Preservative-treated Wood Research Articles

Biodeterioration Field Test and Mechanical Properties of Maesopsis eminii Wood Treated with Boron Preservative and Plant Oils

Boron preservatives have insecticidal and fungicidal effects. The leaching problem of boron preservative-treated wood can be overcome using oil treatment. This study evaluated the resistance in a biodeterioration field test and the mechanical properties of manii wood (Maesopsis eminii Engl.) treated with boric acid and plant oils. Manii wood samples were impregnated in two stages with boric acid and vegetable oils (neem, tamanu, and candlenut oils). The impregnation process was performed in a chamber at a pressure of 7 kg cm−2 for approximately 4 h. Next, the sample was heated at temperatures of 60 °C, 120 °C, and 180 °C. The biodeterioration field test was conducted in ground contact for 100 days. In addition, mechanical tests in terms of modulus of elasticity (MOE), modulus of rupture (MOR), and hardness were conducted using an Instron universal testing machine. The test results prove that the combination of boric acid preservation with neem, tamanu, or candlenut oil treatment increases the resistance of manii wood to subterranean termites, especially when the treatment is accompanied by heating at 120 °C. The combination treatment of boric acid and plant oils also increases the MOE, MOR, and hardness values of manii wood.

Critical Review on the Use of Extractives of Naturally Durable Woods as Natural Wood Protectants.

Naturally durable wood pre-dates preservative-treated wood and has been demonstrated to offer a suitable service life for certain applications where preservative-treated wood is not feasible. Heartwood extractives have been demonstrated to impart bio-deteriorative resistance to naturally durable wood species. These extractives are typically found in the heartwood of living trees and are produced either by the death of parenchyma cells or as the result of external stimuli. The mechanisms of natural durability are not well understood, as heartwood extractives can be extremely variable in their distribution, composition, and efficacy in both living and harvested trees. The underlying complexity of heartwood extractives has hindered their standardization in residential building codes for use as wood preservatives. The use of naturally durable lumber is not always feasible, as woods with exceptionally durable heartwood do not typically yield lumber with acceptable machining properties. A potential approach to overcome the inherent difficulty in establishing guidelines for the appropriate use of naturally durable wood is to focus solely on the extractives as a source of bioactive protectants based on the strategies used on living and dead wood to repel the agents of biodeterioration. This critical review summarizes the relevant literature on naturally durable woods, their extractives, and their potential use as bio-inspired wood protectants. An additional discussion will be aimed at underscoring the past difficulties in adopting this approach and how to overcome the future hurdles.

The use of isothermal calorimetry to measure corrosion rates of metals in contact with preservative-treated wood

The purpose of this paper is to examine whether isothermal microcalorimetry can be used to determine the corrosion rates of metals embedded in wood. Metal fasteners were driven into dowels of wood treated with alkaline copper quaternary, a common wood preservative that increases the corrosiveness of wood. The dowels were stored in a nearly 100% relative humidity environment at 27°C for one year; throughout the exposure period, dowels were removed and the thermal power generated by the sample was measured in an isothermal calorimeter. Measurements over the 1-year exposure showed that the thermal power depended upon the wood moisture content and ranged from 0 to 200 µW. The heat, determined by integrating thermal power over time, was higher than expected compared with the total amount of mass lost due to corrosion at the end of the experiment. Despite this, the technique shows promise as a method to determine how changes in wood moisture content affect the corrosion rates of metals in contact with preservative treated wood.

