**4. Results and discussions**

#### **4.1. The properties of FCI**

For the matrix part samples, the sintering temperature will have an important effect on macroscopic properties, including the moisture absorption capacity and rupture modulus, which are shown in **Figures 2** and **3**, respectively.

First, the characteristic curve in **Figure 2** indicates that for the sample no.1 the rupture modulus increases with the increase of the sintering temperature. When the sintering temperature is 1000°C, the rupture modulus is only 2.52 MPa. Moreover, when the sintering temperature is increased to 1100°C, the corresponding rupture modulus increases to 7.82 MPa, indicating that there is the liquid generation in the sample no.1. Furthermore, when the sintering temperature is over 1200°C, the rupture modulus value reaches to 25.38 MPa. Second, it is interesting to note that in the investigated temperature range (1000–1200°C), the moisture absorption capacity dramatically decreases from 26.85% to 0.25% at the sintering temperature

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**Figure 3.** Moisture absorption capacity values of the sample no. 1 versus sintering temperatures.

It can be concluded that when the sintering temperature is 1200°C the samples have excellent properties (moisture absorption capacity and the rupture modulus), which satisfy the

In addition, the quartz was chosen as an addition to the sample no. 1. **Figures 4** and **5** show the effects of quartz addition on the sample's properties (moisture absorption capacity and rupture modulus). It can be seen that, for the sample no. 2 and no. 3, at 1200°C, the 5% and 10% quartz additions enhance the samples' strength with a little increase in moisture absorption capacity. For instance, for the sample no. 2, the highest rupture modulus reaches 34.28 MPa at 1200°C, which drastically exceeds the property of the sample no. 1 without quartz (25.38 MPa). According to the literature [26], it may be explained that, for the sample no. 2, 5% quartz addition is a benefit to the increase of mullite formation, which will promote the sample's rupture modulus. **Figure 5** shows that 5% quartz addition increases the moisture absorption capacity from 0.25 to 0.83%, but it still satisfies the standards for stoneware

of 1000–1200°C.

porcelain tiles [25].

requirements of fine stoneware tiles [25].

**Figure 2.** Rupture modulus values of the sample no. 1 versus sintering temperatures.

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**Figure 3.** Moisture absorption capacity values of the sample no. 1 versus sintering temperatures.

if *rn* was smaller than the solid material's volume fraction, the thermal conductivity of the solid material would be endowed. Otherwise, this unit would be endowed with the thermal

In this simulation programme, the steady-state energy equation for three-dimensional heat transfer was established as the control equation. For each unit, the sum of heat flow towards this unit was equal to that away from it. In addition, the solution conditions were defined by using the temperature field matrix: *T* = *ones (X, Y, Z).* For the surfaces perpendicular to the heat flow direction, they belonged to the first-class boundary condition and the temperatures of these two surfaces were equalled to 33°C and 17°C. As in the experiment, the sample panel was surrounded by thermal insulation fibre; similarly, the four surfaces that surrounded the

Secondly, the energy-saving effect of FCI was evaluated by EnergyPlus software [22–24]. In this research, an ideal building is applied as the calculation model for energy consumption. In addition, the energy consumption of buildings with different kinds of external walls was

For the matrix part samples, the sintering temperature will have an important effect on macroscopic properties, including the moisture absorption capacity and rupture modulus, which

will be obtained through the iterative calculation.

conductivity of the air (*ka* = 0.026 W/(m•K) [21]).

panel were insulated perfectly. Finally, *ke*

compared systematically.

134 Recent Advances in Porous Ceramics

**4.1. The properties of FCI**

**4. Results and discussions**

are shown in **Figures 2** and **3**, respectively.

**Figure 2.** Rupture modulus values of the sample no. 1 versus sintering temperatures.

First, the characteristic curve in **Figure 2** indicates that for the sample no.1 the rupture modulus increases with the increase of the sintering temperature. When the sintering temperature is 1000°C, the rupture modulus is only 2.52 MPa. Moreover, when the sintering temperature is increased to 1100°C, the corresponding rupture modulus increases to 7.82 MPa, indicating that there is the liquid generation in the sample no.1. Furthermore, when the sintering temperature is over 1200°C, the rupture modulus value reaches to 25.38 MPa. Second, it is interesting to note that in the investigated temperature range (1000–1200°C), the moisture absorption capacity dramatically decreases from 26.85% to 0.25% at the sintering temperature of 1000–1200°C.

It can be concluded that when the sintering temperature is 1200°C the samples have excellent properties (moisture absorption capacity and the rupture modulus), which satisfy the requirements of fine stoneware tiles [25].

