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Properties of wood-based composites formulated with aggregate industry waste
Construction and Building Materials 14 Ž2000. 341᎐350
Properties of wood-based composites formulated with aggregate industry waste b,U A. Ledhema , R.M. Dheilly b, M.L. Benmalek c , M. Queneudec ´ b
a Institut de Genie ´ Ci¨ il Centre Uni¨ ersite´ de Laghouat, Laghouat, Algeria Laboratoire des Transferts et Reacti de Genie ´ ¨ ite´ dans les Milieux Condenses, ´ I.U.T Departement ´ ´ Ci¨ il ᎏ Uni¨ ersite´ de Picardie Jules Verne, A¨ enue des Facultes, ´ 80025 Amiens Cedex 01, France c Institut de Genie ´ Ci¨ il Centre Uni¨ ersite´ de Guelma, Guelma, Algeria
Received 1 October 1999; received in revised form 19 April 2000; accepted 22 May 2000
Abstract The option of using vegetable-based materials is not only one potential response to the lack of aggregate resources in certain regions, but also a way of helping to preserve the environment. These reasons have incited some authors to address the issue of waste reuse in the form of insulating composites. The work presented herein, once the influence of components has been examined, will focus on the influence of various processes on the performances of hardened composites. Aggregate processing by boiling water, followed by a hydraulic binder coating, enables the minimization of the composite’s dimensional variations to a larger extent. This processing technique allows the achievement of an excellent compromise in material properties, although it increases density and, hence, thermal conductivity. 䊚 2000 Elsevier Science Ltd. All rights reserved. Keywords: Wood-based composites; Aggregates processing; Physicomechanical properties
1. Introduction Concrete with wood in its mix design has been the focus of growing interest over the past few years. A thorough review about the building processes using wood aggregates has recently been conducted by Pimienta et al. w1x. The option of using vegetable-based materials is not only one potential response to the lack of aggregate resources in certain regions, but also a way of helping preserve the environment, in as much as, at the present time, the wood industry generates significant quantities of waste which are not being reused. Furthermore, the aggregate industry, stone transformation processes and the heavy use of quarries U
Corresponding author. Tel.: q33-3-22-53-40-16; fax: q33-3-2253-40-16. .. E-mail address: [email protected] ŽM. Queneudec ´
and ores deposits are producing mineral wastes which constitute both an environmental hazard and a loss of raw materials. These various reasons have incited some authors to address the issue of waste reuse in the form of cementitious insulating composites with a view to transform them into insulating or insulating and bearing building units according to their performances. Nevertheless, wood-based composites do, in general, display the disadvantage of being overly sensitive to water, which results in dimensional variations and an overall decline in performance. The use of such composites in construction has often been limited due to this behavioral flaw, despite the number of processes proposed to reduce wood aggregate exchanges in humid environments w2x. Unfortunately, these processes often necessitate sizable energy expenses or highly-sophisticated equipment. For this reason, some of the authors have sought to develop processes which require lower
0950-0618r00r$ - see front matter 䊚 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 0 0 . 0 0 0 3 7 - 4
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quantities of energy and which are simple to implement in developing countries. Such processes, however, can modify the interface between the matrix and the aggregates, and, hence, modify certain mechanical characteristics. Similarly, the resultant increase in density exerts a negative impact on thermal characteristics. The work presented herein, once the influence of components has been examined, will focus on the influence of various processes on the performances of hardened composites.
2. Materials and experimental set-up 2.1. Raw materials The clay-like products used in this work consisted of waste produced from aggregate quarry operations. The sands and gravel used were of the commercialized variety, while the portion of material - 70 m was returned to the extraction site. For the purposes of this study, the clay-like material, extracted in the form of thick mud from settling tanks, was dried, ground and sieved to 70 m in order to eliminate all foreign matter. The results of the laser-based gap-grading analysis of the material obtained are provided in Fig. 1. The mineralogical study shows that the material was consti-
tuted almost entirely of kaolinite, with the quartz and mica contents remaining at less than 5% w3,4x. The schistous fines consisted of residue from the crushing of Brioverian schist which had undergone a slight metamorphism. The portion included herein corresponded to what remained once the fraction of sand and fine gravel particles had been removed. The separation process was performed on dry material. The fines used in this work were characterized by a gapgrading from 88% passing at 500 m to 100% passing at 1 mm. The proportion of grains less than 2 m in size was practically zero, and the residue provided a granular material that lacked both cohesion and plasticity. Its apparent density was 1.05 and its absolute density 2.70. The gap-grading analysis and description of characteristics provided by the operator are given in Fig. 1 and Table 1, respectively. Fir, in the form of shavings, was used as the wood content for this study, due to both its low density and widespread application within the building industry. The apparent density of the chips was approximately 0.05, while their real density was 0.44. The cement used was a CPA CEMI 52.5 ŽNF P15301. whose laser-based gap-grading analysis is given in Fig. 1. Table 2 presents the chemical analysis and the Bogue composition. 2.2. Processing materials In addition to the cement mentioned above, the material used to process the wood shavings was an XHN 100 ŽNF P15130. hydraulic lime added in the form of grout on the shavings during slow mixing ŽEN 196-1.. Linseed oil, with a density of 0.86, was also used to impregnate the shavings. In the present case, this impregnation could be performed by absorption at room temperature and atmospheric pressure thanks to the geometry of the wood aggregates. The oil was pulverized onto the shavings, also during slow mixing ŽEN 196-1..
Fig. 1. Laser granular analysis of mineralogical constituents.
Table 1 Chemical analysis of the schistous fines CaO
MgO
SiO2
Fe2 O3
Al2 O3
SO3
K2 O
TiO2
P 2 O5
Mn2 O3
Na2 O
Cl
Loss on ignition
1.31
3.17
58.34
7.61
18.69
0.45
3.35
0.81
0.13
0.10
1.80
0.007
4.32
C2 S
C3 A
C4 AF
14
2.5
13.1
Table 2 Chemical analysis of the cement and the Bogue composition CaO
MgO
SiO2
Fe2 O3
Al2 O3
SO3
Loss on ignition
64.8
0.8
21.3
4.3
3.7
2.7
1.2
C3 S 62
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343
For both of the cases listed above, the quality of the processing was controlled by scanning electron microscopy. Weighing was carried out in order to verify intensity. An extraction of water-soluble substances, liable to cause swelling of the wood or delays in the cement hydration, was performed by use of boiling water. After processing, the shavings were maintained in a humid room ŽR.H.s 95%, t s 20⬚C. for 48 h and then stored in a climate-controlled room ŽR.H.s 50%, t s 20⬚C. for 1 month.
nected to an electronic comparator, with a numerical display hooked up to a printer. The porosity accessible to water was evaluated from the variations in mass obtained by weighings with a scale accurate to 1r100th of a gram.
2.3. Composite mixes
3.1.1. Influence of the percentage of wood sha¨ ings The mineral portion was set at 100% and the
3. Experimental results 3.1. Influence of constituents on the composite’s characteristics
The clay-like material, schistous fines and cement, previously dried until a constant mass was reached, were initially mixed at low speed in a standardized mortar mixer ŽEN 196-1.. The shavings were added gradually while keeping the mixer at low speed for 2 min. Water was then added gradually while continuing the low-speed mixing for another 2 min. The quantity of water ŽW . was determined by the formula: Ws 0.35C q 0.7Cl q 0.2 S q K. A, where C, Cl, S and A are the percentages, by weight, of cement, clay, schistous fines and wood-aggregates, respectively. The coefficient K takes into account the absorption of water up to saturation by the wood shavings. For nonprocessed shavings, K is equal to 1.8. The value of this coefficient varies according to the type of processing, so as to retain the same level of workability w5x. After mixing, the mixture was poured into molds and the filled molds were then stored in a hygrometrically-controlled and temperature-controlled room ŽR.H.s 95%, t s 20⬚C. for 24 h. 2.4. Measurement techniques Following demolding, the test specimens were placed in a storage room ŽR.H.s 50%, t s 20⬚C. and then dried at 100⬚C until a constant mass before testing. Mechanical tests were carried out for 28 days on three 4 = 4 = 16 cm prismatic samples in compliance with the operating methods specified in the EN 196-1 standard. Thermal conductivity was determined with the help of an experimental device recently developed in the laboratory w4x; the TPS probe was placed between two 10 = 10 = 5 cm parallelepiped samples. The extreme dimensional variations ŽEDV. were determined from the difference between the length of 4 = 4 = 16 cm prismatic samples at dry and saturated states. Immersion took place at 20⬚C, followed by drying in an aerated oven at 100⬚C until a constant mass was reached. Linear dimensional variations, which fill the gap between the dry and saturated states, were measured using a retractometer ŽNF P15-433. con-
Fig. 2. Influence of the constituents on the composite’s density: Ža. clay q cement s 100%; clayrcement s 0.6, wood expressed as a mass percentage of the total dry mixture; Žb. clay q cement s 100%, wood s 20% of mineral fraction, cement expressed as a mass percentage of the total dry mixture; and Žc. clay q cement q schistous fines s 100%, Žclay q schistous fines.rcement s 0.6, schistous fines expressed as a mass percentage of the total dry mixture.
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A. Ledhem et al. r Construction and Building Materials 14 (2000) 341᎐350
Fig. 3. Influence of the different constituents on the mechanical strengths, the proportions of constituents are the same that those of Fig. 2. Compressive strength Ža, b, c.; tensile strength Žd, e, f..
clayrcement ratio at 0.6. The proportion of shavings varied and was expressed as a mass percentage of the total dry mixture. Fig. 2 presents the decrease in the composite’s dry density as the mass proportion of wood increased. The influence of the percentage of shavings on mechanical performance has been summarized in Fig. 3. The compressive strength fell as wood shavings get added. The tensile strength increased by between 0 and 10%. This increase could be explained by a fiber-related effect due to the presence of wood shavings. This effect was offset by both a reduction in the percentage of cement and by the fraction of minerals, with respect to the total mix, which was predominant beyond a 10% rise in the mass of the wood shavings Ž; 40% by volume. and
Fig. 4. Variation of the thermal conductivity as a function of the mass proportion of wood shavings.
A. Ledhem et al. r Construction and Building Materials 14 (2000) 341᎐350
Fig. 5. Variation of E.D.V as a function of the different constituents Ža. clay q cement s 100%, clayrcement s 0.6, wood expressed as a mass percentage of the total dry mixture; Žb. clay q cement s 100%, woods 20% of mineral fraction, cement expressed as a mass percentage of the total dry mixture; and Žc. clay q cement q schistous fines s 100%, Žclay q schistous fines.rcement s 0.6, schistous fines expressed as a mass percentage of the total dry mixure.
which led to a drop in mechanical strength. In contrast, the addition of wood shavings could considerably improve thermal performance Žsee Fig. 4.. Fig. 5 shows that a higher proportion of shavings served to increase the EDV significantly. 3.1.2. Influence of the cement proportion The dry mineral fraction Žclay q cement. was taken as equal to 100%, while the clayrcement ratio was allowed to vary. The added wood amounted to 20% of the mineral fraction, by mass. The quantity of cement has been expressed as a mass percentage of the total dry mixture. Fig. 2 shows a small increase in density as the proportion of cement increased. In contrast, the mechanical strength improved quite noticeably Žsee Fig. 3. and the EDV values fell Žsee Fig. 5..
345
3.1.3. Influence of the addition of schistous fines This study was carried out on a mineral mixture for which the Žclay q schistous fines.rcement ratio s 0.6. The fraction of clay q schistous fines was fixed and the proportion of wood shavings was 20% of the dry mineral fraction. Only the ratio of schistous fines to clay was allowed to vary. The quantity of schistous fines has been expressed as a mass percentage of the total dry mixture. The composite’s density increased with the proportion of schistous fines Žsee Fig. 2.. Fig. 3 shows the evolution in mechanical strength. In general, the addition of schistous fines increased the composite’s mechanical strength. Whereas the compressive strength had a tendency to rise with this added proportion, the tensile strength displayed the onset of saturation above 60%. This finding could be explained by the characteristics of the fines: schistous fines constitute a granular material that lacks both cohesion and plasticity. Beyond a certain volumic proportion, the cement’s binding effect is no longer sufficient. Fig. 5 reveals that the addition of schistous fines did indeed reduce the EDV. In summary, the addition of wood shavings enhances thermal performance while lightening the composite’s weight. Cement and schistous fines allowed the improvement of both the dimensional variations and the mechanical strength. The cost of cement is one constraint to be taken into consideration. Moreover, the curves in Figs. 3 and 5 show that, as of the 50% mark, which corresponds to a concentration of approximately 400 kgrm3, the change in dimensional variations and mechanical characteristics was less significant. This value was thus chosen as the upper limit of cement concentration. Schistous fines, like clay-like co-products, are industrial wastes which must be reused in some way or another. Reuse quantities must be as great as possible within the limit of performance requirements. The addition of schistous fines helps stabilize the EDV, yet also increases density and, hence, reduces the composite’s insulating capacity. A schistous finesrclay-like coproduct ratio equal to 1 allows reducing dimensional variations by approximately 30% while maintaining the density under 0.9. This ratio was, therefore, selected for the remainder of our study. The evolution in thermal conductivity showed that, beyond a concentration in shavings of approximately 20%, the decrease in was relatively low. For this reason, it seemed useful to limit the percentage of shavings to this value, which yielded a composite density of 0.85. This decision was reinforced by the fact that dimensional variations increased very rapidly when the mass percentage of the shavings exceeded 10%. These considerations led us to propose the composition given in Table 3, whose characteristics are presented in Table 4.
