NARC RESEARCH STUDENTSHIP #2

UNIVERSITY OF CAMBRIDGE
RESEARCH STUDENT: Mr Alex Ossa
START DATE: 1st October 2001
END DATE: 30th September 2004
FUNDING: NARC: £55,361

Project Description
An extensive experimental study of the monotonic, recovery and cyclic behaviour of two bitumens commonly used for pavement construction in the U.K. (50 pen and 100 pen) has been performed over a wide range of strain rates, stresses and temperatures.
The steady state monotonic and cyclic behaviour of the material were found to follow linear viscous relationships at low stress levels and power law relationships at high stress levels according to the Modified Cross Model (MCM).
The influence of the parameters affecting cyclic stress controlled behaviour of bitumen were also studied. From these experimental observations a visco-plastic model was developed. It predicts the overall deformation behaviour of pure bitumen for arbitrary loadings.
This model requires six material parameters which are easily found from monotonic creep and recovery tests. The model shows good agreement with experimental results over a wide range of loading conditions. The temperature dependence follows the Arrhenius relationship over the range of temperatures studied.
Figure (a) shows Monotonic tensile results for 100 pen bitumen at 0o C as continuous lines, and model predictions as dotted lines for different stresses. Figure (b) shows cyclic pulse experimental results and model predictions also for 100 pen bitumen at 0o C and two different time gaps Dg between pulses, with Dp = 12 s. The overall permanent deformation is predicted accurately in both cases.

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