Q.: Is it true that superflat floors are built without transverse joints and that they are expected to crack?

Is it possible to build a superflat floor that doesn't crack, with or without transverse control joints?

We need a floor that is crack-free for reasons of sanitation.

A.: Joints are omitted from superflat floors because the joints would tend to become high ridges in the floors.

A possible solution to your problem is to build a post-tensioned superflat floor. This could be post-tensioned in either one or two directions, depending on requirements.

George Garber reported on construction of both one-way and two-way post-tensioned floors in the May 1983 issue of CONCRETE CONSTRUCTION, page 396.

Editor's note

After this question was addressed in Problem Clinic in our July issue, page 679, a reader responded that our answer was incomplete, especially on the subject of control joints, and offered the following information: Another solution is to use shrinkage-compensating cement concrete, as discussed in the following articles in Concrete Construction:

"Shrinkage-Compensating Cement Concrete," February 1976, page 63.

"Good Warehouse Floors Don't Just Happen," September 1977, page 493.

"Shrinkage-Compensating Concrete for Industrial Floors on Ground," February 1979, page 110.

"How Does Shrinkage-Compensating Cement Concrete Help Post-Tensioning?" April 1983, page 331.

Anyone interested in this subject might also want to study ACI 223, "Standard Practice for the Use of Shrinkage-Compensating Concrete."Although some engineers feel that shrinkage-compensating cement concrete is a competitor for post-tensioned concrete, actually the two complement each other when combined on a project.