Investigating the effects of Axle loading on initiation Ravelling.

Abstract

Uganda’s total road network in is estimated to be 129,469 Km long. Of this, the community access roads constitute 50%, district roads 26%, urban roads 7% and national roads 17 %. Between 2010/11- 2014/15, the stock of paved road network increased by 19.7% from 4,364 to 5,224 Km. National paved roads increased by 21.7 % in the last five financial years (from 3264.1 to 3981 Km). There are approximately 800,000 vehicles in the country, with a potential of additional 20,000 vehicles per year. This increase in the traffic has led to rapid deterioration of the roads leading to reduced service life. According to a recent economic evaluation study (UNRA, 2008), it is estimated that over 13.3% of the road life (2 years of the design life) is lost because of transporting heavy cargo on roads in Uganda. It is estimated that over US$200 million is lost annually in road deterioration. (http://www.sgr.go.ug, n.d.). There has been a decreased budget for road maintenance from 417.84 billion in FY2016/2017 to 417.39 billion in FY2017/2018. (Ministry of Works and Transport, 2018). This was compounded by the increase in road network maintenance needs driven by growth in traffic volumes, traffic loading, and maintenance backlog as well as inclement weather. The UNRA strategic plan for 2008 – 2013 asses the annual maintenance need for national roads at US$ 100.0 million in 2008/2009, rising to US$ 121.0 million by 2013/2014. The need is then estimated by NTMP to reach US$ 160.0 million by 2018/2019 (C.Kagina, July 20, 2017).The annual budget allocations are insufficient to cater for this demand. This research was therefore carried out to investigate the impact of Axle Loading on initiation of ravelling on bituminous pavements. Traffic counts were carried out manually using MoWT manual tally sheets and this exercise was conducted for seven days along Busega- Masanafu and Banda Central road. The traffic data showed differences in traffic volumes and axle loadings. The study determined the Construction Defects Indicator (CDS) for the pavement basing on bitumen content. The study established the difference in initiation period to ravelling of the two pavements. Busega – Masanafu was estimated to start ravelling at a period of 1 year and 9 months and Banda Central at 14 years with loadings of 1.999 MESAL/lane/year and 0.0522 MESAL/year/lane respectively. This signifies that there is a positive relationship between the axle loadings and Initiation to ravelling period. The data collected during the research was analysed using the HDM- 4 equation for ravelling that was used to estimate the ravelling initiation period for the pavements in the study. Key words: (Construction defects Indicator (CDS), road network, pavement, axle loads, ravelling, HDM-4, road deterioration, maintenance)