Compression Wood Research Articles

Effects of wood fiber on the properties of silicoaluminophosphate geopolymer

Silicoaluminophosphate geopolymer is an important class of inorganic cementitious material, which attracts increasing attention due to the excellent mechanical properties, high thermal resistance and low dielectric properties. However, like most of the pristine or unreinforced cement based materials, silicoaluminophosphate geopolymer still suffers from brittle failure, which seriously limits its popularization and application. Based on the characteristics that silicoaluminophosphate geopolymer is almost a Ca-free material forming in acidic environment and driving by the demands of low carbon, environmental friendly and low cost, this paper adopts wood fiber as a reinforcing material to improve the toughness of silicoaluminophosphate geopolymer. Results show that the incorporation of wood fiber can effectively reduce the brittleness and increase the fracture toughness of silicoaluminophosphate geopolymer by the excellent bonding performance between reaction products and wood fiber. However, the addition of wood fiber is unfavorable to the setting and hardening behaviour, reaction degree and compressive strength of silicoaluminophosphate geopolymer. Although the hydrolysis of wood fiber in acidic environment results in some local defects on its surface, these defects have little effect on the improvement of silicoaluminophosphate geopolymers toughness due to the repairing effect of reaction products.

ANALYSIS OF ROCKING COLUMN BEHAVIOR CONSIDERING STRESS DISTRIBUTION OF COLUMN USING FIBER ELEMENTS

In this paper, a numerical model considering the embedment reaction of column foot by the beam-column finite element method was proposed for evaluating the restoring force characteristics of the rocking column in traditional timber structures. Wood compression tests in contact with stones were conducted to investigate the characteristics of the embedment reaction and initial deformation generated at the end of the wood, and these characteristics were considered in the column foot numerical model. The validity and applicability of the numerical model were verified by analyzing several static loading tests of the rocking column.

Long-term creep behavior of timber columns: Experimental and numerical protocols

This work deals with an experimental and numerical approach to determining the differed behavior of compressed wood elements subjected to creep loading. An experimental protocol is associated with a mechanical model, whose purpose is to isolate the effects of creep from those of shrinkage-swelling, while allowing for a long duration test to be conducted. The experimental protocol is based on a compression creep test applied to five wooden columns disposed in a climatic room for one year. The numerical model is based on the use of a Kelvin-Voigt rheological model associated with a shrinkage-swelling element. An optimization study is proposed in order to interpolate the model parameters with respect to the experimental measurements. In the context of a linear viscoelastic behavior, the result of this interpolation allows to propose a model extrapolation for long times. Within the framework of the European code, Eurocode 5, this project aims to identify the long-term creep coefficient (kdef) adapted to compressed elements, in addition to evaluating the partial creep coefficients as a function of loading duration class.

The tree-ring anatomy of Robinia pseudoacacia L. As a data source for dendrogeomorphic reconstruction of past landslide movements in the landslide hot-spot of central Europe

The chronology of past landslide movements is a key source of information for effective landslide hazard determination. Dendrogeomorphological methods are currently an effective tool for obtaining chronological data but still encounter limitations in extracting landslide signals from yearly series. These limitations can be reduced by introducing anatomical analyses of the yearly series. Black locust (Robinia pseudoacacia L.), a widespread tree species occupying landslides on river banks, has been surprisingly rare in dendrogeomorphology. Thus, this study focused on the effectiveness of using both standard macroscopic signals (tree-ring eccentricity) and anatomical growth responses of this species in a dendrogeomorphic analysis of landslide movements at one of the landslide hot spots in Central Europe (the Váh River bank). Analysis of the eccentricity of tree rings from 67 individuals of R. pseudoacacia allowed us to reconstruct 13 landslide events over the last 49 years. From an anatomical point of view, a strong association was found between a significant reduction in vessel lumen area and the eccentricity of the tree rings and the tilting of the tree stems. A possible cause of the anatomical response is a combination of root damage from subsurface landslide movements and occasional tension wood formation following tree tilting. The constructed chronology confirmed the known years of landslide activity and generally complemented the known chronology. One of the results of the study is the implication for effective evaluation of the spatial extent of landslide activity, considering tree-ring-based magnitude-frequency relationships. The results of this study will thus allow further extension of the use of dendrogeomorphological methods both methodologically and biogeographically.

