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CONTENTS
Volume 5, Number 5, October 2017
 

Abstract
Today, pozzolans are widely used in construction for various reasons such as technical and economic efficiency. In this research, in order to evaluate some of important properties of concrete, silica fume and fly ash have been used as a replacement for cement in different mass percentages. Concrete mixtures were made from a water-cement ratio of (0.45) and cured under similar conditions. The main focus of this study was to evaluate the permeability and mechanical properties of concrete made from binary and ternary cementitious mixtures of fly ash and silica fume. In this study permeability of concrete was studied by evaluating the sorptivity, water absorption, water penetration depth, electrical resistivity and rapid chloride permeability (RCP) tests. Mechanical properties of concrete were evaluated with compressive strength, splitting tensile strength and modulus of elasticity. Scanning electronic microscopy (SEM) was used to characterize the effects of silica fume and fly ash on the pore structure and morphology of concrete with cement based matrix. The results indicated that the incorporation of silica fume and fly ash increased the mechanical strength and improved the permeability of concrete.

Key Words
silica fume; fly ash; permeability; mechanical strength; SEM

Address
Ali Sadrmomtazi: Department of Civil Engineering, University of Guilan, Khalij-e Fars Highway, Rasht, Iran
Behzad Tahmouresi: Department of Structural Engineering, Civil Engineering, University of Guilan, Khalij-e Fars Highway Rasht, Iran
Morteza Amooie: Department of Structural Engineering, Civil Engineering, South-Tehran Branch, Islamic Azad University, ZIP area 11, Azarshahr Street, North Iranshahr Street, Karimkhan-e-Zand Avenue, Tehran, Iran

Abstract
The present work investigates about the development of a novel construction material by utilizing Granulated Blast Furnace Slag (GBS), an industrial waste product, as substitution of natural fine aggregates. For this, experimental work has been carried out to determine the influence of GBS on the properties of concrete such as compressive strength (CS), modulus of elasticity, ultrasonic pulse velocity (UPV), chloride penetration, water absorption (WA) volume of voids (VV) and density. Concrete mixes of water/cement (w/c) ratios 0.45 and 0.5, and incorporating 20%, 40% and 60% of GBS as partial replacement of natural fine aggregate (sand) are designed for this study. The results of the experimental investigation depict that CS of concrete mixes increases with the increasing percentages of GBS. Moreover, the decrease in chloride penetration, WA and VV, and improvement in the modulus of elasticity, UPV, density of concrete is reported with the increasing percentage of GBS in concrete.

Key Words
compressive strength; granulated blast furnace slag; volume of voids; water absorption; modulus of elasticity

Address
Rakesh Kumar Patra: Department of Civil Engineering, National Institute of Science and Technology, Palur Hills, Brahmapur, Odisha, India
Bibhuti Bhusan Mukharjee: Department of Civil Engineering, Veer Surendra Sai University of Technology, Burla, Sambalpur, Odisha, India

Abstract
The problem of reducing the self-weight of reinforced concrete structures is very important issue. There are two approaches which may be used to reduced member weight. The first is tackled through reducing the cross sectional area by using voids and the second through using light weight materials. Reducing the weight of slabs is very important as it constitutes the effective portion of dead loads in the structural building. Eleven slab specimens was casted in this research. The slabs are made one way though using two simple supports. The tested specimens comprised three reference solid slabs and eight styropor block slabs having (23% and 29%) reduction in weight. The voids in slabs were made using styropor at the ineffective concrete zones in resisting the tensile stresses. All slab specimens have the dimensions (1100x 600x120 mm) except one solid specimens has depth 85 mm (to give reduction in weight of 29% which is equal to the styropor block slab reduction). Two loading positions or cases (A and B) (as two-line monotonic loads) with shear span to effective depth ratio of (a/d=3, 2) respectively, were used to trace the structural behavior of styropor block slab. The best results are obtained for styropor block slab strengthened by minimum shear reinforcement with weight reduction of (29%). The increase in the strength capacity was (8.6% and 5.7%) compared to the solid slabs under loading cases A and B respectively. Despite the appearance of cracks in styropor block slab with loads lesser than those in the solid slab, the development and width of cracks in styropor block slab is significantly restricted as a result of presence a mesh of reinforcement in upper concrete portion.

