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Comparison Some Physical and Mechanical Properties ofAbonos and Recent Oak (Quercus robur L.)

Tomislav Sinković ; Šumarski fakultet Sveučilišta u Zagrebu
Slavko Govorčin ; Šumarski fakultet Sveučilišta u Zagrebu
Tomislav Dubravac orcid.org/0000-0003-3133-8322 ; Šumarski institut Jastrebarsko
Valentin Roth ; Šumarski institut Jastrebarsko
Tomislav Sedlar orcid.org/0000-0002-7124-4470 ; Šumarski fakultet Sveučilišta u Zagrebu

Sažetak

Abonos, eban and bog-wood are the terms for wood exposed to the effects of water and processes of humification in soil for a long period of time. Abonos of several tree species has been discovered so far, but the most common and also most valued is the oak abonos, often named black oak-wood, or bog-oak. Black color of bog-oak is the result of chemical interaction of tanstuff in the wood and iron in water. Water in the environment in which bog-oak is formed provides unfavorable conditions for the development of microorganisms and fungi that would otherwise decompose the wood. Deposition of minerals from the water ensures conservation and durability of wood structural elements. Aforementioned processes that form the bog-oak also change its chemical structure, and physical and mechanical properties. Time period for which the wood was under bog-oak forming conditions spans from several thousands up to several tenths of thousands of years. Uniqueness and high value of bog-oak stems from its durability, aesthetical features, black color, acoustical properties and old age. From bog-oak wood following products can be made: veneer, high-quality and high-value furniture, parts for musical instruments, high-value objects for everyday use, etc. Bog-oak wood is also very highly esteemed in artistic circles among sculptors and other artists. According to past experience, bog-oak is usually found purely by accident, most often during the construction works for the regulation of stream and river beds, ameliorative works, or because of the exploitation of gravel. Equalizing the terms bog-oak and archeological wood by some authors does not reflect the specific properties of those materials. Archeological wood is not necessarily, or very rarely is bog-oak wood, due to the usage of a number of tree species during history other than oak. On the other hand, bog-oak is archeological wood simply because of its age, even if in some cases it does not have any true archeological value.
Samples for this research of technical properties of bog-oak wood were supplied by Benković Hrvoje and Franjić Darko from the area of Oštra Luka (Orašje, Bosnia and Herzegovina). Bog-oak was accidentally found on that area during the exploitation of gravel. After the discovery, it was very difficult to extract and transport parts of trees and stems of bog-oak from the depth of six meters. Divers extracted the wood from the river bed, and wood was transported to the river shore by attaching barrels to the extracted wood. Extracted parts of trees and stems were transported to the roofed warehouse and partly wrapped in plastic foil to slow down the process of drying. Wrapping in foil is necessary to prevent cracking of bog-oak wood in the case of rapid loss of water during drying. Process of slow drying has to be constantly supervised in order to prevent forming of mold. This is achieved by adjusting the surface of bog-oak under plastic foil. After the successful drying of bog-oak wood (i.e. down to the 12–18 % of water content), it is possible to saw the bog-oak wood into desired assortments. Sawed assortments are once again exposed to the process of drying to achieve water content of 12 %. Samples for this research were extracted from bog-oak assortments prepared in the way described above.
Goal of this research is to determine technical, i.e. physical and mechanical properties of bog-oak wood, and to compare them with same properties of recent oak wood. Comparison is possible due to the fact that both materials originate from the same area within the distribution range of pedunculate oak (Quercus roburL.). Values of physical and mechanical properties of pedunculate oak wood were taken from the oak wood from Topolovac and Boljkovo.
From the research results acquired from the testing of physical and mechanical properties of bog-oak and from its comparison with properties of recent oak several conclusions were formed. Average value of density of bog-oak in absolutely dry condition is 0.704 g/cm3, and is 15.8 % higher than that of the wood density in absolutely dry condition of recent oak.
Average value of total radial shrinkage for bog-oak amounts to 10.5 % and is for 105.9 % higher than that of recent oak. Average value of total tangential shrinkage for bog-oak wood is 18.6 %, and is for 104.4 % higher than average value of total tangential shrinkage of recent oak. Average total volumetric shrinkage of bog-oak is 27.6 %, and is for 101.5 % higher than that of recent oak wood. Average value of ultimate strength in static bending for bog-oak wood was 101.3 MPa, which is for 10.8 % higher than ultimate strength in static bending of recent oak wood. Average value of ultimate stress in compression parallel to grain for bog-oak wood was 52.3 MPa and does not significantly differ from the ultimate stress in compression parallel to grain measured in the wood of recent oak, although is 1.5 % smaller.

Ključne riječi

abonos; bog-oak (oakwood buried in the ground); physical and mechanical properties of abonos; physical and mechanical properties of recent oak

Hrčak ID:

45105

URI

https://hrcak.srce.hr/45105

Datum izdavanja:

31.12.2009.

Podaci na drugim jezicima: hrvatski

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