The Chemical and Physical Structure of Peat Bitumens

Peat bitumen obtained by solvent extraction of Irish high moor peat was subjected to chemical, structural and rheological characterisation. The bitumen was fractionated on the basis of solubility in n‐heptane, toluene and ethyl acetate into wax, resin and asphaltene; each of these major constituent groups was further separated into sub‐fractions by column chromatography using solvents of increasing polarity. All materials were chemically characterised by C, H, N and O content and infra‐red spectroscopy. Molecular size distribution of the materials was determined by gel permeation chromatography and vapour pressure osmometry. Heats of fusion, measured using the differential scanning calorimeter, indicated that crystalline species were concentrated in the wax fraction. The rheological properties of the bitumen were investigated between 10 and 50°C, and the fractions were examined at 20°C. Following analysis as yield pseudoplastic fluids, flow behaviour was described in terms of yield stress, flow and consistency indices. The measured flow parameters were examined in the light of the structural implications of the calorimetry and the results of the chemical analysis. Carboxylic acids and esters which are found principally in the wax fraction are considered to be the dominating rheological influence in the bitumen, affecting physical behaviour through their ability to crystallise at low temperature and thus mechanically hinder flow, and through secondary bonding increasing viscosity in the liquid phase.