Wood quality of residual branches of Hymenaea courbaril L. from logging in the Amazon rainforest

Abstract Branches remain in the forest environment as logging activity residue. Considering the large size of many Amazonian trees, their branches have considerable dimensions and can contribute to a sustainable wood alternative for various applications. Due to the formation of reaction wood in the branches, relevant macro and ultrastructural changes can occur in its characteristics in relation to the trunk wood. However, the woods of the branches are not technologically well known. Therefore, this work aimed to evaluate the wood quality of branches of Hymenaea courbaril L., comparing it with wood of trunks. The extractives and lignin contents, basic density, shrinkage, fiber biometry, microfibril angle and mechanical resistance to compression parallel to the fibers were analyzed. The branch wood had smaller fiber dimensions and a higher microfibril angle than the trunk wood. The basic density was similar between these materials. The linear and volumetric shrinkages were smaller in the branch wood than in the trunk, while the axial shrinkage was higher in the branch. The parallel compressive strength was also lower in the branch wood than in the trunk. The branch wood has properties suitable for products with higher added value such as furniture, decorative objects, floors and utensils in general.

Response of Tracheid Structure Characteristics and Lignin Distribution of Taxodium Hybrid Zhongshanshan to External Stress

The Taxodium hybrid Zhongshanshan fast-growing species is susceptible to environment and gravity to form reaction wood. In this study, individual growth rings of reaction wood are used as subjects, and an individual growth ring is divided into three zones: compression zone (CZ), lateral zone (LZ), and opposite zone (OZ). The microanatomical structure and chemical properties of the tracheids in CZ, LZ, and OZ forms by the inclined or bent growth of T. Zhongshanshan are comparatively analyzed by using optical microscopy, scanning electron microscope, laser confocal microscopy, and Raman imaging techniques. In CZ, the length and diameter of compression wood (CW) tracheids decreased, and the shape of cross-sections became rounded as compared to the OZ and LZ tracheids. More notably, threaded fissures appeared on the cell wall of tracheids, and the thickness of the cell wall increased in CW. The analysis of tracheids’ cell wall structure showed that CW tracheids had a complete outer secondary wall middle (S2L) layer, but had no secondary wall inner (S3) layer. In the transition zone (TA) between CW and normal early wood, tracheids were divided into compressed and normal tracheids. Despite the compressed tracheids having a similar cell morphology to normal tracheids, they had a thin secondary wall S2L layer. Tracheids in LZ had a thin S2L layer only at the angle of the cell. No S2L layer was seen in the cell wall of OZ and CZ late wood tracheids. It can be concluded that the response of lignin deposition location to external stress was faster than the change in cell morphology. The above results help provide the theoretical basis for the response mechanism of T. Zhongshanshan reaction wood anatomical structures to the external environment and has important theoretical value for understanding its characteristics and its rational and efficient usage.

Wood Quality along the Trunk Height of Birch and Aspen Growing in the Restoring Forests of Central Russia

The structure of forests has changed with an increase in soft-wooded broadleaved species over the past decade. The demand for hard-wooded broadleaved species can be met by replacing them with compressed wood of soft-wooded broadleaved species. Existing compressed wood technologies do not fully take into account the density variations that exist along the height of a tree trunk. In this study, we examined the variability of birch and aspen microstructures along the height of the trunk, including vessels per square millimeter and the diameter (tangential and radial) of the vessel lumina. The research was carried out on aspen and birch species growing in Central Russia. The vessels per square millimeter in both species increased from the base to the top of the trunk and their diameters decreased from the base to the top of the trunk. Birch demonstrated greater changes in these values than aspen. There was a strong relationship between the diameter of the vessel lumina and the trunk height. A decrease in the density of the stemwood from the base to the top of the trunk was caused by an increase in the vessels per square millimeter. These results affected the density of the stemwood and determined the degree of compression as well as the initial size of the blanks required to obtain material with uniform quality indicators, regardless of the source location of the raw materials in the tree trunk.

