CN112608099B

CN112608099B - C50 steam-free curing concrete for coastal subway segments and preparation method thereof

Info

Publication number: CN112608099B
Application number: CN202011443300.9A
Authority: CN
Inventors: 王鹏刚; 金祖权; 付华; 崔东波; 赵铁军; 孙晓光; 高嵩; 孙培旺; 李宁
Original assignee: Mountain Jingbo Environmental Protection Materials Co ltd; Qingdao University of Technology
Current assignee: Mountain Jingbo Environmental Protection Materials Co ltd; Qingdao University of Technology
Priority date: 2020-12-11
Filing date: 2020-12-11
Publication date: 2021-12-07
Anticipated expiration: 2040-12-11
Also published as: CN112608099A

Abstract

The invention relates to the technical field of concrete, in particular to C50 steam-free curing concrete for coastal subway segments and a preparation method thereof. In the concrete, the preparation raw materials of each cubic meter of the concrete comprise the following components: cement 315-450 kg; 0-67.5kg of fly ash; 0-135kg of mineral powder; 728-732.5kg of sand; 1089-1098.7kg of stones; 18kg of nano C-S-H-PCE early strength agent; 5.85-20kg of water reducing agent; 118.8-135kg of water. The nano C-S-H-PCE is adopted to regulate the early hydration process of cement, accelerate the generation of early hydration products of cement and the formation of microstructures, further optimize the mix proportion of concrete, prepare the non-autoclaved concrete product with low energy consumption and high durability, effectively avoid the heat damage inside the product and the generation of structural defects in the damp-heat curing process, improve the overall performance of the concrete product and reduce the later maintenance cost of the concrete product.

Description

C50 steam-free curing concrete for coastal subway segments and preparation method thereof

Technical Field

The invention relates to the technical field of concrete, in particular to C50 steam-free curing concrete for coastal subway segments and a preparation method thereof.

Background

In recent years, the economic development speed of coastal areas is relatively high, the population density of coastal cities is continuously increased, the original infrastructure construction is overwhelmed, so that many cities face the problem of traffic jam at present, the basic traffic faces huge pressure, the development of underground traffic is urgent, and subways now become important marks for measuring the development level of cities. However, the development of coastal subway segment concrete currently faces many problems. Firstly, according to the production requirement of rapid turnover of practical factory molds, the subway segments are mostly cured by steam at present to improve the early development strength of the subway segments. And steam curing can cause adverse effect to the inside pore structure of concrete, arouses concrete swelling deformation easily, delays ettringite inflation, influences the volume stability of steam-cured concrete to there are the problem such as shrinkage, the fracture risk grow in steam-cured concrete later stage. Meanwhile, the steam curing mode needs coal or gas, so that the energy consumption is high, and the steam loss in the production process greatly increases the energy waste. Secondly, because of the complex environment of coastal areas, coastal groundwater contains a large amount of chloride ions, the coastal groundwater can be exposed to freeze thawing damage in winter, and concrete can be obviously carbonized under the influence of carbon dioxide in the air, so that the service life of the segment concrete is influenced.

The design strength requirement of the subway segment concrete is not lower than C50, and the slump is controlled within the range of 30-50 mm by considering the shape of the segment and the troweling process during molding. According to the specification of GB/T22082-2008 'precast concrete lining segment', the strength of the segment concrete when being demolded is required to be not lower than 15 MPa. According to the relevant regulations of GB/T50476-; the maximum dosage of the cementing material is 500 kg; the 28d chloride ion diffusion coefficient should be less than or equal to 7X 10-12m²S; the minimum protective layer thickness is more than or equal to 55mm, the concentration of carbon dioxide in the subway is usually higher than that of carbon dioxide in the atmosphere, the pore structure of the concrete can be coarsened by carbonization, the number of capillary pores of which the diameter is more than 30nm and the most probable pore diameter can be increased, the Friedel' S generation amount in the concrete is reduced, the binding capacity of the concrete to chloride ions is reduced, the free chloride ion concentration in the concrete is increased, and the concrete is improvedThe longer the carbonization time is, the larger the influence is, and the carbonization depth of 56 days in the subway segment concrete carbonization box is required to be less than 20mm in a safe period; if the structure is in service in a micro-freezing area, the adopted concrete has certain frost resistance, and the loss of the dynamic elastic modulus after 250 times of freeze-thaw cycle is less than 20 percent; in addition, the concrete should have a certain volume stability, and 80d self-shrinkage of less than 350X 10-6.

