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CONTENTS
Volume 10, Number 1, July 2020
 

Abstract
This study intends to produce an ultra-high performance fibre reinforced concrete (UHPFRC) made with hybrid fibres (i.e., steel and polypropylene). Compressive and tensile strength characteristics of the hybrid fibres UHPFRC are considered. A total of 14 fibre-reinforced composites (FRCs) with different fibre contents or types of fibres were prepared and tested in order to determine a suitable hybrid fibre combination. The compressive and tensile strengths of each concrete at 7 days were determined. The results showed that a hybrid mix of micro-polypropylene and steel fibres exhibited good compromising performances and is the ideal reinforcement mixture in a strong, cost-effective UHPFRC. In addition, maximum compressive strength of 167 MPa was achieved for UHPFRC using 1.5% steel fibres blended with 0.5% macro-polypropylene fibres.

Key Words
ultra-high performance fibre reinforced concrete; steel fibre; polypropylene fibre; hybrid fibres; compressive strength; tensile strength

Address
Peem Nuaklong, Jithaporn Chittanurak, Pitcha Jongvivatsakul, Withit Pansuk: Innovative Construction Materials Research Unit, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University,
254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand
Akhrawat Lenwari: Composite Structures Research Unit, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand
Suched Likitlersuang: Centre of Excellence in Geotechnical and Geoenvironmental Engineering, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand

Abstract
Steel corrosion in embedded steel causes a significant durability problems and this usually propagates to structural degradation. Large-scaled concrete structures, PSC (Pre-stressed Concrete) or RC (Reinforced Concrete) structures, are usually constructed with mass concrete and require quite a long construction period. When they are located near to sea shore, chloride ion penetrates into concrete through direct or indirect exposure to marine environment, and this leads durability problems. Even if the structures are sheltered from chloride ingress outside after construction, the chloride contents which have been penetrated into concrete during the long construction period are differently evaluated from the initially mixed chloride content. In the study, chloride profiles in cores extracted from anchorage concrete block in two large-scaled suspension bridge (K and P structure) are evaluated considering the exposure periods and conditions. Total 21 cores in tendon room and chamber room were obtained, and the acid-soluble chlorides and compressive strength were evaluated for the structures containing construction period around 3 years. The test results like diffusion coefficient and surface chloride content from the construction joint and cracked area were also discussed with the considerations for maintenance.

Key Words
anchorage block; construction stage; concrete core; strength; apparent diffusion coefficient; surface chloride content

Address
In-Hwan Yang: Department of Civil Engineering, Kunsan National University, 558 Daehak-ro, Kunsan, Jeonbuk, 54150, South Korea
Yong-Sik Yoon, Seung-Jun Kwon: Department of Civil and Environmental Engineering, Hannam University, 70 Hannam-ro, Daedeok-gu, Daejeon, 34430, South Korea

Abstract
Precast deck joints have larger crack width than cast-in-place concrete decks. The initial crack typically occurs at the maximum moment but cracks on precast joints are significant and lead to failure of the deck. The present crack equation is applied to cast-in-place decks, and requires correction to calculate the crack width of precast deck joints. This research aims to study the crack width correction equation of precast decks by performing static tests using high strength and normal strength concrete. Based on experimental results, the bending strength of the structural connections of the current precast deck is satisfied. However it is not suitable to calculate and control the crack width of precast loop connections using the current design equation. A crack width calculation equation is proposed for crack control of precast deck loop joints. Also included in this paper are recommendations to improve the crack control of loop connections.

