CN111908847B

CN111908847B - Anti-freezing and anti-cracking concrete and preparation method thereof

Info

Publication number: CN111908847B
Application number: CN202010830723.XA
Authority: CN
Inventors: 蔡燕嫦
Original assignee: Jiexi Juta Concrete Co ltd
Current assignee: Jiexi Juta Concrete Co ltd
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2022-04-26
Anticipated expiration: 2040-08-18
Also published as: CN111908847A

Abstract

The invention belongs to the field of building materials, and particularly relates to anti-freezing and anti-cracking concrete and a preparation method thereof. The product developed by the invention comprises graphene oxide accounting for 1-10% of the mass of the concrete; epoxy groups on the graphene oxide interlayer are replaced by octadecylamine; epoxy groups on the graphene oxide interlayer are substituted by amino; the air bubbles in the concrete are dispersed among the graphene oxide layers; the diameter of the bubbles is 10-100 nm. When the product is prepared, octadecylamine and sodium azide are used for modifying graphene oxide, lithium aluminum hydride is used for processing the graphene oxide to obtain modified graphene oxide, and the modified graphene oxide is added into a concrete mixture to prepare concrete. The product obtained by the invention has good frost resistance and crack resistance, and the service life of the concrete is effectively prolonged.

Description

Anti-freezing and anti-cracking concrete and preparation method thereof

Technical Field

The invention belongs to the technical field of building materials. More particularly, it relates to a frost-resistant and crack-resistant concrete and a preparation method thereof.

Background

Concrete is a complex multiphase, multi-component material whose properties are closely related to the internal microstructure. Typically, the pore structure includes the distribution of different pore sizes, the morphology of the pores, and the spatial arrangement of the pores. Thus, factors that can affect the formation of the concrete pore structure can affect the durability of the concrete. Summarizing the research results and engineering practices in the field at present, it can be found that the most important influence factors of the frost resistance of the concrete are the gas content of the concrete, the types of mineral admixtures, the doping amount and quality, and the properties, the pore structure and the like of air bubbles introduced into the concrete.

The air content is a main factor influencing the frost resistance of the concrete, and particularly, tiny, closed, stable and uniform bubbles formed after the air entraining agent is added have an obvious effect on improving the frost resistance of the concrete. The air content in the concrete is increased, the average air bubble spacing is reduced, and under the condition of keeping the optimal air content, the air bubble spacing enables the pressure generated by freezing and thawing to be reduced.

The water-cement ratio is one of important parameters of concrete design, on one hand, the water-cement ratio can directly influence the porosity and the pore structure of the concrete, and along with the increase of the water-cement ratio, the total volume of open pores is increased, the average pore diameter is increased, and the frost resistance of the concrete is reduced.

The degree of frost damage of concrete is closely related to the degree of water saturation of its pores, and it is generally believed that a water content of less than 91.7% of the total volume of the pores does not produce a freezing expansion pressure, a value known as ultimate water saturation. In the fully water-saturated state of the concrete, the freezing expansion pressure is maximum.

Studies have shown that the frost resistance of concrete is greatly improved by adding suitable admixtures, of which air-entraining agents and water-reducing agents are most commonly used. The air entraining agent can introduce a large amount of closed micro bubbles in the stirring process of the concrete and is stably and uniformly distributed, so that the working performance of the concrete is improved, and the frost resistance and durability of the concrete are improved. The water reducing agent can reduce the consumption of water, reduce the porosity and finally improve the frost resistance.

However, in the practical application process of the anti-freezing concrete, in the processes of transporting and pumping the mixture, introduced bubbles are difficult to exist stably, so that the gas content loss is caused, finally, the gas content of a structural entity is reduced, the initial design requirement cannot be met, and the anti-freezing performance of the concrete is reduced; therefore, how to ensure the stability of the introduced bubbles in the processes of transporting and pumping the mixture is one of the technical problems to be solved urgently by the technical personnel in the field.

