Effect of graded fibers on stress strain behaviour of Glass Fiber Reinforced Concrete in tension Hanuma Kasagani ⇑ , C.B.K Rao Department of Civil Engineering, National Institute of Technology, Warangal, India highlights  Mixing of fibers of different lengths (Graded fibers) improves workability and strain hardening.  Graded fibers influenced stress-strain behaviour of GFRC.  Fiber efficiency characteristics were quantified to investigate their effect on the tensile strength of GFRC.  Strength, deformation and energy absorption capacity is higher for GGFRC than MGFRC. article info Article history: Received 21 April 2018 Received in revised form 19 June 2018 Accepted 22 June 2018 Keywords: GFRC Fiber Efficiency Fiber distribution Fiber orientation abstract Effective blending of short length and long length fibers in concrete is termed as Graded fiber reinforced concrete. Earlier research shows that short length fibers primarily control the propagation of micro cracks, and improve the ultimate strength whereas, long length fibers arrest the macro cracks and improve the post crack deformation of concrete. Thus different combinations of short and long length fibers would help in arresting the micro and as well as macro cracks to improve both pre and post crack performances of concrete. An attempt has been made to study the effect of addition of Graded Glass Fibers with different fiber length and volume fraction in Glass Fiber Reinforced Concrete. The experimen- tal work was carried out under uni-axial tension for M30 grade of concrete with the 0.1%, 0.2%, 0.3%, 0.4% & 0.50% fiber volume of Mono Glass Fibers (3 mm, 6 mm, 12 mm and 20 mm length fiber). In 0.3% fiber volume, different fiber volume combination of Glass fibers in Short Graded form (3 mm + 6 mm length fiber), combination of Glass fibers in Long Graded form (12 mm + 20 mm length fiber) and combination of Short Graded + Long Graded fibers to form Combined Graded fibers (3 mm + 6 mm + 12 mm + 20 mm length fiber) were studied. The results shows that the strength, deformation capacity and energy absorp- tion capacity is higher for Graded Glass Fiber Reinforced concrete than Mono Glass Fiber Reinforced Concrete. Graded fibers improved the workability. Fiber efficiency characteristics (Fiber length, Fiber dis- persion, fiber orientation) were quantified to investigate their effect on the tensile strength of Glass Fiber Reinforced Concrete (GFRC). For this purpose, optical microscopic study and an image analysis technique is used to examine the failed specimens of GFRC. The results of image analysis shows that the strength of fiber reinforced composite are dependent on the fiber efficiency characteristics. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction The most important advantage of addition of fibers in concrete is increase of tensile strength and enhancement of energy absorp- tion capacity [1–3]. When the structure is loaded, the micro cracks open up and propagate which may lead to inelastic deformation in concrete [4,5]. Micro or short randomly dispersed fibers in concrete help to resist the opening of micro cracks and enhance the pre crack strength [6]. Moreover, the small fibers dispersed and distributed randomly in concrete help to bridge the internal micro cracks thus improve concrete properties in all directions [7,8]. Higher the volume of fibers, higher will be the strength and toughness of the composite. However addition of higher volume of fibers leads to practical problems such as bundling, balling and reduction in workability, hence, researchers have observed reduc- tion in strength and toughness [9,10]. In a given volume, shorter the length of fiber, closer will be the spacing of fibers and will be as near as possible to the micro cracks. These fibers may initially contribute to delay in formation cracks but may be pulled out after micro cracks transformed into macro cracks. Then long length https://doi.org/10.1016/j.conbuildmat.2018.06.193 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Civil Engineering, National Institute of Technology, Warangal 506 004, India. E-mail address: hanudurga@gmail.com (H. Kasagani). Construction and Building Materials 183 (2018) 592–604 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat