The technology of cement-making has been repeatedly lost and rediscovered — and now “new” super concretes may lead to super bunkers:
The Romans knew how to mix crushed rock (”caementitium”), with burnt lime and water to make a versatile building material. The Pantheon in Rome boasts the world’s largest unreinforced concrete dome, still just as strong after 2,000 years. But cement was unknown in medieval times, with lime mortar serving as a poor substitute.
However, by the 1950s, it was obvious that much modern cement is not as durable as the ancient variety, and many buildings succumbed to concrete cancer caused by water penetration and chemical action. Ukrainian scientist Victor Glukhovsky looked into why the ancient cement recipes were so much more durable than modern ones and found that adding alkaline activators gave a greatly superior product. His work inspired Joseph Davidovits, a French chemical engineer, to discover the chemistry behind geopolymers and how it can be manipulated.
Professor Davidovits was awarded the French Ordre National du Mérite, and is President of the Geopolymer Institute. His most remarkable claim is that the pyramids were built using re-agglomerated stone, a sort of geopolymer limestone concrete, rather than blocks of natural stone. This would explain many of the mysteries of pyramid construction. Handling barrels of liquid concrete and casting in place would be much easier than moving giant blocks of stone. Remarkably, recent X-ray and microscopic study of samples has supported the theory that the pyramids are made of artificial stone.
The progress of geopolymers as building materials has been slow. Builders have an understandable tendency to stick to materials which have been around for decades and whose properties are well understood. However, the U.S. Air Force has been among the more enthusiastic early adopters — I look at military applications in the current issue of Defense Technology International (page 42).
For example Pyrament, a geopolymer-based cement is handy for the rapid repair and construction of runways. After just a few hours a Pyrament runway is ready for the heaviest aircraft, reaching a strength that conventional concrete can only match after several days.
The Air Force Research laboratory has funded geopolymer research for runways, insulation material, rocket nozzles, and other applications. It’s even been developed as special glue for holding satellite components together in the harsh conditions of space.
But the U.S. does not have a monopoly on this sort of technology. A couple of years ago Danger Room reported suggestions that Iranian scientists were working on ultra-high-strength concrete compositions. (Incidentally, high-hardness concrete is used in the construction of nuclear plants.)
The University of Tehran’s Faculty of Civil Engineering has its own Construction Materials Institute, which conveniently lists research papers in English. And it turns out that there is a lot of research into concrete technology, including fiber-reinforced concrete and concrete with ultra-high electrical resistivity. The Iran University of Science and Technology also displays some of its research in English — including a number of patents for new geopolymer cement formulations. The expertise is there; the only question is over whether there are other, unseen Iranian projects in this field.
The giant new Massive Ordnance Penetrator is reckoned to be able to break through 200 feet of 5,000 pounds-per-square-inch concrete, but just 25 feet through 10,000 psi concrete. Much harder concretes might be a real challenge.