The compressive strength of C20 concrete is 20MPa. The factors that affect the strength grade of concrete are mainly related to cement grade, water-cement ratio, aggregate, age, curing temperature and humidity.
The standard value of cube compressive strength refers to the cube specimen with the side length of 150mm, which is manufactured and maintained according to the standard method.
In the overall distribution of compressive strength at the age of 28 days measured by the standard method, the strength percentage below this value (the standard value of compressive strength) is less than 5%, that is, the strength assurance rate is 95%, which is equal to the average value of the overall distribution of strength plus the standard deviation 1.645 times.
Concrete, referred to as "concrete (tóng)", refers to the general name of engineering composite materials in which aggregates are bonded into a whole by cementing materials. Generally speaking, the term concrete refers to cement as cementing material and sand as aggregate.
Cement concrete, also known as ordinary concrete, is made by mixing and stirring water (including admixture and admixture) in a certain proportion, which is widely used in civil engineering.
: specific history:
Archaeologists found that 5,000 years ago, the ancestors of Lingjiatan were not only able to make exquisite jade tools, but also began to plant rice, raise or hunt animals such as pigs, deer and birds to enrich their diet. In addition, in building construction, they learned the construction technology similar to reinforced concrete: "digging ditches to fill the fire soil and supporting the mud wall with wooden bones."
Lingjiatan people 5000 years ago did not simply build houses. Facts have proved that Lingjiatan people at that time already knew the construction technology of "digging ditches to fill the soil and supporting the mud wall with wooden bones", which is very similar to the reinforced concrete now.
The staff said that the primitive ancestors should use burnt soil as the filling material of the foundation trench and the wall, use wooden sticks as the supporting columns of the wall in the foundation trench, then bury the braised clods, and coat thick clay on both sides of the wall, and some may even be reinforced with reed poles.
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 should also be more and more.