Investigation of the structural substance of roads via georadar and ultrasound

Aging of roads and the necessity of planning and performing maintenance measures ask for reliable and economic investigation methods to characterize the structural substance of roads. Nondestructive measurements via georadar and ultrasound have been performed on the surface of a split mastix asphalt test road at the Federal Highway Research Institute of Germany. Sections of the test road had been systematically altered by simulation of traffic load. Common-offset georadar measurements reveal the basic layer structure of the road down to 0.90 m. Common-midpoint measurements show that electromagnetic direct wave speed at loaded road sections is few percent higher and attenuation lower than at non-damaged sections. Reflections at 0.05 m, 0.15 m and 0.90 cm depth could be identified that went along the known road layering. Radar wave propagation velocity decreases with depth by several percent within the road body. Ultrasound common-midpoint measurements at the same locations and nearly identical data processing than for the electromagnetic waves yield wave speeds of P-waves, SH-waves and Rayleigh surface waves and reflections from the road body. Mechanical loads did not affect ultrasound compressional wave velocity but it reduced shear and surface wave speed by few percent. A relation between electromagnetic and dynamic mechanical material properties may be established that could be used to indicate the state of the structural substance of roads by either method and to combine the advantages of fast georadar acquisition with the benefit of ultrasound to probe mechanical properties.