by J. Randolph Kissell and Robert L. Ferry

Today the choice of aluminum as a structural material suffers from a malady similar to that which afflicted tomatoes in the eighteenth century: many people fail to consider it out of superstition and ignorance. Whereas Europeans shunned tomatoes for fear that they were poisonous, engineers seem to avoid aluminum for equally unfounded reasons today.

One myth is that aluminum is not sufficiently strong to serve as a structural metal. The fact is that the most common aluminum structural alloy, 6061-T6, has a minimum yield strength of 35 kips per square inch (240 megapascal), which is almost equal to that of A36 steel.

This strength, coupled with its light weight makes aluminum particularly advantageous for structural applications where dead load is a concern. Its high strength-to-weight ratio has favored the use of aluminum in such diverse applications as bridge rehabilitation, large clear-span dome roofs, and fire truck booms. In each case, the reduced dead load, as compared to conventional materials, allows a higher live or service load.

Resistance to Corrosion

Aluminum is inherently corrosion-resistant. Carbon steel, on the other hand, has a tendency to self-destruct over time by virtue of the continual conversion of the base metal to iron oxide, commonly known as rust. Although iron has given oxidation a bad name, not all metal oxides lead to progressive deterioration.

Stainless steel acquires its feature of being rust-resistant by the addition of chromium to the alloy mixture. The chromium oxidizes on the surface of the metal, forming a thin transparent film. This chromium oxide film is passive and stable, and it seals the base metal from exposure to the atmosphere, thereby precluding further oxidation. Should this film be scraped away or otherwise damaged, it is self-healing in that the chromium exposed by the damage will oxidize to form a new film.   >>>

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Installation of an aluminum deck on aluminum beams for the Smithfield Street Bridge in Pittsburgh, Pennsylvania. Photo: Courtesy Alcoa Aluminum walkway and handrail at a municipal wastewater treatment plant. Photo: Courtesy Conservatek Industries, Inc.   Click on thumbnail images to view full-size pictures.