Durability of Wood Exposed above Ground—Experience with the Bundle Test Method

The durability against decay organisms is an essential material property for wood in outdoor use. A jack of all trades method for above-ground wood durability testing has been sought for decades, but until now no method has found its way into European standardization. The method of choice shall be applicable for untreated and treated wood—ideally also for wood composites. It shall further be reproducible, objective, fast, easy, and inexpensive. Finally, it shall provide high predictive power. This study was aimed at a review of results and practical experience with the Bundle test method which could serve as a standard procedure for above-ground field tests of wood-based materials. The method allows for water-trapping, creates a moderate moisture-induced decay risk typical for UC 3 situations, and was found applicable for a wide range of wood materials. The method allows for rapid infestation and failure of non-durable reference species within five years in Central Europe. Based on results from Bundle tests with different modifications and performed at different locations, a guideline has been developed. The method is recommended as a suitable tool for determining the durability of various wood-based materials including modified and preservative-treated wood and can provide data for durability classification.

Laboratory Durability Testing of Preservative-Treated Wood Products

Recently, certain European standards have allowed for the classification of the biological durability of chemically modified wood and preservative-treated wood, including treated products, but necessary methods for representative sampling and testing are lacking. Instead of sampling from products that can contain areas of varying durability, this study aimed at testing full-size products. Sections of untreated and preservative-treated terrace decking and palisades were incubated with pure cultures of brown and white rot fungi. Instead of mass loss, the decayed cross-sectional area was determined. The spatial distribution of decay and wood moisture content was investigated. After 16 weeks of incubation, all untreated product specimens showed signs of decay independent of the test fungus. The treated specimens were less affected. The mean and the maximum decayed cross-sectional areas were well correlated, for both the total and the sapwood cross-sections. The wood moisture content after incubation was always favorable for fungal decay, but highest where the specimens were in direct contact with the malt agar. Different infestation pathways became evident: (1) from the sapwood mantle, (2) via radial checks, and (3) from the end-grain. The latter should be prevented in order to better mimic real outdoor exposure conditions.

Bioleaching of heavy metals from preservative-treated wood using Aspergillus tubingensis

Abstract Although fungal bioleaching with Aspergillus niger has been investigated to remove metal from treated wood wastes, toxicological concerns limit the practical use of the species, necessitating the search for non-toxic species with comparable or greater metal removal efficiency. The removal of metals from wood treated with chromated copper arsenate (CCA) and copper amine-based preservatives was investigated using the non-ochratoxigenic mold Aspergillus tubingensis in comparison to A. niger via bioleaching. Metals were bioleached for 10 days by immersing treated wood sawdust in fungal culture filtrates. Culture filtrates were prepared by growing fungi in malt extract (ME) and sucrose media and then filtering the fungal biomass. Oxalic acid and citric acid were the predominant organic acids in A. tubingensis culture filtrate in ME and sucrose media, respectively. Citric acid present in sucrose media was found to be a more effective leaching agent for metals from preservative-treated wood. Citric acid produced by A. tubingensis and A. niger in sucrose media removed nearly 95% of copper, 80%–85% of chromium, and arsenic from CCA-treated wood, and 80%–90% of copper from wood treated with copper amine-based preservatives. As a result of its non-toxigenic characteristics and high metal removal efficiency, A. tubingensis may be a useful fungus for bioleaching metal components from inorganic preservative-treated wood.

Comparison of fungal diversity on woods with different fungal susceptibility during above-ground exposure

Sequential fungal changes that occur on three types of wood are described, namely naturally durable wood, preservative-treated wood, and radiata pine (considered as untreated wood) for above-ground use, during a four-year survey period. The surveys were conducted thrice at 1, 2, and 4 years of exposure. During the first and second years of exposure, both total fungal isolates and species diversity were low in each wood sample, with ascomycetes being the most prevalent. Additionally, the predominant species displayed a trivial impact on wood decay. However, after two years of exposure, the number of fungal communities increased sharply, accompanied by a considerable shift in the diversity of basidiomycetes, some of which established themselves as dominant species. The survey provides a snapshot of the initial stages of wood decay. Further, it reiterates that while fungal communities on wood are influenced by spores or hyphae in the surrounding air, colonization is further modulated by fungal susceptibility on the basis of durability. An expanded study is necessary for better comprehension of the processes involved in wood decay in their entirety.

