A case investigation into causes of premature rutting failures in rehabilitated asphalt pavements in Tanzania

Abstract

Tanzania was faced with high incidences of premature rutting failures on their asphalt pavements. Some pavements experienced failures within one to two years after construction/rehabilitation. The objective of this investigation was to identify the factors which contributed to the observed failures on five rehabilitated road sections on a national highway in Tanzania. Pavement temperature data collection, traffic surveys, visual inspection, rut depth measurements, and Falling Weight Deflectometer tests constituted the main activities of the field investigation reported in this paper. Laboratory study included a visual assessment of cores extracted from the studied road sections to determine both physical and engineering properties including density, stiffness, strength, aggregate shape properties, grading and physio-chemical tests on the recovered binders. The results of the study indicated that the degree and extent of rutting on the investigated road sections was rated as severe., i.e., rutting ranged from 38 to 138 mm on the five sections when compared to the acceptable threshold value of 15 mm for high volume roads in Tanzania. The elastic deflection results indicated that the underlying layers of the pavement system were generally in a sound condition, which validated the suggestion that the rutting observed was mostly confined to the asphalt concrete layers. Factors such as relatively high axle loads, poor asphalt mixes and possibly inadequate quality control during construction and rehabilitation were suspected to contribute to the rutting on the sections. Practical measures recommended to the roads agency to avert future occurrences are provided in this paper.