Mechanical and Microstructural Properties of Rubberized Geopolymer Concrete.

What is it about?

The construction industry is increasingly focused on sustainability, with a particular emphasis on reducing the environmental impact of cement production. One approach to this problem is to use recycled materials and explore eco-friendly raw materials, such as alumino-silicate by-products like fly ash, which can be used as raw materials for geopolymer concrete. To enhance the ductility, failure mode, and toughness of the geopolymer, researchers have added crumb rubber processed from scrap tires as partial replacement to fine aggregate of the geopolymer. Therefore, this study aims to develop rubberized geopolymer concrete (RGC) by partially replacing the fine aggregate with crumb rubber (CR). To optimize the mechanical properties of RGC, response surface methodology (RSM) has been used to develop 13 mixes with different levels and proportions of CR (10–30% partial replacement of fine aggregate by volume) and sodium hydroxide molarity (10–14 M) as input variables. The results showed that the strength properties increased as the molarity of NaOH increased, while the opposite trend was observed with CR. The maximum values for compressive strength, flexural strength, and uniaxial tensile strength were found to be 25 MPa, 3.1 MPa, and 0.41 MPa, respectively. Response surface models of the mechanical strengths, which were validated using ANOVA with high R2 values of 72–99%, have been developed. It has been found that using 10% CR with 14 M sodium hydroxide resulting in the best mechanical properties for RGC, which was validated with experimental tests. The result of the multi-objective optimization indicated that the optimum addition level for NaOH is 14 M, and the fine aggregate replacement level with CR is 10% in order to achieve a rubberized geopolymer suitable for structural applications

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Why is it important?

Ordinary Portland cement (OPC) is extensively utilized as a building material globally and is a major source of CO2 emissions. The cement industry accounts for approximately 7% of the total CO2 emissions worldwide, making it one of the largest anthropogenic greenhouse gas sources [1]. The production of OPC has been identified as a significant contributor to CO2 emissions since it requires high-temperature kilns to heat the raw materials, such as limestone, clay, and shale to a temperature of around 1450 °C [2]. This process emits approximately 50% of CO2 emissions due to the decomposition of limestone, with 40% arising from the combustion of fossil fuels, and 10% originating from transportation and electricity usage [3]. There are several alternatives to Ordinary Portland cement (OPC) that are being developed and used in the construction industry. Some of the most promising alternatives, include Portland limestone cement, Portland pozzolana cement, geopolymer concrete, calcium sulfo aluminate cement and magnesium oxide cement. These alternatives have shown potential in reducing the environmental impact of cement production, and their adoption can contribute to the transition towards a more sustainable and low-carbon construction industry [4,5]. Geopolymer concrete is a type of concrete that is made using industrial waste materials such as fly ash, ground granulated blast furnace slag, silica fume, and metakaolin, in combination with alkaline activators. Unlike traditional Portland cement-based concrete, geopolymer concrete does not require the use of limestone or high-temperature kilns, resulting in significantly lower carbon emissions [6]. The geo polymerization process involves a rapid chemical reaction in an alkaline environment, which leads to the formation of a three-dimensional polymer structure and a ring framework made up of Si-O-Al-O bonds [7]. Geopolymer concrete has superior performance compared to traditional Portland cement-based concrete, with advantages including reduced carbon footprint, improved durability, less creep and shrinkage, better fire resistance, and higher strength

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