Disclosure of Invention

The invention aims to provide frost-resistant and crack-resistant concrete and a preparation method thereof, wherein bubbles introduced into the concrete can stably exist for a long time, and can still stably exist even in the processes of transporting and pumping a mixture, so that the defect of the prior art that the frost resistance of the concrete is reduced due to the loss of gas content caused by poor bubble stability is overcome.

In order to achieve the purpose, the invention provides the following technical scheme:

the anti-freezing and anti-cracking concrete comprises graphene oxide accounting for 1-10% of the mass of the concrete;

epoxy groups on the graphene oxide interlayer are replaced by octadecylamine;

epoxy groups on the graphene oxide interlayer are substituted by amino;

the air bubbles in the concrete are dispersed among the graphene oxide layers; the diameter of the bubbles is 10-100 nm.

Preferably, the graphene oxide is folded graphene oxide; the surface roughness Ra of the wrinkled graphene oxide is 20-60.

Preferably, the concrete also comprises fiber aggregate which accounts for 50-80% of the mass of the concrete.

Preferably, the fiber aggregate is a hollow aggregate fiber; the hollow aggregate fiber is carbonized rice husk fiber.

Preferably, the length-diameter ratio of the carbonized rice hull fiber is 10: 1-50: 1; the length of the carbonized rice hull fiber is 50-300 nm.

A preparation method of frost-resistant and crack-resistant concrete comprises the following specific preparation steps:

modification of graphene oxide:

mixing graphene oxide and water according to a mass ratio of 1: 10-1: 20, mixing and dispersing, adding octadecylamine accounting for 5-10% of the mass of the graphene oxide, heating and refluxing for reaction, adding sodium azide accounting for 10-12% of the mass of the graphene oxide, continuing heating and refluxing for reaction, adding lithium aluminum hydride accounting for 10-12% of the mass of the graphene oxide, heating and refluxing for reaction, and drying to obtain modified graphene oxide;

preparing a mixture:

according to the weight parts, 200-10 parts of cement, 8-10 parts of polycarboxylic acid water reducing agent and 150-200 parts of water are sequentially mixed uniformly to obtain a mixture; adding modified graphene oxide accounting for 1-10% of the mass of the mixture into the mixture; stirring and mixing evenly to obtain a mixture.

Preferably, the drying is spray drying.

Preferably, the specific preparation steps further comprise:

adding fiber aggregate which accounts for 50-80% of the mass of the mixture into the mixture;

the preparation steps of the fiber aggregate are as follows:

soaking rice hull fiber in water, freezing, squeezing, drying, and heating under inert gas protection.

Preferably, the temperature-rising carbonization is as follows: heating to 400 ℃ at the speed of 0.6-1.2 ℃/min, keeping the temperature for 3-5h, continuing heating to 700 ℃ at the speed of 8-10 ℃/min, keeping the temperature for 3-5h, and cooling to room temperature.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the technical scheme, self-made modified graphene oxide is added to serve as an air entraining agent, so that epoxy groups between graphene oxide layers are partially substituted by octadecylamine, and partial epoxy groups are substituted by amino; the epoxy groups are distributed in the conjugated region of the graphene oxide, and long carbon chains of the epoxy groups can play a certain steric hindrance role after being substituted by octadecylamine, so that the interlayer distance of the graphene oxide is effectively widened, the carboxyl at the edge region of the graphene oxide is hydrophilic, the long carbon chains of the octadecylamine in the conjugated region are hydrophobic, the epoxy groups can play a role of an air entraining agent in the stirring process, and a generated bubble liquid film is protected by the graphene oxide of a single layer, so that bubbles are dispersed among the graphene oxide layers with widened interlayer spacing; in addition, as part of epoxy groups between graphene oxide layers are substituted by amino groups, positive charges are carried between the layers, and generated bubbles can be firmly adsorbed; the protection effect of the graphene oxide is utilized, so that the bubbles are stably dispersed, and the graphene is coated on the liquid film, so that the bubbles can be stably suspended in the system, and the dissipation of the bubbles is avoided;

