Location and evolution of the speciation of vanadium in bitumen and model of reclaimed bituminous mixes during ageing: Can vanadium serve as a tracer of the aged and fresh parts of the reclaimed asphalt pavement mixture?

Vanadium is well known to promote the ageing of bitumen through oxidation of the carbon matrix. Nevertheless the mechanism by which vanadium may induce organic compound oxidation is not clearly understood. Then the evolution of the speciation of the vanadium into bitumen matrix with ageing was studied. V-K edge XANES (X-ray Absorption Near Edge Structures) experiments showed no evolution of the oxidation state and geometry of V although all bitumen oxidation indexes indicated intense ageing, thus suggesting that vanadium can promote the bitumen oxidation through catalytic phenomena. Micro-XANES experiments at the V-K edge combined with micro-X-ray Fluorescence (XRF) showed that, in a laboratory model of hot reclaimed bituminous mixes, the presence of aggregates (CaCO3 particles) enhanced the oxidation of bitumen, without however affecting the oxidation state of V. As a consequence, the vanadium speciation during bitumen ageing cannot be used as a tracer of the bitumen ageing and mixing between fresh and reclaimed bitumen. (C) 2012 Elsevier Ltd. All rights reserved.