Influence of compaction effectiveness on interlayer bonding of asphalt layers

The paper presents the results of research on the interlayer bonding of asphalt layers compacted in the laboratory and in the field. To measure the interlayer bonding at a temperature of 20 degrees C the Leutner test apparatus was used and load was applied at a rate of 50 mm/minute. Three types of interlayer interfaces were tested: no tack coat and tack coats made of two types of the pure bitumen emulsions. Four compaction techniques were used in laboratory conditions: rolling with and without vibrations, gyratory compaction and compaction with slab compactor, including both hot-to-cold and hot-to-hot. The fields specimens cored from pavements differed in terms of relative compaction. It was found out that interlayer bond strength between the layers of asphalt dependeds strongly on the applied compaction technique, as well as the compaction effort. In some cases efficient compaction produced a maximum shear force without tack coat. The type of emulsion used as the tack coat was also found to be highly relevant to the interlayer bonding.