In the curing stage, straw mats and sacks are used for thermal insulation, and steam curing can be used if necessary.
At the same time, the concrete test block should be maintained under the same conditions, and the strength test should be done after a certain age. If the design strength cannot be reached, the batch of concrete should be completely demolished and rebuilt. If necessary, rebound test can be done to test the strength of concrete.
If the strength of concrete can reach the standard, pressure grouting or local demolition and reconstruction should be taken according to the situation. It is best to use steam at MINUS 8 degrees for maintenance. You don't have to build a shed, just cover it and steam it in.
The following is a detailed introduction.
Concrete is one of the most important civil engineering materials. It is a kind of artificial stone which is made of cementing material, granular aggregate (also called aggregate), water, additives and additives added when necessary, mixed evenly, compacted, cured and hardened in a certain proportion. Concrete has the characteristics of abundant raw materials, low price and simple production technology, so its consumption is increasing. At the same time, concrete also has the characteristics of high compressive strength, good durability and wide range of strength grades. These characteristics make it widely used, not only in various civil engineering, but also in shipbuilding, machinery industry, marine development, geothermal engineering and so on. Concrete is also an important material.
Ethnicity
1900 World Expo showed the use of reinforced concrete in many aspects, which caused a revolution in the field of building materials. French engineer Ainabik 1867 saw monier's flowerpots, tubs and water tanks made of barbed wire and concrete at the Paris World Expo, and was inspired, so he tried to apply this material to building construction. 1879 began to manufacture reinforced concrete floors, and later developed into a set of concrete structural beams strengthened with steel hoops and longitudinal bars. Only a few years later, when he built an apartment building in Paris, he adopted improved reinforced concrete main columns, beams and floors, which are still widely used today.
1884, German construction company purchased monier's patent and conducted the first batch of reinforced concrete scientific experiments to study the strength and fire resistance of reinforced concrete. Bonding force between reinforcement and concrete. 1887, German engineer Collen first published the calculation method of reinforced concrete; Wilson, an Englishman, applied for a patent for reinforced concrete slab; American Hai Ete experimented with concrete beams. From 1895 to 1900, France built the first batch of reinforced concrete bridges and sidewalks. 19 18 Abram published the famous water-cement ratio theory to calculate the strength of concrete. Reinforced concrete has become an important material to change the world landscape.
Concrete can be traced back to ancient times, and its cementing materials are clay, lime, gypsum, volcanic ash and so on. Portland cement appeared from 19 in the 1920s, and was widely used because of its good strength and durability, easily available raw materials, low cost, especially low energy consumption (see inorganic cementing materials).
At the beginning of the 20th century, someone published the theory of water-cement ratio, which laid the theoretical foundation of concrete strength. Later, lightweight aggregate concrete, aerated concrete and other concrete appeared one after another, and various concrete additives began to be 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 entered the field of concrete materials, and polymer concrete appeared; A variety of fibers are used to disperse reinforced fiber concrete. Modern testing technology is also increasingly applied to the research of concrete material science.
main performance
There are mainly the following items:
Peace
The most important performance of concrete mixture. The properties of the mixture, such as consistency, fluidity, plasticity, anti-delamination, segregation and bleeding, and easy plastering, are comprehensively shown. There are many methods and indicators to measure and express the workability of mixture. The slump (mm) measured by truncated cone slump cone and Weibull time (sec) measured by Weibull instrument are mainly used as the main indicators of consistency in China.
intensity
The most important mechanical properties of concrete after hardening refer to the ability of concrete to resist pressure (such as compression, tension, bending and shearing). Water-cement ratio, variety and dosage of cement, variety and dosage of aggregate, and mixing, molding and curing all directly affect the strength of concrete. According to the standard compressive strength of concrete (cube with side length of 150mm as the standard specimen, cured for 28 days under standard curing conditions, the strength grade measured by standard test method with 95% guarantee rate is called label. It is divided into C 10, C 15, C20, C25, C30, C35, C40, C45, C50, C55, C60, C65, C75, C80, C85, C90, C95 and C105. The tensile strength of concrete is only110 ~1/20 of its compressive strength. Improving the tension-compression ratio of concrete is an important aspect of concrete modification.
freaky
Concrete will be deformed under load or temperature and humidity, mainly including elastic deformation, plastic deformation, shrinkage and temperature deformation. The elastic deformation of concrete under short-term load is mainly expressed by elastic modulus. Under long-term load, the phenomenon of constant stress and increasing strain is creep, while the phenomenon of constant strain and decreasing stress is relaxation. The volume deformation caused by cement hydration, carbonation and cement stone dehydration is called shrinkage.
The deformation of hardened concrete comes from two aspects: environmental factors (temperature and humidity changes) and external load factors, so there are:
1). Load deformation
1. Elastic deformation
2. Inelastic deformation
2) No-load deformation
1. Shrinkage deformation (dry shrinkage, autogenous shrinkage)
2. Expansion deformation (wet expansion)
3). Deformation under combined action
1. Spread
keep patience
Generally speaking, concrete has good durability. However, in cold areas, especially in the engineering parts where the water level changes, concrete is easy to be destroyed under the action of frequent freezing and thawing in saturated state. Therefore, there should be certain frost resistance requirements for concrete. When used in seepage control engineering, concrete is required to have good impermeability and corrosion resistance. Impermeability, frost resistance and erosion resistance are the durability of concrete.
