CN103979886A - High early-strength high-performance concrete mixed with nano silicon dioxide powder and preparation method thereof - Google Patents

Abstract

The invention discloses an early-strength ^high -performance concrete mixed with nano-silica powder and a preparation method thereof ^. Material 600--620kg/m ³ , water 225--235kg/m ³ , high-performance water reducing agent 7.77--9.1kg/m ³ , nano-silica 8.1--16.2kg/m ³ , the mixing ratio is sand rate 37~38%, water-cement ratio 0.40~0.43. The fine aggregate is river sand or medium sand, the particle size of the coarse aggregate is 5-35mm, the water reducing rate of the high-performance water reducing agent is not less than 25%, and the average particle size of nano-silica is 30±5nm. Improve the early strength of concrete, it can be used for super high-rise buildings constructed in winter and concrete projects with early requirements for normal and low temperature conditions, and has high practical value.

Description

A kind of early-strength high-performance concrete mixed with nano-silica powder and its preparation method

technical field

The invention belongs to the technical field of civil engineering concrete, and relates to the preparation technology of early-strength high-performance concrete, in particular to improving the early performance of concrete by using nano-silica as an additive.

Background technique

Since the emergence of Portland cement in the 1920s, the concrete prepared with it has the strength and durability required by engineering, and the raw materials are easy to obtain, the cost is low, especially the energy consumption is low, so it is widely used. , has become an important structural material for modern engineering structures such as civil engineering, water conservancy engineering, and transportation.

At the beginning of the 20th century, with the proposal of water-cement ratio and other theories, the theoretical foundation of concrete strength was initially established. Later, light aggregate concrete, air-entrained concrete and other concrete appeared one after another, and various concrete admixtures were also used. Since the 1960s, water-reducing agents have been widely used, and high-efficiency water-reducing agents and corresponding fluid concrete have appeared; polymer materials have entered the field of concrete materials, and polymer concrete has appeared; various fibers have been used to disperse reinforcement. Fiber concrete.

Concrete early strength agent is one of the earliest admixture varieties used in the history of admixture development. So far, people have developed a variety of early-strength admixtures other than chloride salts and sulfates, such as nitrite, chromate, etc., and organic early-strength agents, such as triethanolamine, calcium formate, urea, etc. And on the basis of the early strength agent, a variety of composite admixtures are produced and applied, such as early strength water reducer, early strength antifreeze and early strength pumping agent. These types of early-strength admixtures have been used in practical engineering to improve the performance of concrete. It has played an important role in improving construction efficiency and saving investment costs.

Nanomaterials refer to at least one dimension in three-dimensional space with a size of 1nm to 100nm. Due to its small size, it presents the characteristics of small size effect, quantum size effect, surface interface effect and macroscopic quantum tunneling effect that macroscopic objects do not have. It is hailed as "the most promising material in the 21st century" by scientists. The emergence of nanotechnology marks that human beings' ability to transform nature has extended to the atomic and molecular levels, and it marks that human science and technology have entered a new era-the era of nanotechnology. Nano-SiO ₂ is an amorphous substance with a particle size of only about 20nm. It has been widely used in modified coatings, anti-ultraviolet agents, plastic additives, rubber products, pigments, ceramics, and other fields.

The first nanoscience and technology academic conference officially announced nanomaterial science as a new branch of material science. Since then, nanomaterials have aroused great interest and extensive attention from the material and physical circles around the world. At present, there have been many research results on high-efficiency active mineral admixtures for concrete, and they have been applied in engineering practice. The active mineral admixture contains a large amount of active silica and active alumina, which generates high-strength and stable low-alkaline calcium silicate hydrate during cement hydration, improving the hydration gelling substance. Ultra-fine mineral admixtures can be filled between cement particles, making cement stone dense, and improving interface structure and performance.

The particle size of artificially synthesized nano-SiO ₂ (Nano-SiO ₂ , NS for short) is very small, and its pozzolanic activity is much higher than that of silica fume and fly ash. In cement paste, Ca(OH) ₂ will form more bonds on the surface of nano-SiO ₂ and generate CSH gel, which plays a role in reducing the content of Ca(OH) ₂ and refining the crystal size of Ca(OH) ₂ At the same time, the CSH gel forms a cluster structure with nano-SiO ₂ as the core, and the nano-SiO ₂ acts as a node of the CSH gel network. The above-mentioned effects of nano-SiO ₂ can theoretically improve the strength, compactness, impermeability and other properties of concrete. At present, there are relatively few studies on the incorporation of nano-SiO ₂ in concrete, which are limited to interface modification and macroscopic physical and mechanical properties.

