May 21, 2004
Industrial By-Products To Triple Lives Of Bridges
Concrete bridges that will last for 100 year can be built at a cost that is no higher than the cost of existing bridges.
University Park, Pa. -- Penn State engineers have designed 10 concrete mixtures containing industrial by-products that make it possible for concrete bridge decks to last three times longer, or 75 to 100 years.
"The exact life expectancy of bridges constructed with these mixtures will not be known for many years," said Paul J. Tikalsky, associate professor of civil and environmental engineering, who led the study. "However, in full-scale trials, each of the mixtures optimizes the ingredients to produce concrete with substantially lower permeability, higher electrical resistivity and lower cracking potential than the standard bridge deck concrete used in Pennsylvania for the past 30 years."
He added, "The cost of bridges constructed with these mixtures is nearly identical to the previous generation of bridges. With life expectancies at least three times as long, the life-cycle cost savings will be more than $35 million annually in Pennsylvania with the added benefit of using environmentally friendly materials to contribute to a more sustainable future for the highway infrastructure."
Concrete is used in many other types of structures and so it seems likely these materials will be useful in lengthening the useful life expectancies of other types of structures as well.
The materials used are cheap because they are waste products of existing industrial processes.
"Fly ash, silica fume and slag are all industrial waste products that have been used previously in some types of construction,” Tikalsky noted. “These additives reduce the permeability of concrete and deter salts from entering. The additives also increase electrical resistance. So, in 40 or 50 years when water and salt eventually reach the steel reinforcement rods in the bridge deck, corrosion won't progress as rapidly."
Materials advances will continue to contribute to lengthening lives of all manner of human-built structures. Better materials will lenghten the lives of roads, bridges, buildings, vehicles, ships, and countless other structures and manufactured products. One result of increased durability is that obsolescence rather than decay will be the major reason old structures and old products are torn down and thrown away. Therefore as we develop the ability for most structures to last for centuries we need to ask how to build structures in ways that make them easier to upgrade in order to avoid (or at least delay) future obsolescence.
Future advances in materials science will yield cheap materials that will last for centuries. Humans built some structures centuries ago that are still in use today. But most of those structures require on-going maintenance and most structures that were built in previous centuries are not still around. Given that a much larger fraction of all structures will be long-lasting what should we do differently in designing and choosing the locations for such structures?
About three months ago I read an article about concrete advances that a French company had been making. I think it was in the Economist, which means that no link will still be active. Anyway, they had made similar progress, but another problem has arisen. The concrete was so durable that it was almost impossible to do construction work on it. Occasioanally roads have to be dug up. Buildings have to be torn down to be replaced with newer, better buildings. This new concrete was so durable that it was impossible to do these things.
To address the question you posed, the answer should be obvious. We simply cannot design buildings appropriately. Considering the changes being introduced to the world today by increasingly speedy technological advances, we cannot possibly predict what we will need in the future. Buildings and other structures should not be durable, but rather recyclable.
Our future buildings should be like trees and coral reefs. They should grow, and be a natural and healthy part of the landscape, but also easily broken down into constituent parts by natural or man-made processes. Concrete structures which last for many, many decades or centuries are actually quite useless - or they will be quite quickly. Think about the castles of Europe, or even the more recent structures in America from the 18th and 19th centuries. They are fun to tour and look at, but they serve no purpose today. I can't imagine that our structures will be any more useful to the people of the 22nd century. After all, once the AI-piloted flying cars becomes economical, the Brooklyn Bridge will be an anachronism.
Brock, Yes, I am reminded how back before the October 1973 beginnings of the big rise in oil prices there was a faction in German politics lobbying to require German car companies to build cars that a much longer period of time. But once oil started costing so much it was actually an advantage that more efficient newer cars would gradually replace older and less efficient cars.
Insulation may get so much better in the future that a building built with today's insulation may be too inefficient in the future. Maybe that argues for making the insulation layer more accessible for replacement.
Similarly, really old buildings were not built for electricity or plumbing. Work had to be done on them to upgrade them to be able to accept modern technology. Well, will the best "smart" buildings be built from scratch?
Re: "[W]ill the best "smart" buildings be built from scratch?"
I believe they'll have to be. One of the techs I keep hearing whispers about is embedded sensors in the concrete that tell when micro-fissures start to appear, or can report temperature, stress, etc. Thousands of little sensors aren't something that can be conveniently added in once the concrete has dried - and that's just one example. Your car example in another good one.
Alternatively, you make the [bridges] more cheaply and with less redundancy, and have them last as long as a current model.
