Irina Holleran

Use of the Shear Box Compactor for Porous Asphalt Mix Property Assessment

The most commonly used compaction methodologies for specimen preparation for the assessment of porous asphalt (PA) mix properties are gyratory and Marshall. Even though several individual blocks prepared by one of these test methods are usually considered to be replicates, the heating and handling histories are never identical as these are individual specimens prepared at different times. In contrast, the Shear Box Compaction (SBC) technique allows fabrication of a single slab, at a given time, which is then used to extract multiple specimens that can be considered as true replicates. The SBC can offer significant advantages in preparation of PA specimens for various tests typically performed on gyratory or Marshall specimens. The recently released ASTM D7981-15 test method on SBC of asphalt mixes is written around compaction of dense-graded (DG) mixes, not PA mixes, even though the specific mix type is not stated in the test method. Furthermore, there is a very limited literature on the SBC, with most of the published work focusing on DG mixes. This paper aims to address this gap. In this study, the SBC was used for PA mix compaction with a nominal maximum aggregate size of 10 mm using two different types on aggregates and four bituminous binders. Slab preparation and specimen extraction methodology developed were discussed in details. Variation of the air voids (AV) between the replicate specimens extracted from one slab were within ±0.5% from the average AV value regardless of the aggregate or binder type, or slab height. The total variation of AV in all the 64 extracted specimens tested was 1.9%. This gives the confidence that performance testing such as Dynamic Modulus testing, which requires very stringent control of specimen dimensions, uniformity, and AV consistency among the replicate specimens, can be performed reliably on PA. Also, some recommendations were provided on the changes needed in the ASTM D7981 for PA compaction using SBC.

The Use of Automated Flocculation Titrimetry and SARA Analysis to Predict the Performance of Bituminous Binders in Asphaltic Hot Mix and Bitumen Emulsions

Bitumen is complex chemically, but its composition determines rheology. The Strategic Highway Research Program 1 (SHRP) developed a bitumen microstructural model that relies on the thermodynamic compatibility of the fractions (based on polarity) to create a thermodynamically stable continuum. This stability determines the performance of any bitumen in hot-mix and emulsion applications. Automated Flocculation Titrimetry (AFT) developed by the Western Research Institute (WRI) USA measures Heithaus parameters that define this stability. Chromatographic analysis, known as SARA (saturates, aromatics, resins and asphaltenes) provides a broad compositional analysis that may be used with hiethaus parameters to predict the performance of bitumen in mixes and emulsions. The methodology is based on work from the Western Research Institute at the University of Wyoming Laramie (USA) to measure the known Heithaus (stability) parameters accurately and reproducibly and is detailed in ASTM 6703. In this work, Reclaimed Asphalt Pavement (RAP) binders and virgin binders were examined by SARA analysis and AFT. The properties of the mixes made with these binders are determined and compared to the predictions. A set of emulsion binders with different SARA analysis were also examined for emulsability and the results compared to the AFT results.

Optimizing the durability of the coarse fraction of porous asphalt RAP for effective recycling

Porous asphalt (PA) durability depends not only on the binder used to manufacture the mix, but also on the aggregates chosen, particularly the coarse fraction component. Aggregates for PA should be of the highest quality and highly durable to withstand the effects of weather and traffic. To recycle PA into a new PA mix, without compromising the long-term performance, the durability of the recovered aggregates from PA-derived reclaimed asphalt pavement (RAP) should be assessed alongside the aged binder properties. In this study, the Micro-Deval (MD) Abrasion test, combined with water absorption, was found to be a good predictor of asphalt mix performance for PA. Minerology of the aggregates is an important factor when setting limits for MD loss. New Zealand (NZ) aggregates are significantly younger in geological terms, and chemically and physically less stable compared to the aggregates used in many other countries. This is especially true for greywacke, the most used aggregate in NZ for road construction. If the MD limits reported in some literature are applied to NZ PA-derived RAP aggregates, poor performing material can be erroneously incorporated in asphalt mixes. Findings from this study contributes in understanding how PA-derived RAP can be recycled into new value PA mixes.

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.