Thermal Conductivity and Mechanical Properties of Organo-Clay-Wood Fiber in Cement-Based Mortar

Abstract

This paper orientated to study the compressive resistance and thermal conductivity of compressed and stabilized clay blocks in the cement matrix. The effect of the content of wood fiber (WF) became studied as a reinforcement material in cement mortars. The porosity, compressive energy, thermal conductivity and composite of cement hydration had been investigated. The addition of NFC suggests a very good pore reduction, and the fine result becomes acquired with the emulsion of a combination incorporating 2%wt of WF inside the presence of an anionic surfactant (SDBS). The results revealed that used in this study were a mix of water with ordinary portland cement and organo-clay (OC) modified with Cetyltrimethylammonium bromide at water-to-solid ratios 1%. The effect depending on w/s ratio of OC used samples with cement substitution for organoclay showed from 2% higher compressive strength results than that of the plain cement paste and a decrease of the thermal conductivity by addition of 2%wt of WF from 2.26 to 0.8 W/m °C. It was also observed that with increasing w/s ratio higher amount of cement can be replaced by OC. These analyses have revealed that the presence of WF promoted the hydration, by producing more portlandite and calcium silicate gel.

1. Introduction

Tunisia has plenty of agricultural waste products such as Alfa fiber, Posidonia oceanica, wood and palm fiber. Such as these fibers with many advantages: renewable, cheaper, abundance and easy to use [1] in construction and building materials. These natural fibers are cellular solids with enormous specific surface area, high porosity and low thickness [2, 3]. Currently, various composite based on clay minerals and natural fibers are being tested as cementitious composites in a wide range of applications such as construction. Especially, silica materials have good thermal insulation properties. However, low mechanical [4] resistance. This is the reason that different procedures were created to improve physico-chemical properties of the wood fibers with clay and cement [5, 6, 7]. These days, silica aerogels have numerous applications including thermal and / or acoustic insulation, and additionally acoustic protection, natural remediation, aviation and biomedicine [8, 9, 10, 11, 12].

Lately, as a result of energy consumption and inside the reason of energy-saving, recently works makes a specialty of developing building materials having alluring mechanical and thermal insulating homes. However, improving the mechanical residences induces a lack of thermal insulation overall performance. Today, area heating and cooling comprise the most significant level of general power fed on in homes [13].

The thermal performance of the building envelope is a key factor in determining the measure of the energy required for the comfort of nature. In this regard, a few examinations consider reason that energy consumption can be improved by joining thermal insulation materials in to walls and roofs. Thermal insulation can be characterized as a material that eases back that slows the heat flow in side rout side the building. For its determination, thermal conductivity is the fundamental property to look for. Currently, the research of bio based materials, of natural fiber, of organoclay were used to reinforce cement, to improve the qualities of cementitious materials, to accelerate the formation and the precipitation of hydration [14, 15, 16, 17], works to enhance the mechanical properties of the composite and their resistance. In this sense, numerous scientists investigated clay, which belongs to the phyllosilicate family, was due to the permeable media, in exchange, it could also be mixed with many fibers considered as a material with a wide range of applications. The example of clay-based materials was selected.

In which case, there is good reason to use modified clay such as chlorite, Kaolinite and Illite, are considered as filler in the composite material [18], to enhance the properties of cement thanks to its low cost, availability and its excellent characteristics. Besides, in many studies, it was remarkable to note that the role of organoclay has gained many interests on both academic and industrial research [19] due to the excellent performance as well as the way to modify, to as clay-based composite [20].

It’s important to mention that natural fibers has grown develop environmental-friendly construction materials. These fibers are biodegradable, lighter and abundant resources for examples: sisal, Flax, Hemp, Bamboo, coir and others [21]. Despite all the advantages of natural fibers, there are some disadvantages, which have confined their applications in the cementitious composites. Initially, for natural fiber, the interfacial bond existing between the fiber and the cement matrix is relatively weak and about the degradation of fibers in a high alkaline of cement adversely affects the mechanical properties and durability of natural fiber reinforced composites [22]. Additionally, for the organoclay, one of the most problem it that increasing the amount of organoclay conducts to reduction of mechanical propreties.

