The world energy consumption is constantly increasing and the research point towards novel energy harvesting technologies. In the field of pavement engineering, the exploitable sources are the solar radiation and the vehicle load. At present, these systems are able to convert the sunlight into electricity thanks to some solar cells placed under a semi-transparent layer (photovoltaic roads), or they can harvest thermal heat by means of solar thermal systems. The thermal gradient of the pavement can be exploited by thermoelectric generators, by heat pipes or by heat-transfer fluids (i.e. water) pumped into a medium (asphalt solar collectors, porous layer or air conduits). The traffic load can be exploited by piezoelectric materials, able to convert the vehicle load into an electrical charge. The aim of this paper is to describe the main pavement energy harvesting technologies, pointing out positives and negatives and providing indications for further optimizations. Finally, the systems are compared in terms of initial cost, electrical output, efficiency and technology readiness level.

Polyurethanes are versatile materials and, in civil engineering, they are implemented as bonding elements, injection material to stabilize soil condition, as well as insulating and coating foams. Because of their good adhesion, their transparency, and their mechanical and thermal properties, the idea of the present research is to use it as organic matrix in a glass aggregates/glue composite used as a semi-transparent pavement surface layer.This research takes part in a wider project aiming at designing a hybrid pavement system able to harvest energy from the sun.The aim of this paper is to characterize four different types of thermoset polyurethanes in terms of curing time and visco-elastic properties. For this purpose, an experimental campaign was conducted, performing tests in a dynamic shear rheometer and a dynamic mechanical analysis.Curing time kinetics, defined as the evolution of phase angle, were modelled according to the Arrhenius law. Temperature and frequency dependence on the complex modulus were finally measured. The results demonstrate the strong dependency of the polyurethanes behaviour, overall mechanical performance and especially glass transition temperature, on the curing temperature.

Solar roads are transportation infrastructures able both to generate electricity thanks to solar cells placed under a semi-transparent layer and to ensure heavy traffic circulation. In this paper, a novel transparent top layer made of glass aggregates bonded together using a polyurethane glue is presented. The goal is to design a composite material able to support traffic load, guarantee vehicle skid-resistance, allow the passage of sunlight, and protect the solar cells. For this purpose, the authors investigated the effect of different variables (thickness, glue content, and glass aggregate distribution) on the mechanical and optical performances of the material applying the factorial design method. The semi-transparent layer was characterized by performing the three-point bending test and measuring the power loss. Regarding the vehicle friction, experimental tests with the British Pendulum were conducted in order to measure the skid resistance of the surface and compare it with the specifications of a typical road infrastructure. According to the fraction factorial design and the British Pendulum test, the following mixture was developed: 42.8% of 4/6 mm; 42.8% of 2/4 mm, 14.4% of glue in volume, and a thickness of 0.6 cm. The first results are encouraging, and they demonstrate the feasibility of a semi-transparent layer for future applications in full scale.

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