Experimental verification of the evolution of internal structure of asphalt and modified asphalt

Abstract

The complex nature of asphalt throws open challenges in terms of material characterization, pavement design and analysis procedures. This study is concerned with experimentally verifying the reversible changes in the material and we focus only on the mechanical properties. Two types of asphalt, unmodified parent asphalt and polymer modified asphalt were tested in a Brookfield programmable viscometer. The material was tested from 60 to 90 °C in increments of 5 °C. Each sample was tested before and after short term aging. The experimental plan consisted of subjecting the material to three continuous cycles of shearing, allowing the material to rest for one hour at the testing temperature after these three cycles and subjecting the material to one more cycle of shearing after rest period. The observations in terms of shear stress vs. time for the specific forward and reverse sweep revealed several interesting facts. The polymer modified asphalt shear thickened for every successive cycle before rest period in the temperature range of 60-70 °C. The same material however, started shear thinning beyond 70 °C. The rest periods had a significant effect on polymer modified asphalts. The change in shear stress for different shear rates varied for different asphalts (modified and unmodified, aged and unaged) used in the testing program. The experimental data reported here will not only help in clearly quantifying the changes in the behavior of the material during rest period but also the influence of modification and short term aging. It is also to be highlighted here that all the observations are in terms of raw experimental data without recourse to any model.