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Abstract
A new back-analysis method is suggested to assess the bonding condition between bituminous layers in addition to the pavement layer stiffnesses, from Falling Weight Deflectometer (FWD) test results. The shear bond stiffness at the interface is considered as a variable affecting the FWD deflections and therefore back-calculated in a similar manner to a layer stiffness. A sensitivity analysis carried out on theoretical pavements showed that, assuming full bonding between bituminous layers instead of the actual values will change the FWD back-analysed bituminous and sub-base stiffnesses by up to 50% and will not affect the sub-grade stiffness.
Case studies are presented describing the evaluation of several flexible pavements using the new back-analysis process. Poor bonding was suspected between the bituminous layers due to the following reasons; i) the conventional back-analysis method predicted low effective stiffness for the bituminous layers, ii) separation of the layers during coring was noticed, iii) acceptable laboratory measured bituminous stiffnesses were found.
Re-testing the above pavements after six months indicated an improvement of bonding condition between bituminous layers after trafficking and at higher testing temperatures.