Key Words
monotonic load; one-way slab; structural behavior; styropor block; weight reduction

Address
Adel A. Al-Azzawi, Abbas J and Al-Asdi: Department of Civil Engineering, Al-Nahrain University, Baghdad, Iraq

Abstract
Balanced cantilever construction is extensively used in the construction of prestressed concrete (PSC) box-girder bridges. Shear-lag effect is usually considered in finished bridges, while the cumulative shear-lag effect in bridges during balanced cantilever construction is considered only rarely. In this paper, based on the balanced cantilever construction sequences of large-span PSC box-girder bridges, the difference method is employed to analyze the cumulative shear-lag effect of box girders with varying depth under the concrete segments\' own weight. During cantilever construction, no negative shear-lag effect is generated, and the cumulative shear-lag effect under the balanced construction procedure is greater than the instantaneous shear-lag effect in which the full dead weight is applied to the entire cantilever. Three cross-sections of Jianjiang Bridge were chosen for the experimental observation of shear-lag effect, and the experimental results are in keeping with the theoretical results of cumulative shear-lag effect. The research indicates that only calculating the instantaneous shear-lag effect is not sufficiently safe for practical engineering purposes.

Key Words
box-girder bridges; balanced cantilever construction; shear-lag effect; the cumulative effect; prestress

Address
Xingu Zhong, Tianyu Zhang and Xiaojuan Shu: School of Civil Engineering, Hunan University of Science and Technology; Hunan Provincial Key Laboratory of Structural Engineering for Wind Resistant and Vibration Control, Xiangtan, 411201, China
Hongliang Xu: China CEC Engineering, Corporation, Changsha, China

Abstract
The aim of this paper is to investigate the effect of quartz powder (Qp), quartz sand (Qs), and different water curing temperature on mechanical properties including 7, 14, 28-day compressive strength and 28-day splitting tensile strength of Ultra High Performance Concrete and also finding the correlation between these variables on mechanical properties of UHPC. The response surface methodology was monitored to show the influences of variables and their interactions on mechanical properties of UHPC, then, mathematical models in terms of coded variables were established by ANOVA. The offered models are valid for the variables between: quartz powder 0 to 20% of cement substitution by cement weight, quartz sand 0 to 50% of aggregate substitution by crushed limestone weight, and water curing temperature 25 to 95oC.

Key Words
ultra high performance concrete; quartz powder; quartz sand; different water curing temperature

Address
Mohammad A. Mosaberpanah: Department of Civil Engineering, Cyprus International University (CIU), Nicosia, Cyprus
Ozgur Eren: Department of Civil Engineering, Eastern Mediterranean University (EMU), Famagusta, Cyprus

Abstract
Blast loads may considerably affect the response of structures. In previous years, before computer analysis programs, the parameters of blast effects were calculated with empirical methods, consequently some researchers had proposed equations to find out the phenomenon. In recent year\'s computer analysis programs have developed already, so detailed solutions can be made numerically. This paper describes the blasting response of the structures using numerical and empirical methods. For the purpose, a reinforced concrete retaining wall is modelled using ANSYS Workbench software, and the model is imported to ANSYS AUTODYN software to perform explicit analyses. In AUTDYN software, a sum of TNT explosive is defined 5,5 m away from the wall and solution is done. Numerical results are compared with those of obtained from empirical equations. Similar study is also considered for equal explosive which is the 4 m away from the wall. The results are represented by graphics and contour diagrams of such as displacements and pressures. The results showed that distance of explosive away from the wall is highly affected the structural response of it.