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346 Table 3 Composition of the composite Composition
m3 rm3
kgrkg
kgrm3
Clay-like fines Schistous fines Cement Wood-shavings Dry mix
14 13 19 54 100
23 23 38.5 15.5 100
196 196 327 131 850
3.2. Influence of aggregate processing on composite performance The various processes described above have been applied either on their own or in combination with one another. 3.2.1. Dry density Bulk density can be considered as the primary characteristic of lightweight concrete. All mechanical properties, thermal properties and dimensional variations depend upon bulk density to a certain extent. However, the type of processing used for the wood shavings causes the density to vary. The influence of the various processes on this characteristic must, therefore, be evaluated. Fig. 6 presents the composite’s dry density vs. the mass percentage of the selected process. In the case of processing by means of hydraulic binders, the results revealed an increase in density as the process gained intensity. It could then be considered that an increase in the density of wood shavings, upon the process’s completion, led to an increase in the composite’s density as well. Yet, the observation made by use of the mean SEM Žsee Fig. 7. shows that the matrix’s microstructure densified once the shavings were processed. This phenomenon could be explained by a smaller quantity of water being added during the mixing. The absorption of water by the shavings up to saturation was, in fact, no more than approximately 100% for a cement or limerwood ratio of 1, whereas without processing, this absorption reaches 240%. The coefficient K, which takes into account humidity up to saturation, was, therefore, lower w5x and the excess water not used during the cement’s hydration was also lower. Moreover, Vaquier w6x demonstrated that during the introduction of aggregates into the mortar, the aggregates’ degree of impregnation first increases Table 4 Characteristics of the composite Dry density Open porosity Ž%. Compressive strength ŽMPa. Tensile strength ŽMPa. Extreme dimensional variations Žmmrm.
0.85 46 8.9 3.8 3.5
Fig. 6. Influence of the different treatments of the wood-shavings on the dry bulk density of the composite.
rapidly and then slows to a maximum at the beginning of the cement’s setting. As the cement gel is being formed, the pore diameter in the mortar decreases, and the direction of water movement reverses; hence, the aggregates’ degree of impregnation decreases. Vaquier also showed that these exchanges are dependent on the aggregates’ water content at the time of the test. By modifying the capillarity of the aggregates and their water content at saturation, the process modifies the exchanges occurring between the matrix and the aggregates and, therefore, the porosity of the matrix. This finding is confirmed by the composite’s water absorption which, after this process, decreases by approximately 50%. The composite’s density, however, remained below 1.2 within the adopted concentration limit. Results from oil-based impregnation showed that the density increased as the concentration in oil increased. It should be noted that, as in the case of a hydraulic binder-coating process, the oil-impregnation technique considerably reduced the composite’s water absorption Ž20%, instead of approximately 50%.. The influence of boiling water is negligible. The composite’s dry density displayed no variation as this process was being carried out. Nonetheless, it must be pointed out that this statement only holds for dry density. The composite’s density, when saturated by immersion, was reduced as a result of this process. For a duration of 4 h, for example, water absorption did not exceed about 35%. 3.2.2. Mechanical properties Fig. 8 presents the compressive and tensile strengths of the composite. The mechanical strength of the composites with hydraulically-bound aggregates increased, with the intensity of the lime-based processing being slightly better in terms of compression. As discussed in Section 3.2.1, this behavior can be related to the
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347
Fig. 7. SEM observation of the microstructure of the composite: Ža. with wood-shavings and without treatment, Gs 1000; Žb. with wood-shavings treated with cement Žcementrwoods 1., Gs 5000; Žc. with wood-shavings treated with linseed oil Žoilrwoods 0.75., Gs 300; and Žd. with wood-shavings treated with linseed oil Žoilrwoods 0.75., Gs 5000.
porosity of the matrix: as the intensity of the concentration increases, the matrix’s microstructure becomes more highly compact. In the case of an oil-based process, a small reduction in strength could be observed in comparison with the process’s intensity. This behavior was more heavily pronounced for tensile strength, a finding which can be explained by a decrease in the aggregates’ adhesion to the clay᎐cement paste as the quantity of oil generated rises Žsee Fig. 7.. Furthermore, the quantity of water added during mixing was lower since the amount of water absorbed by the wood shavings was heavily reduced by the oil-based process Ž; 60% for an oilrwood ratio s 0.75, instead of 240% for the non-processed shavings.. Despite the presence of less water, the matrix was still very porous, with the pores being filled by oil droplets Žsee Fig. 7.. In contrast, the cement’s hydration did not seem to be affected Žsee Fig. 7.. Fig. 9 presents the mechanical performance of the composite vs. the processing time using boiling water. The process improved mechanical performance to a
slight extent without introducing any change in dry density. This effect can be explained by the elimination of substances through hydrolysis, which typically causes
Fig. 8. Influence of the different treatments of the wood-shavings on the mechanical strengths of the composite.
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Fig. 9. Influence of the boiling time on the mechanical strengths of the composite.
delays in both cement setting and the hardening of wood concretes w7᎐10x. 3.2.3. Thermal conducti¨ ity The general objective of the work carried out has been to develop insulating materials from recycled industrial waste. It is, therefore, advisable to assess the impact of the various processes available on the these materials’ insulation capacity, i.e. on the composite’s thermal conductivity. In this part of the study, the volumic proportions of the shavings remained the same, whether the shavings were processed or not. Fig. 10 shows that the thermal conductivity of the composite increases with the intensity of the hydraulic binder processing. Since the volumic proportion of wood was not modified, it would thus appear that the change in the composite matrix’s microstructure was chiefly responsible for this increase in thermal conductivity. The densification of the matrix, which has already been discussed, also significantly contributed to the increase in thermal conductivity. In a subsequent study, however, it would be necessary to take into account the phenomena occurring at the aggregatermatrix interface due to the processing of aggregates. An analysis of the results in the case of oil-based processing revealed that the thermal conductivity evolved slowly as the bulk density increased. Since the thermal conductivity of oil is higher than that of air, it is only normal that the filling of wood pores by oil leads to an increase in the composite’s thermal conductivity. The use of boiling water for processing wood shavings exerts no influence whatsoever on the composite’s thermal conductivity. 3.2.4. Dimensional stability Dimensional stability is a key characteristic of build-
ing materials and heavily influences structural durability. The various processes described above have been aimed at decreasing the sensitivity of aggregates to water, so as to increase the composite’s dimensional stability. However, previous research has shown that the dimensional stabilization of aggregates does not necessarily induce a reduction in dimensional variation w11x. It is, therefore, essential to evaluate the impact of the various methods of aggregate processing on the studied composite’s dimensional variations. Fig. 11 displays the influence of this study’s processing techniques. The thickness of the coating layer has a predominant impact on the reduction in dimensional variation. Furthermore, the lime-based processing seems to be the most efficient technique. Oil-based processing also exerts a positive influence, yet its resultant reduction in dimensional variation remains limited. Lastly, while processing by boiling water has proven to be efficient, the major portion of the reduction in
Fig. 10. Influence of the different treatments of the wood-shavings on the thermal conductivity of the composite.
A. Ledhem et al. r Construction and Building Materials 14 (2000) 341᎐350
349
Table 5 Influence of treatments on characteristics of the composite Dry bulk density Žkgrm3 .
Rc ŽMPa.
Rf ŽMPa.
Absorption of water by the shavings Ž%.
Absorption of water by the compositeŽ%.
Without Boiling water Ž4 h. Lime Boiling water q lime Cement Boiling water q cement Linseed oil Target values
240 112 99 89
49 34 25 23
0.85 0.85 1.11 1.12
8.9 9.7 12.7 13.1
3.8 4 4.95 5.1
3.50 2.00 1.18 0.95
0.22 0.22 0.27 0.27
87 79
22 20
1.20 1.20
12.4 12.6
4.4 4.8
1.35 1
0.33 0.28
42
22
1.00 - 1.40
8.5 ) 5.0
2.9
2.20 - 1.00
0.25 - 0.3
dimensional variation takes place within the first 2 h Žsee Fig. 12.. The use of combined processes allows the reduction dimensional variations to values of F 1 mmrm Žsee Table 5..
EDV Žmmrm.
ŽWrmK.
Treatment
3.2.5. Summary of findings Table 5 presents a summary of the results obtained from the use of these various processes. An observation of the results indicated a more significant increase in dry density for processes containing mineral particles than for those containing oil. This difference was essentially due to the density of the processing product, as well as to its influence on the microstructure of the composite’s matrix, as outlined above. The hydraulic lime-based processing, in combination with boiling water, proved to be the most efficient method with respect to the resultant increase in mechanical strength. The results also indicated a more sizable increase in thermal conductivity for hydraulic binder-based processing than for oil-based; yet the values attained did not exceed 0.32 WrmK. The dimensional variations could be compared with
the absorption of water by both wood shavings and the composite. The composite’s water absorption corresponded to that of the shavings. Nevertheless, smaller reductions were observed in the composite due to the water being absorbed by the matrix. With the exception of oil-based processing, the reduction in dimensional variation was greater than the reduction resulting from the absorption of water by both wood shavings and the composite. This finding demonstrated that the dimensional variations were not solely due to the absorption of water by the shavings. Modifications in the porosity of the matrix, as a consequence of these various processes, appeared to be an essential factor in reducing dimensional variation. This conclusion is in agreement with the work conducted by Mougel w11x. Aggregate processing by boiling water, followed by a hydraulic binder coating, enabled the minimization of the composite’s dimensional variations to a large extent. This processing technique allowed us to achieve an excellent compromise in material properties. Although it increased density and, hence, thermal conductivity, this process served to preserve some very valuable properties while complying with the RILEM
Fig. 11. Influence of the different treatments of the wood-shavings on the dimensional variations of the composite.
Fig. 12. Influence of the boiling time on the dimensional variations of the composite.
350
A. Ledhem et al. r Construction and Building Materials 14 (2000) 341᎐350
set of recommendations for lightweight insulating concrete Ž Rc ) 3.5 MPa; - 0.7 WrmK..
4. Conclusion The work presented herein lies within the more general topic of industrial waste reuse. A study of material characteristics has shown that while wood shavings do provide improved insulation performance and weight reduction of clay᎐cement pastes, they also give rise to sizable dimensional variations. Cement and schistous fines help increase the density of composites, which leads, not only to enhanced mechanical strength and dimensional stability to water, but also to an increase in thermal conductivity. A combination of these factors has enabled designing a composite which displays distinct mechanical and thermal advantages, yet which exhibits relatively high extreme dimensional variations. A variety of simplified aggregate processing techniques have been proposed: coating by hydraulic binders, impregnation by vegetable oil, and extraction of soluble components in boiling water. With the exception of boiling water, all of these processes have led to an increase in density, mechanical strength and thermal conductivity, in addition to reducing the extreme dimensional variations. Boiling water followed by a hydraulic binder coating does enable reaching values equal to or less than 1 mmrm. This result is an important one in that it reveals the possibility of attaining good dimensional stability to water for composites made with materials such as clay and wood, which naturally display a high dimensional instability to water. By foreseeing the development of composites made from industrial waste, this technique enables accommodating environmental preservation concerns while promoting the use of local materials within developing countries.
References w1x Pimienta P, Chandellier J, Rubaud M, Dutruel F, Nicole H. Etude de faisabilite´ des procedes ´ ´ de construction `a base de beton ´ de bois. Cahier du CSTB 1994;2703:45p. w2x Ledhem A, Bouguerra A, Dheilly RM, Queneudec M. Simple treatments to reduce the sensitivity to water of clayey concretes lightened by wood aggregates. Proceedings of International Conference on Creating with Concrete., Dundee, 1999:217᎐226. w3x Al-Rim K. Etude de differents facteurs d’allegement des ´ ´ materiaux argileux: le beton argileux leger, generalisation ´ ´ ´ ´ ´ `a d’autres fines de roches et applications ` a la conception d’ele´´ ments de construction prefabriques. ´ ´ These ` de Doctorat. I.N.S.A. de Lyon, 1995. w4x Bouguerra A. Contribution ` a l’etude d’un procede ´ ´ ´ de valorisation de dechets argileux: comportement hygrothermique des ´ materiaux ´ ´elabores. ´ These ` de Doctorat. I.N.S.A. de Lyon, 1997. w5x Ledhem A. Contribution ` a l’etude d’un beton ´ ´ de bois. Mise au point d’un procede ´ ´ de minisation des variations dimensionnelles d’un composite argile-ciment᎐bois. These ` de Doctorat de l’I.N.S.A. de Lyon, 1997. w6x Vaquier A. Influence de la cinetique de remplissage et de ´ vidange des pores des granulats legers sur les proprietes ´ ´ ´ des betons organique ou mixte. These ´ `a matrice minerale ´ ` d’Etat, Toulouse, 1976. w7x Simatupang MH. Abbaureaktion von Glucose, Cellobiose und Holz unter der Einfluss von Portlandzementmortel. Holz¨ forschung 1986;40:149᎐155. w8x Schwartz HG, Simantupang MH. Einfluss der chemischen Zusammensetzung von Portland zement auf die Druck festigkeit von Versuchorpen aus zement und Fichten oder ¨ Buchenspanen. Holz als Roh-und Werkstoff 1983;41:65᎐69. ¨ w9x Moslemi AA, Pfister SC. The influence of cementrwood ratio and cement type on bending strength and dimensional stability of wood-cement composite panels. Wood Fiber Sci 1987;19Ž2.:165᎐175. w10x Moslemi AA, Lim YT. Compatibility of southern hardwoods with Portland cement. For Product J 1984;34Ž7r8.:22᎐26. w11x Mougel E, Biegalke C, Berthier G, Frimat A, Zoulalian A. Mise en œuvre de divers conditionnements du bois en vue d’une limitation des variations dimensionnelles de composites bois-ciment en presence d’eau liquide ou vapeur. Bordeaux, ´ France: ARBORA Actes du 3eme ` Colloque Science et Industries du Bois, 1980.
