Variability in the determination of bulk and maximum density of hot mix asphalt

Abstract

Roads are a vital link, in particular in a country like Australia where distances are extensive. Western Australia is no exception, with Main Roads, Western Australia„s State road authority, managing more than 17,800 kilometres of highways and state roads with a large local government road network of almost 164,000 kilometres (Main Roads Western Australia 2011). For quality control measures, Main Roads Western Australia (MRWA) requires quantification of the variability of test methods to establish accepted parameters, and minimum and maximum air voids for the construction of dense-graded hot mix asphalt concrete. This is done to ensure correct design and quality control of the pavement, and to avoid the prospect of distress that could affect the expected service-life of the hot mix. Western Australia currently uses the Marshall method for hot mix asphalt design which is proven in the production of quality hot mix asphalt and from which long lasting pavement can be constructed. This method has been in use around the world for over 60 years.High quality and specific percentages of aggregates are then required for the durability and quality of the road. Therefore, the accuracy of the measurements of asphalt density hence the results are essential for the acceptance of the product. Payments are dependent on whether or not a certain asphalt density quality has been achieved. One form to measure this quality is by testing the volumetric properties of asphalt. However, it has been noticed in previous results that a high percentage of variability in the bulk and maximum density of the hot mix are present. This variability as a result have produced one of the major concerns in the asphalt hot mix industry, this is having a reliable density determination of compacted hot mix samples.Consequently, this research aimed to examine the possible cause/s of the differences in density determination of dense-graded hot mix asphalt concrete. This translated into a thorough evaluation of previous test results, performed through proficiency and inter-laboratory testing. Investigation and evaluation of the current methods specifically focused on temperature testing and the testing and analysis of the possible causes of variability in the determination of bulk density. Extensive testing was conducted, using MRWA standard methods to measure asphalt density. This involved observing and replicating the methodology established for standard methods. There was a modification to the method for the determination of maximum density and this will be discussed in the report. These factors were considered to be crucial in order to make a significant contribution to promoting and improving standardisation across the industry, and to ensure reliability and consistency in the determination of asphalt density, both bulk and maximum.