Concrete pumping in the United States took a sizable leap upward recently when concrete was pumped 729 feet vertically to place the last of 50 floors in the Capital National Bank Plaza in Houston. The record-breaking level of concrete pumped surpassed the previous U.S. record of 576 feet, established during construction of the Century Plaza in Los Angeles.

Both lightweight and hard rock concrete were pumped to the record level in December 1979. The 3000-psi structural lightweight concrete mix was made with expanded clay aggregate. Batch proportions per cubic yard were: cement, 517 to 564 pounds; coarse aggregate, 3/4-inch maximum, 960; fine aggregate, Colorado River sand, 1625; and water, 192. Concrete was finished on the upper floors at a 4- to 4-inch slump.

The contractor reports that the decision to use pumps exclusively for the job resulted in substantial savings over conventional crane and bucket placement.