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Concrete: pronounce two tones of tong to express concrete. Reinforced concrete is reinforced concrete, which is widely used in building structures. Before pouring concrete, tie the steel bar and set up the formwork, that is, fix the steel bar into the required structural shape with iron wire and then cover it with formwork. Finally, concrete is poured, and after curing reaches the strength standard, the form is removed to obtain reinforced concrete. Classification: According to different construction methods: 1, cast-in-place, 2, assembled, 3, assembled monolithic, 4. Introduction of cast-in-place reinforced concrete floor: Cast-in-place reinforced concrete floor is formed by formwork support, steel bar binding, concrete pouring and maintenance at the construction site. Advantages: good integrity, strong earthquake resistance, irregular shape, reserved holes and convenient pipeline layout. Disadvantages. The construction speed is slow. Precast precast reinforced concrete floor slab in prefabrication factory or construction site has disadvantages: poor integrity of floor slab, and long cracks are easy to occur due to poor joint sealing. Prefabrication of some members of integral reinforced concrete floor → site installation → integral cast-in-place reinforced concrete (English: reinforced concrete or Ferroconcrete or rc for short) is often called reinforced concrete in engineering. It refers to a kind of composite material, which is the most common form of reinforced concrete by adding steel bars to concrete to improve its mechanical properties. [Edit this paragraph] History and development The invention of reinforced concrete appeared in modern times and is generally believed to have been invented in 1848. 1868, a French gardener, obtained a patent including reinforced concrete flowerpots and reinforced concrete beams and columns applied to highway guardrails. 1872, the world's first reinforced concrete structure was completed in new york, USA, and a brand-new era in the history of human architecture began. After 1900, reinforced concrete structures were widely used in engineering. 1928, a new reinforced concrete structure, prestressed reinforced concrete, appeared and was widely used in engineering practice after World War II. /kloc-the invention of reinforced concrete and the application of steel in the construction industry in the middle of the 0/9th century made it possible to build high-rise buildings and long-span bridges. At present, reinforced concrete is the most widely used structural form in China, accounting for the vast majority of the total, and it is also the most widely used area in the world. According to the relevant data of the National Development and Reform Commission, the output of cement, the main raw material in this area, reached1.60 billion tons in 2005, accounting for about 48% of the world's total output. [Edit this paragraph] Material characteristics Concrete is a mixture of cement (usually portland cement) and aggregate. When a certain amount of water is added, the cement hydrates to form a micro-opaque lattice structure, thus wrapping and combining the aggregates into a whole structure. The compressive strength of general concrete structures is very strong (about 3,000 psi, 35MPa). However, the tensile strength of concrete is low, usually only about one tenth of the compressive strength. Any significant tensile bending action will crack and separate its microstructure, which will lead to structural failure. However, most structural members have tensile stress requirements, so unreinforced concrete is rarely used alone in engineering. Compared with concrete, the tensile strength of steel bars is very high, generally above 200MPa, so people usually add stiffening materials such as steel bars to concrete to work together. Steel bars bear tension and concrete bears compressive stress. For example, in the simply supported beam flexural member of Figure 2, when a load p is applied, the upper part of the beam section is compressed and the lower part is stretched. At this time, the steel bars arranged at the bottom of the beam bear tension (4), while the concrete (2) shown in the shaded area above bears pressure (3). In some small-section members, steel bars can be used to bear pressure in addition to tension, which usually happens in columns. The section of reinforced concrete members can be made into different shapes and sizes according to the engineering needs. Like ordinary concrete, reinforced concrete reaches the design strength after 28 days. [Edit this paragraph] The working principle of reinforced concrete The reason why reinforced concrete can work together is determined by its own material characteristics. First of all, the linear expansion coefficients of steel bars and concrete are almost the same, and there will be no excessive stress due to different environments. Secondly, there is a good bonding force between steel bars and concrete, and sometimes the surface of steel bars is processed into spacer ribs (called deformed steel bars) to improve the mechanical bite between concrete and steel bars. When this is still not enough to transfer the tension between the steel bar and the concrete, the end of the steel bar is usually bent with