The lifetime of Porous Asphalt (PA) can be extended by doing preventive maintenance by means of rejuvenation products. The Dutch Road Authority for highways, Rijkswaterstaat (RWS), has constructed several test sections and monitors the development of stone loss by using the DOS/LCMS system. The monitoring runs now for 9 years and shows that in sections treated with rejuvenation products the development of raveling of PA16 is delayed for at least 3 years compared to non-treated sections. For 2-layered PA, 2LPA8 no raveling has been seen, thus no delay has been (yet) observed. Samples have been retrieved from drilled cores, which have been investigated by Rotating Surface Abrasion Test for stone loss, aging and erosion of the mortar. The results of the research are discussed. It is concluded that the method of investigation by taking cores arbitrarily on project level poorly reflect the average stone loss in a 100 m section.