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ŠUMARSKI LIST 11-12/2009 str. 49     <-- 49 -->        PDF

T. Sinković, S. Govorčin, T. Dubravac, V. Roth, T. Sedlar: USPOREDBATEHNIČKIH SVOJSTAVAABONOSA... Šumarski list br. 11–12, CXXXIII (2009), 605-611


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.


Key words:abonos, bog-oak (oakwood buried in the ground), physical and
mechanical properties of abonos, physical and mechanical properties of recent oak