Residual voids content (GPR)

When laying new pavements in a northern climate, it is extremely important to make sure that the road surface is tight (compaction) and that the permanent porosity (air pore volume) of the road surface is sufficiently low. According to the traditional method, up to 12 boreholes per kilometer of road are drilled in the pavement to find out the permanent porosity, but this is time-consuming, damages the new pavement, and most importantly – describes the investigated pavement in steps of only approx. 500 m.

Measurements are made with ground radar, e.g. on a two-way road, typically on three measuring lanes and at the base of the so-called outer wheel tracks of both driving directions, and at the pavement joint on the road axis. In contrast to traditional inspections with drills taken during quality control, radar measurements provide uninterrupted information on the permanent porosity values ​​of the inspected asphalt concrete pavement on the measuring track. This greatly reduces the large component of randomness in compaction factor and permanent porosity determinations and allows problem areas to be identified. The area of ​​effect of deductions is reduced hundreds of times per sector of permanent porosity checked. To calibrate the measurement results, typically 8 boreholes are taken from the inspected section, so the number of inspection boreholes that damage the new coating is reduced tens of times.

A limitation of this method is that measurements cannot be taken when the coating is wet or frozen. Also, it is not possible to reliably measure permanent porosity in coatings with sodium chloride or other anti-slip chemicals.