Paper presented at the 31st Annual Southern African Transport Conference 9-12 July 2012 "Getting Southern Africa to Work", CSIR International Convention Centre, Pretoria, South Africa.
A major airport in Namibia was recently rehabilitated by first milling off a delaminated asphalt layer and inlay with a continuously graded asphalt layer and placing an ultra-thin proprietary surface friction course on top. The asphalt inlay work included a cross fall correction with asphalt wedge build up on the centre line tapering off to the off keel area of the runway. Construction was interrupted for 6 months due to unnaturally high rainfall. This interruption came after the asphalt inlay work was completed and a short section of the surface friction course on the main runway was placed. At resumption of work and prior to completion of the proprietary surface friction course white deposits were observed on the surface. The white deposit tended to concentrate along the longitudinal joints of the previously constructed asphalt. The origin of the white deposit was investigated and could be linked to salt leaching from aggregates in the underlying layers. The delaminated asphalt repair has led to a heightened awareness of durability problems. Previous problems on this airport were linked to stripping, crescent cracking and delamination of the previous asphalt overlay. The subsequent field and laboratory work enabled a clear linkage with the construction quality control of longitudinal joints in general. Densities, air voids and binder content could be checked against specification tolerances via normal quality control testing. Air and water permeability testing were done as well as wet and dry modified Lottmann tests. Cores were also inspected visually to give indicative values of permeability. This investigation served to emphasise the lack of focus of current specifications used on quality control of longitudinal joint construction and their longer term durability impact. The investigation provided the basis for improved quality control and specifications for longitudinal joints of asphalt paving in future.
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