Effect of pressing parameters on dimensional stability and bonding performance of thermally compressed coconut wood

Previous research on thermally compressed (TC) coconut wood has shown potential for structural applications. However, its dimensional stability needed to be improved. This study aimed to improve the dimensional stability of TC coconut wood for further use in laminated products by using relatively high pressing temperatures to make it more hydrophobic. TC specimens with a target compression ratio of 55 % were manufactured from low-density (LD, 332 ± 25 kg/m3) wood, and TC specimens with a target compression ratio of 25 % were manufactured from medium-density (MD, 514 ± 28 kg/m3) wood. Two pressing temperatures (170 °C and 200 °C) and three pressing times (1 h, 2 h and 3 h) were applied. Chemical changes, dimensional stability, physical and mechanical properties, and bonding performance of the specimens were examined. Thermal degradation of the LD specimens was higher than that of the MD specimens. Differences in chemistry between the surface and the interior could explain bonding behavior. Pressing temperature had a greater impact on wood degradation than the pressing time. Dimensional stability could be achieved at 200 °C pressing temperature. Most physical and mechanical properties of the TC specimens had decreased due to thermal degradation. However, compressive strength parallel to the grain and modulus of elasticity were not affected at the chosen pressing parameters. Bonding performance determined by block shear tests was dependent on the original material, panel assembly, and the sanding process. Longitudinally laminated panels made from MD specimens with sanded surfaces provided the highest block shear strength.

Modelling of creep behaviour of timber dowelled beams

Extensive researches have been dedicated to study creep in wooden structures where good insight was gained on the phenomenological behaviour. However, long-term creep laws and practical methods to investigate the creep’s influence on safety and serviceability of wood structures during their life-cycle are still very few or don’t exist. This paper investigates the creep of wooden structures using a combined numerical and experimental study. Uni-axial tests (i.e. compression/tensile tests in different directions) were used to calibrate the constitutive law of spruce species and to identify the elastic parameters of the constitutive law. For creep parameters identification, three point bending tests were performed for compressed and uncompressed spruce wood. Subsequently, the results of the three point bending tests were used in conjunction with the numerical model in an inverse problem to obtain the viscous parameters. This technique was adopted for both compressed and uncompressed wood samples. Furthermore, a parametric study was conducted on laminated beams of uncompressed spruce boards assembled by compressed spruce dowels. The behaviour of the whole hybrid structure was studied and several interesting findings were highlighted.

Effect of Acetylation on the Physical and Mechanical Performances of Mechanical Densified Spruce Wood

Inherent drawbacks (e.g., loose structures, dimensional instabilities, and poor mechanical performances) restrict the applications of fast-growing wood species. In this study, a thermal compression treatment was carried out to densify acetylated spruce wood. The aim of acetylation was to improve the plasticity and water resistance of spruce wood. The water absorption, set-recovery, surface hardness, modulus of rupture, modulus of elasticity, and microstructure of the resulting wood were analyzed. The results show that acetylation can improve the plasticity of wood and reduce the interaction between wood and water, significantly reducing the set recovery of the compressed wood. When the water immersion time reaches 168 h, the water absorption rate of wood is reduced by 37% after acetylation, and the densification can further reduce the water absorption (55% for AD-40 and 70% for AD-60). The hardness of the densified wood is significantly higher than that of control wood and increases with the increase of the compression ratio. The cell wall of acetylated wood is thicker than that of control wood, which could increase the compression density of the wood. As a result, the hardness and MOR of acetylated densified wood are remarkably higher than that of unacetylated densified wood. However, a high compression ratio (60%) could lead to structural damage and, thus, reduce the mechanical properties.

Using deciduous branch wood and conifer spindle wood to manufacture panels with transverse structure

The increasing demand on the wood market makes it necessary to use all secondary resources, including the wood branches and spindles. The properties of deciduous branches and softwood spindles were evaluated in order to create wood panels, highlighting the transverse texture with high value added. The research analyzed the properties of the wood from deciduous (beech, maple) branches and from conifer (spruce, fir) spindles. The methodology of obtaining panels with transversal structure was also presented. The production of minor wood (branches or spindles) was 254 m3/ha/year in the case of beech (branches) and 109 m3/ha/year in the case of spruce (spindles). The proportion of compression wood for spruce had an average value of 40.6%. A similar value of tension wood for beech was obtained. The modulus of elasticity for pine spindle wood was 71.7% lower than the modulus of elasticity for bending strength in the trunk. The quality index was 36.7% lower in the case of spindles than in the case of pine trunk, and the value of the quality ratio in branch maple wood was 2.61% lower than in trunk wood. Thus, even if it is not the only efficient solution, wood in the minor portions can be used to make high value-added panels such as those that highlight the transverse structure.

