New protection systems for the substitution of creosote for railway sleepers, wooden bridges and transmission pylons
In this project, the project partners have investigated possible wood preservative alternatives to creosote for applications in railway sleepers, wooden bridges and wooden transmission pylons. Creosote is one of the oldest industrially used wood preservatives with very high effectiveness in use class 4 (in-ground contact). However, European legislation severely restricts the use of creosote. According to the current state of the discussion about the use of creosote, it is likely that a complete ban will come into force in the future, meaning that a suitable replacement preservative has to be found. The scientific objectives of the project include investigations into the biological properties of the impregnated wood, the development and optimization of impregnation processes for railway sleepers and components for wooden bridges and masts, investigations into the elasto-mechanical properties of the impregnated wood, investigations into properties relevant in application such as corrosion and electrical conductivity, and investigations into environmentally relevant properties such as leaching.
The durability of the protective agents used in the project was investigated in laboratory and field tests. Based on these tests, a concentration limit was determined for each protective agent for the different wood species (beech, pine and oak) and the various applications (railway sleepers, transmission pylons and bridge elements), which were used for further investigations into process optimization. Only oil-based protective agents were used to impregnate the railway sleepers. For transmission pylons and bridge elements, both water-based and oil-based protective agents were used, and also partly in a combined treatment (envelope treatment).
In further investigations, the adaptation and optimisation of impregnation processes for railway sleepers and transmission pylons was investigated. Impregnation processes were developed for railway sleepers made of beech and pine, which are now also to be implemented industrially. Impregnation processes have also been investigated for pine poles. In principle, the results show that impregnation of transmission pylons with the oil-based protective agent used is possible, but the process parameters must be further adjusted. Crude Tall Oil (CTO) products were tested for viscosity and penetration behavior at laboratory level.
In addition, the impregnation of lamellas for the production of glulam and the impregnation of glue-laminated beams were investigated. Overall, a satisfactory result was achieved with regard to the application quantity of the protective agent, especially in the impregnation of the laminated beams.
The investigations of the mechanical and physical properties showed that the protective agents examined have no negative influence on the bending strength and the flexural modulus of elasticity, as well as the breaking impact energy. The tested oil-based protective agents meet the limit value for electrical resistance. The oil-based protective agent tested by the company Koppers has no negative influence on the corrosion phenomena of railway sleeper bolts.