CN112851180B

CN112851180B - Viscosity and shrinkage stress reducing additive for prefabricated thin-wall structure concrete and preparation method thereof

Info

Publication number: CN112851180B
Application number: CN202110000791.8A
Authority: CN
Inventors: 张丰; 白银; 赵文政; 林梅; 张金康; 祝烨然; 陈波; 宁逢伟; 吕乐乐; 蔡跃波; 历丹丹
Original assignee: Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources
Current assignee: Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources
Priority date: 2021-01-04
Filing date: 2021-01-04
Publication date: 2022-06-03
Anticipated expiration: 2041-01-04
Also published as: CN112851180A

Abstract

The invention discloses an additive for reducing viscosity and shrinkage stress for prefabricated thin-wall structure concrete and a preparation method thereof. The preparation method of the viscosity and shrinkage stress reducing additive for the prefabricated thin-wall structure concrete comprises the following steps: firstly, crushing, ball-milling, calcining, cooling and grinding mineral raw materials to prepare a component A of powder; then polymerizing, crushing, drying and crushing the organic raw materials in a specific molar ratio relationship to prepare a modified component B of powder; then modifying the component A with a specific weight part of the modified component B through a liquid coupling agent, and finally adding a powder component C prepared by reacting, cooling, breaking, drying and crushing raw materials such as polyethylene glycol methyl ether methacrylate, acrylamide, maleic anhydride, octadecanol and the like to mix. The materials used in the invention are pollution-free, the active ingredients react in the whole hydration life cycle of the concrete material, and the viscosity and the shrinkage stress of the concrete with the prefabricated thin-wall structure are reduced through the actions of micro-expansion in the whole hydration cycle of the cement, water slow release, reduction of the water loss rate of the concrete, optimization of the hardened cement stone pore structure, reduction of the surface tension of a capillary pore solution of the concrete and the like, so that the constructability and the self crack resistance of the concrete mixture with the prefabricated thin-wall structure are improved.

Description

Viscosity and shrinkage stress reducing additive for prefabricated thin-wall structure concrete and preparation method thereof

Technical Field

The invention belongs to the field of building materials, and relates to an additive for reducing viscosity and shrinkage stress for prefabricated thin-wall structural concrete and a preparation method thereof.

Background

Concrete is the most used building material in the world, but the brittle nature of concrete makes it have poor crack resistance, and micro-cracks are easy to generate during construction or long-term use. The existence and development of these cracks will affect the performance of the concrete structure, reduce the durability and service life of the concrete.

Fabricated precast thin-walled concrete elements (fabricated bridge structures) are generally prestressed structures, the durability risk of which mainly comes from concrete cracking. Due to the requirements of the procedures of form removal, tensioning and the like, the strength grade of the thin-wall concrete of the prefabricated part is high, and the design strength is required to be reached within 5-7 days, so that the consumption of concrete cement materials is large, the cement ratio is low, the cement grade is high, the quality fluctuation of sand aggregate is large, and in addition, the implementation difficulty of maintenance measures is large, the form removal time is early, so that the surface water loss and cooling rate of the prefabricated thin-wall concrete part are high, and the thin-wall part has large shrinkage deformation and high cracking risk. The cracks are mainly divided into superficial cracks and penetrating cracks, the superficial cracks generally belong to plastic cracks, and the penetrating cracks generally belong to shrinkage cracks and temperature cracks. The cracks are serious, the prefabricated parts need to be scrapped, and the slight cracks can be used only by adopting the modes of grouting, reinforcement and the like and demonstrating no safety risk. Therefore, once a crack occurs, it is difficult to handle.

In recent years, with the increase of the infrastructure of China, high-grade concrete gradually enters the construction market due to the characteristics of high strength, high early strength, good integrity and small self weight, and the advantages of the high-grade concrete in the application of prefabricated concrete components are particularly obvious. However, the problems of large viscosity, low flowing speed and the like of high-grade concrete mixtures are caused by the adoption of a large amount of cementing materials and a low water-cement ratio, and the precast thin-wall concrete components are high in reinforcement ratio and small in reinforcement spacing, so that the concrete pouring construction difficulty is increased, and the quality of hardened concrete is poor.

The non-load cracking of the concrete structure becomes a worldwide problem, and great attention is paid at home and abroad. In recent years, related scholars have carried out a series of researches on the crack control technology of precast concrete members, and key technical measures for crack control are proposed, such as: in the production process of the prefabricated part, the quality of raw materials and the grading of aggregates are strictly controlled, and the quality control of the procedures of material distribution, vibration, maintenance and the like is well carried out; and corresponding measures are taken to avoid deformation and cracks of the prefabricated parts caused by stacking and transportation. Among the causes of crack formation of the preform, the most important is shrinkage deformation crack. Shrinkage deformation such as self-shrinkage, dry shrinkage, temperature shrinkage, etc. of concrete can form tensile stress under constraint conditions, and when such stress exceeds the tensile strength of concrete, cracking can be caused. In actual engineering, optimization of the mixing proportion of raw materials and concrete, shrinkage reducing of a shrinkage reducing agent, compensation shrinkage of an expanding agent, fiber crack resistance, concrete temperature control, reinforced concrete maintenance and the like are effective ways for controlling cracks of a concrete structure.

The anti-cracking component is doped in the concrete, which is the basic way for improving the anti-cracking performance of the concrete, such as the expansion agent is doped in the concrete, beneficial expansion deformation is generated, and unfavorable shrinkage deformation is reduced or counteracted; the shrinkage reducing agent is doped to reduce the surface tension of pore water of the concrete, so that the shrinkage stress generated when the capillary pores are dehydrated is reduced; the addition of proper amount of fiber can raise the toughness and stress redistribution capacity of concrete, prevent crack generation and reduce crack width. The related art is applied to concrete, particularly concrete, but the practical application effect is uneven, and the application effect is not good particularly in precast concrete with a thin-wall structure.

For example, CN 110655344 a discloses an anti-crack additive for lining concrete of a strongly-restricted laminated wall, which comprises the following components in percentage by mass: 2-4% of hydration heat regulating material and 1-2% of shrinkage type high-performance polycarboxylic acid powder; 0-0.1% of defoaming agent, 2-5% of water-absorbing resin, 4-7% of water evaporation inhibitor and the balance of whole-course compensation expansion component. However, the invention is mainly aimed at a strong-constraint laminated wall lining concrete structure, the concrete strength grade is not high, and the concrete strength grade is generally C35P8 (the consumption of the glue material is not more than 400 kg/m)³Water-to-gel ratio of over0.44); secondly, related components are mostly prepared by mixing materials such as hydration heat release inhibitor, shrinkage reducing agent, water evaporation inhibitor, water-absorbent resin, expanding agent (paraffin coating modification) and the like in the market according to a certain proportion; thirdly, the temperature rise of the concrete can be inhibited for 1d to 3d, so that the strength of the concrete before 7d is obviously reduced.

CN 108383415A discloses a multifunctional anti-cracking additive, which comprises 90-95 parts (by weight, the same below) of an active mineral admixture, 4-8 parts of an active activator, 10-15 parts of calcium oxide expansion clinker, 1-3 parts of dextrin, the balance of fly ash, 2-8 parts of ethylene glycol, 1-7 parts of triethanolamine, 2-10 parts of sodium lactate, 3-9 parts of lignosulfonate, 1-4 parts of tributyl ester, 5-10 parts of anti-cracking fiber, 3-10 parts of a high-efficiency water reducing agent, 8-10 parts of polyamide epoxy chloropropane resin and the balance of fly ash. The anti-cracking admixture is mainly used for reducing the hydration expansion rate of the calcium oxide expansion components in the early temperature rise stage and establishing more effective expansion in the later temperature rise stage through the regulation and control of the cement hydration rate and the temperature rise of a test piece; and secondly, the generation and the propagation of microcracks are prevented and reduced by adding crack-resistant fibers. However, the patent has no comparison effect of specific examples, and the common single calcium oxide expansion component is directly selected, so that although the hydration expansion rate of the cement hydration temperature rise stage is reduced, the expansion range is still in the early stage (generally before 3d or 7 d), and the expansion range has no compensation effect on the shrinkage of the cement hydration in the middle and later stages.