In order to solve the problems, researchers at home and abroad currently carry out systematic research on the heat damage mechanism of the steamed concrete, the mechanical property evolution in the steaming process and the deterioration mechanism of the steamed concrete, and improve the performance of the steamed concrete by changing the water-cement ratio, the mineral admixture mixing amount, the steaming system and other methods. But the problems of heat damage, high energy consumption, concrete durability damage caused by steam curing and the like caused by steam curing cannot be fundamentally solved. Therefore, many researchers have prepared the C50 non-autoclaved concrete by controlling raw materials and optimizing the mixing proportion of the concrete and various types of early strength agents. The early strength of concrete can be improved by using various types of early strength agents to prepare the non-autoclaved concrete, but many early strength agents have the problems of complex use, influence on the durability of the concrete, high cost and the like. For example: the chloride early strength agent can cause the content of chloride ions in the concrete to be increased, so that reinforcing steel bars in the concrete are corroded; sulfate type early strength agent is due to K⁺And Na⁺The sodium salt or the potassium salt is easy to be separated out from the surface of the concrete after the concrete is dehydrated and dried without participating in the cement hydration process, so that the surface layer of the concrete is easy to crack; although the organic early strength agent does not cause damage to concrete, the reaction is complex, the dosage is difficult to control, and the cost is often high; the composite early strength agent can well play the role of early strength, but the improvement of the early strength of concrete is still limited.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides C50 steam-free curing concrete for coastal subway segments and a preparation method thereof, wherein the early hydration process of cement is regulated and controlled by adopting nano C-S-H-PCE, the generation of early hydration products of the cement and the formation of a microstructure are accelerated, further, the concrete mixing ratio is optimized, a low-energy-consumption and high-durability steam-free concrete product is prepared, the heat damage and the structural defects inside the product in the damp-heat curing process are effectively avoided, the integral performance of the concrete product is improved, and the later maintenance cost of the concrete product is reduced.

The technical scheme of the invention is as follows: a coastal subway segment C50 steam-free curing concrete, wherein, in the concrete, the preparation raw materials of each cubic meter of concrete comprise the following components:

cement 315-450 kg;

0-67.5kg of fly ash;

0-135kg of mineral powder;

728-732.5kg of sand;

1089-1098.7kg of stones;

18kg of nano C-S-H-PCE early strength agent;

5.85-20kg of water reducing agent;

118.8-135kg of water.

The cement of the invention is P.I 52.5 Portland cement, and the specific surface area is less than or equal to 400m²Per kg, initial setting time is more than or equal to 45min, final setting time is less than or equal to 390min, MgO content is less than or equal to 5 percent, C₃The content of A is less than or equal to 8 percent, the content of chloride ions is less than or equal to 0.06 percent, and the loss on ignition is less than or equal to 3 percent. The fly ash is I-grade low-calcium fly ash, the screen residue of a square hole with the diameter of 45 mu m is less than or equal to 12 percent, the water demand ratio is less than or equal to 95 percent, the ignition loss is less than or equal to 5 percent, and SO₃The content is less than or equal to 3.5 percent, the content of free CaO is less than or equal to 1 percent, and the radioactivity is qualified; the mineral powder is S95 grade mineral powder, the fluidity ratio is more than or equal to 95 percent, the ignition loss is less than or equal to 3 percent, and the SO₃The content is less than or equal to 4 percent, the content of chloride ions is less than or equal to 0.06 percent, the content of glass bodies is more than or equal to 85 percent, and the radioactivity is qualified.

The stone adopted by the invention adopts basalt broken stone with 5-20mm continuous gradation, the content of needle-shaped particles in the stone is less than or equal to 10 percent, the crushing value is less than or equal to 12 percent, the mud content is less than or equal to 1 percent, the mud block content is less than or equal to 0.5 percent, the water absorption rate is less than or equal to 1.0 percent, and the content of sulfides and sulfates is less than or equal to 0.5 percent. The sand is river sand with fineness modulus of 2.4-2.9, the mud content of the river sand is less than or equal to 1.5%, the mud block content is less than or equal to 0.8%, the sulfide and sulfate content is less than or equal to 0.5%, the chloride ion content is less than or equal to 0.02%, the fine particle content below 0.315mm is more than or equal to 10%, and the fine powder content below 0.15mm is more than or equal to 3%.

The nanometer C-S-H-PCE early strength agent adopted by the invention is a milk white liquid, the particle size is 50-100nm, the water reducing rate is not less than 25%, and the mixing amount is 2% -4% of the total mass of cement, fly ash and mineral powder.

The invention further optimizes the mixing proportion of the C50 non-autoclaved concrete in the aspects of workability, strength, durability, shrinkage rate and the like of the concrete, the water-gel ratio of the optimized concrete is 0.177-0.300, and the dosage of the cementing material (the sum of cement, fly ash and mineral powder) is not more than 450kg/m³The sand rate is 40-45%.

The invention also discloses a preparation method of the coastal subway segment C50 steam-free curing concrete, wherein the preparation method comprises the following steps:

s1, providing 280-450kg of cement, 0-180kg of fly ash, 0-180kg of mineral powder, 725.8-754kg of sand, 1086-1114.2kg of stones, 16-18kg of nano C-S-H-PCE early strength agent and 115.2-190kg of water;

s2, stirring and dry-mixing the sand, the stones, the cement, the fly ash and the mineral powder to obtain a mixed base material;

s3, adding the nano C-S-H-PCE early strength agent into water, and uniformly mixing to obtain a mixed solution;

s4, adding the mixing solution into the mixed base material, and stirring and mixing to obtain the coastal subway segment C50 steam-free curing concrete.

Pouring the concrete obtained by stirring in the step S4 into a subway segment mould, vibrating and compacting through a vibrating table and an inserted vibrating rod, pulling out a core rod before entering a segment curing kiln after the segment is integrally folded, folding the surface for the second time after the concrete surface is hydrated, and then conveying the subway segment mould to the subway segment curing kiln for normal-temperature curing at the curing temperature of 20 +/-3 ℃ and the relative humidity of more than or equal to 95 percent;

and (3) after the subway segments are cured for 10 hours, pushing out the subway segment mold from the curing kiln, demolding, putting the demolded subway segments into a curing pool for water curing, wherein the curing test piece is 14 days, and the water temperature of the curing pool is 20 +/-3 ℃.

The C50 non-autoclaved concrete for the coastal subway segments, which is prepared according to the requirements of the invention, meets the requirement of 15MPa form removal for 10h, and the chloride ion permeability resistance, the carbonization resistance, the frost resistance and the shrinkage performance respectively meet the requirement that the chloride ion diffusion coefficient is less than or equal to 7 multiplied by 10 in 28 days^-12m²The 56d carbonization depth is less than 20mm, the loss of the dynamic elastic modulus after 250 freeze-thaw cycles is less than 20 percent, and the 80d self-shrinkage is less than 350 multiplied by 10^-6And (4) requiring.

The invention has the beneficial effects that:

(1) the method solves the problems of non-durability, high energy consumption, large shrinkage and easy cracking in the development of the concrete product industry, and adopts the nano C-S-H-PCE early strength agent to regulate the early hydration process of the cement, so as to accelerate the generation of early hydration products of the cement and the formation of microstructures; further, by optimizing the concrete mixing proportion, the non-autoclaved concrete product with low energy consumption and high durability is prepared, the heat damage and the structural defect in the product in the damp and hot curing process are effectively avoided, the overall performance of the concrete product is improved, and the later maintenance cost of the concrete product is reduced;

(2) the application provides a C50 non-autoclaved concrete for coastal subway pipes. The nano C-S-H-PCE early strength agent improves the 10H strength of 30% fly ash concrete by 266%; the nano C-S-H-PCE early strength agent can reduce the chloride ion diffusion coefficient of the C50 non-autoclaved concrete and improve the chloride ion permeation resistance; after the nano C-S-H-PCE early strength agent is added, when the mixing amount of the fly ash is 15%, 30% and 45%, the carbonization depth of the concrete 58d is less than 7.0 mm; the nanometer C-S-H-PCE early strength agent basically does not influence the frost resistance of the C50 concrete; the nano C-S-H-PCE early strength agent can reduce the self-shrinkage of the C50 non-curing concrete; compared with the steam-cured concrete, the C50 steam-cured-free concrete can reduce the cost by 137 yuan/m³。

Drawings

FIG. 1(a) shows the influence of a nano C-S-H-PCE early strength agent on the strength of C50 fly ash concrete in 0-24H;

FIG. 1(b) is the effect of the nano C-S-H-PCE early strength agent on the strength of C50 mineral powder concrete in 0-24H;

FIG. 1(C) is the effect of the nano C-S-H-PCE early strength agent on the strength of the C50 complex blended concrete in 0-24H;

FIG. 2(a) is the effect of the nano C-S-H-PCE early strength agent on the strength of C50 fly ash concrete at 0-90 d;

FIG. 2(b) is the effect of the nano C-S-H-PCE early strength agent on the strength of C50 mineral powder concrete at 0-90 d;

FIG. 2(C) is the effect of the nano C-S-H-PCE early strength agent on the strength of the C50 complex blended concrete at 0-90 d;

FIG. 3 is the effect of the nano C-S-H-PCE early strength agent on the self-contraction performance of concrete with various mixing ratios of C50.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the following description, specific details are set forth in order to provide a thorough understanding of the present invention. The invention can be implemented in a number of ways different from those described herein and similar generalizations can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

The invention discloses a coastal subway segment C50 steam-free curing concrete, wherein in the concrete, the preparation raw materials of each cubic meter of the concrete comprise the following components:

cement 315-450 kg;

0-67.5kg of fly ash;

0-135kg of mineral powder;

728-732.5kg of sand;

1089-1098.7kg of stones;

18kg of nano C-S-H-PCE early strength agent;

5.85-20kg of water reducing agent;

118.8-135kg of water.

