**Table 1.**

*The chemical composition and physical properties of metakaolin compared with ASTM C618-2017.* 

#### *Sustainable Metakaolin-Based Geopolymer Concrete with Waste Plastic Aggregate DOI: http://dx.doi.org/10.5772/intechopen.87836*

 cleaner bottles, etc. Firstly, the waste plastic was cleaned and then crushed and shredded into small flaky particles like chips using plastic scrap grinder machine. Finally, the particles of waste plastic were graded by sieve shaker to comply with the grading of natural coarse aggregate. The shape and physical properties of waste plastic (WPL) aggregate are given in **Table 2** and **Figure 1**, respectively. A superplasticizer (Conplast SP2000) and extra tap water were used to get the applicable workability and improve the mixing process.

#### **2.2 Mixing proportions**

 In this study, many trial mixes were prepared to determine the highest compressive strength for MK-GPC, which was selected as reference mix, at the age of 7 days. For all mixes, the ratio of alkaline activator solution to binder was 0.65, while the dosage of superplasticizer and extra water was fixed at 2 and 10% by weight of binder, respectively. To understand the effect of using waste plastic in MK-GC, four mixtures with waste plastic contents of 0, 10, 20, and 30% as partial volumetric replacement for the natural coarse aggregate were produced and denoted as 0% WPL, 10% WPL, 20% WPL, and 30% WPL, respectively. **Table 3** summarizes the mixing proportions of different MK-GPC mixtures.

#### **2.3 Mixing and casting procedure**

 The procedure of producing the geopolymer concrete is very important; thus, the processes of mixing, casting, and curing were kept constant for all mixtures. All aggregates were prepared to be in saturated surface dry (SSD) condition. Firstly, the coarse, fine, and WPL aggregates were mixed together with the metakaolin (MK) for 2 minutes in an electrical rotating tilting mixer. Then, half the amount of alkali solution was added gradually to the dry mixture to be blended together for 3–4 minutes, while the remaining alkaline solution, superplasticizer, and extra water were mixed manually for about 1 minute and poured into the mixer. The mixing process


### **Table 2.**

*WPL aggregate physical properties.* 

**Figure 1.**  *Shredded waste plastic aggregate.* 


*Sustainable Metakaolin-Based Geopolymer Concrete with Waste Plastic Aggregate DOI: http://dx.doi.org/10.5772/intechopen.87836* 

#### **Table 3.**

*Mix proportions for all MK-GPC mixtures.* 

continued for 7–8 minutes, including 1-minute rest to clean the blades. The homogenous fresh MK-GPC was discharged from the mixer and casted as layers into the required cast iron molds. Each layer was tamped 30 times with a standard steel rod and then followed by 30 seconds on the vibration table.

#### **2.4 Curing method**

The ideal curing regime with respect to period of time and temperature plays a vital role in developing strength and behavior of the geopolymer concrete [20]; thus, many trials on curing process were done to produce a high-compressivestrength MK-GPC, using sustainable curing method. In the current experimental study, immediately after casting, the molds were covered with plastic sheet to prevent water loss due to evaporation and left in ambient condition for 24 hours. Then, the molds were opened and the specimens were sealed with thick plastic bags. All specimens were placed in an electrical oven at 60°C for 4–5 hours, followed by exposure to sunlight in the summer season at 35–49°C until the test time. The previous study [5] had optimized the curing system of MK-GPC in 32–48°C under the sunlight to gain 28.53 MPa 7-day compressive strength. Another study [6] used


**Table 4.**  *Details of testing methods.* 

 the curing regime for MK-GPC in an electrical oven at 45 ± 5°C for 72 hours to attain 22.70 MPa 7-day compressive strength. The adapted curing method in this research had presented a combination of the efficiency and the sustainability to produce the MK-GPC with a high compressive strength (40.93 MPa for 7 days), providing a wide range of civil engineering applications.

#### **2.5 Test methods**

**Table 4** outlines the type of the experimental tests and the geometry of specimens; also it reports the specifications which are required to recognize the characteristics of all MK-GPC mixtures. For each experimental test, the results of the three specimens at 7 and 28 days were used to calculate the final result.