(2) according to the technical scheme, the graphene oxide is treated by spray drying, so that the surface of the graphene oxide is of a folded structure, the surface roughness of the graphene oxide is improved, the friction force between the single-layer structure of the graphene oxide and the whole solidified concrete is enhanced, when the single-layer structure of the graphene oxide and the whole solidified concrete are subjected to external force or expansion and contraction, the folded structure can effectively prevent the graphene oxide and the concrete from sliding relatively, and the freezing resistance of a product is effectively improved;

(3) according to the technical scheme, rice hull fibers with a hollow structure are further introduced, through freezing and squeezing, in the freezing process, moisture between fiber cells and gaps is frozen, ice crystals are broken under the action of pressure, the rice hull fibers are dissociated into short fibers in a nanometer level, in the carbonization process, the temperature rise rate is controlled, organic matters in the rice hull fibers are gradually carbonized, an outer silicon dioxide shell serves as a support body to form the hollow structure, certain air bubbles can exist in the hollow structure in the stirring process, so that the rice hull fibers are stably suspended in a concrete system, the short fibers with the fiber size of the nanometer scale can be dispersed in all corners of the system, when external force is applied, the crack is often expanded from a micro crack, and when the crack meets the uniformly dispersed short fibers, the stress can be rapidly dispersed to all corners of the system; and the number of the short fibers is large, the size is small, and compared with the long fibers, the anti-freezing performance of the product is further improved by breaking the short fibers only by consuming more external force.

Detailed Description

The present invention is further illustrated by the following specific examples, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Unless otherwise indicated, reagents and materials used in the following examples are commercially available.

Example 1

Preparation of fiber aggregate:

according to the mass ratio of 1: 3, mixing and soaking the rice hulls and water for 16 hours, filtering, freezing the rice hulls for 2 hours at the temperature of-18 ℃, and then freezing and squeezing for 10 minutes under the pressure of 8MPa to obtain a squeezed material; then drying the pressed material in vacuum at the temperature of 100 ℃ and the pressure of 100Pa to constant weight to obtain a dried pressed material; and then heating the obtained dried squeezed material to 300 ℃ at the speed of 0.6 ℃/min under the protection of inert gas, preserving heat and carbonizing for 3h, then continuously heating to 600 ℃ at the speed of 8 ℃/min, preserving heat and carbonizing for 3h, cooling to room temperature along with the furnace, discharging, and screening out the material with the length-diameter ratio of 10: 1, a fiber aggregate having a length of 50 nm;

modification of graphene oxide:

mixing graphene oxide and water according to a mass ratio of 1: 10, performing ultrasonic dispersion for 45min under the ultrasonic frequency of 45kHz, adding octadecylamine accounting for 5% of the mass of graphene oxide, performing heating reflux reaction for 6h at the temperature of 85 ℃, adding sodium azide accounting for 10% of the mass of graphene oxide, performing heating reflux reaction for 3h at the temperature of 80 ℃, adding aluminum lithium tetrahydride accounting for 10% of the mass of graphene oxide, performing heating reflux reaction for 3h at the temperature of 80 ℃, and performing spray drying to obtain modified graphene oxide;

preparing concrete:

according to the weight parts, 200 parts of cement, 8 parts of polycarboxylic acid water reducing agent and 150 parts of water are sequentially and uniformly mixed to obtain a mixture; adding modified graphene oxide accounting for 1% of the mixture by mass into the mixture; and fiber aggregate accounting for 50% of the mass of the mixture are uniformly stirred and mixed to obtain a mixture; and pouring, molding and curing the obtained mixture to obtain the concrete.