The cement of the invention adopts P.I 52.5 Portland cement, and the specific surface area is less than or equal to 400m²Per kg, initial setting time is more than or equal to 45min, final setting time is less than or equal to 390min, MgO content is less than or equal to 5 percent, C₃The content of A is less than or equal to 8 percent, the content of chloride ions is less than or equal to 0.06 percent, and the loss on ignition is less than or equal to 3 percent.

The powder of the inventionThe coal ash is I-grade low-calcium fly ash, the screen residue of a square hole with the diameter of 45 mu m is less than or equal to 12 percent, the water demand ratio is less than or equal to 95 percent, the loss on ignition is less than or equal to 5 percent, and SO₃The content is less than or equal to 3.5 percent, the content of free CaO is less than or equal to 1 percent, and the radioactivity is qualified. Fly ash is a fine solid particulate matter captured from flue gas generated in the coal burning process, and does not include ash discharged from a hearth of a coal burning facility. The fly ash is mainly from the production and supply industries of electric power and heat and other industries using coal burning facilities, and along with the development of the electric power industry, the discharge amount of the fly ash becomes one of the industrial waste residues with larger discharge amount in China. After the fly ash is doped into cement, the fly ash is dissolved in an alkaline environment, and can perform secondary reaction with calcium hydroxide generated by cement hydration to generate hydrated calcium silicate with development strength. The activity depends on the fineness of the fly ash particles. The fly ash contains a large amount of spherical glass microspheres, and after the fly ash is mixed into concrete, the fluidity of fresh concrete can be improved, the density of the fly ash is generally lower than that of cement, and under the condition of the same mass, the volume of gelled slurry in the concrete can be increased, and the working performance of the concrete can be improved. Meanwhile, the fly ash contains a large amount of fine particles, so that a water seepage channel in concrete can be cut off, and the anti-permeability performance of the concrete is improved.

The mineral powder in the invention adopts S95 grade mineral powder, the mineral powder adopts S95 grade mineral powder, the fluidity ratio is more than or equal to 95 percent, the ignition loss is less than or equal to 3 percent, and the SO₃The content is less than or equal to 4 percent, the content of chloride ions is less than or equal to 0.06 percent, the content of glass bodies is more than or equal to 85 percent, and the radioactivity is qualified. The mineral powder is a high-fineness and high-activity powder obtained by treating a fused mass mainly containing calcium aluminosilicate obtained by blast furnace ironmaking through processes of drying, grinding and the like, and is a high-quality concrete admixture and cement mixing material. Along with the improvement of the process, the fineness of the mineral powder is continuously improved, so that the activity of the mineral powder is greatly improved, and the manufacturing cost of the mineral powder is only half of that of common portland cement, so that the mineral powder can replace cement to save a large amount of cement, save energy and realize green sustainable development. The mineral powder is used as a mineral admixture in the concrete, so that the later strength is improved, the bleeding performance of the concrete is improved, and the cohesiveness of the concrete is improved.

The stone in the invention adopts basalt broken stone with 5-20mm of continuous gradation, the content of needle-shaped particles in the stone is less than or equal to 10 percent, the crushing value is less than or equal to 12 percent, the mud content is less than or equal to 1 percent, the mud block content is less than or equal to 0.5 percent, the water absorption rate is less than or equal to 1.0 percent, and the content of sulfide and sulfate is less than or equal to 0.5 percent. The sand is river sand with fineness modulus of 2.4-2.9, the mud content of the river sand is less than or equal to 1.5%, the mud block content is less than or equal to 0.8%, the sulfide and sulfate content is less than or equal to 0.5%, the chloride ion content is less than or equal to 0.02%, the fine particle content below 0.315mm is more than or equal to 10%, and the fine powder content below 0.15mm is more than or equal to 3%.

The nanometer C-S-H-PCE early strength agent adopted by the invention is milky liquid, the particle size is 50-100nm, and the water reducing rate is 25%. The doping amount of the nano C-S-H-PCE early strength agent is 2-4% of the total mass of the cement, the fly ash and the mineral powder.

The invention further comprehensively considers the aspects of workability, strength, durability, shrinkage rate and the like of the concrete, provides the preferable water-cement ratio of the concrete, and the water-cement ratio is 0.177-0.475; the dosage of the cementing material is not more than 450kg/m³(ii) a The sand rate is controlled to be about 40 percent, and is generally 40 to 45 percent.

The invention also discloses a preparation method of the coastal subway segment C50 steam-free curing concrete, which comprises the following steps.

