Reclaimed Concrete Material Used as Coarse Aggregate

In general, adequate PCC pavement can and has been constructed using RCM as a coarse aggregate.

Purpose

Coarse aggregate in PCC, aggregate in HMA


Materials

RCM crushed to a predetermined size

Mix Design

Standard PCC mix design.  Most standards consider RCM coarse aggregate to be a conventional coarse aggregate and treat it as such.  If not prewetted, RCM aggregates will absorb a substantial amount of water.


Standard HMA mix design.  RCM is more appropriate for asphalt treated base materials that generally have fewer restrictions on mix design and aggregate properties.  RCM has functioned well as an asphalt treated base material.

Other Information

PCC incorporating more than about 10 to 20 percent fine aggregate will have low workability and require more water to maintain reasonable workability.  This excess water will result in an overall strength reduction.

For a given compressive strength (at 28 days), both the static and dynamic moduli of elasticity for recycled-aggregate concrete are significantly lower (up to 40 percent) than those for concrete containing virgin aggregate (FHWA, 2001e[1]).


PCC incorporating coarse RCM aggregates generally can be expected to develop about 10 percent lower flexural strength than PCC incorporating conventional aggregates with equal water-cement ratios and slumps.

Chlorides may be present in RCM as a result of roadway deicing salt application.  High chloride levels can cause steel corrosion within the PCC (e.g., reinforcing steel in CRCP and dowel bars in JRCP).  Fortunately, the quantity of chloride typically found in old concrete pavement is below critical threshold values (Yrjanson, 1989[2]).



Footnotes    (↵ returns to text)
  1. Reclaimed Concrete Material: Portland Cement Concrete.  Web page on the Turner-Fairbanks Highway Research Center web site.  http://www.tfhrc.gov/hnr20/recycle/waste/rcc2.htm.  Accessed 25 October 2002.
  2. National Cooperative Highway Research Program Synthesis of Highway Practice 154: Recycling of Portland Cement Concrete Pavements.  Transportation Research Board, National Research Council.  Washington, D.C.