Sustainable Building Materials

**165**

**Chapter 13**

**Abstract**

mechanical properties

**1. Introduction**

Plastic Aggregate

Sustainable Metakaolin-Based

Geopolymer Concrete with Waste

*Wasan I. Khalil, Qais J. Frayyeh and Mahmood F. Ahmed*

Nowadays, the sustainability in construction and building sector is a vital issue, and it takes priority worldwide. This study aims to produce sustainable geopolymer concrete by using metakaolin (MK) as a source binder and incorporating waste plastic (WPL) as coarse aggregate in it. To understand the effects of using WPL on the mechanical properties of metakaolin-based geopolymer concrete (MK-GPC), four mixtures have been prepared with 0, 10, 20, and 30% substitution by volume of natural coarse aggregate with mixed shredded WPL particles. The experimental investigation involves studying fresh and dry densities, mechanical properties, ultrasonic pulse velocity (UPV), and the microstructure feature. The results indicate that the MK-GPC mixes containing WPL particles have lower fresh and dry densities compared with the control mix. Also, all MK-GPC mixtures with WPL aggregate show a reduction in the mechanical properties and UPV results. In addition, the outcomes of SEM test reveal a porous structure for MK-GPC containing WPL particles. The evaluation of MK-GPC containing shredded WPL as coarse aggregate demonstrates the ability to produce more eco-friendly concrete with moderate strength, which can be used in wide area of civil engineering applications.

**Keywords:** sustainability, geopolymer concrete, metakaolin, waste plastic, aggregate,

The challenges associated with global warming, population growth, depletion of natural resources, and pollution by wastes have pushed to highlight the sustainability in construction and building sector as a universal priority issue. The utilization of the concrete as a construction material is ubiquitous throughout the world. Annually, the concrete production reaches 10 billion metric tons [1], which causes a significant environmental impact in relation to the use of ordinary portland cement (key ingredient) in concrete manufacturing, ingesting huge amounts of natural aggregate, and consumption of high energy and large amounts of raw materials. Worldwide, the portland cement industry emits up to 1.5 billion tons of CO2 per year [1], which contributes about 5–8% to greenhouse gas emission, and this number could jump up to 10–15% by 2020 [2]. Therefore, many efforts have been exerted to produce an eco-friendly alternative binder to portland cement; one of these innovative binders is "geopolymer" that is synthesized through activating

#### **Chapter 13**

## Sustainable Metakaolin-Based Geopolymer Concrete with Waste Plastic Aggregate

*Wasan I. Khalil, Qais J. Frayyeh and Mahmood F. Ahmed* 

#### **Abstract**

 Nowadays, the sustainability in construction and building sector is a vital issue, and it takes priority worldwide. This study aims to produce sustainable geopolymer concrete by using metakaolin (MK) as a source binder and incorporating waste plastic (WPL) as coarse aggregate in it. To understand the effects of using WPL on the mechanical properties of metakaolin-based geopolymer concrete (MK-GPC), four mixtures have been prepared with 0, 10, 20, and 30% substitution by volume of natural coarse aggregate with mixed shredded WPL particles. The experimental investigation involves studying fresh and dry densities, mechanical properties, ultrasonic pulse velocity (UPV), and the microstructure feature. The results indicate that the MK-GPC mixes containing WPL particles have lower fresh and dry densities compared with the control mix. Also, all MK-GPC mixtures with WPL aggregate show a reduction in the mechanical properties and UPV results. In addition, the outcomes of SEM test reveal a porous structure for MK-GPC containing WPL particles. The evaluation of MK-GPC containing shredded WPL as coarse aggregate demonstrates the ability to produce more eco-friendly concrete with moderate strength, which can be used in wide area of civil engineering applications.

