Development of Dynamic Asphalt StrippingMachine for Better Prediction of MoistureDamage on Porous Asphalt in the Field

Stripping is a major source of pavement distress and takes place in the presence of moisture. Over the years, many laboratory tests have been proposed to evaluate moisture sensitivity of asphalt mixtures. This paper presents the development of a dynamic asphalt stripping machine (DASM) to realistically simulate stripping of porous asphalt mixtures subjected to the dynamic action of flowing water. To assess the effectiveness of the machine, two sets of specimens were prepared. One set was conditioned in the DASM by allowing water at 40oC to continuously permeate through the unextruded samples via water sprinklers at an intensity equivalent to 5400 mm/hr. The other set was stored under dry conditions at ambient temperature. Then, both sets of specimens were extruded and conditioned in an incubator before individually tested for Indirect Tensile Strength (ITS) at 20oC after 1, 3, 5 and 7 days. Resistance to stripping was evaluated from the ratio between ITS when tested wet and dry. Specimen permeability was also measure before and after conditioning. In addition, mortars that stripped from the asphalt samples were filtered on a filter material. The results showed that both ITSR and permeability reduces with conditioning time. The ITSR after 7-day conditioning was 17.2% lower than those conditioned for one day. The quantity of mortars collected on the filter material was found to increase with conditioning time. However, some stripped mortars were believed to be trapped in the mixture capillaries, and this explained the reduction in coefficient of permeability values over time.