Old cars, appliances, and other scrap steel have been melted down at the Jacksonville, Fla.-based Gerdau’s electric arc furnace and cast into 5x5-inch 40-foot-long billets (see the June column). The steel in the billets now meets the ASTM specifications for reinforcing steel (A615 or A706) and are ready to be processed into desired sizes.
First, the billets are reheated in a separate furnace that raises the temperature of the billet to more than 1200º F. At this temperature, the billet keeps its shape, but can be molded. Then the billets speed down a line of extrusion presses at speeds up to 4000 feet per minute, depending on the bar diameter. The smaller the cross section gets, the faster the bar moves. The line of multiple presses compress the red hot billets into even longer lengths and smaller diameters and also cool the material as it continues through the process.
As the heated bar approaches the end of the line of extrusion presses, it is forced through the appropriate mandrel for the rebar size being produced in that run. The mandrel provides the deformations that are seen on reinforcing steel, which provide the mechanical anchoring of the rebar in the concrete. The exact shape of the bar deformations are not mandated, but the size, spacing, and height of the deformations are specified in ASTM A615.
As the final steps of the production process are completed, the bars are imprinted with the appropriate identification marks. These identifying marks indicate the producing mill, the size of the bar, the type of reinforcing steel used in production of the bar, and the grade of steel.
The completed bar comes off the fabrication line in 120-foot lengths. After it has cooled, it is sheared into 60-foot lengths, bundled and tagged, made ready for shipment to fabrication facilities where the reinforcing steel will be cut and bent to conform to the requirements of the particular project, as specified by the engineer.
By using 97% or more scrap steel for the production of reinforcing bar, Gerdau and the other rebar producers keep thousands of tons of ferrous scrap steel from landfills and roadsides across the country. The collection and recycling of scrap steel is a multimillion-dollar business.
The use of steel reinforcing bars produced from recycled scrap provides contractors, owners, and developers with an environmentally friendly material for their projects.
Special thanks to the staff at Gerdau in Jacksonville, Fla.