Swedish Modern and the "Old Reliable"
In this space last month, while discussing earthquakes and adobe codes, I commented that we are beginning to understand that the useful life of reinforced concrete can be as short as seventy years. That statement (of fact, not speculation) provoked a few interesting responses. An engineer friend asked after my sources; several colleagues in the building trades asked just how concrete fails; and one of my employees suggested that we diversify to make a bundle restoring skyscrapers built in the recent past.
The Terra 2000 conference in Torquay, England last May took on the concrete vs. adobe issue with some irony and humor. We devotees of Gaia sat gathered in a hideous concrete and steel conference center and delighted one another with tales of the science and success of earthen buildings around the world. We also commiserated about their continuing loss and replacement with concrete.
In his keynote address, (see Terra 2000 Preprints, ISBN 1902916050) our colleague Giacomo Chiari of the University of Turin bemoaned trading in his solid oak table in the 1950's for Swedish modern. He soon realized the fundamental error in his choice and returned to the antique store to attempt recovery of the old piece. His point was that we act according to the spirit of the times and concrete was, as Formica and chrome furniture were, modern and therefore desirable.
In the case of concrete we see that it is not so universally useful (did anyone ever say appealing?) as once thought. That acknowledgement leads us to a reconsideration of the old reliable -- earth -- where it is appropriate for construction. Certainly, we have to manipulate the details here and there and acknowledge plenty of uses for modern components, including concrete, in earthen construction. The error in judgment is, in my view, using concrete as ubiquitously as we do.
Portland cement is a brilliant engineering material. I'll spotlight just one of its highest and best uses, without Portland our cars wouldn't be very functional. A drive through the construction zone at the intersection of I-40 and I-25 in Albuquerque will affirm that contention: not even I would propose building those overpasses with adobe. Since I've got you on the Interstate, however, check out the bridge over the railroad tracks just west of St. Francis Drive here in Santa Fe, and the underpass at Exit 307 to Pecos National Monument. The former just got reinforced with a steel substructure. Driving under this bridge gives one pause about driving over it on the freeway. The reason? Failing reinforced concrete; and in this case it is less than 30 years old. Look closely at the concrete beams spanning the roadway at the Pecos exit and you will see a series of cracks near the lower edges.
Concrete is a crystal and a very tightly put-together one at that. In large part it sheds water and it is clearly not particularly vapor permeable. (It is this last characteristic that makes it the kiss of death for adobe.) But concrete does admit some moisture, either in liquid form or as a vapor. When that happens, the reinforcing steel begins the process of oxidation; in simple terms, it rusts. The result is a very slow expansion of the steel leading to the "explosion" of the concrete around the rebar. As the steel loses its tensile strength, the stressed concrete begins literally to come apart at its crystalline seams. Concrete by itself has exceptionally high compressive strength (it is hard to crush), but the reinforcing steel provides its span strength. When the steel in the span is compromised -- well, it's toast.
This is not an isolated problem, nor one strictly related to public works projects. Frank Lloyd Wright's Guggenheim Museum and his archetypal residence, Falling Water, are both undergoing analysis and repairs of failed concrete.
When discussing materials, "hard" does not mean permanent and "strong" does not mean invincible. It is a difficult task overcoming the bias for modern materials despite their obvious shortcomings (without even a mention of aesthetics). Merely suggesting a preference for earth sounds regressive to some, but I do tend to believe that we would have a better perspective on things if for each step forward we at least recalled where we were two steps back.
Giacomo, by the way, never did get his old table back. He had to settle for a newer rendition, in oak, which he took without a moment's hesitation. He felt no regret giving up the Formica surfaces.