Raveling Resistance of Grouted Macadam Compared to Conventional Asphalt Mixtures for Wearing Course

Grouted macadam (GM), composed by a porous asphalt mixture whose air voids are filled with a cementitious grout, is efficiently used as wearing course in semi-flexible pavements subjected to heavy-load traffic and low speed. Since high steering angles, applied by vehicle load at low speed, induce high shear stresses on the surface, this research investigated the raveling resistance of GM in comparison with conventional asphalt mixtures usually employed in motorways and airports. Laboratory tests were carried out with the Darmstadt Scuffing Device, which simulates the actual in-field movement of a wheel during steering. Several environmental factors were simulated, varying the testing temperature and the conditioning of the specimens. Experimental results showed that GM ensures a satisfactory raveling resistance in the conditions of dry and wet surface, comparable with those of asphalt concretes. On the contrary, an outstanding behavior was registered for GM in the case of fuel spillage, thanks to its close structure which does not allow penetration and to the grout which guarantees chemical resistance.