Steel is the most recycled material on the planet by tonnage, exceeding the combined recycling volumes of aluminium, glass, paper, and plastic. Approximately 90% of structural steel used in construction is recovered and recycled at the end of a building's service life. Steel's unique property is that it can be recycled indefinitely without degradation of its material properties, unlike paper, which suffers fibre shortening, or plastics, which undergo polymer chain degradation with each thermal cycle. This infinite recyclability is the foundation of steel's position as the dominant sustainable structural material.
EAF vs BOF Production Routes
Steel is produced by two fundamentally different routes with dramatically different recycled content and carbon footprints. The blast furnace and basic oxygen furnace route, abbreviated BF-BOF, converts iron ore into steel. Iron ore, coke, and limestone are charged into a blast furnace operating at approximately 1500 degrees Celsius, producing molten pig iron which is then refined in a basic oxygen furnace by blowing oxygen through the melt to reduce carbon content. The BOF process can accept up to roughly 30% scrap steel as a coolant and supplementary iron source, but is primarily an ore-based process. BOF steel production emits approximately 2.0 to 2.2 tonnes of carbon dioxide per tonne of crude steel produced.
The electric arc furnace route, abbreviated EAF, melts scrap steel using high-power electric arcs. Graphite electrodes carrying currents of 50 to 140 kiloamperes generate temperatures exceeding 1600 degrees Celsius, melting the scrap charge in 40 to 90 minutes. The EAF charge is typically 95 to 100% scrap, making this route fundamentally a recycling process. EAF steel production emits approximately 0.4 to 0.5 tonnes of CO2 per tonne of steel when powered by typical grid electricity, a reduction of roughly 75 to 80% compared to the BOF route. When powered by renewable electricity, as some European EAF mills now operate, the carbon footprint drops further toward 0.1 to 0.2 tonnes per tonne.
Recycled Content: Rebar and Structural Sections
Steel reinforcing bar, or rebar, is almost universally produced via the EAF route and typically contains 95% or more recycled scrap content. In North America, approximately 75% of all steel production now uses the EAF route, with BOF accounting for the remaining 25%. The dominance of EAF production is due to the lower capital cost of mini-mills compared to integrated BOF plants, their flexibility to follow demand cycles, and the abundant availability of scrap steel in mature economies.
Nucor Corporation, headquartered in Charlotte, North Carolina, is the largest steel recycler in the United States. Nucor operates over 20 EAF mini-mills and processes more than 20 million tonnes of scrap steel annually, manufacturing rebar, structural beams, sheet steel, and plate. The company's signature product lines include Nucor Rebar and Vulcraft steel joists, both produced almost entirely from recycled automotive and appliance scrap. Steel Dynamics Inc. and Commercial Metals Company, both operating exclusively EAF mills, are other major US producers of recycled-content construction steel.
LEED Credits and Embodied Carbon Comparison
Steel's high recycled content qualifies construction projects for credits under the LEED v4 Building Design and Construction rating system. The LEED Material and Resources credit for Building Product Disclosure and Optimization, specifically the Sourcing of Raw Materials option, awards points based on the recycled content of building materials. Steel products with documented recycled content above 25% contribute to achieving these credits, and typical North American structural steel and rebar far exceed this threshold.
From an embodied carbon perspective, the choice of EAF versus BOF steel has a substantial impact on a building's total carbon footprint. A typical mid-rise office building might contain 60 to 120 kilograms of steel per square metre of floor area. Using EAF steel at 0.5 tonnes CO2 per tonne rather than BOF steel at 2.1 tonnes CO2 per tonne reduces the building's embodied carbon by approximately 100 to 190 kilograms of CO2 per square metre, roughly equivalent to the emissions from 2 to 4 years of operational energy use in a moderately efficient building. Industry-wide environmental product declarations published by the American Institute of Steel Construction and the Steel Recycling Institute provide verifiable data for project specifications.