Composition materials and structures
Ordinary concrete is an artificial stone which is hardened by mixing cement, coarse aggregate (gravel or pebble), fine aggregate (sand), admixture and water. Sand and gravel play a skeleton role in concrete and inhibit the shrinkage of cement; Cement and water form slurry, which is wrapped on the surface of coarse and fine aggregates and fills the gap between aggregates. The cement slurry plays a lubricating role before hardening, which makes the concrete mixture have good working performance. After hardening, the aggregates are bonded together to form a solid whole.
Main technical characteristics
The properties of concrete include the workability of concrete mixture, concrete strength, deformation and durability.
The workability, also known as workability, refers to the convenience of concrete mixture for the operation of various construction procedures under certain construction conditions to ensure the uniform and dense performance of concrete. Workability is a comprehensive technical index, including fluidity (consistency), cohesiveness and water retention.
Strength is the main mechanical property of concrete after hardening, which reflects the quantitative ability of concrete to resist load. Concrete strength includes compressive strength, tensile strength, shear strength, flexural strength, flexural strength and bond strength. Among them, the compressive strength is the largest and the tensile strength is the smallest.
Deformation of concrete includes deformation under no load and deformation under load. Deformation under no load includes chemical shrinkage, wet and dry deformation and temperature deformation. Too much cement can easily cause chemical shrinkage and micro-cracks in concrete.
The durability of concrete refers to the ability of concrete to resist various destructive factors and maintain its strength and appearance integrity for a long time under actual use conditions. Including frost resistance, impermeability, corrosion resistance and carbonation resistance of concrete.
Main classification
Classification by cementing materials
(1) inorganic cementitious material concrete, such as cement concrete, gypsum concrete, silicate concrete, sodium silicate concrete, etc. ;
② Organic binder concrete, such as asphalt concrete and polymer concrete.
Classification by apparent density
Concrete can be divided into heavy concrete, ordinary concrete and light concrete according to its apparent density. The difference between these three kinds of concrete is the difference of aggregate.
Is the apparent density of heavy concrete greater than 2500Kg/m? ; Made of particularly dense and heavy aggregate. Such as barite concrete and steel chip concrete. , not affected by x-rays and gamma rays.
Ordinary concrete is commonly used in buildings, and its apparent density is 1950 ~ 2500 kg/m? ; Aggregates are sand and stones.
Is the apparent density of lightweight concrete less than 1950Kg/m? ; Concrete. It can be divided into three categories:
1. lightweight aggregate concrete, its apparent density is 800 ~ 1950kg/m? ; , lightweight aggregate including pumice, volcanic slag, ceramsite, expanded perlite, expanded slag, slag, etc.
2. Porous concrete (foamed concrete, aerated concrete), its apparent density is 300 ~ 1000 kg/m? ; . Foam concrete is made of cement slurry or cement mortar and stable foam. Aerated concrete is made of cement, water and gas-generating agent.
3. Macroporous concrete (ordinary macroporous concrete and lightweight aggregate macroporous concrete) does not contain fine aggregate. The apparent density range of ordinary macroporous concrete is 1500 ~ 1900kg/m? ; , is made of crushed stone, soft stone and heavy slag as aggregate. The apparent density of lightweight aggregate macroporous concrete is 500 ~ 1500 kg/m? ; , is made of ceramsite, pumice, brick and slag as aggregate.
Folding is classified by function.
Structural concrete, thermal insulation concrete, decorative concrete, waterproof concrete, refractory concrete, hydraulic concrete, marine concrete, road concrete, radiation-proof concrete, etc.
Folding is classified according to construction technology.
Centrifugal concrete, vacuum concrete, grouting concrete, shotcrete, roller compacted concrete, extruded concrete, pumping concrete, etc. According to the reinforcement methods, there are plain concrete, reinforced concrete, steel wire mesh cement, fiber concrete and prestressed concrete.
Folding is classified according to the processability of the mixture.
Hard concrete, semi-hard concrete, plastic concrete, flowing concrete, high fluidity concrete, flowing concrete, etc.
Making material
Mixing cement, lime, gypsum and other inorganic cementing materials with water to make the concrete mixture plastic; In addition, it condenses and hardens through chemical and physical and chemical actions, thus producing strength. Generally speaking, drinking water can meet the requirements of concrete mixing water. Too much acid, alkali, salt and organic matter in water will have harmful effects on concrete. Aggregate not only has the function of filling, but also has an important influence on the properties of concrete such as bulk density, strength and deformation.
In order to improve some properties of concrete, additives can be added. Because of its obvious technical and economic effects, admixture has increasingly become an indispensable part of concrete. In order to improve the workability of concrete mixture or the performance of hardened concrete and save cement, finely ground mineral materials-additives can also be added during the concrete mixing process. It is divided into active and inactive categories. The nature and content of additives affect the strength, deformation, hydration heat, impermeability and color of concrete.
Preparation process
design of mix proportion
When preparing concrete, first of all, according to the requirements of engineering for workability, strength and durability, the raw materials should be selected reasonably and the proportion should be determined to achieve the purpose of economy and application. The design of concrete mixture ratio is usually carried out according to the requirements of water-cement ratio method. The calculation of material consumption mainly adopts assumed bulk density method or absolute volume method.