Firstly, providing 220-450kg of cement, 0-180kg of fly ash, 0-180kg of mineral powder, 725.8-754kg of sand, 1086-1114.2kg of stones, 16-18kg of nano C-S-H-PCE and 115.2-190kg of water.

And secondly, mixing the sand, the pebbles, the cement, the fly ash and the mineral powder, and stirring and dry-mixing to obtain a mixed base material. Firstly, placing sand and stones into a stirrer to be uniformly stirred, then placing a gel material comprising cement, fly ash and mineral powder into the uniformly stirred sand and stones to be fully stirred, and obtaining a mixed base material after the materials are dry-mixed.

And step three, adding the nano C-S-H-PCE early strength agent into water, and uniformly mixing to obtain a mixed solution.

And fourthly, adding the mixed base material of the mixing solution into the mixed base material, and stirring and mixing to obtain the coastal subway segment C50 steam-free curing concrete.

Next, concrete that will stir the completion is poured to subway section of jurisdiction mould in, and it is closely knit to vibrate through shaking table and bayonet vibrating spear, and the in-process that vibrates adopts the ash sword to wipe out the mould overhead gas bubble to do benefit to the inside bubble of mould and can discharge smoothly. In the whole vibrating process, the conditions of fastening bolts, screws and other embedded parts of the die are observed, and if the die deforms or shifts, the vibrating is stopped immediately for repairing. After the top plate is opened, the steel pressure bar is used firstly to strickle off and remove the redundant concrete, so that the surface of the concrete is smooth and rough-plastered. And after the mould is pushed away from the vibration table, the core rod fixing device is removed, the core rod is slowly pulled, and the core rod cannot be pulled out so as to avoid taking out the bent pipe. After the segment is integrally folded, pulling out the core rod before entering the segment curing kiln, and strictly prohibiting pulling out in advance. And (4) after the concrete surface receives water, carrying out secondary surface collection by using a trowel to ensure that the surface of the duct piece is flat and smooth. And then, conveying the subway segment mould to a subway segment curing kiln for normal-temperature curing, wherein the curing temperature is 20 +/-3 ℃, and the relative humidity is more than or equal to 95%.

And (3) after the subway segments are cured for 10 hours, pushing out the subway segment mold from the curing kiln, demolding, putting the demolded subway segments into a curing pool for water curing, wherein the curing test piece is 14 days, and the water temperature of the curing pool is 20 +/-3 ℃. And after maintenance, the pipe pieces are lifted out of the maintenance pool and stacked in a pipe piece finished product stacking place.

Example 1

In the embodiment, the mix proportion of the segment concrete is designed according to JGJ55-2011 'design rule for mix proportion of common concrete', and when the total amount of the cementing material is 450kg/m³When the fly ash, the single-blended fly ash of the mineral powder and the complex blending of the mineral powder respectively account for 15 percent, 30 percent and 45 percent of the total amount of the cementing material. Fly ashWhen the mineral powder is mixed with the mineral powder, the mixing amount ratio is 1: 2. The recommended matching ratio of the C50 non-autoclaved concrete for the coastal subway segments is shown in Table 1 by comprehensively considering the factors such as workability, 10-hour stripping strength, mechanical property, chloride ion corrosion resistance, carbonization resistance, frost resistance, shrinkage performance, material cost and the like. As can be seen from Table 1, the cost of non-autoclaved concrete is reduced to 137 Yuan/m compared with autoclaved concrete³。

TABLE 1 recommended mix proportion of C50 non-autoclaved concrete for coastal subway segments

Example 2

The cement of this example was P.I 52.5 Portland cement, the total amount of the cement was 450kg/m³The sand rate is uniformly 40%, the doping amount of the nano C-S-H-PCE early strength agent (hereinafter abbreviated as n-C-S-H-PCE) is 4%, and the influence of the addition of the n-C-S-H-PCE on the 10H compressive strength of the C50 non-autoclaved concrete for the coastal subway segments is shown in Table 2.

TABLE 2 influence of n-C-S-H-PCE on 10H compressive strength (MPa) of C50 non-autoclaved concrete for coastal subway segments

As shown in Table 2, when the water-gel ratio is the same, after n-C-S-H-PCE is doped, the 10H strength of the fly ash doped amount is 15% and 30% is respectively improved by 78% and 266%, the 10H strength of the mineral powder doped amount is 15%, 30% and 45% is respectively improved by 107%, 174% and 312%, the 10H strength of the compound doped amount is 15%, 30% and 45% is respectively improved by 92%, 81% and 312%, and all the mixing ratios meet the basic strength requirement of the C50 non-autoclaved concrete for coastal subway segments. The n-C-S-H-PCE promotes the compressive strength of the concrete for 10 hours mainly because the n-C-S-H-PCE increases the precipitation of ions at the early stage of the cement and the content of chemically bound water, promotes the hydration process of the cement, generates more C-S-H gel, makes the structure more compact and further improves the compressive strength of the concrete.

