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CONTENTS
Volume 16, Number 6, December 25 2015
 

Abstract
In this study, shear tests on steel fiber reinforced-prestressed concrete (SFR-PSC) members were conducted with test parameters of the concrete compressive strength, the volume fraction of steel fibers, and the level of effective prestress. The SFR-PSC members showed higher shear strengths and stiffness after diagonal cracking compared to the conventional prestressed concrete (PSC) members without steel fibers. In addition, their shear deformational behavior was measured using the imagebased non-contact displacement measurement system, which was then compared to the results of nonlinear finite element analyses (NLFEA). In the NLFEA proposed in this study, a bi-axial tensile behavior model, which can reflect the tensile behavior of the steel fiber-reinforced concrete (SFRC) in a simple manner, was introduced into the smeared crack truss model. The NLFEA model proposed in this study provided a good estimation of shear behavior of the SFRPSC members, such as the stiffness, strengths, and failure modes, reflecting the effect of the key influential factors.

Key Words
SFRC; steel fiber; PSC, prestress; shear, nonlinear; FEM; shear strain

Address
Jin-Ha Hwang, Min Kook Park, Seung-Ho Choi and Kang Su Kim: Department of rchitectural Engineering, University of Seoul, 163 Seoulsiripdae-ro,Dongdaemun-gu, Seoul 130-743, Republic of Korea
Deuck Hang Lee: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 N. Mathews Ave. Urbana, IL 61801, USA
Zuanfeng Pan: Department of Building Engineering, Tongji University, 1239 Siping Road, Shanghai 200092,P.R. China

Abstract
This study aimed to develop models of sulfate diffusion and ettringite content profile in cement paste for the predication of the damage behavior in cement paste subject to external sulfate. In the models, multiphase reaction equilibrium between ions in pore solution and solid calcium aluminates phases and the microstructure changes in different positions of cement paste were taken into account. The distributions of expansive volume strain and expansion stress in cement paste were calculated based on the ettringite content profile model. In addition, more sulfate diffusion tests and SEM analyses were determined to verify the reliability and veracity of the models. As the results shown, there was a good correlation between the numerical simulation results and experimental evidences. The results indicated that the water to cement ratio (w/c) had a significant influence on the diffusion of sulfate ions, ettringite concentration profile and expansion properties in cement paste specimens. The cracking points caused by ettringite growth in cement paste specimens were predicted through numerical methods. According to the simulation results, the fracture of cement paste would be accelerated when the specimens were prepared with higher w/c or when they were exposed to sulfate solution with higher concentration.

Key Words
modeling; sulfate diffusion; ettringite profile; volume strain; cement paste

Address
Chuansheng Xiong, Linhua Jiang, Yan Zhang and Hongqiang Chu: College of Mechanics and Materials, Hohai University, 1 Xikang Rd., Nanjing, China

Abstract
Standard test method for bulk electrical conductivity (ASTM C1760) provides a rapid indication of the concrete

Key Words
concrete; chloride permeability; conductivity; pore solution

Address
Amirreza Pilvar and Ali Akbar Ramezanianpour: Department of Civil & Environmental Engineering, Amirkabir University of Technology, Tehran, Iran.
Hosein Rajaie: Concrete Technology and Durability Research Center (CTDRc),Amirkabir University of Technology, Tehran, Iran


Abstract
A simultaneous analytical, experimental and numerical analysis of crack initiation,propagation and breaking process of the Central Straight through Crack Brazilian Disk (CSCBD) specimens under diametrical compression is carried out. Brazilian disc tests are being accomplished to evaluate the fracturing process based on stress intensity factors (SIFs). The effects of crack inclination angle and crack length on the fracturing processes have been investigated. The same experimental specimens have been numerically modeled by a higher order indirect boundary element method (HDDM). These numerical results are compared with the existing experimental results proving the accuracy and validity of the proposed numerical method.

