Investigation of the Effect of Different Temperatures on the Mechanical Strength of Industrial Heat-Treated Wood in Terms of Sustainability

*Şemsettin Kılınçarslan, Bilgin İçel and Yasemin Şimşek* 

#### **Abstract**

 Wood material has been used as a sustainable building material for many years. Wood material has many positive properties, but it also has negative features (dimensional changes and biodegradability) that limit its usable area. Various wood modification methods have been developed to minimize these negative features. One of the most important features of wood materials is that the wooden columns and beams do not collapse immediately with increasing temperature (i.e., beginning of fire). The mechanical stability of the heat-treated material with the increase of the temperature constitutes the basis of this study. In this study the effect of different temperatures on the mechanical stability of Iroko wood (heat-treated wood and unheat-treated wood) was investigated. All test samples are exposed to 105, 120, 140, and 160°C temperature for 3, 6, and 9 hours. As a result, heat treatment of the wood material increased the resistance of the material to the temperatures, and the service life of these materials is prolonged. Thus, the resistance against environmental effects of wood materials increased, and the importance of nature is emphasized by using natural materials in sustainable standards.

**Keywords:** modulus of elasticity, heat-treated wood, unheat-treated wood, temperature, dMOE

#### **1. Introduction**

 The concept of sustainability is one of the debated subjects of recent years in our world, where environmental degradations are increasing. The issue of sustainability lies at the heart of the triangle of energy loss, economical power, and environmental consciousness. Therefore, sustainability subject is discussed in a very broad area ranging from social sciences, natural sciences, policy, to local and international environmental organizations [1–3].

Wood as a building material has been used since ancient times [4]. Today, wood material is used in many areas because of its many positive features [5]. Wood material has many positive features but also has negative features. The most important of these negative features is the effect of dimensional changes by environmental influences

 and degradations due to the effects of various tree pests (insects and fungi). In order to prevent the occurrence of this negativity in the wood material, it is a widely used modification method for the penetration of various chemical materials into the wood [6–8]. Wood is less affected by external factors with chemical modifying methods, but it has many negative features such as toxic substances and the need for repetition. These negative features required the development of alternative modification methods for the protection of wood, a nature-friendly and sustainable resource [7]. At the present time, ThermoWood method is one of the most widely used modification methods [9–11]. ThermoWood method was developed in Finland [12]. Looking at the ThermoWood Handbook, heat treatment (ThermoWood) stages takes place in three steps. The steps are warming up, drying, and cooling-conditioning [13].

 The physical, mechanical, and chemical features of wood materials may vary depending on various influences. One of these factors is temperature. One of the most important and interesting knowledge about a wooden beam is that it does not collapse quickly with increasing temperature (i.e., beginning of fire). The lack of scientific information on the mechanical stability of heat-treated wood with increasing temperatures is the main driven force of the study. The aim of this study was to investigate the effect of different temperatures on the heat-treated and unheat-treated Iroko wood. In this study, dynamic modulus of elasticity (dMOE) changes of the Iroko wood (heat-treated, unheat-treated) in the temperature effect were investigated.

For this purpose, heat-treated (HT) and unheat-treated (UT) samples were used in the study. The samples were subjected to ultrasonic wave test after exposure to a temperature of 105, 120, 140, and 160°C, and the modulus of elasticity values of the samples was determined.

#### **2. Material and methods**

 Iroko (*Chlorophora excelsa*) wood (heat-treated and unheat-treated samples) was used in this study. Heat-treated and unheat-treated wood were taken from the forest products firm. Samples were subjected to heat treatment at 190°C for 120 minutes during the main heat treatment period for ThermoWood process in the company. Heat-treated and unheat-treated samples were prepared in 20 × 20 × 60 mm dimensions for ultrasonic wave test. Heat-treated and unheat-treated samples used in this study are given in **Figure 1**.

**Figure 1.**  *Samples that are used in the study. (a) Heat-treated (HT) and (b) unheat-treated (UT) samples.* 

*Investigation of the Effect of Different Temperatures on the Mechanical Strength of Industrial… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

 All test samples (heat-treated, unheat-treated) are acclimatized approximately 6–10 weeks at a stable temperature of 20 ± 2°C and 65% RH conditions. At the end of this period, the density and the MOE of the samples were determined. Densities of heat-treated and unheat-treated samples were determined according to TS 2472 [14]. TS 2472 [14] was calculated densities of the samples using stereometric method which is based on measurements of volume and mass of the sample. Values of MOE were determined by EPOCH 650 device. Kılınçarslan et al. [15] reported that the values of dMOE can be determined using ultrasonic wave method. The EPOCH 650 is an ultrasonic wave method and it is set according to EN 12668-1 [16]. This device was obtained from the Forest Faculty Laboratory of Isparta Applied Sciences University. For determination of sound velocities, 2.25 MHz contact longitudinal transducers were used. Time-of-flight (ToF) values used for calculation of ultrasonic wave velocities were calculated according to EN12668-1. Then, values of dMOE are calculated using Eq. (1):

$$E\_{\rm dyn} = p \times V^2 \times 10^{-6} \tag{1}$$

 where *Edyn* is dynamic elasticity modulus (MPa), *p* is density (kg/m3 ), and *V* is ultrasonic wave velocity (m/s).

