materials Article Factors That Affect the Mechanical Strength of Archaeological Wood—A Case Study of 18th-Century Wooden Water Pipes from Bó ˙ znicza Street in Pozna ´ n, Poland Magdalena Broda 1,2, * , Carmen-Mihaela Popescu 3,4 , Daniel Ilie Timpu 3 , Dawid Rowi ´ nski 1 and Edward Roszyk 1   Citation: Broda, M.; Popescu, C.-M.; Timpu, D.I.; Rowi ´ nski, D.; Roszyk, E. Factors That Affect the Mechanical Strength of Archaeological Wood—A Case Study of 18th-Century Wooden Water Pipes from Bó ˙ znicza Street in Pozna ´ n, Poland. Materials 2021, 14, 7632. https://doi.org/10.3390/ ma14247632 Academic Editors: Tomasz Sadowski and Marco Corradi Received: 13 November 2021 Accepted: 9 December 2021 Published: 11 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Wood Science and Thermal Techniques, Faculty of Forestry and Wood Technology, Pozna ´ n University of Life Sciences, Wojska Polskiego 38/42, 60-637 Pozna´ n, Poland; dawidrowinski@vp.pl (D.R.); edward.roszyk@up.poznan.pl (E.R.) 2 BioComposites Centre, Bangor University, Deiniol Road, Bangor LL57 2UW, Gwynedd, UK 3 Petru Poni Institute of Macromolecular Chemistry of the Romanian Academy, 700487 Iasi, Romania; mihapop@icmpp.ro (C.-M.P.); dtimpu@icmpp.ro (D.I.T.) 4 Centreof Wood Science and Technology, Edinburgh NapierUniversity, Edinburgh EH11 4EP, UK * Correspondence: magdalena.broda@up.poznan.pl 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 Bó ˙ znicza street in Pozna ´ n, 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. Keywords: archaeological wood; water mains; mechanical properties; wood degradation; FT-IR; XRD; cellulose crystallinity; cellulose; infrared spectroscopy; compression strength 1. Introduction 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 [1–3]. Usually, the wooden water main consisted of several sections about 1.8- to 3.6-m long bored logs with an internal diameter at an opening of 80 to 150 mm [4]. For early small-diameter pipes, the connections between sections were made by inserting a tapered end of one log into the broader end of the adjacent one and holding the joint together using an iron band. Sometimes bell-and-spigot joints made of lead were also applied [2,4]. Materials 2021, 14, 7632. https://doi.org/10.3390/ma14247632 https://www.mdpi.com/journal/materials