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Title: Characterisation of the damage of bituminous materials prepared with warm mix asphalt additives
Author: Sadeq, M.
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Warm mix asphalt (WMA) is a relatively new technology that allows asphalt mixtures to be mixed and compacted at lower temperatures than the conventional hot mix asphalt (HMA). Previous WMA investigations have predominantly been limited to basic performance indicators and properties, especially in the Middle East region. Implementing the WMA technology in the asphalt pavement industry in the State of Qatar requires investigation of material properties and performance under the prevailing climatic conditions in the country. This study provides a fundamental material evaluation of WMA material damage using advanced testing and analysis approaches. The results led to a conceptual understanding of the impact of WMA additives on asphalt materials’ performance. It was found that Sasobit is the most effective WMA additive, as it increases the material’s (bitumen and mastic) stiffness, enhances resistance to rutting, and causes a reduction in the ageing effect on fatigue. The study also evaluated the impact of ageing on WMA material damage. Fine Aggregate Mix (FAM) samples were placed in an accelerated weathering machine that was controlled to simulate the climatic condition in Qatar (UV light and heat). The samples showed significant changes after ageing in the weathering instrument. The aged FAM samples were then subjected to repeated creep and recovery testing and the performance of the material at different ageing levels was studied. The results showed that the Sasobit mix had the highest ability to recover damage induced during the loading period. The results showed a high correlation between the recovery modulus of the material and the reduced damage captured during the unloading. In order to further characterise damage, air void sizes in the asphalt mixture before and after adopting the repeated creep and recovery test were examined by scanning them using the X-Ray CT system. The air voids of the control mix (without any WMA additives) iii showed a remarkable change after the repeated creep and recovery test; however, all WMA samples had lower air void sizes and minor changes after testing. The CT imaging also confirmed that ageing using the UV light has an insignificant impact on air void changing before and after the repeated loading test. The results confirmed the benefits of implementing the WMA technology in the asphalt industry in the State of Qatar. This is particularly the case for Sasobit, which showed significant improvement in the performance testing results in comparison with the control mix and other WMA additives.
Supervisor: Al-Khalid, H. K. ; Masad, E. M. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral