Wood-cement Composites Research Articles

Evaluation of using waste timber railway sleepers in wood–cement composite materials

In present study, the suitability of using waste timber railway sleepers (WTRSs) as filler in wood–cement composites was investigated. The effects of two variable factors namely press temperatures (25 and 60 °C) and calcium chloride contents (3%, 5% and 7% w/w cement) on some physico-mechanical properties were also investigated. The following experimental parameters were constant: wood/cement ratio (40:60), board thickness (15 mm), press pressure (40 kg/cm 2), and press time (5 min). Press temperature, calcium chloride and the interaction of both variables had significant effects ( p < 0.01) on all the studied properties. Test results showed that addition of calcium chloride tends to enhance both the physical and mechanical properties of boards. All properties of the boards were improved when the calcium chloride content was increased from 3% to 7%. The results also showed that as the press temperature was increased from 25 to 60 °C, significant increased in water absorption and thickness swelling occurred. Water absorption and thickness swelling (at 2 h and 24 h) compared favorably with values reported for cement-bonded composites produced from virgin wood particles. In general, the strength properties of the boards were found to be a maximum when press temperature and calcium chloride were 25 °C and 7%, respectively. These properties can be exploited in many applications where lightweight concretes are required. Therefore, WTRS is technically suitable for building construction such as paneling, ceiling and partitioning.

Cement-bonded composite boards made from poplar strands

This study was carried out to explore the possibility of making cement-bonded wood composite building products using poplar ( Populus deltoides) chopped strands. The experimental design consisted of two treatments namely wood strand and calcium chloride contents. Boards measuring 450 × 450 × 15 mm 3 were manufactured using wood/cement ratios of 40:60, 60:40 and 70:30 by weight and 3% and 7% of an accelerator (CaCl 2⋅H 2O). At least four replications were fabricated for each treatment, and the mechanical properties and water absorption of the boards were evaluated according to DIN 68763. The mechanical properties in terms of modulus of rupture, modulus of elasticity, internal bond and impact strength were investigated and compared to the neat cement controls. Test results showed that addition of CaCl 2 tends to enhance both the mechanical and water-resistance of wood–cement composites. The bending and impact strengths of the wood–cement specimens increased with an increase in the wood content, and the maximum values were obtained at wood loading of 60% by weight. The negative influence of wood content on the internal bond can be explained by the reduced bonding ability because of weaker wood strands compared to cement. Water absorption and internal bonding were inversely proportional to the increase of cement mixture ratio, and their values increased proportional to the increase of wood ratio in the mixture. In addition, all properties of the boards were improved when the CaCl 2 content was increased from 3% to 7%.

Probing of wood–cement interactions during hydration of wood–cement composites by proton low-field NMR relaxometry

Proton NMR T2 relaxometry has been applied to investigate phenomena involved in wood–cement composites during hydration. The transformation of capillary pore water into hydrates and gel pore water, as well as the microstructural changes occurring in the cement matrix, was continuously monitored during the first 28 days of hydration. Water in wood and its transfer into the matrix as cement hardens were also evidenced with the method. It has been found, for example, that some of the water in the mixture is retained in wood in the form of bound or free water, depending on the initial water content. By measuring the area under the different peaks, the consumption of water during hydration can be measured and the advancement of the hydration process can be evaluated via the hydration advancement coefficient α. The cement hardening within the composite has been also studied in the presence of calcium chloride, an accelerating agent. The acceleration was clearly evidenced at the early stage of the hydration process. The influence of extractives has been evaluated by comparing the hydration behaviour of composites prepared from Eucalyptus saligna (low extractives content) and Afzelia bipendensis (high extractives content), and a new compatibility index based on NMR relaxometry measurements has been proposed.

