Floors in narrow-aisle, high-rack warehouses must be extremely flat to permit adequate forklift speeds without the danger of material falling off pallets while being stored or retrieved. These are the reasons the Pic N' Save Corporation, a large retail chain in the Southwest, selected a superflat floor system. After much research and consulting between the owner and The Edward W. Face Company, floor flatness consultants, one of the most coordinated and controlled concrete installations in Southern California was set into motion.


Bulkhead forms were set by the general contractor one day before placing concrete. The subgrade required compaction to 100 percent of maximum density. Form heights were checked four separate times by transit to a tolerance of 1/32 inch at 6-foot intervals. Bulkhead form sections consisting of an aluminum channel face with plywood insert for nailing were devised by the general contractor.


The concrete mix proportions were selected with the intent of achieving the most uniform time of setting. A strength of 4000 psi was required and the slump was specified at 4 inches. 564 pounds of Type II cement were used for 1 cubic yard of concrete. When a truck arrived at the job, it went to a centrally located control point where a laboratory technician was stationed. He checked the slump, added water up to the allowable amount if necessary, and then directed the truck to one of the placing crews.


The essence of this kind of floor finishing operation is to monitor each day the flatness of the previous day's placement and then to modify the new day's operations. A profilograph reading was taken, and the results helped isolate problem areas that required minor grinding.