| CONCRETE PLANET The Strange and Fascinating Story of the World's Most Common Man-Made Material Robert Courland Dennis Smith (Fwd.) Amherst: Prometheus Books, November 2011 |
Rating: 5.0 High |
|||
| ISBN-13 978-1-61614-481-4 | ||||
| ISBN 1-61614-481-5 | 396pp. | HC/BWI | $? | |
![[Rant Warning]](../../../../RantWarn.gif)
In his last two chapters, Robert Courland shines a light on some significant problems with the ways we today manufacture, use, and promote concrete.
One is that the manufacture of cement releases huge quantities of carbon dioxide — both from the burning of fuel to heat the kilns, and from the necessary chemical transformation of calcium carbonate (limestone) to calcium oxide (lime.) Carbon dioxide, of course, is a greenhouse gas, and our addition of it to the preindustrial atmosphere has increased its atmospheric concentration by 40 percent, measurably warming the planet. This warming is very likely to have unintended consequences.
Another is that, as I note in my review, the durability of modern concrete formulations does not compare to that of the structures built during the Roman empire. Many of those are still intact over eighteen centuries later, while a modern bridge or skyscraper will be lucky to last just one century.
Still another is the vulnerability of the iron or steel in the reinforcing bars used in most modern concrete structures, from dams to domiciles. This "rebar", with its great tensile strength, permits office buildings a hundred stories or more high, towering barriers across rivers like Hoover Dam1, 2 in Arizona, and our Interstate Highway System.3
And finally, he demonstrates a problem with the concrete manufacturing industry (one common to many industries): its perpetuation of overstated claims for the properties of the material. For, as he thoroughly documents with his examination of three professional reports on the results of the 1906 earthquake in San Francisco, the vulnerability of reinforced-concrete structures seen in that disaster was minimized while the authors of the reports over-emphasized the likelihood that brick and masonry structures would collapse as a result of such temblors. In addition, the official death toll for the disaster (some 478 persons) was demolished in the 1970s by Gladys Hansen, then the city's librarian. Years of doggedly poring over hospital records, articles from newspaper "morgues," eyewitness accounts, and unpublished letters led her to conclude that a more realistic toll was at least 3,400 and probably higher.4
Courland's final chapter, however, points to some potential solutions to the problems he outlines. There are alternatives to traditional forms of rebar, made of iron and mild steel. Some are in fairly wide use. Although more expensive, stainless steel rebar postpones the corrosion-induced failure of reinforcement. But it still contains iron, and offers only perhaps double the endurance of traditional rebar. Use of "sacrificial anodes," metals that corrode before iron will, are also useful. For example, coating the rebar with zinc prevents the iron from rusting when exposed to sea water — until the zinc is used up.
Those are passive methods. Then there is an active method: cathodic protection, theoretically providing resistance indefinitely. It uses DC power supplies to place a permanent charge on the iron, making corrosion impossible. Cathodic protection is a good solution for easily accessible metal, such as pipelines and ship hulls, and has been used on them for many years. But for rebar buried in concrete this is expensive; it raises the cost of a typical freeway bridge by about fifteen percent, and the power supplies are something else that requires ongoing maintenance.
More permanent passive methods use non-ferrous reinforcing materials. GFRP (glass-fiber reinforced polymer) is one: it is both stronger and lighter than steel, and has other advantages as well. However, it is more expensive. And unlike steel it is not flexible; it cannot be bent as steel can to match ad hoc changes in the dimensions of a building's forms. But there is one metal that shows promise: aluminum bronze. It costs 35 percent less than stainless steel and forms a surface barrier to corrosion. Like bronze statues, it can potentially endure for hundreds of years.
