SRIA - Steel Reinforcement Institute of Australia

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Environmental Concerns
Environmental steel reinforced concrete today. Explore the advances made in the recycling of waste materials as constituents in steel reinforcement for concrete. Explore the environmental benefits of reinforced concrete structures.
Introduction The extent of the progress made in the recycling of waste material in the production of reinforcing steel and the making of modern cements would surprise most people. Steel reinforced concrete continues to perform in an environmental friendly way, in built structures due to its inherent properties. These properties are used to advantage by designers who utilise its mass for thermal lag cycling to provide free heating in winter; and with night venting, free cooling in summer. This in itself can act to reduce energy consumption. The familiar slab on ground, due to its insulative qualities, is a vital part of the energy efficiency of modern homes. Reinforced concrete is allergy free, contains no harmful chemicals, presents no combustibility danger, is the most durable of any construction material, and is fully recyclable.. While it was originally developed to provide strength, with an appearance matching stone, on an affordable basis, it has certainly more than fulfilled the hopes of its pioneers. No wonder it is the most widely used material in the service of mankind.
	STEEL REINFORCEMENT Steel is said to be the world's most recycled product. The steel industry is working towards attaining over 90% of all steel to be recycled worldwide. (The estimated current rate of recycling is in excess of 60%.)
Australia is doing its part in meeting that goal with the commissioning of mini mills by Smorgon Steel at Laverton in Victoria in the mid 80's, and by BHP at Rooty Hill in Sydney in the early 90's. Prior to the commencement of these new generation electric arc furnace mills, the majority of Australia's scrap steel was exported. This represented a loss of a valuable resource and with it, an opportunity to benefit the environment. Now we are in the situation of finding there is a shortage of scrap feed in a buoyant construction market making heavy demands for steel.
	The majority of recycled scrap steel ends up as steel reinforcing bars, rod, mesh, wire and coil; with the major use as reinforcement to concrete. Other industries are dependent upon a supply of recycled scrap steel, with foundries such the GMH and Ford engine plants being significant users. It is sobering to think that a gleaming new Mercedes is probably going to end up as a steel reinforcing bar.
The steel industry is a good citizen in limiting the production of green house gases. Combustible gases are recycled and used as source of heat for steel production. Carbon Dioxide emissions are a inescapable part of the steel making process, currently there is no feasible alternative to the direct use of fossil-based fuels for crude steel production. Over the last 5 years BHP report that steelmaking operations have achieved a 12% reduction in the amount of energy used per tonne of crude steel produced.(1997 BHP Environmental Report). This in turn reduces carbon dioxide emissions that are thought to contribute to future global warming. Spent liquor is recycled (liquor is the picking solution used to descale steel prior to applying coatings). Even the mill scale is sold for reuse in other commodities. Mill water is recycled. Mills use 'grey water' ie: stormwater, wherever possible as part of their requirements. However, 96% of water usage for process cooling in integrated steel facilities is salt water drawn from the inexhaustible supply of the sea. Care is even being taken to minimise the use of salt water. Steel reinforcement is close to 100% recycled steel. By-products of the coke ovens include benzene, toluene and gas. The gas is used as fuel at the steelworks. The liquid by-products are valuable to the chemical industry. TOP
	Even new virgin steel contains a percentage of scrap. At Australia's three integrated steelworks steel scrap makes up about 15% of the material that goes into the basic oxygen steelmaking (BOS) furnace, together with liquid iron from the blast furnace, to produce steel. The scrap is used to control the temperature generated by the chemical processes in the BOS process, as well a being a source of feed.
Don't think that virgin steel is vastly more energy consuming than remelting scrap steel. Whilst there is a disparity, the difference is largely made up because coal and coke are used as a chemical reductant for virgin steel production. Due to the efficiencies made in the design of the new generation of blast furnaces, as evidenced by the performance of the new BHP Blast Furnace No6 at Port Kembla in NSW, steel has a bright new environmental aware image. This new furnace has allowed the closure of the less efficient Number 2 and Number 4 blast furnaces. An additional benefit of the new technology is that steel making is now a 'clean' process with no visible smoke or particulate matter outfall. An example of the new face of steel is the BHP mini- mill at Rooty Hill in Sydney, surrounded by residential subdivisions in close proximity. Nearby residents to the steel mill are untroubled by any environmental effect from the mill, as all processes are fully enclosed in dust / noise and gas containing structures. Blast furnace slag as a by product of the steel making process was considered a waste product a few years ago. Now, it is a valuable resource and is used as follows: Granulated blast furnace slag (GBFS) is used as a secondary cementitious product in modern blended cements, and in glass manufacture. Air cooled rock slag (ACRS) is crushed and screened and used as concrete aggregate, filter media, railway ballast, road base. Blast furnace slag (BFS) is also used as a resource material for phosphorous fertilizer and as a soil stabiliser. Slag is also being used as a component of clay-shale extruded and sintered bricks.
	GREENHOUSE EFFECTS An aspect of the production of steel and cement for reinforced concrete is the widespread community concern about the release of greenhouse gases into the atmosphere. These gases are believed to contribute to long term global warming with a possible rise in sea levels due to the potential for melting of the polar ice caps.
TOP The steel and cement industries are very visible because of their size, and serve as an easily seen target for criticism. In some respects the critics are right, these industries have been, but are to a diminishing extent, significant emitters of greenhouse gases. As described throughout this paper, the industries are acutely conscious of this fact and are doing whatever they can to reduce their energy needs, with a consequent reduction in the production of these gases. BHP has produced a very informative report on this issue (BHP Greenhouse Report 1997). BHP is committed to the 'Greenhouse Challenge', a program of actions by Australian companies to improve greenhouse performance, which has already produced remarkable results. Not just the steel and cement industries are responsible for the production of these gases. The transport, and residential power consumption are the major contributors. Even termites release more greenhouse gases than steel and cement combined. Take a look at the greenhouse problem, what are these gases? Water vapour is one. Carbon dioxide, ozone, methane, nitrous oxide, and chlorofluocarbons (CFC's) are all included. The CFC issue is being controlled in developed countries by legislation, as it was singled out as the most damaging. The other gases are natural components of the atmosphere. Methane is thought to be 21 times more responsible than carbon dioxide (on a unit basis) for global warming. Hence the concern about the output of this gas not only from industry and mining, but also the surprisingly much larger output from ruminants such a cows and sheep. BHP recognises that achieving reductions in methane emissions provides one of the most cost-effective means of reducing the overall impact of it's activities. Coal seam methane from their Appin and Tower collieries is collected and used to generate more than 90 MW of electricity. This electricity is supplied into the New South Wales electricity grid and as a benefit, reduces the need to burn coal with a greater output of greenhouse gases. Concrete has a role in saving energy, and thus greenhouse emissions in areas such as the insulative properties of slab on ground for housing compared to loss of heat through suspended floors. Multiply this by the huge number of houses constructed each year and the figures for total energy savings are absolutely huge. The draught resistance of solid construction is important. Thermal cycling using the mass thermal storage of concrete is of huge potential. The Steel Reinforcement Institute of Australia has studies which show that huge savings are possible for transport, if national highways were constructed in continuously reinforced concrete pavement due to the lower rolling resistance compared to flexible alternatives. A long lasting additional benefit is the much longer life of the concrete compared to flexible paving. REINFORCED CONCRETE IN USE The environmental benefits of reinforced concrete do not stop at its manufacture but continue for the life of the structure. Concrete's natural advantages:- density - aids thermal cycling noise barrier from external noise quiet in housing (no squeaks) durability strength user friendliness wide availability sourced from Australia for all Australians
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