Browsing by Author "Boateng, Kwadwo Appiah"

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    Towards Improved Quality and Performance of Cold-Mix Asphalts for Bituminous Pavement Maintenance in Ghana
    (KNUST, 2023-02) Boateng, Kwadwo Appiah
    Premature failure and poor performance of cold-mix asphalts (CMAs) used in pothole patching and sectional repairs on bituminous roads are very common in Ghana, and yet, for a long time, the problem has remained unaddressed while the material continues to be used. There is, therefore, the need to improve the quality of cold-mix asphalts used in the country in order to achieve a more successful and durable product in road maintenance. To this end, Ghana’s Ministry of Transportation (MOT) Standard Specification for Road and Bridge Works (2007) was reviewed alongside three foreign specifications on CMAs, namely, Asphalt Institute MS 19 (1997), Chevron USA Incorporated Procedure and Nikolaides Specification (1994), to establish possible commonalities and areas of deviations that could impact the field performance of the material. Also, samples from ready-to-use CMA stockpiles at six contractor sites across the country, and failed road patches were investigated. Further, a series of dense-graded cold-mix asphalts, with simplified material proportioning ratios, were proposed and investigated for adoption and use. Lastly, potential improvement in CMA properties, using montmorillonite nanoclay filler, was explored. It was established that Ghana’s MOT Specification lacked specificity and clarity on the subject of CMAs. In the case of the other Specifications, though variations in mixture design and testing protocols existed, there appeared to be a general consensus on the use of different aggregate gradation structures that lead to high field performance. The asphalt contents of the cold-mix asphalt samples taken from the field tended to range between 3% and 6%, with emulsion mixes having the lower values. In addition, the aggregate structures of the mixes were poor, consisted essentially of single-size aggregates with uniformity coefficient values that ranged between 1 and 4. Some specimens compacted in the laboratory disintegrated during conditioning for stability and flow test, suggesting a lack of stickiness and cohesion within the compacted matrix. It, therefore, appears that the early failures characterizing cold-mix asphalts used in maintenance works in the country could be due principally to inadequate aggregate structure and low binder content of the mixes. For improved cold-mix quality, five aggregate gradation blends that meet GHA dense grading requirements, together with the corresponding emulsionto- aggregate ratio, for easy material batching in the field, have been proposed. Montmorillonite nanoclay used as filler increased the optimum bitumen content and improved the stability of the cold-mixes but resulted in significantly high flows. This suggests that their use in cold-mix asphalts has the potential to induce plastic behaviour and render the mixes more rut-susceptible, especially at high temperatures.