Question: The "Did You Know" item on page 622 of the November 1977 issue could have been more informative. How, pray, did our German friends accomplish their feat of pumping concrete 310 meters high? For example, what was the class of concrete and what was the type and make of pump or pumps? Any other pertinent information would be helpful.

Answer: The concrete for the telecommunications tower in Frankfurt, Germany was grade Bn 450 (design strength of 450 kilograms force per square centimeter or 6400 psi). This was made to a slump of about 110 millimeters (about 4 inches) with a mix containing 420 kilograms of cement per cubic meter (710 pounds per cubic yard) using aggregate of 32millimeter (1 1/4-inch) maximum size. The concrete was pumped through a pipeline 125 millimeters (4.92 inches) in diameter. It was sometimes in the line for an hour and came out quite stiff.

The record pumping height of 310 meters (1017 feet) was set with a Putzmeister concrete pump with an elephant swing valve system. Ordinarily this pump had cylinders 150 millimeters (5.91 inches) in diameter and a 2.10-meter (83-inch) piston stroke. After the tower had reached a height of 246.5 meters (809 feet) these cylinders were replaced with others 130 millimeters (5.12 inches) in diameter to increase the pump pressure by about 30 percent and the pump thus modified was used for the remainder of the job. This modified pump is now available as a standard model. Its allowable output pressure at a safety factor of 2 to 1 is 150 bar (2175 psi) .Actually, the pump was located 7 meters (23 feet) below the base of the tower and the boom reached 13 meters (43 feet) higher than the formwork. Hence, to place the concrete at the record height the pump had to lift the concrete an additional 20 meters (66 feet) for a total of 330 meters (1082.6 feet).The photo is a view of the top of the tower at about the time the concrete work was completed.