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CONTENTS
Volume 1, Number 4, December 2013
 

Abstract
The main objective of this research was to evaluate the potentials of self-compacting concrete (SCC) mixes to develop bond strength. The investigated mixes incorporated relatively high contents of dolomite powder replacing Portland cement. Either silica fume or fly ash was used along with the dolomite powder in some mixes. Seven mixes were proportioned and cast without vibration in long beams with 10 mm and 16 mm steel dowels fixed vertically along the flowing path. The beams were then broken into discrete test specimens. A push-put configuration was adopted for conducting the bond test. The variation of the ultimate bond strength along the flowing path for the different mixes was evaluated. The steel-concrete bond adequacy was evaluated based on normalized bond strength. The results showed that the bond strength was reduced due to Portland cement replacement with dolomite powder. The addition of either silica fume or fly ash positively hindered further degradation as the dolomite powder content increased. However, all SCC mixes containing up to 30% dolomite powder still yielded bond strengths that were adequate for design purpose. The test results demonstrated inconsistent normalized bond strength in the case of the larger diameter compared to the smaller one.

Key Words
self-compacting concrete; bond; pull-out; push-out; filler; dolomite powder

Address
Mounir M. Kamal, Mohamed A. Safan: Department of Civil Engineering, Faculty of Engineering, Menoufia University, Egypt
Mohamed A. Al-Gazzar: Water Research Center, Ministry of Irrigation, Al-Kanater, Egypt

Abstract
A reliable concrete constitutive material model is critical for an accurate numerical analysis simulation of reinforced concrete structures under extreme dynamic loadings including impact or blast. However, the formulation of concrete material model is challenging and entails numerous input parameters that must be obtained through experimentation. This paper presents a damage scale analytical model to characterize concrete material for its pre- and post-peak behavior. To formulate the damage scale model, statistical regression and finite element analysis models were developed leveraging twenty existing experimental data sets on concrete compressive strength. Subsequently, the proposed damage scale analytical model was implemented in the finite element analysis simulation of a reinforced concrete pier subjected to vehicle impact loading and the response were compared to available field test data to validate its accuracy. Field test and FEA results were in good agreement. The proposed analytical model was able to reliably predict the concrete behavior including its post-peak softening in the descending branch of the stress-strain curve. The proposed model also resulted in drastic reduction of number of input parameters required for LS-DYNA concrete material models.

Key Words
concrete material model; damage scale model; finite element analysis; LS-DYNA; reinforced concrete structure; bridge column; dynamic load; impact load; blast; vehicle impact

Address
Tesfaye A. Mohammed and Azadeh Parvin: Department of Civil Engineering, The University of Toledo, OH, USA

Abstract
Engineering properties such as compressive strength, splitting tensile strength, modulus of rupture, modulus of elasticity and Poisson‟s ratio of geopolymer concrete (GPC) and steel fibre reinforced geopolymer concrete (SFRGPC) have been obtained from standard tests and compared. A total of 15 specimens were tested for determining each property. The grade of concrete used was M 40. The percentages of steel fibres considered include 0.25%, 0.5%, 0.75% and 1%. In general, the addition of fibres improved the mechanical properties of both GPC and SFRGPC. However the increase was found to be nominal in the case of compressive strength (8.51%), significant in the case of splitting tensile strength (61.63%), modulus of rupture (24%), modulus of elasticity (64.92%) and Poisson‟s ratio (50%) at 1% volume fraction of fibres. An attempt was made to obtain the relation between the various engineering properties with the percentage of fibres added.

Key Words
geopolymer concrete; modulus of rupture, modulus of elasticity; steel fibres; split tensile strength

Address
N. Ganesan, P.V. Indira and Anjana santhakumar: Department of Civil Engineering, National Institute of Technology Calicut, NIT Campus P.O, Pin.673601, Kerala, India

Abstract
This paper presents a comparative study on the double-K fracture parameters of concrete obtained using four existing analytical methods such as Gauss–Chebyshev integral method, simplified Green\'s function method, weight function method and simplified equivalent cohesive force method. Two specimen geometries: three point bend test and compact tension specimen for sizes 100-500 mm at initial notch length to depth ratios 0.25 and 0.4 are used for the comparative study. The required input parameters for determining the double-K fracture parameters are derived from the developed fictitious crack model. It is found that the cohesive toughness and initial cracking toughness determined using weight function method and simplified equivalent cohesive force method agree well with those obtained using Gauss–Chebyshev integral method whereas these fracture parameters determined using simplified Green

Key Words
three-point bend test; compact tension test; analytical method; double-K fracture parameters; weight function; cohesive stress

Address
Shailendra Kumar: Department of Civil Engineering, Institute of Technology, Guru Ghasidas Vishwavidyalaya, Central University, Bilaspur (C.G.) - 495009, India.
Shashi Ranjan Pandey and A.K.L. Srivastava: Department of Civil Engineering, National Institute of Technology, Jamshedpur-831014, Jharkhand, India

Abstract
Due to fast growth in urbanisation, a highly developed infrastructure is essential for economic growth and prosperity. One of the major problems is to preserve, maintain, and retrofit these structures. To meet the requirements of construction industry, the basic information on all the mechanical properties of various concretes is essential. This paper presents the details of development of various concretes, namely, normal strength concrete (around 50 MPa), high strength concrete (around 85 MPa) and ultra high strength concrete (UHSC) (around 120 MPa) including their mechanical properties. The various mechanical properties such as compressive strength, split tensile strength, modulus of elasticity, fracture energy and tensile stress vs crack width have been obtained from the respective test results. It is observed from the studies that a higher value of compressive strength, split tensile strength and fracture energy is achieved in the case of UHSC, which can be attributed to the contribution at different scales viz., at the meso scale due to the fibers and at the micro scale due to the close packing of grains which is on account of good grading of the particles. Micro structure of UHSC mix has been examined for various magnifications to identify the pores if any present in the mix. Brief note on characteristic length and brittleness number has been given.

Key Words
high strength concrete; ultra high strength concrete; characterization; crack mouth opening displacement, fracture energy; tensile stress vs crack width

Address
A. Ramachandra Murthy, Nagesh R. Iyer: CSIR- Structural Engineering Research Centre, Chennai 600113, India
B.K. Raghu Prasad: ndian Institute of Science, Bangalore 560012, India


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