In this work, concrete based composite materials prepared and reinforced with wood fiber and organoclay (OC) particles is used to improve their mechanical quality and to decrease the alkalinity of the matrix through diminishing the Ca(OH)₂. Another is to upgrade microstructures qualities of the grid and to add to the bonding existing between the matrix and the wood filaments [23].

In which case, there is a valid justification to utilize the SDBS as surfactant between the platelets of clay treated with CTAB, organoclay can respond with Ca(OH)₂ of the concrete hydration products and form structure additional calcium-silica-hydration (CSH) gel. The advantage of the utilization of organoclay is to improve microstructures and mechanical propreties of prepared materials. The wood fibers were characterized via Zeta potential. Fur there more, organoclay in powder form was characterized via structure X-ray diffraction, FTIR and SEM. The organoclay prepared by treating clay with cetyl tri methyl ammonium bromide (CTAB) on the mechanical. Thermal conductivity and physical properties of wood fibers reinforced cement composites is also studied and investigated.

2. Materials and methods

2.1 Materials

Wood Fiber (WF) and organo-clay (OC) modified with CTAB were used as reinforcements for the cement matrix-composites (Figure 1a and b).

Figure 1.

(a) Wood Fiber (b) Organoclay.

The clay platelets used in this investigation is a natural Kaolinite treated with CTAB.

The CTAB (Mw 336.39 g mol⁻¹) is a quaternary alkyl ammonium salt is a cationic surfactant, soluble in water and utilized in the preparation of OC. A bout the SDBS (Mw 348.48 g mol⁻¹) is sodium dodecyl benzene sulfonates is an anionic surfactant utilized in the fabrication of composites.

Ordinary Portland cement (OPC NF P 15–301) was used in all mixes of the cement works of Enfidha (Table 1).

Oxides	Cement (%wt)
CaO	65.47
SiO2	19.82
Al2O3	4.66
Fe2O3	3.03
CaO	65.47
MgO	0.84
K2O	0.64
Na2O	0.10
TiO2	0.16
SO3	2.87
Loss ignition(LOI)	3.5
Density	3.2 g/cm^3
Specific surface area	355 m^2/Kg
Average particle size	18.54 μm

Table 1.

Chemical composition and physical properties of OPC.

2.2 Preparation of Organoclay

Clay was prepared to be modified with CTAB, for 3 hours characterized by XRD and SEM in order to determine the amorphous phase of modified clay. To have organophilic clays, you should introduce 10 ml of chlohydric acid [1M]. Then this acid solution is carried in a temperature of 80°C.

And when this temperature became stable, we introduce 10⁻² moles of CTAB, which we wish to ionize. After three hours of agitation at 80°C, we introduce 10 g of clay. And after three hours of cationic exchange, the clay is filtered and inserted to eliminate the inorganic cations. Finally, the phases of washes are finished and the clay is dried in the steam room at 80°C.

Many works have shown that CTAB surfactant intercalation does not only change the hydrophilic surface characteristics of the clay but also significantly increases the clay interlayer basal spacing.

2.3 Treatment of wood fibers

To treat the surface of the fiber, the wood fibers were immersed in the aqueous solution of Sodium hydroxide (NaOH) at pH = 12 for 1 hour at 80°C. They were then washed until the pH reached about seven. Finally, the wood fibers were subsequently dried at 80°C for 24 hours. This chemical treatment was aimed at enhancing and improving the mechanical properties by ameliorating the adhesion exciting between fibers/matrix.

2.4 Preparation

2.4.1 Composite materials

The (OPC) was substituted with an organoclay (0.5, 1 and 1.5%wt).

The (OPC) and organoclay were first to dry mixed for 5 min in mixer at low speed and then mixed. The samples were prepared with 0.65 mass ratios a water/organoclay –cement.

2.4.2 Curing and samples

Three series of specimens were prepared of (3.5 × 7 × 1.75) in dimension and were cast in the mechanical tests. All specimens demolded after 24 h of casting and kept underwater for approximately 28 days. Bend test was conducted using an “MTSInsight” Material testing Machine to evaluate, compressive strength.

