For norwegian summary description, see information page at the web site of Research Council of Norway / Forskningsrådet.
Creosote is one of the oldest and most effective wood preservatives. The European Commission has however restricted the use of creosote during the last years due to environmental and health concerns. Creosote was added to Annex 1 (list of approved substances) of the European Biocidal Products Directive (BPD) in 2013 for an initial period of five years. This means that the use of creosote is still allowed for specific applications, but it is highly controversial within the European Commission. Creosote’s listing in Annex 1 of the BPD, i.e. the permission to use creosote as wood preservative also after 2013, was justified with the lack of alternatives and significant socio-economic reasons.
Besides its biocidal effect, creosote confers hydrophobicity to wood. The latter counteracts crack formation and thereby reduces the risk of decay. At the search for alternatives, the property of providing hydrophobicity is of special importance considering that highly effective biocides like CCA (copper chrome arsenic) and other chromium containing biocides have been forbidden due to their toxicity in Europe during the last years. Today’s mostly used water-borne wood preservatives do not provide sufficient protection in many heavy-duty applications outdoors. Creosote’s duality of being both biocidal and water repellent is special for a wood preservative and makes great demands on finding substitutes. The current lack of alternative wood protection systems bears the risk that entire key markets for wood, namely railway sleepers, utility poles and timber bridges, will be lost to non-renewable materials. This would not only hit the European timber industry hard, but also the users of creosote-treated wood. Wood has an excellent cost-benefit ratio and several favorable technical properties as compared to other materials.
The overall objective of CreoSub was to develop new bi-functional wood protection systems based on modern, environmentally acceptable biocides in combination with hydrophobic wood-based components with secondary functions. These systems will substitute creosote in the production of railway sleepers, utility poles, and timber bridge components.
The scientific objectives were to assess the new protection systems regarding their:
- impregnation behavior,
- leaching profile,
- efficacy against wood destroying fungi,
- influence on mechanical properties,
- influence on metal corrosion,
- influence on electrical conductivity,
- influence on gluability,
- and environmental impact.
The technological objective was to develop production processes of railway sleepers, timber bridge components, and utility poles treated with new wood protection systems from laboratory to industrial scale, and to assess the performance of the products in laboratory with accelerated methods and under real conditions in the field. This implied to individually consider process-related, economic and environmental aspects for each of the three different product groups mentioned above.
Project Lead: Ulrich Hundhausen, Norsk Treteknisk Institutt
Phone: +47 976 57 599
Responible at REN were
Stig Fretheim, REN AS
Phone: +47 976 57 599
Zvonko Tufekcic, REN AS
Phone: +47 404 00 375
Project partners/participants were
- Norsk Treteknisk Institutt, Norway
- REN AS, Norway
- Moelven Limtre AS, Norway
- Scanpole AS, Norway
- University of Göttingen, Germany
- Koppers Deutschland GmbH, Germany
- Fürstenberg-THP GmbH, Germany
- Lonza Wood Protection, UK
The project included a total of 7 work packages (WP)
WP2 - Protection Systems
Laboratory tests (EN 113, ENV 807, leaching tests) were carried out for short-term screening of protection systems. The laboratory results obtained in CreoSub must be verified outdoors and will therefore be successively supplemented by data from field tests during the next years. EN 252 stakes (500 × 50 × 25 mm3) were installed at test sites in Norway, Germany, and USA in 2015 to cover different soil and climate conditions. The stakes are evaluated annually, also beyond the project end in 2017.
WP3 - Impregnation Processes
Optimal impregnation processes for the protection systems selected in WP2 were developed. This implied to optimize process parameters to obtain ideal solution uptake and impregnation depths with all protection system components. Like the structure of WP2, the investigations were scaled-up from laboratory level to industrial level during the course of the project.
WP4 - Glulam Production
An optimal protection treatment for glulam as timber bridge components was developed. This topic was addressed in its own work package because the production of glulam requires more process steps than that of poles or sleepers. The approach was an impregnation of the glulam lamellae with copper-based preservatives in a first step. In a second step, entire glulam beams were treated with the new oil-based protection systems.
