Research and development of an isocyanate-based bitumen additive for asphalt mixtures : a novel chemical modification for temperature reduction and performance enhancement

• Erforschung eines Isocyanat-basierten Bitumenadditivs für Asphaltmischungen

Carreño Gómez, Nicolás Héctor; Oeser, Markus (Thesis advisor); Radenberg, Martin (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

The construction of flexible pavements is currently facing several challenges. Increasing traffic, as well as rising temperatures, along with a need for a more sustainable approach to the production, construction, disposal and/or reuse of asphalt mixtures; demand to reassess the construction process and the materials used. Since roads and highways play such a crucial role to society and to national and international economies, the entire pavement construction sector (i.e industry, State agencies and universities) is required to come up with possible solutions. The dependence on non-renewable materials, such as bitumen and mineral aggregates, the high production and construction temperatures, and road-availability makes it necessary to come up with innovative solutions to reduce the current economic, social and environmental impacts. In this thesis, the research and development of an isocyanate-based bitumen additive is presented in detail. It summarizes the work of a joint-research project with BASF, where a chemical additive was sequentially tested at different scales, beginning in the laboratory, and afterwards at a real scale asphalt mixing plant. The working principle of the additive is that it reacts with different constituents of the bitumen (different functional groups), forming a cross-linked polymer network within the bitumen. This network increases the elasticity of the bitumen, thus enhancing the properties of bitumen as well as the performance of asphalt mixtures. The additive can be dosed in an in-line blending process at the mixing plant, using the energy (and oxidation) of the own asphalt mixing process to react with the bitumen. Moreover, the production and construction temperature could be reduced, effectively helping to reduce bitumen fumes and aerosols during construction, increasing asphalt worker safety. Due to the chemical nature of the additive, it also showed to work well in mixtures with high amounts of reclaimed asphalt content. Special focus was set on the methodology applied, since during different periods of the research here presented, new challenges appeared that redefined and/or extended the research goals. This thesis presents the findings of the use of this additive on a bitumen and asphalt level, and the properties of these modified materials during the different phases of road construction; during production and construction phases, as well as during its service life. The isocyanate-based additive showed it could extend the service-life of pavements, and that it has a similar thermal ageing behaviour than standard polymer-modified bitumen, from a chemical and mechanical perspective. The analysis presented in this document provides evidence of the potential that this type of modification has on developing more sustainable pavements, from a technical, economic, social and environmental perspective, to a certain extent.