Key Words
concrete-like specimens; CSCBD; SIFs; DDM; higher order elements

Address
Hadi Haeri: Department of Mining Engineering, Bafgh Branch, Islamic Azad University, Bafgh, Iran

Abstract
This article gives analytical dependences for creep of concrete at heating, taking into account conditions of its drying. These dependences are based on the standard nonlinear theory of creep of concrete at a normal temperature and temperature-time analogy. For the description of creep at various stresses and temperatures the principle of superposition are used. All stages of model

Key Words
temperature; creep; concrete; mechanical properties; thermal analysis; reduced time; superposition

Address
Sergei Klovanych: Faculty of Geodesy, Geospatial and Civil Engineering,University of Warmia and Mazury in Olsztyn,ul. Prawocheńskiego 19, 10-720 Olsztyn, Poland

Abstract
This paper presents an experimental study for determining the bond performance of lightweight concretes produced using pumice aggregate coated with colemanite-cement paste. For this purpose, eight hinged beam specimens were produced with four different concrete mixtures. 14 mm deformed bars with 10

Key Words
colemanite; coated pumice aggregate; lightweight concrete; bond strength; hinged beam test

Address
Ahmet Beycioğlu, Mehmet E. Arslan, Özlem S. Bideci and Mehmet Emiroğlu: Department of Civil Engineering, Technology FacultyDüzce University, 81620, Turkey
Alper Bideci: Department of Architecture, Art-Design and Architecture Faculty, 81620, Turkey

Abstract
This paper presents a new method for assessing the three-point-bending (3PB) strength of mortar beams in a non-destructive manner, based on neural network (NN) models. The models are based on the radial basis function (RBF) architecture and the fuzzy means algorithm is employed for training, in order to boost the prediction accuracy. Data for training the models were collected based on a series of experiments, where the cement mortar beams were subjected to various bending mechanical loads and the resulting pressure stimulated currents (PSCs) were recorded. The input variables to the NN models were then calculated by describing the PSC relaxation process through a generalization of Boltzmannn-Gibbs statistical physics, known as non-extensive statistical physics (NESP). The NN predictions were evaluated using k-fold cross-validation and new data that were kept independent from training; it can be seen that the proposed method can successfully form the basis of a non-destructive tool for assessing the bending strength. A comparison with a different NN architecture confirms the superiority of the proposed approach.

Key Words
non-destructive testing; three-point-bending strength; Pressure Stimulated Currents; nonextensive statistical physics; neural networks; radial basis function; fuzzy means

Address
Alex Alexandridis, Ilias Stavrakas, Charalampos Stergiopoulos, George Hloupis,Konstantinos Ninos and Dimos Triantis: Department of Electronic Engineering, Technological Educational Institute of Athens,Ag. Spiridonos, 12210, Aigaleo, Athens,Greece

Abstract
Damage by high-speed impact fracture is a dominant mode of failure in several applications of concrete structures. Numerical modelling can play a crucial role in understanding and predicting complex fracture processes. The commonly used mesh-based Finite Element Method has difficulties in accurately modelling the high deformation and disintegration associated with fracture, as this often distorts the mesh. Even with careful re-meshing FEM often fails to handle extreme deformations and results in poor accuracy. Moreover, simulating the mechanism of fragmentation requires detachment of elements along their boundaries, and this needs a fine mesh to allow the natural propagation of damage/cracks. Smoothed Particle Hydrodynamics (SPH) is an alternative particle based (mesh-less) Lagrangian method that is particularly suitable for analysing fracture because of its capability to model large deformation and to track free surfaces generated due to fracturing. Here we demonstrate the capabilities of SPH for predicting brittle fracture by studying a slender concrete structure (column) under the impact of a high-speed projectile. To explore the effect of the projectile material behaviour on the fracture process, the projectile is assumed to be either perfectly-elastic or elastoplastic in two separate cases. The transient stress field and the resulting evolution of damage under impact are investigated. The nature of the collision and the constitutive behaviour are found to considerably affect the fracture process for the structure including the crack propagation rates, and the size and motion of the fragments. The progress of fracture is tracked by measuring the average damage level of the structure and the extent of energy dissipation, which depend strongly on the type of collision. The effect of fracture property (failure strain) of the concrete due to its various compositions is found to have a profound effect on the damage and fragmentation pattern of the structure.

Key Words
mesh-free method; smoothed particle hydrodynamics; concrete; fracture; impact

Address
Raj Das: Department of Mechanical Engineering, University of Auckland, Auckland 1010, New Zealand
Paul W. Cleary: CSIRO Mathematics, Informatics and Statistics, Clayton, Victoria 3168, Australia

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