Research Article Tensile Behavior and Cracking Pattern of an Ultra-High Performance Mortar Reinforced by Polyethylene Fiber Jeong-Il Choi, 1 Seung Yup Jang, 2 Seung-Jun Kwon, 3 and Bang Yeon Lee 1 1 School of Architecture, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, Republic of Korea 2 Korea Railroad Research Institute, Cheoldobangmulgwan-ro 176, Uiwang, Gyeonggi-do 16105, Republic of Korea 3 Department of Civil Engineering, Hannam University, Daejeon 34430, Republic of Korea Correspondence should be addressed to Bang Yeon Lee; bylee@jnu.ac.kr Received 13 April 2017; Revised 14 June 2017; Accepted 2 July 2017; Published 2 August 2017 Academic Editor: Enzo Martinelli Copyright © 2017 Jeong-Il Choi et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis paper presents an experimental study of the compressive strength, tensile behavior (including the tensile strength, tensile strain capacity, and toughness), and cracking patterns of an ultra-high performance mortar (UHPM) reinforced by polyethylene (PE) fber as well as a discussion of the diferent tensile behaviors of the UHPM according to the types and contents of fbers used. Te UHPM reinforced by microsteel fber of 1.5 vol% and the UHPM reinforced by PE fbers with three diferent fber contents were designed and prepared. A series of experiments was undertaken to assess the efect of PE fber on the properties of the UHPM. Te results found a lower strength level, higher tensile strain capacity and toughness, and a larger crack width in the PE fber-reinforced UHPM compared to microsteel fber-reinforced UHPM. It was also demonstrated that tensile strain capacity and toughness of 4.05% and 0.454 MPa m/m, respectively, can be attained when using the proposed polyethylene-fber-reinforced UHPM. 1. Introduction Ultra-high performance concrete (UHPC) is considered to be one of the most promising and advanced construction materials because it has an ultra-high compressive strength exceeding 150 MPa, good self-compactibility without fber segregation due to its low yield stress and high plastic viscosity when optimizing each component, and the mix- ture proportion based on packing density theory [1–4]. Although UHPC ofers several advantages, it is also asso- ciated with some disadvantages, such as stringent quality control requirements, the possible corrosion of the steel fber, and occasionally the requirement of special curing conditions. In particular, its tensile ductility is comparable to that of high-ductile fber-reinforced composites (HDFRC). HDFRC usually show a high tensile ductility of over 2% [5–10]. On the other hand, the tensile ductility of UHPC is less than 1% [11–13]. Te main reason for the diference in the tensile ductility between UHPC and HDFRC can be attributed to the types of reinforcing fbers used. Straight microsteel fber with a tensile strength of up to 2,400 MPa and a circular cross-section is generally used as a reinforcing fber to ofset the brittle behavior of UHPC [13], whereas synthetic fbers such as polyvinyl alcohol (PVA) or polyethylene (PE) fbers are commonly used for HDFRC. Previous research has reported that synthetic fbers can also be applied to UHPC instead of steel fbers. Kamal et al. developed an ultra-high performance strain-hardening cementitious composite (UHP-SHCC) reinforced by PE fber with 1.5 vol% [14]. Te compressive strength, tensile strength, and tensile strain capacity of the UHP-SHCC at 14 days were 96 MPa, 10 MPa, and 2.8%, respectively. Ranade et al. also developed high-strength high-ductility concrete and reported that tensile ductility as high as 3.4% and a com- pressive strength of 160 MPa can be realized by incorporating 2 vol% of PE fber [15]. Kang et al. reported that the tensile behavior can be improved by combining steel fber and PE fber [12]. Hybrid fber-reinforced UHPC in which 33% of the steel fber was replaced with PE fber showed a higher tensile strength by 14% and a higher tensile strain capacity by 39% than single-type steel-fber-reinforced UHPC. Additionally, Hindawi Advances in Materials Science and Engineering Volume 2017, Article ID 5383982, 10 pages https://doi.org/10.1155/2017/5383982