In-situ visualizing selective lignin dissolution of tracheids wall in reaction wood

As a renewable biological macromolecule with aromatic structure, lignin can serve as matrix substance to maintain cell wall integrity and is regarded as the natural biomass recalcitrance. Substantial differences in the cell wall lignin topochemistry between opposite (Ow) and compression wood (Cw) trachieds in Pinus bungeana Zucc. were visualized during [Emim][OAc] pretreatment at room temperature. The ionic liqiuds treatment induced a more obvious wall swelling for highly lignified Cw tracheids than that of Ow, while dynamic Raman spectra analysis indicated the higher lignin and carbohydrates removal for Ow tracheids. Raman imaging further revealed that both lignin and carbohydrates were dissolved simultaneously within the middle lamella and secondary wall of Ow and pretreatment has little effects on Cw tracheids wall. Moreover, it was demonstrated that lignin composition was the key factor to affect the composition dissolution. In particular, lignin G-units were selectively removed from cell corner middle lamella (52.3 %) and secondary wall (62.0 %) of Ow tracheids. When cotton fiber, as a reference was treated under the same conditions, lattice conversion moving from cellulose I to II occurred. The findings confirmed the important role of lignin compostion in the dissolution behavior of carbohydrate dominant tracheids wall.

Hardness and fracture morphology of reaction wood from Pinus merkusii and Agathis loranthifolia

Hardness and fracture morphology of reaction wood from Pinus merkusii and Agathis loranthifolia

Specifics of slope movements on slopes with contrasting structural conditions: Evidence from tree-ring records

The geological structure of a slope is one of the key factors that drives the development of landslide types. Various landslide types, although occurring in the same locality, can result in different spatio-temporal dynamics of their movements. Moreover, the presence of shallow creep movements on such slopes can modify the effect of slide movements and possibly cause the false impression of landslide activity. The nonstandard combination of detailed tree-ring-based (dendrogeomorphic) approaches involving the careful assessment of growth disturbance properties (the duration, intensity, mutual ratio of different disturbances), the statistical testing of the spatial pattern of disturbed trees, the analysis of possible extreme precipitation triggers, and geophysical sounding was used in this study in an attempt to distinguish creep and slide movements and assess the general slope movement activity on slopes with contrasting geological structures. Data from 1032 tree-ring series of 516 disturbed individuals of common spruce (Picea abies (L.) Karst.) enabled the reconstruction of 13 slope movements on all three studied sites (3, 7, and 3) for the last approximately 70 years. Although some indices correspond with the general assumption of a specific landslide type to the structure of induced growth disturbances (e.g., an increased ratio of reaction wood on rotational landslides), the advanced dendrogeomorphic approach used suggests that not all dated events are of slide origin and that creep movements significantly modify the effect of original slide movement on tree growth. Some dated events are probably the result of only creep movements themselves. Thus, the present study critically assesses results of the dendrogeomorphic dating of various landslides, presents contrasting behavior of slope movements on slopes with contrasting geological structures, and recommends the use of more advanced tree-ring-based approaches for more effective dendrogeomorphic research of landslides.