Key Words
loop joint; crack width; precast deck; high strength concrete; static test

Address
Changsu Shim and Chidong Lee: Department of Civil Engineering, College of Engineering, Chung-Ang University,
84 Heukseok-ro, Dongjak-gu, Seoul 156-756, Republic of Korea

Abstract
This paper deals with a comparative study among three different rehabilitation techniques, namely, (i) carbon fibre reinforced polymer (CFRP), (ii) glass fibre reinforced polymer (GFRP) and (iii) ferrocement on the flexural strengthening of reinforced cement concrete (RCC) beams. As these different techniques have to be compared on a level playing field, tensile coupon tests have been carried out initially for GFRP, CFRP and ferrocement and the number of layers required in each of these composites in terms of the tensile strength. It was found that for the selected constituents of the composites, one layer of CFRP was equivalent to three layers of GFRP and five layers of wiremesh reinforcement in ferrocement. Rehabilitation of RCC beams using these equivalent laminates shows that all the three composites performed in a similar way and are comparable. The parameters selected in this study were (i) the strengthening material and (ii) the level of pre-distress induced to the beams prior to the rehabilitation. It was noticed that, as the levels of pre-distress decreases, the percentage attainment of flexural capacity and flexural stiffness of the rehabilitated beams increases for all the three selected composites used for rehabilitation. Load-deflection behavior, failure modes, energy absorption capacity, displacement ductility and curvature ductility were compared among these composites and at different distress levels for each composite. The results indicate that ferrocement showed a better performance in terms of ductility than other FRPs, and between the FRPs, GFRP exhibited a better ductility than the CFRP counterpart.

Key Words
ferrocement; CFRP; GFRP; flexural strengthening; rehabilitation

Address
N. Ganesan, P. Bindurani and P.V. Indira: Department of Civil Engineering, National Institute of Technology Calicut, Kozhikode, Kerala, 673601, India

Abstract
Precast concrete elements in accelerated bridge construction (ABC) extends from superstructure to substructure, precast pile foundation has proven a benefit for regions with fragile ecological environment and adverse geological condition. There is still a lack of knowledge of the seismic behavior and performance of the precast pile foundation. In this study, a 1/8 scaled model of precast pile foundation with elevated cap is fabricated for quasi-static test. The failure mechanism and responses of the precast pile-soil interaction system are analyzed. It is shown that damage occurs primarily in precast pile-soil interaction system and the bridge pier keeps elastic state because of its relatively large cross-section designed for railways. The vulnerable part of the precast pile with elevated cap is located at the embedded section, but no plastic hinge forms along the pile depth under cyclic loading. Hysteretic curves show no significant strength degradation but obvious stiffness degradation throughout the loading process. The energy dissipation capacity of the precast pile-soil interaction system is discussed by using index of the equivalent viscous damping ratio. It can be found that the energy dissipation capacity decreases with the increase of loading displacement due to the unyielding pile reinforcements and potential pile uplift. It is expected to promote the use of precast pile foundation in accelerated bridge construction (ABC) of railways designed in seismic regions.

Key Words
railway bridge construction; precast concrete pile foundation; elevated pile cap; quasi-static test; seismic performance

Address
Xiyin Zhang, Xingchong Chen, Yi Wang, Mingbo Ding, Jinhua Lu and Huajun Ma: School of Civil Engineering, Lanzhou Jiaotong University, 88 Anning West Road, Lanzhou, Gansu, 730070, China

Abstract
This paper looks into how the shape of headed bars may influence the durability of reinforced concrete structures. Nowadays the only heads used in site works are cylindrical in shape. An alternative shape of head is studied in this piece of work. The new head reduces the concentration of stresses and so the appearance of cracks. In this work durability is studied based on both, first cracking and failure mode. An experimental campaign of 12 specimens and finite element modelling are described. The specimens were subjected to an accelerated corrosion process using an electrical current supply. Direct current was impressed on the specimens until breaking. Test results and the results obtained from numerical models are presented. Results are presented in term of comparison between the two shapes of heads studied. It was shown that the shape of the head has a significant influence on durability of reinforced concrete structures with headed reinforcing bars.