 Densities and dynamic modulus of elasticity values were determined before the samples entered the oven. Later, ultrasonic wave test samples are exposed to 105, 120, 140, and 160°C temperature for 3, 6, and 9 hours (**Figure 2**).

 After the samples were subjected to temperature, they were removed from the oven and wrapped with aluminum foil so as not to be affected by the weather conditions. Densities and modulus of elasticity values of the samples wrapped with aluminum foil and the modulus of elasticity were quickly determined (**Figure 3**).

In the study, modulus of elasticity and density values of samples (heat-treated wood and unheat-treated wood) are determined before entering the oven and after entering the oven. The change in the modulus of elasticity of the heat-treated material compared to the unheat-treated samples was investigated depending on different temperatures.

**Figure 2.**  *The test equipment. (a) Oven. (b) HT and UT samples inside the oven.* 

**Figure 3.**  *Samples wrapped with aluminum foil and ready for measure.* 

#### **3. Results and discussion**

Ultrasonic wave test samples are exposed to 105, 120, 140, and 160°C temperature for 3, 6, and 9 hours. A drying oven that operates in an atmospheric environment was used for temperature treatment. It was determined that the density values decreased in both groups (HT and UT) when the temperature and duration increased (**Figure 4**).

Ünsal et al. [17] examined the effects of thermal treatment on the color and physical and mechanical properties of *Eucalyptus* samples. They determined that heat-treated *Eucalyptus* samples were compared with unheat-treated samples in terms of swelling, hardness, kiln dry weight, and color change. As a result, as the heat treatment temperature and duration increased, the colors were darkened, and the decrease in density values and decrease in hardness were determined. Hill [18] reported that loss of weight is one of the most undesirable properties during the heat treatment of wood material. The weight loss formed due to the heating of the wood and the decrease in the density due to this loss vary depending on the type of wood used, the treatment environment, the treatment method, the temperature, and the time applied. Weight loss at low temperatures is less than high temperatures. Hill [18] stated that the reason for this is that free water and volatile compounds are away from the wood. Gündüz et al. [19] studied the compressive

**Figure 4.**  *Graphic of density-duration for HT and UT samples.* 

*Investigation of the Effect of Different Temperatures on the Mechanical Strength of Industrial… DOI: http://dx.doi.org/10.5772/intechopen.87836* 


**Table 1.** 

*MOE and density values of HT and UT samples for 3-, 6-, and 9-hour duration.* 

strength and hardness results of heat-treated beech wood at different temperatures and different durations. They stated that the compressive strength and hardness values of the wood increased with the increase of the heat treatment temperature and duration. They reported that the maximum density loss occurred at the highest temperature and time.

 Akyıldız et al. [20], Boonstra et al. [21], and Sehlstedt-Persson [22] reported that the density of the HT sample is lower than the UT samples. As seen in **Figure 4**, the density of the HT sample is lower than the UT samples in this study. However, it was determined that the heat-treated samples were less affected than the unheat-treated samples from temperature.

 Modulus of elasticity values was determined by ultrasonic wave test. **Table 1**  shows the dynamic modulus of elasticity (dMOE) changes depending on the temperature and duration.

 Parallel results were also obtained to literature in this study. When the values of MOE varying depending on the temperature are examined in both groups, it has been determined that the modulus of elasticity values decreases with temperature increase. Korkut [23] investigated the effect of heat treatment on some mechanical properties (compressive strength, flexural strength, modulus of elasticity, Janka hardness, and tensile strength) of the Uludağ fir (*A. bornmuellerinana*). At the end of his research, it has been determined that heat treatment decreases the mechanical properties of wood statistically significantly. Korkut et al. [24] reported that the reasons for this decrease in strength values are the weight loss and the loss of hemicellulose due to heat treatment. They stated that the reduction in strength values is not important, and especially good processing properties and stability can be utilized in the areas where stability is important. It was determined that the change of the MOE values in the HT samples is less than the UT samples (**Figure 5**).

