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CONTENTS
Volume 20, Number 2, August 2017
 

Abstract
Time-dependent buckling of embedded straight concrete columns armed with Silicon dioxide(SiO2) nano-particles exposed to fire is investigated in the present study for the fire time. The column is simulated mathematically with Timoshenko beam model. The governing mass conservation equations to describe heat and moisture transport in concrete containing free water, water vapor, and dry air in conjunction with the conversion of energy are considered. The characteristics of the equivalent composite are determined using Mori-Tanaka approach. The foundation around the column is simulated with spring and shear layer. Employing nonlinear strains-displacements, energy methods and Hamilton\'s principal, the governing equations are derived. Differential quadrature method (DQM) is used in order to obtain the critical buckling load and critical buckling time of structure. The influences of volume percent of SiO2nano-particles, geometrical parameters, elastic foundation and concrete porosity are investigated on the time-dependent buckling behaviours of structure. Numerical results indicate that reinforcing the concrete column with SiO2nano-particles, the structure becomes stiffer and the critical buckling load and time increase.

Key Words
concrete column; SiO2nano-particles; fire; DQM; buckling

Address
M. Rabani Bidgoli and M. Saeidifar: Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran

Abstract
Seismic design of reinforced concrete (RC) structures requires a certain minimum level of flexural ductility. For example, Eurocode EN1998-1 directly specifies a minimum flexural ductility for RC beams, while Chinese code GB50011 limits the equivalent rectangular stress block depth ratio at peak resisting moment to achieve a certain nominal minimum flexural ductility indirectly. Although confinement is effective in improving the ductility of RC beams, most design codes do not provide any guidelines due to the lack of a suitable theory. In this study, the confinement for desirable flexural ductility performance of both normal- and high-strength concrete beams is evaluated based on a rigorous full-range moment-curvature analysis. An effective strategy is proposed for flexural ductility design of RC beams taking into account confinement. The key parameters considered include the maximum difference of tension and compression reinforcement ratios, and maximum neutral axis depth ratio at peak resisting moment. Empirical formulae and tables are then developed to provide guidelines accordingly.

Key Words
confinement; curvature ductility factor; flexural ductility design; RC beams; reinforcement ratios; neutral axis depth ratio

Address
X.C. Chen: Department of Bridge Engineering, Tongji University, Shanghai, P.R. China;
Research and Technology Center, Shenzhen WISE-TECH Engineering Consulting Co. LTD. , Shenzhen, China
Z.Z. Bai: Department of Bridge Engineering, Tongji University, Shanghai, P.R. China
F.T.K. Au: Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China


Abstract
In geological engineering, grouting with Portland cement is a common technique for ground improvement, during which micro-fine cement is applied as a slurry, such that it intrudes into soil voids and decreases soil porosity. To determine the utility and behavior of cements with different Blaine values (index of cement particle fineness) for stabilization of fine sand, non-destructive and destructive tests were employed, such as laser-ray determination of grain size distribution, and sedimentation, permeability, and compressive strength tests. The results of the experimental study demonstrated a suitable mix design for the upper and lower regions of the cement-grading curve that are important for grouting and stabilization. Increasing the fineness of the cement decreased the permeability and increased the compressive strength of grouted sand samples considerably after two weeks. Moreover, relative to finer (higher Blaine value) or coarser (lower Blaine value) cements, cement with a Blaine value of 5,100 cm2/g was optimal for void reduction in a grouted soil mass. Overall, study results indicate that cement with an optimum Blaine value can be used to satisfy the designed geotechnical criteria.

Key Words
non-destructive tests; micro-fine cement; grouting

Address
Esmael Aflaki: Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran
Faramarz Moodi: Concrete Technology and Durability Research Center, Amirkabir University of Technology, Tehran, Iran

Abstract
During the past decades, development of reinforcing materials caused a revolution in the structure of high strength and high performance cement-based concrete. Among the most important and exciting reinforcing materials, Steel Fiber (SF) becomes a widely used in the recent years. The main reason for addition of SF is to enhance the toughness and tensile strength and limit development and propagation of cracks and deformation characteristics of the SF blended concrete. Basically this technique of strengthening the concrete structures considerably modifies the physical and mechanical properties of plain cement-based concrete which is brittle in nature with low flexural and tensile strength compared to its intrinsic compressive strength. This paper presents an overview of the work carried out on the use of SF as reinforcement in cement-based concrete matrix. Reported properties in this study are fresh properties, mechanical and durability of the blended concretes.

