Reversible and irreversible dimensional changes of heat-treated wood during alternate wetting and drying

Spruce wood specimens were heat-treated in saturated water vapor (steaming) and in the absence of moisture (dry heating) at 120–180 °C, and their wet volumes were measured during alternate wetting and drying cycles. After the first wetting and drying cycle, the wet volume of steamed wood decreased and then remained unchanged during the following alternate wetting and drying cycles. The wet volume regained its initial level when soaked in dimethyl sulfoxide (DMSO), followed by washing in water, but decreased again after subsequent drying and rewetting. Such reversible changes were not observed in unheated and dry-heated specimens. This suggested a hydrophobic structure formed during drying or plastic expansion of cell lumen due to steaming and soaking in DMSO. Although heat treatments reduced the hygroscopicity of the wood, steamed wood showed more swelling, i.e., lower dimensional stability than unheated and dry-heated wood. This is probably because steaming caused serious degradation of cell wall components, therefore loosening its fiber-reinforced structure restricting the swelling of the cell wall. When wood is exposed to alternate wetting and drying, steaming is not advisable because it may reduce the dimensional stability of the wood

Impact of Wetting–Drying Cycles on the Mechanical Properties and Microstructure of Wood Waste–Gypsum Composites

Large amounts of wood waste are generated each year in the world. In an attempt to identify a good recovery option for those residues, wood waste from construction and demolition works were used as raw materials in gypsum plasters. However, wood is a biodegradable material which implies that the products or materials that contain it are susceptible to su ering an important deterioration, due to exposure in certain environments. For that reason, the aim of this work was to simulate the e ects that, in the long term, the atmospheric exposure of wood waste–gypsum composites would have. To do that, the plasters were subjected to 5, 10, and 15 wetting–drying cycles in a climatic chamber. In this study, the density, flexural and compressive strength, and ultrasonic velocity of these composites were determined by the influence of the aging process on their mechanical properties. Furthermore, in order to detect changes on their internal structure, scanning electron microscopy tests (SEM) were used. The results showed that they were suitable to be used as indoor coverings of buildings. However, a treatment to reduce the moisture absorption of the wood waste must be studied if mixtures with high percentages of wood shavings (WS20) are used in wet rooms

Interpreting Measurements of Small Strain Elastic Shear Modulus under Unsaturated Conditions

Bender element testing of unsaturated isotropically compacted speswhite kaolin samples was used to investigate the variation of small strain elastic shear modulus G under unsaturated conditions. Testing was performed in a suction-controlled triaxial cell and involved combinations of isotropic loading and unloading stages and wetting and drying stages. Analysis of the experimental results indicated that the variation of G could be represented by a simple expression involving only mean Bishop’s stress p* and specific volume v, with the only significant mismatches between measured and predicted values of G occuring at the end of final unloading. No significant improvement of fit was achieved by incorporating additional dependency on degree of saturation Sr or a bonding parameter ζ. The proposed expression for G reverts to a well-established form for saturated soils as Sr tends to 1

Influence of Mechanical Yielding on Predictions of Saturation: The Saturation Line

It is now well accepted that the mechanical and the water retention behaviour of a soil under unsaturated conditions are coupled and, that such coupling, should be incorporated into a constitutive model for a realistic representation of soil’s response. In existing models, the influence of the mechanical behaviour on the water retention is often represented by a shift of the main wetting retention curve to higher values of matric suction (the difference between pore air and pore water pressures) when the specific volume decreases. This means that any variation of total volumetric strains of compression (whether these are elastic or elasto-plastic) will result in a shift of the main wetting and drying curves to the right, when these curves are represented in the water retention plane. This shift of the main water retention curves, however, should not only influence the unsaturated stress states as often described in the literature, it should also have some impact on the saturated stress states and, more specifically, on the predictions of de-saturation (air-entry point) and saturation (air-exclusion point). From a modelling point of view, it is advantageous to represent this influence through the plastic component of volumetric strain of compression only because, in this way, a consistent representation of the mechanical behaviour for both unsaturated and saturated states can be naturally achieved. This and other advantages resulting from this singular approach are demonstrated in the paper in the context of the Glasgow Coupled Model (GCM)

Giant osmotic pressure in the forced wetting of hydrophobic nanopores

The forced intrusion of water in hydrophobic nanoporous pulverulent material is of interest for quick storage of energy. With nanometric pores the energy storage capacity is controlled by interfacial phenomena. With subnanometric pores, we demonstrate that a breakdown occurs with the emergence of molecular exclusion as a leading contribution. This bulk exclusion effect leads to an osmotic contribution to the pressure that can reach levels never previously sustained. We illustrate on various electrolytes and different microporous materials, that a simple osmotic pressure law accounts quantitatively for the enhancement of the intrusion and extrusion pressures governing the forced wetting and spontaneous drying of the nanopores. Using electrolyte solutions, energy storage and power capacities can be widely enhanced

Mitigation of GHGs Emission From Soils by a Catalyzed In-Situ Photo-Oxidative Polymerization of Soil Organic Matter

