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Title: A study of the effect of aggregate on the wet skidding resistance of micro asphalts
Author: Ellis, R. B.
Awarding Body: University of Ulster
Current Institution: Ulster University
Date of Award: 2009
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Micro asphalt is a combination of nominal 6mm aggregate, bitumen emulsion, Ordinary Portland Cement (OPC), water and additive. This is mixed cold and applied in-situ by a purpose- built paver as a thin layer. The process meets many of the ideals of sustainable highway construction. The UK highway surfacing industry is dominated by hot mix asphalt types and a specification that asks for high skid resistant aggregate and texture depth to ensure wet skid resistance. Hot mix asphalt materials can result in a larger carbon footprint compared to micro asphalt. Production, transportation and installation of hot mix materials use higher amounts of energy compared to cold applied micro asphalt. Recent research has questioned whether there is the need to use limited reserves of high skid resistant aggregate in mixes with high texture depth that may generate excessive noise. It has been suggested that the use of smaller sized aggregate of lower skid resistance may provide acceptable levels of wet skid resistance by offering a greater number of contact points with a moving tyre compared to larger stone sizes. This argument formed the basic aim of the research reported in this thesis i.e. to assess whether the use of smaller sized mid range PSV aggregate in smaller carbon footprint micro asphalt would provide acceptable levels of wet skidding resistance. The research methodology has provided the opportunity to gather new data from a range of sources. It has developed new laboratory test methods to assess smaller sized aggregates and micro asphalt surfacing mixes. It has resulted in the first full-scale micro asphalt road trial in the UK to assess differing aggregates in the provision of wet skid resistance. This trial has allowed the development of micro asphalt early life skid resistance to be studied for the first time in detail over a 2-year period. The trial has also' facilitated the first UK SCRIM/GripTester skid resistance measurement correlation study for micro asphalt. The research has provided improved understanding of the role of 2.8-6.3mm porphyritic andesite aggregate in micro asphalt for the provision of wet skid resistance and made significant contributions to knowledge. Both the laboratory and full-scale A26 road trial concluded that the different aggregate combinations used provided a durable surface and safe highway surface. The use of high PSV natural aggregate and the addition of imported calcined bauxite did not cause wet skid resistance to be significantly improved indicating that the mid range skid resistance aggregate offered acceptable performance i.e. a more sustainable use of natural resources. The micro asphalt mixes were found to offer immediate high levels of early life skid resistance and not suffer from early life issues of lower wet skid resistance experienced by some types of hot mix asphalt. The SCRIM / GripTester trial carried out with TRL found that data from the A26 trial followed almost the exact same trend from the 2005 correlation study. This allows the data from the A26 road trial to be quoted as equivalent SCRIM data if required and lets those involved in measuring skid resistance using GripTester know that it behaves in a similar manner. The research concludes that the use of small carbon foot print surfacing materials such as micro asphalt offer considerable opportunity to the UK highway industry in providing a safe, durable and sustainable surfacing material, while showing that there is a modest reduction in greenhouse gas emissions, primarily due to a reduction in travel distance for the micro asphalt material.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available