Key Words
blasting response; explicit analysis; numerical and empirical methods; RC retaining wall; TNT explosive

Address
Ahmet Tugrul Toy and Baris Sevim: Department of Civil Engineering, Yildiz Technical University, 34220, İstanbul, Turkey

Abstract
In this study, the fracture toughness KIC of high performance concrete (HPC) was investigated by conducting three-point bending tests on a total of 240 notched beams of 500 mmx100 mmx100 mm subjected to heating temperatures up to 450oC with exposure times up to 16 hours and various heating and cooling rates. For a heating rate of 3oC/min, KIC for the hot concrete sustained a monotonic decrease trend with the increasing heating temperature and exposure time, from 1.389 MN/m1.5 at room temperature to 0.942 MN/m1.5 at 450oC for 4-hour exposure time, 0.906 MN/m1.5 for 8-hour exposure time and 0.866 MN/m1.5 for 16-hour exposure time. For the cold concrete, KIC sustained a two-stage decrease trend, dropping slowly with the heating temperature up to 150oC and then rapidly down to 0.869 MN/m1.5 at 450oC for 4-hour exposure time, 0.812 MN/m1.5 for 8-hour exposure time and 0.771 MN/m1.5 for 16-hour exposure time. In general, the KIC values for the hot concrete up to 200oC were larger than those for the cold concrete, and an inverse trend was observed thereafter. The increase in heating rate slightly decreased KIC, and at 450oC KIC decreased from 0.893 MN/m1.5 for 1oC/min to 0.839 MN/m1.5 for 10oC/min for the hot concrete and from 0.792 MN/m1.5 for 1oC/min to 0.743 MN/m1.5 for 10oC/min for the cold concrete after an exposure time of 16 hours. The increase in cooling rate also slightly decreased KIC, and at 450oC KIC decreased from 0.771 MN/m1.5 for slow cooling to 0.739 MN/m1.5 for fast cooling after an exposure time of 16 hours. The fracture energy-based fracture toughness KIC\' was also assessed, and similar decrease trends with the heating temperature and exposure time existed for both hot and cold concretes. The relationships of two fracture toughness parameters with the weight loss and the modulus of rapture were also evaluated.

Key Words
HPC; fracture toughness; exposure time; heating rate; cooling rate; weight loss

Address
Binsheng Zhang, Martin Cullen and Tony Kilpatrick: School of Engineering and Built Environment, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 0BA, Scotland, UK


Abstract
In this study, the effects of initial damage of concrete columns on the post-repair performance of reinforced concrete (RC) columns strengthened with carbon-fiber-reinforced polymer (CFRP) composite are investigated experimentally. Four kinds of compression-damaged RC cylinders were reinforced using external CFRP composite wraps, and the stress-strain behavior of the composite/concrete system was investigated. These concrete cylinders were compressed to four pre-damaged states including low -level, medium-level, high-level and total damage states. The percentages of the stress levels of pre-damage were, respectively, 40, 60, 80, and 100% of that of the control RC cylinder. These damaged concrete cylinders simulate bridge piers or building columns subjected to different magnitudes of stress, or at various stages in long-term behavior. Experimental data, as well as a stress-strain model proposed for the behavior of damaged and undamaged concrete strengthened by external CFRP composite sheets are presented. The experimental data shows that external confinement of concrete by CFRP composite wrap significantly improves both compressive strength and ductility of concrete, though the improvement is inversely proportional to the initial degree of damage to the concrete. The failure modes of the composite/damaged concrete systems were examined to evaluate the benefit of this reinforcing methodology. Results predicted by the model showed very good agreement with those of the current experimental program.

Key Words
FRP; confinement; concrete; columns; damage, ductility; strength; model

Address
Habib-Abdelhak Mesbah: L.G.C.G.M., INSA de Rennes, IUT Université de Rennes 1 20, Av. des Buttes de Coësmes-CS 70839-35708-Rennes Cedex7, France
Riad Benzaid: L.G.G., Université Mohammed Seddik Benyahia-Jijel, B.P. 98, Cité Ouled Issa, Jijel-18000, Algeria


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