Agricultural lands under food and bio-energy crops, managed grass and permanent crops including agro-forestry, occupy about 40-50% of the Earth's land surface^1^. In 2005, agriculture accounted for an estimated emission of 5.1 to 6.1 GtCO2-eq/yr (10-12% of total global anthropogenic emissions of greenhouse gases (GHGs))^1^. However, measures to mitigate GHGs emission from agricultural soils are limited to improved cropland practices such as crop rotation, nutrient management, tillage/residue management, agroforestry, and return to natural vegetation^2^. These practices are not only far from substantially reducing GHGs emissions from soils or permanentlystabilizing soil organic matter^1-4^, but are also predicted to hardly match more than amaximum of 25% of the GHGs reductions required by the Kyoto Protocol within 2050^5^.Despite the knowledge that GHGs release from soil largely derives from biochemicaltransformations of plant litter and soil organic matter (SOM)^6-8^, no new and much wished biotechnological measures are adopted so far to augment mitigation^1^. Here we propose an innovative approach to mitigate GHGs emissions from soils based on the insitu photo-polymerization of SOM under biomimetic catalysis. Three Mediterranean soils of different physical and chemical properties were added with a synthetic watersolubleiron-porphyrin, irradiated by solar light, and subjected to 15, and 30 wetting and drying cycles. We found that the in situ catalysed photo-polymerization of SOM increased soil physical aggregation, shifted OC into larger soil aggregates, and reduced CO~2~ released by microbial respiration. Our findings suggest that "green" catalytic technologies can become viable soil management practices to enhance mitigation of GHGs emission from arable soils and contribute to match the expectations of the post-Kyoto Protocol in the agricultural sector

Compaction behaviour of clay

This paper presents an experimental study of the compaction behaviour of non-active clay. One-dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using Trento high-capacity tensiometers. At lower water contents, a transistor psychrometer was used to measure post-compaction suction. Samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses. Three water content regions were identified in the compaction plane depending on whether post-compaction suction increased, decreased or remained constant as the degree of saturation was increased at constant water content. Hydraulic paths of specimens subjected to loading-unloading cycles at constant water content have clearly shown that post-compaction suction may increase as the degree of saturation increases. This non-intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour. To this end, a coupled mechanical water retention model was formulated. Irreversible one-dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress, modified suction and void ratio. Irreversible hydraulic 'wetting' paths were modelled by a boundary surface in the space suction, degree of saturation, and void ratio. This study was completed by investigating the pore size distribution of compacted samples through MIP tests

Understanding and controlling the ingress of driven rain through exposed, solid wall masonry structures

Long term performance of historic buildings can be affected by many environmental factors, some of which become more apparent as the competence of the fabric deteriorates. Many tall historic buildings suffer from water ingress when exposed to driving rain conditions, particularly church towers in the south west of England. It is important to recognise that leakage can occur not only through flaws in the roof of a building but also through significant thicknesses of solid masonry. Identification of the most appropriate intervention requires an understanding of the way in which water might enter the structure and the assessment of potential repair options. While the full work schedule used an integrated assessment involving laboratory, field and archival work to assess the repairs which might be undertaken on these solid wall structures, this paper focuses on the laboratory work done to inform the writing of a Technical Advice Note on the effects of wind driven rain and moisture movement in historic structures (English Heritage, 2012). The laboratory work showed that grouting and rendering was effective at reducing water penetration without retarding drying rates, but that use of internal plastering also had a very beneficial effect

Network modelling of the influence of swelling on the transport behaviour of bentonite

Wetting of bentonite is a complex hydro-mechanical process that involves swelling and, if confined, significant structural changes in its void structure. A coupled structural transport network model is proposed to investigate the effect of wetting of bentonite on retention conductivity and swelling pressure response. The transport network of spheres and pipes, representing voids and throats, respectively, relies on Laplace–Young’s equation to model the wetting process. The structural network uses a simple elasto-plastic approach without hardening to model the rearrangement of the fabric. Swelling is introduced in the form of an eigenstrain in the structural elements, which are adjacent to water filled spheres. For a constrained cell, swelling is shown to produce plastic strains, which result in a reduction of pipe and sphere spaces and, therefore, influence the conductivity and retention behaviour

The water factor in harvest-sprouting of hard red spring wheat

Sprouting in unthreshed, ripe, hard red spring wheat (Triticum aestivum L.) is induced by rain, but sprouting does not necessarily occur because the crop is wetted. The spike and grain water conditions conducive to sprouting were determined in a series of laboratory experiments. Sprouting did not occur in field growing wheat wetted to 110% water concentration until the spike water concentration was reduced to 12% and maintained at this concentration for 2 days before wetting. When cut at growth stage 11.3, Feekes scale, Saratovskaya 20 (USSR) sprouted after 4 days drying, Olaf and Alex between 7 and 15 days drying and Columbus, recognized for its resistance to harvest time sprouting, after more than 15 days drying. Sprouting potential was enhanced after 4 wetting drying cycles in which any wetted interval was too brief to permit sufficient water imbibition to initiate sprouting. At harvest ripeness, grain water concentration exceeded spike water concentration by 0.7 percentage units. Following 6 months storage, 20% of the kernels in 300 spike bundles (simulating windrows) sprouted within 28 hrs after initiation of wetting to saturation (150% water concentration). Ninety percent sprouting occurred within 8 days in bundles maintained at 75% water concentration and higher, but less sprouting occurred in bundles dried to 50% water concentration before resaturation