Elisa Pecoraro

Quantitative evaluation by attenuated total reflectance infrared (ATR-FTIR) spectroscopy of the chemical composition of decayed wood preserved in waterlogged conditions.

This paper reports on the assessment of lignin and holocellulose by means of ATR-FTIR analysis and multivariate PLS regression. The analysis was conducted on 59 samples coming from different excavations where wood had been preserved in waterlogged conditions. A range of results from different wood species (Alnus sp.p., Cupressus sempervirens, Larix decidua, Picea abies, Pinus sp.p., Quercus sp.p., Ulmus sp.p.), states of preservation, waterlogged environments, and burial times are presented. A calibration model was selected after comparing different reference data (samples extracted and not-extracted, and ash-rich and ash-free bases of calculation for the calibration values), and two different post-acquisition spectroscopic manipulations (both in terms of normalisation procedures and of spectral ranges used for the calibration). Results showed that the best models were different depending on which considered component (lignin or holocellulose) was measured and to which data set (softwood or hardwood) the samples belonged. It is shown that the predictive ability of the models is affected by high ash content (too contaminated samples had to be excluded in order to attain good results, because of excessive overlapping of bands related to the inorganic fraction) but not by the preliminary extraction of sample. Furthermore, the stability of best models is also demonstrated and a procedure of external validation carried out on an external set of samples confirmed the general validity of the identified models.

A New Method to Quantitatively Evaluate the Chemical Composition of Waterlogged Wood by Means of Attenuated Total Reflectance Fourier Transform Infrared (ATR FT-IR) Measurements Carried Out on Wet Material

Wood degradation in waterlogged conditions, although slow, is relevant in some specific contexts, such as in the case of cultural heritage preservation (e.g., ancient shipwrecks found under the water table). This decay process induces the selective depletion of the biopolymers constituting wood cell walls and mainly of their structural polysaccharides (both cellulose and hemicelluloses). Assessment of residual composition of cell walls is normally carried out using conventional chemical analyses, which, however, require elevated amounts of material. The present work reports on a new approach to quantitatively determine the residual chemical composition of wood (in terms of amount of lignin and holocellulose) and therefore its extent of degradation. This was accomplished by acquiring attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectra on material still in waterlogged conditions, which was simply placed in optical contact with the ATR crystal. Data for the calibration set were obtained by means of wet analyses, and the calibration model was based on multivariate statistical analysis through partial least square regression. Acquired spectra showed signals higher and better resolved than for dry wood. Calibration was selected after comparing two different normalization procedures and after processing signals of two different spectral ranges. Furthermore, the exclusion of some outliers led to a substantial improvement in the error parameters (R2 and root mean square error of cross validation) associated with the calibration model, thus allowing for the selection of the best model. The stability of this best model was also established by means of the leave-more-out method. Finally, a procedure of external validation confirmed that the proposed model also could be applied to similar (for instance, belonging to Pinaceae) wood remains from other excavations.

Dynamic mechanical analysis (DMA) of waterlogged archaeological wood at room temperature

Abstract The viscoelastic properties of waterlogged wood (WLW) were investigated via dynamic mechanical analysis (DMA) at room temperature and under water saturated conditions, aiming at the investigation of the relationships between viscoelasticity and chemical composition. Different softwoods (SWs) and hardwoods (HWs) from several archaeological sites were sampled, which had different levels of decay (from highly-decayed to little changed). The analytical methods included lignin and holocellulose determination by Fourier transform infrared (FTIR) spectroscopy, moisture content (MC), basic density (BD), micromorphological observations, and the DMA was performed in three-point bending and submersion mode. Both HWs and SWs showed an exponential decrease of both storage modulus (E′) and loss modulus (E″), which are related to the amount of crystalline and paracrystalline cellulose left in the cell wall, respectively. The ratio E″/E′ (tanδ) varied with the frequency in different ways depending on the preservation state of the samples. Less decayed material had a higher tanδ than the fresh reference wood and lower (or similar) tanδ in the case of highly decayed samples. Accordingly, the long-term behaviour under a certain sustained load of WLW is decay dependent.

Understanding Spanish Timber Jack Arch Floors: Examples of Assessment and Conservation Issues

Jack arch floors are structures made of timber joists, with round or squared section, and segmental vaults either made of flat tiles or poured plaster conglomerate. They are especially diffused along the Mediterranean coast of Spain and can be considered as a main feature of the historical and vernacular architecture of the area. In order to assess and grade these structures several Spanish standards have been considered; however, even if the information contained is useful the Italian standard for the on-site diagnosis UNI 11119 of 2004 has been preferred. The method described in this standard leads the assessment through the grading of each and every timber element and the assignation of bearing properties that are essential for the consolidation project. This article will expose three examples of jack arch floors of the Valencian Community graded using the Italian standard and the conservation issues that arise from the results.

A Peculiar Spanish Timber Floor, the "Revoltón": A Diagnostic Example at the "Palacio del Marqués de Benicarló"

The paper deals with the application of the Italian method for assessing on-site and diagnosing timber elements to a distinctive Spanish type of horizontal structure called “revoltón” i.e. jack arch floor. As in Spain does not exist a specific regulation for the on-site diagnosis of timber elements, this analysis was performed according to the Italian standard UNI 11119. Due to the peculiar features of the jack arch floor some modifications were applied to the method.During spring 2012 the authors had the opportunity to carry out a pilot project by making a diagnostic analysis on a whole three stories building. The building, “Palacio del Marqués de Benicarló”, located in Spain in the town of Benicarló, between Barcelona and Valencia, was erected during the second half of the XVIII century. It maintains the original internal distribution and structure, and it is characterized by precious ceramic decorations on walls and floors. All the horizontal structures studied inside the palace were jack arch floor except the roof structure that was also made of timber.The results of the project described in the paper clarify the specific problems of the horizontal structures and the roof surveyed during the fieldwork. These results are accompanied by several plans that represent the information recovered on-site and lead to a complete assessment of the structures. The plans include the grading based on wood defects, the local moisture content of wood, the superficial and inner decay due to insects and rot and the deformation of the joists. In this way it was possible to locate the areas of the palace where more problems were concentrated, and better understand the causes and origin of the damages.