By adding steel mesh, steel plate or fiber to concrete, composite materials can work together with it to improve the mechanical properties of concrete.
When transmitting the tensile force between steel bar and concrete, the end of steel bar is usually bent into 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.
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Corrosion of steel bars and freeze-thaw cycles of concrete will destroy the structure of concrete. 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.
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.
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