2.5 Study of physical properties

Porosity and density were measured and conducted to define the quality of composites. The length, thickness, width and weight are measured to determine the bulk density which was carried out by using the following Eq. (1) [20]:

$$\mathrm{D}=md/\nu$$E1

Where D is the density in g/cm³,m_d is the mass of the test specimen (g) and V is the volume of the test specimen (cm³). The porosity Ps was calculated using the following Eq. (2).

$$Ps=\left(m_s-m_d\right)/\left(m_s-m_i\right)$$E2

mi = mass of the sample saturated in water.

ms = mass of the sample saturated in air.

2.6 Characterization of composite materials

The (OC) prepared was analyzed by X-ray diffraction (XRD) in the 2ϴ range between 20 and 80° using CuKα (γ = 1.54060 Å) radiation and was completed by Fourier transform infrared spectroscopy (FTIR) using a Perkin Elmer. The morphology of the organoclay was observed by scanning electron microscopy (SEM) (Hitachi SEM type SU8030 microscope operated at an acceleration voltage of 10 KV and a probe current of 15 pA). The thermal conductivity of different samples was measured by using a “Heat transmission Study Bench – PTC 100”.

2.7 Characterization of wood fibers and natural clay

2.7.1 Zeta (ξ) potential

A ξ potential analyzer (Malven 2000) was used to measure the electrophoretic mobility of wood fibers in the aqueous suspension. Measurements were conducted on the fine fraction obtained after filtration of the original fiber suspension through a 45-μm screen. ξ-potential measurement repeated on the whole suspension using the streaming potential technique (Mute kSZP06,using a 40-μm screen as an electrode) matched ξ-potential values obtained by electrophoresis. The ξ-potential values reported are the average of four measurements.

2.7.2 X-ray diffraction (XRD)

The X-ray diffraction patterns were measured with an X-ray diffractometer using CuKα radiation at 40 KV and 30 mA.

2.7.3 Fourier transform infrared spectroscopy (FTIR)

Fourier transform infrared spectroscopy (FTIR) was used to analyze the change of functional groups at the wood fibers and the natural clay after treatment with NaOH, sulfuric acid and CTAB respectively. This test was carried out with a spectrum FTIR, Perkin Elmer. Samples were measured at room temperature and a resolution of 4 cm⁻¹. All FTIR measurements were done in transmittance mode after baseline correction.

2.7.4 Scanning electron microscopy (SEM)

Samples of natural clay and organoclay for Scanning electron microscopy were prepared and analyzed with Scanning Electron Microscopy (Hitachi SEM type SU8030 microscope operated at an acceleration voltage of 10 KV and a probe current of 15pA).

2.7.5 Thermal conductivity

The measurements of the thermal conductivity characterize the ability of materials to conduct heat energy. The thermal conductivity of different samples of dimensions (24.5 × 1.5 × 24.5 cm) was measured by using a “Heat Transmission Study Bench – PTC 100”.

3. Results and discussion

3.1 Particle size of wood fiber

The particles of wood fiber were clearly in the scale range with size 40 μm. The displayed a monomodal size distribution (Figure 2) which was relatively narrow (PDI) around 0.2.

Figure 2.

Particle size of wood fibers.

3.2 Zeta (ξ) potential

The process of the evolution of (ξ)-potential as a function of pH of the cement particles saturated with the SDBS surfactant are showing in Figure 3. The introduction of the SDBS during the preparation of samples passes by several stages. Indeed, for a low concentration of SDBS in order of 0.1 mmol/L, the (ξ) potential is 35 mV. This value results from the ionization of calcium during the hydration of the cement. When the concentration of the SDBS solubilized, Zeta potential decreased. This allows us to deduct the essential role of SDBS in the hydration of the cement, thus in the neutralization of these ions (Ca²⁺).

Figure 3.

Variation of the zeta potential according to the initial concentration according to the initial concentration by surfactant.

Figure 3 shows the quantity adsorbed of surfactant as a function of initial concentration. We notice the existence of three zones:

The first one for low concentration (I) we can see equilibrium. This phenomenon was attributed to the micelles, which gives an idea about the formation of micelles beyond a critical concentration. From a certain critical concentration, the hydrophobic interaction between the surfactant molecules of surfactant becomes important compared to the hydrophobic surfactant/water interactions that form spontaneously an association.

The second zone (II), we observe an increase of the slope which is explained by the intercalation of the surfactant molecules with water to form the saturation of the first layer [22]. It is the beginning of mineralization. Thus we observed agglomerations of micelles together, this part is called the micellisation phase.

