Forensic study into the causes of premature failures in asphalt pavements in Tanzania

Abstract

Tanzania is faced with challenges of premature failures in roads and highways. Some asphalt pavements fail prematurely in less than five years of their expected 20 years design life cycle. These failures have been identified as mostly permanent deformation (rutting) in the asphalt concrete layers. The Tanzania National Roads Agency (TANROADS) and the Council for Scientific and Industrial Research (CSIR) have jointly initiated a collaborative study in premature failures in Tanzanian roads. The aim is to better understand the causes and mechanisms, which lead to these failures, with the primary objective of finding plausible solutions to the problem. This paper presents preliminary findings and outcomes of a forensic study into 12 road sections that have failed prematurely on a national highway referred to as the Tanzam highway. The methodology used in the study is discussed, and the conditions of the road sections as well as the observed rutting are presented. It was found that rutting on most of the road sections occurred in the outer wheel tracks. The minimum and maximum rut depths measured from the overlay rehabilitated road sections were 70 mm and 138 mm, respectively, which far exceed the acceptable rut depth of not more than 15 mm on Tanzanian roads. Remedial actions to be considered by TANROADS and practical recommendations to prevent future occurrences of similar incidences are presented.