Folks, I just found this interesting site about the history of the uses of lime and development of pozzolonic materials ...lime and clay - Roman Cement - that I think will be interesting to the group. I highly recommend David Moore's book "The Roman Pantheon" at $25.00 - a very thorough research into the uses and development of Roman Cement....lime and clay/pozzolonic ash; the making and uses of lime in building. The book covers ancient kilns, and ties it all to modern uses of cement and concrete. I find it almost impossible to put down - as the writing flows easily - interesting, entertaining, and enlightening. David Moore spent over 10 years learning just how the Romans were able to construct large buildings, structures, etc., with simply lime and volcanic ash - structures that have lasted over 2000 years. A great testimonial to the Roman builders; and good background information for sustainable builder folks. Thank you, Mr. Moore. I highly recommend the site and especially the Book. <A HREF="http://www.romanconcrete.com/">Roman Concrete Research by David Moore</A> Regards, Harry Francis