CN 109987871A discloses an anti-crack additive for concrete mortar, its preparation method and use, the additive is prepared by adding acrylic acid into the commonly used butyronitrile latex (toughening agent) for copolymerization, and carboxyl activated groups are introduced into the main chain, so as to improve the impermeability and hydrophobicity of the mortar in the concrete. The invention firstly adds carboxyl and nitrile groups on the nitrile latex branched chain to adjust the water retention capacity of the mortar, secondly reduces the generation of concrete surface cracks by solving the problem of heat release generated in the hydration process of the mortar concrete, but the concrete mortar anti-crack additive has no specific implementation effect data; the coating is only suitable for rendering, coating, plugging, interface and pasting, is generally used as a coating, and is only limited to improving the microcracks on the surface layer of the concrete mortar with small deformation; it has little effect on the through cracks (shrinkage cracks and temperature cracks) with large deformation.

CN 105271873A discloses an early strength anti-cracking admixture for cement stabilized base, a preparation method and a use method thereof, which comprises the following raw material components by weight percentage: 46.7-78.5% of aluminate cement, 7.8-29.6% of magnesium nitrate, 6.3-25.7% of anhydrous sodium sulphate, 5.5-17.3% of caustic soda, 0.8-5.5% of sodium oxalate, 3.6-9.8% of a water reducing agent and 6.9-32.8% of brucite fiber. However, the effect of the corresponding anti-cracking component in the high-grade prefabricated thin-wall member concrete is unknown in the cement-stable base material and only in the early hydration stage (48 h and 72 h) of the cement.

CN 104529225A discloses a high and ultra-high strength concrete viscosity reducer, which is composed of the following substances by mass percent: 0.5-5% of nano particles; 2-20% of sulfate; 1-4% of carbonate; 0.1-2% of functional auxiliary agent; the rest is water. The viscosity reducer disclosed by the invention is doped into high-strength or ultrahigh-strength concrete by 0.1-0.5% of the mass of a cementing material, so that the viscosity of the concrete can be reduced by more than 10-30%, the workability of the concrete is obviously improved, and the problems of high viscosity and difficult construction of the high-strength or ultrahigh-strength concrete are effectively solved. The core of the invention is to mix sulfate and carbonate to reduce the solution viscosity of the residual water reducing agent in the slurry by the strong electrolyte action and the mode of reducing the residual amount of the water reducing agent, thereby reducing the viscosity of the concrete. But the kind of the concrete water reducing agent directly determines the action effect of the viscosity reducing agent, and has the problem of adaptability.

CN 106008784A discloses a concrete viscosity reducer and a preparation method thereof, wherein the viscosity reducer is prepared by polymerizing 4-hydroxybutyl vinyl ether, unsaturated amide and unsaturated phosphate ester as raw materials; the modified polyvinyl chloride resin has good adaptability with a polycarboxylic acid water reducing agent, and can obviously improve the workability of concrete by adding 0.01-0.03% of glue material into the concrete. The core of the invention is that nonpolar functional groups (such as hydroxyl, amido and phosphate) with proper proportion are introduced into the molecular structure of the polymer, and the dispersion effect of the nonpolar groups on cement particles is improved and the apparent viscosity of concrete is reduced by utilizing the space effect of the nonpolar groups and the capability of reducing the interfacial tension. However, the viscosity reducer is liquid, the viscosity reduction effect is not accurately characterized by the fact that concrete mixture flows out of an inverted slump cone, and in addition, the additive has no anti-cracking effect on hardened concrete.

CN 110885389A discloses a concrete viscosity reducer synthesized by a simple method and a preparation method thereof, wherein the concrete viscosity reducer is prepared by standing and self-polymerizing unsaturated carboxylic ester, a molecular regulator, an initiator and a reducing agent. The core is to adjust the viscosity of high-grade concrete by controlling the molecular weight of unsaturated carboxylate polymer, and the high-grade concrete has a certain water reducing effect.

CN 108610455A discloses a concrete viscosity reducer and a preparation method thereof, wherein, the synthesis of maleic anhydride polyethylene glycol ester solution: adding 500 parts of polyethylene glycol into a four-neck flask, heating to 50 ℃, starting stirring, adding 86 parts of maleic anhydride, sequentially adding 0.1 part of hydroquinone and 0.9 part of catalyst, heating to 70-80 ℃, reacting for 3-4 hours under continuous stirring, and stopping esterification to obtain yellow or red liquid, namely a polyethylene glycol maleate solution; the concrete viscosity reducer has certain water reducing performance. However, the viscosity reducer is liquid, and the viscosity reduction effect is not accurately characterized by the time when the concrete mixture flows out of the inverted slump cone.

CN 107601955A discloses a concrete viscosity reducer, which comprises the following components of 15-22 parts (by weight) of methacrylamide, 3-8 parts of sodium thiosulfate, 1-5 parts of a stabilizer, 2-3 parts of a retarder, 4-8 parts of maleic anhydride, 0.5-1 part of sodium dodecyl benzene sulfonate, 5-8 parts of bentonite and 10-12 parts of water. However, the specific data for the viscosity reduction effect are not available in the specific implementation of the invention.

The related anti-cracking functional materials reported in the existing Chinese patent do not aim at the materials and construction characteristics of a prefabricated thin-wall concrete structure (such as a prefabricated box girder, a T-shaped girder, a pier stud and the like) (large using amount of concrete glue, low water-glue ratio, high viscosity of mixture, high structural reinforcement rate, thin structure wall, early form removal time, 5-7 d tensioning, difficult implementation of maintenance measures and the like), are not suitable for the anti-cracking and pouring construction of the current prefabricated thin-wall concrete structure, have poor implementation effect and high anti-cracking technical difficulty, and need to be controlled and designed from the whole life cycle (early stage, middle stage and later stage) of the concrete material. The related viscosity reducer reports only consider the reduction of the viscosity of the mixture, mostly act on a water reducing agent, are all liquid, and do not consider the anti-cracking effect on hardened concrete. In conclusion, it is an urgent need to develop an admixture which is simple and convenient to construct, does not affect the strength of concrete, and can be applied to the prefabricated thin-wall structure concrete to reduce the viscosity and the shrinkage stress.

Disclosure of Invention

The invention aims to provide a preparation method of an additive with the functions of reducing viscosity and reducing shrinkage stress aiming at the material and construction characteristics of a prefabricated thin-wall concrete structure (such as a prefabricated box girder, a T-shaped girder, a pier stud and the like), and solves the problems of high cracking risk, high viscosity of concrete mixture, low flowing speed and the like of the prefabricated thin-wall concrete structure. The viscosity and shrinkage stress reducing additive for the prefabricated thin-wall structure concrete has the remarkable characteristics that the active ingredients react in the whole cement hydration period, and the shrinkage deformation (self-shrinkage, dry shrinkage, temperature shrinkage and the like) of the concrete is reduced and the self crack resistance of the prefabricated thin-wall structure concrete is improved through the effects of micro-expansion, water slow release, concrete water loss rate reduction, hardened cement stone pore structure optimization and the like; meanwhile, the operability of the construction of the high-grade concrete (high strength and high early strength) mixture is improved by reducing the surface tension of the concrete capillary solution and the like.