In the third zone (III), of SDBS, we have (ξ) potential of negative charge (Figure 4).

Figure 4.

Evolution of the quantity adsorbed by additive according to the concentration insolution.

In this case we can say that we have a neutralization of material by the existence of the electrostatic strengths. (The surfactant is cationic and the surface of fibers is negatively charged). The molecules of surfactant are adsorbed at the air/water interface and the superficial concentration increases. From a certain value, a monomolecular layer of surfactant occupies the surface and interfacial tension decreases linearly with the logarithm of the concentration.

3.3 XRD

The XRD patterns of natural clay and organoclay modified by the CTAB are shown in (Figures 5 and 6). It can clearly be seen that the natural clay characteristics peaks are present sat 2θ = 7.05°, 12.55°, 25.5° these peaks refer to the presence of Kaolinite the peak at 2θ = 12,55° corresponding at Kaolinite contending Illite. Typical XRD patterns of organoclay after the treatment with the CTAB appears many diffraction peaks at 5.13° until 20°, this result due to the linear structure of CTAB (19 carbons). The CTAB Kaolinite matrix has the highest value of the interfoliar space d001 = 19.10 A° corresponds to the interplanar spacing [23].

Figure 5.

XRD patterns of natural clay.

Figure 6.

XRD patterns of Organoclay.

3.4 FTIR of wood Fibers

The FTIR spectra in the range 4000 cm–500 cm⁻¹ of the different samples are shown in Figure 7. The main characteristic bands of non-treated and treated wood fibers are listed as follows:

Figure 7.

FTIR spectra of the non-treated wood and the treated wood with NaOH.

The presence of a large band in the 3386 cm⁻¹ corresponds to hydroxyl group characteristics of polysaccharides. The band sat 2930 and 2898 cm⁻¹ are due successively to sym and usym CH₂ in polysaccharides and fats. The FTIR spectrum exhibits the presence of carbonyl and acetyl groups in the xylan component of (C=O stretching vibration) at 1732 cm⁻¹. However, this peak almost disappears when these fibers are treated with 2% of NaOH. The band at 1635 cm⁻¹ is characterized by the vibration of water molecules. Furthermore, the band at 1436 cm⁻¹, assigned to the asymmetric C-H deformation in lignin and hemicelluloses structures. Concerning the FTIR of (WFNT), the peak at 1512 cm⁻¹ is indicative of the presence of lignin and is attributed to the C=C aromatic skeletal vibration. In the spectra of WF treated 5% NaOH, this peak was reduced, due to the elimination of lignin by chemical treatments. The small peak sat 1375 cm⁻¹ in the spectrum of untreated WF, WF treated 0.5%, 2% are related to CH2 vibration. The band at 1168 cm⁻¹, which appears in all the FTIR spectra, corresponds to the C-O-C asymmetric stretching of the hemicelluloses and lignin. The peak at 1042 cm⁻¹, is assigned to ether linkage (C-O-C) from lignin or hemicelluloses. The peak at 810 cm⁻¹ is associated with cellulose, the C-H rock vibrations the cellulose.

3.5 FTIR of Organoclay

Figure 8 shows the characteristics of natural clay and OC treated with CTAB. The peak assignments in the spectra represented OH stretching vibration (3624–3390 cm⁻¹. The treatments of the natural clay with the CTAB make the appearance of two peaks have (2921–2881 cm⁻¹) two peaks attributed to OH stretching vibration. The bond OH (1633 cm⁻¹) can be attributed to water molecules adsorbed on the biomaterial structure.

Figure 8.

Infrared spectral characteristics of natural clay and clay treated with CTAB.

FTIR exhibits the existence, of a strong band in the range of 750–400 cm⁻¹ it was associated with the characteristic Si-O-Si stretching vibration of pure clay. Peaks at 1420 cm⁻¹ and 3434 cm⁻¹ corresponding to the O-H stretching vibration. Peaks at 1263 cm⁻¹, 2866 cm⁻¹ and 2920 cm⁻¹ corresponded to the stretching vibrations of –CH, –CH3 and –CH2 respectively. Moreover, characteristic band at 1470 cm⁻¹ is assigned to the symmetric vibrations of the COO⁻ group in the main chain of 1634 cm⁻¹ is attributed to the OH bending vibration in the water chemically bond.

