*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 and Mechanical Properties of Organo-Clay-Wood Fiber in Cement… DOI: http://dx.doi.org/10.5772/intechopen.102321*

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.

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

*Thermal Conductivity and Mechanical Properties of Organo-Clay-Wood Fiber in Cement… DOI: http://dx.doi.org/10.5772/intechopen.102321*

clay–matrix adhesion plays an important role in the overall performance of the composite.