The effects of composition and carbon dioxide injection time on the properties of wood-cement composites

The effects of wood fiber/cement ratio, water/cement ratio and carbon dioxide injection time on the carbonation reaction and strength of wood-cement composites were evaluated. Increasing fiber content usually led to stronger composites and lower carbonation degree while increasing water amount decreased strength of composites in most cases. Either insufficient water or excessive water reduced carbonation reaction rate. There was a significant interaction effect between fiber content and water content, which had to be considered in optimizing the variables. Prolonging carbon dioxide injection time gradually increased carbonation degree, but did not affect the ultimate strength of composites.

An investigation of the suitability of some Greek wood species in wood-cement composites manufacture

Eight Greek wood species were examined as potential raw materials for wood-cement composites. Hydration tests were carried out to determine the inhibitory index in order to classify wood-cement compatibility. The mixture with the highest compatibility (low inhibition) was that of poplar and cement with an inhibition index of 7.44.

Characterizing the setting of cement when mixed with cork, blue gum, or maritime pine, grown in Portugal I: temperature profiles and compatibility indices

Data are presented on the effects that cork, blue gum, or maritime pine, all grown in Portugal, have on cement setting. These materials were mixed with cement either without any treatment or after being extracted previously with a range of solvents (ranging from nonpolar to very polar). Other experiments were carried out in which extractives or calcium chloride were added to the cement paste. All lignocellulosic substrates have detrimental effects on cement setting, which is mostly seen by a delay in attaining the maximum temperature in the process. However, the addition of calcium chloride was able to overcome this disadvantage. Extraction of the substrates with some polar extraction agents before addition to the cement paste only slightly improved compatibility, and the addition of water-based extractives to a cement paste affects the setting much less than the lignocellulosic material by itself. Several thermal compatibility indices, including a new index proposed in this article, were calculated from data taken from temperature profiles, and conclusions are presented on the performance of the setting systems, as compared with a neat cement paste. In addition, comments are expressed on the level of accuracy offered by the indices applied in this study, and how such accuracy can be checked or improved by matching them to the physical properties of the wood-cement composites.

Characterizing the setting of cement when mixed with cork, blue gum, or maritime pine, grown in Portugal II: X-ray diffraction and differential thermal analyzes

It is already known by the scientific and industrial communities that lignocellulosic substrates are, to a certain extent, inhibitors of the hydration reaction of cement. The extent to which and how they influence such reactions is still a matter of debate. Several techniques, such as calorimetry, i.e., the measurement of the heat evolved or obtaining temperature profiles during the hydration, the determination of extractive contents of lignocellulosic substrates and their relation with the characteristics of the hydration curves, or even testing of the mechanical properties of the wood-cement composites, have been used in previous research. This study complements past research using two techniques that have been used in the analysis of cement hydration but are not usually applied to lignocellulose-cement mixes, namely X-ray diffraction (XRD) and differential thermal analysis (DTA). The raw materials for this study were three lignocellulosic materials of Portuguese origin: cork (the bark of Quercus suber L.), blue gum (Eucalyptus globulus Labill.), and maritime pine (Pinus pinaster Ait); and Portland cement. The two techniques allowed tracking of the evolution of the main cement constituents during hydration. It was found that all the lignocellulosic substrates had detrimental effects on cement hydration. The blue gum exhibited the fastest hydration kinetics in the initial stage of reaction, but was then overtaken by cork, which at the end gave the highest hydration conversion amongst the three lignocellulosic substrates. Although pine caused the slowest initial hydration kinetics, with the passage of time its effect approached that of blue gum. At the end of the hydration period, specimens containing either species had similar quantities of hydration reaction products. The DTA and XRD results were consistent and are in good agreement with the temperature profiles and compatibility indexes reported in a previous work.

