Modified superfine limestone powder for concrete and preparation process of modified superfine limestone powder

Abstract

The preparation process comprises the following steps: collecting stone powder generated in an aggregate production process, screening twice, purifying until the passing rate of 325-mesh sieve pores is greater than or equal to 95% to obtain superfine limestone powder, adding a modified material and a powdery additive for improving workability, and uniformly mixing to obtain the modified superfine limestone powder. The modified superfine limestone powder is used for concrete to improve the working performance, the mechanical performance and the durability of the concrete, the cement consumption is greatly reduced, carbon emission is directly reduced from the source, the mixing cost of the concrete is reduced, and the construction efficiency of the concrete is improved. In tunnel construction, the modified superfine limestone powder is doped, so that the rebound rate of the sprayed concrete is greatly reduced, the cohesiveness of the concrete is greatly improved on the premise that the flowability and the water-retaining property are not changed, and the strength is improved compared with the original mix proportion, so that the utilization rate of the concrete is greatly improved, and relatively high economic benefits are created.

Description

Technical Field

[0001] The invention relates to the technical field of concrete, in particular to modified ultrafine limestone powder for concrete and a preparation process thereof. Background Art

[0003] Concrete is an important building material in engineering projects. Cement and fly ash are the main components of concrete. Therefore, the amount of the two is the key factor in determining the carbon emissions of concrete.

[0004] Fly ash is a waste product of power plants. The production capacity is limited by the amount of power generated. The coal used by different power plants in different regions produces different quality of fly ash. According to the technical requirements of the high-performance concrete used in the construction of high-speed rail projects, fly ash, a raw material of cementitious materials in concrete, is indispensable. However, its resources are limited, and finding a substitute is the goal that engineering researchers have been pursuing.

[0005] In the aggregate industry, stone powder is a production derivative that is difficult to handle. In principle, it can be added to concrete as an admixture, but unscreened and untreated stone powder often does not meet the requirements. On the contrary, blind use will have a greater negative impact on the mechanical properties and working performance of concrete. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the existing defects and provide a modified ultrafine limestone powder for concrete and a preparation process thereof, which are used to improve the mechanical properties and durability of concrete, improve its working performance, reduce the amount of cement, replace fly ash or mineral powder, and also bring greater economic benefits, promote the green, healthy and sustainable development of the industry, and can effectively solve the problems in the background technology.

[0007] To achieve the above-mentioned purpose, the present invention provides the following technical scheme: a modified ultrafine limestone powder for concrete, wherein the main component of the modified ultrafine limestone powder comes from stone powder produced in the aggregate production process, wherein the weight of the stone powder accounts for 50% to 90%, the weight of the modified material accounts for 10% to 50%, and the weight of the admixture accounts for 0.1% to 1%.

[0008] As a preferred technical solution of the present invention, the modified material is an active mineral admixture for concrete, such as high-fineness silica fume, S95 mineral powder, etc., which is selected according to the actual construction site.

[0009] As a preferred technical solution of the present invention, the admixture is a surfactant, such as dry powder polycarboxylate water reducer, fatty acid salt water reducer, etc., which is selected according to the actual construction site.

[0010] A process for preparing modified ultrafine limestone powder for concrete, characterized in that: stone powder generated in the aggregate production process is collected, screened twice and purified to a 325-mesh sieve with a pass rate of more than 95% to obtain ultrafine limestone powder, modified materials and powdered admixtures for improving workability are added, and the mixture is mixed evenly after accurate weighing, and the finished product is obtained after packaging.

[0011] As a preferred technical solution of the present invention, the stirring time is more than 6 minutes to ensure the uniformity of the product.

[0012] Application of modified ultrafine limestone powder for concrete in shotcrete: In each cubic meter of shotcrete, the cement addition amount is 350kg~354kg, and the modified ultrafine limestone powder addition amount is 118kg~136kg. The slump of the shotcrete is 215mm, 215mm, and it has good workability and fluidity.

[0013] Application of modified ultrafine limestone powder in commercial concrete mix: The commercial mix ratio is as follows: water-binder ratio is 0.50, cement dosage is 238kg / m 3 ~255kg / m 3 , the amount of limestone powder is 85kg / m 3 ~102kg / m 3 , water consumption is 170kg / m 3 .

[0014] Application of modified ultrafine limestone powder for concrete in self-compacting concrete: In each cubic meter of self-compacting concrete, the amount of cement added is 236kg~261kg, and the amount of modified ultrafine limestone powder added is 107kg~128kg.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] This modified ultrafine limestone powder can be used in concrete to improve its working performance, mechanical properties and durability, significantly reduce cement usage, directly reduce carbon emissions from the source, save concrete mix costs, and improve concrete construction efficiency. It can be applied to different operating methods and different grades of concrete, and has extremely broad market prospects.