This final chapter also points to a solution for the cement industry's greenhouse-gas problem, and it turns out to be a win-win situation. Slag and fly ash, currently unwanted byproducts of steel refining and coal combustion respectively, are largely discarded in slag heaps and slurry ponds. Retrieved, pulverized, and combined with Portland cement, they make a superior product. But let Courland tell it:
"As with the millstone refuse in Andernach, Germany, some three hundred years ago, people discovered that the chemical composition of slag and fly ash made the combination ideal for producing cement. Even better, while the Andernach chips were suitable only as a pozzolanic element, slag and fly ash have both pozzolanic and cementitious components. In other words, they can replace not only much of the kilned clay in Portland cement but much of the kilned limestone as well. That's not all: because of the high percentage of silicates in some fly ash, it can also be used as a filler to replace some of the sand used to make the concrete. Adding gravy to this good news is that when slag or fly ash is mixed with Portland cement, the result is a high-performance product that has both high compressive strength and long durability, thus, no early cracking and premature rebar corrosion to worry about. "The only downside in this otherwise upbeat story is that most fly ash and slag suitable for cement is still not being utilized for this purpose. Conventional Portland cement still predominates, as well as the pollution and wasted resources that come with its production. The cement industry lobbies hard to block any government legislation or Environmental Protection Agency (EPA) regulations that it feels would limit its freedom to do as it pleases. This is often the case: industry will always lobby for or against anything that it sees as furthering or countering its perceived interests. However, narrow and short-term commercial policies often conflict with the wider public good, as in the case of concrete cements. The US government has been successful in specifying fly ash concrete cement in a number of construction projects, but such measures have had little effect on the private sector, where standard Portland cement or, worse, its old high-strength/low-durability counterpart, can still be used. Taking into account the proven costly and/or dangerous flaws of the latter substance, an outright ban should be seriously considered." – Page 332 (emphasis his) |
This makes me doubly glad that the author persisted in writing this book. I now see that he is not only a gifted author, but has the heart and mind of a reformer. (If some read this as equivalent to "radical" or "revolutionary," I do not mean it in that sense. But consider: Marc and Isambard Brunel were reformers in that they persevered in the use of hydraulic cement in the Thames Tunnel, thereby demonstrating its superiority, as well as pioneering new methods of tunnel construction.) Although it was a long struggle, in the end the Brunels benefitted, their suppliers benefitted, other construction companies benefitted, local railroads benefitted, the British government benefitted, and the people of Greater London benefitted. In his last two chapters, Corland makes the point that we have a similar situation right now: the changes he proposes will help every side.5
Here's something that really drives his point home. He compares the cost of building and maintaining a bridge over five hundred years for three rebar materials: traditional mild steel, stainless steel, and aluminum bronze. The bridge is an "average" design, chosen arbitrarily, and he assumes aluminum bronze costs the same as stainless. I show the results in this table, taken from data on page 337.
| Rebar Material | Construction Cost | Life Span | Total Cost |
|---|---|---|---|
| Mild steel | $56,000,000 | 75 Years | $336,000,000+ |
| Stainless steel | $66,640,000 | 110 Years | $266,560,000+ |
| Aluminum bronze | $66,640,000 | 500+ Years | $66,640,000 |
The thing to notice about these cost figures is that the bridge reinforced with aluminum bronze needs no maintenance (at least for the integrity of the rebar.6) The inherent properties of that alloy make it exceedingly unlikely that corrosion problems will crop up in the projected 500-year lifetime of the bridge. Indeed, Courland expects such a bridge might well endure for 2,000 years. Also noteworthy is that the other two bridge designs, even with expensive maintenance, fail well before the half-century mark.
In the face of obdurate resistance to much-needed changes in cement manufacturing and application today (and in so many other areas), we urgently need the sort of thinking Robert Courland displays here. The phrase "thinking outside the box" is common parlance, but how often is it more than a marketing slogan? We need real and widespread innovation; but in so many cases innovation receives only lip service. Industry leaders tell us that solutions will be forthcoming. They fail to explain what they are doing to actually bring those solutions about, meanwhile putting their major efforts and investments behind business as usual. When the needed innovation will — after a period of development — benefit both their shareholders and society, who are the radicals: the proponents of change, or those who resist it? And if we truly wish to plan for the future, continue improving the general standard of living, and leave a better world to our descendants — as everyone professes to do — why do our actions so often turn out to have the opposite result?
"Such are the values of this world we have created, one in which we have come to accept the short life expectancy of not only our infrastructure but of our memorials as well." – Page 341 |
If even innovations that pay for themselves are spurned, what does this say about the vaunted wisdom of capitalism? If every substantive solution to an approaching crisis is blocked, what is the likely result? How long can society itself endure if this value system and this behavior continue to predominate?
To contact Chris Winter, send email to this address.