4. Characterization methods used

4.1 Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS)

Aggregate and bitumen samples were studied using scanning electron microscopy (ESEM XL 30 from Philips, accelerating voltage 10 keV). Concrete samples were characterized at high resolution using a field-effect SEM (FEG Quanta 400 from FEI Company, USA), with an accelerating voltage of 15 keV. EDS spectroscopy is used to analyze the first few micrometers of sample depth. It has been used to identify the specific elements (K, Na, Ca, S, etc.) characterizing certain minerals and bitumen.