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CONTENTS
Volume 21, Number 3, March 2018
 

Abstract
A strain-hardening highly ductile composite based on an alkali-activated slag binder and synthetic fibers is a promising construction material due to its excellent tensile behavior and owing to the ecofriendly characteristics of its binder. This study investigated the effect of different types of synthetic fibers and water-to-binder ratios on the compressive strength and tensile behavior of slag-based cementless composites. Alkali-activated slag was used as a binder and water-to-binder ratios of 0.35, 0.45, and 0.55 were considered. Three types of fibers, polypropylene fiber, polyethylene (PE) fiber, and polyparaphenylene-benzobisethiazole (PBO) fiber, were used as reinforcing fibers, and compression and uniaxial tension tests were performed. The test results showed that the PE fiber series composites exhibited superior tensile behavior in terms of the tensile strain capacity and crack patterns while PBO fiber series composites had high tensile strength levels and tight crack widths and spacing distances.

Key Words
alkali-activator; cementless composite; compressive strength; slag; synthetic fiber; tensile behavior

Address
Seung-Jun Kwon: Department of Civil Engineering, Hannam University, Daejeon 34430, Republic of Korea
Jeong-Il Choi, Huy Hoang Nguyen and Bang Yeon Lee: School of Architecture, Chonnam National University, Gwangju 61186, Republic of Korea


Abstract
This study developed and investigated a precast slab track system partially reinforced with glass fiber reinforced polymer (GFRP) rebars in the transverse direction, which mitigated the loss of track circuit current by reducing magnetic coupling between the rails and steel reinforcements. An electric analysis was conducted and the results of the analysis verified that the GFRP rebars mitigate the reduced current strength produced by electro-magnetic induction. In the study, a threedimensional finite element method and flexural experiments were used to study the mechanical behavior of the proposed slab track.

Key Words
slab track; concrete; track circuit current; magnetic coupling; glass fiber reinforced polymer (GFRP)

Address
Seung-Jung Lee, Chi-Hyung Ahn: Korea Railroad Research Institute, 176 Cheoldobangmulgwan-ro, Uiwang, Gyeonggi-do 16105, Republic of Korea
Do-Young Moon: Department of Civil Engineering, Kyungsung University, 309 Suyeong-ro, Nam-gu, Busan 48434, Republic of Korea
Jong-Woo Lee: Department of Railway Electrical & Signaling Engineering, Seoul National University of Science and Technology,232 Gongneung-ro, Nowon-gu, Seoul 01811, Republic of Korea
Goangseup Zi: School of Civil, Environmental & Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea

Abstract
The use of recycled aggregate in concrete is gaining much attention due to the growing need for sustainability in construction. In the present study, Self Compacting Concrete (SCC) is made using both natural and recycled aggregate (crushed recycled concrete aggregate from building demolished waste) and performance of recycled aggregate based SCC for the bond behaviour of reinforcement is evaluated. The major factors that influence the bond like concrete compressive strength (Mix-A, B and C), diameter of bar (Db=10, 12 and 16 mm) and embedment length of bar (Ld=2.5Db, 5Db and full depth of specimen) are the parameters considered in the present study in addition to type of aggregates (natural and recycled aggregates). The mix proportions of Natural Aggregate SCC (NASCC) are arrived based on the specifications of IS 10262. The mix proportions also satisfy the guidelines of EFNARC. In case of Recycled Aggregate SCC (RASCC), both the natural coarse and fine aggregates are replaced 100% by volume with that of recycled aggregates. These mixes are also evaluated for fresh properties as per EFNARC. The hardened properties like compressive strength, split tensile strength and flexural strength are also determined. The pull-out test is conducted as per the specifications of IS 2770 (Part-1) for determining the bond strength of reinforcement. Bond stress versus slip curves were plotted and a typical comparison of RASCC is made with NASCC. The fracture energy i.e., area under the bond stress slip curve is determined. With the use of recycled aggregates, reduction in maximum bond stress is noticed whereas, the normalised maximum bond stress is higher in case of recycled aggregates. Based on the experimental results, regression analysis is conducted and an equation is proposed to predict the maximum bond stress of RASCC. The equation is in good agreement with the experimental results. The available models in the literature are made use to predict the maximum bond stress and compare the present results.

