Selling Cheap Concrete Iron from CV. Timur Sarana Persada in Surabaya. Concrete iron or also known as reinforcing iron is a construction iron used to strengthen concrete structures in buildings. Using concrete steel will increase the flexural strength of the concrete, so that it is resistant to static loads and dynamic loads and is not easily cracked when due to small shocks or when an earthquake occurs. In Indonesia, iron is grouped into 2 types namely plain iron and cast iron.