WP 5 - Physics and mechanics
The influence of the new protection systems on several mechanical properties, corrosion and conductivity were investigated.
WP 6 – Environmental assessment
Life cycle assessments (LCA) were performed on railway sleepers, utility poles, and timber bridges made of wood treated with the newly developed protection systems. These products were compared with wood product treated with creosote and non-wood products of relevance.
WP7 - Dissemination and Industrial Implementation
The structure of CreoSub implied that results were directly implemented in the industry throughout the project duration, which is reflected in the dedication of sub-work packages to industrial trials. The project results about poles presented Treteknisk for REN and the Norwegian utility companies at a final seminar in April 2018. For other publication activities, see Chapter 3 (Project results and publications).
Project results and publications
Water repellent agents are of special interest at the search for alternatives to creosote. In this regard, the performance of tall oil impregnated wood samples was analyzed in CreoSub that had been exposed in both in-ground trials and above-ground trials for a decade. Tall oil is a bio-based by-product in the Kraft process of wood pulp manufacture, which is mostly burned for energy generation today. The results revealed that raw tall oil or tall oil derivatives alone without the addition of biocides do not provide sufficient protection in heavy-duty applications outdoors; consequently, the main focus in CreoSub was on oily systems containing inorganic and organic biocides.
Laboratory decay tests according to EN 113 included 6 oil- or water-borne preservatives in up to 4 concentrations. The systems were tested against the white rot fungus Trametes versicolor and the brown rot fungi Poria placenta, Coniophora puteana, and Lentinus lepideus for 16 weeks. The results of the EN 113 tests gave initial indications for the required minimum uptakes (retentions) of the new systems that are necessary to sufficiently protect Scots pine and beech against wood destroying fungi.
In addition to laboratory tests in Kolle flasks, laboratory decay tests in ground contact (Use Class 4) were carried out according to ENV 807. The investigations were done parallel at the University of Göttingen/Germany and NIBIO/Norway in different soil types. Potential decay was assessed by determining the mass loss and dynamic modulus of elasticity (stiffness). The tests included samples of pine and beech impregnated with 8 treatments in up to 6 concentrations. The test duration was double the duration given by the standard since the preservatives are meant to preserve wood in heavy-duty applications outdoors. The results of the EUV 807 tests gave important information on required preservative retentions under real-use conditions, and on the up-scaling of impregnation processes.
The laboratory results obtained in CreoSub must be verified outdoors and will therefore be successively supplemented by data from field tests during the next years. EN 252 stakes were installed at test sites in Norway, Germany, and USA to cover different soil and climate conditions. Though the stakes have been exposed and evaluated for approximately two years by the end of CreoSub in June 2017), it is too early to draw reliable conclusions. According to EN 252, the minimum test duration is five years. The project partners will therefore follow up the performance of the test stakes during the next years.
Besides the investigations on biocidal efficacy, the ability of the preservatives to protect wood from crack formation under accelerated weathering conditions has been being investigated. Preliminary results of the ongoing test indicate that the new oil borne systems are as effective as creosote.
As a follow-up of durability tests performed in CreoSub, 160 poles were installed at two sites in coastal and interior Norway in 2018 to establish profound documentation on the performance of two of the most promising new preservatives under real-use conditions. The poles will be frequently inspected for decay and preservative migration during the next 20 years.
The driving force behind the legislative movement to ban creosote from the European market are health and environmental concerns. In this context, the stability of the preservatives against water leaching is of particular interest. Oily products showed less leaching of copper than water-borne products.
Investigations on the influence of the new protection systems on mechanics did not reveal any negative impact on the modulus of elasticity (stiffness), 3-point bending strength (static strength property), and impact bending strength (dynamic strength property). Moreover, drilling patterns to improve impregnability were optimized with respect to mechanics.
Electrical conductivity is an important material property for utility poles and railway sleepers regarding safety and signaling, respectively. Investigations in CreoSub did not show any increase in conductivity due to the new preservatives. Other aspects as metal corrosion and gluability are currently investigated.
CreoSub included life cycle analyses (LCA) to assess the impact of utility poles, railway sleepers, and timber bridge elements made of different materials on global warming and toxicity. The analyses considered following stages: the production of raw materials, transport to manufacturing, manufacturing process, use phase emissions, waste processing, and disposal.