Copper Distribution in Preservative-Treated Wood to Maintain Preservative Performance in Domestic Above-Ground Wood Environment

Copper Distribution in Preservative-Treated Wood to Maintain Preservative Performance in Domestic Above-Ground Wood Environment

Compatibility of preservative with adhesive in Eucalyptus grandis laminates

ABSTRACT The fundamental factors responsible for the complexities in adhesive bonding of preservative-treated wood are predominantly wood species, preservative composition, and adhesive system. It is post-effect of these factors that process variables such as assembly times and bonding pressure exert secondary influences on adhesive-bond development in preservative-treated laminates. Hence, this study investigated the effect of copper azole (CA) and disodium octaborate tetrahydrate (DOT) impregnations on E. grandis heartwood (HW) and sapwood (SW) bonding with melamine–urea–formaldehyde and polyurethane adhesives. Based on the adhesives and bonding conditions investigated, the CA and DOT-treated E. grandis laminates do not satisfy at least one of the shear strength and delamination requirements according to EN 14080:2013. Contrary to delamination, shear strength was significantly affected by the HW–SW difference. This study established the basis for further considerations on adapting bonding conditions for improved adhesive-bond performance in CA and DOT-treated E. grandis laminates towards manufacturing durable hardwood composite for tropical and subtropical environments.

Radial variation in bonding performance of preservative-treated wood within Pinus elliottii trees and its relationships with wood density and adhesive penetration

Pinus elliottii wood from different radial locations within trees was used to prepare two-layer preservative-treated wood joints with alkaline copper quaternary preservative and emulsion polymer isocyanates (EPI) or resorcinol-phenol-formaldehyde (RPF) adhesives. The radial variations in shear strength and wood failure percentage were analyzed. Radial variations in wood density and average penetration depth (AP) of adhesives were investigated to establish relationships between shear strengths and characteristics of bonded joints. The shear strengths of EPI- and RPF-bonded joints showed similar increasing trends from pith to bark, and they varied in ranges of 2.92 to 8.13 MPa and 2.03 to 7.12 MPa, respectively. The wood failure percentage of EPI joints (93% to 100%) had no significant differences in all the radial locations, but that of RPF joints (60% to 100%) showed a clear decreasing trend from pith to bark. High positive linear correlations were found between the shear strengths and wood density, and Pearson’s correlation coefficients for EPI and RPF were 0.934 (p < 0.01) and 0.931 (p < 0.01), respectively. Wood density is a very important factor influencing radial variations of bonding strengths. The correlation between the AP and shear strength was not significant at the 0.05 level.

Bending and Impact Testing of Wood Guardrail Posts Evaluated using Stress Wave Timing Inspection

Guardrail systems throughout the U.S.A. often use preservative-treated wood posts. When a vehicle strikes the system, the posts should have sufficient fracture resistance to ensure they perform as intended by rotating in the soil, dissipating crash energy. Preservative chemicals used in wood guardrail posts do not always penetrate deep into the wood; therefore, the outer shell can appear to be in good condition, with a core that is decayed. Stress wave timing (SWT) is a proven technology for evaluating the condition of wood, especially for detecting possible internal decay. This study examines the efficacy of the new SWT prototype to detect internal decay, and to indicate if posts are compromised with respect to flexural strength and impact resistance. SWT proved to be an effective non-destructive testing method for field inspection of wood guardrail posts with 86% accuracy of decay detection. Post-bending stress grade was found not to be a reliable predictor of guardrail post impact integrity. Of 66 posts tested with internal decay, only nine failed to meet the AASHTO M168-07 minimum stress grade in static flexure. However, dynamic impact testing clearly demonstrated that the impact resistance of decayed posts was significantly lower than that of sound posts. Therefore, if SWT is deployed for inspection of wood guardrail posts it is recommended that any posts with stress wave velocity less than a predetermined threshold (such as that reported here) be further inspected using a minimally invasive tool and removed from service to decrease the likelihood of fracture during a collision.

