Fish oil in Icelandic road constructions. : A case study of bituminous binder mixtures modified with bio-oil.

Abstract: In this thesis an extensive background study on the use of bio-oil modified binder, used in surface dressings in Iceland, was carried out. Surface dressings, or chip seals, are paved by first spraying out binder and then distributing aggregates over the surface before compaction. The bio-oil, most notably fish oil ethyl ester or rape seed oil, is included in a binder mixture to lower its viscosity, enabling the binder to be sprayed out at a lower temperature than unmodified bitumen. In January 2013, severe bleeding of binder was noticed on road sections paved with bio-oil modified surface dressings in the northern part of Iceland. Following the bleeding, the Icelandic Road and Coastal Administration (IRCA) sent samples of the sections in question, as well as binder samples, for testing at the laboratory of Highway and Railway Engineering at KTH Royal Institute of Technology (KTH) in Stockholm, Sweden. The conclusions of that study were that the fish oil ethyl ester was highly polar and had solubility issues with the bitumen. This was found to have led to the fish oil separating from the binder mixture and covering the stones, preventing bonding between aggregates and binder [1]. The laboratory tests in this thesis extend on the aforementioned research. Through the background investigation it was found thatWetfix N, an adhesion promoter, was used in the binder mixture to facilitate bonding to the aggregates. Based on these findings, previous work and field experience in Iceland, two sample sets were created. The first sample set included 7.5% of either fish oil ethyl ester or rape seed oil by weight, while the second set included 4% of the same bio-oils by weight. To determine the effect of the adhesion promoter, all samples were tested with and without Wetfix N. Furthermore, all samples were put through a short-term aging treatment to simulate the process during mixing and paving, and tested again. The findings of this study suggest that the fish oil ethyl ester is more suitable for road constructions, compared to the rape seed oil, and that adhesion promoter should always be included when paving surface dressings in Iceland. Furthermore, the samples tested cannot be recommended for field use due to high polarity in the sample with a fish oil concentration of 7.5% and too high viscosity in the sample which includes 4% of fish oil. Therefore, it can be said that the upper and lower limits have been narrowed to the range between the two concentrations tested. To better understand the properties and behavior of the sample mixtures, a complete adhesion test with aggregates is advisable. Viscosity testing of samples which include between 4.5% and 7% of fish oil by weight are recommended and the mixture with the lowest concentration that passes IRCA’s guidelines for spraying viscosity at a desired temperature should be used in practice.