In addition, the quartz was chosen as an addition to the sample no. 1. **Figures 4** and **5** show the effects of quartz addition on the sample's properties (moisture absorption capacity and rupture modulus). It can be seen that, for the sample no. 2 and no. 3, at 1200°C, the 5% and 10% quartz additions enhance the samples' strength with a little increase in moisture absorption capacity. For instance, for the sample no. 2, the highest rupture modulus reaches 34.28 MPa at 1200°C, which drastically exceeds the property of the sample no. 1 without quartz (25.38 MPa). According to the literature [26], it may be explained that, for the sample no. 2, 5% quartz addition is a benefit to the increase of mullite formation, which will promote the sample's rupture modulus. **Figure 5** shows that 5% quartz addition increases the moisture absorption capacity from 0.25 to 0.83%, but it still satisfies the standards for stoneware porcelain tiles [25].

**Figure 4.** Rupture modulus values of the sample nos. 1–5 with different quartz addition.

ceramic system, the new sample broadens the traditional ceramic crystal phase area (blue) to

**Figure 6.** Ternary diagram of the traditional ceramic and sample no. 2 (blue indicates the traditional ceramic crystal

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In addition, the powder of both raw materials and sintered sample no. 2 is separately analysed by XRD. Firstly, XRD patterns in **Figure 7** depict that there is none or only a small amount of glass phase in the sintered sample no. 2, which is a benefit to the improvement of its mechanical property. The previous research [27] has shown that in the traditional porcelain stoneware tiles, glass is one of the major phases in addition to quartz and mullite. Therefore, compared to the traditional ceramic tile, the matrix part tile prepared by our research has better mechanical property. In addition, it is interesting to note that there is no quartz in sintered sample no. 2; it is replaced by a large amount of mullite, which will further

Moreover, **Figure 8** shows the DTA-TG curve of the sample. At 200°C, the mass loss is caused by the dehydroxylation of gypsum with an exothermic peak. At the temperature of 400–600°C, the mass loss is caused by the dehydroxylation process of boehmite (with an endothermic peak at 450°C) and kaolinite (with an endothermic peak at above 550°C). Finally, an exother-

Secondly, for the foam sample no. 6, the sintering temperature likewise has an important effect on the foam sample's properties, including the bulk density and volume, which are

mic peak at about 1000°C is attributable to mullite crystallisation [28].

O3

and CaO

a new phase area. This change of the ceramic system is due to the increase of Al<sup>2</sup>

obtained from FA.

phase area and red shows the phase area of sample no. 2).

promote its strength.

shown in **Figure 9**.

**Figure 5.** Moisture absorption capacity values of the sample nos. 1–5 with different quartz addition.

In order to explain the above phenomenon, the ternary diagram of sample no. 2 was calculated by FactSage. From **Figure 6**, it can be seen that the new sample's raw materials belong to SiO2 -Al<sup>2</sup> O3 -CaO-K<sup>2</sup> O system, as shown in red. Therefore, unlike the conventional ternary

**Figure 6.** Ternary diagram of the traditional ceramic and sample no. 2 (blue indicates the traditional ceramic crystal phase area and red shows the phase area of sample no. 2).

ceramic system, the new sample broadens the traditional ceramic crystal phase area (blue) to a new phase area. This change of the ceramic system is due to the increase of Al<sup>2</sup> O3 and CaO obtained from FA.

In addition, the powder of both raw materials and sintered sample no. 2 is separately analysed by XRD. Firstly, XRD patterns in **Figure 7** depict that there is none or only a small amount of glass phase in the sintered sample no. 2, which is a benefit to the improvement of its mechanical property. The previous research [27] has shown that in the traditional porcelain stoneware tiles, glass is one of the major phases in addition to quartz and mullite. Therefore, compared to the traditional ceramic tile, the matrix part tile prepared by our research has better mechanical property. In addition, it is interesting to note that there is no quartz in sintered sample no. 2; it is replaced by a large amount of mullite, which will further promote its strength.

Moreover, **Figure 8** shows the DTA-TG curve of the sample. At 200°C, the mass loss is caused by the dehydroxylation of gypsum with an exothermic peak. At the temperature of 400–600°C, the mass loss is caused by the dehydroxylation process of boehmite (with an endothermic peak at 450°C) and kaolinite (with an endothermic peak at above 550°C). Finally, an exothermic peak at about 1000°C is attributable to mullite crystallisation [28].

