Air entraining agent for aerated concrete After this air entraining agent is mixed into concrete, the concrete has evenly distributed fine pores, the volume density is reduced, and it has the properties of impermeability, fire prevention and heat preservation. It is a common thermal insulation and sound insulation wall material for modern hall buildings and high-rise buildings.
With the rapid development of China's construction industry, concrete structure technology
The level has developed rapidly, and a large number of advanced scientific and technological achievements have been made in construction projects.
Widely used in. More and more attention has been paid to the construction quality of concrete engineering.
Especially in winter and rainy season, while concrete works are constructed in summer.
Quality is easily overlooked. This paper discusses the construction of concrete engineering in summer.
The existing problems and protective measures are discussed.
! Problems in concrete construction in summer
In summer, when the average temperature is above-,water
The hydration speed of mud becomes faster and the evaporation of water intensifies, which leads to the appearance of concrete construction.
Under the prominent problems.
! "! The increase of unit water consumption
With the increase of temperature, the slump loss of concrete is accelerated. In order to protect
Certificate a certain consistency to meet the requirements of construction workability, in summer
It is necessary to appropriately increase the unit water consumption of concrete. At the temperature of $ (). ),
Keep the slump at "(). ), for every dollar added to concrete.
Water consumption' 0&; 12 (according to cement type, unit cement dosage, slump
The slump value depends on the air content). Therefore, the commercial concrete mixing station
(Ready-mixed concrete factory), prefabricated mixing table, which needs to be adjusted in time in summer.
Standard mixing ratio.
! "# slump value decreases during transportation.
Judging from the test results of hard concrete, after mixing (#-3,
Under the temperature condition of "()". And $ (. ), the slump is similar.
No. But! 3. When $ (.is higher than "(
. The slump is about 4/ lower, even with retarder, it cannot be changed.
Change this phenomenon. For plasticity! The slump is at 3,
But more than that! #-3, slump drops sharply.
! "$ concrete setting time is shortened.
High temperature will accelerate the hydration reaction of cement, so the concrete will soon open.
Initial solidification. The main effects of shortening the setting time of concrete are: concrete lap joint
Poor connection and severe chills in the joint; It is difficult to repair the concrete surface.
! "%gas content change
For aerated concrete, if the same amount of air entraining agent is added, it will change with
With the increase of temperature, the air content in concrete decreases.
! "& concrete strength decreases.
Concrete with the same mixture ratio and water-cement ratio, such as high temperature curing.
Protection, there will be a rapid increase in strength in the early stage and insufficient growth in the later stage; location
When water is added to compensate slump, its strength decreases with the increase of water-cement ratio.
A large number of experiments show that concrete is mixed at the temperature of $ ().
Compared with the mixed concrete, the strength of the same grade concrete "%5" decreased by -6.
0! (6.
! "'concrete cracks.
After concrete pouring, the water secreted from the surface gradually evaporates.
Put it down. If the evaporation rate is faster than the separation rate of water, the concrete surface has not hardened.
Solid particles on the surface will be in direct contact with the atmosphere and will not appear on the concrete surface.
Regular cracks are called plastic shrinkage cracks. Summer, except
Besides high temperature, wind and dry (low humidity) weather are easier.
This kind of crack appears. In severe cases, the concrete surface will fall off.
! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !
Humidity cracks are due to the limitation of humidity in hardened concrete.
Correctly treating the foundation is better than blindly checking the problems found after the trough.
Pursue a solid foundation, safety and economy.
Chapter II Self-waterproofing of Civil Air Defense Engineering Structures
The first section waterproof principle
Self-waterproofing method of structure is to improve the impermeability of structure itself by using its compactness, hydrophobicity and rigidity, which is usually called rigid waterproofing, and its waterproof materials are mainly waterproof concrete and waterproof mortar. Self-waterproofing of structure is a powerful measure to improve the waterproof performance of underground engineering. Even if the underground engineering lining is waterproof with coiled material and coating, structural self-waterproofing should be adopted as far as possible.
