Concrete Mixer Truck

Concrete mixer trucks, or transit mixers, are used to mix and transport ready-mix concrete from the batch plant to the job site. The drum has its own hydraulic drive, which means the truck does not have to power the drum. On older transit mixers, the drum was powered by the truck's engine or by its own gas engine.

There are a couple of different types of mixer trucks: Transit mixers (pictured right); volumetric trucks, which are loaded with raw materials and mix the concrete and agitator or agitator trucks, whose bodies have an open top and an agitator paddle inside the box. Originally, concrete was either mixed at the pour ;or delivered by horse-drawn cart. Dry materials were delivered by cart, then by narrow gauge flatcars carrying batch boxes filled with proportioned amounts of aggregate and cement. When trucks took over general construction hauling, batch trucks - which were dump trucks with compartmentalized boxes to hold up to five batches of aggregates per load - delivered the raw materials to the mixer.

Concrete pavement and large slabs were laid by dry batch pavers. The dry materials were dumped into a skip at one end of the paver, and the skip was raised to charge the mixer. Concrete would be mixed in one, two or three drums; on multiple-drum pavers, known by such names as Duo-batch, Dual Batch or Tri-batch pavers, the drums were arranged in line, passing concrete from one to the next. When mixed, the concrete would be discharged into a bucket on a boom that could be swung or raised. The operator directed the bucket to where the concrete would be poured, trip the bucket to dump the concrete, and return the bucket to receive another batch of concrete. One to one and a half yards of concrete could be placed per batch. Dry batch pavers were developed in the late 1910s, and were the standard machine for this work until central mix batch plants rendered them obsolete; a handful of dry batch pavers were converted to mixers at central mix plants by removing the skips and booms. Very few dry batch pavers exist today.

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