Yasushi Hiramatsu

Hydration behavior and compressive strength of cement mixed with exploded wood fiber strand obtained by the water-vapor explosion process

Poor compatibility was found between exploded wood fiber strand (WFS) and cement due to the excessive presence of water-soluble degraded polysaccharides in extractives of exploded WFS obtained from weathered wood waste treated by the water-vapor explosion process (WVEP). This study presents some comparative results from a continuing investigation on the compressive strengths of exploded WFS–cement mixtures. Based on results previously obtained with the hydration test, the relation between hydration behavior and compressive strength of the mixture was explored. In addition, the effect of the curing age on compressive strength development of the mixture with selected additive chemicals was examined. The results supported the results of early studies with hydration tests indicating that adding MgCl2 to the mixtures of exploded WFS mixed with quick-curing cement or ordinary Portland cement and a composite of MgCl2 + CaO added to the mixture of exploded WFS and furnace-slag cement effectively improved the hydration behaviors; it greatly enhanced the compressive strengths of mixtures as well. Compressive strengths were strongly correlated to maximum hydration temperatures (Tmax) of wood–cement mixtures influenced by the cement type, wood wastes (treated or not with WVEP), additive chemicals, and their content levels. The results also indicated that adding selected chemicals had no significant effect on compressive strength among the mixtures of exploded WFS mixed, respectively, with three types of cement at a curing age of 180 days. X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy were used to identify the hydration products and to probe the element distribution of the mixture in the wood–cement interface zone from a fractured surface.

A preliminary investigation on microstructural characteristics of interfacial zone between cement and exploded wood fiber strand by using SEM-EDS

The hydration behavior and strength performance of cement mixed with exploded wood fiber strand (WFS) obtained by the water-vapor explosion process have been studied previously. In the current study, the microstructural characteristics of cement–exploded WFS interfacial zone were examined using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). The Ca/Si ratios at the interfacial zones and the elemental compositions of hydration products deposited in the tracheid lumen were investigated. In addition, the morphological differences and compositional variations of hydration products that developed on the wood surfaces were examined. The results revealed that the Ca/Si ratios at the interfacial zones were strongly influenced by the mixture compositions, and that the elemental compositions of the hydration products that filled the tracheid lumen were significantly different from those of the cement paste in the mixtures. Differences in morphology and composition of hydration products at the wood surfaces were also observed to correspond to the different mixture compositions. These characteristics are considered to be directly related to the bond property, and thus, to the mechanical performance of WCM.

Study of hydration behaviors of wood-cement mixtures: compatibility of cement mixed with wood fiber strand obtained by the water-vapor explosion process

To provide information on the feasibility of using exploded wood fiber strand (WFS) obtained by the water-vapor explosion process in wood-cement mixtures, the compatibility between cement and exploded WFS and its improvement with various additive chemicals were investigated by observation and analysis on hydration behaviors in terms of hydration characteristics: maximum hydration temperature (Tmax) and required time (tmax). The three types of cement, six additive chemicals, and exploded WFS (sugi, air-dried and water-soaked) were employed as raw materials in this study. The hydration behaviors of mixtures demonstrated that exploded WFS had strong retarding effects on cement hydration and completely prevented mixtures from setting. The analysis of sugar revealed that the sugar contents of exploded WFS were much higher than those in unexploded wood and increased to about 20-fold (air-dried) and 10-fold (water-soaked), respectively. The degraded polysaccharides became a major factor and played an important role in inhibiting the setting of cement. Moreover, high-performance liquid chromatography analysis proved that the main peaks representing the molecular weight of polysaccharides in extractives of exploded WFS shifted markedly to a lower range of polymerization. MgCl2 was determined to be an effective additive chemical for restraining the inhibitory influences. Addition contents of 2%–3% and 4%–5% were available and acceptable for quick-curing cement and ordinary Portland cement, respectively. As for the furnace-slag cement, the composite additive chemicals of MgCl2 (4%) and CaO (2%) were found to have an obvious accelerating effect.

Effect of volatile matter from wood chips on the activity of house dust mites and on the sensory evaluation of humans

The effect of volatile matter from various wood chips on house dust mites and their influence on human comfort were measured. To investigate the effect of volatile matter on the mite speciesDermatophagoides pteronyssinus, the activity of the mites was observed after exposure to volatile matter from six species of wood chips. The degree of activity of the mites was classified into two categories: (1) walking or moving and (2) immobilized. To measure their influence on human comfort, the smells of those wood chips were evaluated by the subjects. Among softwoods, volatile matter fromChamaecyparis obtusa andThujopsis dolabrata var.hondai chips suppressed the activity of the mites highly and made the subjects feel refreshed and unexcited.Cryptomeria japonica showed slight suppression of the mites and was considered to be refreshing, natural, and unexciting by the subjects. Among hardwoods,Cinnamomum camphora highly suppressed mites activity and was considered to be non-refreshing and exciting by the subjects.

