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CONTENTS
Volume 7, Number 4, June 2019
 

Abstract
Concrete structures in marine environment are susceptible to chloride attack, where chloride diffusion results in the corrosion of steel bar and further lead to the cracking of concrete cover. This process causes structural deterioration and affects the response of concrete structures to different forms of loading. This paper presents the use of ABAQUS Finite Element Software in simulating the processes involved in concrete\'s structural degradation from chloride diffusion to steel corrosion and concrete cover cracking. Fick\'s law was used for the chloride diffusion, while the mass loss from steel corrosion was obtained using Faraday\'s law. Pressure generated by steel corrosion product at the concrete-steel interface was modeled by applying uniform radial displacements, while concrete smeared cracking alongside the Extended Finite Element Method (XFEM) was used for concrete cover cracking simulation. Results show that, chloride concentration decreases with penetration depth, but increases with exposure time at the concrete-steel interface. Cracks initiate and propagate in the concrete cover as pressure caused by the steel corrosion product increases. Furthermore, the crack width increases with the exposure time on the surface of the concrete.

Key Words
concrete; steel; chloride; corrosion; cracking; extended finite element method; ABAQUS

Address
Olawale O. Ayinde, Xiao-Bao Zuo and Guang-Ji Yin: Department of Civil Engineering, School of Science, Nanjing University of Science and Technology, 210094, Nanjing, China

Abstract
Predictions about shrinkage and creep of concrete are very important for evaluating time-dependent effects on structural performance. Some prediction models and formulas of concrete shrinkage and creep have been proposed with diversity. However, the influence of reinforcement ratio on shrinkage and creep of concrete has been ignored in most prediction models and formulas. In this paper, the concrete shrinkage and creep with different ratios of reinforcement were studied. Firstly, the shrinkage performance was tested by the 10 reinforced concrete beams specimens with different reinforcement ratios for 200 days. Meanwhile, the creep performance was tested by the 5 reinforced concrete beams specimens with different ratios of reinforcement under sustained load for 200 days. Then, the test results were compared with the prediction models and formulas of CEB-FIP 90, ACI 209, GL 2000 and JTG D 62-2004. At last, based on ACI 209, an improved prediction models and formulas of concrete shrinkage and creep considering reinforcement ratio was derived. The results from improved prediction models and formulas of concrete shrinkage and creep are in good agreement with the experimental results.

Key Words
concrete creep; concrete shrinkage; reinforcement ratio; prediction model

Address
Guojun Sun, Suduo Xue: The College of Architecture & Civil Engineering, Beijing University of Technology, Beijing 100124, China
Xiushu Qu: The College of civil and transportation Engineering, Beijing University of Civil Engineering and Architecture, Beijing 100044, China
Yifeng Zhao: The Fan Gongxiu Honor college, Beijing University of Technology, Beijing 100124, China

Abstract
This paper presents an experimental study on the structural performance of an innovative ultra-high performance fiber reinforced concrete (UHPFRC) deck with coarse aggregate of composite bridge under shear force. Test parameters included curing method and shear span-to-height ratio. Test results indicated that more short fine cracks developed beside the existing cracks due to the randomly dispersed fibers, resulting in re-distributing and homogenizing of the concrete stress beside cracks and allowing for the occurrence of more cracks with small spacing compared to normal strength concrete beams. Curing methods, incorporating steam curing and natural curing, did not have obvious effect on the nominal bending cracking strength and the ultimate strength of the test specimens. Shear reinforcement need not be provided for UHPFRC decks with a fiber volume fraction of 2%. UHPFRC decks showed superior load resistance ability after the appearance of cracks and excellent post-cracking deformability. Lastly, the current shear provisions were evaluated by the test results.

Key Words
composite bridge; deck; ultra-high performance fiber reinforced concrete (UHPFRC); shear; steel fiber

Address
Jianan Qi, Jingquan Wang and Yu Feng: Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, School of Civil Engineering,
Southeast University, Nanjing, China

Abstract
The present study deals with the development of metakaolin-based geopolymer concrete (GPC) and thereafter studying the effects of adding ultra-fine slag on its mechanical and permeability characteristics. The mechanical characteristics including compressive, split tensile, flexural strengths and elastic modulus were studied. In addition, permeability characteristics including water absorption, porosity, sorptivity and chloride permeability were studied up to 90 days. The results showed the effective utilization of metakaolin for the development of elevated temperature cured geopolymer concrete having high 3-day compressive strength of 42.6 MPa. The addition of ultra-fine slag up to 15%, as partial replacement of metakaolin resulted in an increase in strength characteristics. Similar improvement in durability properties was also observed with the inclusion of ultrafine slag up to 15%. Beyond this optimum content of 15%, further increase in ultra-fine slag content affected the mechanical as well as permeability parameters in a negative way. In addition, the relationship between various properties of GPC was also derived.

