An article suggested by Anne Charest
Assistant to the President, AGF Group
By: Robert Risser, Michael Hoffman
www.concreteconstruction.net
Where does rebar come from? A common industry joke is that most people on the jobsite know that it comes on a truck. After that, the knowledge base can drop off pretty quickly. But a little insight into the changes that have taken place in domestic steel production over the last 40 years might help you understand your reinforcing steel better. This is the first in a series of columns aimed at walking readers through the rebar manufacturing and fabrication process, and its potential impact on your concrete projects.
Today’s reinforcing steel comes almost entirely from old cars, appliances, and other scrap steel. Most people associate steel manufacturing with large integrated furnaces fired by coal using iron ore and limestone. For most of the 20th century, this was true. In the 1960s and ’70s, this began to change with greater use of electric arc furnaces for making what is known as “long products.” Today, all domestically produced rebar is made from at least 97% recycled scrap steel for normal grades (ASTM A615 or A706). This is important for contractors to know if they are trying to meet sustainability goals for recycled materials on a project.
To get a closer look at the process, we recently visited Gerdau Ameristeel’s Jacksonville, Fla. mill. Scrap is segregated into distinct piles based on its steel properties, such as its iron content. The scrap blend is made up of five scrap steel components: No. 1 and No. 2 heavy melt, shred (which comes from auto bodies, refrigerators, etc.), cast iron, and structural plate. The material is placed into the furnace bucket, or ladle, in 93-ton batches to be melted down.
In the furnace, the scrap material, or charge, is directly exposed to an electric arc produced by giant electrodes inserted into the scrap mix. The charge is heated both by the current passing through the charge material and by the radiant energy created by the arc. The sound is deafening—more than 2900 MW of current passes through the electrodes—and the arc jumping across the scrap ignites pockets of gases over the furnace bucket. The glowing electrodes are slowly raised and lowered to thoroughly melt the steel. Each batch takes about 40 minutes in the furnace to reach the desired molten temperature, almost 2800º F.
Quality control is a critical step in the steel-making process. As it nears completion, a sample of the molten material is checked to ensure the material meets chemical specifications.
This molten steel is cast into 40-foot-long rectangular sections known as billets and cooled. Gerdau’s mill produces wire rod and rebar 7 days a week, 24 hours a day—transforming recycled metal scrap into useful construction products. Next month, this column will describe how billets are transformed into reinforcing steel.
Special thanks to the staff at Gerdau Ameristeel in Jacksonville, Fla.
