Visiting the Colosseum in Rome last year, I was surprised to see that it wasn't made of brick, but that the brick is really just acting as formwork for the Roman concrete inside. I am not a big fan of concrete; the manufacture of cement is responsible for about 5% of the world's annual CO2 production, and the mining of aggregate is chewing up the countryside. However a new study shows that Roman concrete was in fact a lot better than the stuff we mix today. The Utne Reader points to a new study:
Researchers from the University of California, Berkeley, summarized their findings in the Journal of the American Ceramic Society, and found the ancient Roman combination of limestone, volcanic ash, and seawater required far less heat (which means far less fuel) for solidification than modern concrete does. This suggests that contemporary application of the ancient Roman method may yield stronger, more durable concrete with a much smaller environmental footprint.
The Romans didn't use portland cement, which is made from limestone heated to 1,450 degrees Celsius; they mixed lime with pozzolana, or volcanic ash. This requires far less energy as the lime only needs to be heated to 900 degrees. Conservation Magazine notes:
The mixture of lime and ash from nearby volcanoes reacts with seawater to form an extremely strong and stable material. This recipe could provide a model for producing durable, environmentally friendly concretes, say the researchers, since volcanic ash is found in many areas of the world.
Read also David Moore's Roman Concrete.