Key Words
concrete; steel fiber; physical properties; mechanical properties

Address
Alireza Najigivi: Institute for Nanoscience & Nanotechnology (INST), Sharif University of Technology, Iran
Amin Nazerigivi and Hamid Reza Nejati: Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Iran

Abstract
Textile Reinforced Cementitious Composite (TRCC) became the most common construction material lately and have excellent properties. TRCC can be employed in the manufacture of thin-walled facade elements, load-bearing integrated formwork, tunnel linings or in the strengthening of existing structures. These composite materials are a combination of matrix and textile materials. There isn\'t much research done about the usage of polymer modified matrices in textile reinforced cementitious composites. In this study, matrix materials named as fine grained concretes (dmax 1.0 mm) were investigated. Air entraining effect of polymer modifiers were analyzed and air void content of fine grained concretes were identified with different methods. Aim of this research is to study the effect of polymer modification on the air content of fine grained concretes and the role of defoamer in controlling it. Polymer modifiers caused excessive air entrainment in all mixtures and defoamer material successfully lowered down the air content in all mixtures. Latex polymer modified mixtures had higher air content than redispersible powder modified ones. Air void analysis test was performed on selected mixtures. Air void parameters were compared with the values taken from air content meter. Close results were obtained with tests and air void analysis test found to be useful and applicable to fine grained concretes. Air void content in polymer modified matrix material used in TRCC found significant because of affecting mechanical and permeability parameters directly.

Key Words
fine grained concrete; polymer modification; air void; textile reinforced cementitious composite; defoamer

Address
Esma Gizem Daskiran, Mehmet Mustafa Daskiran and Mustafa Gencoglu: Istanbul Technical University, Department of Civil Engineering, Istanbul, Turkey

Abstract
The characteristics of lightweight aggregate (LWA) with a low specific gravity and high water absorption will significantly change the properties of lightweight aggregate concrete (LWAC). This study aimed at exploring the effect of presoaking degree of LWA on the strength degeneracy of LWAC and flexural behavior of LWAC members exposed to elevated temperatures. The residual mechanical properties of the LWAC subjected to elevated temperatures were first conducted. Then, the residual load tests of LWAC members (beams and slabs) after exposure to elevated temperatures were carried out. The test results showed that with increasing temperature, the decreasing trend of elastic modulus for LWAC was considerably more serious than the compressive strength. Besides, the presoaking degree of LWA had a significant influence on the residual compressive strength and elastic modulus for LWAC after exposure to 800C. Moreover, owing to different types of heating, the residual load bearing capacity of the slab specimens were significantly different from those of the beam specimens.

Key Words
lightweight aggregate; reinforced concrete members; fire damage

Address
Chao-Wei Tang: Department Civil Engineering & Geomatics, Cheng Shiu University, No. 840, Chengcing Rd.,
Niaosong District, Kaohsiung City, Taiwan R.O.C.


Abstract
Durability problems initiated from steel corrosion are unseen but critical issues, so that many researches are focused on chloride penetration evaluation. Even if RC (Reinforced Concrete) structures are exposed to normal environment, chloride ingress varies with concrete surface conditions and exposed period. This paper presents an analysis technique for chloride behavior evaluation considering time effect on diffusion and surface conditions assumed as double-layered system. For evaluation of deteriorated surface condition, field investigation was performed for concrete pavement exposed to deicing agent for 18 years. In order to consider enhanced surface concrete, chloride profiles in surface-impregnated concretes exposed to chloride attack for 2 years from previous research were investigated. Through reverse analysis, effectively deteriorated/ enhanced depth of surface and the related reduced/enlarged diffusion coefficient in the depth are simulated. The proposed analysis technique was evaluated to handle the chloride behavior more accurately considering changes of chloride ingress within surface layer and decreased diffusion coefficient with time. For the concrete surface exposed to deicing agent, the deteriorated depth and enlarged diffusion coefficient are evaluated to be 12.5~15.0 mm and 200% increasing diffusion coefficient, respectively. The results in concrete containing enhanced cover show 10.0~12.5 mm of impregnated depth and 85% reduction of chloride diffusion in tidal and submerged conditions.

