ALT-evaluation of high stiffness base layers with high percentages of reclaimed asphalt
New Road Construction Concepts (NR2C) is a FEHRL-project supported by the European Commission under the Sixth Framework Programme. NR2C develops perspectives and specific innovations, so that long-term visions are linked to short-term action. One of the ideas towards sustainable road construction concerns the development of high performance asphalt base layers (High Modulus Asphalt – HMA) with high percentages of recycled materials. High stiffness layers are largely used in Europe, but re-use has been very restricted until now. This project aims to optimize the design of these mixes to guarantee their long-term performance and their low and high temperature behaviour, even with high percentages of reclaimed asphalt. Three different mixes were designed, optimized and compared, namely with 0%, 25% and 40% reclaimed asphalt The performance of these mixes relating to stiffness, fatigue cracking, durability/adhesion and permanent deformation was determined and compared in the laboratory. Three selected solutions (8-cm base layers with a 3-cm wearing course) have been further studied in the full-scale ALT facility of LAVOC. The first step was to evaluate fatigue behaviour by applying 100.000 – 200.000 12-ton axle loads at 15°C. Then low temperature behaviour was investigated by load applications during a number of temperature cycles where the air temperature varied between +2 °C and -7 °C. The structures were instrumented at different depths with temperature, stress and strain gauges and deflexion sensors in order to analyse the performance. High temperature behaviour of the three mixes was tested in the Danish Asphalt Rut Tester on large slabs extracted from undisturbed areas of LAVOC’s ALT facility. Each of the three slabs was subjected to 110.000 loads at 40 °C, and 44.000 loads at 50 °C. Based on the performance characteristics of the mixtures determined in the laboratory study and on the results of the accelerated loading, the impact on structural design of the road and the lifetime of the pavement will be investigated.