Potential improvements in montmorillonite-nanoclay-modified Cold-Mix Asphalt

Over the years, Cold-Mix Asphalts (CMAs) used principally for pothole patching and partial-depth repairs in Ghana have performed abysmally. Given the convenience, environmental friendliness and low cost associated with CMA production, the use of the material in Ghana is likely to continue for a long time to come. Therefore, to justify it continual use in road maintenance, especially pothole patching, the material must be improved in quality considerably beyond what currently pertains to achieve a more successful product. Fillers used in bituminous mixtures have been identified as having the potential to improve mixture properties positively. In view of this, in the quest to improve CMAs, montmorillonite- nanoclay filler (pulverized clay particles of size 1-100 nm) was incorporated in CMAs formulated from five dense gradation regimes adopted from the Asphalt Institute M-19 Specification. The nanoclay filler was added from 1-3% by weight of aggregate at 1% incremental levels. Using the Marshall Mix Design procedure, mixture properties (Stability, Flow, Optimum Bitumen Content and Voids) were accordingly determined. It was observed that when montmorillonite nanoclay was introduced as a filler in the cold mixes, all the gradation groups recorded improvements in their stability at each nanoclay content. At 2% nanoclay content, all the mixtures yielded optimum values. The increase in stability can be attributed partly to the increase in adhesion between bitumen and aggregate and also partly to the possible increase in inter-particle friction occasioned by the presence of the nanoclay particles which add to the rigidity of the compacted matrix. However, on the contrary, flow values increased significantly. In between the nanoclay contents, from 1-2% and 2-3%, average flow increased by 1.8% and 12%, respectively. The same could be said of the Optimum Bitumen Content which increased for all gradation groups when nanoclay was added. The increase in Optimum Bitumen Content can be said to be accountable for the flow increases realized for mixtures with nanoclay. Even though high stability reflects the bitumen binding strength and the internal friction, a benchmark of the interlocking and friction resistance of aggregates, the high flow values observed are also indicative of the potential susceptibility of the cold mixes to rutting deformation, especially at elevated temperatures.