Remediation and re-use of weathered hydrocarbon residue for the preparation of dense asphaltic mixtures

Legacy sites used for petroleum storage and refining exist in various parts of the world, and many contain soils with very viscous petroleum hydrocarbons produced by poor historical practices and many decades of weathering, especially in tropical and subtropical climates. This contamination causes land-use restrictions and may threaten natural resources and living organisms. The possibility of re-valorization of such a weathered hydrocarbon residue (WHR) was investigated for road-base (dense asphaltic mixture), considering site restrictions (re-use only on-site, construction possibilities, volume of residue, sandy soil). Fifty different mixtures were prepared in an iterative process to (1) use the maximum amount of WHR possible, (2) use the minimum amount of gravel possible, (3) meet the main national construction criteria for medium-traffic roadways, and (4) avoid leachate contamination of subsoil and groundwater. The ideal asphaltic mixture achieved was composed of 16.7% hydrocarbon residue, 60.17% sand (from the site), 20.00% commercial gravel and 3.13% Portland cement (filler). It met construction criteria (≥ 700 Kgf, 2–4 mm flux, according to the Marshall protocol) and had 3.39 mg/L of total petroleum hydrocarbons in TCLP-leachates, which were also non-toxic (filter-paper earthworm bioassay). Thus, the exploitation of a very WHR was shown to be an alternative to replace conventional asphaltic mixtures (thus providing another option for revalorization instead of landfill disposal or alternative treatment). Also demonstrated was the value of very WHRs, which may be present in old refineries, for asphalt production without using additives to strengthen the binding characteristics.