**Keywords:** sustainability, geopolymer concrete, metakaolin, waste plastic, aggregate, mechanical properties

#### **1. Introduction**

The challenges associated with global warming, population growth, depletion of natural resources, and pollution by wastes have pushed to highlight the sustainability in construction and building sector as a universal priority issue. The utilization of the concrete as a construction material is ubiquitous throughout the world. Annually, the concrete production reaches 10 billion metric tons [1], which causes a significant environmental impact in relation to the use of ordinary portland cement (key ingredient) in concrete manufacturing, ingesting huge amounts of natural aggregate, and consumption of high energy and large amounts of raw materials. Worldwide, the portland cement industry emits up to 1.5 billion tons of CO2 per year [1], which contributes about 5–8% to greenhouse gas emission, and this number could jump up to 10–15% by 2020 [2]. Therefore, many efforts have been exerted to produce an eco-friendly alternative binder to portland cement; one of these innovative binders is "geopolymer" that is synthesized through activating

the aluminosilicate source materials like metakaolin, fly ash, and slag with alkaline solution (usually sodium hydroxide and sodium silicate) in a fast chemical reaction named geopolymerization process [3]. There are some studies that have investigated the properties of geopolymer concrete based on Iraqi metakaolin as the source material and the factors affecting its behavior [4–6]. Another research has also examined the effects of using metakaolin on the properties of fly ash-based geopolymer concrete containing recycled aggregate [7].

Furthermore, the excessive use of plastic products has led to the generation of million tons (Mt) of plastic waste around the world [8]. The global plastic consumption jumped from 313 (Mt) in 2014 to 322 (Mt) in 2015, and the number could reach to 485 (Mt) in 2030 [9, 10]. Most of this waste is usually disposed as landfill or dumped into the rivers or oceans. Due to the low biodegradability and persistence of waste plastic, associated with poor waste management [8], plastic waste pollution has become a vital environmental problem, which requires serious and sustainable solution. The utilization of the waste plastic in concrete as partial replacement for natural (fine or coarse) aggregate is beneficial not only for minimizing the environmental pollution but also for preserving the natural resources [9]. Although the notable studies [8–16] that have been carried out on the use of different types of waste plastic in normal concrete have reported the effects of these wastes on the concrete properties, still there is a missing information about using the waste plastic in geopolymer concrete. Therefore, the novel contribution of this research is to use the shredded waste plastic as partial replacement for natural coarse aggregate in the synthesis of metakaolin-based geopolymer concrete (MK-GPC). Accordingly, the objectives of this study are to investigate the physical, mechanical, and microstructural properties of MK-GPC specimens with different contents of WPL aggregate (0, 10, 20, and 30% by volume) as replacements for natural coarse aggregate and to show the feasibility of reusing the waste plastic in the production of superior ecofriendly geopolymer concrete toward the development of sustainable construction industry.

#### **2. Experimental works**

#### **2.1 Materials**

 Iraqi kaolin was burnt in furnace at 700°C for 2 hours to produce the metakaolin (MK) which was used in this study. **Table 1** shows the oxide composition obtained from X-ray fluorescence (XRF) analysis and physical properties of MK which comply with the requirements of ASTM C618-2017 [17] as a natural pozzolan Class N. For the purpose of preparing the activator solution, sodium silicate (Na2SiO3) containing 54% H2O, 32.5% SiO2, and 13.5% Na2O was mixed with sodium hydroxide (NaOH) solution at a ratio of 2:1 for all mixes. The NaOH solution with 14 molarity concentrations was achieved by dissolving the pellets from 98% pure NaOH in distilled water to minimize the influence of impurities. The final solution was left for 24 hours to be cooled at room temperature before using.

For all mixes, the coarse and fine aggregates fulfilled the requirements of the Iraqi specification No. 45/1984 [18]. The natural coarse aggregate was crushed with a particle size of 5–14 mm, dry-rodded density of 1595 kg/m3 , specific gravity of 2.61, and absorption of 1.3%, while the fine aggregate was natural sand zone 1 with fineness modulus of 3.3, dry-rodded density of 1787 kg/m3 , specific gravity of 2.58, and absorption of 1.6%. The waste plastics were a mixture of different plastic types, but most of them were high-density polyethylene (HDPE) which was obtained from vegetable boxes, garbage container, plastic jerrycan, shampoo and dishwasher