The invention provides a method for preparing a component A containing various different active expansion sources by adopting various mineral raw materials and adopting the processes of calcining and grinding in proportion; then one or more raw materials of ice crystal-shaped acrylic acid, sodium acrylate and vinyl acetate are adopted to generate a modified component B through polymerization reaction; and then crosslinking and modifying the A component particles with the modified component particles by a liquid coupling agent. By utilizing the functions of water absorption, water storage and slow release of the modified component B, water is absorbed in the concrete mixing process, and water is slowly released in the cement hydration process, so that the full internal relative humidity is provided, the water loss rate of the concrete is reduced, the volume shrinkage of the cement concrete is reduced, and the generation of cracks is inhibited; providing water for the component A containing different active expansion sources, so that the component A can better and fully react in the whole cement hydration period (early stage, middle stage and later stage) to generate volume micro-expansion, thereby reducing the shrinkage stress of the concrete; and thirdly, the full hydration of the unhydrated cement particles in the later period is promoted, the hardened cement stone pore structure is optimized, and the strength of the concrete structure is improved. Finally, a certain amount of viscosity reduction components prepared by polymerizing polyethylene glycol methyl ether methacrylate, acrylamide, maleic anhydride, octadecanol and other raw materials are compounded, and the fluidity of the concrete mixture is improved by reducing the surface tension of a capillary solution of the concrete and other effects, so that the construction operability and the concrete pouring quality of the concrete are improved. In addition, the additive for reducing viscosity and shrinkage stress for the prefabricated thin-wall structure concrete is powder, is simple and convenient to use, is only required to be weighed according to the mass ratio of the using amount of the glue material in the using process, adopts an external doping method (the doping amount is about 4-6%), is firstly doped into the glue material and is uniformly mixed, and then water, a water reducing agent and the like are added for stirring; the admixture for reducing viscosity and shrinkage stress has no adverse effect on the strength (compression resistance and fracture resistance) of the hardened concrete at each age.

The invention relates to a preparation method of an additive for reducing viscosity and shrinkage stress for precast thin-wall structure concrete, which comprises the following steps:

(1) crushing, ball-milling and sieving mineral raw materials, mixing the raw materials in proportion, calcining the mixture at high temperature, cooling and grinding the mixture, and sieving the mixture by using a 300-400-mesh sieve to prepare a component A of powder;

(2) adding organic raw materials into a reactor with stirring blades according to a certain molar ratio, adding deionized water to prepare a solution with the concentration of 20-40%, then adding a proper amount of 5mol/L sodium hydroxide to adjust the pH value of the solution to 5-7 and 0.01-2.00% (mass percentage, the same applies later) of a catalytic component, stirring while adding the solution, controlling the feeding speed, carrying out polymerization reaction under certain conditions, and sieving with a 120-400-mesh sieve to prepare a modified component B of powder after crushing, drying and crushing;

(3) the mass ratio of (6-15): 1, respectively weighing a component A and a component B, fully mixing the component A with a quantitative liquid coupling agent, then adding the component B for fully mixing, and then drying at a low temperature to obtain modified components A and B for later use; the modified component B is coated on the surface of the component A to form a protective layer, so that the reaction loss of the component A in the concrete plasticity stage can be reduced, and the water can be provided for the hydration reaction of the component A in the middle and later stages of the concrete hydration to fully play the expansion effect, thereby more effectively compensating the shrinkage of the whole hydration period of the concrete and being beneficial to reducing the using amount of the component A.

(4) Preparing polyethylene glycol methyl ether methacrylate, acrylamide, maleic anhydride and octadecanol into a solution, adding the solution into a reactor with stirring blades, introducing nitrogen or argon to remove air in the container, and stirring to uniformly mix the solution; adding a mixture of 0.01-0.05% of persulfate and sulfite as a reaction initiator, reacting under a certain condition, cooling, breaking, drying and crushing a product, and sieving the product with a 300-400-mesh sieve to prepare a powder component C;

(5) modifying the modified A & B components prepared in steps 3) and 4): and (3) uniformly mixing and stirring the component C with the weight ratio of (70-85) to (15-30) to obtain a finished product.

In the preparation process of the viscosity and shrinkage stress reducing additive for concrete, the component A is modified by the prepared modifying component B through a liquid coupling agent, and then the third component C is added for mixing. Therefore, on one hand, the modified component B is coated on the surface of the component A to form a protective layer, so that in the hydration process, water is slowly released, the time of the expansion reaction of the water and the component A in contact is delayed, and the reaction loss of the component A in the concrete plasticity stage is reduced; on the other hand, by utilizing the water storage function of the modified component B, the internal relative humidity of the concrete is ensured, the water loss rate of the concrete is reduced, the volume shrinkage of the cement concrete is reduced, meanwhile, water is provided for the hydration reactions in the middle and later stages of the hydration of the component A concrete, the expansion effect of the component A is fully exerted, and the pore structure of the concrete is improved, so that the shrinkage of the whole hydration period of the concrete is more effectively compensated.

The mineral raw materials of the invention are two or more than two of dolomite, magnesite, calcite and bauxite; the mass portion proportion of the mixture is dolomite: magnesite: calcite: the bauxite ratio is (60-80): (20-40): (0-20): (0-10).

The mineral raw materials are crushed and ball-milled and then screened by a sieve with the size of 80 mu m.

The high-temperature calcination process in step 1) may be a conventional high-temperature calcination process, for example, the heat-preservation calcination is performed at 400-1100 ℃, or the temperature-programmed calcination may be performed, for example: firstly, heating to 400-600 ℃ at a heating rate of (6-10) DEG C/min, and preserving heat for 60-90 min; then heating to 800-1100 ℃ at a heating rate of (10-15) DEG C/min, and preserving the heat for 30-60 min.

The cooling process for preparing the component A in the step 1) is to carry out quenching at the wind speed of more than 5 m/s.

The organic raw material in the step 2) is one or more of ice crystal-shaped acrylic acid, sodium acrylate and vinyl acetate. The organic raw material can be a mixture of sodium acrylate and vinyl acetate, and the two raw materials are mixed according to a molar ratio (0.5-3): 1.

The proportion of the mineral raw materials for preparing the component A and the amount of the modified component B in the cross-linking can be adjusted according to the actual working conditions, and the expansion deformation of the concrete at different stages of hydration can be regulated and controlled.

The catalytic component of step 2) consisting of K₂S₂O₈One or more of propylene oxide and N, N-methylene bisacrylamide.

The catalytic component may be composed of K₂S₂O₈And the propylene oxide is mixed according to the mass ratio of (1-3) to 1.

And 2) carrying out polymerization reaction for preparing the modified component B under the conditions of controlling the temperature to be 70-90 ℃ and the air pressure to be 0.10-0.25 MPa, wherein the reaction time is 3-6 h.

And the crushing and drying processes in the step 2) are that the particles are crushed into particles of 5-10 mm and are placed in a blast drying oven at the temperature of 60-80 ℃ to be dried to constant weight.

The liquid coupling agent in the step 3) is one or more of gamma-aminopropyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane and vinyl triethoxysilane, and the dosage of the liquid coupling agent is 0.5-2% of the component A by mass.

The raw materials in the preparation process of the viscosity reducing component C in the step 4) are prepared into a solution, polyethylene glycol methyl ether methacrylate, acrylamide, maleic anhydride and octadecanol are added into water according to the molar ratio of (6-10): 1-2): 0.02-0.04): 0.02-0.06 at the normal temperature (15-25 ℃), and the raw materials are dissolved. The reaction process for preparing the viscosity reducing component C is carried out for 3-5 hours at the constant temperature of 40-60 ℃.

And 4) the reaction initiator is a mixture of persulfate and sulfite with the mass ratio of 1 (0.5-2).

