Pressure to Change; November 1996; Scientific American Magazine; by Gibbs; 2 Page(s)

About 2,000 years ago construction workers used the latest high-tech materials to pour an enormous concrete dome for a new temple in Rome. Millennia later the Pantheon¿s roof is still intact--in fact, it is hardening as calcium compounds in the structure gradually react with carbon dioxide in the atmosphere to form limestone and other minerals that are even stronger than concrete. In May a construction engineer from Reno, Nev., patented an inexpensive way to shorten that hardening process from several thousand years to just a few minutes. Preliminary studies suggest the innovation could yield products ranging from less expensive wallboard to safer radioactive waste disposal.

Concrete normally hardens so slowly because water seals its pores against carbon dioxide in the air. "But an article in Scientific American on the use of [highpressure] CO2 for making cheaper plastics got me thinking," recalls Roger H. Jones, an engineer with Materials Technology Limited. "I took my pressure cooker, wrapped it in wire and tried an experiment." Jones discovered that exposing concrete mixed with portland cement to high-pressure CO2 drove water out of the material and changed its chemical composition. Standard compression tests, he says, show that on average the treatment increases the strength of portland cement by 84 percent. Subsequent experiments at Los Alamos National Laboratory have demonstrated that the process can transform a wide range of inexpensive materials--including some that are currently considered waste products--into stronger, more useful forms.