Properties of wood-based composites formulated with aggregate industry waste b,U A. Ledhema , R.M. Dheilly b, M.L. Benmalek c , M. Queneudec ´ b
a Institut de Genie ´ Ci¨ il Centre Uni¨ ersite´ de Laghouat, Laghouat, Algeria Laboratoire des Transferts et Reacti de Genie ´ ¨ ite´ dans les Milieux Condenses, ´ I.U.T Departement ´ ´ Ci¨ il ᎏ Uni¨ ersite´ de Picardie Jules Verne, A¨ enue des Facultes, ´ 80025 Amiens Cedex 01, France c Institut de Genie ´ Ci¨ il Centre Uni¨ ersite´ de Guelma, Guelma, Algeria
Received 1 October 1999; received in revised form 19 April 2000; accepted 22 May 2000
Abstract The option of using vegetable-based materials is not only one potential response to the lack of aggregate resources in certain regions, but also a way of helping to preserve the environment. These reasons have incited some authors to address the issue of waste reuse in the form of insulating composites. The work presented herein, once the influence of components has been examined, will focus on the influence of various processes on the performances of hardened composites. Aggregate processing by boiling water, followed by a hydraulic binder coating, enables the minimization of the composite’s dimensional variations to a larger extent. This processing technique allows the achievement of an excellent compromise in material properties, although it increases density and, hence, thermal conductivity. 䊚 2000 Elsevier Science Ltd. All rights reserved. Keywords: Wood-based composites; Aggregates processing; Physicomechanical properties
1. Introduction Concrete with wood in its mix design has been the focus of growing interest over the past few years. A thorough review about the building processes using wood aggregates has recently been conducted by Pimienta et al. w1x. The option of using vegetable-based materials is not only one potential response to the lack of aggregate resources in certain regions, but also a way of helping preserve the environment, in as much as, at the present time, the wood industry generates significant quantities of waste which are not being reused. Furthermore, the aggregate industry, stone transformation processes and the heavy use of quarries U
Corresponding author. Tel.: q33-3-22-53-40-16; fax: q33-3-2253-40-16. .. E-mail address: [email protected] ŽM. Queneudec ´
and ores deposits are producing mineral wastes which constitute both an environmental hazard and a loss of raw materials. These various reasons have incited some authors to address the issue of waste reuse in the form of cementitious insulating composites with a view to transform them into insulating or insulating and bearing building units according to their performances. Nevertheless, wood-based composites do, in general, display the disadvantage of being overly sensitive to water, which results in dimensional variations and an overall decline in performance. The use of such composites in construction has often been limited due to this behavioral flaw, despite the number of processes proposed to reduce wood aggregate exchanges in humid environments w2x. Unfortunately, these processes often necessitate sizable energy expenses or highly-sophisticated equipment. For this reason, some of the authors have sought to develop processes which require lower
0950-0618r00r$ - see front matter 䊚 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 0 0 . 0 0 0 3 7 - 4
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quantities of energy and which are simple to implement in developing countries. Such processes, however, can modify the interface between the matrix and the aggregates, and, hence, modify certain mechanical characteristics. Similarly, the resultant increase in density exerts a negative impact on thermal characteristics. The work presented herein, once the influence of components has been examined, will focus on the influence of various processes on the performances of hardened composites.
2. Materials and experimental set-up 2.1. Raw materials The clay-like products used in this work consisted of waste produced from aggregate quarry operations. The sands and gravel used were of the commercialized variety, while the portion of material - 70 m was returned to the extraction site. For the purposes of this study, the clay-like material, extracted in the form of thick mud from settling tanks, was dried, ground and sieved to 70 m in order to eliminate all foreign matter. The results of the laser-based gap-grading analysis of the material obtained are provided in Fig. 1. The mineralogical study shows that the material was consti-
tuted almost entirely of kaolinite, with the quartz and mica contents remaining at less than 5% w3,4x. The schistous fines consisted of residue from the crushing of Brioverian schist which had undergone a slight metamorphism. The portion included herein corresponded to what remained once the fraction of sand and fine gravel particles had been removed. The separation process was performed on dry material. The fines used in this work were characterized by a gapgrading from 88% passing at 500 m to 100% passing at 1 mm. The proportion of grains less than 2 m in size was practically zero, and the residue provided a granular material that lacked both cohesion and plasticity. Its apparent density was 1.05 and its absolute density 2.70. The gap-grading analysis and description of characteristics provided by the operator are given in Fig. 1 and Table 1, respectively. Fir, in the form of shavings, was used as the wood content for this study, due to both its low density and widespread application within the building industry. The apparent density of the chips was approximately 0.05, while their real density was 0.44. The cement used was a CPA CEMI 52.5 ŽNF P15301. whose laser-based gap-grading analysis is given in Fig. 1. Table 2 presents the chemical analysis and the Bogue composition. 2.2. Processing materials In addition to the cement mentioned above, the material used to process the wood shavings was an XHN 100 ŽNF P15130. hydraulic lime added in the form of grout on the shavings during slow mixing ŽEN 196-1.. Linseed oil, with a density of 0.86, was also used to impregnate the shavings. In the present case, this impregnation could be performed by absorption at room temperature and atmospheric pressure thanks to the geometry of the wood aggregates. The oil was pulverized onto the shavings, also during slow mixing ŽEN 196-1..
Fig. 1. Laser granular analysis of mineralogical constituents.
Table 1 Chemical analysis of the schistous fines CaO
MgO
SiO2
Fe2 O3
Al2 O3
SO3
K2 O
TiO2
P 2 O5
Mn2 O3
Na2 O
Cl
Loss on ignition
1.31
3.17
58.34
7.61
18.69
0.45
3.35
0.81
0.13
0.10
1.80
0.007
4.32
C2 S
C3 A
C4 AF
14
2.5
13.1
Table 2 Chemical analysis of the cement and the Bogue composition CaO
MgO
SiO2
Fe2 O3
Al2 O3
SO3
Loss on ignition
64.8
0.8
21.3
4.3
3.7
2.7
1.2
C3 S 62
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For both of the cases listed above, the quality of the processing was controlled by scanning electron microscopy. Weighing was carried out in order to verify intensity. An extraction of water-soluble substances, liable to cause swelling of the wood or delays in the cement hydration, was performed by use of boiling water. After processing, the shavings were maintained in a humid room ŽR.H.s 95%, t s 20⬚C. for 48 h and then stored in a climate-controlled room ŽR.H.s 50%, t s 20⬚C. for 1 month.
nected to an electronic comparator, with a numerical display hooked up to a printer. The porosity accessible to water was evaluated from the variations in mass obtained by weighings with a scale accurate to 1r100th of a gram.
