Research On Pavement And Mechanical Performances Of Stress Absorbing Layer Asphalt Mixture

Reflective cracking is one of the main disasters for semi-rigid asphalt pavement and asphalt concrete overlay. It is the effective measure for preventing reflective craking to set stress absorbing layer between semi-rigid base course and asphalt overlay. The performance of the stress absorbing layer asphalt mixture is the key factor to prevent reflective craking. Based on the function characteristics of the stress absorbing layer, the stability rubber-modified asphalt and stress absorbing asphalt mixture were researched and developed in this paper. The main researching contents include the following aspects.Firstly, the analysis and evaluation of pavement performance for the stability rubber-modified asphalt and stress absorbing asphalt were carried out according to asphalt conventional and SHRP experimental results, which were compared with Qilu 70# asphalt experimental data. It was found that the performance parameters of the stability rubber-modified asphalt and stress absorbing asphalt are superior to those of Qilu #70 asphalt. PG grade of the both asphalts is up to PG76-28. The above asphalts have better regional suitability and usability than Qilu #70 asphalt. The storing stability of the rubber-modified asphalt is very good. The viscosity is low for the stability rubber-modified asphalt, which has good workability.The design of mix proportion of stress absorbing layer asphalt mixture was operated. The oil-to-stone ratio,8%, and void content,2.0%～2.5%, were achieved when Qilu 70# asphalt, stability rubber-modified asphalt and stress absorbing asphalt were used as asphalt binders, respectively, for the same gradation of "AC-5 fine". Other volume indices are also satisfied with specification requirmets.Secondly, the experiment research on pavement performances were carried out for the above three types of stress absorbing layer asphalt mixture. The experiment results showed that the performance of stability rubber-modified asphalt and stress absorbing asphalt mixture, compared with that of ordinary asphalt mixture, were improved obviously. The dynamic stability of rubber-modified and stress absorbing asphalts were increased 4.7 and 9.5 times, respectively. The bending and tension strains under low temperature were raised 29.2% and 26.7% for the modified asphalts, rspectively. The freeze-thaw split strength ratios (TSR) of the modified asphalts were comparatively enhanced 6.3% and 13.9% with TSR of ordinary asphalt, separately. The fatigue performance of rubber-modified and stress absorbing asphalts were increased 96% and 318%, respectively. The rubber-modified and stress absorbing asphalts have superior characteristics of high temperature stability, low temperature anti-cracking, water stability, and anti-fatigue performance to ordinary asphalt. The comprehensive performance of stress absorbing asphalt is the best, while the ordinary asphalt mixture is the lowest, among these materials.The third part of the research is the analysis and evaluation on mechanical performances for stability rubber-modified asphalt, stress absorbing asphalt, and ordinary asphalt mixture. The dynamic modulus main curves, the phase angle main curves and the shift factors of time-temperature were presented, respectively, according to viscoelasticity principle and the results of dynamic modulus tests. From the experimental data, the conclusion that the performance of rubber-modified and stress absorbing asphalts mixture is superior to that of ordinary asphalt mixture is verified furtherly. The evaluation of these materials is consistent with the results of rutting test and freeze-thaw split test, etc. The parameters, such as dynamic modulus main curve, shift factors of time-temperature, and phase angle main curve, obtained from the corresponding experiments, can be as the basic input parameters for mechanical response analysis of the asphalt pavement.Finally, the anti-cracking effect of three materials was analyzed according to finite element method (FEM). The numerical results showed that the effect of stress absorbing layer on dissipation and weakness of stress concentration on the cracks is noticeable, while the rubber-modified and stress absorbing asphalts superior to ordinary asphalt mixture.