The admixture is prepared by coating a modified component B on the surface of a component A to form a protective layer and then mixing the protective layer with a component C; the component A is composed of dolomite: magnesite: calcite: the bauxite comprises (60-80) by mass: (20-40): (0-20): (0-10) mixing and calcining; the modified component B is one or more of ice crystal-shaped acrylic acid, sodium acrylate and vinyl acetate; the component C is formed by mixing polyethylene glycol methyl ether methacrylate, acrylamide, maleic anhydride and octadecanol according to the molar ratio of (6-10) to (1-2) to (0.02-0.04) to (0.02-0.06).

The component A and the modified component B are (6-15) by mass: 1, mixing and modifying to form a modified component A and a modified component B, wherein the component B is coated on the surface of the component A; modified a & B components: the component C is mixed and stirred uniformly according to the weight ratio of (70-85) to (15-30).

According to the invention, the proportion of the mineral raw materials for preparing the component A and the amount of the modified component B in crosslinking can be adjusted according to actual working conditions, and the expansion deformation of the concrete at different stages of hydration can be regulated and controlled.

The additive for reducing viscosity and shrinkage stress for the prefabricated thin-wall structure concrete is applied to the prefabricated thin-wall structure concrete engineering.

When concrete is prepared, the additive for reducing viscosity and shrinkage stress is weighed according to the mass ratio of the dosage of the glue material, and the additive is firstly mixed into the glue material and then is evenly mixed, and then water, a water reducing agent and the like are added for stirring, so that the effect of reducing viscosity and shrinkage stress can be exerted; the dosage of the viscosity and shrinkage stress reducing additive is 4-6% of the total mass of the cementing material.

The viscosity and shrinkage stress reducing admixture for the prefabricated thin-wall structure concrete prepared by the invention is applied to the prefabricated thin-wall structure concrete engineering.

Has the advantages that: compared with the prior art, the invention has the following advantages:

firstly, the prepared viscosity and shrinkage stress reducing admixture contains a plurality of components A of different active expansion sources, and can expand in the whole cement hydration period (early stage, middle stage and later stage), so that the shrinkage deformation of the prefabricated thin-wall structural concrete in different age periods can be counteracted, and the self crack resistance of the whole life cycle of the prefabricated thin-wall component is improved; and the proportion of the mineral raw materials for preparing the component A and the amount of the modified component B in crosslinking can be adjusted according to actual working conditions, and the expansion deformation of the concrete at different stages of hydration can be regulated and controlled.

And secondly, the prepared admixture for reducing the viscosity and the shrinkage stress has the functions of reducing the viscosity and the shrinkage stress, the material and the actual construction characteristics (large consumption of concrete glue material, low water-glue ratio, large viscosity of a mixture, high structural reinforcement ratio, thin-wall structure, early form removal time, 5-7 d tensioning, difficult implementation of maintenance measures and the like) of the prefabricated thin-wall concrete structure (such as a prefabricated box girder, a T-shaped girder, a pier stud and the like) are considered, and the problems of large shrinkage deformation, high cracking risk, large viscosity of a concrete mixture, low flowing speed and the like of the prefabricated thin-wall concrete are effectively solved. In addition, the viscosity-reducing and shrinkage stress-reducing admixture has no adverse effect on the strength (compression resistance and bending resistance) of the hardened concrete at various ages.

And thirdly, the prepared modified component B is used for modifying the component A through a liquid coupling agent, and the modified component B is coated on the surface of the component A to form a protective layer, so that the reaction loss of the component A in the concrete plasticity stage can be reduced, and moisture can be provided for the hydration reaction of the component A in the middle and later stages of the concrete hydration to fully play the expansion effect of the component A, thereby more effectively compensating the shrinkage of the concrete hydration whole period and being beneficial to reducing the using amount of the component A.

Fourthly, all the components (the component A, the modified component B and the component C) of the admixture for reducing the viscosity and the shrinkage stress for the prefabricated thin-wall structure concrete are prepared by mineral raw materials, chemical reagents and the like according to a specific process, the existing components are not mixed and compounded, and the product quality is controllable; and the finished product is powder, and only the glue material needs to be mixed by adopting an external mixing method when in use, so that the operation is simple and convenient, and the related anti-cracking treatment measures on the construction site can be simplified.

Drawings

FIG. 1 is a design dimension diagram of a typical fabricated bridge structure with a simply supported prestressed concrete precast box girder structure;

FIG. 2 is a schematic diagram of a typical fabricated bridge structure for modeling a simple-supported prestressed concrete precast box girder concrete structure.

Detailed Description

In order to more clearly describe the technical solutions of the present invention, the following embodiments are further described in detail, which are only used for better explaining the contents of the present invention, but not limiting the present invention, and all similar embodiments listed based on the present invention should fall into the protection scope of the present invention.

In order to clearly express the effect of the admixture for reducing viscosity and shrinkage stress on the precast thin-wall structural concrete, a small simply supported prestressed concrete precast box girder for a typical fabricated bridge structure of a certain project is taken as a research object (the structure is shown in figures 1 and 2, the structure size is 35m in span, 2.4m in width, 1.6m in height and 18-20 cm in precast plate thickness), the precast box girder C60 concrete matching ratio is shown in Table 1, the water-cement ratio is 0.33, and the total consumption of cement is 468kg/m³. Concrete raw materials: the cement is P.O 52.5 grade, and the standard thickening water demand is 27.7 percent; the fly ash is F class II grade, and the water demand ratio is 103 percent; the fine aggregate is natural sand, and the fineness modulus is 2.7; mixing 5-16 mm small stones and 16-25 mm medium stones in a ratio of 3:7 as coarse aggregates; the water reducing agent is a polycarboxylic acid high-performance water reducing agent, the solid content is 17.8%, and the water reducing rate is more than 25%.

Example 1

The embodiment provides an additive for reducing viscosity and shrinkage stress for precast thin-wall structure concrete and a preparation method thereof, and the additive comprises the following steps:

1) the preparation steps of the component A are as follows: firstly, two raw materials of dolomite and magnesite are adopted, crushed and ball-milled, and then sieved by a sieve with the diameter of 80 mu m, and then the mixture is mixed according to the weight ratio of the dolomite: the magnesite mass ratio is 80:20, mixing; secondly, high-temperature calcination is carried out, the mixture is heated to 500 ℃ at the heating rate of 6 ℃/min and is kept for 90min, and then heated to 1000 ℃ at the heating rate of 15 ℃/min and is kept for 30 min; taking out after calcining, and immediately quenching at the wind speed of more than 5 m/s; cooling to room temperature, grinding and sieving with a 300-mesh sieve to prepare the powder.

2) The preparation steps of the modified component B are as follows: firstly, adding ice crystal-shaped acrylic acid serving as a raw material into a reactor with stirring blades, and adding deionized water to prepare a solution with the concentration of 40%; adding a proper amount of 5mol/L sodium hydroxide to adjust the pH value of the solution to 7.0, adding the solution while stirring, and controlling the feeding speed; ③ successively adding 0.3 percent of K₂S₂O₈(mass percent, then, the same) +0.3% of propylene oxide as a catalytic component, and adding the solution while stirring; fourthly, the polymerization is carried out under the conditions of controlling the temperature to be 80 ℃ and the air pressure to be 0.10MPa, and the reaction time is 6 hours; fifthly, taking out the reaction product after the reaction product is cooled to room temperature, breaking the reaction product into particles with the size of 5mm, and placing the particles in a blast drying oven at 70 ℃ for drying until the weight is constant; sixthly, adding the dried materials into a pulverizer, pulverizing, and sieving with a 120-mesh sieve to prepare powder.