Improving the early strength of cement concrete is an important direction for the development of concrete materials, and it is also a research hotspot in the field of concrete materials. Applying nano-silica powder to concrete materials will greatly improve the early performance of concrete, which has significant innovative significance and major engineering application value.

Contents of the invention

The invention provides an early-strength high-performance concrete mixed with nano-silica powder and a preparation method thereof, aiming at improving the early-stage strength of the concrete.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

The early-strength high-performance concrete mixed with nano-silica powder of the present invention is characterized in that the components and contents are as follows: cement 519--550kg/m ³ , coarse aggregate 1010-1040kg/m ³ , fine aggregate 600-- 620kg/m ³ , water 225--235kg/m ³ , high-performance water reducing agent 7.77--9.1kg/m ³ , nano-silicon dioxide 8.1--16.2kg/m ³ , the mix ratio is 37-38% of sand rate , water-cement ratio 0.40 ~ 0.43.

The cement is Portland cement with a strength grade not lower than PC32.5.

The fine aggregate is river sand or medium sand with a mud content of less than 3%.

The particle size of the coarse aggregate is 5-35mm.

The water reducing rate of the high-performance water reducing agent is not less than 25%.

The high-performance water reducer is a naphthalene-based concrete high-efficiency water-reducer or a polycarboxylate high-efficiency water-reducer.

The average particle size of the nano-silica is 30±5nm, the surface is nano-treated, and the content of the nano-silica is

≥99.5%, weight loss on ignition ≤6.0%.

The preparation method comprises the steps of:

1) High-performance water reducer, nano silicon dioxide, 60-70% water, stir well to form a mixture;

2) Stir the coarse aggregate, fine aggregate and cement in a concrete mixer to form a solid mixture;

3) Stir the mixed solution in step 1), the solid mixture in step 2) and the remaining 30-40% water at high speed for 180-240 seconds, and stir evenly to form a concrete mixture.

The stirring speed is the stirring shaft speed 30r/min.

Fine aggregate: river sand, medium sand and other mud content is less than 3%.

Coarse aggregate: particle size 5-35mm, fineness modulus 4.3, bulk density 1460kg/m ³ , apparent density 2.85g/cm ³ , crushing value 3.45%, meeting GB/T14684-2001 "Building Pebbles, Gravel requirements.

High-performance superplasticizer: the water-reducing rate is not less than 25%; there are naphthalene-based concrete superplasticizers and polycarboxylate superplasticizers.

Nano silicon dioxide: average particle diameter 30±5nm, specific surface area 200±30mm ² /g, content ≥99.5%.

The mix design of concrete is calculated according to the mass method. The sand rate is 37-38%, and the water-binder ratio is 0.40-0.43.

Weigh the raw materials according to the above mass ratio, and stir them mechanically. The mixing process is:

Add water reducing agent to nano powder, add 60-70% of water consumption, and stir evenly to form a mixed liquid; in a concrete mixer, mix coarse and fine aggregate and cement evenly to form a solid mixture; add the remaining 30-40% to the mixed liquid and solid mixture Water consumption, high-speed stirring for 180-240 seconds, stirring evenly into a concrete mixture.

Beneficial effects: the addition of nano-silica in the formula of the present invention can improve the strength of concrete, especially significantly improve the early strength of concrete, and play an important role in improving concrete performance, improving construction efficiency and saving investment costs. Carry out group experiments according to "Standard GB/T50081-2002 for Test Methods of Mechanical Properties of Ordinary Concrete". Different examples prove that the early-strength high-performance concrete mixed with nano-silica powder prepared by this method is compared with ordinary concrete designed with the same mix ratio. The flexural strength at the age of 7 days can be increased by 214%-396%, the splitting tensile strength can be increased by 28.9%-43.0%, and the compressive strength can be increased by 6.13%-17.2%; The tensile strength can be increased by 7.8%-22.2%. This early-strength concrete can be used for super high-rise buildings constructed in winter and concrete projects with early requirements for normal and low temperature conditions, and has great engineering practical value and significant technical and economic significance.

Detailed ways

The specific implementation manner of the present invention will be described in detail below in conjunction with the technical solutions.

