The Los Alamos process transforms common portland or lime cemented materials and clays by treatment with carbon dioxide under high pressure, making them chemically stable, nearly impermeable and stronger. The process also makes inexpensive building products out of waste materials, including fly ash from coal-burning power plants, alum sludge from water treatment plants and blast furnace slag. Treated cement also may improve the safe storage of radioactive waste.
The process, patented by Roger Jones, Jr. of Materials Technology Limited of Reno, Nev., may lead to new building materials, consumer goods, auto parts and other products. According to Jones, the process creates recyclable materials that will be competitive with certain metals, plastics and wood products.
Under increasing pressure and temperature, carbon dioxide gas first reaches a liquid phase, then enters a region called "supercritical" where it has useful properties of both gas and liquid. Supercritical carbon dioxide expands to fill its container and diffuses into the tiniest pores like a gas. On the other hand, because supercritical carbon dioxide has a high density like a liquid, it can dissolve substances and carry them. In this case, it grabs water molecules and pulls them out of the cement.
Chemically, the process converts the hydroxide of cement to a carbonate, with water as the byproduct. This chemical reaction occurs naturally, too, but may take thousands of years.
"The cement in the Great Wall of China has not yet reached a chemically neutral state," said Craig Taylor, principal investigator for the Supercritical Fluids Development Center at Los Alamos. "But the supercritical carbon dioxide treatment achieves the chemically stable condition in minutes or hours. It's not really cement anymore, but a whole new material. It is really pourable limestone."
Taylor demonstrates the effect of supercritical carbon dioxide with two chunks of bonded fly ash, a waste product from coal-burning power plants. Set in a pan of water, the untreated sample quickly crumbles and dissolves, obviously useless as a building material. The treated sample, however, remains impervious to the water. Treated fly ash could make a strong, lightweight and economically attractive material for wall board, flooring and other construction products.
Large-scale use of supercritical carbon dioxide is not new to industry. For example, commercial operations have applied the same technology for years to make vegetable oils and to decaffeinate coffee. So Taylor does not foresee difficulties treating large volumes of cement blocks or massive columns and slabs. Even the U.S. Air Force has expressed interest in the technology - for building high-strength concrete slabs for runways.
Using supercritical carbon dioxide through a high pressure nozzle, large surfaces of existing concrete structures might be hardened and sealed against penetration of chemicals, improving wear-resistance and durability. The treated surfaces will resist chipping or scaling because the transition from the thin, very hard exterior to normal strength interior concrete would be gradual.
Large amounts of carbon dioxide produced by coal and oil burning power plants and by gasoline burning cars are blamed in part for a trend toward global warming, called the greenhouse effect. But the cement treatment process, by permanently removing carbon dioxide from the atmosphere and locking it into building products, actually helps reduce the impact of coal and petrochemical use. (Total curing of 2.2 pounds of cement permanently removes about 25 gallons of carbon dioxide from the atmosphere.) Research is under way to use both the fly ash and carbon dioxide expelled by coal-burning plants to produce construction materials.
"Like living coral, now we can take carbon dioxide out of the environment and build our houses with it. The process is good for ourselves and good for the environment," said Taylor.
Los Alamos' continuing role in development of the improved cement will be to optimize treatment conditions and help design a treatment facility. And researchers see a major new area of materials science to pursue.
"It's a new bulk material not well characterized," said Taylor. "Materials scientists will be busy with this for decades."
Since supercritical carbon dioxide readily dissolves many polymers, the process can be used to drive polymers into the surfaces of products made from cements, ceramics or other water-based pastes. Polymer-impregnated structures are better able to resist shock and impact forces and could be useful for a range of products from buildings to auto bodies.
Los Alamos, with the only operational plutonium facility in the country, also is interested in the chemistry of cement because radioactive waste often is mixed with cement for long-term storage and disposal. Because regular cement contains water, however, chemical reactions occur inside these cemented wastes, sometimes resulting in a hazardous buildup of hydrogen gas. If the cemented waste could be treated with the supercritical carbon dioxide process, dangerous chemical reactions would be eliminated.
Los Alamos' supercritical carbon dioxide research is funded internally through the Nuclear Materials Stabilization Technologies group. Commercial research continues through agreements with Materials Technology Limited and Custom Building Products of Seal Beach, Calif.
Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, The Babcock & Wilcox Company, and the Washington Division of URS for the Department of Energy's National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.