#### **3. Results and discussions**

#### **3.1 Fresh density**

**Figure 2** shows the influence of incorporating the WPL aggregate on the fresh density of all MK-GPC mixes. It can be seen that the fresh density decreases with the increase of WPL aggregate amount. The fresh density of the reference mix (0% WPL) drops from 2360 to 2147 kg/m3 for the mix with 30% WPL. This behavior is attributed to the lower density and specific gravity of WPL aggregate compared with that for natural coarse aggregate [8].

#### **3.2 Dry density**

The dry density values of MK-GPC with different WPL aggregate contents at 7 and 28 days are shown in **Figure 3**. Generally, the continuity of geopolymerization process has improved and made the microstructure more dense; thus, the dry density of all mixes increased with time. Also, for a specific age, as the replacement dosage of WPL aggregate increased, a reduction in dry density occurred. At the 28th day, the dry density of reference mix (0% WPL aggregate) declined from 2206 kg/m3 to 2153, 2115, and 1981 kg/m3 for WPL aggregate replacement at the dosage of 10, 20, and 30%, respectively. This reduction in dry density is due to

**Figure 2.**  *Fresh density of MK-GPC with different WPL aggregate contents.* 

*Sustainable Metakaolin-Based Geopolymer Concrete with Waste Plastic Aggregate DOI: http://dx.doi.org/10.5772/intechopen.87836* 

**Figure 3.**  *Dry density of MK-GPC with different WPL aggregate contents.* 

the lower density of WPL aggregate (about 71%) than natural coarse aggregate [8, 11, 16]. Also, more pores in matrix would be formed due to the elongated and flaky shape of WPL particles which can attribute to this decrement [8].

#### **3.3 Compressive strength**

 The effect of different WPL aggregate contents on compressive strength of MK-GPC at 7 and 28 days is presented in **Figure 4**. The results show that, regardless of the WPL aggregate content, the compressive strength of all geopolymer specimens tends to increase with time because the geopolymerization process development increases the density of the microstructure. As expected, the compressive strength of MK-GPC decreases gradually with the increase of the WPL aggregate substitution level. It is observed that the 44.03 MPa compressive strength of the reference mix decreases by 14.08, 31.11, and 35.27% for the specimens containing 10, 20, and 30% WPL aggregate on the 28th day, respectively. This reduction is similar to that of normal concrete which incorporated the recycled plastic waste as coarse aggregate. The main reasons that cause this decline are the lower strength and stiffness of WPL aggregate than that of natural aggregate, weakness of the

**Figure 4.**  *Compressive strength of MK-GPC with different WPL aggregate contents.* 

bond strength between the surface of WPL aggregate and geopolymer paste, and the generation of more pores in the concrete microstructure due to shape and size of waste plastic aggregate [8, 11, 16].

#### **3.4 Splitting tensile strength**

 **Figure 5** shows the variation of the splitting tensile strength with various percentages of WPL aggregate. For all mixes, the splitting tensile strength increases with time; for reference mix the results are 1.76 MPa at 7 days and 2.55 MPa on the 28th day. As in the compressive strength, the splitting strength decreases with the increase in the quantity of WPL aggregate. Compared with the control mix, the reduction in the splitting tensile strength for specimens 10% WPL, 20% WPL, and 30% WPL are 31, 35, and 53%, respectively. This could be attributed to the difference in shape, stiffness, and roughness of aggregates, since the WPL aggregate has plane and flaky shape with smooth surface, different from gravel, which is angular and stiff [8, 16].

#### **3.5 Flexural strength**

 The values of the flexural strength for all MK-GPC mixtures at 7 and 28 days are illustrated in **Figure 6**. As in the cases of compression and splitting strengths, the replacement of natural aggregate with WPL aggregate has negative impacts on the flexural strength of geopolymer concrete. For the mixes 10, 20, and 30% WPL, the flexural strength drops at 7.57, 18.2, and 25.75%, respectively, with respect to the 0% WPL mix. Similar to the explication of the reduction in compressive and splitting tensile strengths, the low strength of waste plastic particles and weak adherence between the surface of WPL aggregate and geopolymer paste cause this deterioration in flexural strength [8, 11].

