Optimization of Fiber Aspect Ratio in Strain-Hardening Geopolymer Composites

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 (Jb/ 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.

About the author

Nemkumar Banthia, University Killam Professor and Canada Research Chair, University of British Columbia, Vancouver, BC, Canada

Nemkumar (Nemy) Banthia is a University Killam Professor, Distinguished University Scholar and Canada Research Chair at The University of British Columbia. His primary area of research is in Sustainable Concrete Infrastructure with emphasis on nano-modified fiber reinforced composites, 3D printing, ultra-high performance concrete materials, waste recycling, fracture analysis, earthquake strengthening and sensor based structural health monitoring. He also serves as the Founding CEO and Scientific Director of India-Canada Centre for Innovative Multidisciplinary Partnerships to Accelerate Community Transformation and Sustainability (IC-IMPACTS)—a Research Centre of Excellence with over 50 participating universities, 100 collaborating companies and 260 faculty members receiving research support.

A mentor to many, Dr. Banthia has graduated over 75 doctoral and post-doctoral students. He holds 9 patents, has published over 475 refereed papers, and has edited 20 volumes. He serves on the Editorial Boards of nine international journals and is the Editor-in-Chief of the J. of Cement and Concrete Composites— a journal with a 2022 Impact Factor of 10.5. This is currently the Journal with the second highest Impact Factor in the field.

His awards include the Wason Medal of American Concrete Institute, Solutions Through Research Award of the BC Innovation Council, Wolfson Merit Award of the Royal Society of the UK, Killam Research Prize from the Killam Foundation, Horst Leipholz Medal of the Canadian Society for Civil Engineering, Mufti Medal of Excellence of the International Society for Health Monitoring of Infrastructure, Leadership in Science and Technology Award of the Drishti Foundation, Industry Marvel Award of the Darpan Society and Global Citizenship Award of alumni-UBC. In 2018, Visvesvaraya National Institute of Technology recognized him with Excellence in Technology and Innovation Award. In 2020, IIT-Delhi recognized him with a Distinguished Alumni Award for Contributions to Teaching and Research. More recently, in March 2022, Dr. Banthia received the Jacob Biely Faculty Research Prize which is regarded as UBC’s premier award for research across all disciplines. More recently, Dr. Banthia received the Dean’s Medal of Distinction from the Faculty of Applied Science, UBC. In January 2023, UBC appointed Dr. Banthia as the University Killam Professor, which is the highest honor UBC can confer on a member of its faculty. In its 110 year history, UBC has appointed only 23 University Killam Professors.

Dr. Banthia is a fellow of the American Concrete Institute, Canadian Society for Civil Engineering, Indian Concrete Institute, Canadian Academy of Engineering (CAE), Indian National Academy of Engineering (INAE), and the Royal Society of Canada. He is one of Top 25 ‘Most Cited in the field of Construction & Building Materials’ as per Platinum H- Index. His Google Scholar Citations exceed 21,000 with an  h-index of 79.

About the author

Seung-kyun Lee earned his M.S. Architectural Engineering from Hanyang University in Seoul. His main research areas include the development of cement-free high-performance geopolymer concrete, performance improvement through fiber coating, and performance improvement of geopolymer concrete using nanomaterials.

His total number of citations is 95 and h-index is 6 (Scopus).

About the author

Taekgeun Oh is an Ph.D. student of Architecture and Architectural Engineering at Yonsei University in Seoul, Korea. He earned his B.S. degree in Department of Civil and environmental engineering from Gachon University in Seungnam and M.S. degrees in the Architectural Engineering from Hanyang University in Seoul, South Korea. His research interests include the development of fiber treatment technology of fiber in construction materials, development of ultra-high-performance concrete and strain hardening cementitious composites using various nanomaterials, and chemical behavior of cement-based matrix. His most recent major interest is development cementless eco-friendly ultra-high-performance concrete without the use of cement.

His total number of citations is 316 and h-index is 10 (Scopus). Over the 5 years, he has published 34 peer-reviewed international journal papers and 3 domestic patents in the fields of construction materials and structures. He has received two awards: Silver Award, Design competition for Civil Infrastructures (Korean Society of Civil Engineers, South Korea) and Best Student Presentation Award, Materials Section (Korea Concrete Institute, South Korea).

About the author

Doo-Yeol Yoo is an Associate Professor of Architecture and Architectural Engineering at Yonsei University in Seoul, Korea. He earned his B.S. and Ph.D. degrees in the Department of Civil, Environmental, and Architectural Engineering from Korea University in Seoul, South Korea. He also served as a post-doctoral researcher at the University of British Columbia (UBC), BC, Canada. His research interests include the development of cementless eco-friendly ultra-high-performance concrete, performance enhancement through novel fiber developments, and the achievement of ultra-high ductility in cement-based composites with a strain capacity exceeding 10%.

His total number of citations is 9,398 and h-index is 54 (Scopus). Over the past decade, he has published 225 peer-reviewed international journal papers and 1 book chapter and holds 8 domestic patents in the fields of construction materials and structures. He holds 5 highly cited papers (WoS) and his 13 published papers in journals of Elsevier have been selected as one to the topmost cited and downloaded papers. He serves on the editorial board of six international journals, including Cement and Concrete Composites with an impact factor of 10.5. He is ranked #66 in the world and #1 in Korea in the field of Building & Construction in terms of c-score (Elsevier). He has received several prestigious awards: World’s Top 2% Scientists 2022, 2023 (Stanford University-Elsevier); Member of Young Korean Academy of Science and Technology; The 25th Young Scientist Award (Ministry of Science and ICT, Korea); HYU Young Researcher Awards (Hanyang University); Best Paper Award, Int. J. Concr. Struct. Mater. (Springer); Ministry’s Commendation (Ministry of Education, Korea).

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.

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