According to the survey data, there are serious water seepage in a large number of underground masonry projects, and some even have serious accidents of loose masonry and bricks falling off one by one. The main reason is that the integrity of masonry is poor, and the joints of masonry are difficult to meet the quality requirements. After bearing water pressure, they leak like a sieve, which is rarely used in underground engineering.
Section 2 Waterproof Concrete
Waterproof concrete is based on ordinary concrete, by adjusting the mix proportion or adding additives to improve the compactness of concrete, so that it has better impermeability (≥0.6MPa). Generally, it can be divided into waterproof cement and new cement waterproof concrete, admixture waterproof concrete and plastic concrete.
Admixture waterproof concrete is the most important, and there are many varieties; Concrete made of waterproof cement and new varieties of cement is also commonly used; The use of plastic concrete is limited because of its high price and inconvenient construction.
Waterproof concrete has the following advantages:
(1) The waterproof quality is reliable. As long as the materials are properly selected, the ingredients are reasonable, and the operation procedures are strictly observed in the construction, the waterproof concrete can have reliable impermeability.
(2) Good durability. Waterproof concrete improves frost resistance and erosion resistance, is durable and easy to check and maintain.
(3) simple construction. The structure itself is waterproof, which saves the extra waterproof layer, simplifies the process and is not limited by the shape of the structure.
(4) Low cost. Compared with ordinary concrete, waterproof concrete needs more cement, but it saves other waterproof layers, thus reducing the cost.
Waterproof concrete is often used in the covering section under static load, but it is not suitable for projects with high impact load and strength.
Impermeability labels are usually selected according to Table 2- 1.
Table 2- 1 permeability label selection table
Design impermeability label (MPa) of the ratio of the maximum calculated water head H to the corresponding concrete thickness D.
H/d≤ 10 S6
10 152535≤H/d S20
First, ordinary waterproof concrete
(A) waterproof principle
Ordinary waterproof concrete is developed on the basis of ordinary concrete. Ordinary concrete is prepared according to the strength requirements of the structure, and ordinary waterproof concrete is prepared according to the impermeability requirements of the structure.
By studying the mechanism of ordinary waterproof concrete, it is known that its waterproof and impermeability is mainly related to the formation and distribution characteristics of pores in concrete. As we all know, in the hydration process of cement, after excess water evaporates, pores will be left in concrete. The more residual water, the thicker pores left after evaporation, and the greater the possibility of water seepage. The number and size of capillary holes are directly related to water-cement ratio, hydration degree of cement and curing conditions. In concrete, because the specific gravity and particle size of aggregate and cement are inconsistent, under the action of gravity, there will be different degrees of relative settlement, resulting in settlement cracks, while the deformation between mortar and aggregate is inconsistent, resulting in contact holes. These two kinds of pores are often interlinked and larger than capillaries. If the proportion of concrete is improper, the cement slurry will be poor, which is not enough to fill the pores between coarse and fine aggregates. In this way, atmospheric water and groundwater will penetrate into the remaining pores of concrete. Therefore, in order to improve the impermeability of concrete, we must start from two aspects: material and construction, and restrain and reduce the formation of pores in concrete. The effective methods are to adopt a smaller water-cement ratio, appropriately increase cement dosage and sand ratio, rationally use natural gradation, limit the maximum particle size of aggregate, and ensure the construction quality. Cement mortar not only fills and bonds coarse aggregate, but also forms a certain amount and quality (concentration) of mortar coating around coarse aggregate. In this way, the porosity of concrete can be reduced, the pore characteristics can be changed, and the communication between pores can be inhibited, so that it does not depend on other additional waterproof measures, but only depends on improving the compactness of concrete itself, enhancing the impermeability of concrete and meeting the requirements of engineering use.
(2) Gradation selection requirements
1. Raw materials
(1) cement
The cement used to prepare ordinary waterproof concrete must meet the requirements of GBJ75-85, which requires good water resistance, small bleeding, low hydration heat and certain corrosion resistance. Therefore, portland cement should be used first, and other types of cement, such as pozzolanic portland cement or slag portland cement, can also be used after taking corresponding measures.