Water-Borne Wood Preservation and End-of-Life Removal History and Projection

Use of water-borne wood preservatives began in approximately the 1950s. Residential and commercial uses rapidly developed for products such as decking, fences, and other outdoor structures. Nearly all such products were treated by preservatives using arsenic as a major ingredient. The most common preservative was chromated copper arsenate (CCA). A smaller volume used ammoniacal copper zinc arsenate (ACZA). Preservative label changes made in 2003 limited uses of these arsenical treatments to industrial or agricultural type uses, such as poles, piles, ties, bridges, and fencing. Use volumes of preservative-treated wood continued to grow after the label change, but the types of preservatives used changed greatly. The amounts of water-borne treated wood reaching end-of-life and being disposed also continued to grow, reflecting the increasing inventory of volume in service. However, the volume of arsenical-treated wood being disposed peaked in approximately 2008 and is now only approximately one-quarter of that volume. Most of the arsenical-treated wood now being disposed consists of large, easily identified and separated pieces, such as round poles, piles, and fence posts and timbers, which can be easily managed separated from other wood construction and demolition (C & D) waste. Thus, managing C & D waste to limit arsenic contamination of potential products, such as mulch, will be much more practical than some have feared.

2018 Railroad Tie Survey

This article reports results of a survey of railroad tie management conducted by the Association of American Railroads (AAR) reflecting 2017 practices. Similar surveys were previously conducted for 2013 and 2008 practices. North American railroads purchase approximately 23 million new wood crossties annually. Most ties are used to replace worn ties. Through this survey, the AAR seeks to provide clarity to its member railroads, the regulators, and other interested parties, regarding how the railroads’ tie purchase preferences and used tie management choices have been changing in response to changing technologies and regulations. Technology changes include use of borate preservatives to dual-treat wood ties to provide longer service life in high decay environments, non-wood ties made of concrete or plastic, and energy conversion methods for used ties such as gasification and torrefaction. Passage of the EPA Non-Hazardous Secondary Materials (NHSM) rule in 2011, including updates in 2013, 2016, and 2018, is reducing the potential for recycling used ties as fuel. However, the EPA is also promoting use of biological materials, such as wood, to produce energy without increasing carbon dioxide (CO2) levels in the atmosphere, thus reducing human caused climate change. Purchase and tie management trends are indicated by the survey results. Approximately 95% of all ties purchased are preservative-treated wood. Due to demonstrated longer service life in high decay zones for wood ties that are dual treated with borate and either creosote or copper naphthenate, the fraction of concrete and plastic tie purchases has decreased while the faction of dual treated wood tie purchases has increased. Recycling used ties for energy remains the most common practice, at 66% of ties, but has declined from 81% in 2013. Reuse of ties for other treated wood uses, such as landscape and agricultural type purposes, remains common at approximately 18%. Landfill disposal remains uncommon, but seems to be increasing at 6% of removed ties. The shift away from recycling for energy is thought to result from the both impact of the EPA NHSM rule and the low cost of natural gas. The smaller market tie users, mainly the short line railroads in contrast to the Class 1 railroads, manage far fewer ties per company, but purchase and manage approximately 31% of all ties. The short lines recycle to landscape and agricultural uses at about half the rate of the Class 1s and dispose in landfills at a much higher rate of 76% versus 1.2% for the Class 1s. This difference is thought to result from the economics and availability of local versus distant management options.

