ABSTRACT
This research is a study of the structural performance of the asphaltic concrete pavement of the Zuba-Gwagwalada-Sheda section of the Lokoja-Abuja highway from chainage 1km+500m to chainage 29km+800m. A Pavement Serviceability Rating (PSR) was conducted, followed by a Pavement Condition Index (PCI) study. A Truck traffic study was then conducted and used to determine Equivalent Standard Axle Loads (ESALs). Further, the Benkelman Beam (BB) and the Dynamic Cone Penetrometer (DCP) tests were carried out. Laboratory tests including bitumen penetration and bitumen content, Marshall Stability and Flow, Particle size distribution, and California Bearing Ratio (CBR) among others were then conducted on the pavement layer materials to obtain engineering properties relevant to pavement performance. Whereas the visual pavement distress survey recorded alligator cracking and rutting or permanent deformation as the most prominent distresses, PSR and PCI studies individually rated the pavement as "poor". The predicted ESALs were obtained as 13.76 million standard axles. Whereas the BB study indicated that the pavement has failed, the DCP test results indicated that strength properties of the lower pavement layers exceeded minimum requirements. Results of laboratory tests compared fairly well with requirements of national and international specifications which constitute the benchmark for good performance. Resultsof the 13.76 million ESALs and CBR of subgrade of 16.2%from these tests and the American Association of State Highway and Transportation Officials' (AASHTO's) flexible pavement performance equation were used to obtain the Structural Number (SN) of 4.9, required of the pavement to support the predicted loads. The actual Structural Number of 4.33 of the existing pavement based on pavement layer thicknesses and layer structural coefficients was less than the required SN. This difference between the required and the actual (or applied) Structural Numbersis a major determinant of pavement life span.Future truck loads were also predicted to cumulate to 26.63 million ESALs in the next 20 years: an indication therefore that the pavement under study may require to be reconstructed to the standard of a perpetual (long lasting) pavement if premature failure is to be avoided.