The waste of the production of steel are ordinarily used in asphalt concrete pavements. The by-product named slag, whose chemical properties are similar to effusive rocks, is transformed into course aggregates. It is used for bituminous surfacing as a valuable replacement to natural aggregates, which are becoming increasingly rare. Moreover, the wearing coarse made with this material maintain good values of micro-texture, even after the action of the traffic loads for a long time. This technique is used on the road network of Friuli Venezia Giulia since many years. The study has the main purpose to identify a decay curve (deterioration) of the indicators of friction with the number of passing accumulated of vehicles over the years. The indicator monitored is the micro-texture indirectly assessed by measures of BPN. The sections of the measures have been carefully chosen, so as to be homogeneous for the geometric characteristics of the axis, for organization of the cross section and type of the wearing course. The measures BPN regarding more points in the same section. In particular on the wheel paths and the shoulders not affected by the traffic. The measures in situ were related to the number of passing vehicles, and compared with the values of Polished Stone Value test.
