Single-Measurement Estimation of In Situ Asphalt-Layer Moduli with Portable Falling Weight Deflectometer

Abstract

The portable falling weight deflectometer (FWD) was introduced some time ago. The use of this measuring device in Israel was stimulated by the contradictory results of various studies described in the technical literature. These studies indicated that significant deviations may exist between the in situ FWD-backcalculated asphalt-layer moduli and the expected true moduli values from laboratory testing. In addition to these deviations, it is known that uncertainties associated with the backcalculation procedure do not allow the backcalculation of moduli for thin asphalt layers less than 75 to 100 mm thick. Therefore, the need for an additional in situ testing device that would produce reasonable results for the in situ asphalt-layer moduli became obvious. In Israel, the portable FWD was considered to be a promising testing device to serve this need. In situ tests showed that the new device required additional testing on the asphalt surface after coring the asphalt layers to their bottom. This type of double-testing enabled the derivation of the in situ asphalt-layer modulus using a straightforward backcalculating technique. It was also thought, however, that the double-testing procedure may be sometimes too clumsy and costly. Therefore, it was decided to examine the possibility of conducting a single measurement to obtain a good estimate of the asphalt-layer modulus. The current study led to a proposed procedure for estimating the in situ asphalt-layer modulus after only one run.