Rock Products

MAR 2013

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

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ported to a central crushing facility. Concrete at this stage may contain reinforcement, soil, asphalt pavement, brick or other debris. The crushing operations typically include pri��� mary crushing equipment to break down the concrete to a more manageable size and then proceed through a series of secondary crushing and screening processes. Magnetic sepa��� ration systems are effective in removing and recovering re��� inforcing steel along with visual and manual inspection stages to remove excess amounts of other materials such as brick and asphalt pavement. Both mobile and fixed process��� ing systems have the capability to break down and separate the crushed material into the desired sizes and gradation blends, such as aggregate base course material. The steps for a typical crushing plant to produce RCA were described in a Transportation Research Board paper and are listed below. (Donaldson, 2011) n n n n n n Demolition: Reducing concrete to a manageable size. Manual or Mechanical Pre���Separation: Removal of large pieces of wood, iron, brick, and other undesirable materials. Primary Screening: Removal of soil, gypsum, etc. Primary Crushing: Initial crushing operations. Magnetic Separation: Removal of ferrous materials. Secondary Screening: Initial separation into n n n desired sizes. Manual or Mechanical Removal of Contaminants: Lightweight material removal such as plastic, paper and wood. Secondary Crushing: Final crushing of concrete. Washing (if required), Screening, or Air���Sifting: Final sizing and removal of remaining contaminants such as plastic, paper and wood. Resulting RCA is ready for transport to site and incorporated into the project. Available technology allows for the production of aggregates that meet the same criteria as virgin materials, and can re��� sult in economic savings for the owner, especially when mo��� bile crushers are used on site. Many state highway agencies and municipalities have recognized the value and perform��� ance of RCA and have included it in their specifications. RCA can be produced in the same sizes and gradations as virgin aggregates, and has been successfully used in many different applications but using it as an aggregate base allows large quantities to be used. Using RCA as a base course also ac��� commodates more of the finer sizes generated from crushing than does producing several different sizes of clean stone. A survey was sent to the State Materials Engineers in Sep��� tember 2012 requesting basic information about each state���s allowance for the use of RCA. Information was also re��� RECYCLED CONCRETE AGGREGATE BASE USE FIGURE 1 ROCKproducts ��� MARCH 2013 23

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