As shown in the figures 1(a) to 2(C), under the same water-cement ratio, within 0-24H, the n-C-S-H-PCE has obvious effect of increasing the compressive strength of the concrete doped with the mineral admixture, and the maximum effect can reach more than 80%. And within 3d-90d, the n-C-S-H-PCE has no obvious effect of increasing the compressive strength of the concrete. Analysis shows that after the n-C-S-H-PCE is doped, the hydration product C-S-H gel in the early stage nucleates and grows on the surface of cement particle minerals and also on the surface of the n-C-S-H-PCE, and simultaneously the chemical binding water content in the system and the silicate polymerization are increased, so that the early cement hydration speed is greatly accelerated, and the matrix strength is improved. However, as the hydration progresses, a large amount of C-S-H interweaving growing on the nucleation surface of the n-C-S-H-PCE can generate more C-S-H phase interfaces after the C-S-H interweaving growing together, namely, gel pores begin to form, at the moment, the cement hydration enters a deceleration period, the matrix becomes loose due to the increase of the gel pores, and the effect of enhancing the overpressure resistance is not obvious. In addition, within 0-90d, under the same n-C-S-H-PCE doping amount, no matter the fly ash and the mineral powder are singly doped or doped, the compressive strength of the concrete is in a continuously reduced trend along with the reduction of the water-cement ratio and the increase of the mineral admixture doping amount, and the increase trend of the compressive strength of the concrete is gradually slowed down along with the increase of the age, because the hydration reaction of the fly ash and the mineral powder is mainly OH^-The pozzolanic effect is stimulated, the cement content decreases with increasing mineral content, so that the cement hydration products Ca (OH)₂The content is reduced, the fly ash can not fully react, so that the content of C-S-H gel and C-A-H crystal is reduced, and further the compressive strength is reduced.

Example 3

The cement of this example was P.I 52.5 Portland cement, the total amount of the cement was 450kg/m³The sand rate is uniformly 40%, the doping amount of n-C-S-H-PCE is 4%, and the influence of the added n-C-S-H-PCE on the chloride ion diffusion system of the non-autoclaved C50 concrete for the coastal subway segments is shown in Table 3.

TABLE 3 chloride ion diffusion coefficient of n-C-S-H-PCE for coastal subway tube piece C50 non-autoclaved concrete (10)^-12m²Influence of/s)

As shown in Table 3, when the water-gel ratio is the same, the permeability coefficient of chloride ions is obviously reduced by doping n-C-S-H-PCE, and the reduction amplitude is between 2 and 28 percent. The reason is consistent with the reason that the n-C-S-H-PCE enhances the compressive strength for 10H.

When the doping amount of the fly ash is less than 30 percent, the permeability coefficient of chloride ions is reduced along with the increase of the doping amount of the fly ash and the reduction of the water-cement ratio, and when the doping amount of the fly ash exceeds 30 percent, the impermeability of concrete is reduced, so the optimum doping amount of the fly ash in the embodiment is 30 percent. The concrete chloride ion permeability coefficient is reduced along with the increase of the mixing amount of the mineral powder and the reduction of the water-gel ratio. The main reason is that the mineral powder absorbs alkali metals such as potassium, sodium and the like in the cement under the alkaline condition, the interface strength and the compactness are improved, the porosity is reduced, and meanwhile, the alkali excitation effect of the mineral powder enables the concrete to have higher chloride ion adsorption capacity.

When the doping amount of the fly ash is equal to n-C-S-H-PCE and is less than 30%, the permeability coefficient of chloride ions is reduced along with the reduction of the water-gel ratio, and when the doping amount is greater than 30%, the permeability coefficient of chloride ions is increased, so that the optimal doping amount of the fly ash is about 30%.

Example 4

The cement of this example was P.I 52.5 Portland cement, the total amount of the cement was 450kg/m³The sand rate is uniformly 40%, and the doping amount of n-C-S-H-PCE is 4%. The effect of n-C-S-H-PCE on the carbonization depth of the C50 non-autoclaved concrete 56d for coastal subway segments is shown in Table 4.

TABLE 4 influence of n-C-S-H-PCE on carbonization depth (mm) of coastal subway segments with C50 non-autoclaved concrete 56d

As shown in Table 4, under the condition of the same water-gel ratio, the n-C-S-H-PCE is doped to reduce the carbonization depth of the concrete, so that the anti-carbonization capacity is increased, and the reduction range of the carbonization depth is 10-40 percent, which is mainly caused by the increase of the content of the C-S-H gel of the carbonizable substance.

