Characterization of in Situ Modulus of Asphalt Pavement and Its Relation to Cracking Performance Using SASW Method

Asphalt material is generally characterized by the modulus, whose change and decay under the same condition could be considered an indicator of pavement performance deterioration. A nondestructive seismic method, the spectral analysis of surface waves (SASW), has been developed for assessing the in situ elastic modulus of the pavement material, which has some unique advantages compared to other methods. This study presents two case studies to evaluate the attenuation characteristics of the in situ modulus of asphalt pavement using the seismic-based SASW method and relate the reduction in modulus with pavement cracking performance. An accelerated pavement testing (APT) using an MLS66 facility study was first conducted on a newly constructed semirigid asphalt pavement test section to evaluate the attenuation of pavement modulus under accelerated loading. The SASW method was used to develop the characteristic dispersion curves for localized pavement sections and obtain the elastic modulus of each layer in different directions after the inversion analysis. In the second case study, the relationship between the modulus properties and the cracking distresses of the pavement was developed. It was found that the overall trend of modulus attenuation in the asphalt layer can be divided into four stages. The trends of variation were different in each asphalt layer and in different directions, which can be used to relate to damage occurrence. The modulus measured in the longitudinal direction was considered to be a better indicator of pavement deterioration in asphalt layers. In addition, based on the case study results, it was suggested that the potential modulus reduction rate for crack occurrence was approximately 40%-50%, which was consistent with the laboratory fatigue criterion of 50% initial modulus reduction. This study confirmed the feasibility of using SASW testing to monitor the attenuation of in situ pavement modulus and predicting impending cracks in specific asphalt layers.