| Pavement structures are subjected to multiple dynamic effects, such as traffic loads and environment changes. Asphalt mix, as the main material for highway, is of typical viscoelastic properties. Its mechanic behavior is greatly affected by the changes of temperature and time. The mechanic responses of asphalt mix to dynamic load and static load are very different. Dynamic analysis of pavement structure and material is very popular, and dynamic modulus is adopted by AASHTO-2002 M-E methods for pavement design. Studying dynamic modulus based on real situations in China is of great significance.There are many ways to study dynamic modulus, in which two-point bending applies both flexural-tensile stress and shear stress on specimens, which is very similar to the real stress situation in pavement. M2 F is used to exert two-point bending on trapezoidal beam to study dynamic modulus, referring to EN. We also used SPT to do some contrastive study.This thesis reviewed the current research status of dynamic modulus in and abroad. Relevant concepts including viscoelasticity, TTS, and master curve were introduced.Four SAC asphalt mixes were designed. Trapezoidal beam and cylinder specimens were manufactured for M2 F and SPT, respectively. M2 F was used to carry out the two-point bending test on trapezoidal beams under different temperatures, load frequencies and strain levels. The influence factors of the dynamic modulus were analyzed, especially the impact of strain level on dynamic modulus. Master curves of dynamic modulus were plotted. With the consideration of strain level, master curve was expanded into master surface. SPT was used to do comparative dynamic test on specimens of the same gradations and materials as the trapezoidal beam. Master curve of dynamic modulus was also plotted.The two dynamic methods were compared and evaluated: SPT was recommended for dynamic modulus test for upper layers, while M2 F was recommended for middle and lower layers. |
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