2.3. Composite mixes
3.1.1. Influence of the percentage of wood sha¨ ings The mineral portion was set at 100% and the
3. Experimental results 3.1. Influence of constituents on the composite’s characteristics
The clay-like material, schistous fines and cement, previously dried until a constant mass was reached, were initially mixed at low speed in a standardized mortar mixer ŽEN 196-1.. The shavings were added gradually while keeping the mixer at low speed for 2 min. Water was then added gradually while continuing the low-speed mixing for another 2 min. The quantity of water ŽW . was determined by the formula: Ws 0.35C q 0.7Cl q 0.2 S q K. A, where C, Cl, S and A are the percentages, by weight, of cement, clay, schistous fines and wood-aggregates, respectively. The coefficient K takes into account the absorption of water up to saturation by the wood shavings. For nonprocessed shavings, K is equal to 1.8. The value of this coefficient varies according to the type of processing, so as to retain the same level of workability w5x. After mixing, the mixture was poured into molds and the filled molds were then stored in a hygrometrically-controlled and temperature-controlled room ŽR.H.s 95%, t s 20⬚C. for 24 h. 2.4. Measurement techniques Following demolding, the test specimens were placed in a storage room ŽR.H.s 50%, t s 20⬚C. and then dried at 100⬚C until a constant mass before testing. Mechanical tests were carried out for 28 days on three 4 = 4 = 16 cm prismatic samples in compliance with the operating methods specified in the EN 196-1 standard. Thermal conductivity was determined with the help of an experimental device recently developed in the laboratory w4x; the TPS probe was placed between two 10 = 10 = 5 cm parallelepiped samples. The extreme dimensional variations ŽEDV. were determined from the difference between the length of 4 = 4 = 16 cm prismatic samples at dry and saturated states. Immersion took place at 20⬚C, followed by drying in an aerated oven at 100⬚C until a constant mass was reached. Linear dimensional variations, which fill the gap between the dry and saturated states, were measured using a retractometer ŽNF P15-433. con-
Fig. 2. Influence of the constituents on the composite’s density: Ža. clay q cement s 100%; clayrcement s 0.6, wood expressed as a mass percentage of the total dry mixture; Žb. clay q cement s 100%, wood s 20% of mineral fraction, cement expressed as a mass percentage of the total dry mixture; and Žc. clay q cement q schistous fines s 100%, Žclay q schistous fines.rcement s 0.6, schistous fines expressed as a mass percentage of the total dry mixture.
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Fig. 3. Influence of the different constituents on the mechanical strengths, the proportions of constituents are the same that those of Fig. 2. Compressive strength Ža, b, c.; tensile strength Žd, e, f..
clayrcement ratio at 0.6. The proportion of shavings varied and was expressed as a mass percentage of the total dry mixture. Fig. 2 presents the decrease in the composite’s dry density as the mass proportion of wood increased. The influence of the percentage of shavings on mechanical performance has been summarized in Fig. 3. The compressive strength fell as wood shavings get added. The tensile strength increased by between 0 and 10%. This increase could be explained by a fiber-related effect due to the presence of wood shavings. This effect was offset by both a reduction in the percentage of cement and by the fraction of minerals, with respect to the total mix, which was predominant beyond a 10% rise in the mass of the wood shavings Ž; 40% by volume. and
Fig. 4. Variation of the thermal conductivity as a function of the mass proportion of wood shavings.
A. Ledhem et al. r Construction and Building Materials 14 (2000) 341᎐350
Fig. 5. Variation of E.D.V as a function of the different constituents Ža. clay q cement s 100%, clayrcement s 0.6, wood expressed as a mass percentage of the total dry mixture; Žb. clay q cement s 100%, woods 20% of mineral fraction, cement expressed as a mass percentage of the total dry mixture; and Žc. clay q cement q schistous fines s 100%, Žclay q schistous fines.rcement s 0.6, schistous fines expressed as a mass percentage of the total dry mixure.
which led to a drop in mechanical strength. In contrast, the addition of wood shavings could considerably improve thermal performance Žsee Fig. 4.. Fig. 5 shows that a higher proportion of shavings served to increase the EDV significantly. 3.1.2. Influence of the cement proportion The dry mineral fraction Žclay q cement. was taken as equal to 100%, while the clayrcement ratio was allowed to vary. The added wood amounted to 20% of the mineral fraction, by mass. The quantity of cement has been expressed as a mass percentage of the total dry mixture. Fig. 2 shows a small increase in density as the proportion of cement increased. In contrast, the mechanical strength improved quite noticeably Žsee Fig. 3. and the EDV values fell Žsee Fig. 5..
345
3.1.3. Influence of the addition of schistous fines This study was carried out on a mineral mixture for which the Žclay q schistous fines.rcement ratio s 0.6. The fraction of clay q schistous fines was fixed and the proportion of wood shavings was 20% of the dry mineral fraction. Only the ratio of schistous fines to clay was allowed to vary. The quantity of schistous fines has been expressed as a mass percentage of the total dry mixture. The composite’s density increased with the proportion of schistous fines Žsee Fig. 2.. Fig. 3 shows the evolution in mechanical strength. In general, the addition of schistous fines increased the composite’s mechanical strength. Whereas the compressive strength had a tendency to rise with this added proportion, the tensile strength displayed the onset of saturation above 60%. This finding could be explained by the characteristics of the fines: schistous fines constitute a granular material that lacks both cohesion and plasticity. Beyond a certain volumic proportion, the cement’s binding effect is no longer sufficient. Fig. 5 reveals that the addition of schistous fines did indeed reduce the EDV. In summary, the addition of wood shavings enhances thermal performance while lightening the composite’s weight. Cement and schistous fines allowed the improvement of both the dimensional variations and the mechanical strength. The cost of cement is one constraint to be taken into consideration. Moreover, the curves in Figs. 3 and 5 show that, as of the 50% mark, which corresponds to a concentration of approximately 400 kgrm3, the change in dimensional variations and mechanical characteristics was less significant. This value was thus chosen as the upper limit of cement concentration. Schistous fines, like clay-like co-products, are industrial wastes which must be reused in some way or another. Reuse quantities must be as great as possible within the limit of performance requirements. The addition of schistous fines helps stabilize the EDV, yet also increases density and, hence, reduces the composite’s insulating capacity. A schistous finesrclay-like coproduct ratio equal to 1 allows reducing dimensional variations by approximately 30% while maintaining the density under 0.9. This ratio was, therefore, selected for the remainder of our study. The evolution in thermal conductivity showed that, beyond a concentration in shavings of approximately 20%, the decrease in was relatively low. For this reason, it seemed useful to limit the percentage of shavings to this value, which yielded a composite density of 0.85. This decision was reinforced by the fact that dimensional variations increased very rapidly when the mass percentage of the shavings exceeded 10%. These considerations led us to propose the composition given in Table 3, whose characteristics are presented in Table 4.
