Effects of Alkali Activator and High Curing Temperature on Thermal Properties of Expanded Perlite-Based Thermal Insulation Panels

*Gökhan Durmuş, Damla Nur Çelik and Ümit Ağbulut* 

#### **Abstract**

 Buildings have the most imperative factor in global energy consumption all over the world. Therefore, it has increasing importance to reduce the energy consumption from buildings and so provides not only to conserve the energy but also to contribute positively economic growth of countries. In order to reduce energy losses from the buildings, this paper mainly focused on expanded perlite-based heat insulation materials. In this study, the effects of different sodium hydroxide (NaOH) concentrations and curing conditions on heat insulation panels were experimentally investigated. Binder was prepared from different NaOH concentrations (6, 8, 10, and 12 M) and sodium silicate (Na2SiO3) for the samples. Prepared mortars were firstly cured at 60°C throughout 24 h. Then, the panels were held at 300, 400, and 500°C for 3 h. The results showed that the thermal conductivity values of insulation panels can be decreased by applying high temperatures. Additionally, the lowest thermal conductivity value of manufactured panels in this paper was obtained as 44.37 mW/m K for the panel with 6 M NaOH and cured at 500°C. On the other hand, the thermal cracks were obtained, and the panels were negatively influenced for higher temperature degree of more than 500°C.

**Keywords:** insulation panel, expanded perlite, geopolymer, alkali activator, curing

#### **1. Introduction**

Today, energy production and consumption strongly affect the economic growth of a country and are the most important factors that provide the sustainability of economic development. However, Turkey generally imports 75% of its total energy demand owing to its limited energy resources, and energy issue is, therefore, the biggest obstacle to the economic growth for Turkey. In terms of energy dependency ranking and share rates, Turkey has been holding onto the 20th rank in the list for a while. **Table 1** shows the energy import ratio and ranks for Turkey [1].

As is shown in **Table 1**, Turkey should rapidly cut off its energy import ratio in the short-time run. Actually, it has limited energy resources and must import energy at a high ratio. To reduce energy dependency, Turkey started to take concrete


**Table 1.** 

*Turkish energy import ratio and ranking in the world from 2010 to 2014 [1].* 

 steps and tended to increase renewable and alternative energy plants in the country. For example, it began its third nuclear energy plant in the country and aimed to meet the electricity demand at the ratio of 15% [2, 3]. Another effective method to decrease its energy bill is reduced energy consumption ratio for the countries with limited energy sources. In recent years, there has been an increasing interest in energy conservation because energy generation is largely achieved by burning the fossil fuels which will run out in the near future. Today, the total global primary energy consumption has met the rate of approximately 85% from fossil fuels such as coal, oil, and natural gas [4]. Approximately 50% of this consumption has been directly spent on buildings. Therefore, it is important to decrease the energy consumption particularly from buildings, and this positively affects the economic growth of the countries in the short and long run because Turkey, for example, meets its energy demand at the dominant rate from foreign sources. Turkey petroleum and other liquid consumptions, productions, and net import data between the year 2005 and 2014 are given in **Figure 1** [5].

The buildings are considered as the most dominant contributor to the world energy consumption. In order to reduce dependence of countries on fossil fuels, the biggest step to take is undoubtedly possible by renewable energy sources or energy conservation. Here, we focused on reducing the energy consumption by applying expanded perlite-based heat insulation panels to the buildings. Superior properties such as low thermal conductivity coefficient, low density, non-flammability, and high sound absorption capability of expanded perlite give the potential to be a good insulation panel.