When the doping amount of the n-C-S-H-PCE is the same, the carbonization depth is gradually increased along with the increase of the doping amount of the mineral admixture, and the carbonization resistance is reduced. For example, after the n-C-S-H-PCE is added, the carbonization depth of 15% of the fly ash at 56d is 2.87mm, and the carbonization depth of 45% of the fly ash at 56d is 3.52 mm. This is because, when the mineral admixture replaces cement, the cement quality is reduced, and the cement hydrates to produce carbonizable substances Ca (OH)₂The content is reduced, and the content of the C-S-H gel of the carbonizable substances generated by the secondary hydration reaction of the mineral substances is also reduced, finally resulting in the reduction of the anti-carbonization capability of the concrete. Meanwhile, the carbonization depth of the concrete with different mixing ratios is continuously increased along with the increase of the age.

By analyzing the influence of the three minerals on the carbonization performance of the concrete, the carbonization depth of the concrete is the lowest when the mineral powder is doped, namely the carbonization resistance is the best. For example, when the n-C-S-H-PCE is added, the maximum values of the carbonization depths of the mineral powder, the fly ash and the 30% blended concrete 56d are respectively 2.98mm, 3.36mm and 3.56 mm.

Example 5

The freeze-thaw damage is an important index for evaluating the durability of the concrete, and the coastal subway segment C50 non-autoclaved concrete has to have good durability when meeting the early strength.

The cement of this example was P.I 52.5 Portland cement, the total amount of the cement was 450kg/m³The sand rate is uniformly 40%, and the doping amount of n-C-S-H-PCE is 4%. The influence of n-C-S-H-PCE on the relative dynamic elasticity modulus of the coastal subway tube piece after 250 times of freeze-thaw cycle of the non-autoclaved concrete with C50 is shown in Table 5.

TABLE 5 influence of n-C-S-H-PCE on the relative dynamic elastic modulus after 250 cycles of freeze-thaw cycling of C50 non-autoclaved concrete for coastal subway segments (%)

As shown in Table 5, when the content of the fly ash is 15%, the relative dynamic elastic modulus of the concrete with the content of 0% and 4% of the n-C-S-H-PCE is reduced along with the increase of the number of freeze-thaw cycles, and the reduction rate is basically consistent. After 250 times of freeze-thaw cycle, the relative dynamic elastic modulus of the n-C-S-H-PCE concrete with different doping amounts is basically kept consistent, and the relative dynamic elastic modulus is over 90 percent. This indicates that the incorporation of n-C-S-H-PCE has no influence on the frost resistance of C50 concrete.

Example 6

The cement of this example was P.I 52.5 Portland cement, the total amount of the cement was 450kg/m³The sand rate is uniformly 40%, and the doping amount of n-C-S-H-PCE is 4%. The performance of the self-shrinkage performance of the n-C-S-H-PCE on the C50 non-autoclaved concrete for the coastal subway segments is shown in FIG. 3.

The n-C-S-H-PCE has the function of reducing the self-shrinkage of the concrete with each mixing ratio. The n-C-S-H-PCE promotes the internal hydration process of the concrete, particularly the hydration of the cementing material within 24 hours, generates more C-S-H gel, enables the concrete to form a compact microstructure at an early stage, and reduces the occurrence of self-contraction.

In view of the above, it is desirable to provide,

(1) when the total gelled material is the same, the conductivity, the chemical bonding water content and the polymerization degree of the C-S-H gel are improved along with the increase of the doping amount of the n-C-S-H-PCE within 0-24H, the cement hydration process is promoted, and the content of the C-S-H gel is increased.

(2) When the water-gel ratio is the same, the n-C-S-H-PCE obviously increases the compressive strength of the concrete within 0-24H, and the n-C-S-H-PCE has no obvious effect on enhancing the compressive strength of the concrete within 3d-90 d. In addition, the compressive strength is continuously reduced along with the increase of mineral admixtures when the n-C-S-H-PCE addition amount is the same and the total amount of the cementing material is the same.

(3) When the water-gel ratio is the same, the n-C-S-H-PCE increases the chloride ion corrosion resistance and the carbonization resistance of the concrete, reduces the self-contraction deformation of the concrete, and has no obvious effect on the frost resistance of the concrete.

(4) The doping amount of the n-C-S-H-PCE is the same, the total amount of the cementing material is the same, the permeability coefficient of the concrete doped with the fly ash and the complex doped with the fly ash is reduced firstly and then increased, and the optimal doping amount is 30 percent. The chlorine ion permeability resistance of the concrete doped with the mineral powder is continuously increased along with the increase of the doping amount. In addition, the anti-carbonization performance of the concrete of the three doping modes is continuously reduced along with the increase of the mineral admixture, and when the doping amount of the n-C-S-H-PCE is 15%, the frost resistance of the compound concrete is the best.