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346 Table 3 Composition of the composite Composition
m3 rm3
kgrkg
kgrm3
Clay-like fines Schistous fines Cement Wood-shavings Dry mix
14 13 19 54 100
23 23 38.5 15.5 100
196 196 327 131 850
3.2. Influence of aggregate processing on composite performance The various processes described above have been applied either on their own or in combination with one another. 3.2.1. Dry density Bulk density can be considered as the primary characteristic of lightweight concrete. All mechanical properties, thermal properties and dimensional variations depend upon bulk density to a certain extent. However, the type of processing used for the wood shavings causes the density to vary. The influence of the various processes on this characteristic must, therefore, be evaluated. Fig. 6 presents the composite’s dry density vs. the mass percentage of the selected process. In the case of processing by means of hydraulic binders, the results revealed an increase in density as the process gained intensity. It could then be considered that an increase in the density of wood shavings, upon the process’s completion, led to an increase in the composite’s density as well. Yet, the observation made by use of the mean SEM Žsee Fig. 7. shows that the matrix’s microstructure densified once the shavings were processed. This phenomenon could be explained by a smaller quantity of water being added during the mixing. The absorption of water by the shavings up to saturation was, in fact, no more than approximately 100% for a cement or limerwood ratio of 1, whereas without processing, this absorption reaches 240%. The coefficient K, which takes into account humidity up to saturation, was, therefore, lower w5x and the excess water not used during the cement’s hydration was also lower. Moreover, Vaquier w6x demonstrated that during the introduction of aggregates into the mortar, the aggregates’ degree of impregnation first increases Table 4 Characteristics of the composite Dry density Open porosity Ž%. Compressive strength ŽMPa. Tensile strength ŽMPa. Extreme dimensional variations Žmmrm.
0.85 46 8.9 3.8 3.5
Fig. 6. Influence of the different treatments of the wood-shavings on the dry bulk density of the composite.
rapidly and then slows to a maximum at the beginning of the cement’s setting. As the cement gel is being formed, the pore diameter in the mortar decreases, and the direction of water movement reverses; hence, the aggregates’ degree of impregnation decreases. Vaquier also showed that these exchanges are dependent on the aggregates’ water content at the time of the test. By modifying the capillarity of the aggregates and their water content at saturation, the process modifies the exchanges occurring between the matrix and the aggregates and, therefore, the porosity of the matrix. This finding is confirmed by the composite’s water absorption which, after this process, decreases by approximately 50%. The composite’s density, however, remained below 1.2 within the adopted concentration limit. Results from oil-based impregnation showed that the density increased as the concentration in oil increased. It should be noted that, as in the case of a hydraulic binder-coating process, the oil-impregnation technique considerably reduced the composite’s water absorption Ž20%, instead of approximately 50%.. The influence of boiling water is negligible. The composite’s dry density displayed no variation as this process was being carried out. Nonetheless, it must be pointed out that this statement only holds for dry density. The composite’s density, when saturated by immersion, was reduced as a result of this process. For a duration of 4 h, for example, water absorption did not exceed about 35%. 3.2.2. Mechanical properties Fig. 8 presents the compressive and tensile strengths of the composite. The mechanical strength of the composites with hydraulically-bound aggregates increased, with the intensity of the lime-based processing being slightly better in terms of compression. As discussed in Section 3.2.1, this behavior can be related to the
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347
Fig. 7. SEM observation of the microstructure of the composite: Ža. with wood-shavings and without treatment, Gs 1000; Žb. with wood-shavings treated with cement Žcementrwoods 1., Gs 5000; Žc. with wood-shavings treated with linseed oil Žoilrwoods 0.75., Gs 300; and Žd. with wood-shavings treated with linseed oil Žoilrwoods 0.75., Gs 5000.
porosity of the matrix: as the intensity of the concentration increases, the matrix’s microstructure becomes more highly compact. In the case of an oil-based process, a small reduction in strength could be observed in comparison with the process’s intensity. This behavior was more heavily pronounced for tensile strength, a finding which can be explained by a decrease in the aggregates’ adhesion to the clay᎐cement paste as the quantity of oil generated rises Žsee Fig. 7.. Furthermore, the quantity of water added during mixing was lower since the amount of water absorbed by the wood shavings was heavily reduced by the oil-based process Ž; 60% for an oilrwood ratio s 0.75, instead of 240% for the non-processed shavings.. Despite the presence of less water, the matrix was still very porous, with the pores being filled by oil droplets Žsee Fig. 7.. In contrast, the cement’s hydration did not seem to be affected Žsee Fig. 7.. Fig. 9 presents the mechanical performance of the composite vs. the processing time using boiling water. The process improved mechanical performance to a
slight extent without introducing any change in dry density. This effect can be explained by the elimination of substances through hydrolysis, which typically causes
Fig. 8. Influence of the different treatments of the wood-shavings on the mechanical strengths of the composite.
348
A. Ledhem et al. r Construction and Building Materials 14 (2000) 341᎐350
Fig. 9. Influence of the boiling time on the mechanical strengths of the composite.
delays in both cement setting and the hardening of wood concretes w7᎐10x. 3.2.3. Thermal conducti¨ ity The general objective of the work carried out has been to develop insulating materials from recycled industrial waste. It is, therefore, advisable to assess the impact of the various processes available on the these materials’ insulation capacity, i.e. on the composite’s thermal conductivity. In this part of the study, the volumic proportions of the shavings remained the same, whether the shavings were processed or not. Fig. 10 shows that the thermal conductivity of the composite increases with the intensity of the hydraulic binder processing. Since the volumic proportion of wood was not modified, it would thus appear that the change in the composite matrix’s microstructure was chiefly responsible for this increase in thermal conductivity. The densification of the matrix, which has already been discussed, also significantly contributed to the increase in thermal conductivity. In a subsequent study, however, it would be necessary to take into account the phenomena occurring at the aggregatermatrix interface due to the processing of aggregates. An analysis of the results in the case of oil-based processing revealed that the thermal conductivity evolved slowly as the bulk density increased. Since the thermal conductivity of oil is higher than that of air, it is only normal that the filling of wood pores by oil leads to an increase in the composite’s thermal conductivity. The use of boiling water for processing wood shavings exerts no influence whatsoever on the composite’s thermal conductivity. 3.2.4. Dimensional stability Dimensional stability is a key characteristic of build-
ing materials and heavily influences structural durability. The various processes described above have been aimed at decreasing the sensitivity of aggregates to water, so as to increase the composite’s dimensional stability. However, previous research has shown that the dimensional stabilization of aggregates does not necessarily induce a reduction in dimensional variation w11x. It is, therefore, essential to evaluate the impact of the various methods of aggregate processing on the studied composite’s dimensional variations. Fig. 11 displays the influence of this study’s processing techniques. The thickness of the coating layer has a predominant impact on the reduction in dimensional variation. Furthermore, the lime-based processing seems to be the most efficient technique. Oil-based processing also exerts a positive influence, yet its resultant reduction in dimensional variation remains limited. Lastly, while processing by boiling water has proven to be efficient, the major portion of the reduction in
Fig. 10. Influence of the different treatments of the wood-shavings on the thermal conductivity of the composite.
