silica". In this system, micron-sized stone powder fills the micron-sized voids between cement particles (10-100 μm), nano-calcium carbonate fills the nano-sized gel pores between cement hydration products, and nano-silica fills the finer CSH gel interlayer voids and ITZ microcracks. The particles of three progressively decreasing particle sizes form a continuous particle size distribution curve, achieving a stepwise dense filling from the micron to the nanoscale. This significantly reduces the total porosity of concrete, refines the pore structure distribution, and substantially reduces the proportion of harmful pores (>50 nm) and highly harmful pores (>100 nm), while significantly increasing the proportion of harmless pores (<20 nm).

[0016] 2. This invention achieves a dual chemical strengthening mechanism through the co-doping of nano-calcium carbonate and nano-silica. On the one hand, nano-calcium carbonate, acting as heterogeneous nucleation sites, promotes the uniform precipitation and growth of cement hydration products on its surface, accelerating the early hydration reaction process. Simultaneously, it reacts with C3A in the cement to generate the Mc phase. This reaction consumes the aluminum phase component, stabilizes the long-term existence of ettringite, and inhibits the conversion of ettringite to monosulfide-type calcium sulfoaluminate, thereby maintaining the volume stability of the hydration products and promoting the sustained development of long-term concrete strength. On the other hand, the silanol groups on the surface of nano-silica rapidly ionize in the alkaline environment of the cement pore solution, releasing active [SiO4]. 4- The tetrahedral monomers undergo a high pozzolanic reaction with the large amount of calcium hydroxide produced during cement hydration, generating additional CSH gel and consuming CH crystals. CH is the weakest link in the ITZ; its substantial consumption and conversion into CSH gel significantly improves the microstructure of the ITZ, reduces its thickness and porosity, and creates a denser chemical bond interface between the aggregate and cement paste. This allows the concrete to maintain high strength, good uniformity, and workability even with reduced total cementitious materials and cement content.

[0017] 3. Optionally, this invention incorporates coal gangue powder as an auxiliary cementing component, forming a synergistic effect of silicon-aluminum-calcium multi-components with the core components (calcareous dry-processed sand, nano-calcium carbonate, and nano-silica). The resource utilization of coal gangue powder as a bulk industrial solid waste further reduces raw material costs and carbon emissions. The active Al2O3 in coal gangue powder releases Al2O3 in an alkaline environment. 3+Ions can chemically react with CaCO3 provided by calcareous dry-processed sand and nano-calcium carbonate, promoting the formation of more Mc phases; simultaneously, the active SiO2 in coal gangue powder reacts with the pozzolanic reaction of nano-silica to form a relay effect, continuously consuming CH and generating CSH gel. The two work together to form a CASH composite gel system, in which Al... 3+ Al / Si isomorphic substitution of silicate tetrahedral chains can extend silicate chain length, improve gel crosslinking and density, thereby further enhancing the mechanical properties and impermeability of concrete. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below through specific embodiments. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0019] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0020] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0021] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical connection or internal connection between two components. They can be direct connection or indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0022] To better understand the technical solution of the present invention, the present invention will be described in detail below.

[0023] Example 1: This example provides a low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand, obtained through the following preparation steps: Step 1: Add 6.7 parts of nano-calcium carbonate and 3.3 parts of nano-silica to 55 parts of water, and disperse using high-speed shear for 5 minutes to fully disperse the nanoparticles and obtain nano-dispersion suspension A. Step 2: Weigh 300 parts cement, 100 parts mineral powder, 60 parts fly ash, 40 parts coal gangue powder, 725 parts calcareous dry-process manufactured sand, 1000 parts crushed stone, 5.5 parts admixture and 100 parts water and mechanically mix them evenly to obtain slurry B. Step 3: Add the nano-dispersed suspension A obtained in Step 1 to the slurry B in Step 2, and mechanically stir until the slurry is uniform and the workability meets the design requirements, thus obtaining the nano-modified calcium dry-process manufactured sand low-carbon high-strength concrete mixture.