Corrosion of metal fasteners embedded in acetylated and untreated wood at different moisture contents

ABSTRACT Acetylated wood is now commercially available and designed to be used in certain outdoor applications as an alternative to preservative-treated wood. Fastener corrosion can be a concern in preservative treated wood when the wood remains wet for long periods. However, little data on the corrosiveness of acetylated wood exists beyond the product literature. Here we examine the corrosiveness of commercially obtained acetylated wood and compare it against unmodified (untreated) southern pine (Pinus spp.). Corrosion rates of plain carbon steel, hot dip galvanized steel, and stainless steel were calculated gravimetrically after a one year exposed in the wood. Four different moisture conditions were examined: 90% relative humidity (RH), 95% RH, 100% RH, and a fully water saturated condition. When compared to literature data on the corrosion of fasteners in preservative treated wood at 100% RH, the acetylated wood had much lower steel corrosion rates than all preservatives examined; the measured corrosion rates for galvanized steel were lower than all preservatives except chromated copper arsenate. These measured corrosion rates across a range of moisture conditions can be used to inform the selection of appropriate corrosion resistant fasteners when building with acetylated wood.

Evaluation of Deterioration of Larix kaempferi Wood Heat-treated by Superheated Steam through Field Decay Test for 12 Months

In this study, the decay resistance of larch wood, which was heat treated by superheated steam, was evaluated by the field decay test. During the field decay test of 12 months, non-treated wood has been severely damaged by termite, however, no visible damage has occurred in the preservative-treated wood and superheated steam heat-treated wood. Results of field decay test showed approximately 5% mass loss of the non-treated wood and the preservative-treated wood, and approximately 1% mass loss of the superheated steam heat-treated wood. After the field decay test for 12 months, the residual amount of preservatives remaining in the preservative-treated wood was lower than that before the field decay test. It was considered that the preservative was partially eluted during the field decay test, and the mass loss of the preservative-treated wood was thought to be similar to that of the non-treated wood. Through this study and additional long-term monitoring test, superheated steam heat treatment can be considered to be an environmental-friendly method to enhance the decay resistance of wood against rot fungi and/or insect without chemical treatment such as preservative injection.

Metals content of recycled construction and demolition wood before and after implementation of best management practices

A limitation to recycling wood from construction and demolition (C&D) waste is contamination of metals from the inadvertent inclusion of preservative treated wood, in particular wood treated with chromated copper arsenate (CCA) and newer copper-based formulations. To minimize contamination many regions have developed best management practices (BMPs) for separating treated from untreated wood. The objective of this study was to evaluate the fraction of preservative treated wood in recycled C&D wood after the implementation of BMPs, using Florida as a case study. Methods involved collecting recycled C&D wood samples from throughout the state, measuring metals concentrations (As, Cu, and Cr) in the samples to compute the fraction of recycled wood treated with waterborne wood preservatives, and comparing measurements with those taken prior to the formalization of BMPs. Metals concentrations were measured using two methods, one based on traditional laboratory digestion methods and another using a more rapid hand-held X-ray Fluorescence (XRF) device in the field. The proportion of waterborne preservative-treated wood in recycled wood products has reduced significantly in the intervening 20 years (from 6% to 2.9%), and the fraction of CCA-treated wood has been reduced even further, to 1.4%. The remaining fraction of waterborne preservative-treated wood is comprised of new formulations of copper-based preservatives. This suggests that restrictions from the wood preservation industry and best management practices implemented at recycling facilities have been effective in reducing heavy metal contamination from pressure treated lumber in recycled wood products.

Fungal–copper interactions in wood examined with large field of view synchrotron-based X-ray fluorescence microscopy

ABSTRACTThe goal of this study was to demonstrate how synchrotron-based X-ray fluorescence microscopy (XFM) can be used to better understand the mechanisms of copper tolerance in wood decay fungi. Copper is a major component in commercial wood preservatives as it is toxic to many wood decay fungi. However, certain fungi are copper tolerant and can attack preservative-treated wood, resulting in structural damage to treated wood members. Here we used large-field XFM to visualize six different elements (K, Ca, Mn, Fe, Cu, and Zn) in the mycelia and wood inoculated with four different species of brown rot wood decay fungi. Wood blocks were partially dipped into a solution of copper sulfate, exposed to fungi in malt extract agar petri dish assays for nine weeks, and then imaged and compared to blocks that were partially dipped in water. The blocks were imaged immediately adjacent to an end-matched control that was placed in malt extract agar petri dish assays for 9 weeks, but not exposed to the fungi so that the differences in the elemental distributions could be directly compared. The colonized wood and mycelia were rich in K, Ca, Mn, and Fe; however, the elements and the spatial distribution in the mycelia and wood differed across fungal species. The most interesting results were the maps showing the copper distribution. While three of the four fungi grew on the copper-rich region of the wood, only one species, Fibroporia radiculosa, dramatically reduced the copper concentration in the region of fungal growth.