3) Gamma-aminopropyl triethoxysilane is selected as a liquid coupling agent, and the liquid coupling agent with the mass of 1.0 percent is added into the component A for full mixing; fully mixing the component A and the component B according to the mass ratio of 15: 1; finally, drying at low temperature to obtain modified A & B components for later use;

4) the preparation steps of the component C are as follows: the molar ratio of the components is 7: 1: 0.02: 0.03 polyethylene glycol methyl ether methacrylate: acrylamide: maleic anhydride: adding the octadecanol raw materials into water in sequence to prepare a solution, and dissolving the raw materials; secondly, adding the solution into a reactor with stirring blades, introducing nitrogen or argon to remove air in the container, and stirring to uniformly mix; thirdly, 0.01 percent of mixture of persulfate and sulfite with the mass ratio of 1:1 is added as a reaction initiator, the temperature is controlled to 60 ℃, and the reaction is carried out for 3 hours; fourthly, pouring out the reactant, cooling the reactant to room temperature, disintegrating the reactant into particles with the diameter of 10mm, and placing the particles in a forced air drying oven with the temperature of 70 ℃ for drying until the weight is constant; fifthly, adding the dried materials into a pulverizer, and sieving the crushed materials through a 300-mesh sieve to prepare powder.

5) Mixing and stirring the components prepared in the steps 3) and 4) uniformly according to the mass ratio of 80:20 to obtain a finished product.

When the concrete is prepared, the additive for reducing the viscosity and the shrinkage stress is weighed according to 4 percent of the total mass of the rubber material, the additive is mixed into the rubber material outside the concrete and is stirred uniformly, and then water, a water reducing agent and the like are added and stirred to play the roles of reducing the viscosity and the shrinkage stress.

Example 2

1) the preparation steps of the component A are as follows: firstly, two raw materials of dolomite and magnesite are adopted, crushed and ball-milled, and then sieved by a sieve with the diameter of 80 mu m, and then the mixture is mixed according to the weight ratio of the dolomite: the mass ratio of the magnesite is 80:20, mixing; secondly, high-temperature calcination is carried out, the mixture is heated to 500 ℃ at the heating rate of 6 ℃/min and is kept for 90min, and then heated to 1000 ℃ at the heating rate of 15 ℃/min and is kept for 30 min; taking out after calcining, and immediately quenching at the wind speed of more than 5 m/s; cooling to room temperature, grinding and sieving with a 300-mesh sieve to prepare the powder.

2) The preparation steps of the modified component B are as follows: firstly, adding sodium acrylate and vinyl acetate with a molar ratio of 1:1 into a reactor with stirring blades, and adding deionized water to prepare a solution with a concentration of 40%; adding a proper amount of 5mol/L sodium hydroxide to adjust the pH value of the solution to 6.0, stirring while adding the solution, and controlling the feeding speed; adding 2% N, N-methylene bisacrylamide as a catalytic component, adding the solution while stirring, and controlling the feeding speed; fourthly, the polymerization is carried out under the conditions of controlling the temperature to be 80 ℃ and the air pressure to be 0.10MPa, and the reaction time is 6 hours; fifthly, taking out the reaction product after the reaction product is cooled to room temperature, breaking the reaction product into particles of 10mm, and placing the particles in a 70 ℃ forced air drying oven to dry the particles to constant weight; sixthly, adding the dried materials into a pulverizer, pulverizing, and sieving with a 120-mesh sieve to prepare powder.

3) Gamma-aminopropyl triethoxy silane is selected as a liquid coupling agent, and the liquid coupling agent with the mass of 0.5 percent is added into the component A for full mixing; fully mixing the component A and the component B according to the mass ratio of 7: 1; finally, drying at low temperature to obtain modified A & B components for later use;

4) the preparation steps of the component C are as follows: the molar ratio of the components is 10: 2: 0.04: 0.06 parts of polyethylene glycol methyl ether methacrylate: acrylamide: maleic anhydride: adding the octadecanol raw materials into water in sequence to prepare a solution, and dissolving the raw materials; secondly, adding the solution into a reactor with stirring blades, introducing nitrogen or argon to remove air in the reactor, and stirring to uniformly mix; thirdly, 0.01 percent of mixture of persulfate and sulfite with the mass ratio of 1:1 is added as a reaction initiator, the temperature is controlled to 60 ℃, and the reaction is carried out for 3 hours; fourthly, pouring out the reactant, cooling the reactant to room temperature, disintegrating the reactant into particles with the diameter of 10mm, and placing the particles in a forced air drying oven with the temperature of 70 ℃ for drying until the weight is constant; fifthly, adding the dried materials into a pulverizer, and sieving the crushed materials through a 300-mesh sieve to prepare powder.

When the concrete is prepared, the admixture for reducing the viscosity and the shrinkage stress for the concrete is weighed according to 5 percent of the total mass of the rubber material, the admixture is firstly doped into the rubber material and is uniformly dry-mixed, and then water, a water reducing agent and the like are added for stirring, so that the effects of reducing the viscosity and the shrinkage stress can be exerted.

Example 3

1) the preparation steps of the component A are as follows: firstly, two raw materials of dolomite and magnesite are adopted, crushed and ball-milled, and then sieved by a sieve with the diameter of 80 mu m, and then the mixture is mixed according to the weight ratio of the dolomite: the magnesite mass ratio is 60: 40, mixing; secondly, high-temperature calcination is carried out, the mixture is heated to 600 ℃ at the heating rate of 10 ℃/min and is kept for 60min, and then heated to 1100 ℃ at the heating rate of 15 ℃/min and is kept for 30 min; taking out after calcining, and immediately quenching at the wind speed of more than 5 m/s; cooling to room temperature, grinding and sieving with a 400-mesh sieve to prepare the powder.

2) The preparation steps of the modified component B are as follows: firstly, adding ice crystal-shaped acrylic acid serving as a raw material into a reactor with stirring blades, and adding deionized water to prepare a solution with the concentration of 35%; adding a proper amount of 5mol/L sodium hydroxide to adjust the pH value of the solution to 6.5, adding the solution while stirring, and controlling the feeding speed; ③ successively adding 0.3 percent of K₂S₂O₈+0.3% propylene oxideAs a catalytic component, adding the solution while stirring and controlling the feeding speed; fourthly, the polymerization is carried out under the conditions of controlling the temperature to be 85 ℃ and the air pressure to be 0.25MPa, and the reaction time is 3 hours; fifthly, taking out the reaction product after the reaction product is cooled to room temperature, breaking the reaction product into particles with the size of 5mm, and placing the particles in a blast drying oven at 70 ℃ for drying until the weight is constant; sixthly, adding the dried materials into a crusher, crushing, and sieving with a 400-mesh sieve to prepare powder.

3) Gamma-methacryloxypropyl trimethoxy silane is selected as a liquid coupling agent, and the liquid coupling agent with the mass of 2.0 percent of that of the component A is added into the component A to be fully mixed; then, fully mixing the component A and the component B according to the mass ratio of 7: 1; finally, drying at low temperature to obtain modified A & B components for later use;

4) the preparation steps of the component C are as follows: the molar ratio of the components is 7: 1: 0.02: 0.03 polyethylene glycol methyl ether methacrylate: acrylamide: maleic anhydride: adding the octadecanol raw materials into water in sequence to prepare a solution, and dissolving the raw materials; secondly, adding the solution into a reactor with stirring blades, introducing nitrogen or argon to remove air in the reactor, and stirring to uniformly mix; thirdly, 0.05 percent of mixture of persulfate and sulfite with the mass ratio of 1:1 is added as a reaction initiator, the temperature is controlled to 50 ℃, and the reaction is carried out for 5 hours; fourthly, pouring out the reactant, cooling the reactant to room temperature, crushing the reactant into particles of 5mm, and placing the particles in an air-blast drying oven at 70 ℃ for drying until the weight is constant; fifthly, adding the dried materials into a crusher, crushing, and sieving with a 400-mesh sieve to prepare powder.