AS usual, Stewart Brand was there before most of us.
Check out his book "How Buildings Learn"
"Brand argues that a building can ``grow'' and should be treated as a ``Darwinian mechanism,'' something that adapts over time to meet certain changing needs."
From this review http://www.arch.ksu.edu/seamon/Brand.htm :
"[A]ny building is actually a hierarchy of pieces, each of which inherently changes at different rates. In his business-consulting manner, he calls these the "Six S's" (borrowed in part from British architect and historian F. Duffy's "Four S's" of capital investment in buildings).
The Site is eternal; the Structure is good for 30 to 300 years ("but few buildings make it past 60, for other reasons"); the Skin now changes every 15 to 20 years due to both weathering and fashion; the Services (wiring, plumbing, kitchen appliances, heating and cooling) change every seven to 15 years, perhaps faster in more technological settings; Space Planning, the interior partitioning and pedestrian flow, changes every two or three years in offices and lasts perhaps 30 years in the most stable homes; and the innermost layers of Stuff (furnishings) change continually.
A design imperative emerges: An adaptive building has to allow slippage between the differently-paced systems of Site, Structure, Skin, Services, Space Plan, and Stuff. Otherwise the slow systems block the flow of the quick ones, and the quick ones tear up the slow ones with their constant change. Embedding the systems together may look efficient at first, but over time it is the opposite, and destructive as well. Thus, pouring concrete on the ground for an instant foundation ("slab-on-grade") is maladaptive--pipes are foolishly buried, and there’s no basement space for storage, expansion, maintenance, and Services access. Timber-frame buildings, on the other hand, conveniently separate Structure, Skin, and Services, while balloon-frame (standard stud construction) over-connects them (p. 20).
Over-connection is only one flaw Brand notes in the difficulty of modifying modern (and particularly Modern) buildings. In a central series of chapters, Brand takes great glee in blasting 20th-century architects from Wright to Pei for their pictorial over-emphasis on the central layers of the model--Structure, Skin and Services, and primarily the central of these three--and a willingness to divorce these from the layers before and after.
These buildings have been designed as sculptural (and eminently photographable) objects, unable to move or adapt, perfect in their moment of pre-habitation. In criticizing this practice, Brand uses the very tool that the "magazine architects" have used for justification: the still photograph. But Brand subverts the formal purity of the designs by photographing these buildings with people using them, by stacking up photos taken over time, and by comparing these photos with similar images of other buildings less hindered by the immaculate moment of their creation."
Randall, you have done a wonderfull job of keeping up on a lot of scientific and technical areas that I would normally not see as much of, but I think there is a problem with this post. In both this blog and in Parapundit, you have made it clear that the human race is facing terrible challenges and possibly civilization-wrecking disaster in this century, so any new concrete technology that makes buildings and bridges much stronger and longer-lasting for only slightly more money is a good thing. If civilization goes smash, buildings and transportation facilities that last much longer will allow human effort to be put into recovery, rather than replacing stuff that should have lasted longer. Color me a pessimist; I think we should be making our structures for extreme longevity, while making them as versitile as possible. The comment just before this one gives some clues as to how this may be possible. Make 'em flexible, make 'em superinsulated, make 'em fireproof and blastproof, and make 'em independent of external sources of electricity and heat and cooling. A physically fragile civilization cannot be psychologically, economically, militarily, and politically tough; it will crack under stress, and stress is what it will get in the 21st century!
One has to consider what sorts of civilizational collapse scenario one is trying to prepare for. A really long collapse would be easier to handle if we have very long lasting structures. But for a shorter collapse what would be far more valuable is widespread use of photovoltaics. Then collapse of big energy distribution networks would be less immediately disruptive of life.
Even under a longer term collapse scenario energy would be more valuable than longer-life structures.
Note that I do push heavily in many posts for research into photovoltaics, batteries, and other energy tech that would be helpful under a civilizational collapse scenario. Though obviously I'm pushing for the research for many other reasons unrelated to civilizational collapse the tech would make civilization less fragile.
As for what threatens to make civilization more fragile I see two biggies: nuclear proliferation and bioengineered bioweapons. Both increase the value of living away from major population concentrations. Nukes are going to be exploded in cities. Pathogens that are transferred person-to-person will be transmitted more easily in more densely populated areas. Nukes destroy structures. Pathogens only destroy people. So under the biowarfare scenario that killed a lot of people we'd have a huge surplus of structures.
In any case, I am not opposed to the developmet and ues of longer lasting materials. I am in favor of more research into such materials. Anything that we can make once and use for a long time makes us richer.