M.Sc Student | Piotrekovsky Lior |
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Subject | The Influence of Air Voids on the Characteristics of an Asphalt Mixture under Cyclic Loading |

Department | Department of Civil and Environmental Engineering |

Supervisors | Dr. Arieh Sidess |

Professor Tomer Toledo | |

Full Thesis text |

Asphalt mixtures are heterogeneous material composed of three main components: graded aggregates, binder (bitumen), and Air Voids (AV). The Air Void Content (AVC) in the asphalt mixtures is one of the key factors which significantly affect the pavement performance throughout service life. The AVC is determined by the level of compaction and many pavement agencies using it as the first pavement’s design input. In order to avoid different pavement distresses, it must be determined that the AVC will not be too high or too low. It is known from the literature that at low AVC (less than 2%) the binder almost totally fills the voids space between the aggregate particles, so that the mix acts as a fluid and it less resistant to rutting when subjected to heavy traffic. High AVC (more than 6%) is associated with permeability of water and air, resulting in moisture damage, oxidation, raveling and cracking.

Evaluation of the effect of AVC on asphalt mixture performance in terms of dynamic modulus, permanent deformation and creep compliance are the objectives of this thesis work. Therefore, asphalt specimens with three level of AVC - 3%, 4.5% and 6% were compacted using the gyratory compactor. Each sample was tested through three laboratory tests: Dynamic Modulus, Creep - Recovery and Permanent Deformation tests.

Under the assumption of linear viscoelasticity, mathematical relationships exist between different material properties. There is a great importance to apply precise interconversion Procedure from one material property to another. Such a procedure can save time, money and provide properties which are difficult to obtain directly from experiments. In the frame of this research, the possibility to calculate the relaxation modulus using the dynamic modulus and the creep compliance results are presented.

The comparable results indicate that: (1) The smaller the AVC the higher the dynamic modulus values at all the loading frequencies and temperatures. An increase of 1.5% AVC by volume leads to decrease in the dynamic modulus by approximitly 18%. (2) The smaller the AVC the higher the resistance to permanent deformation. Reduction of 1.5% in the specimens AVC reflected in approximately 3 times greater and 2.5 times greater . (3) The smaller the AVC the smaller the creep compliance. Reduction of 3% in the specimens AVC lowers the creep compliance by nearly 2 times. (4) The smaller the AVC the higher the correlation of the relaxation modulus. (5) An efficient numerical method of interconversion between linear visco-elastic functions is presented.