Use of Intelligent Compaction in Detecting and Remediating Under-Compacted Spots During Compaction of Asphalt Layers

Under-compaction of asphalt layers results in premature distresses like rutting, localized depressions and pot-holes. Over-compaction may crush the aggregates which can result in unstable asphalt mixes. It is therefore highly important to achieve the required air voids or relative density (6–8% air voids or 92–94% relative density). Real-time monitoring of the relative density can certainly be helpful in achieving the required relative density. The traditional quality control procedure, which involves collecting cores and conducting volumetric analysis on them, does not provide any measure of the air voids or relative density level during the compaction itself, thus under-compacted spots, if any, remain undetected. Intelligent compaction methods are able to continuously monitor the air voids or density of asphalt layers during the compaction process. The University of Oklahoma has developed an intelligent compaction analyzer (ICA). The ICA is based on the hypothesis that the vibratory roller and the underlying pavement form a coupled system whose response during compaction is influenced by the stiffness of the pavement layers. The ICA is capable of generating as-built maps providing information on coverage and quality of compaction of the compacted asphalt layers. This paper discusses the principle of ICA, and its application in measuring the density of asphalt layers. Results from one demonstration are included in this paper. The ICA measured densities were validated by comparing them with densities obtained from cores. It was found that the ICA measured densities and core densities correlated well with an R² between 0.85 and 0.93. Also, t-test conducted with the ICA-estimated densities and core densities verified that the difference between the above-mentioned two types of densities are insignificant at 95% confidence level. ICA was able to detect several under-compacted spots which were then remediated with additional roller passes. The application of the ICA certainly helped in achieving higher and uniform density throughout the test section.