Bio bitumen - bitumen substitute based on renewable raw materials and resulting in energy efficient asphalt
Point of departure / motivation:
Crude petroleum is a fossil mineral resource and fuel source that will be used up within the next 50 years. Bitumen, the residue left over from petroleum distillation is throughout the world the most significant bonding agent used for roadway construction. Concrete roadways are not a fully equivalent substitute for asphalt roads since the manufacture of cement is costly in terms of energy and entails carbon dioxide emission and concrete is a rather poor building material, particularly in the most widespread and less prioritised roadway network.
Austria alone annually consumes about 400,000 tons of bitumen and the worldwide demand lies around 200 million tons. Currently there are no alternative bonding agents for production of asphalt which could replace bitumen in view of its significant availability at an acceptable price.
Contents and objectives
The marked rise in the price of bitumen to about four times its original price in the last seven years and the supply bottlenecks that frequently occur in the building season show that it would be reasonable and necessary to establish a permanent supply of a bonding agent. A number of natural substances are known that have bonding agent-like properties which are suitable bitumen substitutes in their pure form or when mixed with other natural substances. But their availability is, with the current state of the art, completely inadequate.
The objective of this project was to develop a more efficient bitumen substitute product based on regenerative raw materials. But no foodstuff or animal feed cultivation acreage should be sacrificed to do so. Rather, it is primarily the use of plant remnant materials that are intended. Using the example of Austria, it can be calculated that only about 1% of the annual biomass increase could supply the necessary quantities of bonding agent.
First of all, with a broadly based study of available literature the existing potential of regenerative raw materials was estimated in respect of the usable portion of such substances. Thereafter, in an empirical evaluation procedure, the basic suitability of selected constituents was reviewed. In the main project phase, synthetic processes were developed in order to transfer the substances isolated from the relevant natural materials to modified substances with acceptable bonding agent properties. The syntheses could be of the bio-conversion method type as well as of the classical chemical reaction kind, but would in any case need to have the potential for mass production in economic and technical respects. Both source raw material from domestic or foreign traditional or future-optimised agriculture and forestry as well as by-products of energy recovery processes that will increase in importance in the future using regenerative raw materials are feasible.
In a comprehensive screening study, from the entire available supply of regenerative raw materials a selection was made for potential suitability as a bitumen substitute. In order to do justice to the basic requirement of using only remnants, all materials currently used intensely for foodstuff and animal feed purposes were excluded. Under the aspect of adequate availability in view of the huge volumes required, the wood component lignin as well as oil plant-based natural materials were selected as promising synthesis stocks. In the initial synthesis series, different available variants of lignin were tested for their suitability. Depending on their origin and the form of their recovery, those variants proved to differ in their suitability. Of the manufactured synthesis products, material properties like stickiness and adhesiveness as well as rheological properties were examined. The methodology used was laboratory synthesis reactions; processes suitable for mass production were not the subject of this project. Studies on bio-technical lignin decomposition were likewise conducted and, additionally, remnants from synthetic fuel technology, a procedure for recovering energy sources from regenerative raw materials, were included in the basic investigations.
In additional practically oriented studies it could be shown that it is currently already possible to produce high-quality pioneer types of asphalt on the basis of a mixture of fossil bitumen and regenerative raw materials.
Biotechnological processes for fuel production (2nd generation biofuels) are a potential source of raw material for bitumen replacement products indeed. However further intensive study of the topic will be necessary still, and collaborations between large companies must be established in order to provide sufficient amounts of bitumen replacement products in medium-term future.
DI Dr. Johann Bleier
Österreichische Vialit-Gesellschaft m.b.H.
Project or cooperation partner
- Technische Universität Wien, Institut für Angewandte Synthesechemie
AO.Univ.Prof. Dr. Simone Knaus
- C.A.R.M.E.N. e.V. - Straubing, Bayern
(Centrales Agrar-Rohstoff-Marketing- und Entwicklungs-Netzwerk)
Dr. Bettina Schmidt
- OÖ-Boden- und Baustoffprüfstelle GmbH
- Direktion Straßenbau und Verkehr, Land OÖ