Key Words
sustainable construction; recycled concrete aggregates; pull-out test; bond stress and slip

Address
Rakesh Siempu, Rathish Kumar Pancharathi: Department of Civil Engineering, National Institute of Technology, Warangal, India

Abstract
This paper discusses a study of cement mortar reinforced with Graphene Oxide (GO) flakes carried out at the University of Plymouth. Over 60 specimens were prepared and tested to obtain the tensile, compressive and flexural strengths of cement mortar with/without 0.5% GO flakes by weight of cement. The dispersion of the GO flakes and the effect of the use of polycarboxylate ether superplasticizer (0.2% by weight of cement) on the material strength are discussed. Images of the particle sizes of GO are presented from the transmission electron microscopy analysis. In addition, the images from the field emission scanning electron microscope analysis are also presented to show the difference of the microscopic structure of cement mortar with/without GO. The results of the strength tests are presented. It is shown that the inclusion of the GO flakes in general led to positive results, which suggest that GO improved the tensile, compressive and flexural strengths of cement mortar.

Key Words
Graphene Oxide flakes; mechanical properties; strength; cement mortar; microscopic structure

Address
Boksun Kim, Lawrence Taylor, Andrew Troy, Matthew McArthur and Monika Ptaszynska: School of Engineering, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK

Abstract
In this paper, two methods M1 and M2 to determine long-term deflection through finite element analyses including the effect of creep and relaxation are proposed and demonstrated for a PSC box-girder. In both the methods, the effect of creep is accounted by different models from international standards viz., ACI-209R-92, CEB MC 90-99, B3 and GL2000. In M1, prestress losses due to creep and relaxation and age adjusted effective modulus are estimated through different models and have been used in finite element (FE) analyses for individual time steps. In M2, effects of creep and relaxation are implemented through the features of FE program and the time dependent analyses are carried out in single step. Variations in time-dependent strains, prestress losses, stresses and deflections of the PSC box-girder bridge through M1 and M2 are studied. For the PSC girder camber obtained from both M1 and M2 are lesser than simple bending theory based calculations, this shows that the camber is overestimated by simple bending theory which may lead to non-conservative design. It is also observed that stresses obtained from FEM for bottom fibre are lesser than the stresses obtained from bending theory at transfer for the PSC girder which may lead to non-conservative estimates.

Key Words
finite element model; prestressed concrete bridge girder; creep; relaxation

Address
M.C. Lalanthi, P. Kamatchi, K. Balaji Rao and S. Saibabu: CSIR-Structural Engineering Research Centre, Chennai - 600 113, India

Abstract
Hydration heat and thermal induced cracking have always been a fatal problem for massive concrete structures. In order to study a massive reinforced concrete wall of a storage tank for liquefied natural gas (LNG) during its construction, two mock-ups of 0.8 mx0.8 mx0.8 m without and with metal corrugated pipes were designed based on the actual wall construction plan. Temperature distribution and strain development of both mock-ups were measured and compared inside and on the surface of them. Meanwhile, time-dependent thermal and mechanical properties of the concrete were tested standardly and introduced into the finite-element (FE) software with a proposed hydration degree model. According to the comparison results, the FE simulation of temperature field agreed well with the measured data. Besides, the maximum temperature rise was slightly higher and the shrinkage was generally larger in the mock-up without pipes, indicating that corrugated pipes could reduce concrete temperature and decrease shrinkage of surrounding concrete. In addition, the cooling rate decreased approximately linearly with the reduction of heat transfer coefficient h, implying that a target cooling curve can be achieved by calculating a desired coefficient h. Moreover, the maximum cooling rate did not necessarily decrease with the extension of demoulding time. It is better to remove the formwork at least after 116 hours after concrete casting, which promises lower risk of thermal cracking of early-age concrete.