 Actually, there are a number of studies which aim to obtain expanded perlite heat insulation panels with low thermal conductivity. For example, Uluer et al. [6] experimentally investigated to obtain the expanded perlite-based heat insulation panel with the lowest thermal conductivity at different rate binders. The authors reported that the thermal conductivity values of heat insulation panels decreased depending on the decreasing of binder ratios in the mixture. However, a decrease on the binder ratio has negatively influenced the strength of the panels. In a related study, the strength values were not given: however, the lowest thermal conductivity value was obtained as 43.5 W/m K under the same curing conditions [6]. Tian et al. [7] investigated the curing conditions to obtain the most compressive strength with the low thermal conductivity values from expanded perlite material. It is reported that it reached the maximum compressive strength with the value of 0.38 MPa at 105°C [7]. In another important issue for heat insulation panels, Papadopoulos emphasized that insulation panels must have fire resistance [8]. Actually, expanded perlite gives a positive result for heat insulation because it has A1 degree at fire resistance and provides the composite mortar better fire resistance [9]. Durmuş and Çelik [10] mixed concrete, fly ash, and expanded perlite aggregate in certain proportions, and obtained results indicated that the mixed concrete retains its void space for high temperature owing to the presence of the expanded perlite

*Effects of Alkali Activator and High Curing Temperature on Thermal Properties of Expanded… DOI: http://dx.doi.org/ 10.5772/intechopen.87836* 

**Figure 1***.* 

*The consumption, production, and net import amount of Turkey petroleum and other liquids [2].* 

 aggregate. As the density of expanded perlite is very low compared to other building materials (cement, aggregate, etc.), it plays a key role on decreasing the dead load on the structures and improving the thermal properties of the manufactured material [9, 11]. For example, Sun and Wang [12] used paraffin and expanded perlite to improve the thermal and mechanical properties of the cement mortars. Cement, paraffin, and expanded perlite were directly mixed, and the mechanical and thermal properties of the mixture were experimentally investigated. The authors added paraffin and expanded perlite up to 65% of the total composition in the experiments. The results show that as the ratio of paraffin and expanded perlite increased in the mortar, mechanical properties decreased, while thermal properties improved. They determined that the optimum paraffin/expanded perlite addition was 20% of the total composition, and the thermal conductivity value was obtained as 0.52 W/m K [12]. In another similar topic, Sengül et al. [13] experimentally examined the changes in thermal conductivity values and mechanical properties of lightweight concrete containing expanded perlite aggregate. In the related study, expanded perlite aggregates with different densities were used instead of natural aggregates, and it was observed that depending on the increase of the expanded perlite in the mixture, the compressive strength and the modulus of elasticity increased. In the experiments, expanded perlite aggregates were used instead of natural aggregate. As a consequence, thermal conductivity value was decreased from 0.6 W/m.K to 0.13 W/m.K adding expanded perlite aggregates at 80% of the total composition [13]. As is known, the concrete shows structural deterioration after it reached 300°C. On the other hand, the expanded perlite can resist 870°C without structural deterioration [9]. This is one of the most desired properties for thermal insulation materials.

Because of the low thermal conductivity coefficient of heat insulation panels, it is very difficult to dissipate the temperature completely and homogenously inside of cured materials during the curing process. Therefore, a number of researchers have tended to investigate the curing conditions, curing methods, curing temperature, curing time, etc. Unlike curing at conventional ovens, Durmuş et al. [14] cured the expanded perlite-based heat insulation panels by CO2 (carbon dioxide) method, and the authors claimed that CO2 curing is a method that has low cost and is a shorttime process. In another study, Skubic et al. [15] cured the expanded perlite-based heat insulation panels in the microwave, and the authors emphasized that more homogeneous panels could be obtained in the microwave.

In addition to low thermal conductivity, expanded perlite is a good sound absorber material, and this property of expanded perlite has a big importance for using it in the outer walls of the buildings. Argunhan et al. added the expanded perlite vol. by 10, 20, 30, 40, 50, and 60% to cement mixtures and examined the heat and sound insulation

properties of the obtained concrete. According to the results of experimental studies, it was observed that the strength and density of the concrete obtained by using expanded perlite decreased, while the heat and sound insulation properties developed highly. As a result of the related study, the thermal conductivity value of the samples decreased by 75%, and the ultrasound transition rate decreased by 35% [16].