Strength and water absorption characteristics of cement-bonded particleboard produced from coconut husk

Wood-Cement composites were produced from coconut (Cocos nucifera) husk, an agricultural residue with minimal economic utilization in Nigeria. Contrary to conventional practice, the boards were fabricated in the laboratory without external pressure application. The effects of calcium chloride (CaCl2) addition on the hardening time, appearance, bending and compressive strength, and water absorption properties of the boards were also investigated. The boards had a relatively low density with values ranging from about 594 to 650 Kg/m3. The addition of CaCl2 reduced the hardening time of the board by about 50% (from 36 to 12 hours) and also imparted glossiness in the treated boards. The Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) of the untreated boards (677 N/mm2 and 1.25 N/mm2 respectively) were slightly lower than those of the treated boards (1104 N/mm2 and 1.48 N/mm2 respectively). The mean compressive strength of the CaCl2–treated boards (3.68 N/mm2) was also slightly higher than that of the untreated boards (3.39 N/mm2). However, the observed differences were not significant. The rate of water absorption (< 25% after 24 hours) and the resultant thickness swelling (

Cement bonded wood wool boards from podocarpus spp. for low cost housing

This paper gives results of a preliminary study on the properties of cement bonded woodwool boards manufactured as composites by using wood wool (excelsior) from podocarpus spp. wood species and ordinary Portland cement. Two main parameters were varied during the investigation and these were the width of the wood wool and the cement to wood wool ratio. Results show that the optimum mix proportion is three parts of cement to two parts of wood wool by weight and that a smaller excelsior width gives higher board strengths. The results from tests on flexural strength, compressive strength and tensile strength far exceeded the requirements of the German Standard DIN 1101:1989. Results of water absorption and swelling were, however, higher than those specified in the standard but this was attributed to insufficient pressure on the boards during manufacture an anomaly which can be corrected. The potential uses of the boards are in basements, floor units, permanent shuttering, partitioning, sound insulation in walls, ceilings and floors, roofs, sound barriers and thermal insulation. Further research is required to investigate the use of different wood species and different mineral binders. Keywords: podocarpus spp, wood-wool, wood-cement composites Journal of Civil Engineering Research and Practice Vol. 3(1) 2006: 51-64

Modification of cement hydration at early ages by natural and heated wood

Heat treatments of wood are widely used for the reduction of wood swelling and dimensional instability of wood-cement composites. The effect of natural and heated wood on the hydration of cement at early ages was investigated by isothermal calorimetry, thermogravimetry (TGA) and Fourier transform infrared (FTIR) spectroscopy. The addition of wood strongly delays and inhibits the hydration of the silicate phases. Consequently, the amount of portlandite is lower in composites than in neat cement. Approximately 30% of the inhibition of portlandite precipitation is due to an increase of calcium carbonate content in cement paste. The absorption of a part of water by wood produces a decrease in gypsum consumption. Nevertheless, the ettringite formation is not significantly affected since a diffusion of sulfate ions from wood occurs.

Adsorption of Cations from a Cement Suspension onto Lignocellulosic Substrates and its Influence on Cement Setting

The calcium (Ca), sodium (Na), and potassium (K) contents of blue gum, maritime pine, and cork increased after these lignocellulosics were stirred with the filtrate of a cement suspension or a solution of calcium hydroxide. The adsorbed cations could be released easily by treatment with an acidic solution. It is suggested that those raw materials, and lignocellulosics in general, act as cation exchange substrates when they are mixed with cement and water to make wood–cement composites. The implications that such phenomena may have on cement hardening reactions, and how they could hinder them are discussed. The possibility that the phenomenon is related to well‐known compatibility problems that many woods present when manufacturing wood–cement composites is discussed.

Effect of carbon dioxide injection on production of wood cement composites from waste medium density fiberboard (MDF)

The possibility of recycling waste medium density fiberboard (MDF) into wood–cement composites was evaluated. Both new fibers and recycled steam exploded MDF fibers had poor compatibility with cement if no treatment was applied, due to interference of the hydration process by the water soluble components of the fiber. However, this issue was resolved when a rapid hardening process with carbon dioxide injection was adopted. It appears that the rapid carbonation allowed the board to develop considerable strength before the adverse effects of the wood extractives could take effect. After 3–5 min of carbon dioxide injection, the composites reached 22–27% of total carbonation and developed 50–70% of their final (28-day) strength. Composites containing recycled MDF fibers had slightly lower splitting tensile strength and lower tensile toughness properties than those containing new fibers especially at a high fiber/cement ratio. Composites containing recycled MDF fibers also showed lower values of water absorption. Unlike composites cured conventionally, composites cured under CO 2 injection developed higher strength and toughness with increased fiber content. Incorporation of recycled MDF fibers into wood cement composites with CO 2 injection during the production stage presents a viable option for recycling of this difficult to manage waste material.

