Crisp hardening and Softening Tendencies of Reinforcing Steels
Reinforcing steels, also known as reinforcing bars, are a type of steel bar used in concrete structures in order to increase the strength and integrity of the structure. The steel bars are typically used in tension and are a key component of reinforced concrete, which is widely used in construction, especially in areas where earthquake resistance is a priority.
When reinforcing steel is exposed to certain environmental conditions, such as humidity and temperature, it can undergo a number of physical changes. These changes can result in either a crisp hardening or softening tendency. The crisp hardening tendency results in a decrease in ductility and tensile properties, while the softening tendency increases ductility and allows for better bending and welding. In order to ensure that the reinforcing steel maintains its strength, it is important for engineers to be aware of these tendencies and take steps to ensure that the steel is adequately protected against environmental conditions that could cause these changes to occur.
The crisp hardening tendency of reinforcing steel is caused by a phenomenon known as hydrogen embrittlement. During hydrogen embrittlement, moisture enters the metal on a molecular level and causes the steel to harden and become brittle. This leads to a decrease in the ductility of the steel, reducing its tensile strength. Over time, this brittle state can become a permanent feature of the metal and the metal can reach a point where it can no longer be used as a reinforcing bar.
The softening tendency of reinforcing steel is caused by a phenomenon known as plastic yielding. This is a process where a metal is subjected to a compression that is greater than the tensile strength of the metal. This compression deforms the metal, resulting in a decrease in tensile strength but an increase in ductility. This increased ductility allows for better bending and welding of the steel, making it more suitable for use as a reinforcing bar.
In order to minimize the risks of either the crisp hardening or the softening tendencies of reinforcing steels, it is important for engineers to take steps to protect steel bars from any adverse environmental conditions that may lead to the development of these tendencies. This can include the use of coatings to protect the steel from corrosion, proper caulking and jointing of the steel bars, and regular inspections of the steel bars to detect any signs of deterioration.
Furthermore, engineers should also pay attention to the properties of the reinforcing steel bars and choose the ones that best suit the environmental conditions of the project. Certain types of reinforcing steel may be better suited for certain climates, for example if the area is exposed to high humidity or extreme temperature changes. It is also important to ensure that the steel bars are properly joined together, as improper joining can also lead to a decrease in ductility.
By taking these steps, it is possible to ensure that the reinforcing steels used in a project maintain their strength and integrity over the long term. This in turn can protect the integrity of the structure and enhance its durability.