[0024] The nano-calcium carbonate is a white powder, existing in the calcite crystal form, with a particle size of 40-80 nm, a specific surface area of ​​not less than 24 m² / g, a calcium carbonate weight content of not less than 95%, and a pH value of 9.5-10.0. The nano-silica is fumed silica, an amorphous white powder with a primary particle size of 7-40 nm, a BET specific surface area of ​​150-380 m² / g, a silica content of not less than 99.8%, and a surface rich in silanol groups with a density of 3-4.5 OH / nm². The calcareous dry-process manufactured sand is manufactured sand prepared from limestone through a series of dry crushing, screening, and air classification processes. The parent rock is limestone, with a stone powder content of 8%-12%, a fineness modulus of 2.5-3.0, an MB value of not more than 1.0, and a crushing index of not more than 16%. The coal gangue powder is prepared by grinding coal gangue, calcining it at high temperature, and then activating it. The coal gangue powder consists of SiO2 and Al2O3. The cement is P·O 52.5 grade ordinary Portland cement with a specific surface area of ​​not less than 350 m² / kg. The mineral powder is S95 grade granulated blast furnace slag powder with a density of not less than 2.8 g / cm³, a specific surface area of ​​not less than 400 m² / kg, and a 28-day activity index of not less than 95%; the fly ash is Grade I fly ash with a fineness of not more than 2.5% residue on a 45 μm square-hole sieve; the crushed stone is 5-25 mm continuously graded limestone crushed stone with a crushing index of not more than 15%, a needle-like and flaky particle content of not more than 8%, and a mud content of not more than 0.5%; the admixture is a polycarboxylate-based high-performance water-reducing agent with a water reduction rate of not less than 25%; the water is deionized water or clean tap water that meets the standard for concrete mixing water (JGJ 63).

[0025] Comparative Example 1 provides a manufactured sand concrete, which is obtained by the following preparation steps: weighing 320 parts of cement, 120 parts of mineral powder, 80 parts of fly ash, 725 parts of ordinary manufactured sand, 1000 parts of crushed stone, 5.5 parts of admixture and 155 parts of water, mixing the above raw materials and mechanically stirring to mix evenly, thus obtaining the manufactured sand concrete mixture.

[0026] Comparative Example 2 provides a calcareous dry-process manufactured sand concrete, which is obtained by the following preparation steps: weighing 300 parts of cement, 120 parts of mineral powder, 80 parts of fly ash, 725 parts of calcareous dry-process manufactured sand, 1000 parts of crushed stone, 5.5 parts of admixture and 155 parts of water, mixing the above raw materials and mechanically stirring to mix evenly, thus obtaining the calcareous dry-process manufactured sand concrete mixture.

[0027] Comparative Example 3 provides a calcareous dry-process manufactured sand concrete, which is obtained by the following preparation steps: weighing 300 parts of cement, 100 parts of mineral powder, 40 parts of coal gangue powder, 725 parts of calcareous dry-process manufactured sand, 1000 parts of crushed stone, 5.5 parts of admixture and 155 parts of water, mixing the above raw materials and mechanically stirring to mix evenly, thus obtaining the calcareous dry-process manufactured sand concrete mixture.

[0028] Comparative Example 4 provides a low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand, obtained through the following preparation steps: Step 1: Add 10 parts of nano-silica to 55 parts of water and disperse using high-speed shear for 5 minutes to fully disperse the nanoparticles and obtain nano-dispersion suspension A. Step 2: Weigh 300 parts cement, 100 parts mineral powder, 60 parts fly ash, 40 parts coal gangue powder, 725 parts calcareous dry-process manufactured sand, 1000 parts crushed stone, 5.5 parts admixture, and 100 parts water, and mechanically mix them evenly to obtain slurry B. Step 3: Add the nano-dispersed suspension A obtained in Step 1 to the slurry B in Step 2, and mechanically stir until the slurry is uniform and the workability meets the design requirements, thus obtaining the nano-modified calcium dry-process manufactured sand low-carbon high-strength concrete mixture.

[0029] Comparative Example 5 provides a low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand, obtained through the following preparation steps: Step 1: Add 10 parts of nano-calcium carbonate to 55 parts of water and disperse using high-speed shear for 5 minutes to fully disperse the nanoparticles and obtain nano-dispersion suspension A. Step 2: Weigh 300 parts cement, 100 parts mineral powder, 60 parts fly ash, 40 parts coal gangue powder, 725 parts calcareous dry-process manufactured sand, 1000 parts crushed stone, 5.5 parts admixture, and 100 parts water, and mechanically mix them evenly to obtain slurry B. Step 3: Add the nano-dispersed suspension A obtained in Step 1 to the slurry B in Step 2, and mechanically stir until the slurry is uniform and the workability meets the design requirements, thus obtaining the nano-modified calcium dry-process manufactured sand low-carbon high-strength concrete mixture.

