Clear asphalt concrete for energy saving in road tunnels

Nowadays the interest in clear pavements for road tunnel applications is rapidly increasing, as their high photometric properties assure an important reduction of power consumption for electric lighting and an improvement of safety conditions. One of the solutions for manufacturing clear pavements consists in mixing light-colored mineral aggregates with particular transparent asphalt binders. This production technique was used in 2012 to manufacture the clear asphalt concrete for wearing courses of two road tunnels in the north of Italy. The present paper deals with the mix design and the evaluation of mechanical and photometric properties of the clear asphalt concrete used for paving these tunnels. In particular, tests were carried out on the raw materials and on both lab-manufactured and plant-manufactured mixes. At the end of the tests clear mixtures showed good mechanical properties, similar to a traditional “black” asphalt concrete in terms of indirect tensile strength and indirect tensile stiffness modulus. In addition clear mixtures showed very high photometric properties after five months from the opening to traffic.