It is best to use cement grade above 425 and not below 325. The storage period of cement shall not exceed three months. Cement with wet caking is strictly prohibited. The finer the cement particles, the better the waterproof performance.
The dosage of cement is about 300 ~ 400 kg per cubic meter. When admixtures are added, the dosage of cement can be reduced appropriately.
(2) sand
River sand containing clean solid rock particles, or artificial sand made of broken solid rocks, shall have a silt content of less than 3%, and there shall be no lump or wrapped soil on the sand surface.
The sand ratio of medium and coarse sand in aggregate (refers to the percentage of sand in the total weight of sand and gravel) is controlled at 35% ~ 40%. It is best not to use fine sand. When it must be used, the sand content should be controlled at about 30%, and the particle composition of sand is shown in Table 2-2.
Table 2-2 Table of Particle Composition of Sand
Grid spacing (mm) 52.5 1.20.60.30.6438+05
Cumulative sieve residue (wt%) 0 ~ 510 ~ 35 20 ~ 5545 ~ 7570 ~ 9590 ~100.
(3) Gravel
Particles must be dense, hard and tidy, preferably pebbles and gravel. Porous and loose stones are not allowed, in which the content of weak and weathered particles (calculated by the total weight of stones) shall not be greater than 65,438+00%, and the content of needle-like and flaky particles shall not be greater than 65,438+05%. The maximum particle size of stones is usually 40 mm, and the dosage is controlled between 50% and 60% to ensure their strength. See Table 2-3 for the particle composition of crushed stone.
Table 2-3 Particle Composition of Stone
The maximum particle size of stone is 40mm 1/2, and the maximum particle size is 20mm 5mm.
Cumulative sieve residue (wt %) 0 ~ 5 30 ~ 60 95 ~ 100
(4) Water
Drinking water or clean natural water should be used for mixing, and the pH value (pH value) is in the range of 4 ~ 9. The total salt content shall not exceed 3500mg per liter.
Account number: Yu Yunfei
Grade: Master Sergeant
Integral: 22634
Experience: 2565
[Apply for a blog] Leave a message [Support (0)][ Quote ]2004-09-07 13:54:46.0 2 Floor (3) Calculation Example
Trial design and preparation of 200 # waterproof concrete
1. Portland cement No.425 is used as the cement, with a specific gravity of 3. 1.
2. The sand is medium sand with an average particle size of 0.33mm and a specific gravity of 2.6.
3. Gravel with the maximum particle size of 40mm is used as the stone, with a specific gravity of 2.7; Stone is divided into two grades: 30% is 5 ~10 mm; 10~40
Millimeter accounts for 70%.
4. The water cement ratio is 0.55, the water consumption is per cubic meter 170.5kg, and the sand ratio is 35%.
5. Calculation of material consumption and cement consumption: (kg/m3).
6. Calculate the mixture ratio of sand and gravel
7. Calculate the mixed weight of sand and gravel
(kg/m3)
8. Calculate the amount of sand and gravel
(kg/m3)
(kg/m3)
9. Determine the mixing ratio
Cement: sand: stone = 1: 2.2: 4.08
Second, the admixture waterproof concrete
(A) waterproof principle
Admixture waterproof concrete is one of the methods to improve the impermeability of concrete by adding a small amount of organic or inorganic substances to meet the needs of waterproof engineering.
The floorboard of concrete series. At present, the main admixtures used in China are organic admixtures, and surfactants are used in organic admixtures.
The widest. It mainly includes inorganic salts such as air entraining agent, water reducing agent, triethanolamine early strength agent and ferric chloride waterproofing agent.
(2) Aerated waterproof concrete
Aerated concrete is suitable for general waterproof engineering and waterproof engineering with high frost resistance and durability requirements. Using air entraining agent can make up for slag.
Cement bleeding, pozzolanic cement water demand, etc., the use of air entraining agent can also effectively improve the workability of concrete mixture, saving
Saving cement consumption can make up for the difficulties caused by poor aggregate gradation. There are many kinds of additives currently used in China, but
Choose additives according to different needs. Before using the admixture, the instruction manual of the admixture should be checked and sent to the laboratory for testing.