Design and performance prediction of timber bridges based on a factorization approach

ABSTRACTService life of timber bridges is predominantly affected by the site-specific climatic conditions in terms of moisture and temperature over time, the overall design, the design of details, and the choice of materials. In recent years, a performance-based methodology has been developed to predict (1) the material climatic conditions within timber components from macro climate data and comparison between design details, (2) decay intensity from material climate data, and (3) the material resistance as a combined effect of wood-inherent properties and its moisture dynamics. Within the WoodWisdomNet project ‘Durable Timber Bridges’ we emphasized on utilizing exposure, decay, and resistance models for a comprehensive guideline for the design of timber bridges. Therefore, a factorization approach is presented based on dose–response relationship between wood material climate and responding fungal decay. The concept does also allow for quantifying the material resistance of untreated, modified, and preservative-treated wood using factors based on laboratory and field durability tests and short-term tests for capillary water uptake, adsorption, and desorption dynamics. The findings from the present study have the potential to serve as an instrument for design and service life prediction of timber structures and will be implemented in an engineering design guideline for timber bridges.

Segregating wood wastes by repetitive principal component analysis of near infrared spectra

To improve the recycling rate of wooden materials, it is necessary to classify wood waste by disposal method and usage. In the industrial manufacture of these materials, rapid and accurate determination of their chemical and physical properties is critical for a stable supply of wood products with reliable quality. In this study, we investigated a discriminant analysis process for waste wood products using hyperspectral imaging with a newly developed repetitive principal component analysis. Hyperspectral images of four types of wood waste (plywood coated with resin, preservative-treated wood, hardwood and softwood) were acquired. The mean spectrum of each sample was extracted from a hypercube in order to build a classification model. A novel classification method based on principal component analysis, named repetitive principal component analysis, was developed. A total of three repetitions of principal component analysis were performed to classify the four types of wood waste. Cross-validated results of repetitive principal component analysis resulted in classifications greater than 85% for any of the four wood waste types. The discriminant model was then applied to single-pixel spectra of the hypercube to form a prediction map. Hyperspectral imaging, with the aid of the new repetitive principal component analysis discriminant analysis, is a powerful tool in wood recycling processes.

Modulus of Elasticity Loss as a Rapid Indicator of Rot-fungal Attack on Untreated and Preservative-treated Wood in Laboratory Tests

The modulus of elasticity (MOE) of wood is a sensitive indicator of rot-fungal attack. To develop an alternative method of rapid assessment of fungal decay in the laboratory, changes in static MOE of untreated and preservative-treated wood were measured during exposure to the brown-rot fungus, Gloeophyllum trabeum, and the white-rot fungus, Trametes versicolor, in a standard soil bottle assay. Static MOE loss was compared with mass loss. The results showed that the MOE of wood was a sensitive and reliable indicator of rot-fungal attack, regardless of fungus or wood species. The MOE analysis of untreated wood reduced the 12- to 16-week exposure time necessary for the standard mass loss measurement to four weeks. Also, the exposure time for preservative-treated wood was reduced to eight weeks. Untreated wood was determined to be susceptible to decay if the MOE loss was 40% or more after a four-week exposure, while treated wood was considered susceptible to decay if the MOE loss was 40% or more after an eight-week exposure.