[0030] Table 1 shows a comparison of the raw material components of Example 1 and Comparative Examples 1-5:

[0031] Table 2 shows a comparison of the test data of the prepared concrete in Example 1 and Comparative Examples 1-5:

[0032] As shown in Example 1 and Comparative Example 1, the simultaneous introduction of calcareous dry-process manufactured sand, nano-modifier, and coal gangue powder into concrete can increase the 28-day compressive strength of concrete from 62.0 MPa to 74.5 MPa, reduce the drying shrinkage value, and achieve a significant increase in strength under the condition of reducing cement content by 20 kg / m³ and total cementitious material by 20 kg / m³. This is attributed to the triple effect of micro-aggregate filling, CSH nucleation, and Mc phase formation of limestone powder in calcareous dry-process manufactured sand; the "nucleation acceleration-volcanic ash densification" relay enhancement mechanism formed by the combination of nano-calcium carbonate and nano-silica; and the combined effect of active Al2O3 and SiO2 in coal gangue powder synergistically forming a CASH composite gel system with the above components. Comparative Examples 1 and 2 show that replacing ordinary manufactured sand with calcareous dry-process manufactured sand increases the slump of concrete. Although the 28-day strength decreases slightly due to the reduction in total binder and cement content, it still meets the strength requirements. This is attributed to the fact that calcareous dry-process manufactured sand does not contain harmful clay minerals such as montmorillonite. The complexation effect between stone powder particles and the carboxyl groups of water-reducing agent delays the consumption of water-reducing agent molecules. At the same time, the triple effect of limestone powder in dry-process sand partially compensates for the strength loss caused by the reduction in binder. Comparing Example 1 with Comparative Examples 4 and 5, it can be seen that the combined admixture of nano-calcium carbonate and nano-silica has a better effect on improving the concrete strength than either admixture alone. The combined admixture can achieve a 28-day compressive strength of 74.5 MPa, which is higher than that of the single admixture groups of nano-calcium carbonate and nano-silica. This indicates that the nucleation acceleration effect of nano-calcium carbonate and the pozzolanic densification effect of nano-silica form a relay synergistic mechanism in the chemical pathway: the more CH and CSH produced by the accelerated early hydration of nano-calcium carbonate provide more pozzolanic reaction substrates for nano-silica. The reinforcing CSH generated by nano-silica further fills the capillary pores in the denser initial microstructure. In addition, the micro-expansion of the Mc phase generated by nano-calcium carbonate can partially offset the effect of the water loss and shrinkage of the large amount of CSH gel in nano-silica. As a result, Example 1 has the highest strength and the drying shrinkage value is better than that of the single admixture groups. Comparative Examples 2 and 3 show that adding coal gangue powder to calcareous dry-process manufactured sand concrete increases the 28-day compressive strength of the concrete. This is attributed to the reaction of active Al2O3 and CaCO3 in the coal gangue powder to form the Mc phase, and the participation of active SiO2 in the pozzolanic reaction, both of which together form a CASH composite gel. 3+ For Si 4+ The isomorphic substitution extended the silicate chain length, thereby increasing the crosslinking degree of the gel; The nano-modified calcareous dry-process manufactured sand low-carbon high-strength concrete prepared by this invention utilizes a nano-modifier, calcareous dry-process manufactured sand, and coal gangue powder to produce a triple synergistic effect. The combination of nano-calcium carbonate and nano-silica creates a relay reinforcement mechanism, while the Si-Al-Ca synergistic effect of coal gangue powder, along with the interaction of multiple substances, enables full utilization of industrial solid waste, reduces cement usage and building material energy consumption, reduces carbon emissions, and enhances the workability of concrete while meeting construction requirements. It has the advantages of good workability, high compressive strength, low drying shrinkage, low cost, environmental protection, low energy consumption, and easy preparation.

[0033] This invention combines the multi-effect modification mechanism of calcareous dry-processed sand and gravel powder with the "micro-nano" synergistic modification technology of nanomaterials to develop a low-carbon, high-strength concrete formula and preparation method. It can significantly reduce the amount of cement and cementitious materials used and reduce carbon emissions, while effectively improving the mechanical strength and volume stability of concrete. It has important engineering application value and environmental significance.

