PCC Recycling

Reclaimed concrete material (RCM), sometimes referred to as recycled concrete pavement (RCP), is typically generated by rigid pavement rehabilitation or reconstruction. When crushed, RCM can be used in a variety of ways:

• As an aggregate in PCC and HMA.
• As a granular base course.
• As a fill or embankment material.

Generally, recycling PCC involves breaking it up, removing embedded metal (e.g., steel reinforcing bars, dowels, etc), then crushing it to a specified size. For small projects, RCM is usually broken up into large pieces and loaded into dump trucks for removal from the site. This RCM is typically hauled to a central facility for stockpiling and processing (FHWA, 2001d^[1]). The central processing facility crushes, screens and removes ferrous metal from the RCM. Present crushing systems, with magnetic separators, are capable of removing reinforcing steel without much difficulty, however welded wire mesh reinforcement may be difficult or impossible to remove effectively (FHWA, 2001d^[1]). For large projects, RCM is usually processed on site using a mobile plant or processed in place using one or several machines.

Some general conclusions about RCM material properties from NCHRP Synthesis 154: Recycling of Portland Cement Concrete Pavements (Yrjanson, 1989^[2]) are:

• Aggregate particle characteristics. The aggregate particles produced by crushing have good particle shape, high absorptions, and low specific gravity compared with conventional mineral aggregates.
• Mixture design and workability.
  • The use of recycled coarse aggregate has no significant effect on mixture proportioning or workability compared with conventional PCC mixtures.
  • When crushed RCP is used as a fine aggregate, the mixture is less workable and requires more cement because of its increased water demand. As a result, most state agencies do not use recycled fines in concrete mixtures, and if they are used they are limited to a maximum of 30 percent of the fine aggregate portion of the mixture.
• Durability.
  • PCC made from RCP aggregate has shown an increase in freeze-thaw resistance compared with PCC made from normal conventional aggregates.
  • The durability of PCC made with aggregate subject to D-cracking can be substantially improved by recycling. The addition of fly ash may reduce D-cracking potential even more.
• Strength. The strength of PCC made with RCP aggregate can be equivalent to conventional PCC mixtures when recycled fines are omitted or used in small amounts.

RCM can be used in the following manner:

• Coarse aggregate
• base material
• embankment/fill