In this paper, we experimentally aimed to evaluate the thermal conductivity values and compressive strength values for the expanded perlite-based heat insulation panels that were manufactured at different NaOH concentrations (6, 8, 10, and 12 M) and cured at different temperatures.

#### **2. Materials**

#### **2.1 Expanded perlite**

The expanded perlite aggregate was provided by Genper Company, in Kütahya, Turkey. The chemical and physical properties of expanded perlite, used in this study, were shown in **Tables 2** and **3**, respectively. The sieve analysis of expanded perlite aggregate is seen in **Figure 2**.

#### **2.2 Alkali activator**

Sodium silicate and sodium hydroxide were firstly used to prepare the alkali activator, and then the prepared alkali activator was blended with expanded perlite in order to bind. Physical and chemical properties of sodium silicate and sodium hydroxide were given in **Tables 4** and **5**.

#### **2.3 Mold**

 The mold was made of wood material. The mold dimension detail and schematic view were given in **Figure 3**. The mold cavity is 300 × 300 × 50 mm. This cavity was fully filled with expanded perlite mortar.


**Table 2***.* 

*Chemical composition of expanded perlite (data was obtained from the supplier).* 


#### **Table 3***.*

*Pysical properties of expanded perlite aggregate (data was obtained from the supplier).* 

*Effects of Alkali Activator and High Curing Temperature on Thermal Properties of Expanded… DOI: http://dx.doi.org/ 10.5772/intechopen.87836* 

#### **Figure 2***.*

*Sieve analysis of expanded perlite*.


#### **Table 4***.*

*Technical properties of sodium silicate with two moduli*.


#### **Table 5***.*

*Technical properties of sodium hidroxide*.

**Figure 3***. Dimension details and schematic view of panel mold.* 

### **3. Methods**

The flow charts of this study were briefly given in **Figure 4**.

#### **3.1 Preparation of alkali activator**

 Sodium silicate and sodium hydroxide were used as alkali activator to bind the expanded perlite particles. Sodium hydroxide (NaOH) was used with different molarities between 6 and 12 M, and sodium silicate (Na2SiO3) was used with two moduli. In order to prepare alkali activator used in the mixture, the sodium hydroxide solution was first added. Then, sodium silicate was added to sodium hydroxide at the rate of 1% volume of expanded perlite. Then, the mechanical mixer was stirred at 400 rpm for 10 min in order to obtain a homogeneous mixture.

#### **3.2 Preparation of mortar**

For each molarity, three samples were prepared. In order to prepare the mortar, 6 L of expanded perlite was added for each sample. Then, alkali activator mixture was added to expanded perlite. While preparing the mortar, the mixture was stirred by hand for 20 min without causing damage to the expanded perlite particles. After the preparation of the mortar mixture was completed, the sample was allowed to rest for 1 h under room conditions.

#### **3.3 Molding**

The mortar was poured into 300 × 300 × 50 mm molds in three sections. A total of 4.5 L of the mixture was added to the mold for each sample. The molded sample is shown in **Figure 5**. After the sample was filled in the molds, the sample was subjected to 1000 N force. The manufactured heat insulation sample was held throughout 3 min at a constant press force with1000 N.

**Figure 4***. A brief flow chart mechanism of the study.* 

*Effects of Alkali Activator and High Curing Temperature on Thermal Properties of Expanded… DOI: http://dx.doi.org/ 10.5772/intechopen.87836* 

#### **Figure 5***. The molded mortar*.


#### **Table 6***.*

*Technical specification of thermal conductivity measuring device.* 

**Figure 6.**  *HFM300 thermal conductivity measuring device.* 

#### **3.4 Curing**

 The molded sample was placed in a drying oven. Then, prepared mortars were cured at 60°C throughout 24 h. After that, the panels were held at 300, 400, and 500°C in an oven for 3 h. Afterwards, the cured sample was allowed to cool at room temperature (25°C) for 3 h.