Key Words
headed bars; shape of the heads; durability; anchorage

Address
M. Jose Martinez-Echeverria, Jose Rodriguez Montero: Department of Construction Engineering and Engineering Projects, University of Granada (UGR), Campus Universitario de Fuentenueva s/n, 18072 Granada, Spain
Luisa Maria Gil-Martin, Enrique Hernandez-Montes: Department of Structural Mechanics, University of Granada (UGR). Campus Universitario de Fuentenueva s/n. 18072 Granada, Spain

Abstract
Ultra-high-performance concrete (UHPC) is recognized as a promising material in future civil engineering projects due to its outstanding mechanical and durability properties. However, the lack of local UHPC materials and official standards, especially for prestressed UHPC structures, has limited the application of UHPC. In this research, a large-scale prestressed bridge girder composed of nonproprietary UHPC is produced and investigated. This work has two objectives to develop the mixing procedure required to create UHPC in large batches and to study the flexural behavior of the prestressed girder. The results demonstrate that a sizeable batch of UHPC can be produced by using a conventional concrete mixing system at any precast factory. In addition, incorporating local aggregates and using conventional mixing systems enables regional widespread use. The flexural behavior of a girder made by this UHPC is investigated including flexural strength, cracking pattern and development, load-deflection curve, and strain and neutral axis behaviors through a comprehensive bending test. The experimental data is similar to the theoretical results from analytical methods based on several standards and recommendations of UHPC design.

Key Words
local UHPC; prestressed girder; flexural behavior; large-scale testing; bridge

Address
Hoa D. Pham, Tung Khuc, Hung V. Cu, Danh B. Le and Thanh P. Trinh: Department of Bridges and Highways Engineering, National University of Civil Engineering, Vietnam
Tuan V. Nguyen: Department of Building Materials, National University of Civil Engineering 55 Giai Phong road, Hai Ba Trung district, Hanoi, Vietnam

Abstract
Flexural and splitting strength behavior of conventional concrete can significantly be improved by incorporating the fibers in it. A significant number of research studies have been conducted on various types of fibers and their influence on the tensile capacity of concrete. However, as an important property, tensile capacity of fiber reinforced concrete (FRC) is not modelled properly. Therefore, this paper intends to formulate a model based on experiments that show the relationship between the fiber properties such as the aspect ratio (length/diameter), fiber content, compressive strength, flexural strength and splitting strength of FRC. For the purpose of modeling, various FRC mixes only with steel fiber are adopted from the existing research papers. Automated neural network search (ANS) is then developed and used to investigate the effect of input parameters such as fiber content, aspect ratio and compressive strength to the output parameters of flexural and splitting strength of FRC. It is found that the ANS model can be used to predict the flexural and splitting strength of FRC in a sensible precision.

Key Words
fiber aspect ratio; fiber content; compressive strength; flexural strength; splitting strength, FRC; ANS

Address
Zhenhao Zhang: School of Civil Engineering, Changsha University of Science and Technology, 960 2nd Section of Wanjiali South Road, Changsha, Hunan, China
Suvash C. Paul: Civil Engineering, School of Engineering, Monash University Malaysia, Jalan Lagoon Selatan, 47500 Bandar Sunway, Selangor Darul Ehsan, Malaysia
Biranchi Panda: Singapore Centre for 3D Printing, School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore
Yuhao Huang: Intelligent Manufacturing Key Laboratory of Ministry of Education, Shantou University, 243 Daxue Road, Jinping District, Shantou City, Guangdong Province, China
Ankit Garg: Department of Civil and Environmental Engineering, Shantou University, 243 Daxue Road, Jinping District, Shantou City, Guangdong Province, China
Yi Zhang: Leibniz Universität Hannover, 1 Welfengarten, Hannover, Germany
Akhil Garg: Intelligent Manufacturing Key Laboratory of Ministry of Education, Shantou University, 243 Daxue Road, Jinping District, Shantou City, Guangdong Province, China
Wengang Zhang: School of Civil and Architectural Engineering, Shandong University of Technology, 266 Xincun West Road, Zhangdian District, Zibo City, Shandong Province, China


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