3.6 Scanning electron microscopy (SEM)

The micrograph (Figure 9) shows the morphology of the surface of raw clay and clay treated with the CTAB, modified by the addition of a low percentage of silica gel. This figure showed that the morphology of the clay surface appeared in the form of plaques, these plaques, of size of 200 nm is plied the some on the others in a characteristic package of structure sheet.

Figure 9.

MEB micrographs of (a) natural clay and (b) Organoclay with silica gel.

After this treatment by the CTAB and its modification by the addition of a silica gel, we can notice the good separation of some of plaques, layers, also, the appearance of spheres between these leaves in the micrometric size which asserts clearly that the silica gel is well inserted in to the OC.

3.7 Density and porosity

The density values of WF reinforced cement are shown in Figure 10. Generally, the composites containing WF exhibit low density than these without WF. This could be attributed to the formation of void sat the interfacial are as between WF and cement matrix. For composite materials with 10% wt of WF, the density decreases by 43%. This indicates that WF has a filling effect on the density of cement composites with or without WF, where the density of cement composites is decreased by the addition of hemp fiber. In Figure 10 the addition of 10% wt of WF decreased the density of cement composite. That improvement indicated that the addition of WF leads to decrease density and to obtain a composite material with a consolidated microstructure.

Figure 10.

Porosity and density as a function of treated wood fibers content for control cement and its composites.

The results of porosity and water absorption of values of cement paste, WF reinforced composite, WF–OC reinforced composites are shown in Figure 11. Generally, the composites containing WF exhibit higher porosity than that without WF. This could be assigned to the formation of the voids at the interfacial are as between WF and matrices. For composite with 2 and 4% wt of WF, the porosity decreases by 1.82% (4%wt (WF)). The porosity of these composites indicates that WF has a felling effect on the porosity of cement paste composite [24] and this 2% wt and 4% wt are capable of saturating the surface and of reducing pores.

Figure 11.

Porosity as a function of organo clay content for control cement.

Figure 11 shows that the addition of OC in the composite materials has reduced their porosity. The optimum addition was found as1% wt of OC, which decreased the porosity of composites by 18.75% when compared to the OPC. This implies that organo clay played a pore-filling role to reduce the porosity and to saturate pores. However, adding less than 1% wt of organo clay increased the porosity of all samples due to the agglomeration effect when less than 1% wt organo clay was added. This finding is comparable with the study where the porosity of the OPC is decreased due to the addition of 1% wt of organo clay to cement paste. We can say that composites containing 1% wt organo clay, are different from those of cement paste; the structure is less dense, and contain more pores. But composites with 1% wt of OC are different from those of OPC. The structure is more compact with few pores [25].

3.8 Mechanical studies

The incorporation of OC and WF with NaOH in to the cement composites improves the mechanical properties of the cement matrix. This addition leads to good improvement of the mechanical properties of samples [26].

3.8.1 Compressive resistance

• Effect of the Wood Fibers

The effect of WF treated by NaOH on the compressive strength of cement composite can also be seen evaluated. The compressive strength of WF reinforced cement composite is increased from 9,8 to 18.41 MPa about, 90% increases compared to treated WF reinforced cement composite. This enhancement improvement is explained as follows: To enhance the interfacial bond between fibers and the OPC, the matrix could be modified by reducing or consuming the calcium hydroxide. The low value of the compressive strength can be explained by the high sugar and hemicelluloses content of fast-growing wood. Conversely, the chemical treatment proved good mechanical properties.

• Effect of the Amount Organoclay

Effect of OC on the compressive strength of 0, 0.5, 1, and 1%wt. WFT-cement–composites of 28 days age are shown in histograms (Figure 12). It can be deduced that the compressive strength was increased by the addition of OC after (28 days) and the greater, the improvement. After 28 days, the compressive strength of 1%wt was 21.76 MPa higher than that of 0.5%wt of OC was 10.11 MPa. The reasons for the enhancement in mechanical properties of composites are as follows. Firstly, the physical effects of 1%wt of OC, including filling, can reduce the voids or the porosities in the cement matrix, in which the OC was uniformly dispersed in the matrix. Thus improving the microstructure of composites denser than the WFT-cement composite, Secondly, another mechanism is the pozzolanic reaction, in which OC reacts with calcium hydroxide (CH) in the cement matrix to produce calcium-silicate-hydrate (C-S-H). However, the addition of more than 1%wt of OC caused a marked decrease in compressive strength. For example, the compressive strength of 2% wt OC was 11.47 MPa. This is due to the poor dispersion and agglomeration of the OC in the cement matrix ata higher percentage of OC contents, which increase of porosity and reduce the bond strength between the fiber and the matrix adhesion. The compressive decreases in the cement-composite with a higher dosage of organo clay.

