Placing Concrete with Belt Conveyors ACI 304.4R-95

Description

Belt conveyors for handling concrete are special in that they transport plastic concrete which is about 48 percentheavier than aggregate or other commonly conveyed materials. They transport plastic concrete from a supply sourcesuch as a truck mixer or a batching and mixing plant to the point of placement or to other equipment which is used to place the concrete. Concrete placement by belt conveyors should be a continuous operation.

Maximum success for conveyor placing requires a constant supply of properly mixed concrete for charging the belt conveyor and a provision for moving the discharge point during placement so that the plastic concrete is deposited over the entire placement area without the need for re handling or excessive vibration. Concrete belt conveyors are classified into three types: 1)portable or self contained, 2) feeder or series, and 3) spread-er; radial or side discharge.

The earliest recorded use of belt conveyors in North America was to handle grain. A grain belt conveyor was de-scribed in the 1795 “Millers Guide.” The first recorded useof belt conveyors to handle material heavier than grain did not come until the early 1890s when belt conveyors were in-stalled at an ore processing plant in Edison, N.J. The commercial introduction of antifriction bearings in idler rollers paved the way for the modern belt conveyor.

In 1923 conveyors were first successfully used in handling coal.1The first known successful use of concrete belt conveyors was in 1929 when Cor betta Construction Co., Inc., used a600-ft (183-m) conveyor to place structural concrete for the East 238th Street Bridge, Bronx County, City of New York. The concrete mix (1:2:4) contained 3/4-in. (19-mm) NMSA(nominal maximum size aggregate).