Effects of Pressurized Superheated Steam Treatment on Dimensional Stability and Its Mechanisms in Surface-Compressed Wood

Shape stability is one of the most important properties of surface-compressed wood used as a substitute for other energy-intensive adhesives, concrete, and metals. This study evaluated the dimensional stability, surface wettability, chemical structure, cellulose crystalline structure, and microstructure of surface-compressed wood. The surface-compressed wood was then treated with pressurized superheated steam. The equilibrium moisture content, thickness swelling ratio, and wettability of the wood decreased by 20.39%, 30.63% (moisture absorption), 40.51% (water absorption), and 86.95% after pressurized superheated steam treatment, respectively. In the pressurized steam environment, hemicelluloses were significantly degraded, significantly reducing the strong hygroscopic groups, particularly hydroxyl groups. The crystallinity and crystal width of cellulose in the compressed wood also increased by 8.02% and 37.61%, respectively, after pressurized superheated steam treatment, corresponding to dimensional stability. Dimensional stability, namely the shape fixation of the surface-compressed wood, is a complex mechanism, including the hydrophobization of cell walls, the formation of cross-linkages, the reformation of microfibril chains, microstructural changes, and the relaxation of inner stresses, which reduced or even eliminated the recovery. This study demonstrates that pressurized steam treatment can effectively enhance dimensional stability in surface-compressed wood, which contributes to the substantial use of surface-compressed wood in the building and construction industries. We will further explore the relationship and mechanism between superheated steam pressure, treatment time, and dimensional stability.

Diversification of landslide areas as a means for reducing noise in dendrogeomorphic dating

The result of tree-ring-based reconstruction of past landslide events is often the development of a single total chronology. This approach can be very effective for small homogeneous landslides. However, compiling chronological data from heterogeneous (often independent) zones of large complex landslide areas into one chronology can induce over- or underestimation of some events, resulting in lowered reliability of the reconstruction. The solution for elimination of this effect can lie in the diversification of complex landslide areas into homogeneous zones with separate analyses. The aim of this study was to quantify the effect of this separation on detected slope movement events and to define parameters whose investigation could distinguish events (sliding) from noise (creeping). For this purpose, 412 tree-ring series from 206 disturbed common spruce ( Picea abies (L.) Karst.) occupying complex landslide areas were dendrogeomorphically analysed. The landslide area was divided into five homogeneous zones using geomorphic mapping, LiDAR-based DEM and geophysical sounding (ERT). Five events (verified in individual zones) were detected in the total chronology. Two extra events in the total chronology (28.6%) were considered noise. Moreover, two zonal events were detected but not recorded in the total chronology. This indicates that the noise in the total chronology of the complex landslide area could reach more than a quarter of dated events. Next, true slide events and noise (caused by creep) were differentiated in the structure of growth disturbances (reaction wood vs. abrupt growth suppression) and their proportion in event reconstruction, spatial patterns of trees containing slope movement signals, and the character of triggers. Thus, for better filtering of noise from signals in tree-ring-based chronologies of landslides, not only observations of dendrogeomorphic index values but also the morphology of landslides and characteristics of dated processes must be considered.

Modification of Poplar Wood via Polyethylene Glycol Impregnation Coupled with Compression

Wood permeability and compressibility are affected by cell wall structure and chemical composition. These properties can be improved by appropriate wood pretreatments. Low-density poplar wood was converted to a more dense structure by the following steps: First, lignin and hemicellulose were removed using a mixture of NaOH and Na2SO3. Second they were impregnated with polyethylene glycol (PEG, mean molecular weight of 1200), nano-SiO2, and a silane coupling agent at atmospheric temperature and pressure. Finally, impregnated wood was compressed at 150 °C. Results showed that the tracheid lumens on the transverse section of the compressed wood almost vanished. Specifically, the lumens in the wood cells, especially those that were compressed, were almost completely filled with PEG. In FTIR, the asymmetric absorption peaks of Si–O–Si at 1078–1076 cm−1 were clearly observed, which confirms the existence of bonding between nano-SiO2 and wood. The highest melting enthalpy and crystallization enthalpy showed a heat storage capacity of modified wood, which were 20.7 and 9.8 J/g, respectively. Such phase change capabilities may have potential applications in regulating the rate of change of room temperature. In summary, the modified wood could be utilized as material for construction to conserve energy.

