Full scale evaluation of tack coat effectiveness with simultaneous laying of asphalt concrete

The application of a tack coat before overlaying with a new asphalt concrete (AC) layer is used to promote pavement interface bonding in order to pursue a monolithic multilayered structure, ensuring structural integrity and preventing fatigue cracking, delamination, and slippage. To speed up the laying process and avoid the risk of tack coat damage from construction vehicle traffic, specific equipment known as spray pavers was designed. This equipment allows the bituminous emulsion to be sprayed through nozzles positioned before the discharge of the asphalt concrete and, at the same time, the asphalt concrete to be laid. Consequently, the need to protect the fresh bituminous emulsion from construction traffic is eliminated, and the site management, condensed into a single phase carried out by a single machine, becomes easier and efficient. However, the AC overlaying on the freshly sprayed bituminous emulsion, still containing water, requires careful verification of the interface performance, as this plays a fundamental role in the bonding between the overlapping layers and the integrity of the pavement. This paper focuses on the full-scale evaluation of tack coat application effectiveness with simultaneous laying of AC using a spray paver. To verify the effectiveness of this innovative construction process, a real-scale trial section was designed and built to compare the traditional method with the innovative one. The trial section included five interface configurations considered representative of the most common cases observed in practice. Samples were extracted for laboratory testing aimed at characterizing the flexural and shear strength of the interface. This paper reports the design and construction phases of the trial section, as well as the analysis of the experimental results. The specimens taken from the trial section built with the innovative method showed shear and flexural performance comparable to that of those produced using the traditional construction approach. • Full-scale evaluation of tack coat effectiveness with simultaneous laying of asphalt concrete using a spray paver. • The trial section includes five interface configurations representative of the most common practices. • Laboratory testing on samples extracted from the trial section to verify the flexural and shear strength of the interface. • Specimens from the trial section built with the new method showed shear and flexural performance like the traditional ones.