Secondly, for the foam sample no. 6, the sintering temperature likewise has an important effect on the foam sample's properties, including the bulk density and volume, which are shown in **Figure 9**.

In order to explain the above phenomenon, the ternary diagram of sample no. 2 was calculated by FactSage. From **Figure 6**, it can be seen that the new sample's raw materials belong

**Figure 5.** Moisture absorption capacity values of the sample nos. 1–5 with different quartz addition.

**Figure 4.** Rupture modulus values of the sample nos. 1–5 with different quartz addition.

O system, as shown in red. Therefore, unlike the conventional ternary

to SiO2


136 Recent Advances in Porous Ceramics


**Figure 7.** XRD patterns of the sample no. 2.

**Figure 9** indicates the effect of sintering temperature on the volume results and the bulk density values of the sample no. 6 with 1% SiC as a foaming agent. It can be seen that the volume results of the sample no. 6 first shrank and then expanded with the increase in the sintering temperature from 1010–1200°C. Therefore, it is noted that the corresponding bulk density of

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**Figure 9.** The volume results and the bulk density values of the sample no. 6 at different sintering temperature.

This phenomenon is attributed to two typically changing processes in the sintering of foamed ceramics, which are matrix densification and closed-pore generation. Firstly, in the sintering process, with the increase in sintering temperature, liquid phase is generated, which led to the matrix densification [29]. Secondly, there is SiC in CW and so with the sintering temperature increase SiC began to decompose, resulting in the closed-pore generation. In the process

Moreover, the measured thermal conductivity of the sample no. 6 as a function of the bulk density is demonstrated in **Figure 11**. It can be seen that the measured thermal conductivity decreases from 0.3876 W/(m•K) to 0.1184 W/(m•K) with the increase in the bulk density of the sample no. 6. It is concluded that the sample no. 6 at high sintering temperature (1200°C) has an excellent heat insulation performance, indicating that it can be utilised as the foam part of FCI.

C, followed by a rapid decrease with further increasing

or CO) is generated in the presence of oxygen, which is

at 1200°

, and then,

C, which is

sample no. 6 shows a consistent trend. At 1010°C, the bulk density is 1.714 g/cm<sup>3</sup>

at 1060°

sintering temperature, and reaches the minimum value of 0.471 g/cm3

it increases up to 1.984 g/cm3

of SiC decomposition, the gas (CO2

shown in **Figure 10** [30–32].

decreased by 76%.

**Figure 8.** DTA-TG curve of the green sample no.2.

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**Figure 9.** The volume results and the bulk density values of the sample no. 6 at different sintering temperature.

**Figure 9** indicates the effect of sintering temperature on the volume results and the bulk density values of the sample no. 6 with 1% SiC as a foaming agent. It can be seen that the volume results of the sample no. 6 first shrank and then expanded with the increase in the sintering temperature from 1010–1200°C. Therefore, it is noted that the corresponding bulk density of sample no. 6 shows a consistent trend. At 1010°C, the bulk density is 1.714 g/cm<sup>3</sup> , and then, it increases up to 1.984 g/cm3 at 1060° C, followed by a rapid decrease with further increasing sintering temperature, and reaches the minimum value of 0.471 g/cm3 at 1200° C, which is decreased by 76%.

This phenomenon is attributed to two typically changing processes in the sintering of foamed ceramics, which are matrix densification and closed-pore generation. Firstly, in the sintering process, with the increase in sintering temperature, liquid phase is generated, which led to the matrix densification [29]. Secondly, there is SiC in CW and so with the sintering temperature increase SiC began to decompose, resulting in the closed-pore generation. In the process of SiC decomposition, the gas (CO2 or CO) is generated in the presence of oxygen, which is shown in **Figure 10** [30–32].

Moreover, the measured thermal conductivity of the sample no. 6 as a function of the bulk density is demonstrated in **Figure 11**. It can be seen that the measured thermal conductivity decreases from 0.3876 W/(m•K) to 0.1184 W/(m•K) with the increase in the bulk density of the sample no. 6. It is concluded that the sample no. 6 at high sintering temperature (1200°C) has an excellent heat insulation performance, indicating that it can be utilised as the foam part of FCI.

**Figure 8.** DTA-TG curve of the green sample no.2.

**Figure 7.** XRD patterns of the sample no. 2.

138 Recent Advances in Porous Ceramics

**Figure 10.** The reaction principle of SiC as a foaming agent.

to note that, when the bulk density continues decreasing to a certain level (1.600 g/cm3

effective thermal conductivities, with the average deviation of 4%.

ke = 0.15002‐1.25 × 10‐<sup>4</sup> *ρ<sup>b</sup>* + 1.23 × 10‐<sup>7</sup> *ρ<sup>b</sup>*

250-mm reinforced concrete with the thermal conductivity of 1.95 W/(m•K).

ductivity and the bulk density for the foam sample at 25°C.

density.

