Asphalt mixtures modified with tall oil pitches and cellulose fibres: Dissertation

Tall oil pitch and fibre-modified asphaltic mixtures were characterised in this work. The tall oil pitches were crude distillation residues of crude tall oil. The cellulose fibres were of a commercial grade and consisted of selected sulphate cellulose and spruce fibres originating from recycled paper materials like from old newspapers. Tall oil pitches formed a very homogenous and stable mixture with bitumen. Soft tall oil pitches were added to bitumen in amounts of 15-20 % of the weight of the hard bitumen. Adhesion, measured by the water resistance tests with the modified mixtures, improved significantly. Adhesion was shown to be due to strong acid adsorption, caused by carboxyl groups of the resin acids, which are the main constituents of the pitch. The acid numbers of the pitch-modified mixtures were 2-7 mg KOH/g. With these acidified binders adhesion was improved by 30-60 % in the rolling flask tests with different granitic aggregates. The lower penetration index values were typical of the pitch-bitumen mixtures. An increase in the stiffness modulus of the modified mixtures at -20°C was achieved. However, in the elongation tests of the pitch-modified asphalt beams at -5°C and -20°C no weaknesses were indicated as compared to the reference paving mixture. It was shown that the wear of the pitch-modified paving surfaces was approximately at the level of the reference. The additions of pitch were made to the bituminous asphaltic concretes, AC 16 and AC 20. On the basis of the results, the pitches are shown to be suitable for use in these asphalts. The short cellulose fibres were the best fillers in the open-graded aggregate mixture of the splitt (stone) mastic asphalt, SMA, as well as in the gap-graded asphalt concrete, GAC. The best carrying effect of bitumen was obtained with cellulose fibres. Their surface area was larger, even as high as 2.6 m²/g, than that of the mineral fibres, whose surface area was of the order of 0.1 m²/g. Cellulose fibres thus carried bitumen on to their filaments most effectively and the additive level could be kept low. Cellulose fibres were of the ribbon type. This filament structure increased their ability to carry bitumen. Cellulose fibres in asphalt concrete are affected by increased bitumen contents, this resulting in lower stability. This was also due to the traditional Marshall stability method. The SMA and GAC mixtures, which use cellulose fibres, wore significantly less than the traditional asphalt concrete AC. This was mainly due to the quality and the quantity of the coarse aggregate. Fibres as a material were indirectly influenced in wear by the homogenous binder blend. Cellulose fibres were used as cohesive carrying additives for the aggregates in the bituminous SMA mixture. When wear was measured at -20°C, it was noticed that the elastic and homogenously distributed surface of the fibre-bitumen blends resisted wearing of the SMA mixtures very well. The nature of the cellulose fibres is hydrophilic. The cellulose fibres are blended in bitumen, however, so homogenously that there was no penetration of water into the asphaltic mixtures. Based on the results obtained with the cellulose fibres, their continued use in asphalt concretes is recommended.