[0017] This modified ultrafine limestone powder can help construction units to quickly open up the market in the field of concrete engineering construction. While improving the working performance, mechanical properties and durability of tunnel concrete, it can significantly reduce the amount of cement in tunnel concrete and solve the quality defects of fly ash. In particular, the improvement effect on shotcrete is particularly outstanding, increasing the workability and viscosity of concrete, reducing the rebound rate of shotcrete, improving work efficiency, reducing construction costs, and creating good economic benefits for enterprises.

[0018] This modified ultrafine limestone powder can also be used as a low-energy, low-carbon alternative to cement adhesive. When used in tunnel concrete, it can significantly reduce the amount of cement used, directly reducing carbon emissions from the source. While improving the working performance, mechanical properties and durability of tunnel concrete, it can significantly reduce the amount of cement used in shotcrete and the rebound rate of shotcrete. It can significantly reduce the construction cost of shotcrete from both the mix ratio and rebound rate levels, and significantly reduce the carbon emissions of tunnel concrete. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The present invention provides a technical solution: a modified ultrafine limestone powder for concrete, wherein the main component of the modified ultrafine limestone powder comes from stone powder produced in the aggregate production process, wherein the stone powder accounts for 50% to 90% by weight, the modified material accounts for 10% to 50% by weight, and the admixture accounts for 0.1% to 1% by weight.

[0021] The preparation process of modified ultrafine limestone powder for concrete is as follows: stone powder generated in the aggregate production process is collected, and after being screened twice, it is purified to a 325-mesh sieve with a passing rate of more than 95% to obtain ultrafine limestone powder, and active mineral admixtures for modified concrete and a powdered admixture for improving workability, namely, a surfactant, are added, and after being accurately weighed, they are stirred for more than 6 minutes to ensure the uniformity of the product, and the finished product is obtained after packaging.

[0022] Among them, active mineral admixtures for concrete can be selected from high-fineness silica fume, S95 mineral powder, etc. according to the construction site, and surfactants can be selected from dry powder polycarboxylate water reducer, fatty acid salt water reducer, etc. according to the construction site.

[0023] Embodiment 1

[0024] The C25 shotcrete used in the initial support of the tunnel requires a large amount of cement, has a large amount of concrete rebound, and lacks concrete strength. In the mix ratio of C25 shotcrete used in the project, the amount of cement used is 497 kg per cubic meter, and the rebound is large, with a rebound rate of more than 30%, and some parts are even as high as more than 50%, which greatly increases the cost of tunnel construction.

[0025] Among them, the concrete rebound rate refers to the proportion of the total amount of shotcrete that cannot be solidified in time and cannot be avoided from rebounding and falling during the shotcrete process.

[0026] After improving the shotcrete mix ratio and using modified ultra-fine limestone powder, the amount of cement in each cubic meter of concrete was reduced from 497Kg to 350Kg, and 136Kg of modified ultra-fine limestone powder was added, while the other components remained unchanged. The working performance test of the finished concrete showed that the slump of the concrete was 220mm from the time it left the mixing station to the sampling before the test spraying, and the workability, fluidity, cohesion, water retention, etc. were good, meeting the requirements of on-site construction.

[0027] The experiment started from the arch foot, and the rebounded concrete was collected. After measurement, the rebound rate was about 13.8%, which reduced the concrete rebound rate by more than 60%. The 28-day strength of the cut sample of the shotcrete construction part was 38.2MPa, 39.8MPa, and 37.5MPa, respectively, which was slightly improved compared with the original mix ratio.

[0028] The corresponding table of building material mix ratio is as follows:

[0029]

[0030] Table 1

[0031] Embodiment 2

[0032] The shotcrete used for initial support of tunnels, after using modified ultra-fine limestone powder, the cement content per cubic meter of concrete was reduced from 474Kg to 354Kg, and 118Kg of modified ultra-fine limestone powder was added. The other components remained unchanged. Experiments were carried out in different batches at different locations. The results are as follows:

[0033] The first rebound rate is 20%, the strength after 1 day is 18.2MPa, and the strength after 28 days is 35.4MPa;

[0034] The second rebound rate is 5%; the strength is 16.7MPa in 1 day and 32.4MPa in 28 days;

[0035] The third rebound rate is 8%, the strength after 1 day is 22.1MPa, and the strength after 28 days is 34.0MPa;

[0036] The fourth rebound rate is 5.4%; the strength after 1 day is 15.1MPa, and the strength after 28 days is 30.4MPa

[0037] The fifth rebound rate was 6.8%;

[0038] The sixth rebound rate was 8.0%.

[0039] The corresponding table of building material mix ratio is as follows:

[0040]

[0041] Table 2

[0042] The data shows that the addition of modified ultrafine limestone powder greatly reduces the rebound rate of shotcrete. Under the premise of keeping fluidity and water retention unchanged, it greatly improves the cohesion of concrete. The strength is slightly increased compared with the original mix ratio, which greatly improves the utilization rate of concrete and creates higher economic benefits.

