The next step in the optimisation process was a comprehensive
performance analysis with quality ratings for a wide spectrum of pavement types.
Deterioration mechanisms caused by roughness, cracks, aggregate losses and bleeding in the
case of paved roads as well as by ruts, gravel loss, corrugation, dust, loose material,
stoniness, pot-holes, skid resistance and surface drainage in the case of unpaved roads
were investigated. The identification of these deterioration mechanisms resulted in
revised material specifications for different pavement technologies. Furthermore, they
resulted in optimised maintenance models for Namibian conditions. A further result of the
investigations was the establishment of limits of statistical acceptance and rejection
criteria by questioning road users. These criteria showed the distress modes leading to
unacceptable riding qualities which enabled the creation of cost and quality optimised
pavement types.
Taking all the given parameters into consideration, and on the basis of the economic
analyses, the optimal points of grading, gravelling and paving of earth and gravel roads
were determined.
The suggested appropriate construction standards for different road types were compared
with the standard for roads in the Third World as proposed by the German Ministry of
Economic Co-operation.
The research carried out for this thesis lead to significant new knowledge, which has
resulted in new concepts for road maintenance in developing countries. In realising the
findings considerable savings can be expected.