Determine the dosage of admixture and test the effect of admixture. The dosage of admixture is generally based on cement, and its dosage is determined by product performance.
According to the test results.
(3) Water reducing agent waterproof concrete
It is suitable for general waterproof engineering and waterproof engineering with special requirements on construction technology, such as pumping concrete thin-wall waterproof and tamping difficulty.
Water structure. Choose retarded or accelerated water reducer, which can be used for waterproof concrete with special requirements on concrete setting time in summer or winter.
The varieties of water reducing agent are:
Sodium methylene diphenyl ether (NNO)
Sodium methylene naphthalene sulfonate
Lignosulfonate and molasses (by-products of sugar mills)
Dosage:
The dosage of NNO and MF is 0.5% ~ 1% of the cement dosage.
The content of calcium lignosulfonate is 0.2% ~ 0.3% of cement.
The content of molasses is 0.2% ~ 0.3% of cement.
The above four are the dosage of powder. During construction, the powder must be dissolved in water at 60℃ (according to 20% concentration), and then the admixture solution is mixed with cement.
Mud.
(4) Triethanolamine admixture concrete
Concrete mixed with trace triethanolamine admixture is called triethanolamine waterproof concrete. Triethanolamine can improve the impermeability of concrete, and it is early.
Strong, good reinforcement effect, especially suitable for waterproof projects that need early strength, which can improve the turnover speed of formwork and improve labor productivity.
Three basic formulas for the application of triethanolamine early strength agent;
Formula 1: triethanolamine 0.05% (weight percentage of cement)
Formula 2: triethanolamine 0.05%+ sodium chloride 0.5%
Formula 3: triethanolamine 0.05%+ sodium chloride 0.5%+ sodium sulfite 1%.
See Figure 2- 1 for the relationship between the three formulas and the early strength.
Fig. 2- 1 influence of triethanolamine early strength waterproofing agent on setting time of slag cement concrete
1- no additive; 2- 1 formula; Formula 3-2; Formula 4-3
(5) Ferric chloride waterproof concrete
Ferric chloride waterproof concrete is made by adding a small amount of ferric chloride waterproof agent into concrete mixture and stirring, which has high impermeability and high density.
Concrete. Ferric chloride has wide sources, low price and convenient manufacture. The high-permeability waterproof concrete prepared with it is widely used in civil air defense projects.
Mountain tunnels, mines, pools, water towers, basements, etc. Mortar prepared with ferric chloride is also used for plastering and bedding in underground engineering.
Accumulate and plug up. However, because the ferric chloride waterproofing agent contains chlorine, it has a certain corrosive effect on steel bars.
Aluminum sulfate content accounts for 5% of ferric chloride content, and the dosage of ferric chloride waterproofing agent is generally controlled at 3% ~ 5% of cement dosage.
(6) Expansive cement waterproof concrete
Concrete mixed with expansive agent is called expansive cement waterproof concrete. In the process of water hardening, expansive cement forms a large number of nodules with increased volume.
Crystal (ettringite) can produce a certain expansion energy. Under constraint conditions, expansive cement waterproof concrete has two characteristics:
Firstly, the pore structure of concrete is improved, so that the total porosity and capillary pore size are reduced, thus improving the impermeability.
The second is to improve the compression condition of concrete, so as to improve the crack resistance of concrete.
At present, expansive cement concrete is widely used in roofing engineering, and many construction companies began to use it in roofing engineering in the 1970s.
Use.
According to the principle of hydration phase crystallization, expansive cement can be divided into the following categories:
1. calcium sulphoaluminate type
The preparation method comprises adding bauxite cement, gypsum, alum and anhydrous calcium sulphoaluminate clinker into cement.
2. Magnesium oxide type
The preparation method is as follows: 5% ~ 9% magnesite or dolomite calcined at 800 ~ 900℃ is added into portland cement and ground into powder.
