THE EXPERIMENTAL DETERMINATION OF AXLE LOAD FACTOR EXPONENTS FOR THIN FLEXIBLE PAVEMENTS IN ZIMBABWE . THIRD INTERNATIONAL CONFERENCE ON BEARING CAPACITY OF ROADS AND AIRFIELDS. PROCEEDINGS, NORWEGIAN INSTITUTE OF TECHNOLOGY, TRONDHEIM, NORWAY, JULY 3-5 1990. VOLUMES 1-2

Road designers in developing countries still use the damage factor exponent of 4.2, derived from the AASHTO Road test, in the absence of more applicable data. This paper describes an investigation to test this exponent, applying three different wheel loads to test pavements of three different thicknesses at the circular test track at the University of Zimbabwe. The track has six sectors, with different total depths of compacted natural quartz gravel base from 15 to 30 cm. The subgrade was thought to be compacted red silt throughout, and the surfacing was a prime coat covered by asphaltic concrete about 1 cm thick. Benkelman beam measurements were recorded on each section, and showed variations of the order of 25%, apparently due to unmeasured subgrade moisture; this effectively concealed effects due to time and fatigue effects. Other measurements, using levelling and a lattice bridge and wedge, were even more variable. It was again shown that pavement experiments on the test track were difficult to construct and execute, and that excess moisture and wheel loading were undesirable. The observed values of the damage factor exponent were variable, but all less than 4.2. (TRRL)