**5. Determination of the thermal conductivity of the samples (with black layer)**

In order to determine the thermal conductivity value of the sample, we have deposed a thin ink layer of few microns thick at the sample surface which we have taken into account in our theoretical model. The ink layer absorbs the entire light beam and therefore considerably increases the amplitude of the photothermal signal and makes the signal sensitive to the thermal conductivity of the sample.

values of thermal conductivity. The samples of magnesium oxychloride cement with different percentages present a minimum of thermal conductivity at 10% addition with a slight increase to 15 and 20% of PVAc. Indeed, the insulating effect and the amorphous structure of PVAc particles [11–12] are responsible for the reduction of thermal conductivity. We conclude that the incorporation of PVAc improves the thermal properties of the MOC. Values of thermal conductivity and thermal diffusiv-

*Experimental and theoretical variation of the normalized amplitude (a) and phase (b) of the photothermal*

/s, respectively.

ity decreased from 0.9 to 0.45 w/mk, and 0.4 <sup>10</sup><sup>7</sup> to 0.18 <sup>10</sup><sup>7</sup> m2

28 days. The results of compressive strength are shown in **Table 1**.

**6. Compressive strength**

*signal with the square root of modulation frequency.*

*Improvement of the Thermal Properties of Sorel Cements DOI: http://dx.doi.org/10.5772/intechopen.91774*

**Figure 9.**

**Table 1.**

**131**

Moreover, an optimum of 10% is obtained, which corresponds to a reduction of approximately 50% in thermal conductivity and 55% in thermal diffusivity which can be explained by the appearance of the smallest pore-size in the cement matrix [12].

In order to study the effect of the incorporation of polymers on the mechanical properties, compressive strength measurements made on samples air-cured for

The incorporation of PVAc losses the mechanical strength and it presents a varia-

tion from 64.88 to 23.07 MPa corresponds to a reduction approximately of 64%. Furthermore, the reduction in compressive strength of the thermal optimum is approximately 55%. However, it maintains good mechanical strength. Indeed, we improve the thermal properties of magnesium oxychloride cement while keeping a good resistance. The phase 5 (5 Mg(OH)2.MgCl2.8H2O) is the source for strength and hardening of Sorel cement. At the atomic scale, phase 5 formation can be explained by the adsorption of the atoms Mg2+, OH and Cl when mixing MgO and MgCl2.6H2O on

the surface of MgO. **Figure 10** shows the microstructures of both magnesium

SC0 64.88 SC5 41.33 SC10 29.05 SC15 26.40 SC20 23.07

*Compressive strength of Sorel cement for different percentage of PVAc.*

**Samples Compressive strength (MPa)**

#### **5.1 Thermal conductivity of Sorel cement without PVAc**

Indeed, these curves represent the experimental and theoretical variation of normalized amplitude and phase of the photothermal signal versus the square root of the modulation frequency (**Figure 8**). The best adjustment is obtained for a thermal conductivity equal to 0.9 Wm<sup>1</sup> K<sup>1</sup> . This suggests that the thermal conductivity (0.9 Wm<sup>1</sup> K<sup>1</sup> ) and thermal diffusivity (0.4 <sup>10</sup><sup>7</sup> <sup>m</sup><sup>2</sup> /s) values are reasonably accurate.

#### **5.2 Thermal conductivity of Sorel cement with PVAc**

The curves on **Figure 9** show the experimental and theoretical variation of the normalized amplitude (a) and phase (b) of the photothermal signal with the square root of modulation frequency. The best adjustment of experimental and theoretical curve leads to the determination of thermal conductivity value with precision. We notice that magnesium oxychloride cement (without PVAc) present the greatest

#### **Figure 8.**

*Normalized amplitude (a) and phase (b) of experimental Photothermal signal versus square root modulation frequency of PVAc fitted with theoretical curves (line).*

*Improvement of the Thermal Properties of Sorel Cements DOI: http://dx.doi.org/10.5772/intechopen.91774*

#### **Figure 9.**

photothermal signal versus square root of modulation frequency of the magnesium oxychloride cement with PVAc fitted with theoretical curves. The theoretical curves that best coincide with the experimental curves allow deducing the thermal diffusivity of the samples (**Figure 7**). The difference between theses curves is due to their different thermal diffusivity. We note that the addition of PVAc significantly influences on the diffusivity values. Indeed, the thermal diffusivity decreases with the percentage of PVAc and reaches their minimum values at 10% and begins to increase after this value. The reduction of thermal diffusivity of cement is due to the insulating effect of polyvinyl acetate particles. The thermal diffusivity of PVAc is

