AUSTROADS formed a Working Group to resolve difficulties with the satisfactory introduction of a `thin layer density gauge' or more precisely a dual-detector-set nuclear surface density gauge. It has been claimed that these devices can accurately measure the density of thin asphalt overlays, ranging from 25-100mm, without influence from underlying areas. The paper reports on laboratory and field investigations carried out by the Department of Transport in its contribution to this national effort. The investigations have resulted in recommendations for modification in the procedure for derivation of system constants for gauge density determinations. A clearer understanding of the variables involved in the determination of the top layer density also has resulted in an extension of the theory associated with this aspect and the concept of an equivalent density for the top layer has been introduced. The effect of surface voids is still seen as a major stumbling block to the satisfactory introduction of the gauge and investigations into minimising this effect are continuing. (A)
Samenvatting