• Effect The Amount of SDBS

Figure 12.

Compressive strength as a function of organo clay content for control OPC with 6% wt.

The effect of SDBS on compressive strength of composites with the non-treated wood fiber it shows that the addition of SDBS in cement matrix increased the compressive strength from 9.81 to 11.47 MPa, about 14.47% improvements can be explained by the adhesion and the collusion of fibers in the matrix in the presence of the SDBS.

The SDBS has an essential role in the surface packaging of the fiber; it is defined as a super plasticizer that covers the surface of the fibers and render them hydrophobic. In our case, anionic surfactant is able to agglomerate during the cement to fill the existing pores in the fibers.

3.9 Thermal conductivity

3.9.1 Effect of the number of fibers

The resulting curve shows that the thermal conductivity varies with the content of wood cement fibers. Decrease in the conductivity between 0 and 8% of the wood fiber. From 2.25 Wm⁻¹ K⁻¹ for non-stabilizing blocks, it increases to 0.9 Wm⁻¹ K⁻¹ when the wood fiber content is 2.5%. The thermal conductivity has increased for wood fiber contents ranging from 3–8%. For these wood fiber contents, the thermal conductivity ranges from 0.9 to 1.6 W m⁻¹ K⁻¹.

The thermal conductivity of a material depends on several parameters such as the nature of the constituent elements of the material [27], the water content, the temperature and the porosity since the blocks are manufactured under the same conditions and the conductivity measurements are made in a stationary regime, the variation in conductivity can be related to the variation of porosity of the material, to the intrinsic composition of each sample and to the cohesion of the material. The decrease in thermal conductivity may be due to increased pore quantity or increased pore diameter due to poor distribution of wood fiber. In fact, it is considered that for this interval, the quantity of wood fibers is insufficient to favor the establishment of a homogeneous structure. Under the conditions of measurement of the thermal conductivity used, it is considered that the heat transfer takes place mainly by conduction. Thus, the pores represent a space in the transfer, an increase in their diameter or their quantity causes a slowing down of the heat transfer, hence the low measured thermal conductivity [28].

3.9.2 Effect of wood and Organoclay

At 30°C the study of 4 samples (1: Cement −2: C + WFNT, 3: C + WFT, 4: C + OC).

Generally, the thermal conductivity “λ” depends on the nature of the constituents, the temperature, the porosity and the water content. The decrease in thermal conductivity for these different samples could be related to the increase in the number of pores or the increase in pore diameter caused by poor and by poor distribution of cement. In this case, the heat transfer is by conduction only as well as the pores are shown gaps in the heat transfer since an increase in their diameter and their quantity causes the transfer of heat which confirms the weakness of the thermal conductivity.

An increase in thermal conductivity may be related to an increase in the temperature of the cohesion at different constituents of the sample.

Following the effect of cement hydration which allows the formation of portlandite and C-S-H which allow a strengthening of the bonds between the constituents that which promotes a decrease in porosity so we obtain a homogeneous structure; this structure is favorable for good heat transfer.

We note that the addition of 4% of the untreated fiber can decrease the thermal conductivity from 2.26 to 1.01. The Figure 13 shows the addition of 1% OC causes a decrease in thermal conductivity from 1.39 to 1.08 W/m °C up to 22.30% this result proved that the addition of OC in the cementitious composite conducted to curb the heat exchange and to put the insulation capacity.

Figure 13.

Effect of amount of wood fiber on the thermalconductivity.

3.9.3 Effect of the porosity and the thermal conductivity

Figure 12 which examined the evolution of the porosity as a function of the percentage of addition, we observe that the addition of the wood fibers in the cement makes it possible to increase the porosity of this material (reinforcement by the natural and treated wood) by contrast, we notice that by adding Organo clay this porosity decreases and in this case we can conclude that the OC has just saturated the pores.

