Concrete plant

Types

A Dry mix Concrete Plants, also known as Transit Mix Plants, weighs sand, gravel and cement in weigh batchers via digital or manual scales . All the ingredients then are discharged into a chute which discharges into a truck. Meanwhile, water is either being weighed or volumetrically metered and discharged through the same charging chute into the mixer truck. These ingredients are then mixed for a minimum of 70 to 100 revolutions during transportation to the jobsite.

A Wet mix Concrete Plants, combines some or all of the above ingredients (including water) at a central location into a Concrete Mixer - that is, the concrete is mixed at a single point, and then simply agitated on the way to the jobsite to prevent setting (using agitors or ready mix trucks) or hauled to the jobsite in an open-bodied dump truck. Dry mix differ from Wet mix plants in that Wet Mix contain a central mixer whereas dry , which can offer a more consistent mixture in a shorter time (generally 5 minutes or less). Dry mix plants typically see more break strength standard deviation and variation from load to load because of inconsistencies in mix times, truck blade and drum conditions, traffic conditions, etc. With a Central Mix plant, all loads see the same mixing action and there is an initial quality control point when discharging from the central mixer. Certain plants combine both Dry and Wet characteristics for increased production or for seasonality. le A Mobile batch plant can be constructed on a large job site.

Both Wet Mix batch plant and a Dry Mix plant can be computer assisted using a batch computer. Different types of concrete batch plants types are available for a variety of applications.

Mobile Concrete Batching Plant

Batch plants can be Portable, Stationary, or Semi-portable. Certain batch plant designs may be considered mobile, but not necessarily easy to setup and teardown.

These categories typically differ in the ease of startup and teardown and the presence of portable features such as axles, brakes, and lights. Mobile batching plants are typically a single unit, made up of a cement silo, an aggregate bin, an aggregate conveyor and the cement and aggregate batchers, but at higher hourly production capacities may require numerous loads for a single plant. 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 to reduce transportation costs.

The mobile batch plant, also known as a portable concrete plant is a very productive, reliable and cost effective piece of equipment to produce batches of concrete. It allows the user to batch concrete at most any location then move to another location and batch concrete. It was invented in 1956 by Vince Hagan and was patented in 1966 as a convenient alternative to stationary batch plants that cannot be moved easily (U.S. patent #3,251,484). Portable plants are the best choice for temporary site projects or even stationary locations where the equipment height is a factor or the required production rate is lower.

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. With concrete performance so dependent on accurate water measurement, systems often use digital scales for cementitious materials and aggregates, and moisture probes to measure aggregate water content as it enters the aggregate batcher to automatically compensate for the mix design water/cement ratio target. Many producers find moisture probes work well only in sand, and with marginal results on larger sized aggregate.

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 the same proportion as the concrete recipe stipulates is the ultimate test of any control system. It is important that the Control System achieves the closest value to target weight. The fastest controls limit the number of jogs to maximize plant production rates. Variations in materials, weather and humidity, numerous mechanical points, and human input cause even the most accurate automation control to overweigh or underweigh material.

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

Dust and Water Pollution

Municipalities, especially in urban or residential areas, have been concerned at the pollution by concrete batching plants. The absence of suitable dust collection and filter systems in cement silos or at the truck loading point is the major source of particulate matter emission in the air. The loading point is a large emission point for dust pollution, so many concrete producers utilize central dust collectors to contain this dust. Notably, many transit mix (dry loading) plants create significantly more dust pollution than central mix plants due to the nature of the batching process. A final source of concern for many municipalities is the presence of extensive water runoff and reuse for water spilled on a producer's sites.