Study the effect of wax on bitumen and bituminous mixes

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Study the effect of wax on bitumen and bituminous mixes

 

Author: Lee, Hong-nin
Title: Study the effect of wax on bitumen and bituminous mixes
Degree: M.Phil.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Bituminous materials
Bitumen
Department: Dept. of Civil and Structural Engineering
Pages: xvi, 177 leaves : ill. (some col.) ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2393044
URI: http://theses.lib.polyu.edu.hk/handle/200/5956
Abstract: Wax naturally exists in crude oil from which bitumen is produced, and it crystallizes on cooling and melts on heating. Wax in bitumen affects the performance of bituminous materials on roads. Bituminous mixes with high wax content tend to become soft leading to rutting problem on pavement under hot weather and brittle in cold seasons. The road length in Hong Kong is about 2,000 km and about 75% of the road network is of flexible construction consisting of multi-layers of bituminous materials. Bitumen is one of the main constituents used in the bituminous layers giving the performance to sustain design traffic loading. The use of Penetration-grade 60-70 bitumen has been set as a standard requirement in the local specifications. Though basic tests on bitumen are required to verify its physical properties, no test for determining the wax content is specified and hence it is unable to assess the effect of wax content on the quality of the bitumen. The study aims at investigating the effect of the wax content on bitumen and bituminous mixtures by means of performance-related tests with a view to reviewing the local specifications of bitumen. It also provides basic information and paves the way for developing performance specifications for bitumen and further research on bitumen and bituminous materials. This study investigates the physical and rheological properties of seven sources of bitumen of similar Penetration-grades but of various wax content levels. Two typical bitumens of different wax contents were then selected for preparing bituminous mixes according to the local mix design for further tests on their mechanical properties. The evaluations were twofold. Firstly, a comparative study on the physical properties, wax content and rheological properties of bitumen was made. Secondly, the mechanical properties of the two bituminous mixes including stiffness, strength and resistance to performance deformation were compared for verifying and supplementing the findings of the first stage. The results show that though all seven bitumens are of Penetration-grade 60-70 and satisfy the requirements of the local specifications, they have different levels of wax content and rheological properties. In other words, the basic tests in the local specifications fail to assess the effect of wax content on the performance of bitumen. In addition, the test results for the two bituminous mixes indicate that the mix made of bitumen with lower wax content exhibits better performance in the mechanical properties. The local road authority should review the bitumen specifications and specify appropriate requirements on the wax content or Performance-grade with a view to ensuring that the bitumen to be selected for producing the bituminous mixes is able to provide the required mechanical properties and to prevent inferior performance and premature defects during the service life. This study also recommends a large-scale field trial by the use of accelerated pavement tester.

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