NETWORK MORPHOLOGY OF STRAIGHT AND POLYMER-MODIFIED ASPHALT CEMENTS

Asphalt cements are often regarded as a colloidal system containing se veral hydrocarbon constituents: asphaltenes, resins, and oils. The hig h molecular weight asphaltene particles are considered to be covered i n a sheath of resins and dispersed in the lower molecular weight oily medium [Whiteoak (1990) The Shell Bitumen Handbook (Shell Bitumen UK, Riversdell House, Surrey, UK)]. However, the exact arrangement of the asphaltene particles within the oily phase will vary depending on the relative amounts of resin, asphaltene, and oils. It is this arrangemen t and the degree of association between asphaltene particles that gove rn the rheological properties of the cement [Simpson et al. (1961) J. Chem. Eng. Data 6:426-429; Whiteoak (1990)]. Here we report for the fi rst time the observation of a three-dimensional network of asphaltene strands within straight, polymer-modified, and aged asphalt cements. W hile the existence of a asphaltene/resin micelle network has been prop osed in previous studies [Whiteoak (1990)], direct observation has not been reported. The network is expected to greatly influence the rheol ogical properties of the asphalt binder and ultimately the properties of asphalt concretes. In situ fracture studies of asphalt cement/aggre gate composites indicate a possible correlation between the network st ructure and adhesion between the cement binder and aggregate. (C) 1997 Wiley-Liss, Inc.