April 2019

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> Part   of   the   training   was   on   the   retro- calculation which makes it possible to convert the measured deflections into elastic modulus for each of the layers composing the roadway.


The data necessary to perform a retro- calculation are:

> deflections and loads of each test FWD / HWD,

> pavement thicknesses, (from core samples and / or GPR data),

> asphalt temperatures.

It is an iterative process performed by specific software. For example, at São Luis airport in Brazil, a retro-calculation was performed from the data:

> of deflections,

> the types and thicknesses of materials determined from geotechnical surveys,

> the temperature of the asphalt at the time of the tests.


The modulus of asphalt changes with the temperature. It is recalculated for a temperature of 25 °. This retro-calculation made it possible to obtain the modulus of the different layers composing the roadway, (chart attached).

Rincent BTP Services SAS

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