It is called magnesia expansive cement.
3. Alumina type
It is made by adding 3% ~ 10% limestone calcined at 1250 ~ 1350℃ into portland cement and grinding, also known as lime system.
Expansive cement.
4. Iron type
It is an additive made of iron powder and oxidant (chromate, permanganate or hydrogen peroxide) directly or in advance, and silicate is added.
The cement made is called iron expansive cement.
5. Aluminum type
It is made by adding a small amount of aluminum powder and dispersant into ordinary cement. Aluminum powder reacts with water to produce aluminum hydroxide.
Hydrogen bubbles make cement obtain micro-expansion characteristics.
There are many kinds of admixture waterproof concrete. In recent years, China has developed silicone and SH with high performance.
Account number: Yu Yunfei
Grade: Master Sergeant
Integral: 22634
Experience: 2565
[Blog Application] Message [Support (0)] [Quote] 2004-09-07 13:54:59.0 Second, silicone waterproof mortar, 3rd floor.
(A) waterproof principle
Silicone waterproof mortar is a new and efficient waterproof material with sodium (potassium) methyl silanol and high boiling sodium (potassium) silanol as main components. it
It is a water-soluble mixture of small molecules, which is easily decomposed by weak acids and can generate methyl silicon under the action of carbon dioxide and moisture in the air.
The hydrophobic substance of siloxane further condenses into a reticular methyl silicone waterproof film, which can block the capillary channels inside the cement slurry and enhance the density.
Solid, improve impermeability, thus playing a waterproof role.
(2) Technical performance
The technical performance of silicone waterproof mortar is shown in Table 2-6.
Table 2-6 Technical Performance of Silicone Waterproof Mortar
Serial number item type
Sodium methyl silanol, high boiling point sodium silanol
1 Pale yellow to colorless and transparent appearance
2 Solid content (%) 30 ~ 32.5 3 1 ~ 35
3 pH 14
4 Specific gravity (25℃)1.23 ~1.251.25 ~1.26
5 sodium chloride content (%) < 2 <; 2
6 Silicon content (%) 1 ~ 3
7 methylsiloxane content (%) 18 ~ 20
8 Total alkali content (%) <18 <; 20
(3) Preparation of waterproof mortar
Waterproof mortar is made by mixing cement, sand and silicon water evenly according to a certain proportion. There are two kinds of silicon water: alkaline and neutral. See Table 2-7 for the proportion.
Show.
Table 2-7 Proportion of Silicon and Water as Waterproofing Agent in Silicone
Type, weight ratio, volume ratio and purpose
Waterproofing agent aluminum sulfate (aluminum nitrate) Waterproofing agent water
Alkaline silica-water ratio17 ~ 919 ~11waterproof mortar.
Neutral silica-water ratio 1.5 ~ 6 0.4 ~ 0.5 with waterproof layer.
1. Raw materials and requirements
Cement: No.425 ordinary portland cement.
Sand: hard, rough and clean medium sand, with a particle size of 1 ~ 2mm.
Water: drinking water.
Silicone waterproofing agent: the suitable specific gravity is 1.24 ~ 1.25, and the pH value is 12.
2. Mix proportion of waterproof mortar
The mixture ratio of waterproof mortar is shown in table 2-8.
Table 2-8 Mix Proportion of Waterproof Mortar Layer
Mix proportion of silica-water mortar layer by layer
Waterproofing agent: water cement: sand: silicon water
Bond layer cement mortar 1: 7 1: 0: 0.6
Bottom waterproof mortar 1: 8 1: 2: 0.5
Surface waterproof mortar 1: 9 1: 2.5: 0.5
Waterproof concrete for pipe plugging and sealing 1: 9 cement: sand: pisolite: silicon water 1: 2: 3: 0.5
Three, neoprene latex cement mortar
(A) waterproof principle
Neoprene latex waterproof mortar is made by mixing a proper amount of cationic neoprene latex, composite additives and water (cement content 10% ~ 20%).