Example 1

A seaport project uses self-compacting high-strength freeze-thaw-resistant concrete. The raw materials and properties used are as follows:

Cement: PI42.5 Portland cement, purchased from Nanjing Yuhua Cement Factory.

Fine aggregate: river sand, fineness modulus 2.3, medium sand; apparent density 2.57g/cm ³ , washed and dried before use.

Coarse aggregate: high-density limestone with a nominal particle size of 5-35mm and an apparent density of 2.85g/cm ³ .

Water: tap water.

Water reducer: polycarboxylate water reducer, water reducing rate 42%. Purchased from Nanjing Pioneer Technology Industrial Co., Ltd.

Nano-SiO ₂ powder: the content of nano-SiO ₂ is greater than 99.5%, and the particle size is 30±5nm. Purchased from Hangzhou Wanjing New Material Co., Ltd.

According to the "Ordinary Concrete Mix Design Regulations (JGJ55-2011)", the concrete mix design is as follows (sand ratio 37%, water-cement ratio 0.4):

Weigh raw materials according to the above-mentioned mass ratio, mechanically stir, and stir process:

Water reducer plus nano powder plus 60% of water consumption, stir evenly to form a mixed solution; mix coarse and fine aggregate and cement to form a solid mixture; add solid mixture to the mixed solution and add the remaining 40% of water consumption, high-speed 30r/min) stirring for 240 seconds.

According to "Standard GB/T50081-2002 for Test Methods of Mechanical Properties of Ordinary Concrete", the strength test results:

The 7-day compressive strength is 35.7MPa, the 7-day flexural strength is 3.8Mpa, and the 7-day splitting tensile strength is 1.69MPa.

Example 2

Raw materials:

Cement: Conch brand PC42.5 composite portland cement

Fine aggregate: river sand, fineness modulus 2.3, medium sand; apparent density 2.65g/cm ³ , washed and dried before use.

Coarse aggregate: basalt crushed stone in Nanjing area, with a nominal particle size of 5-35mm.

Water: Nanjing tap water.

Water-reducing agent: Richlam240 naphthalene-based concrete high-efficiency water-reducing agent produced by Nanjing Pioneer Technology Industrial Co., Ltd., with a water-reducing rate of 25%.

Nano-SiO ₂ powder: Nano-SiO ₂ powder produced by Zhejiang Hangzhou Wanjing New Material Co., Ltd., with a nano-material content greater than 99.5%, an average particle size of 30nm, a specific surface area of 200mm ² /g, and an ignition weight loss rate of 3.5%.

In this example, the early-strength concrete with nano-SiO ₂ powder and the ordinary concrete without nano-SiO ₂ powder are set. (GB/T50080-2002)", "Standard for Test Methods of Mechanical Properties of Ordinary Concrete (GB/T50081-2002)".

The mix ratio is designed as (water-cement ratio 0.43, sand ratio 38%):

test results:

Example 3

Raw materials:

Cement: Conch brand PC32.5 composite Portland cement

Fine aggregate: river sand, fineness modulus 2.3, medium sand; apparent density 2.65g/cm ³ , washed and dried before use.

Coarse aggregate: basalt crushed stone in Nanjing area, with a nominal particle size of 5-35mm.

Water: Nanjing tap water.

Water-reducing agent: Richlam240 naphthalene-based concrete high-efficiency water-reducing agent produced by Nanjing Pioneer Technology Industrial Co., Ltd., with a water-reducing rate of 25%

Nano-SiO ₂ powder: Nano-SiO ₂ powder produced by Zhejiang Hangzhou Wanjing New Material Co., Ltd., with a nano-material content greater than 99.5%, an average particle size of 30nm, a specific surface area of 200m ² /g, and an ignition weight loss rate of 3.5%.

In this example, the early-strength concrete with nano-SiO ₂ powder and the ordinary concrete without nano-SiO ₂ powder are set. (GB/T50080-2002)", "Standard for Test Methods of Mechanical Properties of Ordinary Concrete (GB/T50081-2002)".

The mix ratio is designed as (water-cement ratio 0.43, sand ratio 38%):

type Water cement ratio water cement fine aggregate Coarse aggregate Nano NS Superplasticizer No NS 0.43 235 535 620 1010 0 8.01 mixed with NS 0.43 235 519 620 1010 16.2 7.77

test results:

Example 4

Raw materials:

Cement: Conch brand PC32.5 composite Portland cement

Fine aggregate: river sand, fineness modulus 2.3, medium sand; apparent density 2.65g/cm ³ , washed and dried before use.

