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Long-term leaching from recycled concrete aggregates applied as sub-base material in road construction
Christian J Engelsen1, Hans A van der Sloot2, Gordana Petkovic3
1SINTEF Building and Infrastructure, PO Box 124, Blindern, NO-0314, Oslo, Norway.
The Science of the Total Environment
|February 28, 2017
Summary
Metal leaching from recycled concrete aggregates (RCA) in road sub-bases over 10 years shows pH-dependent release of elements like Al, Ca, and Mg. Leached amounts remained within safe environmental limits for water bodies.
Area of Science:
- Environmental Science
- Geochemistry
- Materials Science
Background:
- Recycled concrete aggregates (RCA) are increasingly used in road construction.
- Long-term metal leaching from RCA in sub-base applications requires thorough investigation.
- Understanding leaching behavior is crucial for assessing environmental impact.
Purpose of the Study:
- To investigate metal leaching from RCA in road sub-bases after over 10 years of exposure.
- To assess the influence of pH variations and de-icing salts on inorganic constituent release.
- To perform speciation modeling for major elements and evaluate environmental risks.
Main Methods:
- Field exposure of RCA sub-base for >10 years.
- Monitoring of pH, inorganic constituents, and trace metals.
- Speciation modeling using geochemical principles.
- Simplified risk assessment against water quality criteria.
Main Results:
- Leachability of Al, Ca, and Mg strongly correlated with pH, with good agreement between measured and predicted values.
- Speciation modeling confirmed gibbsite, calcite, and magnesite control Al, Ca, and Mg solubility.
- Increased oxyanion concentrations observed with larger pH fluctuations; vanadium showed a distinct pH-dependent leaching profile.
- Trace metal cations (Cd, Cu, Ni, Pb, Zn) leaching was not significantly affected by traffic-induced pH changes.
- Released metal quantities were within acceptable limits for groundwater and fresh water.
Conclusions:
- RCA in road sub-bases exhibits pH-dependent metal leaching, controlled by mineral precipitation/dissolution.
- Environmental risk associated with metal leaching from RCA is low under typical conditions.
- The use of RCA in road sub-bases is environmentally acceptable concerning metal release.
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