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Mobile Volumetric concrete mixer truck

Volumetric concrete mixers include all mixing devices that measure the raw materials using volume rather than weight to produce a concrete mix.

HistoryEdit

The history of the volumetric mixing comes from several directions;

  • The mobile auger mixer was invented in 1964 by Harold Zimmerman, Ephrata, PA USA. His design allowed all of the ingredients (sand, stone, water, and cement) necessary to produce the concrete to be stored in separate bins and compartments directly on the batching unit.
  • The drum for trailer mounted volumetric mixer was designed in 1979, by Fred Caron and Neal Surry, Sacramento, CA USA. They mimicked the larger transit-mix truck's mixing drum, on a smaller scale and loaded the drum from a batching unit that metered the volume.
  • The paddle mixers exact history is un-recorded, but these volumetric mixers have been in use by masons for at least 100-years. Usually these produce smaller batches. Mechanical concrete and mortar mixers being produced in the late 1800s by several firms. earlier mixer were used in the clay & brick making industrys to mix the clay for extruding int bricks or molding into clay sanitary ware and tile, pipes atc. Early precast plants in the 1800s also used mechanical mixers


TypesEdit

Their are Three main types;

  • Static batch plant with capacities from a few m^3 / hour up to production units of a 100 m^3 per hour, usually of the Paddle mixer design which is usually mixed in smaller batches directly on the jobsite or in the factory. The mix being transfered by small skips or dumpers to the point of use.
  • Mobile truck mounted units (see photo above) These units are used for generally smaller jobs were 'normal' transit mixers bringing concrete from a depot are expensive and wastefull as due to the transit time the concrete is going off before it gets to site and thus has a short standing time on site. The Mobile unit can mix just enougth for the job (no waste & fresh) and can provide different mixes as required for several small jobs at one site per visit. There are auger blenders with the supply rate can be better matched to placing rate when access is poor & wheel barrows are required to transfere to final location.
  • Semi-mobile drum mixers which are mounted on trailers and are pulled to a jobsite using a pick-up truck. These drums usually have a mixing capacity of between 1-yard and 1.75 yards per batch. (some types used weight based batching)


OperationEdit

The volumetric mixer blends the concrete mixture using an auger or a paddle or a drum device to mix the ingredients with water.

The volumetric mixing process starts with a batch metering system that allows the volume of raw materials to be measured prior to entering the mixing chamber. This process can be as simple as using a measured bucket, to highly sophisticated and computerized batch plants that feed the correct volume.

The mixing chamber can vary depending upon the application and the mix design of the concrete.

  • An auger mixes the materials with water as it moves up and through the curved fins. Auger lengths can vary from about 5-feet to 15-feet depending upon the amount of time needed to complete a mix. They will vary in diameter and RPM.
  • A paddle mixer blends the concrete mix using a rotational motion and is used to blend finer gravels and sand, as in mortar.
  • A drum mixer tumbles the mixture in a folding motion using curved fins and paddles. The drum mixer is the most universal mode of volumetric mixing in the form of the Transit mixer, which is charged up at the batch plant with the materials and mixes it during transit to the site of use.

ManufacturersEdit

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