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349
Table 5 Influence of treatments on characteristics of the composite Dry bulk density Žkgrm3 .
Rc ŽMPa.
Rf ŽMPa.
Absorption of water by the shavings Ž%.
Absorption of water by the compositeŽ%.
Without Boiling water Ž4 h. Lime Boiling water q lime Cement Boiling water q cement Linseed oil Target values
240 112 99 89
49 34 25 23
0.85 0.85 1.11 1.12
8.9 9.7 12.7 13.1
3.8 4 4.95 5.1
3.50 2.00 1.18 0.95
0.22 0.22 0.27 0.27
87 79
22 20
1.20 1.20
12.4 12.6
4.4 4.8
1.35 1
0.33 0.28
42
22
1.00 - 1.40
8.5 ) 5.0
2.9
2.20 - 1.00
0.25 - 0.3
dimensional variation takes place within the first 2 h Žsee Fig. 12.. The use of combined processes allows the reduction dimensional variations to values of F 1 mmrm Žsee Table 5..
EDV Žmmrm.
ŽWrmK.
Treatment
3.2.5. Summary of findings Table 5 presents a summary of the results obtained from the use of these various processes. An observation of the results indicated a more significant increase in dry density for processes containing mineral particles than for those containing oil. This difference was essentially due to the density of the processing product, as well as to its influence on the microstructure of the composite’s matrix, as outlined above. The hydraulic lime-based processing, in combination with boiling water, proved to be the most efficient method with respect to the resultant increase in mechanical strength. The results also indicated a more sizable increase in thermal conductivity for hydraulic binder-based processing than for oil-based; yet the values attained did not exceed 0.32 WrmK. The dimensional variations could be compared with
the absorption of water by both wood shavings and the composite. The composite’s water absorption corresponded to that of the shavings. Nevertheless, smaller reductions were observed in the composite due to the water being absorbed by the matrix. With the exception of oil-based processing, the reduction in dimensional variation was greater than the reduction resulting from the absorption of water by both wood shavings and the composite. This finding demonstrated that the dimensional variations were not solely due to the absorption of water by the shavings. Modifications in the porosity of the matrix, as a consequence of these various processes, appeared to be an essential factor in reducing dimensional variation. This conclusion is in agreement with the work conducted by Mougel w11x. Aggregate processing by boiling water, followed by a hydraulic binder coating, enabled the minimization of the composite’s dimensional variations to a large extent. This processing technique allowed us to achieve an excellent compromise in material properties. Although it increased density and, hence, thermal conductivity, this process served to preserve some very valuable properties while complying with the RILEM
Fig. 11. Influence of the different treatments of the wood-shavings on the dimensional variations of the composite.
Fig. 12. Influence of the boiling time on the dimensional variations of the composite.
350
A. Ledhem et al. r Construction and Building Materials 14 (2000) 341᎐350
set of recommendations for lightweight insulating concrete Ž Rc ) 3.5 MPa; - 0.7 WrmK..
4. Conclusion The work presented herein lies within the more general topic of industrial waste reuse. A study of material characteristics has shown that while wood shavings do provide improved insulation performance and weight reduction of clay᎐cement pastes, they also give rise to sizable dimensional variations. Cement and schistous fines help increase the density of composites, which leads, not only to enhanced mechanical strength and dimensional stability to water, but also to an increase in thermal conductivity. A combination of these factors has enabled designing a composite which displays distinct mechanical and thermal advantages, yet which exhibits relatively high extreme dimensional variations. A variety of simplified aggregate processing techniques have been proposed: coating by hydraulic binders, impregnation by vegetable oil, and extraction of soluble components in boiling water. With the exception of boiling water, all of these processes have led to an increase in density, mechanical strength and thermal conductivity, in addition to reducing the extreme dimensional variations. Boiling water followed by a hydraulic binder coating does enable reaching values equal to or less than 1 mmrm. This result is an important one in that it reveals the possibility of attaining good dimensional stability to water for composites made with materials such as clay and wood, which naturally display a high dimensional instability to water. By foreseeing the development of composites made from industrial waste, this technique enables accommodating environmental preservation concerns while promoting the use of local materials within developing countries.
References w1x Pimienta P, Chandellier J, Rubaud M, Dutruel F, Nicole H. Etude de faisabilite´ des procedes ´ ´ de construction `a base de beton ´ de bois. Cahier du CSTB 1994;2703:45p. w2x Ledhem A, Bouguerra A, Dheilly RM, Queneudec M. Simple treatments to reduce the sensitivity to water of clayey concretes lightened by wood aggregates. Proceedings of International Conference on Creating with Concrete., Dundee, 1999:217᎐226. w3x Al-Rim K. Etude de differents facteurs d’allegement des ´ ´ materiaux argileux: le beton argileux leger, generalisation ´ ´ ´ ´ ´ `a d’autres fines de roches et applications ` a la conception d’ele´´ ments de construction prefabriques. ´ ´ These ` de Doctorat. I.N.S.A. de Lyon, 1995. w4x Bouguerra A. Contribution ` a l’etude d’un procede ´ ´ ´ de valorisation de dechets argileux: comportement hygrothermique des ´ materiaux ´ ´elabores. ´ These ` de Doctorat. I.N.S.A. de Lyon, 1997. w5x Ledhem A. Contribution ` a l’etude d’un beton ´ ´ de bois. Mise au point d’un procede ´ ´ de minisation des variations dimensionnelles d’un composite argile-ciment᎐bois. These ` de Doctorat de l’I.N.S.A. de Lyon, 1997. w6x Vaquier A. Influence de la cinetique de remplissage et de ´ vidange des pores des granulats legers sur les proprietes ´ ´ ´ des betons organique ou mixte. These ´ `a matrice minerale ´ ` d’Etat, Toulouse, 1976. w7x Simatupang MH. Abbaureaktion von Glucose, Cellobiose und Holz unter der Einfluss von Portlandzementmortel. Holz¨ forschung 1986;40:149᎐155. w8x Schwartz HG, Simantupang MH. Einfluss der chemischen Zusammensetzung von Portland zement auf die Druck festigkeit von Versuchorpen aus zement und Fichten oder ¨ Buchenspanen. Holz als Roh-und Werkstoff 1983;41:65᎐69. ¨ w9x Moslemi AA, Pfister SC. The influence of cementrwood ratio and cement type on bending strength and dimensional stability of wood-cement composite panels. Wood Fiber Sci 1987;19Ž2.:165᎐175. w10x Moslemi AA, Lim YT. Compatibility of southern hardwoods with Portland cement. For Product J 1984;34Ž7r8.:22᎐26. w11x Mougel E, Biegalke C, Berthier G, Frimat A, Zoulalian A. Mise en œuvre de divers conditionnements du bois en vue d’une limitation des variations dimensionnelles de composites bois-ciment en presence d’eau liquide ou vapeur. Bordeaux, ´ France: ARBORA Actes du 3eme ` Colloque Science et Industries du Bois, 1980.