Key Words
diffusion; durability; double-layer; deicing agent; chloride attack; surface impregnation

Address
Bang Yeon Lee: School of Architecture, Chonnam National University, 77 Yongbong-no, Buk-gu, Gwangju, 61186, Republic of Korea
Mohamed A. Ismail: Department of Civil and Construction Eng., Faculty of Engineering and Science, Curtin University Malaysia, CDT 250, 98009 Miri, Sarawak, Malaysia
Hyeok-Jung Kim: Elastomer TS&D Team, Kumho Petrochemical R & BD Center, 15577 Yuseong-daero, Yuseong-gu, Daejeon, 34044, Republic of Korea
Sung-Won Yoo: Department of Civil and Environmental Eng., Gachon University, 1342 Seongnam Daero, Seongnam-Si 13120, Republic of Korea
Seung-Jun Kwon: Department of Civil and Environmental Eng., Hannam University, 133 Ojeong-dong, Daejeon, 34430, Republic of Korea



Abstract
Typically, high lime fly ash (Class C) has been characterized as a fly ash, which at lower replacement levels is not as effective as the low lime (Class F) fly ash, in mitigating alkali-silica reaction (ASR) in portland cement concrete. The influence of fineness of Class C, obtained by grinding virgin fly ash into finer particles, on its pozzolanic reactivity and ASR mitigation performance was investigated in this study. In order to assess the pozzolanic reactivity of mortar mixtures containing virgin or ground fly ashes, the strength activity index (SAI) test and thermo-gravimetric analysis (TGA) were conducted on the mortar cubes and paste samples, respectively, containing virgin fly ash or two ground fly ashes. In addition, to evaluate any improvement in the ASR mitigation of ground fly ashes compared to that of the virgin fly ash, the accelerated mortar bar test (AMBT) was conducted on the mortar mixtures containing different dosages of either virgin or ground fly ashes. In all tests crushed glass aggregate was used as a highly reactive aggregate. Results from this study showed that the finest fly ash (i.e., with an average particle size of 3.1 microns) could increase the flow ability along with the pozzolanic reactivity of the mortar mixture. However, results from this study suggested that the fineness of high lime fly ash does not seem to have any significant effect on ASR mitigation.

Key Words
class C fly ash; fineness; pozzolanic reactivity; ASR; mitigation

Address
Kaveh Afshinnia and Prasada R. Rangaraju: Glenn Department of Civil Engineering, Clemson University, Clemson, SC 29634, USA

Abstract
The Hydraulically driven test system and 100 mm split Hopkinson pressure bar(SHPB) test device were employed to research the quasi-static and dynamic mechanical properties of concrete specimens which has been immersed for 60 days in sodium sulfate (group S1) and sodium chloride (group S2) solution, the evolution of their mass during corrosive period was explored at the same time, and the mechanism of performances lost was analyzed from the microscopic level by using scanning electron microscope. Results of the experimental indicated that: their law of mass both presents the trend of continuous rising during corrosive period, and it increases rapidly on the early days, the mass growth of group S1 and group S2 in first 7 days are 76.78% and 82.82% of their total increment respectively; during the corrosive period, the quasi-static compressive strength of specimens in two groups are significantly decreased, both of which present the trend of increase first and then decrease, the maximum growth rate of group S1 and group S2 are 7.52% and 12.71% respectively, but they are only 76.23% and 82.84% of specimens which under normal environment (group N) on day 60; after immersed for 60 days, there were different decrease to dynamic compressive strength and specific energy absorption, and so as their strain rate sensitivities. So the high salinity environment has a significant effect of weaken the quasi-static and dynamic mechanical performance of concrete.

Key Words
sulfate ion; chlorine ion; mass; strain rate; compressive strength; specific energy absorption

Address
Liangxue Nie and Erlei Bai: Department of Airfield and Building Engineering, Air Force Engineering University, Xi\'an 710038, China
Jinyu Xu: Department of Airfield and Building Engineering, Air Force Engineering University, Xi\'an 710038, China
College of Mechanics and Civil Architecture, Northwest Polytechnic University, Xi\'an 710072, China


