Feasibility of Deformation Strength for Estimation of Rut Resistance of Asphalt Concrete

There has been a need for developing a simple mechanical test method to estimate deformation resistance that can be used for estimation of rut tendency of asphalt mixtures. Some dynamic and triaxial tests are available for this purpose, but have limitations in their use due to complexity and high variation in output. Currently, one of the best ways of judging rut tendency is to run wheel tracking (WT) test. At high temperature, if the load and deformation at the limited area, where load is directly contacted, are properly considered, a strength measured thereby will have better correlation with rut parameters. Based on this assumption, a new approach is introduced for estimation of rut tendency. A static load through a round-edge loading head was applied to a Marshall-type specimen in the direction of compaction at 60°C, and the maximum load (P) and deformation (y) at the P were obtained. A strength value defined as deformation strength (SD) is calculated using , in which D is loading head diameter and r is radius of edge curvature. Regression analyses based on wheel tracking parameters showed that R2 for the depth of rut vs. SD is over 0.95 and R2 for the dynamic stability vs. SD is over 0.81 for data obtained using D=4cm with r=1cm loading head. Total mean R2 was over 0.87 for three loading heads and two aggregate mixes. This level of R2 is much higher than that of other static strengths of asphalt mixture. Therefore, if the SD value is higher, the mixture shows smaller rut depth and requires more number of repetition (cycle) for inducing unit depth of rut in WT test. This is a sign that the mixture with higher SD will perform better against rutting. Therefore, it is found that there is a good possibility of using SD as a relative index of rut estimation of the asphalt mixture.