Concrete plant
A concrete plant, also known as a batch plant or batching plant or a concrete batching plant, is a device that combines various ingredients to form concrete. Some of these inputs include sand, water, aggregate (rocks, gravel, etc.), fly ash, potash, and cement. There are two types of concrete plants: Dry mix plants and Wet mix plants. A concrete plant can have a variety of parts and accessories, including: mixers (either tilt-up or horizontal or in some cases both), cement batchers, aggregate batchers, conveyors, radial stackers, aggregate bins, cement bins, heaters, chillers, cement silos, batch plant controls, and dust collectors (to minimize environmental pollution). The center of the concrete batching plant is the mixer. There are many types of mixer like Tilt, Pan, Planetary, Single Shaft and twin shaft mixer. The twin shaft mixer can ensure an even mixture of concrete and large output, while the tilt mixer offers a consistent mix with much less maintenance labor and cost.[1]
Types
A Dry mix plant weighs the sand, gravel and cement in weigh batchers which can be computer assisted. All the ingredients then combine in a confining chute which discharges into the agitator (or mixer) truck. Meanwhile, water is either being weighed or volumetrically metered and discharged through the same confining chute into the agitator truck. These ingredients are then mixed for a minimum of 10 minutes during transportation to the job site.
A Wet mix Concrete Batching plant combines some or all of the above ingredients (including water) at a central location in a Concrete Mixer. The mixer can be Single/Double Shaft type, Pan type or a Planetary type. The final product is then transported to the desired location. Dry mix differ from Wet mix plants in that Wet Mix contain a central mixer, which can offer a more consistent mixture in a shorter time (generally 5 minutes or less). A Mobile batch plant can be constructed on a large job site.[1]
Both Wet Mix batch plant and a Dry Mix plant can be computer assisted using a batch computer. Different types of concrete batching plants are available for a variety of applications.
Application
Concrete batching plants are widely used to produce various kinds of concrete including quaking concrete and hard concrete, suitable for large or medium scale building works, road and bridge works and precast concrete plants, etc.
More recently is the availability of the mobile concrete batch plant, patented in 1975 by Vincent Hagan.[2] This innovative device was designed for the production of all types of concrete, mixed cements, cold regenerations and inertizations of materials mixed with resin additives. The design includes multiple containers that separately transport all the elements necessary for the production of concrete, or any other mixture, at the specific job site. In this way, the operator can produce exactly what he wants, where he wants and in the quantity he wants through the use of an on-board computer. Once production is started, the various components enter the mixer in the required doses and the finished mixed product comes out continuously ready for final use. It is also suitable for the recovery of materials destined for landfill disposal, such as cement mixtures regenerated from masonry rubble. The mobile batching plant is easy to transport. It can be fixed-mounted on a truck, mounted on a truck with tipping box or mounted on an interchangeable cradle.
Of late, several municipalities have been concerned at the pollution by concrete batching plants, especially if they are located within residential areas. Of special interest is the duct created during discharge of sand and aggregates in the plant. Absence of suitable filter systems in cement silos can also be a major source of particulate matter pollution in the air.
Mobile Concrete Batching Plant
Mobile batching plants are typically a single unit, made up of a cement silo, an aggregate bin, an aggregate conveyor and the cement batcher. Sometimes a water batch is included in the unit as well. Typically, a mobile batching plant can be dismantled and reassembled in a few days time. As a result, they can be used at multiple construction sites.
Aggregate bins have 3-4 compartments for storage of various sand and aggregate (rocks, gravel, etc.) sizes. Conveyors are between 24-48 inches wide and carry aggregate from the batcher.
Automation and control
Modern concrete batch plants (both Wet mix and Dry mix,) employ computer aided control to assist in fast and accurate measurement of input constituents or ingredients, as well as tie together the various parts and accessories for coordinated and safe operation. With concrete performance so dependent on accurate water measurement, systems often use moisture probes to measure the amount of water that is part of the aggregate (sand and rock) material while it is being weighed, and then automatically compensate the mix design water target.
Concrete usage in superstructures like Burj Khalifa in Dubai have tested the limits to which a Control System can manufacture precision concrete. Dosing of Cement, Sand, Crushed Stone, Chemicals and Water in exactly same proportion as the concrete recipe stipulates is the ultimate test of any control system. It is important that the Control System does iterations to achieve the closest value of an ingredient as it keeps on manufacturing the concrete.
Concrete Plant Manufacturers Bureau
A non-profit association brings together all of the main concrete plant manufacturers on common matters related to the industry. According to the CPMB's website, "The National Ready Mixed Concrete Association (NRMCA) endorses the members of the Concrete Plant Manufacturers Bureau as the preferred providers of concrete plants and associated equipment as providing quality equipment conforming to the standards and specifications of NRMCA’s plant certification program and the concrete plant manufacturers standards." "The primary function of the CPMB is to establish minimum standards for rating various components of concrete plants for the protection and assurance to the user that the plated components of the plants conform to these Standards."http://www.cpmb.org/about_CPMB.htm
References
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