Q.: We have heard of cutting concrete by high pressure water jet but the only information we can find is about equipment used for one of two purposes: (1) exposing aggregate in the surface of concrete soon after forms have been stripped, and (2) removing hardened concrete from steel in concrete mixers or other equipment. Can you direct us to any manufacturers who make water jet equipment that will make a saw type of cut?

A.: As far as we know the high pressure water jet equipment currently on the market is useful only for things like exposing aggregate or removing concrete from steel. Depending on the manufacturer, pressures available range from a few thousand psi to about 20,000 psi and rates of water flow range from a few gallons per minute to 300 gallons per minute.

Water-jet equipment is under development for the express purpose of cutting hardened concrete in the manner of a saw but it is not yet commercially available. It has been reported to us that when the equipment has been fully developed it should emit water jets at pressures of 40,000 to 60,000 psi but with low rates of water flow, such as 6 to 8 gallons per minute. A 3000- to 4000-gallon tank truck would supply such equipment with enough water for about 8 hours of cutting. Development of the equipment has been under way for some time at Illinois Institute of Technology in Chicago (see "Water Jet Contributes to Economy of Road Repairs," Concrete Construction, July 1981 issue, page 605).