*4.2.2. The forecast of the energy saving of FCI in an ideal building*

decrease rate of the effective thermal conductivity becomes small. In addition, it can be seen that the simulated effective thermal conductivities are well in agreement with the measured

**Figure 12.** The simulation results of the effective thermal conductivity of the sample no. 6 as a function of the bulk

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From **Figure 12**, we can also get the following relationship between the effective thermal con-

In this part, a building (3 m\*3 m\*2.8 m) in Beijing is used as the calculation model for energy consumption (**Figure 13(a)**). In this building model, there are two kinds of external walls, traditional wall and foam ceramic insulation wall. As shown in **Figure 13(b)**, the foam ceramic insulation wall is composed of four layers: the cement mortar (20 mm, 0.97 W/(m•K)), the matrix part of the foam ceramic insulation (200 mm), the foam part of the foam ceramic insulation (50 mm), and the composite mortar (20 mm, 0.65 W/(m•K)). For the traditional wall, the matrix and foam parts of the foam ceramic insulation were removed and were replaced with a

**Figure 14** shows the annual energy consumption for the ideal building with different external walls. It can be seen that, compared with the traditional wall, the FCI wall significantly reduces the annual energy consumption by 44–57%. In addition, for the building with FCI wall, the annual average heating and cooling rate decreases with the decrease in the bulk

), the

141

<sup>2</sup> (5)

**Figure 11.** The measured thermal conductivity of the sample no. 6 as a function of the bulk density.

#### **4.2. The forecast of the thermal conductivity and energy saving of FCI**

#### *4.2.1. Numerical simulation results of the effective thermal conductivity*

The relationship between the effective thermal conductivity and the bulk density can be calculated through the present proposed model. The results of the effective thermal conductivity, *ke* , as a function of the bulk density, are indicated in **Figure 12**. It can be seen that the effective thermal conductivity decreases with the decrease of the bulk density. It is interesting Preparation and Numerical Modelling of Ceramic Foam Insulation for Energy Saving in Buildings http://dx.doi.org/10.5772/intechopen.71393 141

**Figure 12.** The simulation results of the effective thermal conductivity of the sample no. 6 as a function of the bulk density.

to note that, when the bulk density continues decreasing to a certain level (1.600 g/cm3 ), the decrease rate of the effective thermal conductivity becomes small. In addition, it can be seen that the simulated effective thermal conductivities are well in agreement with the measured effective thermal conductivities, with the average deviation of 4%.

From **Figure 12**, we can also get the following relationship between the effective thermal conductivity and the bulk density for the foam sample at 25°C.

$$k\_o = 0.15002 \text{-} 1.25 \times 10^4 \,\rho\_b + 1.23 \times 10^7 \,\rho\_b \,\tag{5}$$

#### *4.2.2. The forecast of the energy saving of FCI in an ideal building*

**4.2. The forecast of the thermal conductivity and energy saving of FCI**

**Figure 11.** The measured thermal conductivity of the sample no. 6 as a function of the bulk density.

The relationship between the effective thermal conductivity and the bulk density can be calculated through the present proposed model. The results of the effective thermal conductiv-

, as a function of the bulk density, are indicated in **Figure 12**. It can be seen that the effective thermal conductivity decreases with the decrease of the bulk density. It is interesting

*4.2.1. Numerical simulation results of the effective thermal conductivity*

**Figure 10.** The reaction principle of SiC as a foaming agent.

140 Recent Advances in Porous Ceramics

ity, *ke*

In this part, a building (3 m\*3 m\*2.8 m) in Beijing is used as the calculation model for energy consumption (**Figure 13(a)**). In this building model, there are two kinds of external walls, traditional wall and foam ceramic insulation wall. As shown in **Figure 13(b)**, the foam ceramic insulation wall is composed of four layers: the cement mortar (20 mm, 0.97 W/(m•K)), the matrix part of the foam ceramic insulation (200 mm), the foam part of the foam ceramic insulation (50 mm), and the composite mortar (20 mm, 0.65 W/(m•K)). For the traditional wall, the matrix and foam parts of the foam ceramic insulation were removed and were replaced with a 250-mm reinforced concrete with the thermal conductivity of 1.95 W/(m•K).