Example 2

Preparation of fiber aggregate:

according to the mass ratio of 1: 10, mixing and soaking rice hulls and water for 32 hours, filtering, freezing the rice hulls for 3 hours at the temperature of minus 50 ℃, and then freezing and squeezing for 30 minutes under the pressure of 20MPa to obtain a squeezed material; then drying the pressed material in vacuum at the temperature of 105 ℃ and the pressure of 300Pa to constant weight to obtain a dried pressed material; and then heating the obtained dried squeezed material to 400 ℃ at the speed of 1.2 ℃/min under the protection of inert gas, preserving heat and carbonizing for 5 hours, then continuously heating to 700 ℃ at the speed of 10 ℃/min, preserving heat and carbonizing for 5 hours, cooling to room temperature along with the furnace, discharging, and screening out the material with the length-diameter ratio of 50: 1, a fiber aggregate with a length of 300 nm;

modification of graphene oxide:

mixing graphene oxide and water according to a mass ratio of 1: 20, performing ultrasonic dispersion for 60min under the condition that the ultrasonic frequency is 60kHz, adding octadecylamine accounting for 10% of the mass of graphene oxide, performing heating reflux reaction for 8h at the temperature of 90 ℃, adding sodium azide accounting for 12% of the mass of graphene oxide, performing heating reflux reaction for 5h under the condition that the temperature is 85 ℃, adding aluminum lithium tetrahydride accounting for 12% of the mass of graphene oxide, performing heating reflux reaction for 5h at the temperature of 85 ℃, and performing spray drying to obtain modified graphene oxide;

preparing concrete:

according to the weight parts, 300 parts of cement, 10 parts of polycarboxylic acid water reducing agent and 200 parts of water are sequentially and uniformly mixed to obtain a mixture; adding modified graphene oxide accounting for 10% of the mixture by mass into the mixture; and fiber aggregate accounting for 80% of the mass of the mixture, and uniformly stirring and mixing to obtain a mixture; and pouring, molding and curing the obtained mixture to obtain the concrete.

Example 3

Preparation of fiber aggregate:

according to the mass ratio of 1: 5, mixing and soaking the rice hulls and water for 22 hours, filtering, freezing the rice hulls for 2.5 hours at the temperature of minus 30 ℃, and then freezing and squeezing for 20 minutes under the pressure of 10MPa to obtain a squeezed material; then drying the pressed material in vacuum at the temperature of 102 ℃ and the pressure of 200Pa to constant weight to obtain a dried pressed material; and then heating the obtained dried squeezed material to 350 ℃ at the speed of 1.0 ℃/min under the protection of inert gas, keeping the temperature for carbonization for 4h, continuing heating to 650 ℃ at the speed of 9 ℃/min, keeping the temperature for carbonization for 4h, cooling to room temperature along with the furnace, discharging, and screening out the material with the length-diameter ratio of 20: 1, fiber aggregate with the length of 200 nm;

modification of graphene oxide:

mixing graphene oxide and water according to a mass ratio of 1: 15, performing ultrasonic dispersion for 50min under the condition that the ultrasonic frequency is 50kHz, adding octadecylamine accounting for 8% of the mass of graphene oxide, performing heating reflux reaction for 7h at the temperature of 88 ℃, adding sodium azide accounting for 11% of the mass of graphene oxide, performing heating reflux reaction for 4h under the condition that the temperature is 82 ℃, adding aluminum lithium tetrahydride accounting for 11% of the mass of graphene oxide, performing heating reflux reaction for 4h at the temperature of 82 ℃, and performing spray drying to obtain modified graphene oxide;

preparing concrete:

according to the weight parts, 250 parts of cement, 9 parts of polycarboxylic acid water reducing agent and 180 parts of water are sequentially mixed uniformly to obtain a mixture; adding modified graphene oxide accounting for 5% of the mixture by mass into the mixture; and fiber aggregate accounting for 60% of the mass of the mixture, and uniformly stirring and mixing to obtain a mixture; and pouring, molding and curing the obtained mixture to obtain the concrete.

