Quality of cold-mix asphalt in bituminous pavement maintenance in Ghana: Preliminary indications

Prevalence of premature patch failures in bituminous pavement maintenance in Ghana, involving pothole and partial-depth repairs using cold-mix asphalt (CMA), has become a major concern as the failures call for repeated patching in the face of limited maintenance budget and repeated disruption to traffic. The most commonly documented failures associated with CMA patches in the country are disintegration, shoving, and dishing. All three failure modes suggest a deficiency in binder coupled with a weakness in aggregate functionality often attributable to a compromised aggregate skeletal structure lacking sufficient interlock/load-bearing ability resulting in a patch with no rigidity and stability. In this study, samples of stockpiled ready-to-use cold-mix asphalt concrete from six contractor sites and three failed patches from roads in the Ashanti, Volta, and Bono Regions in Ghana, were investigated to assess material quality. Bitumen extraction, aggregate gradation, stability, and volumetric analysis of compacted specimens were carried out on the samples. The results indicated poor CMA aggregate structure which consisted essentially of single-sized aggregates having uniformity coefficients between 4 and 6 and residual asphalt contents between 3% and 6%. All mixtures formulated using bitumen emulsion binder had values lower than those formulated with cutbacks and none satisfying specifications. Specimens compacted in the laboratory disintegrated during conditioning for stability and flow test, suggesting the absence of stickiness and cohesion within the compacted matrix. Our results suggest that pothole patching failures prevalent in the country may be blamed principally on inadequate aggregate structure and low binder content of the CMA mixes.