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FWD (Falling Weight Deflectometer)
PTS are a specialist consultancy in the measurement and utilisation of road network survey data.
What is it used for.
The Falling Weight Deflectometer is designed to apply a load pulse which replicates a high speed heavy goods vehicle (load range 7 to 120kN, approximate speed 50kph). Multiple deflections due to the applied load are measured up to a radial distance of 2.5m.
The deflection under the central load gives an idea of overall pavement performance, whilst the inner deflection (up to a distance of 450mm) indicates the condition of the bound pavement layers. The outer deflections can be used to give an assessment of the subgrade condition.
Changes in pavement construction can be identified when the measured deflections are plotted according to the distance along the site, which allows the development of maintenance recommendation to be based on localised pavement conditions.
Construction thicknesses of bound and unbound material are required in order that the effective stiffness of the different layers can be assessed. These stiffnesses can be used as specifications for the quality control of the pavement layers, such as the foundation. Alternatively using they may be used in the analytical design method in order to determine the residual life of the pavement. The required treatment (in terms of overlay or inlay of bound material) can then be specified according to the site requirement.
The use of Coring and Dynamic Cone Penetrometer (DCP), or Ground Penetrating Radar (GPR) can be used in order to determine the construction thicknesses. Pavement Testing Services are experienced in the use of such techniques.
When testing on jointed pavements, typically Concrete Highways or Industrial Floors, in addition to the stiffness assessment techniques described above, it is possible to assess the load transfer and slab support of joints.