No Clear Winner Yet in Concrete v. Steel Contest

By Andrea Ward
This article originally appeared on BuildingGreen.com

It is notoriously difficult to make an apples-to-apples evaluation of the life-cycle impacts of different building materials. Comparisons by weight or functional unit, while more easily made, cannot easily account for the fact that materials are used in different amounts even when serving the same purpose, such as a concrete frame as opposed to a steel one. A new study attempts to compare the impacts of these two materials when used in framing systems for similar buildings, based on data already known about the average outputs of the U.S. concrete and steel industries.

According to Geoff Weissberger, director of sustainability for the American Institute of Steel Construction (AISC), who wrote a recent column on this study in Modern Steel Construction, the industry group commissioned the structural engineering firm HDR and the environmental consultancy Five Winds to perform a life-cycle assessment (LCA) of a steel-framed building relative to a concrete-framed building using case studies of two similar structures in the same geographic location. Even though AISC is publicizing the study results, they have not yet made the study available to the public for review.

According to Weissberger, researchers compared two healthcare facilities in Omaha, Nebraska, built within a few years of one another, one with a steel frame and the other framed in concrete. The steel building, at five stories and about 150,000 square feet, contains about 1,200 tons of steel and about 5,800 cubic yards of concrete in its structural system. The concrete building, meanwhile, is nearly twice as large at eight stories and 280,000 square feet, and contains nearly 2,000 tons of steel and 15,600 cubic yards of concrete. Because of the differing sizes of the two buildings, the study compares life-cycle impacts on a per-square-foot basis. It does not address non-framing components of the buildings, like roofing or HVAC systems.

Using data from the GaBi 4 LCI database, the study measures environmental impacts in five categories: global warming potential (kilograms of carbon dioxide equivalent), acidification potential, eutrophication potential, smog potential, and primary non-renewable energy demand. Researchers found that the steel-framed building outperformed the concrete-framed one in all categories except primary energy demand, and the concrete production process was the largest contributor to the environmental impact of both framing systems. Weissberger acknowledges in his column, though, that none of the five comparison categories reaches a confidence threshold of 15 percent—“they were all close games,” he writes. The study will soon be submitted for peer review and undergo the ISO 14040 process (the standard for LCAs).

What may be more interesting to some practitioners than the results of this particular study is the possibility that more and better LCA data will be available in the future to more decisively inform decisions about building systems. Bruce Maine, a sustainable design consultant with HDR, says he tries to work with project teams to pursue the new LEED pilot credit dealing with LCAs. “I think eventually we will be able to use such information as LEED moves to integrating environmental life cycle costs in the equation,” Maine said, as it is doing through an LCA credit in the new LEED pilot credit library. But he is more sanguine about the value of specific LCAs like this one commissioned by AISC: “So much depends on framing requirements, local availability, program requirements, etc., that it is difficult to now suggest we could select a framing system based solely on LCA results.”

Copyright 2010 by BuildingGreen, LLC

share: more »