Study of properties of sand asphalt using a torsional rheometer



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Texas A&M University


The modeling of Sand Asphalt and experiments to measure their rheological properties are of vital concern to many industrial processes especially highway and roadway pavement construction industry. A variety of hot mix asphalt mixtures are used in highway and runway pavement construction, with each mixture catering to a specific need. These mixtures vary in type and percentage of aggregates and asphalt used and consequently exhibit marked differences in their response. The main thrust of this research is to provide experimental data which would be helpful in determining the efficacy of the constitutive models that have been developed for these hot mix asphalt mixtures. Here we attempt to provide experimental data in the raw form for Sand Asphalt mixtures that would be helpful in the theoretical modeling efforts involving asphalt materials using a continuum point of view. For example the data obtained can be of immense help to evaluate the constitutive model developed by Murali Krishnan and Rajagopal. The Sand Asphalt mixture in their model is modeled as homogenized' single constituent due to the peculiarity of its makeup. The constitutive model of Murali Krishnan and Rajagopal is based on a thermodynamical framework for materials possessing multiple natural configurations (multiple stress free states) to derive the constitutive equations. Recently an Orthogonal Rheometer was built to characterize the granular solids by Gupta and Rajagopal which was later used by Baek in the torsional mode. In this work we have used the same Torsional Rheometer with some minor modifications in the design to measure some general properties of Sand Asphalt mixtures. Sand Asphalt mixtures, due to their non-linear viscoelastic character, exhibit normal stress effects' and `stress relaxation'. The Rheometer that we used was able to capture these responses with high precision. We have laid out proper procedures for the further testing of asphalt related mixtures. A typical sand asphalt mixture sample in cylindrical shape was used as the test specimen. From this work some interesting data was obtained. A remarkable observation was that as the shear rate is increased, the normal force and torque generated initially decrease, but beyond a certain shear rate they attain a constant value.