Christian Brischke

Short-term performance of wooden windows and facade elements made of thermally modified and non-modified Norway spruce in different natural environments

ABSTRACT Thermally modified wood is becoming an increasingly popular material for different applications in buildings. Laboratory tests indicated a positive effect of thermal modification on durability, dimensional stability and thermal conductivity of wood. Therefore, windows and facade elements made of thermally modified Norway spruce and non-modified Norway spruce were tested in the field and installed in different test objects which were exposed at five locations in Europe (Slovenia, Germany, Sweden, and Spain). Results from monitoring showed that elements and windows made of thermally modified spruce (TMS) had considerably lower wood moisture content compared to the ones made of non-modified spruce and that wax further positively influenced moisture performance. Colour changes of TMS were more intensive compared to non-modified spruce but were successfully retarded by adding pigments to the wax. Mould and stain growth was largely dependent on the location, amount of precipitation and relative humidity.

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

ABSTRACT Service 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.

Dual borate and copper naphthenate treatment of bridge timbers – potential cost savings by various performance enhancements

ABSTRACT Dual-treatment technology combining diffusible preservatives with oil-borne preservatives, widely used for crossties in the USA, has now also been commercialized with bridge ties/timbers. In order to understand the implications of these changes, the historic service life of creosote-treated bridge timbers in northern and southeastern USA were considered as well as field-test data for both creosote and copper naphthenate. These were used to estimate potential future service life. Estimates on life expectancy with added borates were also made from published data on performance. Cost–benefit analysis based on creosote and copper naphthenate costs as well as assumptions made from field-test efficacy data suggest cost savings of up to

Moisture behavior of weathered wood surfaces during cyclic wetting: measurements and modeling

20 per timber per year of additional service. Service life extension and the resulting cost savings could be achieved in a number of ways: change preservative from creosote to copper naphthenate; increase active ingredient retention; and/or add dual-treatment protection. A preservative change from creosote to copper naphthenate would be the simplest and lowest cost way of increasing service life of bridge timbers, with potential savings to both treater and railroad. An increase in copper retention could also give significant life extension, could be carried out at little additional cost and without increasing bleeding. The addition of borate to protect the heartwood also provides significant assumed increase bridge tie life, and can be used with either creosote or copper naphthenate treatments.

Performance of wood in the Franja partisan hospital

The effects of weathering on the in-service moisture behavior of wood have received only limited attention so far, with much focus being on the effect of photodegradation on the hydrophobicity of the wood surface. The objective of the present study was to examine the effect of weathering surfaces on the overall moisture behavior of wood specimens exposed to short-term cyclic spraying, with special emphasis on the surface conditions involved. Specimens cut from eight different species including hardwoods and softwoods were weathered for 8xa0years and continuously monitored during a single-sided cyclic spraying together with a set of axially matched controls. After each spray cycle, the duration of surface wetness was evaluated by resistance moisture sensors as well as an optical approach (colorimetric) based on time-lapse images. The moisture content in the core was monitored simultaneously by use of resistance moisture sensors. The optical method correlated well with the electrical resistance measurements and provided a simple and practical measure of the areal distribution of the surface wetness. The results showed specimens with a weathered surface to sustain a wet surface for about twice the duration of their axially matched control. A considerable, albeit smaller, effect was also observed deeper in the core. By adapting the length of the wet period on the exposed boundary, the corresponding response at the core of the Norway spruce specimens was reproduced numerically.

