Q.: Our company is building an 8-foot-thick mat foundation for a sewage treatment plant. We want to use expanded metal as a forming material at the vertical construction joints. Since the mat is heavily reinforced, there are many penetrating reinforcing bars. We think it would save us time and money to use expanded metal instead of building solid bulkhead forms, but the engineer refuses to approve this unless we can show that it is "approved by ACI." Can you help?

A.: We were unable to find any reference pro or con in published American Concrete Institute (ACI) standards and committee reports. However, we did learn that a photograph of expanded metal has been selected for inclusion in the next edition of Formwork for Concrete (ACI Special Publication No. 4), and an accompanying description will be added about the use of expanded metal as a bulkhead form.

In current books, we found that John Richardson of the English Cement and Concrete Association mentions it in Formwork Construction and Practice in this way. "Another method of forming joints is by using expanded metal on supporting frames. The expanded metal forms a textured surface and when torn away from the surface at the joint provides an excellent key for further work." It is likely that Richardson refers to a generic form of expanded metal, rather than the ribbed products manufactured in the United States specifically for forming operations. It's hard to imagine ripping off the metal at a joint that looks like the one in the photograph, nor would it be necessary.

There is growing precedent for acceptance of expanded metal as a bulkhead form, and manufacturers can supply information on enough existing installations to satisfy most of the skeptical specifiers. A full description of the material and ways to use it were presented in CONCRETE CONSTRUCTION, July 1983, page 552. NOTE: The Richardson book, Formwork Construction and Practice, (275 pages) published by Viewpoint Publications in England can be ordered from Scholium International, 265 Great Neck Road, Great Neck, New York 11021. The current price is $50.00. The current edition of the ACI book, Formwork for Concrete (463 pages), by M. K. Hurd is available from Concrete Construction Publications, 426 South Westgate, Addison, Illinois 60101 for $49.95 postpaid.