Pumping concrete from the bottom up made good sense to engineers and superintendents assigned to the Providence Hospital construction project in Mobile, Alabama. Massive 20-foot-high arches at ground level varied in thickness from 8 to 20 inches and concrete could be placed using conventional methods. But serpentine walls above the arches were 8 inches thick with enough reinforcement to make consolidation difficult. There wasn't much room to get a vibrator into the concrete, especially near the windows. A decision was made to pump the walls from the bottom up using a superplasticized concrete that would require only minimal vibration. While concrete for columns and piers has frequently been placed using this method, it is seldom used for walls.
CONCRETE PROPORTIONS AND PROPERTIES
A 3/4-inch-top-size crushed limestone coarse aggregate was used and the cement content was 564 pounds per cubic yard. An air-entraining agent and a superplasticizer were also added, reducing the water content and producing design strength levels in 5 to 10 days. Concrete was batched to produce a 2- to 4-inch slump and the low-slump-loss superplasticizer was added at the plant to bring the slump up to about 8 inches for placing. The combination of good sand grading, adequate cement content, high slump, and extended slump life helped to ensure pumpable concrete, even at high placing temperatures.
THE PUMPING METHOD
The 5-inch-diameter slickline was connected by hose to a Y section and 5-inch to 4-inch reducers were coupled to each leg of the Y. Two 4-inch diameter hoses were clamped to the Y and to form-mounted valves approximately 14 to 18 feet apart. For most of the pours, window openings were centered between the two ports used for pumping. The entire section of wall was then pumped with a single setup. Once pumping started it took only 10 minutes to fill the nearly 11-foot-high section of wall with about 10 cubic yards of concrete. Concrete flowed horizontally as well as vertically but no segregation occurred because the high-slump mixture was very cohesive. When one section of wall was completed, a crane lifted the Y connection and moved it to the next setup.