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The use of chemical wood modifications to protect wood against wood-borers in the marine Environment

Summary of the Project

Wood is a widely available, inexpensive, renewable material and is used in lots of marine structures. Despite these favourable characteristics, a principal restriction has been its susceptibility to destructive attack by wood-borers. Degradation of wood by marine woodboring species causes world-wide major economic losses. Wooden structures are usually designed for a life span of 40 to 50 years, but because of the ravages of wood borers, untreated European wood constructions have a much shorter service life time. Therefore the use of wooden materials is hardly satisfactory, particularly as the substructure placed on the piles involves a couple of million euros per unit. Data confirm that the yearly costs to repair or renew wooden constructions in the marine environment can be really high. The most destructive wood-borers found in Europe include shipworms (from the family Teredinidae), wood piddocks (e.g. from the family Pholadidae) and gribbles (from the families Limnoriidae, Sphaeroma and Chelura). Other groups of wood-borers cause only superficial damage to submerged wood and are not of major concern. Since quite some species are warm water species, their activity might also increase in the future, due to global warming. Another trend that can be observed is that the territory of wood-borers increases. Wood-borers prefer normally environments with a higher salt level, however in the last decades it seems that they start to accept also lower salt concentrations, making it possible to survive also in places like the Baltic Sea. Various types of wraps, physical barriers, and chemical biocides or wood preservatives have already been used to discourage or remediate borer attack. They can protect wood by limiting oxygen supplies, preventing settlement of larvae or restore structural integrity to damaged piles. Until now they are not completely successful since they may present significant design challenges, are effective only when intact or have shown effectiveness only against certain wood-borer species. Also the borer hazard from some sites in European coastal waters is not representative of that in other sites. In addition, the EU directive in now limiting the use of established and proven preservatives, such as creosote and copper-chrome-arsenic in wood destined to be used in marine construction. Considering that wood is renewable material with low embodied energy, which can be reused and captures CO2 in its structure, it is retaking its place as a very valuable construction material and its use for maritime applications should be favoured. Thus research to improve the durability of wooden materials in the marine environment is of great importance. It is important to develop alternative wood treatments that are effective, inexpensive, and environmentally acceptable. In this project, several chemical modifications and concentrations will be screened and it will be defined how the chemicals are bound to the wood. Evidence that chemical reaction has taken place can be followed by infrared spectroscopy and other spectroscopic techniques. Its influence will be followed on the most destructive wood borer species. Since each wood borer species has different habits, it will be interesting to do lab-tests on each species separately in aquaria with seawater on the right temperature: 1) feed them with the treated wood 2) to see what happens if only half the wood is treated and 3) to see what happens if they have the choice between treated and untreated wood. With the most promising results we will do a bigger test in the sea, where several wood-borers live together. Also leaching tests of the modified wood will be performed. The different processes and its variables need to be studied and understood and will be therefore backed up with IT-tools for modelling and prediction, which will be developed/customised in the project. Environmental impacts will be considered in each step by a thorough life-cycle assessment analysis of the materials and processes. The Slovene and Serbian collaborating institutions will contribute to the project, each with its strengths (equipment, knowledge, experience, expertise) for the particular challenges.

Relevance of the results expected from research project

The new knowledge about the influence of wood modification agents on wood borers and interactions between wood modification agents, wood and the marine environment will be amalgamated into and presented in minimum 3 publications in professional or high-ranking scientific journals, and minimum 3 presentations at scientific conferences. New IT-supported databases will be prepared with information about short and long term effects of modification agents on wood, the necessary wood treatment processes and its chemistry, which gives a promise for the development of so-called »rational design« of wood applications in marine environment in the future. These databases can be also a valuable prediction tool for wood modification emphasizing environmental friendliness of new products, its impact on different wood-borer species as well as service life and after service life scenarios for the modified wood. Recommendations will be prepared to assist authorities and researchers concerned with the protection of wood in the sea. The project will be also a great opportunity for a certain amount of early stage researchers to develop their careers, starting with their thesis preparation and defence. The collaboration with Serbia will not be only a scientific exchange, but also, equally important a cultural exchange and people will learn to work together with others with different backgrounds (cultural, socio-economic, education, etc.). As the protection against wood borers would be of a great economic importance, a further development of the most economical and environmental promising chemical wood modification procedure is foreseen, beyond the scope of this basic project, in collaboration with the industrial partners.