From this figure the thermal conductivity decreases as the percentage of fibers increase for reinforcement with 2 and 4%: this can be explained by the replacement of cement, an excellent natural insulator and a good thermal conductor. When the mass of the fibers reaches 8%, the thermal conductivity decreases in this case, the heat exchange by conductions weak in front of the convective exchange, as well as by the proportion of the pores which increases at the same time. Also in Figure 14, the variation of the thermal conductivity as the function of the mass of fibers and concerning the results, the thermal conductivity of cement materials reinforced with wood fiber and OC, showed a decrease with the increase of percentage in the mass of fiber in comparison with the reference sample. This reduction is essentially awed to the big porosity of the wood fiber and the big composite materials. To explain the decrease of different specimens, it can be concluded that 4%wt of wood fibers and OC contribute are to the thermal conductivity of the composites materials compared to the reference sample. Hence, incorporation of 6% wt of wood increase the thermal conductivity of the composite, but the thermal conductivity of hybrids composite is less than the reference.

Figure 14.

Evolution of thermal conductivity as a function of additions (FT, FNT andOC).

Reasons for this type of behavior may be given as follows as: it has been found that the surface of the wood fiber exhibit the presence of the pore, which may reduce the adhesion of the fibers with the cement matrix, so we can say that the fibers-organo clay–matrix adhesion plays an important role in the overall performance of the composite.

3.10 Interaction study between the fibrous suspension modified by an adjuvant and by the cement matrix

The interaction between the cement, wood fibers and clay modified by CTAB can be summarized in the following pictures Figures 15 and 16:

1. An adsorption of molecules having SO₃²⁻, COO⁻ type functions or a polar function such as OH.

2. The interaction describes a phenomenon of an intergranular repulsion; in particularly is due to the case of superplasticizers, it is an adsorption of charged polymers.

3. The formation of micelles at the solid–solution interface.

4. This mechanism explain the chemisorption of polynaphthalene sulphonate on specific reaction sites such as these two aluminates.

5. This figure proposes the action of sugars or hydroxyl carboxylic acids by complexation in the interstitial solution. This complexation can then delay the precipitation of hydrates such as portlandite or C-S-H.

6. The mechanism (f) suggests that the CTAB surfactant have the role of potentially inhibiting the growth of hydrates by adsorbing on specific crystallographic growth sites.

7. The figure (g) describes the insertion of the polymer into the structure of the hydrate.

Figure 15.

Process describing the interaction between the composite and the surfactant.

Figure 16.

Dispersion of WF and state of the environment of cement grains.

4. Conclusions

In this work, the wood fiber potential, as support for a cementitious matrix was examined.

The mechanical properties and the thermal conductivity of WFT/OC reinforced cement composite demonstrated the optimum content of organo clay is found to be 1%wt. For this situation, of composite, decrease in porosity (20%), thickness, improvement in compressive quality (20%) and a decline of thermal conductivity are improved by the expansion of 2%wt of wood.

Introducing OC and WFT in to the cement matrix would lead to a considerable increase in early age compressive strength and thermal conductivity. The compressive strength and the thermal conductivity of cement composites could be enhanced by the addition of treated wood fibers and organo clay. The optimum contents of OC and WFT are 1% wt and 6% wt respectively.

Moreover, introducing organo clay treated by the CTAB and wood fibers in to the cement matrix could lead to improve, accelerate hydration and reduce the thermal conductivity to ensure good insulation.

Acknowledgments

Authors are grateful to the Laboratory of Energy and Materials (LABEM), university of Sousse and Laboratoire Sciences des Matériaux et Environnement (LMSE), University of Sfax, Tunisia for the financial support of this work.

Conflict of interest

The authors declare no conflict of interest.

Notation
CTAB	Cetyltrimethylammonium bromide
CSH	Calcium-silica-hydration
NaOH	Sodiumhydroxide
OPC	Ordinary Portland cement NF P 15-301
OC	Organoclay
SDBS	Sodium dodecylbenzenesulfonate
W	Water
WFNT	Wood fiber nontreated
WFT	Wood fiberTreated