Wood-cement composites: a review

This paper reviews the research reported mostly in the last 10 years in the most common journals on the wood-cement composites field. The focused topics include: the problem of the compatibility (or not) between cement and woods, what causes it, ways of overcoming the problem; methods for manufacture and the properties exhibited by common wood-composites; special techniques to accelerate the curing of cement and to improve the properties of wood-cement composites; manufacture of nonwood vegetable raw materials-cement composites; durability against weathering and fungi; and construction materials. A discussion on the state-of-the-art is also presented.

The suitability of five Western Australian mallee eucalypt species for wood–cement composites

There are currently around 10 000 ha of mallee eucalypt plantations in Western Australia that have been established primarily for the production of eucalypt leaf oils. Planting rates are projected to increase dramatically in future. The financial viability of these plantations is dependent upon finding a commercial outlet for the small diameter wood and bark residues, which may constitute up to half of the harvested material. The potential for such residues to be utilised in cement-bonded wood composite panels was investigated here. The woody residues of five species of mallee eucalypts, as expected, inhibited the hydration reaction of Portland cement, but not to such an extent as to make the wood unsuitable for cement composites. The bark of one of the species, E. loxophleba ssp. lissophloia, inhibited the setting of Portland cement to such an extent that the residue of this species (with bark present) was unsuitable for use in wood–cement composites. Three out of the five mallee eucalypt species retained relatively good compatibility with cement even when bark was present in the residues. The flexural properties (MOR and MOE) of cement-bonded panels manufactured from chipped mallee eucalypt residues were low in comparison to similar boards made from radiata pine, probably because of the smaller particle size and lower aspect ratio of the eucalypt wood residues. Boards made from E. polybractea, E. horistes and E. kochii ssp. plenissima were stronger and more resistant to water than those made from E. angustissima and E. loxophleba ssp. lissophloia. On the basis of our findings, opportunities and challenges for the commercial utilisation of mallee eucalypt wood for wood–cement composites are discussed.

Compatibility of 8 temperate Australian Eucalyptus species with Portland cement

Few of the over 800 species of Eucalyptus have been screened for their compatibility with Portland cement and suitability for the manufacture of wood-cement composites. The compatibility with Portland cement of 8 temperate species of Eucalyptus native to SE Australia was measured, and the effects of sapwood content and of extractive removal on wood-cement compatibility were assessed.

Study of hydration behavior of wood cement-based composite II: effect of chemical additives on the hydration characteristics and strengths of wood-cement composites

The influence of the 30 chemical additives on the hydration characteristics of birch wood-cement-water mixture was determined by measuring the maximum hydration temperature (T max) and the time (t max) required to reach the temperature. The chemical additives were tested and divided into two types depending on the pattern of exothermic reaction peak within the 24-h observation period. The wood-cement-water mixtures with additions of each of the 11 type I chemical additives showed a two-peak temperature-time curve similar to that for neat cement. CaCl2, FeCl3, and SnCl2 reached the highestT max above 50°C. When the 19 type II chemical additives were included, the mixtures offered only one peak hydration temperature-time curve. Among them, the 10 chemical additives caused an obvious temperature increase at the beginning of the hydration reaction. The most significant effect was with the addition of diethanolamine, where the mixture produced aT max above 50°C. The strength values (modulus of rupture, internal bond strength) of word-cement board were tested with separate additions of the 10 chemical additives arranged by the highestT max. There was a good positive correlation betweenT max and the strength values. In addition, the composite chemical additives were preliminarily examined to determine if they accelerated the hydration reaction of blast-furnace slag cement. The results revealed that composite chemical additives evidently accelerated the hydration reaction and the setting of blast-furnace slag cement mixed with wood. Blast-furnace slag cement can thus be considered for use as an acceptable inorganic bonding material for wood-cement panel manufacture.