5) Mixing and stirring the components prepared in the steps 3) and 4) uniformly according to the mass ratio of 75:25 to obtain a finished product.

Example 4

1) the preparation steps of the component A are as follows: the dolomite, magnesite and calcite raw materials are crushed and ball-milled, and then sieved by a sieve of 80 mu m, and the dolomite is prepared by the following steps: magnesite: the mass ratio of calcite is 60: 20: 20, mixing; secondly, high-temperature calcination is carried out, the mixture is heated to 600 ℃ at the heating rate of 6 ℃/min and is kept for 60min, and then heated to 1000 ℃ at the heating rate of 10 ℃/min and is kept for 30 min; taking out after calcination, and immediately carrying out quenching at a wind speed of more than 5 m/s; cooling to room temperature, grinding and sieving with a 400-mesh sieve to prepare powder.

2) The preparation steps of the modified component B are as follows: firstly, adding sodium acrylate and vinyl acetate with a molar ratio of 1:1 into a reactor with stirring blades, and adding deionized water to prepare a solution with a concentration of 40%; adding a proper amount of 5mol/L sodium hydroxide to adjust the pH value of the solution to 6.5, adding the solution while stirring, and controlling the feeding speed; adding 2% N, N-methylene bisacrylamide as a catalytic component, adding the solution while stirring, and controlling the feeding speed; fourthly, the polymerization is carried out under the conditions of controlling the temperature to be 80 ℃ and the air pressure to be 0.20MPa, and the reaction time is 3 hours; fifthly, taking out the reaction product after the reaction product is cooled to room temperature, breaking the reaction product into particles of 10mm, and placing the particles in a 60 ℃ forced air drying oven to dry the particles to constant weight; sixthly, adding the dried materials into a crusher, crushing, and sieving with a 400-mesh sieve to prepare powder.

3) Gamma-methacryloxypropyltrimethoxysilane is selected as a liquid coupling agent, and the liquid coupling agent with the mass of 2.0 percent is added into the component A for full mixing; fully mixing the component A and the component B according to the mass ratio of 7: 1; finally, drying at low temperature to obtain modified A & B components for later use;

4) the preparation step of the component C: the molar ratio of the components is 10: 2: 0.04: 0.06 parts of polyethylene glycol methyl ether methacrylate: acrylamide: maleic anhydride: adding the octadecanol raw materials into water in sequence to prepare a solution, and dissolving the raw materials; secondly, adding the solution into a reactor with stirring blades, introducing nitrogen or argon to remove air in the container, and stirring to uniformly mix; thirdly, 0.05 percent of mixture of persulfate and sulfite with the mass ratio of 1:2 is added as a reaction initiator, the temperature is controlled to 60 ℃, and the reaction is carried out for 3 hours; fourthly, pouring out the reactant, cooling the reactant to room temperature, crushing the reactant into particles of 5mm, and placing the particles in a 60 ℃ forced air drying oven to dry the particles to constant weight; fifthly, adding the dried materials into a crusher, crushing, and sieving with a 400-mesh sieve to prepare powder.

Example 5

1) the preparation steps of the component A are as follows: firstly, four raw materials of dolomite, magnesite, calcite and bauxite are adopted, crushed and ball-milled, and then sieved by a sieve of 80 mu m, and then the dolomite: magnesite: calcite: the mass ratio of bauxite is 65: 20: 10: 5, mixing; secondly, high-temperature calcination is carried out, the mixture is heated to 600 ℃ at the heating rate of 6 ℃/min and is kept for 60min, and then heated to 1000 ℃ at the heating rate of 10 ℃/min and is kept for 30 min; taking out after calcining, and immediately quenching at the wind speed of more than 5 m/s; cooling to room temperature, grinding and sieving with a 400-mesh sieve to prepare the powder.

2) The preparation steps of the modified component B are as follows: firstly, adding sodium acrylate and vinyl acetate with a molar ratio of 1:1 into a reactor with stirring blades, and adding deionized water to prepare a solution with a concentration of 40%; adding a proper amount of 5mol/L sodium hydroxide to adjust the pH value of the solution to 6.5, adding the solution while stirring, and controlling the feeding speed; adding 2% N, N-methylene bisacrylamide as a catalytic component, adding the solution while stirring, and controlling the feeding speed; fourthly, the polymerization is carried out under the conditions of controlling the temperature to be 80 ℃ and the air pressure to be 0.10MPa, and the reaction time is 6 hours; fifthly, taking out the reaction product after the reaction product is cooled to room temperature, breaking the reaction product into particles with the size of 5mm, and placing the particles in a blast drying oven at 70 ℃ for drying until the weight is constant; sixthly, adding the dried materials into a crusher, crushing, and sieving with a 400-mesh sieve to prepare powder.

3) Selecting vinyl triethoxysilane as a liquid coupling agent, adding the liquid coupling agent with the mass of 2.0% of that of the component A to the component A, and fully mixing; fully mixing the component A and the component B according to the mass ratio of 6: 1; finally, drying at low temperature to obtain modified A & B components for later use;

4) the preparation steps of the component C are as follows: under the condition of normal temperature of 20 ℃, the molar ratio is 10: 2: 0.04: 0.06 parts of polyethylene glycol methyl ether methacrylate: acrylamide: maleic anhydride: adding the octadecanol raw materials into water in sequence to prepare a solution, and dissolving the raw materials; secondly, adding the solution into a reactor with stirring blades, introducing nitrogen or argon to remove air in the container, and stirring to uniformly mix; thirdly, 0.05 percent of mixture of persulfate and sulfite with the mass ratio of 1:2 is added as a reaction initiator, the temperature is controlled to 40 ℃, and the reaction is carried out for 5 hours; fourthly, pouring out the reactant, cooling the reactant to room temperature, disintegrating the reactant into particles with the diameter of 5mm, and placing the particles in a forced air drying oven with the temperature of 70 ℃ for drying until the weight is constant; fifthly, adding the dried materials into a crusher, crushing, and sieving with a 400-mesh sieve to prepare powder.

When the concrete is prepared, the additive for reducing the viscosity and the shrinkage stress for the concrete is weighed according to 6 percent of the total mass of the rubber material, the additive is firstly mixed into the rubber material outside the concrete and is stirred uniformly, and then water, a water reducing agent and the like are added for stirring, so that the effect of reducing the viscosity and the shrinkage stress can be exerted.

In order to facilitate the practical effect of the admixture for reducing the viscosity and the shrinkage stress for the prefabricated thin-wall structure concrete in the comparative example, a plurality of pairs of proportions are set as follows:

comparative example 1

The CaO expanding agent which is sold in the market and produced by a certain company in Henan is added, and the adding amount of the CaO expanding agent is 5 percent of the total amount of the cementing material.

Comparative example 2

The MgO expanding agent which is sold in the market and produced by a certain company in Hubei is added in an amount of 6 percent of the total amount of the cementing material.

Comparative example 3

The liquid viscosity reducer produced by Nanjing company sold in the market is added in an amount of 0.5 percent of the total amount of the cementing material.

Comparative example 4

CaO expanding agent (produced by a certain company in Henan) accounting for 5 percent of the total mass of the cementing material and liquid viscosity reducer (produced by a certain company in Nanjing) accounting for 0.5 percent of the total mass of the cementing material are added.

Comparative example 5

MgO expanding agent (produced by a certain company in Hubei) and 0.5% liquid viscosity reducer (produced by a certain company in Nanjing) are added in the external admixture, wherein the total mass of the MgO expanding agent is 6%.