Coarse aggregate: basalt crushed stone in Nanjing area, with a nominal particle size of 5-35mm.

Water: Nanjing tap water.

Water-reducing agent: Richlam240 naphthalene-based concrete high-efficiency water-reducing agent produced by Nanjing Pioneer Technology Industrial Co., Ltd., with a water-reducing rate of 25%

Nano-SiO ₂ powder: Nano-SiO ₂ powder produced by Zhejiang Hangzhou Wanjing New Material Co., Ltd., with a nano-material content greater than 99.5%, an average particle size of 30nm, a specific surface area of 200m ² /g, and an ignition weight loss rate of 3.5%.

In this example, the early-strength concrete with nano-SiO ₂ powder and the ordinary concrete without nano-SiO ₂ powder are set. (GB/T50080-2002)", "Standard for Test Methods of Mechanical Properties of Ordinary Concrete (GB/T50081-2002)".

The mix ratio is designed as (water-cement ratio 0.43, sand ratio 38%):

type Water cement ratio water cement fine aggregate Coarse aggregate Nano NS Superplasticizer No NS 0.43 235 535 620 1010 0 8.01 mixed with NS 0.43 235 527 620 1010 8.1 7.89

test results:

Different examples prove that the early-strength high-performance concrete mixed with nano-silica powder prepared by this method can increase the flexural strength of 7-day age by 214%--396% compared with ordinary concrete designed with the same mix ratio, and the splitting The tensile strength can be increased by 28.9%-43.0%, the compressive strength can be increased by 6.13%-17.2%; the splitting tensile strength at 28 days can be increased by 7.8%-22.2%. This early-strength concrete can be used for super high-rise buildings constructed in winter and concrete projects with early requirements for normal and low temperature conditions, and has great engineering practical value and significant technical and economic significance.

Claims (9)

1. An early-strength high-performance concrete mixed with nano-silica powder, characterized in that the components and contents are as follows: cement 519~550kg/ m ³ , coarse aggregate 1010~1040kg/ m ³ , fine aggregate 600~620kg / m ³ , water 225~235kg/ m ³ , high performance water reducing agent 7.77~9.1kg/ m ³ , nano silicon dioxide 8.1~16.2kg/ m ³ , the mixing ratio is: sand rate 37~38%, water ash Ratio 0.40~0.43. 2. The early-strength high-performance concrete mixed with nano-silica powder as claimed in claim 1, wherein the cement is Portland cement with a strength grade not lower than PC32.5. 3. The early-strength high-performance concrete mixed with nano-silica powder as claimed in claim 1, wherein the fine aggregate is river sand or medium sand, and the mud content is less than 3%. 4. A kind of early-strength high-performance concrete mixed with nano-silica powder as claimed in claim 1, characterized in that: the particle diameter of the coarse aggregate is 5-35mm. 5. The early-strength high-performance concrete mixed with nano-silica powder as claimed in claim 1, characterized in that: the water-reducing rate of the high-performance water-reducing agent is not less than 25%. 6. A kind of early-strength high-performance concrete mixed with nano-silica powder as claimed in claim 5, characterized in that: the high-performance water-reducer is a naphthalene-based concrete high-efficiency water-reducer or a polycarboxylate high-efficiency water-reducer Aqua. 7. A kind of early-strength high-performance concrete mixed with nano-silica powder as claimed in claim 1, characterized in that: the average particle diameter of the nano-silica is 30±5nm, the specific surface area is 200± ^30mm2 /g, Content ≥ 99.5%. 8. the preparation method of a kind of nano-silica powder-doped early-strength high-performance concrete described in any one of claims 1 to 7, is characterized in that comprising the steps: 1) High-performance water reducer, nano-silica, 60-70% water, stir evenly to form a mixture; 2) Stir the coarse aggregate, fine aggregate and cement in a concrete mixer to form a solid mixture; 3) Stir step 1) mixed liquid, step 2) solid mixture, and the remaining 30-40% water for 180-240 seconds, and stir evenly to form a concrete mixture. 9. The method for preparing early-strength high-performance concrete doped with nano-silica powder according to claim 8, characterized in that: the stirring speed is 30r/min.