Glynn Holleran

Bitumen performance and chemistry in solvent refined bitumen blends

In years gone past most oil companies in Australia and New Zealand (NZ) developed experts that bridged the divide between refining and paving. This was supported by laboratories in Australia and sometimes Asia. This is no longer the case and many refineries have ceased bitumen production or closed. With the market moving towards imports and control to supply companies disconnects on bitumen passing a national specification and performance on the road. This reduces both durability and increases costs. This has been addressed by development in NZ of a performance specification for hot mix asphalt binders (including modified) and work being done on sealing grades. This paper discusses the development of the HMA specification with respect to crude sources and the development of methodologies to assess imported binders for suitability in all applications including emulsion. The conclusion is that bitumen quality may be maintained by use of these methodologies that include, chromatographic analysis, measurement of thermodynamic internal stability (Heithaus), aging, and Dynamic Shear Rheometry testing and mix performance testing in the laboratory. This forms a regime capable of use in any context and this leads to better durability of surfaces and extended service life.

Improving Recycled Asphalt Mix Performance Through Rejuvenation

Developing technologies that provide sustainable solutions for future pavement construction is vital given the ever-increasing demand on the supply of bitumen and good-quality pavement construction materials. Recycled asphalt pavement (RAP) is a technology that presents many advantages in cost and environmental savings. This study investigated the performance of RAP mixes containing rejuvenation additives to determine the effects of those additives on the deformation (rutting) resistance, cracking resistance, and fatigue performance of RAP mixes. Laboratory testing was conducted on 11 RAP mixes that were manufactured with RAP proportions of 15% and 30%, as well as with the addition of different types of rejuvenating agents. Results produced useful performance indicators for the use of rejuvenation additives in RAP. The mixes that had rejuvenation additives preserved the high deformation resistance of RAP mixes, particularly at the higher RAP proportion of 30% when compared with a mix with no RAP, and concurrently the addition of rejuvenators counteracted against overstiffening effects of RAP. The addition of RAP, especially 30% RAP proportion, had poorer fatigue performance than when only 15% RAP was used, but with the use of rejuvenation agents, the fatigue performance of the high RAP mixes improved significantly. Use of a maltene fraction for RAP rejuvenation had marginally better fatigue performance than a chemical rejuvenation agent. The research results provide a valuable understanding of the behavior of RAP mixes and, in particular, the positive performance results that can be gained by using rejuvenation additives.

Using Multiple Investigative Techniques to Assess Flushing of Chip Seal Surfaces

Flushing is a defect that has a damaging effect on the functional performance of chip seal pavements. The reported study was conducted to develop techniques to identify and assess flushed pavements effectively. The main aims of the study were first to investigate the effects of chip seal volumetrics on development of flushing and second to develop a model to forecast flushing of chip seal pavements. The study methodology consisted of mechanical testing of chip seal pavement samples and analysis of pavement performance data. Laboratory testing was conducted on samples obtained from flushed chip seal pavements from four regions in New Zealand. Samples were loaded by using a wheel-tracking device, and imaging techniques were used to assess the effects of micromechanical changes on development of flushing. Data analysis was performed on pavement condition data to identify factors providing the best prediction of flushing, and regression analysis was performed to develop a model to predict the initiation and progression of flushing. Study results revealed a direct relationship between flushing and reduction in air void volume that occurred as a result of loading. Data analysis revealed that the combination of factors providing the best indication of flushing was surface thickness, surface age, rut depth, and grade of aggregates. The flushing initiation model had an accuracy of 76%, and the flushing progression model was robust at predicting the quantity of flushing. By using the study outcomes, a pavement condition assessment guideline was developed to aid with assessing and managing flushed chip seal pavements.