Erected atop a high-rise, placing booms can put concrete where you want it, not just where the pumpline happens to end. Some of the larger placing booms can reach more than 100 feet, pivoting through a complete circle and covering an area up to 34,600 square feet. Smaller placing booms may cover only a 30-foot radius. They can reach straight down, straight out and all points in between without missing a spot all operated by hand controls located on the boom or a remote control box. According to one pumping contractor, a separate placing boom can provide 20 to 30 cubic yards per hour production and with 3 to 4 fewer men.
Separate placing booms are mounted on masts within the structure or towers adjoining it. If the lower floors of a building are to be pumped with the aid of a separate boom, a freestanding mast can be erected near the center of the building so that the boom's reach will cover the entire floor area. The typical tubular mast available from one supplier is braced and bolted to a steel cross frame that is either anchored to a specially cast 10x10x3-foot concrete slab or bolted to a larger ballast frame loaded with big concrete blocks. Once all the floors below this freestanding boom have been cast, the mast is raised in order for the boom to reach the next floor.
The mast and boom can be raised by either the tower crane or a special hydraulic jack positioned under the base of the mast. The hydraulic climbing device is used when the available crane does not have the lifting capacity to handle the boom or, when the crane must be kept free to perform other activities. To power the boom while atop the building a separate electric-hydraulic pack is also needed, since the boom cannot be powered by the truck's engine as it is when it is mounted on the truck. Each time the mast is raised, a section of pipe is simply added to the pumpline which is continuous from the pump on the ground up to the boom atop the structure.