Performance of materials used for gravel roads construction in Tanzania.

This thesis describes a study of the performance of gravel as a wearing course material for unpaved roads in Tanzania. The research was done by monitoring newly reconstructed roads as well as existing roads. Three ravel roads in two different regions (Kilimanjaro and Coast regions) were chosen in order to obtain results that have general application across the country. To reduce the cost of the research, the research was linked with actual road construction projects. A minimum number of three trial sections per road were established and monitored for a period of over one year. The performance were measured and quantified in terms of gravel loss of the wearing course, surface roughness and rut depths. The performance of the test sections was related to cumulative traffic volume, traffic speed, material properties, maintenance strategy and climate. The measurements of the road surface deterioration were based on optical levelling which was used to monitor rutting and gravel loss. These standard measurements were supplemented by visual inspection to identify features such as surface texture or the development of potholes. Surface roughness was measured with a vehicle mounted Bump Integrator. Materials testing comprised of grading, plasticity, compaction, bulk density and California Bearing Ratio (CBR). It was found that, the rate of deterioration depends on the standard of construction, maintenance input, traffic volume and speed, material properties like plasticity, dust ratio, coarseness index and type of gravel used in the wearing course. The careful selection of materials and the choice of maintenance policy is necessary to obtain satisfactory performance. The analysis performance forms the basis for the calibration of existing Pavement Management Systems (PMS) models or establishment of new models to be used in unpaved gravel roads in Tanzania. The findings of the study can also be used with other findings in similar studies made in the country to draft gravel road specifications which should then be subjected to more research to refine it.