Abstract:
This research provides a review of the in situ performance of foamed bitumen stabilised (FBS) pavements in New Zealand. Data used to conduct this research were derived from falling weight deflectometer (FWD) investigations performed on FBS pavements throughout New Zealand since 2004, when FBS technology was first introduced into New Zealand. FWD derived parameters and models for FBS are compared to international guidelines (Australian and South African), as well as currently recommended FBS design parameters and models in use in New Zealand. Interpretation of FWD derived data strongly indicates that moduli of FBS (and cement treated) layers are primarily dependent on the stiffness of supporting layers (subbase and subgrade). Consequently, alternative models which quantify characteristic FBS moduli based on supporting layer stiffness and standard central deflection have been determined. Analysis of the FBS database of New Zealand case histories shows that FBS modular ratios cover a wide range, contrary to New Zealand Supplement (TNZ, 2007) recommendations which sets an absolute value for FBS moduli. Therefore, alternative models suggesting the range of modular ratios which can be achieved between FBS layer and the supporting layer have been presented. An assessment of FWD recorded surface temperatures (at the time of testing) versus FBS moduli indicates that in service pavements constructed in accordance with ‘New Zealand customary practice’ exhibit significant temperature sensitivity (as would be expected owing to the inclusion of bitumen in the FBS layer). Therefore, appropriate correction factors for standardising moduli to a reference temperature have been evaluated. FBS layers can be expected to act visco-elastically, hence the stiffness (moduli) will be dependent on the rate of loading applied to the pavement. Therefore, further correction factors for standardising moduli to account for vehicle speed are suggested.