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Significance
High-strength strain-hardening geopolymer composites (SHGCs) are advanced materials in the field of civil engineering and materials science. They exhibit unique properties that differentiate them from traditional concrete. For instance, unlike ordinary Portland cement-based concrete, these composites are made using geopolymers which are inorganic polymers formed by the reaction of aluminosilicate materials, such as fly ash or slag, with alkaline solutions. This composition results in a more environmentally friendly material, as it often uses industrial by-products and reduces CO2 emissions. These composites have the benefit of exhibiting high compressive and tensile strengths. This is achieved through the chemical composition and the microstructure of the material, which is denser and more uniform than traditional concrete. Additionally, SHGCs can undergo significant plastic deformation beyond its initial yield point without failing. In practical terms, it means that these composites can bear more load and undergo larger deformations before failing, enhancing their durability and safety in structural applications. They also show excellent resistance to various forms of degradation such as corrosion, heat, and chemical attack. SHGCs composites are ideal for use in infrastructure where high strength, durability, and environmental sustainability are priorities. This includes bridges, high-rise buildings, and other critical structures. In a new study published in Journal of Cement and Concrete Composites by graduate student Seung Kyun Lee from Hanyang University and PhD candidate Taekgeun Oh from Yonsei University together with Professor Nemkumar Banthia from the University of British Columbia and Associate Professor Doo-Yeol Yoo from Yonsei University, the researchers in the study conducted detailed experiments to optimize the fiber aspect ratio for 90 MPa SHGC with a tensile strain capacity over 7.5%.
The new study involved high-strength SHGCs containing 2% polyethylene (PE) fibers by volume. The matrix was composed of liquid crystal display glass powder and ground granulated blast furnace slag, aiming for a compressive strength of over 100 MPa. The authors tested five different types of PE fibers, with aspect ratios ranging from 300 to 900 to determine the optimal aspect ratio for enhancing tensile performance. The team found that PE fibers with higher aspect ratios were more effective in improving the tensile performance of SHGC. A robust strain-hardening characteristic with saturated micro-crack patterns was observed when the fiber aspect ratio exceeded 600. The best tensile performance was achieved with a fiber aspect ratio of 900, demonstrating a tensile strength of 5.73 MPa, strain capacity of 7.58%, and strain energy density of 309.6 kJ/m³. According to the authors, the average bond strength of PE fibers in the geopolymer matrix was around 1.55 MPa, similar to high-strength cement matrices. They also found that energy-based pseudo strain-hardening index (J‘b/ Jtip) increased with the fiber aspect ratio, reaching 104.3 at an aspect ratio of 900. The new study also included a detailed analysis of crack patterns and used scanning electron microscopy to examine the fiber surfaces after tensile tests. They observed severe deformations on the fibers’ surfaces, indicating intense interaction between the fibers and the matrix during the strain-hardening process. Importantly, the study contributes to sustainable construction practices by developing a composite material that does not contain cement, thereby reducing carbon emissions.
In conclusion, the authors successfully identified an optimal fiber aspect ratio that enhances the tensile strength and strain capacity of SHGCs. These findings demonstrate the potential of engineered composites in revolutionizing the construction industry, offering a sustainable, high-performance alternative to traditional materials.
Reference
Seung Kyun Lee, Taekgeun Oh, Nemkumar Banthia, Doo-Yeol Yoo, Optimization of fiber aspect ratio for 90 MPa strain-hardening geopolymer composites (SHGC) with a tensile strain capacity over 7.5%. Cement and Concrete Composites, Volume 139, 2023, 105055.