Wooden utility poles impregnated with the new preservatives have a significantly lower impact on global warming (CO2) than poles made of steel, composite (glass fibre reinforced polystyrene coated with polyethylene), or concrete reinforced with 100% recycled steel (Figure 3). Steel poles have clearly the highest effect on human toxicity, mainly due to outputs in the production phase.
A direct comparison between creosote and the new wood preservatives shows similar performances in all LCA; however, one important difference is creosote’s classification by the International Agency for Research on Cancer as a potential carcinogen based on adequate animal evidence and limited human evidence. This classification drives the debate on banning creosote, especially due to causing skin cancer. In an LCA, however, carcinogenicity related to direct skin contact is not addressed. The impact category toxicity is only based on emissions to air, soil and water, which in turn are considered as very difficult to assess due to high uncertainty regarding the characterization factors.
- Gellerich A, Bollmus S (2014). Mögliche Alternativen zur Kreosotbehandlung von Bahnschwellen. Proceedings of Deutsche Holzschutztagung, Braunschweig, Germany. 18-19 September 2014. p 71-76
- Hundhausen U, Mahnert K-C, Bollmus S, Militz H (2014). CreoSub: New protection technology to substitute creosote in railway sleepers, timber bridges, and utility poles. Proceedings of the 10th Meeting of the Northern European Network for Wood Science and Engineering. Edinburgh, Scotland, 13-14 October 2014. p 116-121
- Hundhausen U, Mahnert K-C, Gellerich A, Militz H (2014). CreoSub – New protection technology to substitute creosote in railway sleepers, timber bridges, and utility poles. Proceedings of the 45th annual meeting of the International Research Group on Wood Protection. Utah, USA, 11-15 May 2014. IRG/WP 14-30644
- Alfredsen G, Flæte P-O (2015). Tall oil - Performance after a decade of exposure. Proceedings of the 46th annual meeting of the International Research Group on Wood Protection. Viña del Mar, Chile, 10-14 May 2015. IRG/WP 15-30672
- Mahnert K-C, Hundhausen U (2016). Encapsulation of poles to prevent moisture uptake - a laboratory test. Lisbon, Portugal, 15-19 May 2016. IRG/WP 16-40753
- Starck M, Gellerich A, Militz H (2016). Impregnation of railway sleepers – Pressure gradient and transversal penetration. Lisbon, Portugal, 15-19 May 2016. IRG/WP 16-40731
- Starck M, Gellerich A, Militz H (2016). Neue Schutzsysteme zur Substituierung von Kreosot für Bahnschwellen. Proceedings of Deutsche Holzschutztagung, Dresden, Germany. 22-23 September 2016. P 247-262
- Stolze H (2016). Specific sorting of beech and pine sapwood according to criteria for testing the elasto-mechanical characteristics. Bachelor thesis, University of Göttingen, Wood Biology and Wood Products
- Tellnes L G F, Hundhausen U (2016). Life cycle assessment of creosote treated wood and tall oil treated wood with focus on end-of-life. Proceedings of the 47th annual meeting of the International Research Group on Wood Protection. Lisbon, Portugal, 15-19 May 2016. IRG/WP 16-50320
- Mahnert K-C, Hundhausen U (2017). Review on protection of timber bridges in Norway and other countries. Proceedings of the 48th annual meeting of the International Research Group on Wood Protection. Ghent, Belgium, 4-8 June 2017. IRG/WP 17-40809
- Starck M, Gellerich A, Militz H (2017). Penetration behavior of different hydrophobic carrier substances for oily wood preservatives in Beech and Scots pine sapwood. Proceedings of the 48th annual meeting of the International Research Group on Wood Protection. Ghent, Belgium, 4-8 June 2017. IRG/WP 17-40804
- Tellnes L G F (2017). Uncertainty in life cycle assessment of preservative treated wood – copper and freshwater ecotoxicity. Proceedings of the 48th annual meeting of the International Research Group on Wood Protection. Ghent, Belgium, 4-8 June 2017. IRG/WP 17-50331
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