Cement Hydration Tests Using Wood Flour may not Predict the Suitability of Acacia mangium and Eucalyptus pellita for the Manufacture of Wood-Wool Cement Boards

Summary Wood-wool cement boards (WWCBs) are manufactured in many tropical countries which have extensive eucalypt and acacia plantations. Wood from such plantations could act as a potential raw material for WWCBs, but the suitability of most tropical eucalypts and acacias for the manufacture of such products is unknown. This study was undertaken to assess whether the standard laboratory test for wood-cement compatibility, which measures heat of hydration in wood flour-cement mixtures, is an appropriate method for screening tropical eucalypts and acacias for their compatibility with cement and suitability for the manufacture of WWCBs. Wood samples from a tropical eucalypt (E. pellita) and a tropical acacia (A. mangium) were tested in two forms, i. e. flour and wool, for their compatibility (expressed by maximum hydration temperature and CA-factor) with Portland cement. Form significantly influenced the effect of the wood on cement hydration, resulting in a different species compatibility ranking for flour and wool. As the heartwood content of wood-wool-cement hydration test samples increased, Tmax. and CA factor increased whereas the opposite occured for those containing wood flour. Tests using wood flour ranked E. pellita as being more compatible with cement than A. mangium whereas the ranking was reversed when wood-wool was used. Furthermore at low wood levels the compatibility of samples containing wood-wool or wood flour with cement was similar whereas at high wood levels, samples containing wood-wool were much more compatible with cement than those containing wood flour. Laboratory tests designed to screen eucalypts and acacias for their compatibility with cement should use wood in a coarser form with a lower surface-to-volume ratio than flour. Caution should be exercised if using results from wood flour-cement hydration tests to estimate the suitability of wood species for the manufacture of WWCBs and possibly other wood-cement composites.

A Study of Ordinary Portland Cement Hydration With Wood by Isothermal Calorimetry

Summary As an essential preliminary to understand the hydration of wood-cement composites, the effects of some additives on the delayed setting due to wood of an Ordinary Portland Cement have been investigated by isothermal calorimetry. With the addition of calcium chloride and activated charcoal, an increase of 50% of the total enthalpy is observed in wood-cement composites hydration, because calcium chloride mostly influences aluminate phases and activated charcoal silicate phases.

Controlled Dimensional Variations of a Wood-Cement Composite

At present wood-cement composites are used in pressed panels and unpressed blocks. These elements present interesting physical, acoustic and mechanical properties as well as good manufacturing properties. However, dimensional variations with external humidity remain high and prevent external use of the composites without an additional treatment. Dimensional variations are linked with wood, the wood-matrix interface and the cement matrix. A specific treatment for each of these previous elements allows reduction of dimensional variations. However, these deformations still remain higher than the standard values measured under conditions fixed by the French standard i.e. 1 mm/m. On the other hand, an appropriate combination of the three treatments achieves the expected objective at a reasonable cost compared to the one obtained for a conventional cement-sand-gravel composite.

Investigations on the influence of the addition of carbon dioxide on the production and properties of rapidly set wood-cement composites

This paper gives a short description of the manufacturing process of cement particle boards. Production methods currently used are characterized by a pressing time of boards of about 8 h. Also, flakes from only a limited number of wood species are suitable as reinforcing material. A new process is described where pressing time is reduced to only 4 min, and which allows the utilization of wood species not known as suitable so far. This prcess is distinguished by the injection of carbon dioxide into the furnish during pressing, where-upon the cement sets within a few minutes. A similar process, also described in this paper, uses carbonates of ammonium, sodium or potassium as additives to the mixture of wood flakes, cement and water. The carbonates decompose during pressing and carbon dioxide is released to react with calcium hydroxide from the hydration process. Thus, the cement sets within a very short time. The paper compares the properties of cement particle boards made according to these new processes with those from the old process.