Key Words
geopolymers; metakaolin; ultra-fine slag (alccofine); mechanical properties; permeability properties

Address
Parveen: Department of Civil Engineering, DCRUST, Murthal-131039, Sonipat, Haryana, India
Ankur Mehta: Amity School of Engineering and Technology, Amity University, Sector-125, Noida, U.P, India
Saloni: Department of Civil Engineering, DCRUST, Murthal-131039, Sonipat, Haryana, India

Abstract
In this paper the effect of bedding layer on the failure mechanism of rock in direct shear test has been investigated using particle flow code, PFC. For this purpose, firstly calibration of pfc2d was performed using Brazilian tensile strength. Secondly direct shear test consisting bedding layer was simulated numerically. Thickness of layers was 10 mm and rock bridge length was 10 mm, 40 mm and 60 mm. In each rock bridge length, bedding layer angles changes from 0o to 90o with increment of 15o. Totally 21 models were simulated and tested. The results show that two types of cracks develop within the model. Shear cracks and tensile cracks. Also failure pattern is affected by bridge length while shear strength is controlled by failure pattern. It\'s to be noted that bedding layer has not any effect on the failure pattern because the layer interface strength is too high.

Key Words
direct shear test; anisotropy; bedding layer; tensile crack; PFC2D

Address
Hadi Haeri: State Key Laboratory for Deep GeoMechanics and Underground Engineering, Beijing, 100083, China
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Zheming Zhu: MOE Key Laboratory of Deep Underground Science and Engineering, School of Architecture and Environment,
Sichuan University, Chengdu 610065, China
Reza Nejati: Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Iran

Abstract
In this study, high strength aluminum alloys (AA) plates are proposed as a new construction material for strengthening reinforced concrete (RC) beams. The purpose of this investigation is to evaluate AAplate\'s suitability as externally bonded reinforcing (EBR) materials for retrofitting shear deficient beams. A total of twenty RC beams designed to fail in shear were strengthened with different spacing and orientations. The specimens were loaded with four-points loading till failure. The considered outcome parameters included load carrying capacity, deflection, strain in plates, and failure modes. The results of all tested beams showed an increase up to 37% in the load carrying capacity and also an increase in deflection compared to the control un-strengthened beams. This demonstrated the potential of adopting AA plates as EBR material. Finally, the shear contribution from the AA plates was predicted using the models available in the ACI440-08, TR55 and FIB14 design code for fiber reinforced polymer (FRP) plates. The predicted results were compared to experimental testing data with the ratio of the experimentally measured ultimate load to predicted load, range on the average, between 93% and 97%.

Key Words
aluminum alloy; shear capacity; externally bonded plates; FRP; reinforced concrete

Address
Adi S. Abu-Obeidah: Department of Civil Engineering, Rutgers, The State University of New Jersey, USA
Jamal A. Abdalla, Rami A. Hawileh: Department of Civil Engineering and Materials Science and Engineering Research Institute (MSERI), American University of Sharjah, UAE

Abstract
In the present work, Granulated Blast Furnace Slag (GBFS) and Fly ash (FA) were used as partial replacement of Natural Sand (NS) and Ordinary Portland Cement (OPC) by weight. One control mix, one with GBFS, three with FA and three with GBFS-FA combined mixes were prepared. Replacements were 50% GBFS with NS and 20%, 30% and 40% FAwith OPC. Preliminary investigation on development of compressive strength was carried out at 7, 28 and 90 days to ensure sustainability of waste materials in concrete matrix at room temperature. After 90days, thermo-mechanical study was performed on the specimen for a temperature regime of 200o-1000oC followed by furnace cooling. Weight loss, visual inspection along with colour change, residual compressive strength and microstructure analysis were performed to investigate the effect of replacement of GBFS and FA. Although adding waste mineral by-products enhanced the weight loss, their pozzolanicity and formation history at high temperature played a significant role in retaining higher residual compressive strength even up to 800oC. On detail microstructural study, it has been found that addition of FA and GBFS in concrete mix improved the density of concrete by development of extra calcium silicate gel before fire and restricts the development of micro-cracks at high temperature as well. In general, the authors are in favour of combined replacement mix in view of high volume mineral byproducts utilization as fire protection.

Key Words
fly ash; GBFS; elevated temperatures; weight loss; compressive strength; microstructure

Address
Ashok Kr. Sahani, Amiya K. Samanta and Dilip K. Singha Roy: Department of Civil Engineering, NIT Durgapur, MGAvenue-713209, India

Abstract
The formulation of self-compacting concretes (SCC) and the study of their properties at the laboratory level were currently well mastered. The aim of this work is to characterize SCC under hot climatic conditions and their effects on the properties of fresh and hardened SCC. Particularly, the effect of the initial wet curing time on the mechanical behavior such as the compressive strength and the durability of the SCCs (acid and sulfate attack) as well as the microstructure of SCCs mixtures. In this study, we used two types of cement, Portland cement and slag cement, three water/binder (W/B) ratio (0.32, 0.38 and 0.44) and five curing modes. The obtained results shows that the compressive strength is strongly influenced by the curing methods, 7-days of curing in the water and then followed by a maturing in a hot climate was the optimal duration for the development of a better compressive strength, regardless of the type of binder and the W/B ratio.

Key Words
self-compacting concrete; hot climate; initial curing time; compressive strength; acid attack; microstructure; XRD

Address
M. Salhi: Department of Civil Engineering, University of Relizane, Bourmadia, Algeria; Laboratory of Civil Engineering, University of Reims Champagne Ardennes, Reims, France; Geomaterials Laboratory, Hassiba Benbouali University of Chlef, P.O. Box 151, Chlef 02000, Algeria
A. Li: Laboratory of Civil Engineering, University of Reims Champagne Ardennes, Reims, France
M. Ghrici: Geomaterials Laboratory, Hassiba Benbouali University of Chlef, P.O. Box 151, Chlef 02000, Algeria
C. Bliard: CNRS UMR 7312 ICMR Université de Reims, France


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