Physical, mechanical and biological properties of thermo-mechanically densified and thermally modified timber using the Vacu3-process

ABSTRACT Wood is one of the most important construction materials and its use in building applications has further expanded in recent decades. In order to enable even more extensive and reliable use of wood, factors affecting wood’s service life need to be understood. It is well known that fungal degradation of wood is predominantly affected by moisture content (MC) and temperature (T). In order to elucidate the influence of these two factors, long-term monitoring of T, relative humidity (RH) and wood MC was carried out at the WWII partisan hospital Franja, Slovenia. The results clearly showed that fungal degradation of wood is influenced by MC and T. A model to predict brown and white/soft rot decay of wood was applied to predict the expected service lives of different building components of the hospital cabins. The predicted times until onset of decay were well in accordance with findings made during visual assessments and drill resistance measurements at this historical site. The monitoring concept in combination with a mathematical decay prediction model can provide accurate data and valuable guidance for building modern structures and maintaining the cultural heritage.

Incipient brown rot decay in modified wood : patterns of mass loss, structural integrity, moisture and acetyl content in high resolution

Densification and thermal modification change wood properties in different ways depending on the treatment conditions and the wood species. In the presented investigations, densification and thermal modification were applied consecutively. The primary objective of this treatment combination was the compensation of reduced mechanical properties due to the thermal modification by densification. The combined processes were applied to five European wood species: poplar (Populus nigra L.), beech (Fagus sylvatica L.), Norway spruce (Picea abies Karst.), English oak (Quercus robur L.) and European ash (Fraxinus excelsior L.). Depending on the mean density of the species, a thermo-mechanical densification of 43 or 50% was imposed to improve mechanical strength parallel to the grain. Subsequently, the densified material was thermally modified in the so-called Vacu3-process at 230xa0°C and 20 or 80% vacuum and at 240xa0°C and 20% vacuum. The thermal modification resulted in changing wood colour, mechanical strength, hardness, dimensional stability and durability. All the wood modification processes were carried out at industrial scale after pre-tests at laboratory scale. The modified material was characterized regarding flexural properties, static and dynamic hardness, structural integrity, abrasion resistance, moisture dynamics, dimensional stability, and durability against white, brown and soft rot fungi. In summary, the test results showed that the consecutive application of thermo-mechanical densification and thermal modification leads to significantly improved durability whilst mechanical properties at least for beech, ash and poplar remained and the material is dimensionally stable.

Natural durability of timber exposed above ground - A survey [Prirodna trajnost drva izlozenoga iznad zemlje - Pregled istrazivanja]

ABSTRACT The study of degradation and growth patterns of fungi in modified wood may increase the understanding of their mode of action and may lead to more accurate service-life predictions. The aim of this paper was to study the degradation and growth patterns of brown rot fungi in modified wood and to measure moisture content (MC), structural integrity and the acetyl content by frequent monitoring over 300 days. Mass loss (ML) in the modified wood materials increased slowly up to 3% for 50–100 days after which it flattened out and remained constant during the remainder of the test. Structural integrity and acetyl content were maintained in the modified wood materials and MC was lower compared to untreated wood throughout the decay test. ML results of untreated wood indicate that fungi in solid wood go through distinct phases; the degradation patterns in the modified wood materials were more difficult to interpret.

Material moisture content of wood and cement mortars – Electrical resistance-based measurements in the high ohmic range

Besides its inherent resistance against degrading organisms, the durability of timber is infl uenced by design details and climatic conditions, making it diffi cult to treat wood durability as an absolute value. Durability classifi cation is, therefore, based on comparing performance indicators between the timber in question and a reference timber. These relative values are grouped and related to durability classes, which can refer to a high range of service-lives. The insuffi cient comparability of such durability records has turned out to be a key challenge for service-life prediction. This paper reviewed literature data, based on service-life measures, not masked by a durability classifi cation. It focused on natural durability of timber tested in the fi eld above-ground. Additionally, results from ongoing aboveground durability studies in Europe and Australia are presented and have been used for further analysis. In total, 163 durability recordings from 31 different test sites worldwide based on ten different test methods have been considered for calculation of resistance factors. The datasets were heterogeneous in quality and quantity; the resulting resistance factors suffered from high variation. In conclusion, an open platform for scientifi c exchange is needed to increase the amount of available service-life related data.