ORIGINAL ARTICLE Evaluation of the effects of gyratory and field compaction on asphalt mix internal structure Panos Georgiou • Lazaros Sideris • Andreas Loizos Received: 4 September 2014 / Accepted: 8 January 2015 Ó RILEM 2015 Abstract This study investigates the effect of gyratory and field compaction on the internal structure of asphalt mixtures. For this purpose, three new full- scale pavement test sections with different HMA mixes were selected for sampling loose material and field cores. Loose material was compacted using the gyratory compactor and adjusting several parameters, namely the gyration angle, compaction temperature and specimen geometry. Internal structure of the gyratory and field compacted specimens was quanti- fied in terms of the aggregate contact points, orienta- tion and segregation by means of 2-D image analysis. From the laboratory investigation it was demonstrated that the gyration angle and specimen geometry significantly affected the internal structure. The results also indicated that the field compaction produced similar internal structure in asphalt pavements and, especially, compaction with gyration angle of 1.45 o best simulated the internal structure of field cores. Keywords Asphalt mixture Á Gyratory compaction Á Gyration angle Á Internal structure Á Image analysis Á Steel slag 1 Introduction Asphalt mix compaction has a significant influence on hot mix asphalt (HMA) performance. Hence, the challenge is to use a compaction method in the laboratory that accurately simulates field production and construction conditions. Over time numerous laboratory compaction methods have been developed and integrated in modern mix design methods attempting to prepare mixture samples that are repre- sentative of samples compacted in the field. Studying the relationship between laboratory and field compac- tion methods pavement engineers have long recog- nized that different laboratory compaction methods create volumetrically identical, but mechanically different specimens and hence density cannot alone characterize asphalt mix performance. While yet no consensus has evolved as to which laboratory method best resembles field compaction [2, 9, 13, 17, 22, 26], there is agreement among researchers that the com- paction method has a direct impact on the aggregate structure within the compacted mixture and hence characterization of internal structure of asphalt mix- ture is needed [11, 12, 24, 25]. Previous researches have demonstrated that asphalt mixture internal structure, which refers to the distribution of aggregates and their associated voids, can be charac- terized using imaging techniques [11, 14, 15, 19, 27]. With advancements in technology, the capabilities of these techniques in terms of image capturing, processing and analysis have been improved significantly over time, P. Georgiou (&) Á L. Sideris Á A. Loizos Laboratory of Pavement Engineering, School of Civil Engineering, National Technical University of Athens (NTUA), Athens, Greece e-mail: georgp@central.ntua.gr Materials and Structures DOI 10.1617/s11527-015-0528-3