Abstract
This paper is aimed at assessing the in-service performance of asphalt pavements in tropical climate under severe conditions. The main defect observed on the asphalt pavement was rutting of the asphaltic surfacing, with top-down cracking being experienced on a few sections and not widespread but rather intermittent. Field and laboratory investigations were conducted as well as a review of design and construction records. The defects observed were confined to the wearing course layer of the surfacing with the other underlying layers performing well. Rutting was a result of heavily loaded trucks that moved at very slow speeds due to steep gradients, hence resulting in severely loaded sections. High temperatures due to the warm tropical environment exacerbated the situation and caused the asphalt to flow, hence resulting in rutting and deformation. Also, low air voids in the asphalt mix which were below the recommended design air voids specification aggravated the situation as well as the air voids after refusal density compaction being below the specified critical minimum of 3% after secondary compaction. Top-down cracking was due to binder age hardening and embrittlement resulting from overheating of bitumen during the construction process coupled with heavy truck axles and high tyre pressures. Defects observed, therefore, resulted from an unstable asphalt mix that was not suitable for severe loading conditions; hence, the asphalt concrete laid was out of specification. The Modified Marshall Mix Design method should be used for severe sites where slow speed or heavier traffic is expected.
Highlights
Majority of the paved road network worldwide is comprised of bituminous pavements because they largely provide a safe, long-lasting, and comfortable surface capable of adequately performing over its design life with minimal maintenance
It can be concluded that the cracking observed on a few sections of the road resulted from binder ageing due to overheating of bitumen during the construction process coupled with heavy truck axles
Defects experienced on Kampala–Masaka road have been investigated in order to come up with appropriate measures to rectify them. e main defect observed on the road was the rutting of the asphaltic surfacing
Summary
Majority of the paved road network worldwide is comprised of bituminous pavements because they largely provide a safe, long-lasting, and comfortable surface capable of adequately performing over its design life with minimal maintenance. Is negatively impacts on the economic performance of developing countries and results in direct costs to taxpayers through rising costs of deferred work or through a stopgap approach that does not represent good value for money in the long term. One of such roads on the paved national road network in Uganda that has experienced early pavement deterioration is Kampala–Masaka road. Advances in Civil Engineering e construction of the trunk road which started in 2009 was completed in 2015 It is surfaced with 130 mm asphalt concrete comprising of 80 mm and 50 mm binder and wearing courses, respectively. The road that was designed to last 20 years has experienced significant defects in less than 5 years after completion including rutting, deformation of the road surface, and cracking
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