Comparative example 6

Referring to example 5, there is provided a viscosity and shrinkage stress reducing admixture for precast thin-walled structural concrete and a method for preparing the same, in this comparative example, component a and component C were prepared in the same manner, but component a was not modified by modifying component B, and component a and component C were directly mixed and stirred uniformly in a certain ratio to obtain a final product, and the comparative example provides the viscosity and shrinkage stress reducing admixture and the method for preparing the same comprising the steps of:

2) The preparation steps of the component C are as follows: under the condition of normal temperature of 20 ℃, the molar ratio is 10: 2: 0.04: 0.06 parts of polyethylene glycol methyl ether methacrylate: acrylamide: maleic anhydride: adding the octadecanol raw materials into water in sequence to prepare a solution, and dissolving the raw materials; secondly, adding the solution into a reactor with stirring blades, introducing nitrogen or argon to remove air in the reactor, and stirring to uniformly mix; thirdly, 0.05 percent of mixture of persulfate and sulfite with the mass ratio of 1:2 is added as a reaction initiator, the temperature is controlled to 40 ℃, and the reaction is carried out for 5 hours; fourthly, pouring out the reactant, cooling the reactant to room temperature, disintegrating the reactant into particles with the diameter of 5mm, and placing the particles in a forced air drying oven with the temperature of 70 ℃ for drying until the weight is constant; fifthly, adding the dried materials into a pulverizer, and sieving the materials with a 400-mesh sieve after pulverization to prepare powder.

3) Mixing and stirring the components prepared in the steps 1) and 2) uniformly according to the mass ratio of 75:25 to obtain a finished product.

The admixture for reducing the viscosity and the shrinkage stress for the precast thin-wall structure concrete listed in the examples 1 to 5 and the admixture listed in the comparative examples 1 to 6 are respectively mixed into the mixing ratio of the C60 concrete for the precast box girder of the actual engineering by adopting an external mixing mode, and the mixing ratio information and the serial number of each group of concrete are shown in the table 1 by contrasting the mixing ratio of blank groups.

TABLE 1C 60 concrete mixing ratio

Testing the slump expansion degree of the concrete mixture in each proportion by referring to GB/T50080-2012 standard of the performance test method of the common concrete mixture; adopting a self-made portable concrete rheometer, filling the stirred concrete into a measuring barrel of the portable rheometer, installing a torque measuring device, testing corresponding torques under corresponding torques at different rotating speeds, and calculating the viscosity and the yield shear stress of the concrete according to a rheology principle; an SBT-II type pore negative pressure automatic test system (comprising a ceramic head, a cavity, a gas collection chamber, a computer acquisition system and other components) is adopted to test the change condition of the negative pressure of a capillary pore at the position of 100mm on the surface of a local mixture along with time; determining the 7d and 28d cubic compressive strength of concrete according to JTG E30-2005 'test Specification for road engineering cement and cement concrete'; the axial tensile strength of 7d and 28d axes of the concrete is measured by referring to the concrete axial tensile test method in SL 352-2006 Hydraulic concrete test procedure, and the related test results are shown in Table 2.

As can be seen from Table 2, under the condition of the same glue material consumption and water consumption, compared with the blank group, after the admixture for reducing the viscosity and the shrinkage stress for the concrete in the embodiments 1 to 5 is added, the construction performance of the C60 concrete mixture is obviously improved, the viscosity and the yield shear stress of the mixture are obviously reduced, the slump expansion degree is increased by 70 to 175mm, and the fluidity of the mixture is obviously improved; the capillary negative pressure peak value is also reduced, which shows that the water loss rate in the concrete is reduced in the early hydration hardening process of the concrete, the volume shrinkage is reduced, and the construction performance is obviously improved; in the embodiments 1 to 5, the addition of the viscosity and shrinkage stress reducing admixture for concrete optimizes the hardened cement stone pore structure and improves the microcosmic compactness, thereby slightly improving the mechanical properties of the hardened concrete. After the admixture for reducing the viscosity and the shrinkage stress for the concrete in the embodiment 5 is doped, the viscosity, the yield shear stress and the capillary negative pressure peak value of the mixture are respectively reduced by 50 percent, 71 percent and 26 percent compared with the blank group, the 28d compressive strength and the flexural strength are respectively improved by 9 percent compared with the blank group, and the action effect is obvious.

After the expanding agent in the comparative examples 1-2 is doped, the viscosity and the yield shear stress of the mixture are obviously increased, the slump expansion degree is reduced, and the construction performance of the mixture is poor; after the liquid viscosity reducer in the comparative example 3 is doped, although the viscosity and the yield shear stress of a mixture are reduced compared with those of a blank group, the effect is not as obvious as that of the additives for reducing the viscosity and the shrinkage stress for the concrete in the examples 1-5, in addition, the mechanical property of the hardened concrete is reduced by the liquid viscosity reducer, and the 28d compressive strength and the 28d flexural strength are respectively reduced by 10% and 8%; when the expanding agent and the liquid viscosity reducer are mixed, the effect is between that of a single mixed component, the viscosity of concrete mixtures of a comparative example 4 and a comparative example 5 is still higher, and the effect is not as obvious as that of the concrete admixture for reducing the viscosity and the shrinkage stress in the examples 1-5. As can be seen from comparative example 6, when component A and component C prepared by the same method as in example are directly mixed and blended into C60 concrete, the effect is far related to the effect of mixing and blending with modified component A and component C in example, the viscosity of concrete mixture is still larger after the admixture described in comparative example 6 is blended, the result of performance parameter of the mixture is equivalent to that of blank group, and the mechanical property of concrete is also reduced. This shows that the component A is directly mixed with the component C, and the viscosity reducing effect of the admixture is influenced to a certain extent.

TABLE 2C 60 concrete mixture Properties and mechanical Properties

Forming a 100 multiplied by 515mm drying shrinkage test piece according to JTG E30-2005 'highway engineering cement and cement concrete test regulation', and testing the change of the length of the concrete test piece along with the curing age by adopting an LVDT data acquisition system; referring to a self-generated volume deformation testing method in SL 352 and 2006 Hydraulic concrete test regulations, a DI-15 type differential resistance strain gauge is adopted to test the change of the strain of a concrete test piece along with the maintenance age; the total cracking area in unit area is tested according to the concrete early cracking test method in GB/T50082-2009 Standard test method for testing the long-term performance and durability of common concrete; performing a concrete ring method crack resistance test according to ASTM C1581, and measuring the cracking time of the concrete ring; on the basis of testing the mechanical, deformation and thermal properties of the concrete, B4Cast software is adopted to simulate and analyze the stress development rule of the member concrete, and the maximum tensile stress borne by the concrete is measuredσAnd simultaneous tensile strengthf _tAnd (4) comparing, calculating corresponding anti-cracking safety coefficients (ratio for evaluating high and low anti-cracking safety of concrete), and showing related test results in table 3.

As can be seen from table 3, compared with the blank group, when the additives for reducing the viscosity and the shrinkage stress for the concrete in the embodiments 1 to 5 are added, the shrinkage strain values of the autogenous volume deformation and the dry shrinkage deformation of the C60 concrete are both obviously reduced, and the shrinkage strain values of the concrete hydration full cycle (at the early stage 3d, the middle stage 28d and the later stage 120 d) are both obviously reduced through the hydration reaction of different active expansion sources in the additives for reducing the viscosity and the shrinkage stress for the concrete; the early crack resistance of the C60 concrete is obviously improved, the cracking area of a flat plate is reduced by 76-100% compared with that of a blank group, the cracking time of a circular ring is delayed by 116-284 h, and the crack resistance safety coefficient of the precast box girder structure is obviously increased (from 0.63 to 2.15-3.50). After the admixture for reducing the viscosity and the shrinkage stress for the concrete in the example 5 is mixed, the self-generated volume deformation of the concrete 3d and 28d is in a volume expansion state, and the self-generated volume deformation of the concrete 120d is converted into a shrinkage state, but the self-generated volume shrinkage deformation value is only-2.7 mu epsilon; the dry shrinkage deformation of the concrete 3d, 28d and 120d is respectively reduced by 89%, 66% and 68% compared with that of a blank group, which shows that the concrete admixture for reducing the viscosity and the shrinkage stress can generate effective expansion to counteract the shrinkage caused by cement hydration in different ages; in addition, after the admixture for reducing the viscosity and the shrinkage stress for the concrete in the embodiment 5 is doped, no obvious microcrack is generated after a concrete slab cracking test is carried out for 24 hours, no crack is generated when a ring cracking test is carried out for 336 hours (14 d), the crack resistance safety coefficient of the prefabricated box girder structure is as high as 3.50, and the action effect is obvious.