Quantitative anatomy or macroscopic parameters of compression wood of Picea abies (L.) H. Karst.? Defining the optimal parameters for dendrogeomorphic purposes

Summary The quantification of the intensities of tree growth responses to the impact of geomorphic processes is a modern research trend in dendrogeomorphology. It enables a more sensitive assessment of the activity of the studied geomorphic process compared to the traditional use of growth disturbances. The advanced definitions of individual intensity classes of growth disturbances are based exclusively on macroscopic observations. This study evaluates the possibility of anatomical quantification of compression wood (CW) intensity in the case of common spruce (Picea abies (L.) Karst.) and compares it with subjective macroscopic evidence of CW with respect to stem tilting intensity. In total, 25 disturbed (tilted) individuals of P. abies occupying a landslide active during July 1997 were sampled, and 21 of them were analysed. The intensity of external disturbance (stem tilting) was compared against the macroscopic (intensity and duration) and microscopic (quantitative change of the tracheid lumen area and the cell wall proportion) parameters of compression wood suitable for practical application in common dendrogeomorphic analysis. Generally, the macroscopic indices of CW were strongly correlated with stem tilting. The intensity of the anatomical growth response was stronger in the earlywood zone than in the latewood zone. Nevertheless, their dependence on stem tilting was not detected. Results suggest that CW classification based on the quantification of anatomical changes is not possible for dendrogeomorphic purposes. Nevertheless, based on the obtained results, the present study suggests preferring the most intensively tilted trees during future dendrogeomorphic research to obtain the most intensive macroscopic and subjective observable anatomical evidence for studying compression wood.

Wood compression in four-dimensional in situ tomography

Wood deformation, in particular when subject to compression, exhibits scale-free avalanche-like behavior as well as structure-dependent localization of deformation. We have taken three-dimensional (3D) x-ray tomographs during compression with constant stress rate loading. Using digital volume correlation, we obtain the local total strain during the experiment and compare it to the global strain and acoustic emission. The wood cells collapse layer by layer throughout the sample starting from the softest parts, i.e., the spring wood. As the damage progresses, more and more of the softwood layers throughout the sample collapse, which indicates damage spreading instead of localization. In 3D, one can see a fat-tailed local strain rate distribution, indicating that inside the softwood layers, the damage occurs in localized spots. The observed log-normal strain distribution is in agreement with this view of the development of independent local collapses or irreversible deformation events. A key feature in the mechanical behavior of wood is then in the complex interaction of localized deformation between or among the annual rings.

Microscopic mechanism of contraction of tension wood G-fiber due to boiling

Many woody eudicot plants form a secondary xylem composed of gelatinous fibers (G-fibers) called "tension wood" (TW) along the upper side of the tilted stem or branch. TW generates a large tensile growth stress in the longitudinal direction, allowing the tilted stem or a branch to develop negative-gravitropism in response to the strong gravitational stimulus. This is because the G-fiber tends to contract in the longitudinal direction as it matures. The matured G-fiber also contracts upon boiling in water (= hygrothermal treatment, i.e., HT-treatment), and moisture desorption (= drying treatment). These contractions occur in the cellulose-rich gelatinous layer (G-layer) as an innermost layer of the G-fiber. It is still an unsolved mystery how the G-layer, which is composed of highly crystallized and longitudinally oriented cellulose microfibrils (CMFs), contracts during maturation, boiling, and drying. In the present study, TW specimen of Konara oak (Quercus serrata L.) was subjected to HT-treatment under different temperature and time conditions, and strain due to treatment was followed. Besides, the mass loss due to HT-treatment was also followed. Obtained results are summarized as follows. (1) Green TW specimen of Konara oak contracted in the longitudinal direction when subjected to the HT-treatment at a treatment temperature higher than 40 °C, which eventually converged to a constant value according to each treatment temperature. Magnitude of the longitudinal HTR-strain in the TW specimen was positively correlated with the treatment temperature in the range from 40 to 120 °C, whereas in the normal wood (NW) specimen, it does not occur explicitly when the temperature is less than 100 °C. (2) Both TW and NW specimens showed mass loss when subjected to the HT-treatment. The mass loss rate increased rapidly by the HT-treatment at 120 °C, while it was only slight below 100 °C. There was no significant difference between the mass loss behavior of TW and NW by the HT-treatment. From analyzing those results, physical behavior of CMF and other non-cellulosic matrix components in the G-layer during the HT-treatment was estimated. The discussion was further developed to associate HT-contraction with microscopic mechanisms of the other two characteristic contractions of the G-fiber, i.e., maturation strain and drying shrinkage.