This report reviews South African experience of modifying aggregates with bitumen and a trial use of bitumen to modify two unsealed roads in the Central Otago district. The test programme consisted of laboratory tests and NAASRA roughness counts and field observations.
Initial observations on the trials and control sections indicated that surface wear of the pavement will steadily increase the roughness of the road to a point within five years where additional maintenance work will be required to restore the surface and ride. Modified aggregates resulted in reduced maintenance costs with a significant reduction in grading and dust.
These trials indicate that bitumen modification is generally less economic over the longer term than conventional seal extension particularly where aggregates are obtained at low cost.
Keywords: bitumen modification, lime, foam, bitumen, unsealed roads, Central Otago, New Zealand