WHY SPACER?
After the two major earthquakes we experienced in the Marmara region in 1999, citizens living in our major cities, especially Istanbul, started to give importance to the inspection of their buildings against a possible earthquake. During the inspections they carried out themselves or through an expert, a formation called corrosion was encountered in the concrete load-bearing elements, especially in the basement floors of the buildings. Although there are many reasons for the formation of corrosion in concrete elements, the most important reason is accepted by experts to be the insufficient concrete cover layer called spacer.
WHAT IS A SPACER?
One of the reasons for the collapse of buildings in an earthquake is the improper and insufficient use of spacers. Using appropriate and sufficient spacers extends the life of buildings.
In the specifications related to reinforced concrete, the spacer, also known as the net concrete cover, is defined as: “The thickness measured from the outermost reinforcement inside a concrete element to the end of the concrete surface.” In the TS 500 standard, which has been in use since 1985, there was no detailed information on this thickness. Only in article 12.2.1, it was stated that “The concrete cover in beams should be at least 1.5 cm for internal elements and 2 cm for external elements.” With the new TS 500 standard that came into effect in February 2000, detailed information on this subject was provided, thus preventing the long-standing lack of regulation. In fact, experienced project engineers who signed serious projects were addressing the deficiency of TS 500 by considering the articles specified in the German DIN 1045 standards, but it is understood that the serious inclusion of the spacer in the Turkish Standards was due to the Marmara earthquake.
THE IMPORTANCE OF SPACER IN TERMS OF CORROSION
Many reasons can be cited for the formation of corrosion, which causes the steel reinforcements inside the reinforced concrete elements to rust and lose their diameter and quality. These include the insufficient net concrete cover (spacer) in concrete elements, the high humidity levels and chloride ions in the air, especially in constructions near the sea, which increase the importance of the spacer in terms of corrosion.
The insufficient quality of the concrete used. For many years, high-strength concrete was aimed for when defining good concrete among builders. In recent years, the definition of good concrete has started to consider not only the strength of the concrete but also its durability, known as durability. Durability includes making impermeable concrete to prevent corrosion of the steel reinforcement inside, ensuring sufficient thickness of the concrete spacer, and adding chemicals to increase fluidity in the concrete when necessary. After pouring the concrete, it is also important to prevent contamination, water it, or cover the surface with protective chemicals. Another important point to note is that the insufficiency of the spacer cannot be remedied solely with plaster mortar without taking special measures (such as special liquids made with chemicals). The thickness of the spacer also becomes important in reinforced concrete elements exposed to intense external factors (such as wind, rain). Due to the insufficiency of the spacer, it has been observed that in such elements, all stirrups are completely lost, and the main load-bearing reinforcements can increase their diameter up to seven times due to rust, causing the concrete to crack rapidly. The thickness of the spacer can be kept smaller in factory-produced concrete precast elements and prefabricated building elements. The DIN 1045 standard allows the thickness of the spacer to be reduced to 1 cm in such elements.