Investigating the effect of pavement structural deterioration (cracking) on the surface of a bituminous pavement surface in Kampala
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The road network is the backbone of transport systems in Uganda. Road transport is the most dominant mode of transport and it accounts for over 90% of the cargo freight and passenger movement. The entire road network in Uganda totals to 144,785 km of this only5,100 km (4%) is paved, the rest being gravel or earth roads. Kampala (the study area) has an estimated road network of 2,110 km of which only 578 km is paved. One of the challenges faced by road users is cracking that affects the roughness of the road which is a measure of user comfortability. The cracking on the roads is caused by a number of factors including increasing traffic volumes (estimated at 6%) which lead to increased loading, climatic and environmental factors among others. When these roads are exposed to these factors, the pavements deteriorate faster resulting in poor road conditions during the time in which the road is in service, especially when maintenance interventions are not duly scheduled. This research was conducted to investigate the effect of pavement structural deterioration (cracking) on roughness of a bituminous pavement in order to determine at what point in time a pavement should be maintained. Measurements for cracks along the study roads were obtained, the IRI values estimated for the roads based on the obtained measurements. A roughness model was then used to obtain new IRI values for each of the roads and a trend for change in roughness determined. Environmental conditions were incorporated into the research by using an environmental coefficient that was given in the HDM– 4. It was observed that roughness of the roads increased over the years if cracks were left to progress further and become bigger and especially if these progressed into potholes. The rate of increase in roughness was also observed to be greater if the rate of incremental change in area of total cracking, ΔACRCA, was greater. That is to say, ΔACRCA=15%, for a period of 20 years, IRI for Makerere Hill Road increased from 2.5 to 3.5 for a period of 20 years, IRI for Kevina Road increased from2.5 to 2.58, IRI for Wavamunno Road increased from 3.0 to 3.56, IRI for Masiro Road increased from 5.0 to 9.48, IRI for Lubiri Ring Road increased from 5.0 to 34.47 and IRI for Sir Apollo Kaggwa Road increased from 3.5 to 9.48. it was noted that roads that have existing potholes deteriorated much faster than those without existing potholes. This can be attributed to the ingress of water into the pavement through the openings caused by potholes.