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Title: Influence of polymer modification on cracking and fatigue of asphalt mixtures
Author: Lancaster, I. M.
ISNI:       0000 0004 6059 1594
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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Efficient road networks are an integral aspect of the transport infrastructure of any modern economy and sound pavement design, along with effective maintenance programmes, are crucial to the continued quality and value of these assets. Polymer modification of the asphalt is frequently used to enhance the pavement durability performance. However, the benefits of polymer modification are not always clear to the designing engineer. Laboratory tests to assess asphalt performance often require large quantities of material, highly specialised test equipment and considerable amounts of time. Whilst the advantages of polymer modification on deformation resistance are well accepted, its impact on cracking and fatigue is less well defined. This research was therefore undertaken to quantify the effect of polymer modification on the cracking and fatigue performance of asphalt, and to develop methods to minimise the time and materials required to perform the laboratory assessments. A novel technique to analyse the performance of full asphalt mixtures utilising a standard laboratory dynamic shear rheometer (DSR) was developed using very small sample sizes. The technique was validated by comparing the results to existing testing geometries, with the new method shown to depict the viscoelastic behaviour of the asphalt. The asphalt’s fundamental fracture mechanics properties were investigated via the semi circular bending geometry, with the improved performance of the polymer modified asphalts in terms of fracture toughness and strain energy release rate demonstrated. A crack growth law based on the generalised J-integral was developed and used to determine characteristic material parameters which were used to predict pavement service life. Crack propagation of the semi-circular bending geometry under monotonic loading was modelled using the Extended Finite Element Method with the time dependent viscoelastic properties within the model determined using the small sample size technique, and modelled using a fractional viscoelastic element. ii The calibrated model was used to predict the load-displacement behaviour of specimens, and the improved crack resistance of the polymer modified asphalts verified. Binder fatigue behaviour was analysed using the DSR and the improved damage resistance of increasingly polymer modified binders verified. Asphalt fatigue was assessed using traditional large scale trapezoidal two point bending, cyclic semi-circular bending and small specimen sized tests on the DSR with the effect of polymer modification evaluated. Viscoelastic Continuum Damage (VECD) theory was successfully applied to the results with the potential for significant reductions in test durations using this approach demonstrated.
Supervisor: Al-Khalid, H. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral