Relaxed Hybrid

In the joint research project "Relaxed Hybrid", the STRABAG competence center TPA and the Federal Highway Research Institute (BASt) collect characteristic values for the optimisation of maintenance and renewal measures for concrete carriageways through asphalt paving (overlay resurfacing).

Compared to the fundamental renovation in the inlay process (replacement of the concrete ceiling), renovations in hybrid construction require a shorter construction time and are therefore often more technically and economically expedient. In the run-up to an asphalt overlay, the concrete surface must be relaxed with an impactor (polygon roller). However, there are no fixed guidelines for the required layer thickness of the asphalt pavement to be installed. The aim of the two-year cooperation project “Relaxed Hybrid” (1/19-12/20) is to minimize the required asphalt layer thicknesses. This would reduce resource consumption and optimise construction site logistics (fewer transports).

Relaxation of the concrete surface using an impactor (polygon roller). Photo: BASt 

On the demonstration, examination and reference area of the BASt (duraBASt) in Cologne, BASt and TPA therefore carry out an extensive load simulation to check whether an asphalt surface of 14 cm (10.5 cm base layer; 3.5 cm surface layer) is sufficient for the hybrid construction is. In the course of the construction process, a total of 40 sensors (temperature, acceleration, expansion) were installed in the superstructure of the load area for continuous measurements. This was followed by the time-lapse load test  in the standardised APT examination program (Accelerated Pavement Testing), in which a Mobile Load Simulator (MLS30) applies approximately 40,000 and a total of approx. 3.4 million truck rollovers with 5t wheel load per day. The simulation was accompanied by load capacity and georadar (GPR) measurements. In addition, laser texture measurements were carried out once a week with the surface drone of the TPA and regular grip measurements with the SRT pendulum of the TPA and the grip tester of the BASt. Since the end of the load tests in November 2019, the TPA intensively examines numerous drill cores from the load section in the laboratory.

Installation of the asphalt layer on the duraBASt (left) and load area including sensors and measured value acquisition

The evaluation of the data collected in 2020 should form the basis for the development of an algorithm for predictive maintenance.