**1. Introduction**

Thermal insulation consists in using a material or a combination of materials in order to limit heat losses by conduction, convection and radiation between the interior and exterior of a building due to its low thermal conductivity. Thus, thermal insulation acts as a thermal barrier. The two main criteria for thermal insulation of buildings are the optimization of energy consumption and the protection of buildings against climatic factors. In some countries, people spend up to 90% of their time indoors (offices, factory, workshops, homes, … ) so they need a viable artificial environment that requires energy. Thermal insulation reduces heat loss, saves heating, limits greenhouse gas emissions, and improves living comfort.

In addition, cement will remain the main material that meets the needs of modern infrastructure and participates in the construction of large structures. Thus the development of cement performance to meet current needs has prompted several research projects to improve its thermal insulation without reducing its resistance.

One of the most promising cements for thermal insulation is magnesium oxychloride cement (MOC). During the last decade, the development of magnesium oxychloride cement was motivated by environmental considerations. The MgO production temperature was lower than the conversion temperature of CaCO3 into Portland cement. The energy savings associated with this reduced temperature have led many researchers to believe that magnesium oxychloride cements are the future of green cement. In addition, MgO has the capacity to potentially absorb CO2 unlike Portland cement. It is "carbon neuter" cement. These two interdependent aspects have a recent academic and commercial interest in the field of MgO cements.

Measurement of thermal conductivity was performed in dry state using the

The micro-morphology on the fractured surface of MOC was characterized by scanning electron microscopy (SEM, JEOL-JSM- 5400). The sample is previously coated with a layer of gold and SEM was operated at 15 kV of acceleration voltage.

The sample is heated by modulated and uniform light pump beam. The optical absorption of the sample will generate a unidimentional thermal wave that will propagate into the sample and in the surrounding fluid near the surface of the sample, inducing a temperature gradient then a refractive index gradient in the fluid. The absorbed light is transformed into heat by a nonradiative de-excitation process. A laser beam skimming parallely the sample surface and passing through this refractive index gradient is deflected. This deflection is related to the thermal

The deflection of the probe laser beam <sup>ψ</sup> is complex number <sup>ψ</sup> ¼j <sup>ψ</sup><sup>j</sup> ej<sup>φ</sup> � � given

j j *T*<sup>0</sup> *e*

T0 which is the periodic temperature rise at the sample surface is a complex number that written T0 <sup>¼</sup> <sup>∣</sup> T0 <sup>∣</sup> <sup>e</sup><sup>j</sup><sup>θ</sup>, Z0 is the distance between the probe laser beam axis and the sample surface, L is the sample length in the direction of the laser probe beam, n is the fluid refractive index. Where ð Þ <sup>μ</sup><sup>f</sup> <sup>¼</sup> Df*=*π<sup>f</sup> <sup>1</sup>*=*<sup>2</sup> is the thermal diffusion length of the fluid with Df the thermal diffusivity of the fluid and j<sup>2</sup> ¼ �1*:*<sup>∣</sup> <sup>ψ</sup><sup>∣</sup> and <sup>φ</sup> are respectively the amplitude and the argument of the laser pump beam deflection

� *z*0 *<sup>μ</sup> <sup>f</sup> e* *<sup>j</sup> <sup>θ</sup>*<sup>þ</sup> *<sup>π</sup>* <sup>4</sup>� *<sup>z</sup>*<sup>0</sup> *μ f* � �

*e <sup>j</sup>ω<sup>t</sup>* (1)

*<sup>μ</sup> <sup>f</sup>* (2)

<sup>4</sup> (3)

photothermal deflection technique.

**3. Photothermal deflection technique**

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

and optical properties of the sample.

ψð Þ¼ *z*, *t*

*L n*0

*dn dT <sup>f</sup>*

j j <sup>ψ</sup>ð Þ*<sup>z</sup>* ¼ � *<sup>L</sup>*

calculate the periodic temperature T0 at the sample surface.

*n*0

*<sup>φ</sup>* <sup>¼</sup> �*z*<sup>0</sup> *μ f*

In order to determine the deflection of the probe laser beam, we have to

**3.2 Calculation of the periodic elevation temperature T0 at the sample surface**

The sample consists of only one layer (**Figure 1**) of thermal conductivity ks, thermal diffusivity Ds and thickness ls. It is fixed at backing of kb, Db, lb respectively thermal conductivity, thermal diffusivity and thickness. The sample and backing are in a fluid (air) of thermal conductivity kf, thermal diffusivity Df and thickness lf. To determine

*dn dT <sup>f</sup>*

ffiffi 2 p *μ f*

<sup>þ</sup> *<sup>θ</sup>* <sup>þ</sup> *<sup>π</sup>*

j j *T*<sup>0</sup> *e*

� *<sup>z</sup>*<sup>0</sup>

ffiffi 2 p *μ f*

by [11]:

given by:

*3.2.1 Bulk sample*

**125**

*3.2.1.1 Calculation of T0*

**3.1 Principle of the photothermal deflection technique PTD**

MOC cement is synthesized by dissolving the magnesia MgO into aqueous solution of magnesium chloride hexahydrate MgCl2, forming a homogeneous gel from which the basic salts of magnesium chloride precipitate. These salts are expressed by xMg(OH)2.yMgCl2.zH2O phases which depend on the temperature, the reactivity of magnesium and the relationships between the number of moles of MgCl2 to that of the water molecules, the temperature and the reactivity of magnesium [1]. It has several performances and has become popular due to its attractive appearance, similar to that of marble. Indeed, it rapid hardening rate and it has high mechanical strength and good resistance to abrasion. The abrasion resistance is three times that of ordinary Portland cement. Generally, the compressive strength is greater than 50 MPa after curing for 28 days [2–7]. In addition, a peculiarity of this cement is its resistance to salt and saline solutions. The main applications used are architectural applications such as the construction of thermal and acoustical insulating panels [8], the construction of industrial floors and other prefabricated building boards [9].

