Too hot to handle, too cold to control - influence of compaction temparature on the mechanical properties of asphalt

Density is one of the most prominent measures for road quality. Often nuclear density measurements are taken during compaction operations. It is expected that the layer will reach the specified properties if the asphalt mixture is compacted within a desired temperature window. But what happens when the compaction process is undertaken outside of this ideal “temperature window of opportunity”? This paper deals with these questions and proposes a method to determine the optimal temperature and time frames to compact hot-mix asphalt. It demonstrates this procedure for one mixture by determining the influence of compaction temperature on the density and mechanical properties. The research project combined a literature review, laboratory-experiments, and data-collection on a construction project. In the laboratory a Roller Sector Compactor was used to compact 24 slabs at four different temperature windows and the mechanical properties were verified by the ITS-test (indirect tensile strength) and the CC-test (cyclic compression). On the construction project, three lanes were compacted within three different temperature windows. Paver and roller movements were tracked with high resolution GPS-technology and the asphalt temperature was measured with infraredcameras, thermocouples and an infrared laserlinescanner. The results of this study show that while similar densities can be reached for all temperature windows, other mechanical properties such as tensile strength and fracture toughness may suffer. This means in quality control that it is not sufficient to only check and steer on density, but also the compaction temperature and the representative properties should be taken into account.