Key Words
hydration degree; time-dependent thermal property; thermal analysis; finite-element simulation; LNG storage tank; reinforced concrete; strain monitoring

Address
Yan Geng, Xiongyan Li, Suduo Xue: College of Architecture and Civil Engineering, Beijing University of Technology,
No.100, Pingleyuan, Chaoyang District, Beijing 100124, China
Jinguang Li, Yanjie Song: Department of Civil Engineering, China Huanqiu Contracting & Engineering Co. Ltd.,
No.1, Chuangda 2nd Road, Chaoyang District, Beijing 100012, China

Abstract
In this study, the flexural fatigue performance of concrete beams made with 100% Coarse Recycled Concrete Aggregates (RCA) and 100% Coarse Natural Aggregates (NA) were statistically commanded. For this purpose, the experimental fatigue test results of earlier researcher were investigated using two parameter Weibull distribution. The shape and scale parameters of Weibull distribution function was evaluated using seven numerical methods namely, Graphical method (GM), Least-Squares (LS) regression of Y on X, Least-Squares (LS) regression of * on Y, Empherical Method of Lysen (EML), Mean Standard DeviationMethod (MSDM), Energy Pattern FactorMethod (EPFM) andMethod of Moments (MOM). The average of Weibull parameters was used to incorporate survival probability into stress (S)-fatigue life (N) relationships. Based on the Weibull theory, as single and double logarithm fatigue equations for RCA and NA under different survival probability were provided. The results revealed that, by considering 0.9 level survival probability, the theoretical stress level corresponding to a fatigue failure number equal to one million cycle, decreases by 8.77% (calculated using single-logarithm fatigue equation) and 6.62%(calculated using double logarithm fatigue equation) in RCAwhen compared to NAconcrete.

Key Words
fatigue; stress level; survival probability; Weibull parameters; regression; aggregates

Address
G. Murali, T. Indhumathi: School of Civil Engineering, Sastra University, Thanjavur, Tamil Nadu, India
K. Karthikeyan: SMBS, VIT University, Chennai, Tamil Nadu, India
V.R. Ramkumar: Division of Structural Engineering, Anna University, Chennai, India

Abstract
When reinforced concrete structures are subjected to strong seismic forces, their beam-column connections are very susceptible to be damaged during the earthquake event. Consequently, structural designers try to fit an important quantity of steel reinforcement inside the connection, complicating its construction without a clear justification for this. The aim of this work is to evaluate –and demonstrate- numerically how the quantity and the array of the internal steel reinforcement influences on the nonlinear response of the RC beam-column connection. For this, two specimens (extracted from an experimental test of 12 RC beam-column connections reported in literature) were modeled in the Finite Element code FEAP considering different stirrup\'s arrays. The nonlinear response of the RC beam-column connection is evaluated taking into account the nonlinear thermodynamic behavior of each component: a damage model is used for concrete; a classical plasticity model is adopted for steel reinforcement; the steel-concrete bonding is considered perfect without degradation. At the end, the experimental responses obtained in the tests are compared to the numerical results, as well as the distribution of shear stresses and damage inside the concrete core of the beam-column connection, which are analyzed for a low and high state of confinement.

Key Words
beam-column connection; reinforced concrete; nonlinear material behavior; finite element

Address
Norberto Dominguez, Jesus Perez-Mota: Seccion de Estudios de Posgrado e Investigación (SEPI) ESIA UZ, Instituto Politecnico Nacional of Mexico, Mexico

Abstract
This study used a volumetric method for design. The control group used waste Liquid Crystal Displayplay (LCD) glass powder to replace cement (0%, 10%, 20%, 30%), and the PZT group used Pd-Zr-Ti piezoelectric (PZT) powder to replace 5% of the fine aggregate to make cement mortar. The engineering and the mechanical and electricity properties were tested; flow, compressive strength, ultrasonic pulse velocity (UPV), water absorption and resistivity (SSD and OD electricity at 50 V and 100 V) were determined; and the correlations were determined by linear regression. The compressive strength of the control group (29.5-31.8 MPa) was higher than that of the PZT group (25.1-29 MPa) by 2.8-4.4 MPa at the curing age of 28 days. A 20% waste LCD glass powder replacement (31.8 MPa) can fill up finer pores and accelerate hydration. The control group had a higher 50 V-SSD resistivity (1870-3244 o.cm), and the PZT group had a lower resistivity (1419-3013 o.cm), meaning that the resistivity increases with the replacement of waste LCD glass powder. This is because the waste LCD glass powder contains 62% SiO2, which is a low dielectric material that is an insulator. Therefore, the resistivity increases with the SiO2 content.