In this chapter, we investigated the thermal properties of Sorel cement. The aim of this research was to improve the thermal insulation of Sorel cement by using a polyvinyl acetate (PVAc) polymer. We have determined the thermal conductivity and thermal diffusivity of various blended PVAc cements and we are studying the effect of PVAc on the compressive strength of composite materials.

#### **2. Experimental procedures**

#### **2.1 Specimen preparation**

The main materials used to synthesize the MOC are Magnesia (MgO), magnesium chloride (MgCl2) and water (H2O). Magnesium oxide powder used in this study is mostly produced by calcinations of magnesite powder (HiMedia, India) at a temperature around 900°C. We dissolved magnesium chloride hexahydrate (Scharlab, Spain) in distilled water to prepare a saturated solution of magnesium chloride. The mass concentration of the solution was 217 g for 100 g of water. The mass ratio of MgCl2.6H2O/MgO = 2.22 [10]. The PVAc polymer (SICOP, Tunisia) is a fluid of low cost whose viscosity at 20°C is 10,000 500 Pa s and the PH = 6 1.

The samples were prepared by mixing at the same time magnesium oxide powder, saturated magnesium chloride solution and PVAc polymer. The polyvinyl acetate polymer is replaced by MgO. Five samples are synthesized; four samples with the incorporation of PVAc and a control sample (without addition). The obtained samples which are SC0 (0% PVAC), SC5 (5% PVAC), SC10 (10% PVAC), SC15 (15% PVAC) and SC20 (20% PVAC). The mixtures were cast into the cylindrical molds of height 50 mm and diameter about 25 mm, stored for 24 h, then unmolded and air-cured for 28 days.

#### **2.2 Methods**

The compressive strength of specimens was tested using Liyold mechanical testing instrument with a load of 300 KN. At the age of 28 days, the compressive strength for samples with diameter 25 mm and height 50 mm were measured at a loading speed of 2 mm/min at ambient temperature.

unlike Portland cement. It is "carbon neuter" cement. These two interdependent aspects have a recent academic and commercial interest in the field of MgO

*Zero-Energy Buildings - New Approaches and Technologies*

MOC cement is synthesized by dissolving the magnesia MgO into aqueous solution of magnesium chloride hexahydrate MgCl2, forming a homogeneous gel from which the basic salts of magnesium chloride precipitate. These salts are expressed by xMg(OH)2.yMgCl2.zH2O phases which depend on the temperature, the reactivity of magnesium and the relationships between the number of moles of MgCl2 to that of the water molecules, the temperature and the reactivity of magnesium [1]. It has several performances and has become popular due to its attractive appearance, similar to that of marble. Indeed, it rapid hardening rate and it has high mechanical strength and good resistance to abrasion. The abrasion resistance is three times that of ordinary Portland cement. Generally, the compressive strength is greater than 50 MPa after curing for 28 days [2–7]. In addition, a peculiarity of this cement is its resistance to salt and saline solutions. The main applications used are architectural applications such as the construction of thermal and acoustical insulating panels [8], the construction of industrial floors and other prefabricated

In this chapter, we investigated the thermal properties of Sorel cement. The aim of this research was to improve the thermal insulation of Sorel cement by using a polyvinyl acetate (PVAc) polymer. We have determined the thermal conductivity and thermal diffusivity of various blended PVAc cements and we are studying the

The main materials used to synthesize the MOC are Magnesia (MgO), magnesium chloride (MgCl2) and water (H2O). Magnesium oxide powder used in this study is mostly produced by calcinations of magnesite powder (HiMedia, India) at a

temperature around 900°C. We dissolved magnesium chloride hexahydrate (Scharlab, Spain) in distilled water to prepare a saturated solution of magnesium chloride. The mass concentration of the solution was 217 g for 100 g of water. The mass ratio of MgCl2.6H2O/MgO = 2.22 [10]. The PVAc polymer (SICOP, Tunisia) is a fluid of low cost whose viscosity at 20°C is 10,000 500 Pa s and the PH = 6 1. The samples were prepared by mixing at the same time magnesium oxide pow-

der, saturated magnesium chloride solution and PVAc polymer. The polyvinyl acetate polymer is replaced by MgO. Five samples are synthesized; four samples with the incorporation of PVAc and a control sample (without addition). The obtained samples which are SC0 (0% PVAC), SC5 (5% PVAC), SC10 (10% PVAC), SC15 (15% PVAC) and SC20 (20% PVAC). The mixtures were cast into the cylindrical molds of height 50 mm and diameter about 25 mm, stored for 24 h, then

The compressive strength of specimens was tested using Liyold mechanical testing instrument with a load of 300 KN. At the age of 28 days, the compressive strength for samples with diameter 25 mm and height 50 mm were measured at a

effect of PVAc on the compressive strength of composite materials.

cements.

building boards [9].

**2. Experimental procedures**

unmolded and air-cured for 28 days.

loading speed of 2 mm/min at ambient temperature.

**2.2 Methods**

**124**

**2.1 Specimen preparation**

Measurement of thermal conductivity was performed in dry state using the photothermal deflection technique.

The micro-morphology on the fractured surface of MOC was characterized by scanning electron microscopy (SEM, JEOL-JSM- 5400). The sample is previously coated with a layer of gold and SEM was operated at 15 kV of acceleration voltage.
