Q.: We're considering using steel fibers instead of rebar to reinforce a concrete slab on grade. However, we're concerned about the effects of these fibers on floating, restraightening and troweling operations, and on floor flatness. What floor flatnesses are achievable when steel fibers are used in the concrete?

A.: Eldon Tipping, Structural Services Inc., Dallas, says he's seen no effect on floor flatness or levelness when 25 to 30 pounds of steel fibers are used per cubic yard of concrete. This is a typical steel-fiber content for floors with close joint spacings or for elevated decks. Tipping says you can expect more wear on float blades or pans when floating such floors, but after the floors are floated, finishing procedures and achievable flatnesses are similar to those for conventionally reinforced floors.

Tipping hasn't had any experience with floors where higher steel-fiber contents--70 to 90 pounds per cubic yard--are used to permit larger joint spacings. Do any of our readers have flatness data for these floors?