Key Words
waste LCD glass powder; Pd-Zr-Ti piezoelectric (PZT); Engineering and electricity properties; cement mortar; linear regression

Address
Shu-Chuan Chang, Her-Yung Wang: Department of Civil Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, 807, Taiwan, R.O.C.
Chien-Chih Wang: Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung, 833, Taiwan, R.O.C.

Abstract
Flat-slabs, being a significant structural component, not only reduce the dead load of the structure but also reduce the amount of concrete required for construction. Moreover the use of recycled aggregates lowers the impact of large scale construction to nearby ecosystems. Recycled aggregate based concrete being a quasi-brittle material shows enormous cracking during failure. Crack growth in flat-slabs is mostly in sliding mode (Mode II). Therefore sufficient sections need to be provided for resistance against such failure modes. The main objective of the paper is to numerically determine the ultimate load carrying capacity of two self-similar flat-slab specimens and validate the results experimentally for the natural aggregate as well as recycled aggregate based concrete. Punching shear experiments are carried out on circular flat-slab specimen on a rigid circular knife-edge support built out of both normal (NAC) and recycled aggregate concrete (RAC, with full replacement). Uniaxial compression and bending tests have been conducted on cubes, cylinders and prisms using both types of concrete (NAC and RAC) for its material characterization and use in the numerical scheme. The numerical simulations have been conducted in ABAQUS (a known finite element software package). Eight noded solid elements have been used to model the flat slab and material properties have been considered from experimental tests. The inbuilt Concrete Damaged Plasticity model of ABAQUS has been used to monitor crack propagation in the specimen during numerical simulations.

Key Words
punching shear; flat slabs; Mode II crack propagation; recycled aggregate concrete

Address
Saikat Dan, Manpreet Chaudhary, Sudhirkumar V. Barai: Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India

Abstract
More and more special-shaped structural systems have been widely used in various industrial and civil buildings in order to satisfy the new structural system and the increasing demand for architectural beauty. With the popularity of the specialshaped structure system, its seismic performance and damage form have also attracted extensive attention. In the current research, an experimental analysis of six groups of (2/3 scale) T-shaped column joints was conducted to investigate the seismic performance of T-shaped column joints. Effects of the beam cross section, transverse stirrup ratio and axial compression ratio on bearing capacity and energy dissipation capacity of column joints were obtained. The crack pattern of T-shaped column joints under low cyclic load was presented and showed a reversed \"K\" mode. According to the crack configurations, a tensile-shear failure model to determine the shear bearing capacity and crack propagation mechanisms is developed.

Key Words
T-shaped column joint; experimental analysis; crack configuration; tensile-shear model; shear resistance

Address
Changhong Chen, He Gong, Yao Yao: School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi\'an 710012, China
Ying Huang: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China
Leon M. Keer: Civil and Environmental Engineering, Northwestern University, Evanston, IL 60286, USA

Abstract
This paper approaches to improve the mechanical and durability properties of low calcium fly ash geopolymer concrete with the addition of Alccofine as a mineral admixture. The mechanical and durability performance of GPC was assessed by means of compressive strength, flexural strength, permeability, water absorption and permeable voids tests. The correlation between compressive strength and flexural strength, depth of water penetration and percentage permeable voids are also reported. Test results show that addition of Alccofine significantly improves the mechanical as well as permeation properties of low calcium fly ash geopolymer concrete. Very good correlations were noted between the depth of water penetration and compressive strength, percentage permeable voids and compressive strength as well as between compressive strength and flexural strength.

Key Words
geopolymer concrete; microstructure; permeability; water absorption; flexural strength; compressive strength; permeable voids

Address
Bharat Bhushan Jindal: K. Gujral Punjab Technical University, Kapurthala, Punjab, India
Dhirendra Singhal, Parveen: Department of Civil Engineering, DCRUST Murthal, Haryana, India
Sanjay Sharma: Department of Civil Engineering, NITTTR, Chandigarh, India



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