Utilization of Recycled Materials in Illinois Highway Construction
Recycled Concrete Material
- Recycled Concrete Material (RCM), also known as crushed concrete, is reclaimed PCC pavement material. Primary sources of RCM are demolition of existing concrete pavement, bridge structures, curb and gutter, and from central recyclers, who obtain raw feed from commercial/private facilities. This material is crushed by mechanical means into manageable fragments and stockpiled. RCM may include small percentages of subbase soil and related debris (1).
- Physical Properties:
- Comprised of highly angular conglomerates of crushed quality aggregate and hardened cement, RCM is rougher and more absorbent than its virgin constituents. Furthermore, differences among concrete mixes and uses result in varying aggregate qualities and sizes; for example, pre-cast concrete is less variable than cast-in-place (1).
- Engineering Value:
- Crushed concrete's physical characteristics make it a viable substitute for aggregate and can be used as such, for example in granular bases, as well as a material fill, such as riprap. Ultimately, RCM obtained on site may be employed immediately for project use or stockpiled for future use.
The cementitious component has a high amount of alkalinity by nature, and chlorides from deicing salts may be present-a concern in regards to steel reinforcement corrosion. RCM may also contain aggregates susceptible to alkali-silica reactions or D-cracking (1, 3).
- Present Application:
- The Department allows the use of RCM as a coarse aggregate in aggregate surface courses, granular embankments, stabilized bases, and subbase courses provided the project materials' specifications are not compromised. This material has also been widely used as an aggregate in membrane waterproofing and in drainage layers as protection against erosion (3, 8).
- Quantity Used:
- 321,300 tons (2001 MISTIC estimate).
- Economic Impact:
- The use of RCM impacts the economy as a substitute for natural aggregates by reducing landfill space needs. The use and number of central recyclers have increased over the last few years. In 2001, overall departmental spending was approximately $1,600,000.