**5. Determination of the thermal conductivity of the samples (with black**

In order to determine the thermal conductivity value of the sample, we have deposed a thin ink layer of few microns thick at the sample surface which we have taken into account in our theoretical model. The ink layer absorbs the entire light beam and therefore considerably increases the amplitude of the photothermal signal

Indeed, these curves represent the experimental and theoretical variation of normalized amplitude and phase of the photothermal signal versus the square root of the modulation frequency (**Figure 8**). The best adjustment is obtained for a

The curves on **Figure 9** show the experimental and theoretical variation of the normalized amplitude (a) and phase (b) of the photothermal signal with the square root of modulation frequency. The best adjustment of experimental and theoretical curve leads to the determination of thermal conductivity value with precision. We notice that magnesium oxychloride cement (without PVAc) present the greatest

*Normalized amplitude (a) and phase (b) of experimental Photothermal signal versus square root modulation*

. This suggests that the thermal con-

) and thermal diffusivity (0.4 <sup>10</sup><sup>7</sup> <sup>m</sup><sup>2</sup> /s) values are

and makes the signal sensitive to the thermal conductivity of the sample.

**5.1 Thermal conductivity of Sorel cement without PVAc**

**5.2 Thermal conductivity of Sorel cement with PVAc**

measured by the same technique (PTD) [12].

*Zero-Energy Buildings - New Approaches and Technologies*

thermal conductivity equal to 0.9 Wm<sup>1</sup> K<sup>1</sup>

*frequency of PVAc fitted with theoretical curves (line).*

ductivity (0.9 Wm<sup>1</sup> K<sup>1</sup>

reasonably accurate.

**Figure 8.**

**130**

**layer)**

*Experimental and theoretical variation of the normalized amplitude (a) and phase (b) of the photothermal signal with the square root of modulation frequency.*

values of thermal conductivity. The samples of magnesium oxychloride cement with different percentages present a minimum of thermal conductivity at 10% addition with a slight increase to 15 and 20% of PVAc. Indeed, the insulating effect and the amorphous structure of PVAc particles [11–12] are responsible for the reduction of thermal conductivity. We conclude that the incorporation of PVAc improves the thermal properties of the MOC. Values of thermal conductivity and thermal diffusivity decreased from 0.9 to 0.45 w/mk, and 0.4 <sup>10</sup><sup>7</sup> to 0.18 <sup>10</sup><sup>7</sup> m2 /s, respectively. Moreover, an optimum of 10% is obtained, which corresponds to a reduction of approximately 50% in thermal conductivity and 55% in thermal diffusivity which can be explained by the appearance of the smallest pore-size in the cement matrix [12].

### **6. Compressive strength**

In order to study the effect of the incorporation of polymers on the mechanical properties, compressive strength measurements made on samples air-cured for 28 days. The results of compressive strength are shown in **Table 1**.

The incorporation of PVAc losses the mechanical strength and it presents a variation from 64.88 to 23.07 MPa corresponds to a reduction approximately of 64%. Furthermore, the reduction in compressive strength of the thermal optimum is approximately 55%. However, it maintains good mechanical strength. Indeed, we improve the thermal properties of magnesium oxychloride cement while keeping a good resistance. The phase 5 (5 Mg(OH)2.MgCl2.8H2O) is the source for strength and hardening of Sorel cement. At the atomic scale, phase 5 formation can be explained by the adsorption of the atoms Mg2+, OH and Cl when mixing MgO and MgCl2.6H2O on the surface of MgO. **Figure 10** shows the microstructures of both magnesium


**Table 1.** *Compressive strength of Sorel cement for different percentage of PVAc.*

physics mathematics quantum modeling and mechanical design laboratory in Preparatory Institute for Engineering Studies of Nabeul and the National Research

Centre of Materials Sciences in Borj Cedria Technological Park.

*Improvement of the Thermal Properties of Sorel Cements DOI: http://dx.doi.org/10.5772/intechopen.91774*

\*, Amal Brichni<sup>2</sup> and Noureddine Yacoubi<sup>1</sup>

Institute for Engineering Studies of Nabeul, Nabeul, Tunisia

Materials Sciences, Technopole Borj Cedria, Soliman, Tunisia

\*Address all correspondence to: rim.zgueb@fsb.u-carthage.tn

provided the original work is properly cited.

1 Physics Mathematics Quantum Modeling and Mechanical Design, Preparatory

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Useful Material Valorization Laboratory, National Center for Research in

**Author details**

Rim Zgueb1

**133**

**Figure 10.** *Microstructure of SC5, SC10, SC15 and SC20.*

oxychloride cement without and with PVAc (5 μm). We see in these images the needle shaped crystals. These needles shaped crystals is the P5 (5Mg(OH)2.MgCl2.8H2O). We note that the incorporation of PVAc does not affect for the development of P5.
