University of Qom Civil Infrastructure Researches 2783-140X 11 2 2025 12 22 Enhancing the Flexural Characteristics of Stabilized Kaolinite Clay by Reinforcing with Composite Fiber Enhancing the Flexural Characteristics of Stabilized Kaolinite Clay by Reinforcing with Composite Fiber 141 157 3852 10.22091/cer.2025.13895.1652 FA Mahmood Reza Abdi Faculty of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran. 0000-0002-3473-9677 Elham Abbasi Faculty of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran. 0009-0007-2549-9679 Mahdi Safdari Seh Gonbad Faculty of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran. 0000-0003-0612-535X Journal Article 2025 09 16 In this research, a new type of fiber known as composite fibers has been utilized to enhance the flexural properties of stabilized clay. The core of the composite fiber consists of elastane, while its shell is composed of numerous polyester fibers. In this regard, kaolinite clay, lime at weight contents of 1, 3, and 5%, and composite fibers at weight contents of 1.5, 2.5, and 3.5%, with lengths of 6 and 12 mm, have been employed for sample preparation, along with curing periods of 7 and 28 days. For quantitative and qualitative investigations, three-point bending tests, as well as optical and scanning electron microscopy, have been employed. The results indicated that the reinforcement of stabilized kaolinite with composite fibers led to improvements of 10 to 78% in flexural strength and a factor 3.1 to 41.5 in the corresponding strain. The findings also demonstrated that the performance of composite fibers in enhancing the strength and ductility of stabilized kaolinite is directly related to the content and length of the fibers, the lime content, and the curing time. Furthermore, quantitative evaluations revealed that the dual structure of the composite fibers, particularly the polyester shell wrapped around the elastane core, created suitable mechanical interaction with the soil due to their high number and perpendicular orientation to the tensile direction, effectively strengthening resistance against pull-out forces. In this research, a new type of fiber known as composite fibers has been utilized to enhance the flexural properties of stabilized clay. The core of the composite fiber consists of elastane, while its shell is composed of numerous polyester fibers. In this regard, kaolinite clay, lime at weight contents of 1, 3, and 5%, and composite fibers at weight contents of 1.5, 2.5, and 3.5%, with lengths of 6 and 12 mm, have been employed for sample preparation, along with curing periods of 7 and 28 days. For quantitative and qualitative investigations, three-point bending tests, as well as optical and scanning electron microscopy, have been employed. The results indicated that the reinforcement of stabilized kaolinite with composite fibers led to improvements of 10 to 78% in flexural strength and a factor 3.1 to 41.5 in the corresponding strain. The findings also demonstrated that the performance of composite fibers in enhancing the strength and ductility of stabilized kaolinite is directly related to the content and length of the fibers, the lime content, and the curing time. Furthermore, quantitative evaluations revealed that the dual structure of the composite fibers, particularly the polyester shell wrapped around the elastane core, created suitable mechanical interaction with the soil due to their high number and perpendicular orientation to the tensile direction, effectively strengthening resistance against pull-out forces. https://cer.qom.ac.ir/article_3852_b5a00ca39ec4757aea29d0b83deb08f3.pdf