Abstract
Large amounts of archaeological wood are often excavated during groundworks in cities and towns. Part of the unearthed artefacts is usually saved, conserved and then presented in museums. However, if the finding contains several similar objects, some of them could potentially be further employed for some other practical purposes. The research aimed to determine the mechanical performance of the remains of wooden water mains excavated at Bóżnicza street in Poznań, Poland and evaluate its potential usefulness for any practical purposes. First, wood density was determined along with its mechanical strength in compression. The density of archaeological wood identified as Scots pine was lower than contemporary pinewood (383 kg × m−3 vs. 572 kg × m−3); therefore, its mechanical properties in compression tests were also lower, as expected, making the wood unsuitable for any practical applications. However, the differences in modulus of elasticity and compressive strength were not justified by the differences in wood density. Further infrared spectroscopy and X-ray diffraction analyses revealed additional differences in chemical composition and cellulose crystallinity between archaeological and contemporary wood. The results indicated the decrease in carbohydrate content and cellulose crystallinity in degraded wood, which, in addition to wood density, apparently contribute to the deterioration in mechanical strength of archaeological wood. The case study of the excavated archaeological wooden pipes shows that they have historical value but are not useful for practical purposes. It also revealed that not only wood density but also its chemical composition and cellulose crystallinity level has a substantial impact on the wood mechanical properties, particularly in compression.
Highlights
The history of wooden water pipes dates back to the 17–19th centuries
Archaeological wooden log used in the study was selected among the excavated water pipes based on the ability to obtain a sufficient number of appropriately oriented and defectless wood samples required for mechanical tests
To modulus of elasticity (MOE), the relative/compressive strength (Rc) values show a typical order dependent on the anatomical direction (RcL >> RcR ≥ RcT). They are within the range of compressive strength specific for the species [61], and they are higher than archaeological wood (2.2, 3.5, and 3.3 times in L, T and R, respectively)
Summary
The history of wooden water pipes dates back to the 17–19th centuries. They replaced stone, clay and terracotta water mains and aqueducts invented by ancient Greeks and Romans and, together with complex networks of pumps, water towers and reservoirs, they enabled the development of modern cities worldwide [1,2,3]. In the light of this discovery, a question has been raised whether the archaeological wooden logs that undoubtedly provide us with a valuable picture of the ingenuity and skills of our ancestors should only serve as a witness of our history being publicly exhibited in the museum or maybe it could be employed for any other useful purposes Whatever counterintuitive it may seem, it has been shown several times that selected mechanical properties of wood can remain unchanged or even improve slightly upon hundreds of years of ageing [42,43,44,45]. Images of wood tissue were captured using a microscope-attached camera Moticam 2.0 (MoticEurope, S.L.U., Barcelona, Spain) coupled with a computer and analysed with a Motic Images Plus 2.0 (2017, MoticEurope, S.L.U., Barcelona, Spain) ML image analysis software
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