Mixture Production
A cold central recycling plant is preferred for producing RAP maintenance mixes. This equipment results in good control of both material size and asphalt emulsion content. The plant consists of a feeder hopper, screening and crushing unit, and a twin-shaft mixer for adding the asphalt emulsion. The mixer has a belt scale and computer controlled liquid additive system for accurately adding the emulsion. The mix is removed from the mixing unit by a belt conveyor and stacked for immediate use or for stockpiling at the mixing or other site for later use.

Maximum material size is controlled by the screening and crushing unit with no large pieces as can occur if RAP is used directly from the stockpile. Also, the coarseness of the mixture can be adjusted by changing the screen size with a coarser gradation for deep patching or made finer if to place in a thin layer as for skin patching. Typical mix sizes are 100% passing a 7/8 inch or 5/8 inch screen. Eliminated is tearing of the mat by the asphalt paver or motor grader due to large over-sized material.

Mixture Stockpiling
Stockpile height must be maintained as low as possible, preferably not greater than about 8 to 10 feet (2.5 to 3 meters), to prevent the asphalt coated particles from sticking together and producing chunks. This is of particular concern as mix moisture content decreases and air temperatures rise. Also, bucket loader front wheels should be kept off of stockpiles as large chunks may result due to compaction by the wheels. Stockpiles should be checked periodically with a bucket loader to determine if the mix is maintaining workability and a reduction in asphalt content possibly is needed. A thin crust may form on the stockpile surface but this is typical for these types of mixes.