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Deflectograph Surveys

Highway Authorities have used Deflectograph Surveys for more than 30 years to indicate the strength of their asphalt roads.

By measuring the condition of all road layers, not just those that can be seen at the road surface, it’s possible to define the backlog and long term budget requirements needed to maintain the structural integrity of highway networks.

The method of interpretation has been shown to give reliable estimates of the residual life of a flexible road and is equally applicable to properly designed roads and those that evolved over time by the successive application of surface dressings and asphalt layers.

The County Surveyors Society recommends that routine network surveys of structural strength are carried out, but the extent of the surveys needs to be planned to minimise disruption to road users.

The maximum deflection of the road surface is measured at about 4m intervals simultaneously in each wheel path while the Deflectograph travels at a constant speed of 2.5 km/h.

The close spacing of the measurements enables short lengths of weakness to be identified. The results therefore provide in a single survey both network level assessment of condition and project level detail where the need for strengthening is identified.

Although the measurements are taken on the road surface the deflection measured is the sum of deflections in all layers of the road, including the sub-grade on which the road has been built.

This means that the measurements reflect not just weakness visible at the surface, but also weaknesses that are developing within the pavement.

This ability to ‘look below the surface’ is the unique aspect of Deflectograph surveys that enables prediction of future condition to be made and to estimate the residual life of the pavement.

Management of the structural condition of a network and the control of structural condition performance indicators can be achieved only if the residual life of the network is known. With knowledge of residual life long term plans can be prepared to target structural maintenance and obtain best value.

On those sections of the network where strengthening is required the deflection measurements can be used to design the thickness of overlay necessary to extend the life of the road.

Alternatively, on those sections of the network where the routine network coverage shows long residual lives, high cost surface treatments can be applied with confidence to solve surface deterioration identified from SCANNER surveys and low skid resistance from SCRIM® surveys.

SCRIM is the registered trade mark of W.D.M. Limited

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