Influence Treatment in Laboratory of Stone Surface on the Surface Roughness

Adhesion properties of asphalt mixtures are very important. Especially for porous asphalt adhesion problems are immediately a possible cause of low durability. At Delft University of Technology, research on the adhesive zone between the bituminous mortar and the stone is in progress. Small test specimens were produced and the aggregates received all kinds of treatments (sawing, coring, sandblasting, etc). An important question is if these test specimens are representative for the actual surfaces of the aggregates in the mixture. In this paper the possible influence on bitumen-aggregate adhesion of different stone surface characteristics is discussed. For this purpose, roughness tests are conducted on treated aggregate surfaces for columns used in the laboratory tests and the real stone particles as used in mixtures. Roughness (stereo-, confocal, and electron microscope), specific surface area (stereo- and confocal microscope), and surface free energy (sessile drop) are determined. It is concluded that sawing and sandblasting influence the roughness strongly compared to the aggregate surface. Also, the specific surface area of 4/8 aggregate is much larger than of the treated specimens. It is important to take this in consideration when using test results.