#### **3.6 Ultrasonic pulse velocity (UPV)**

In order to evaluate the uniformity and structure of MK-GPC containing WPL aggregate, the ultrasonic pulse velocity test was conducted for all mixes at 7 and 28 days, and the results are shown in **Figure 7**. It can be observed that for all specimens, the UPV values increase intensively with time since the microstructure is

**Figure 5.**  *Splitting tensile strength of MK-GPC with different WPL aggregate contents.* 

*Sustainable Metakaolin-Based Geopolymer Concrete with Waste Plastic Aggregate DOI: http://dx.doi.org/10.5772/intechopen.87836* 

#### **Figure 6.**

*Flexural strength of MK-GPC with different WPL aggregate contents.* 

**Figure 7.**  *Ultrasonic pulse velocity of MK-GPC with different WPL aggregate contents.* 

enhanced by geopolymerization activity. Nevertheless, the incorporating of WPL aggregate by 10, 20, and 30% decreases the UPV results from 4.368 km/sec for 0% WPL specimens to be 4.156, 3.739, and 3.711 km/sec, respectively. The performance of UPV in geopolymer concrete containing waste plastic particles is the same as that which was found in previous studies for normal concrete. When using waste plastic as aggregate in normal concrete, the air voids, pores, and heterogeneity of the matrix will increase, so the transmitting pulse velocity decreases [8, 11].

#### **3.7 Microstructural analysis by scanning electronic microscopy (SEM)**

To investigate and reveal the effect of WPL aggregate incorporation on the MK-GPC microstructural feature, the mixes 0 and 30% WPL were tested, and the typical microstructural aspect of both mixes is shown in **Figures 8** and **9**, respectively. As it can be seen in **Figure 8**, the SEM micrographs of 0% WPL mix indicate more dense and homogenous geopolymer paste, associated with fewer small pores and microcracks, thus the interfacial transition zone (ITZ) characteristics.

#### **Figure 8.**

*SEM micrographs of MK-GPC without WPL aggregate (reference mix).* 

**Figure 9.**  *SEM micrographs of MK-GPC with 30% WPL content.* 

The micrographs of 30% WPL mix illustrate a nonhomogeneous microstructure with many large pores, multi-microcracks, and less compacted geopolymer paste, which are related to the irregular and flaky shape of WPL particles that caused a random distribution of waste plastic particles in the matrix. On the other hand, due to the smooth surface of WPL aggregate, a large gap as well as poor bond between the WPL particle and geopolymer paste has been observed at the interfacial transition zone. This explains the reasons behind the drawbacks of the mechanical strengths of the MK-GPC which contains WPL aggregate and enhances the results obtained in this research.

#### **4. Conclusion**

Based on the assessment of the physical and mechanical properties of MK-GPC containing waste plastic, the most important findings can be summarized as follows:

• There is a reduction in fresh and dry density of MK-GPC as the content of WPL aggregate increases. Although all MK-GPC produced in this investigation are not classified as lightweight concrete, the reduction in density has provided appropriate solution for applications where self-weight represents a problem.


### **Author details**

Wasan I. Khalil, Qais J. Frayyeh and Mahmood F. Ahmed\* Civil Engineering Department, University of Technology, Baghdad, Iraq

\*Address all correspondence to: mahmodmfa81@gmail.com

© 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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**179**

**Chapter 14**

**Abstract**

temperature, dMOE

**1. Introduction**

environmental organizations [1–3].

Sustainability

Investigation of the Effect of

Different Temperatures on the

Heat-Treated Wood in Terms of

*Şemsettin Kılınçarslan, Bilgin İçel and Yasemin Şimşek*

Mechanical Strength of Industrial

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,

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

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

#### **Chapter 14**
