Evaluating the Use of Nanomaterials to Enhance Properties of Asphalt Binders and Mixtures

0-6854Traditional polymer modified binders are typically used to achieve a target performance grade (PG) and also to enhance resistance of the binder to distresses such as rutting, fatigue cracking, and low- temperature cracking. Conventional modifiers used with asphalt binders are often expensive and are not very effective to improve the low-temperature properties. Recent advances in nanotechnology have allowed for development of novel materials that can be tailored to deliver improvements in both high and low-temperature properties of the modified composite. Several existing studies have shown an improvement in the high temperature properties of asphalt binders due to the addition of nanomaterials. The main objectives of this study were to evaluate a number of different nanomaterials in terms of their ability to (i) disperse effectively in the asphalt binder at a nanometer length scale (as opposed to forming micrometer sized or larger agglomerates), (ii) provide beneficial effects in terms of high-,intermediate-, and low-temperature properties (or at least benefits in a certain temperature range without compromising the properties in other ranges), and (iii) provide a cost-effective solution to modify asphalt binders. Initially the study was focused on the use of carbon nanotubes. However, owing to the cost of these nanomaterials and based on a review of the literature, the study was expanded to include other nanomaterials. These were nanosilica, nanoclay, nanoalumina, and nanoglass. In an effort to improve dispersion, nanosilica was also surface functionalized using two different agents. Several techniques were used to evaluate the mixing conditions required to fully disperse nanomaterials as well as assess the extent of dispersion of these nanomaterials. Direct observations using SEM, AFM, and mechanical tests, complemented by indirect observations in reference solvents, show that in most cases nanomaterials do not disperse as nanometer sized particles but rather form agglomerates that are several micrometers in size. Under such circumstances, the benefits of using nanomaterials are rather limited. Amongst the nanomaterials used in this study, nanoglass was the only material that had maximum dispersion approaching a nanometer length scale, was cost-effective, and demonstrated improvement in mechanical properties as observed using the binder, mortar, and mixture tests. This study also presented procedures to rapidly evaluate whether dispersion can be achieved by the nanomaterials in an asphalt binder as a screening tool before subscribing to the use of such materials for material property enhancement