 When the rate of decrease in the modulus of elasticity is taken into account, it is determined that the HT samples are less affected by the temperature than the UT samples. It was determined that the modulus of elasticity was increased from 105 to 160°. In addition, the maximum change was determined to be 160° in 9 hours and the minimum change was 105° in 3 hours. *Pyrus elaeagrifolia* Pall. wood were heat treated at two different temperatures (160, 180°C) and three different times (2, 4, and 6 hours), and Karakaş [25] examined the changes in physical and mechanical properties of these samples. The results showed an improvement in physical properties and loss of mechanical properties. The sixth hour showed

**Figure 5.**  *Graphic of difference of dMOE for HT and UT samples.* 

*Investigation of the Effect of Different Temperatures on the Mechanical Strength of Industrial… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

#### **Figure 6.**

*Comparison of dynamic modulus of elasticity-density values for before-oven.* 

**Figure 7.** 

*Comparison of dynamic modulus of elasticity-density values for after-oven.* 

that the decrease in mechanical properties was higher than the second and fourth hours. **Figures 6** and **7** have represented a comparison between dynamic modulus of elasticity and density values.

There are reasonable and strong relation between dynamic modulus of elasticity and density values. Correlation values of 0.993 and 0.8614 were obtained for before-oven and after-oven, respectively.

#### **4. Conclusion**

In this study, heat-treated and unheat-treated samples were subjected to an ultrasonic wave test after exposure to a temperature of 105, 120, 140, and 160°C, and the MOE values of samples were detected. When the data obtained in the study were evaluated:

 • Density values of the HT Iroko samples were lower than the UT samples. As the temperature and time increased, the density values decreased in both groups (heat-treated and unheat-treated samples).


 Water-resistant building materials are materials that consume little energy during their service life and do not harm the environment and people. Wood material, which is a sustainable and renewable material, has many field uses. However, the material is limited due to some negative effects (i.e., water, biological pests). Therefore, many researchers have been focused on eco-friendly wood modification methods. Nowadays, heat-treated materials are used to protect from these negative features. One of the most important and interesting knowledge about a wooden beam is that it does not collapse quickly with increasing temperature (i.e., beginning of fire). Failure to demolish the material for a long time when exposed to this high temperature will prevent loss of life and property. As seen in the study, the change in the modulus of elasticity of the heat-treated material is less than in unheat-treated material depending on the temperature. In addition, this material has a higher resistance to biological pests. Therefore, it can be considered as a sustainable building material in terms of being a longer-lasting and more environmentally friendly material.

#### **Acknowledgements**

This study was supported by Suleyman Demirel University Scientific Research Projects. The authors would like to thank SDU-BAP for their support.

*Investigation of the Effect of Different Temperatures on the Mechanical Strength of Industrial… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

### **Author details**

Şemsettin Kılınçarslan1 \*, Bilgin İçel2 and Yasemin Şimşek1

1 Department of Civil Engineering, Süleyman Demirel University, Isparta, Turkey

2 Department of Materials and Material Processing Tech, Çanakkale Onsekiz Mart University, Çanakkale, Turkey

\*Address all correspondence to: semsettinkilincarslan@sdu.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.

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**191**

**Chapter 15**

**Abstract**

regression model

**1. Introduction**

Experimental Investigation

of 12 Molar Concentration

the Compressive Strength of

*Solomon Oyebisi, Anthony Ede and Festus Olutoge*

This study investigates the influence of the total concentration of all dissolved salts

)

 

of activators on the compressive strength of geopolymer concrete (GPC). Sodium silicate (Na2SiO3) and six various samples of sodium hydroxide (NaOH) pellets were used as activators. The eco-friendly waste products which are ground-granulated blast-furnace slag (GGBFS) and corncob ash (CCA) were used as binding agents. The study also adopted Grade 40 MPa concrete as a design mix proportion. The activators were prepared to obtain 12 molar concentration, while the salinities were measured with the aid of JENWAY 4510 conductivity metre. The concrete constituents were cast and cured under the ambient conditions, and its compressive strengths were determined at days 7, 28, 56, and 90 of curing. Regression models were also developed using Minitab 17. The experimental investigation indicates that compressive strength increases as the activators' salinity increases. The coefficients of determinations (R2

show that the models are 97.10, 96.80, 98.10 and 96.20% sufficiently fit to forecast the correlation between the activators' salinities and the compressive strength of geopolymer concrete at days 7, 28, 56, and 90, respectively. This developed model equations can be used to develop new methods for strength applications that can enhance the

One of the important factors which affect the strength of geopolymer concrete (GPC) is the activators' salinity. Various researches have been carried out on the mechanical property of geopolymer concrete, but the influence of activators' salinity on the compressive strength is still limited. The alkaline activators are from soluble alkali metals particularly sodium (Na) and potassium (K), and they are formed from the combinations of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) or potassium hydroxide (KOH) and potassium silicate (K2SiO3). The combination of sodium hydroxide and sodium silicate solutions are the most alkaline liquids used

**Keywords:** salinity, sodium hydroxide, sodium silicate, compressive strength,

short-term mechanical properties of geopolymer concrete.

of Activators' Salinity on

Geopolymer Concrete

#### **Chapter 15**
