Introduction to reinforced concrete

Development status of reinforced concrete structures

At present, reinforced concrete is the most widely used structural form in China, accounting for the vast majority of the total. At the same time, it is also the area with the most reinforced concrete structures in the world. The output of its main raw material cement reached 1.882 billion tons in 2010, accounting for about 70% of the world’s total output.

Working principle of reinforced concrete

The reason why reinforced concrete can work together is determined by its own material properties. Firstly, steel bars and concrete have approximately the same coefficient of thermal expansion, and the dislocation between steel bars and concrete is very small at the same temperature. Secondly, when the concrete hardens, there is a good bond between the cement and the reinforcement surface, so that any stress can be effectively transferred between them; Generally, the surface of reinforcement is also processed into rough and spaced corrugated ribs (called rebar) to further improve the bond between concrete and reinforcement; When this is still insufficient to transfer the tension between the reinforcement and the concrete, the end of the reinforcement is usually bent 180 degrees. Third, alkaline substances in cement, such as calcium hydroxide, potassium hydroxide and sodium hydroxide, provide an alkaline environment, which forms a passive protective film on the surface of reinforcement, so it is more difficult to corrode than reinforcement in neutral and acidic environment. Generally speaking, the environment with pH value above 11 can effectively protect the reinforcement from corrosion; When exposed to the air, the pH value of reinforced concrete decreases slowly due to the acidification of carbon dioxide. When it is lower than 10, the reinforcement will be corroded. Therefore, it is necessary to ensure the thickness of protective layer during project construction.

Specification and type of selected reinforcement

The content of stressed reinforcement in reinforced concrete is usually small, ranging from 1% (mostly in beams and slabs) to 6% (mostly in columns). The section of reinforcement is circular. The diameter of reinforcement in the United States increases from 0.25 to 1 inch, increasing by 1 / 8 inch in each grade; In Europe, from 8 to 30 mm, increasing by 2 mm at each stage; The Chinese mainland is divided into 19 parts from 3 to 40 millimeters. In the United States, according to the carbon content in reinforcement, it is divided into 40 steel and 60 steel. The latter has higher carbon content, higher strength and stiffness, but it is difficult to bend. In corrosive environment, steel bars made of electroplating, epoxy resin and stainless steel are also used.

Post time: Aug-10-2021