(5) In combination with the measured concrete durability analysis, the mix proportions meeting the requirements of the C50 non-autoclaved concrete are listed. Meanwhile, production cost analysis is carried out, and steam-free curing can be found to greatly reduce the production cost.

The C50 steam-free curing concrete for the coastal subway segments and the preparation method thereof provided by the invention are described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The coastal subway segment C50 steam-free curing concrete is characterized in that the concrete is prepared from the following raw materials per cubic meter:

cement 315-450 kg;

0-67.5kg of fly ash;

0-135kg of mineral powder;

728-732.5kg of sand;

1089-1098.7kg of stones;

18kg of nano C-S-H-PCE;

5.85-20kg of water reducing agent;

118.8-135kg of water;

the nano C-S-H-PCE early strength agent is a milk white liquid, the particle size is 50-100nm, the water reducing rate is not less than 25%, and the doping amount of the nano C-S-H-PCE early strength agent is 2% -4% of the total mass of cement, fly ash and mineral powder.

2. The coastal subway pipe piece C50 steam-free curing concrete as claimed in claim 1, wherein said cement is P.I 52.5 Portland cement, specific surface area is less than or equal to 400m²Per kg, initial setting time is more than or equal to 45min, final setting time is less than or equal to 390min, MgO content is less than or equal to 5 percent, C₃The content of A is less than or equal to 8 percent, the content of chloride ions is less than or equal to 0.06 percent, and the ignition loss is less than or equal to 3 percent; the fly ash is I-grade low-calcium fly ash, the screen residue of a square hole with the diameter of 45 mu m is less than or equal to 12 percent, the water demand ratio is less than or equal to 95 percent, the ignition loss is less than or equal to 5 percent, and SO₃The content is less than or equal to 3.5 percent, and the content of free CaO is less than or equal to 1 percent; the mineral powder is S95 grade mineral powder, the fluidity ratio is more than or equal to 95 percent, the ignition loss is less than or equal to 3 percent, and the SO₃The content is less than or equal to 4 percent, the content of chloride ions is less than or equal to 0.06 percent, and the content of glass bodies is more than or equal to 85 percent;

the stone adopts basalt broken stone with 5-20mm of continuous gradation, the content of needle-shaped flaky particles in the stone is less than or equal to 10 percent, the crushing value is less than or equal to 12 percent, the mud content is less than or equal to 1 percent, the mud block content is less than or equal to 0.5 percent, the water absorption rate is less than or equal to 1.0 percent, and the content of sulfide and sulfate is less than or equal to 0.5 percent; the sand is river sand with fineness modulus of 2.4-2.9, the mud content of the river sand is less than or equal to 1.5%, the mud block content is less than or equal to 0.8%, the sulfide and sulfate content is less than or equal to 0.5%, the chloride ion content is less than or equal to 0.02%, the fine particle content below 0.315mm is more than or equal to 10%, and the fine powder content below 0.15mm is more than or equal to 3%.

3. The coastal subway pipe piece C50 steam-free curing concrete as claimed in claim 1, wherein the water-to-gel ratio of concrete is at most 0.35, and the total amount of cement, fly ash and mineral powder is not more than 450kg/m³The sand rate is 40-45%.

4. A method for preparing the coastal subway segment C50 non-steam curing concrete according to any one of claims 1-3, which comprises the following steps:

s1, providing 315-450kg of cement, 0-67.5kg of fly ash, 0-135kg of mineral powder, 728-732.5kg of sand, 1089-1098.7kg of stones, 18kg of nano C-S-H-PCE and 118.8-135kg of water;

s2, mixing sand, pebbles, cement, fly ash and mineral powder, and stirring for dry mixing to obtain a mixed base material;

s3, adding the nano C-S-H-PCE into water, and uniformly mixing to obtain an additive;

s4, adding the mixed base material into the additive, stirring and mixing to obtain the coastal subway segment C50 steam-free curing concrete.

5. The method according to claim 4, wherein the concrete obtained by stirring in the step S4 is poured into a subway segment mould, is compacted by vibration of a vibration table and an inserted vibration rod, after the integral surface folding of the segment is completed, a core rod is pulled out before the segment enters a segment curing kiln, after the concrete surface is subjected to water collection, the second surface folding is carried out, then the subway segment mould is conveyed to the subway segment curing kiln for normal-temperature curing, the curing temperature is 20 +/-3 ℃, and the relative humidity is more than or equal to 95%;

and after the subway segments are cured for 10 hours, pushing the subway segment mold out of the curing kiln, demolding, putting the demolded subway segments into a curing pool for water curing, wherein the curing time is 14 days, and the water temperature of the curing pool is 20 +/-3 ℃.