Measurement of Bitumen Relaxation Modulus with Instrumented Indentation
Instrumented indentation testing was used to determine viscoelastic properties of bitumen, i.e. shear relaxation modulus. Review of previous studied reveals that indentation testing technique has been drawing increasing attempts in investigations of binder material mechanical properties. Various properties of bitumen, e.g. elastic, viscoelastic, have been successfully determined by indentation testing at different scales and test conditions. The response of bitumen to indentation was studied extensively under a wide range of test parameters such as temperature, loading rate, indenter geometry, etc. This experimental tool was also applied to asphalt cements grading and microstructure study. However, there have been limited numbers of studies at macro levels with the use of spherical indenters to characterize bitumen properties. This motivated the present study. Spherical indentations have been performed with balls of different curvature radii at -5
oC. Load – displacement curves have been measured and used to determine the relaxation moduli of the studied bitumen. Repeatability of the measurements has been evaluated. Obtained results were compared with the observations from DSR relaxation test. The influence of the measurement scale and load level on the results of instrumented indentation testing has been investigated.
It has been found that instrumented indentation was able to characterize accurately the viscoelastic behavior of bitumen which can be described by Prony series and agrees well with the results from DSR tests. Nevertheless, the elastic solution failed to produce a proper description of bitumen response during loading phase.
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