Abstract
A finite element model (FEM) for predicting early-age behavior of reinforced concrete (RC) bridge deck slabs with fiber-reinforced polymer (FRP) bars is presented. In this model, the shrinkage profile of concrete accounted for the effect of surrounding conditions including air flow. The results of the model were verified against the experimental test results, published by the authors. The model was verified for cracking pattern, crack width and spacing, and reinforcement strains in the vicinity of the crack using different types and ratios of longitudinal reinforcement. The FEM was able to predict the experimental results within 6 to 10% error. The verified model was utilized to conduct a parametric study investigating the effect of four key parameters including reinforcement spacing, concrete cover, FRP bar type, and concrete compressive strength on the behavior of FRP-RC bridge deck slabs subjected to restrained shrinkage at early-age. It is concluded that a reinforcement ratio of 0.45% carbon FRP (CFRP) can control the early-age crack width and reinforcement strain in CFRP-RC members subjected to restrained shrinkage. Also, the results indicate that changing the bond-slippage characteristics (sand-coated and ribbed bars) or concrete cover had an insignificant effect on the early-age crack behavior of FRP-RC bridge deck slabs subjected to shrinkage. However, reducing bar spacing and concrete strength resulted in a decrease in crack width and reinforcement strain.

Key Words
GFRP; concrete; deck slabs; early-age cracking; finite element modeling; serviceability

Address
Amir Ghatefar: Department of Civil Engineering, Urmia Branch, Islamic Azad University, Urmia, Iran
Ehab ElSalakawy and Mohamed T. Bassuoni: Department of Civil Engineering, University of Manitoba, Winnipeg, Manitoba, Canada

Abstract
The dynamic bending response of single walled carbon nanotube reinforced composite (SWCNTRC) plates subjected to hygro-thermo-mechanical loading are investigated in this paper. The mechanical load is considered as wind pressure for dynamic bending responses of SWCNTRC plate. The dynamic version of the High Order shear deformation Theory (HSDT) for a composite plate with Matrix and SWCNTRC plate is first formulated. Distribution of fibers through the thickness of the SWCNTRC plate could be uniform or functionally graded (FG). The dynamic displacement response is predicted by using Nemarck integration method. The effective material properties of SWCNTRC are estimated by using micromechanics based modeling approach. The effect of different environmental condition, volume fraction of SWCNT, Width-to-thickness ratio, wind pressure, different SWCNTRC-FG plates, boundary condition, E1/E2 ratio, different temperature on dynamic displacement response is investigated. The dynamic displacement response is compared with the available literature and it shows good agreement.

Key Words
dynamic analysis; SWCNTRC-FG plate; HSDT; hygro-thermo-mechanical load; micromechanics; newmark integration method

Address
Shivaji G. Chavan and Achchhe Lal: Department of Mechanical Engineering, S.V.N.I.T, Surat - 395007, India

Abstract
This study aimed to develop a Rule Based Mamdani Type Fuzzy Logic (RBMFL) model to predict the flexural strengths and compressive strengths of blended cements under elevated temperatures. Clinoptilolite was used as cement substitution material in the experimental stage. Substitution ratios in the cement mortar mix designs were selected as 0% (reference), 5%, 10%, 15% and 20%. The data used in the modeling process were obtained experimentally, after mortar specimens having reached the age of 90 days and exposed to 300C, 400C, 500C temperatures for 3 hours. In the RBMFL model, temperature (C) and substitution ratio of clinoptilolite (%) were inputs while the compressive strengths and flexural strengths of mortars were outputs. Results were compared by using some statistical methods. Statistical comparison results showed that rule based Mamdani type fuzzy logic can be an alternative approach for the evaluation of the mechanical properties of concrete under elevated temperature.

Key Words
blended cement; clinoptilolite; compressive strength; flexural strength; rule based fuzzy logic

Address
Ahmet Beycioğlu and Adil Gültekin: Department of Civil Engineering, Technology Faculty, Düzce University, Düzce, Turkey
Hüseyin Yilmaz Aruntaş: Department of Civil Engineering, Technology Faculty, Gazi University, Beşevler, 06500 Ankara, Turkey
Osman Gencel: Department of Civil Engineering, Faculty of Engineering, Bartin University, Bartin 74100, Turkey
Magdalena Dobiszewska: Department of Civil Engineering, Faculty of Civil and Environmental Engineering and Architecture, UTP University of Sciences and Technology, Bydgoszcz, Poland
Witold Brostow: Laboratory of Advanced Polymers and Optimized Materials (LAPOM), Department of Materials Science and Eng. and Department of Physics, University of North Texas, 3940 North Elm Street, Denton, TX 76207, USA




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