Forensic Investigation of Distressed Pavement Supported on a Base Course Containing Recycled Concrete Aggregate

• Published in: Transportation research record 2011-01, Vol.2253 (1), p.22-31
• Main Authors: Ooi, Phillip S. K., Rajabipour, Farshad, Shafaatian, Afshin, Joo, Seungdon
• Format: Article
• Language: English
• ISSN: 0361-1981; 2169-4052
• DOI: 10.3141/2253-03

The pressure for pavement and geotechnical engineers to incorporate sustainability into engineering projects has led to a rise in the use of recycled concrete aggregate (RCA) as fill and in pavement sublayers. Although the use of RCA has many economical, environmental, and engineering advantages, an oversight in quality control can lead to the use of contaminated RCA in the unbound layers. This can lead to premature deterioration that is costly to repair but, more important, can slow down the market acceptance of RCA. The authors forensically investigated an asphalt concrete pavement supported on a base course containing RCA and that had experienced a significant number of eruptions. Significant amounts of a white substance were found within the base course below each eruption. Sampling and testing showed the primary constituent of the substance to be bayerite, an unstable form of gibbsite, which could form when aluminum metal corroded in an alkaline environment. The adjacent ground topography would have encouraged drainage through the pavement site and thereby rendered the base course moisture susceptible to high alkalinity, because RCA in an aqueous solution has a high pH. Exposing aluminum metal to alkali in the laboratory to duplicate the field reaction confirmed the formation of bayerite. Moreover, exposing aluminum powder to an alkaline environment in a Geonor H-200 apparatus attained a maximum swell pressure of 430 kPa. When the pavement was numerically subjected to this swell pressure, the calculated deflections were found to be consistent with the observed pavement deflections and thus corroborated the hypothesized cause of distress. Suggestions are offered to avoid this type of distress.