**Figure 14** shows the annual energy consumption for the ideal building with different external walls. It can be seen that, compared with the traditional wall, the FCI wall significantly reduces the annual energy consumption by 44–57%. In addition, for the building with FCI wall, the annual average heating and cooling rate decreases with the decrease in the bulk

simulation methods are applied to study the effects of sintering temperature and the addi-

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For the matrix part of FCI, at 1200°C, the sample with 50 wt% FA and 5 wt% quartz addition shows the best complex properties. The rupture modulus is 34.28 MPa, and the corresponding moisture absorption capacity is only 0.83%. In addition, for the foam sample with 1 wt% silicon carbide, the lowest bulk density and thermal conductivity at 1200°C are 0.471 g/cm3

Moreover, the thermal conductivities of CFI and its effect on energy saving in buildings were simulated by a simulation model and EnergyPlus, respectively. Firstly, the proposed simulation model was applied to predict the effective thermal conductivity of the sample no. 6 as a function of bulk density. The simulation results show that the effective thermal conductivity of the sample no. 6 decreases with the decrease in its bulk density, and the simulation values are in good agreement with the measured results, with an average deviation of 4%. These simulation methods are desirable not only for the practical purpose of predicting the thermal properties of CFI, but also for the fundamental knowledge required in developing other new porous ceramics. Furthermore, the EnergyPlus results indicate that FCI can efficiently reduce the thermal load caused by the heat loss of the external construction, so the proposed FCI

This chapter was supported by the Fundamental Research Funds for the Central Universities (FRF-TP-15-085A1) and China Postdoctoral Science Foundation (2016 M600927). The authors gratefully acknowledge financial support by the Key Projects in the National Science & Technology Pillar Program (2013BAC14B07). Supports by the National Natural Science Foundation of China (51708022, 51522401 and 51472007) and National Key R&D Plan of China

1 School of Civil and Resource Engineering, University of Science and Technology Beijing,

2 Department of Energy and Resources Engineering and Beijing Key Laboratory for Solid Waste Utilization and Management, College of Engineering, Peking University, Beijing,

3 Nuclear Power (Bidding) Dept. 1, China Nuclear Energy Industry Corp., Beijing,

tive agent on properties of the samples.

and 0.1184 W/(m•K), respectively.

exhibits excellent energy conservation effect.

(2017YFC0702600) are acknowledged.

and Yang He<sup>3</sup>

\*Address all correspondence to: jiru@ustb.edu.cn

Beijing, The People's Republic of China

The People's Republic of China

The People's Republic of China

**Acknowledgements**

**Author details**

\*, Xidong Wang<sup>2</sup>

Ru Ji<sup>1</sup>

**Figure 13.** The ideal calculation building model.

**Figure 14.** Heating and cooling annual loads in ideal building with different external walls.

density of the foam part of FCI. For instance, when *ρ<sup>b</sup>* = 0.471 g/cm3 , for the ideal building the annual average heating and cooling rate is only 95 W, and compared with that of the building with a traditional wall, the rate is reduced by 57%. Therefore, the energy conservation of the FCI wall is especially pronounced.

#### **5. Conclusion**

In this research, solid wastes, such as FA and CW, were effectively utilised for the manufacture of FCI, leading to low-cost and environmental protection. The experiment and simulation methods are applied to study the effects of sintering temperature and the additive agent on properties of the samples.

For the matrix part of FCI, at 1200°C, the sample with 50 wt% FA and 5 wt% quartz addition shows the best complex properties. The rupture modulus is 34.28 MPa, and the corresponding moisture absorption capacity is only 0.83%. In addition, for the foam sample with 1 wt% silicon carbide, the lowest bulk density and thermal conductivity at 1200°C are 0.471 g/cm3 and 0.1184 W/(m•K), respectively.

Moreover, the thermal conductivities of CFI and its effect on energy saving in buildings were simulated by a simulation model and EnergyPlus, respectively. Firstly, the proposed simulation model was applied to predict the effective thermal conductivity of the sample no. 6 as a function of bulk density. The simulation results show that the effective thermal conductivity of the sample no. 6 decreases with the decrease in its bulk density, and the simulation values are in good agreement with the measured results, with an average deviation of 4%. These simulation methods are desirable not only for the practical purpose of predicting the thermal properties of CFI, but also for the fundamental knowledge required in developing other new porous ceramics. Furthermore, the EnergyPlus results indicate that FCI can efficiently reduce the thermal load caused by the heat loss of the external construction, so the proposed FCI exhibits excellent energy conservation effect.