[0043] Embodiment 3

[0044] At the invitation of the commercial concrete mixing station, we optimized the mix ratio. Since the fly ash is far away from the power plant, the quality is unstable and deviated, and the purchase price is high, so it is recommended to use modified ultrafine limestone powder to replace fly ash. The comparative experiment is as follows:

[0045] The original mix ratio was designed to have a water-binder ratio of 0.50 and a cementitious material of 340 kg / m 3 , bulk density 2358kg / m 3 , including cement 272kg / m 3 , fly ash 68kg / m 3 , water 170kg / m 3 The slump of the trial concrete was 220mm, the actual 7-day strength was 27.1MPa, and the 28-day strength was 38.3MPa.

[0046] The first improvement of the mix ratio was to add modified ultrafine limestone powder, the water-binder ratio remained unchanged, and the cement dosage was 255kg / m 3 , the cement consumption is reduced by 17kg / m 3 , modified ultra-fine limestone powder completely replaces fly ash, with a dosage of 85kg / m 3 The amount of other raw materials remains basically unchanged. The slump of the trial concrete is 220mm. The concrete has good workability. The average strength after 7 days is 24.3MPa and the average strength after 28 days is 40.7MPa. The strength increases significantly in the later period.

[0047] The second improvement further reduces the amount of cement on the basis of Example 3, the water-cement ratio remains unchanged, and the cement consumption is reduced to 238kg / m3, which is 34kg / m3 less than the original cement consumption. Limestone powder replaces fly ash in an amount of 102kg / m3, and the amount of other raw materials remains basically unchanged. The slump of the trial-mixed concrete is 220mm, the concrete has good workability, the measured 7-day strength average value is 22.5MPa, and the 28-day strength average value is 38.0MPa, which meets the construction requirements and further reduces the manufacturing cost.

[0048] The corresponding table of the mix ratio of the commercial concrete mixing station and the mix ratio of the new composite materials is as follows:

[0049]

[0050] Table 3

[0051] Embodiment 4

[0052] It is understood that the strength surplus coefficient of some high-performance concretes on railways is too large, and the 56d strength of most concretes even reaches more than 150%. Based on this calculation, the 56-day strength of C30 reaches 45MPa, and the surplus coefficient greatly exceeds the design value.

[0053] At the invitation of China Railway Guangzhou Engineering Bureau of Guinan High-speed Railway Section 2, the research team optimized the high-performance concrete used in construction. Experts worked on the selection of raw materials and the optimization of mix ratio. Taking self-compacting concrete as an example, 107kg and 128kg of modified ultrafine limestone powder were used in each cubic meter of concrete to replace the corresponding amount of cement for verification.

[0054] The mix ratio and strength are as follows:

[0055]

[0056] Table 4

[0057] The core samples of the construction section were tested for 56d compressive strength. The core samples were dense in appearance and the aggregates were evenly distributed, meeting the strength requirements.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A modified ultrafine limestone powder for concrete, characterized in that: The main component of modified ultrafine limestone powder comes from stone powder produced in the aggregate production process, of which the weight of stone powder accounts for 50% to 90%, the weight of modified materials accounts for 10% to 50%, and the weight of admixtures accounts for 0.1% to 1%.

2. The modified ultrafine limestone powder for concrete and its preparation process according to claim 1, characterized in that: The modified material is an active mineral admixture for concrete, including but not limited to high-fineness silica fume and S95 mineral powder.

3. The modified ultrafine limestone powder for concrete and its preparation process according to claim 1, characterized in that: The admixture is a surfactant, including but not limited to dry powder polycarboxylate water reducer and fatty acid salt water reducer.

4. A process for preparing modified ultrafine limestone powder for concrete, characterized in that: The stone powder produced in the aggregate production process is collected, screened twice and purified to a 325-mesh sieve with a pass rate of more than 95% to obtain ultrafine limestone powder. Modified materials and powdered admixtures to improve workability are added, and after precise weighing, they are stirred evenly and packaged to obtain the finished product.

5. The preparation process of modified ultrafine limestone powder for concrete according to claim 3, characterized in that: The stirring time is more than 6 minutes to ensure the uniformity of the product.

6. Application of modified ultrafine limestone powder for concrete in shotcrete, characterized in that: In each cubic meter of shotcrete, the amount of cement added is 350kg~354kg, and the amount of modified ultrafine limestone powder added is 118kg~136kg. The slump of the shotcrete is 215mm, 215mm, and it has good workability and fluidity.

7. Application of modified ultrafine limestone powder for concrete in commercial mixing, characterized in that: The commercial mix ratio is as follows: water-cement ratio is 0.50, cement dosage is 238kg / m 3 ~255kg / m 3 , the amount of limestone powder is 85kg / m 3 ~102kg / m 3 , water consumption is 170kg / m 3 .

8. Application of modified ultrafine limestone powder for concrete in self-compacting concrete, characterized in that: For every cubic meter of self-compacting concrete, the amount of cement added is 236kg to 261kg, and the amount of modified ultrafine limestone powder added is 107kg to 128kg.

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