ABSTRACT
The use of concrete overlays in asphalt pavements could be an effective and economical alternative to the common rehabilitation solutions. The Ultra-Thin Whitetopping (UTW) technique consists in the casting of a thin concrete slab (from 50 to 100 mm) over damaged wearing courses in order to limit the high level of distresses typical of the Asphalt Concrete (AC) pavements. Otherwise, the efficiency of such system is strictly related to the interlayer bonding developed between the existing bituminous surface and the concrete overlay: in fact, the degree of adhesion between materials of different nature could be not sufficient to guarantee the structural continuity of the layers, thus it can cause differential expansions and contractions due to vehicular and thermal loads, as well as excessive stress-strain state within the structure. The present paper illustrates a laboratory study aimed at evaluating the experimental performance of double-layered systems prepared with the same UTW and asphalt concrete but with different interlayers. In particular, direct bond tests were executed to identify the shear performance of four different interfaces (plain, with bituminous tack coat emulsion, with bituminous tack coat emulsion and gravel, brushed AC). The same systems were also tested to determine the stiffness characteristics through 3-point bending tests. Mainly, the characteristics of the selected interface deeply influenced the structural behavior and the failure mechanism of the UTW-AC systems. With respect to the other alternatives, plain asphalt concrete used as laying surface for UTW gave the best results in terms of shear resistance and stiffness.