a hook of 180 degrees. In addition, the alkaline environment provided by calcium hydroxide in concrete forms a passive protective film on the surface of steel bars, which makes steel bars less susceptible to corrosion than neutral and acidic environments. [Edit this paragraph] Specification and model selection of reinforcement. The content of reinforced concrete is usually very small, ranging from 65,438+0% (mostly in beams and slabs) to 6% (mostly in columns). The cross section of the steel bar is round. In the United States, it ranges from 0.25 to 1 ft, and increases by 1/8 ft per liter; Europe ranges from 8 to 30 mm, with an increase of 2 mm per liter; In Chinese mainland, from 3 to 40mm, * * * is divided into 19 and so on. In the United States, steel bars are divided into 40 steel and 60 steel according to their carbon content. 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. In humid and cold climate conditions, reinforced concrete pavement, bridge, parking lot and other structures that may use deicing salt should use epoxy reinforcement or other composite concrete, and epoxy reinforcement can be easily identified by light green paint on the surface. Corrosion of steel bars and freeze-thaw cycles of concrete will cause damage to damaged concrete structures. When the steel bars are corroded, the corrosion spreads, which leads to the cracking of concrete and the loss of bonding force between steel bars and concrete. When water permeates the concrete surface and enters the interior, the volume of frozen and condensed water expands, and after repeated freeze-thaw cycles, concrete cracks are generated and deepened at the microscopic level, thus crushing concrete and causing permanent and irreversible damage to concrete. Pore water in carbonated concrete is usually alkaline. According to pourbaix diagram [3], steel bars are inert and will not corrode when the pH value is greater than 9.5. Carbon dioxide in the air reacts with alkali in cement, which makes the acidity of pore water stronger, thus lowering the pH value. From the moment the component is made, carbon dioxide will carbonize the concrete on the surface of the component and deepen it continuously. If the component cracks, carbon dioxide in the air will enter the concrete more easily. Usually, in the process of structural design, the minimum protective layer thickness of steel bars is determined according to building codes. If the carbonation of concrete weakens this value, it may lead to structural damage caused by corrosion of steel bars. The method to detect the degree of carbonization on the surface of the component is to drill a hole on its surface and drop phenolphthalein. The carbonized part will turn pink, and the depth of the carbonized layer can be known by observing the discolored part. Chlorination corrodes chloride, including sodium chloride, which will corrode steel bars in concrete. Therefore, only clear water is allowed when mixing concrete. It is also forbidden to deice concrete pavement with salt. Alkali-aggregate reaction Alkali-aggregate reaction or alkali-silicic acid reaction (AAR, or alkali-silicic acid reaction, ASR) refers to that when the alkalinity of cement is too strong, the active silicon component (SiO2 _ 2) in aggregate reacts with alkali to form silicate, which causes uneven expansion of concrete and leads to cracking and damage. Its occurrence condition is that (1) the aggregate contains relevant active ingredients (2) the environment has enough alkalinity (3) the concrete has enough humidity of 75%RH. Crystal transformation of high-alumina cement High-alumina cement is resistant to weak acids, especially sulfate, and its early strength increases rapidly, so it has high strength and durability. It was widely used after World War II. However, due to the transformation of internal hydrate crystals, its strength will decrease with time, which is more serious in hot and humid environment. In Britain, with the collapse of three roofs using high-alumina prestressed concrete beams, 1976 banned this kind of cement locally. Although it was later proved that there were manufacturing defects, the ban still existed. Sulfate in sulfate-eroded groundwater will react with portland cement to produce expansion by-products such as ettringite or xonotlite, which will lead to early damage of concrete. [Edit this paragraph] The invention of reinforced concrete Reinforced concrete is one of the most important building materials today, but its inventor is neither an engineer nor an expert in building materials, but a French gardener named monineath. There is a big garden in monineath with beautiful flowers all year round, but the flower beds are often crushed by tourists. To this end, monineath often thinks: "Is there any way to let people step on the flower bed without being easily crushed?" One day, when monineath was arranging flowers, he accidentally broke a pot of flowers, and the flowerpot broke into pieces, but the soil around the flower root was just wrapped in a ball. "oh! The roots of flowers and trees are criss-crossed and firmly connected to soft soil! " Inspired by this incident, he weaved the wire into a net like the roots of flowers and trees, and then stirred it with cement and sand to make a flower bed, which was really strong.