Ageing Prediction of Porous Asphalt

In order to be able to make a realistic life cycle analysis for porous asphalt (PA) surface layers, it is very important to be able to predict the PA surface layer properties during service life. As ageing of these very high voids content mixes will change properties dramatically and initiate ravelling as the major cause of failure, in depth knowledge of the field ageing of a PA layer is needed. In this paper a study is reported to develop a laboratory ageing procedure for PA mixtures. The aim was to realize approximately 10 years of field ageing in 10 days in a laboratory ageing procedure with standard laboratory equipment. Conventional empirical (penetration, softening point ring and ball), sophisticated fundamental rheological tests (DSR), chemical tests (FTIR) and adhesion tests (Wilhelmy plate) were conducted on binders recovered from field cores and on binders recovered from specimens aged in the laboratory. Several ageing methods were tried, resulting in two promising ageing procedures: one for the mortar in PA and one for the loose PA mix. To accomplish the same ageing of the bitumen as for a 10-year period in the field, the mortar has to be heated in an oven for 2 hours at 165°C and then be placed in a PAV at 90°C for 7 days under air pressure of 2.1 MPa. The loose PA mix was heated for 44 hours at 135°C to accomplish the same degree of ageing.