UNBOUND AGGREGATEBASE COURSE CONSTRUCTION PRACTICES IN RELATIONTO PAVEMENTQUALITY IN HAWASSACITY

Abstract

Sub-standard quality unbound aggregate base course layers are prevalent in Hawassa city with the major cause often placed on inadequate construction practices. In this study, unbound aggregate base course construction practices in Hawassa city were investigated. The objective was to relate the potential effect of the practices on pavement quality. Data and information on unbound aggregate base course construction practices were collected through a questionnaire survey and observation of practices at a number of sites where base course layer construction works were on-going. In addition, laboratory and field tests on base course aggregates and base course layers respectively, were carried out on selected road construction projects. The results indicated that unbound aggregate base course construction practices in City do not exhibit existing advancements within the road paving industry and are partly to blame for the quality deficiencies associated with road pavements. Several benefits of current advances in the unbound aggregate base course construction such as the use of either a batch or a continuous type mixing plant, self-propelled paving machine (Paver), material transfer vehicles, stringent quality control and proper material selection, handling and storage at all stages were not appropriated. More importantly, the absence of strict follow-up and supervision for rejecting segregated and sub-standard pavement sections was the main factor worsening the problem. In principle, absence of strict supervision and adherence to the standards allows poor construction practices to prevail and provide no inspiration for contractors to pursue high construction quality because doing so entails extra cost and contractors do not suffer penalties for substandard works. Therefore, to improve the city’s road pavement construction practices and hence to improve the quality and durability of road pavements in Hawassa, strict follow-up and supervision for road construction, adherence to the standards, improving the capacity of contractors and adoption of innovative performance based contracting arrangements are necessary