Example 4

This example differs from example 1 in that: the length of the equal mass is 3mm, the length-diameter ratio is 10: 1 as fiber aggregate, the rest conditions being kept unchanged.

Example 5

This example differs from example 1 in that: vacuum freeze drying is adopted to replace spray drying, and other conditions are kept unchanged.

Comparative example 1

This comparative example differs from example 1 in that: sodium dodecyl benzene sulfonate with equal mass is adopted to replace the modified graphene oxide, and the other conditions are kept unchanged.

Comparative example 2

In comparison with example 1, the graphene oxide of this comparative example was not modified, and the remaining conditions were maintained.

The products obtained in examples 1-5 and comparative examples 1-2 were tested for their properties, the test specimens were 100mm × 100mm × 100mm, and cured for 28 days, and the specific test methods and test results were as follows:

by adopting a quick freezing method, according to the regulation of GB/T50082-2009 Standard test method for the long-term performance and the durability of the common concrete, the test can be stopped when one of the following conditions occurs in a freezing-thawing cycle: (1) reaching the specified number of freeze-thaw cycles; (2) the relative dynamic elastic modulus of the test piece is reduced to 60 percent; (3) the mass loss rate of the test piece reaches 5 percent; the frost resistance grades of different examples and comparative products are obtained by testing, and the details are shown in table 1;

compressive strength: the concrete test is carried out according to GB/T50081-2002 standard of common concrete mechanical property test method, and specific test results are shown in Table 1;

table 1: product performance test results

As can be seen from the test results in Table 1, the compressive strength of the test piece after the product obtained in the embodiment of the application is maintained for 28 days is 48.9-55.3MPa, the frost resistance level can reach more than F300, and compared with a comparative example, the mechanical property and the frost resistance are obviously improved.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein, and any reference thereto is therefore intended to be embraced therein.

Claims

1. The anti-freezing and anti-cracking concrete is characterized by comprising graphene oxide accounting for 1-10% of the mass of the concrete;

epoxy groups on the graphene oxide interlayer are replaced by octadecylamine;

epoxy groups on the graphene oxide interlayer are substituted by amino;

the air bubbles in the concrete are dispersed among the graphene oxide layers; the diameter of the bubbles is 10-100 nm;

the graphene oxide is folded graphene oxide; the surface roughness Ra of the folded graphene oxide is 20-60;

the concrete also comprises fiber aggregate which accounts for 50-80% of the mass of the concrete; the fiber aggregate is a hollow aggregate fiber; the hollow aggregate fiber is carbonized rice husk fiber.

2. The antifreeze anti-cracking concrete of claim 1, wherein the aspect ratio of the carbonized rice hull fiber is 10: 1-50: 1; the length of the carbonized rice hull fiber is 50-300 nm.

3. The preparation method of the anti-freezing and anti-cracking concrete is characterized by comprising the following specific preparation steps:

modification of graphene oxide:

preparing concrete:

according to the weight parts, 200-10 parts of cement, 8-10 parts of polycarboxylic acid water reducing agent and 150-200 parts of water are sequentially mixed uniformly to obtain a mixture; adding modified graphene oxide accounting for 1-10% of the mass of the mixture into the mixture; stirring and mixing uniformly to obtain a mixture; pouring, molding and curing the obtained mixture to obtain concrete;

the specific preparation steps further comprise:

the preparation steps of the fiber aggregate are as follows:

4. The method for preparing a frost-resistant and crack-resistant concrete according to claim 3, wherein the drying is spray drying.

5. The method for preparing antifreeze anti-cracking concrete according to claim 3, wherein the temperature-rise carbonization is as follows: heating to 400 ℃ at the speed of 0.6-1.2 ℃/min, keeping the temperature for 3-5h, continuing heating to 700 ℃ at the speed of 8-10 ℃/min, keeping the temperature for 3-5h, and cooling to room temperature.