After the CaO expanding agent of the comparative example 1 is doped, the volume shrinkage deformation of the C60 concrete in the early hydration stage (mainly before 3 d) can be reduced, and the effect on the middle and later hydration stages is not obvious; the MaO expanding agent of the comparative example 2 only has a certain effect on reducing the volume shrinkage deformation of the concrete in the middle and later stages of hydration (mainly after 28 d); in addition, the expanding agents doped in the comparative examples 1-2 cannot obviously improve the crack resistance of the concrete, and the crack resistance safety coefficient of the precast box girder structure is only 0.79-0.98. The liquid viscosity reducer of comparative example 3 has no significant effect on improving the shrinkage strain and crack resistance of concrete. As can be seen from comparative examples 4 and 5, when the expansive agent and the liquid viscosity reducer are compounded, the anti-cracking effect of the concrete is slightly improved but is not obvious, and the anti-cracking effect is far inferior to that of the admixture for reducing the viscosity and the shrinkage stress, which is compounded in the concrete in examples 1 to 5; in addition, the blending of the liquid viscosity reducer and the powder expanding agent not only does not reduce the autogenous volume shrinkage deformation value and the dry shrinkage deformation value of the concrete, but also has the tendency of weakening the expansion efficiency of the expanding agent. As can be seen from comparative example 6, the component A and the component C are directly mixed and externally added into the C60 concrete, the autogenous volume shrinkage deformation value and the dry shrinkage deformation value of the concrete are equivalent to those of the blank group, the action effect is not even as good as that of comparative examples 1-2, and the crack resistance of the concrete is only slightly improved, which shows that the component A is modified by the modifying component B through the liquid coupling agent, and the modifying component B plays a decisive role in effectively exerting the effects of the component A on reducing the shrinkage stress of the concrete and improving the crack resistance of the member concrete.

Overall, the crack resistance improvement effect of the concrete with the high grade C60 by adding the expanding agent or viscosity reducer in the comparative example is far from the effect of the concrete viscosity and shrinkage stress reducing admixture in examples 1-5.

TABLE 3C 60 concrete deformation behavior, crack resistance

In conclusion, the viscosity and shrinkage stress reducing admixture for the prefabricated thin-wall structure concrete can obviously improve the construction performance of a high-grade concrete mixture, obviously reduce the viscosity and yield shear stress of the mixture, obviously increase the slump expansion degree, reduce the negative pressure peak value of capillary pores and has no adverse effect on the mechanical property of hardened concrete; the volume shrinkage deformation of concrete in the whole cement hydration period (early stage, middle stage and later stage) can be improved, the early crack resistance of high-grade concrete is improved, the crack resistance safety coefficient of a prefabricated box girder structure is obviously increased, and the cracking risk of the high-grade prefabricated thin-wall concrete structure can be effectively reduced.

The above embodiments are only for illustrating the preferred embodiments of the present invention and do not constitute a limitation to the present invention, and it should be noted that obvious modifications to those skilled in the art without departing from the core concept of the present invention are within the scope of protection of the present invention.

Claims

1. A preparation method of an additive for reducing viscosity and shrinkage stress for precast thin-wall structural concrete is characterized by comprising the following steps: the method comprises the following steps:

1) crushing, ball-milling and sieving mineral raw materials, mixing the raw materials in proportion, calcining the mixture at a high temperature, cooling the mixture, grinding the mixture into powder, and sieving the powder to prepare a powder component A;

2) adding organic raw materials into a reactor with stirring blades, adding deionized water to prepare a solution with the concentration of 20-40%, adjusting the pH of the solution to 5-7, adding a catalytic component with the mass fraction of 0.01-2.00%, carrying out polymerization reaction, and sieving to prepare a powder modified component B after crushing, drying and crushing;

3) the mass ratio of (6-15): 1, respectively weighing a component A and a component B, fully mixing the component A with a liquid coupling agent, then adding the component B for fully mixing, and then drying at a low temperature to obtain modified components A and B for later use;

4) preparing polyethylene glycol methyl ether methacrylate, acrylamide, maleic anhydride and octadecanol into a solution, introducing nitrogen or argon to remove air in a container, and stirring to uniformly mix; adding a mixture of 0.01-0.05% of persulfate and sulfite as a reaction initiator, reacting, cooling, crushing, drying and crushing a product, and sieving to prepare a powder component C;

5) modifying the modified A & B components prepared in steps 3) and 4): mixing and stirring the component C uniformly according to the weight ratio of (70-85) to (15-30) to obtain a finished product;

the mineral raw materials in the step 1) are two or more than two of dolomite, magnesite, calcite and bauxite;

the organic raw material in the step 2) is one or more of ice crystal-shaped acrylic acid, sodium acrylate and vinyl acetate.

2. The method for preparing an admixture for reducing viscosity and shrinkage stress for precast thin-walled structural concrete according to claim 1, wherein: high-temperature calcination in step 1): heating to 400-600 ℃ at a heating rate of (6-10) DEG C/min, and preserving heat for 60-90 min, and then heating to 800-1100 ℃ at a heating rate of (10-15) DEG C/min, and preserving heat for 30-60 min.

3. The method for preparing an admixture for reducing viscosity and shrinkage stress for precast thin-walled structural concrete according to claim 1, wherein: the catalytic component in the step 2) is composed of K₂S₂O₈One or more of propylene oxide and N, N-methylene bisacrylamide.

4. The method for preparing an admixture for reducing viscosity and shrinkage stress for precast thin-walled structural concrete according to claim 1, wherein: the polymerization reaction in the step 2) is carried out under the conditions of controlling the temperature to be 70-90 ℃ and the air pressure to be 0.10-0.25 MPa, and the reaction time is 3-6 h.

5. The method for preparing an admixture for reducing viscosity and shrinkage stress for precast thin-walled structural concrete according to claim 1, wherein: the liquid coupling agent in the step 3) is one or more of gamma-aminopropyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane and vinyl triethoxysilane, and the dosage of the liquid coupling agent is 0.5-2% of the component A by mass.

6. The method for preparing an admixture for reducing viscosity and shrinkage stress for precast thin-walled structural concrete according to claim 1, wherein: in the step 4), polyethylene glycol methyl ether methacrylate, acrylamide, maleic anhydride and octadecanol are added into water to be dissolved according to the molar ratio of (6-10) to (1-2) to (0.02-0.04) to (0.02-0.06).

7. The viscosity and shrinkage stress reducing admixture for precast thin-walled structural concrete prepared by the preparation method according to any one of claims 1 to 6.

8. The admixture for reducing viscosity and shrinkage stress for precast thin-walled structure concrete according to claim 7, applied to precast thin-walled structure concrete works, wherein: when the concrete is prepared, the admixture is weighed according to the mass ratio of the using amount of the glue material, and the admixture is firstly mixed into the glue material by an external mixing method and is uniformly mixed, and then water and a water reducing agent are added for stirring, so that the effects of reducing the viscosity and the shrinkage stress can be exerted.