#### **3.5 Measurement of thermal conductivity coefficient**

 The thermal conductivity values of manufactured heat insulation samples were measured by the aid of HFM 300 device. The technical specification of the thermal conductivity testing device was given in **Table 6**. In addition, the sample cured and placed in the HFM 300 device is shown in **Figure 6**.

#### **4. Results and discussion**

 At the beginning of experimental studies, expanded perlite was supplied from Genper Company in Kütahya, Turkey. The samples were prepared from different NaOH molarities to obtain optimum alkali activator solution. Also, the samples were cured at different temperatures to obtain optimum curing condition. First of all, the average thermal conductivity of the samples which were cured at 60°C was determined. The results were shown in **Figure 7**.

 As **Figure 7** is examined, the lowest thermal conductivity value of panels was obtained as 46.38 mW/m K manufactured with 6 M NaOH. On the other hand, the highest thermal conductivity value of panels was obtained as 59.43 mW/m K manufactured with 12 M NaOH. In addition, the percentage change of the thermal conductivity values of the panels depending on the curing temperature is shown in **Figure 8**.

 When **Figure 8** is examined, thermal conductivities of panels changed with curing temperature. The lowest thermal conductivity value of panels was obtained as 44.37 mW/m K prepared with 6 M NaOH and cured at 500°C. On the other hand, the highest thermal conductivity value of panels was obtained as 52.36 mW/m K prepared with 12 M NaOH and cured at 300°C. And also, mass loss of panels was determined. With the increase of the curing temperature, the mass loss of the panels changed. The determined mass losses which belong to the panels were shown in **Figure 9**.

 As **Figure 9** is examined, the lowest mass loss of panels was obtained as 258.657 g prepared with 6 M NaOH and cured at 300°C. The highest mass loss of panels was obtained as 434g prepared with 12 M NaOH and cured at 500°C. The graphs indicated the relationship between mass loss and thermal conductivity value. Based on the experimental data obtained in this study, the decrease on thermal conductivity value is directly related to mass loss, i.e., the panels, which have low density and have also low thermal conductivity value as well.

**Figure 7***.* 

*Thermal conductivity values of the samples depending on the changes of concentration.* 

*Effects of Alkali Activator and High Curing Temperature on Thermal Properties of Expanded… DOI: http://dx.doi.org/ 10.5772/intechopen.87836* 

**Figure 8***.* 

*Percentage differences of thermal conductivities compared with the first panel cured at 60°C*.

**Figure 9***. Mass loss of panels by temperature changes.* 

#### **5. Conclusions**

This study investigated the effect of alkali activator and curing conditions on thermal properties of expanded perlite-based thermal insulation panel. The following conclusions are drawn based on the given outputs in the study:


increasing temperature, the temperature affected the thermal properties positively. Moreover, thermal conductivity depends on temperature and mass loss directly. On the other hand, the thermal cracks were obtained, and the panels were negatively influenced for higher temperature degree of more than 300°C. In order to obtain the lowest thermal conductivity, 6 M NaOH and 500°C curing temperature should be used.


### **Acknowledgements**

This study was supported by the Scientific and Technological Research Council of Turkey (Project no.: 115 M041). We are indebted to TÜBİTAK for its financial support.

### **Author details**

Gökhan Durmuş 1 \*, Damla Nur Çelik1 and Ümit Ağbulut<sup>2</sup>

1 Department of Civil Engineering, Gazi University, Ankara, Turkey

2 Department of Mechanical and Manufacturing Engineering, Düzce University, Düzce, Turkey

\*Address all correspondence to: gdurmus@gazi.edu.tr

© 2019 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, provided the original work is properly cited.

*Effects of Alkali Activator and High Curing Temperature on Thermal Properties of Expanded… DOI: http://dx.doi.org/ 10.5772/intechopen.87836* 

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#### **Chapter 19**