The liquid is added into the dry mixture of cement and sand, and stirred evenly to make polymer cement mortar with waterproof performance. Because the emulsion is homogeneous
The materials evenly dispersed on the surface of aggregate gradually cross-link under certain temperature conditions, thus making rubber, aggregate and cement
Rubber aggregate network membranes form each other and close the capillary channels in the material, thus playing a waterproof and impermeable role.
(2) Technical performance
The technical properties of cationic neoprene latex are shown in Table 2-9.
Table 2-9 Technical Performance of Cationic Neoprene Emulsion Waterproof Mortar
Project technical index serial number
1 tensile strength (28 days) 5.3 ~ 6.7 MPa.
2 flexural strength (28 days) 8.2 ~ 12.5 MPa
3 compressive strength (28 days) 34.8 ~ 40.5 MPa
4 Bond strength (28 days) Rough surface: 3.6 ~ 5.8 MPa; glossy surface: 2.5 ~ 3.8 MPa.
5 Dry shrinkage value (28 days) 7× 10-4 ~ 7.3× 10-4
The water absorption rate is 2.6% ~ 2.9%
7 impermeability > 1.5MPa
8 Freeze-thaw resistance for 50 times (freezing at-15℃ ~-20℃ for 4 hours and melting at 15℃ ~ 20℃ for 4 hours, the cyclic tensile strength is 4.4 ~ 5.6 MPa.
The bending strength is 8.3 ~10.4mpa.
The compressive strength is 33.4 ~ 40 MPa.
(3) Preparation of waterproof mortar
The formula of cationic neoprene latex waterproof mortar is shown in Table 2- 10.
Table 2- 10 Reference Formula of Cationic Neoprene Emulsion Waterproof Mortar (weight ratio)
Material Name Mortar Formula Ⅰ Mortar Formula Ⅱ Mortar Formula Ⅲ
Portland cement 100 100 100
Medium sand (φ
Neoprene latex 20 ~ 50 20 ~ 50 30 ~ 40
13 ~ 14, and a proper amount of compound additives.
Proper amount of water
During preparation, the stabilizer, defoamer and water are mixed with cationic neoprene latex in proportion, and evenly stirred to prepare mixed emulsion. then
Cement and sand are mixed in proportion and dry mixed, and then mixed with mixed emulsion. Prevent water loss when preparing.
Mortar ratio: cement: medium sand: latex: water = 1: 2: 0.4: 0.2.
The ratio of cement, latex and water = 1: 0.3: 0.25.
(4) Scope of application
(1) as the waterproof layer of underground engineering and water storage facilities.
(2) Roof waterproofing works.
(3) Crack repair of underground and above-ground buildings.
Fourth, "guarantee time" waterproof powder
Time-keeping waterproof agent is a non-toxic, odorless and non-combustible inorganic powder waterproof agent, which can be made of cement and sand.
Inorganic multifunctional waterproof material.
(A) Characteristics
(1) Cement mortar waterproof layer is a solid cement component, which can be integrated with concrete and masonry structures, not just the back.
The water surface can be used as a waterproof layer, and it can also be used as a waterproof layer.
(2) It can be used as waterproof plastering material and plugging material, and has multiple functions such as waterproof, moisture-proof and leak-patching.
(3) It has waterproof and decorative functions, and can be prepared by adding various pigments (the pigment content is less than 5% of the cement weight) as required.
A decorative waterproof material is suitable for waterproof decoration of basements and bathrooms.
(4) It has good aging resistance and is suitable for underground waterproofing of industrial and civil buildings. Because it is a rigid waterproof material, it is not suitable for replacement.
Waterproof treatment of displacement position, such as waterproof plugging of three joints.
(2) Technical performance
See table 2- 1 1 for the technical performance of "time-keeping" waterproof mortar.
Table 2- 1 1 Technical performance of "guaranteed time" waterproof mortar
Project performance of serial number
1 Compressive strength: 25MPa cement paste and 22MPa mortar.
2 The flexural strength is 6MPa, and the mortar is 5MPa.
3 impermeability strength coating >: 1.5MPa, mortar