Effect of hinoki (Chamaecyparis obtusa) wood-wool in tatami mat on the activity of house dust mite Dermatophagoides pteronyssinus

To suppress the activity of house dust mites in tatami mats, where they tend to breed, a tatami mat consisting of hinoki (Chamaecyparis obtuse) wood-wool was prepared. The suppressive effect of hinoki wood-wool on house dust mites (Dermatophagoides pteronyssinus) was then measured. To investigate the effective period of the wood-wool on the mites, 5-day exposure tests were conducted every few weeks for a total of 52 weeks. In the tests of the first and sixth weeks, the activity of the mites was strongly suppressed, and no walking or moving mite was found after 5 days of exposure. The suppressive effect on mites was maintained for 52 weeks. It was concluded that using hinoki wood-wool to produce tatami mats is an effective method of suppressing the activity of mites for about 1 year.

Effective period of volatiles from softwood veneers embedded in tatami mats on the activity of house dust mites

To suppress the activity of house dust mites in tatami mats, where they tend to breed, tatami mats were prepared with embedded softwood veneers. The effective period of the volatiles from the veneers on the mites was then measured. To investigate the effective period of volatiles from hiba (Thujopsis dolabrata var. hondai) and hinoki (Chamaecyparis obtusa) veneers on house dust mites (Dermatophagoides pteronyssinus), 5-day exposure tests were conducted every few weeks for 54 weeks. In the exposure tests, the activity of the mites was observed after 5 days of exposure to the volatiles. Volatiles from hiba veneers strongly suppressed the activity of the mites for 15 weeks. The suppressive effect decreased gradually after that, but it was maintained for 54 weeks. Volatiles from hinoki veneers showed moderate to high suppression of mite activity for 11 weeks, but no suppressive effect was observed after that. In conclusion, embedding hiba or hinoki veneers in tatami mats is an effective method of suppressing the activity of mites for about a year or for slightly less than 3 months, respectively.

Improvement of dimensional stability and weatherability of composite board made from water-vapor-exploded wood elements by liquefied wood resin impregnation.

High-density and high-resin-content boards were produced by phenolic resin impregnation into board materials prepared by the water-vapor-explosion process (WVE) to develop high-durability wood composite boards for exterior use. Wet-dry cyclic tests and accelerated weathering tests were conducted, and the fundamental properties were determined to examine the effect of resin impregnation on board qualities. Bending and internal bond strength of resin-impregnated boards (I-board) satisfied the criterion for 18-type particleboard described in JIS A 5908. Thickness swelling (TS) after 24-h water immersion was approximately 2%. Resin impregnation improved the dimensional stability of the boards. In wet—dry cyclic testing, TS of I-board was the same as that of plywood. The retention ratio of modulus of rupture of I-board was large; thus, I-board had high bond durability. Color change of I-board was less than that of ordinary particleboard after a 500-h accelerated weathering test. I-Board had lower surface roughness than boards produced by a spray application method (S-board) and higher water repellency, although the difference in resin contents of the face layer was small. Thus, it is suggested that the surface properties and weatherability of I-board were improved by impregnation of phenolic resin. High-density and resin-impregnated boards made from the WVE elements are expected to withstand actual exterior use.

Strength properties of laminated veneer lumber in compression perpendicular to its grain

Tests of compression perpendicular to the grain were carried out on laminated veneer lumber (LVL) and timber. The species tested were sugi, radiata pine, karamatsu, akamatsu, and dahurian larch; two sets of sugi specimens were tested, with the sugi LVL products being manufactured in different plants. The strength properties of the materials for different loading directions were compared for LVL and timber. At 5% compressive strain in the same materials, the average stress in the tangential direction of timber was larger than that in the radial direction for all species except for radiata pine, and the average stress in the edge-wise direction of LVL was larger than that in the flat-wise direction for all species except for radiata pine. When the stress at 5% strain was compared in the same direction, the average stress of LVL in the edge-wise direction was larger than that in timber in the tangential direction for all species, but there were no great differences between the average stress of LVL in the fl at-wise direction and that of timber in the radial direction for all species except for radiation pine. There was a close relationship between density and stress at 5% strain in LVL, especially in the edge-wise direction. For all results, radiata pine did not follow the trend of the other species; The large annual ring width of radiata pine was considered to have affected the results.

House dust mites and their sensitivity to wood oils and volatiles

Allergic diseases such as bronchial asthma, perennial rhinitis, and atopic dermatitis caused by the house dust mites Dermatophagoides pteronyssinus and Dermatophagoides farinae, which are dominant species in homes, have recently become serious health problems. Reducing the number of and exposure to mites and mite allergens are the most important factors in preventing allergic diseases. Recently, the effects of essential oils of plants on house dust mites have received much attention with a view to producing natural mite-killing agents. Essential oils and their components of wood and their leaves have also received much attention. In this article, we summarize the biology of house dust mites, mite allergens, and their concentration in homes, and discuss the control of house dust mites by using plant and wood extractives, especially in relation to the influence of essential oils and volatiles from wood on house dust mites.

The composition of volatiles from tatami mats containing hinoki (Chamaecyparis obtusa) wood-wool and its decline over the long term

Volatiles inside tatami mats containing hinoki (Chamaecyparis obtusa) wood-wool as padding were analyzed. Volatiles were collected with solid-phase microextraction (SPME) fibers in a small chamber prepared in tatami mats and assayed by gas chromatography. Most of the detected compounds are typically found in hinoki extractives. Monoterpenes rapidly decreased at the beginning of the experiment, while the dispersion of sesquiterpenes that contain hydroxyl groups was observed to last more than 1 year. These sesquiterpenes, T-cadinols, and α-cadinols may play a role in the suppression of house dust mites.