[0034] This invention improves the compressive strength of calcareous dry-process manufactured sand concrete and reduces the amount of cementitious materials by adding a composite modifier of nano-calcium carbonate and nano-silica to the concrete. Nano-calcium carbonate and nano-silica, as inorganic nanomaterials, have the characteristics of small particle size, large specific surface area, and high surface activity. When nano-calcium carbonate and nano-silica are added to concrete, the heterogeneous nucleation sites provided by nano-calcium carbonate induce the uniform precipitation and growth of cement hydration products on its surface, accelerating the early hydration reaction process. Simultaneously, nano-calcium carbonate reacts chemically with tricalcium aluminate in the cement to generate… Mc phase inhibits the early-formed ettringite from transforming into monosulfide calcium sulfoaluminate and stabilizes expansive hydration products; the silanol groups on the surface of nano silica rapidly release active silicate ions in the alkaline environment of cement, reacting with calcium hydroxide produced by cement hydration to generate additional CSH gel, which can significantly improve the microstructure of ITZ, reduce ITZ thickness and porosity, and enhance the chemical bonding force between aggregate and cement paste, so that concrete can still maintain high strength, good uniformity and workability under the condition of reducing total cementitious materials and cement content.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A low-carbon, high-strength concrete using nano-modified calcareous dry-process manufactured sand, characterized in that, By weight, it includes: The mixture comprises 5-10 parts modifier, 725-750 parts calcareous dry-process manufactured sand, 0-40 parts coal gangue powder, 300-320 parts cement, 100-120 parts mineral powder, 60-80 parts fly ash, 950-1050 parts crushed stone, 5.5-5.6 parts admixture, and 155-165 parts water; wherein the modifier is a compound mixture of nano-calcium carbonate and nano-silica, and the mass ratio of nano-calcium carbonate to nano-silica is 1:0.

5. The nano-calcium carbonate is a white powder, existing in the calcite crystal form, with a particle size of 40-80 nm, a specific surface area of ​​not less than 24 m² / g, a calcium carbonate weight content of not less than 95%, and a pH value of 9.5-10.0; the nano-silica is fumed silica, an amorphous white powder with a primary particle size of 7-40 nm, a BET specific surface area of ​​150-380 m² / g, a silica content of not less than 99.8%, and a surface rich in silanol groups with a density of 3-4.5 OH / nm². The calcareous dry-process manufactured sand is manufactured sand prepared from limestone through a series of dry crushing, screening and air classification processes. The parent rock is limestone, the stone powder content is 8%-12%, the fineness modulus is 2.5-3.0, the MB value is not greater than 1.0, and the crushing index is not greater than 16%.

2. The low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand according to claim 1, characterized in that, The coal gangue powder is prepared by grinding coal gangue, calcining it at high temperature, and then activating it.

3. The low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand according to claim 1, characterized in that, The cement is P·O 52.5 grade ordinary Portland cement with a specific surface area of ​​not less than 350 m² / kg; the mineral powder is S95 grade granulated blast furnace slag powder with a density of not less than 2.8 g / cm³, a specific surface area of ​​not less than 400 m² / kg, and a 28-day activity index of not less than 95%; the fly ash is Grade I fly ash with a fineness of not more than 2.5% residue on a 45 μm square-hole sieve.

4. The low-carbon, high-strength concrete made from nano-modified calcareous dry-process manufactured sand according to claim 1, characterized in that, The crushed stone is 5-25mm continuously graded limestone crushed stone, with a crushing index of no more than 15%, a needle-like and flaky particle content of no more than 8%, and a mud content of no more than 0.5%; the admixture is a polycarboxylate-based high-performance water-reducing agent with a water reduction rate of no less than 25%; the water is deionized water or clean tap water that meets the standards for concrete mixing water.

5. A method for preparing high-strength concrete, characterized in that, The concrete is the nano-modified calcareous dry-process manufactured sand low-carbon high-strength concrete according to any one of claims 1-4, comprising the following steps: S1, add 5-10 parts of modifier to 55 parts of water, and disperse by high-speed shear for 5 minutes to fully disperse the nanoparticles and obtain nano-dispersion suspension A; S2: Weigh 725-750 parts of calcareous dry-process manufactured sand, 0-40 parts of coal gangue powder, 300-320 parts of cement, 100-120 parts of mineral powder, 60-80 parts of fly ash, 950-1050 parts of crushed stone, 5.5-5.6 parts of admixture and 155-165 parts of water, and mechanically mix them evenly to obtain slurry B; S3, add the nano-dispersed suspension A obtained in step S1 to the slurry B in step S2, and mechanically stir until the slurry is uniform and the workability meets the design requirements, thus obtaining the nano-modified calcium dry-process manufactured sand low-carbon high-strength concrete.

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