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CONTENTS
Volume 3, Number 1, March 2015
 

Abstract
China accounts for nearly half of the global steel production. As a waste material or a by-product in the manufacture process, a large amount of blast furnace slag is generated every year. The majority of recycled blast furnace slag is used as an additive in low-grade blended cement in China (equivalent to the UK CEM II or CEM III depending on the slag content). The cost of using ground granulated blast furnace slag (GGBS) in such low-grade applications may not be entirely reimbursed based on market research. This paper reports an on-going project at Xi\'an Jiaotong-Liverpool University (XJTLU) which investigates the feasibility of using GGBS in long-span concrete structures by avoiding/reducing the use of crack control reinforcement. Based on a case study investigation, with up to 50% of CEM I cement replaced with GGBS, a beneficiary effect of reduced thermal contraction is achieved in long-span concrete slabs with no significant detrimental effect on early-age strengths. It is believed that this finding may be transferable from China to other Asian countries with similar climates and economic/environmental concerns.

Key Words
concrete thermal contraction; finite element analysis

Address
Kangkang Tang: Department of Civil Engineering, Xi

Abstract
Ongoing efforts for improved fracture toughness of engineered cementitious materials address the inherent brittleness of the binding matrix at several different levels of the material\'s geometric scale through the addition of various types of reinforcing fibers. Crack control is required for crack widths that cover the entire range of the grain size spectrum of the material, and this dictates the requirement of hybrid mixes combining fibers of different size (nano, micro, macro). Use of Carbon Nano-Tubes (CNT) and Carbon Nano-Fibers (CNFs) as additives is meant to extend the crack-control function down to the nano-scale where cracking is believed to initiate. In this paper the implications of enhanced toughness thus attained at the material nanostructure are explored, with reference to the global smeared constitutive properties of the material, through consistent interpretation of the reported experimental evidence regarding the behavior of engineered cementitious products to direct and indirect tension.

Key Words
carbon nanotubes/nanofibers; constitutive relations; stress-strain; cementitious materials; fibers; bond; hybridization

Address
Nikolaos D. Archontas: Electrical & Computer Engineering Department, Democritus University of Thrace, 67100, Greece

S.J. Pantazopoulou: Department of Civil & Environmental Engineering, University of Cyprus, P.O. Box 20537, 1678 Cyprus

Abstract
Relative humidity and strains within a massive concrete cylinder (450 mm X 900 mm) in the drying and the re-saturating process were measured for elucidating the process of ASR surface cracking in concrete. The expansion behavior of mortars in dry atmospheres with various R.H. values and the re-saturating process was revealed. Non- or less-expansive layers were formed in near-surface regions in the concrete cylinder in the drying process, but ASR expansions actively progressed in inner portions. After re-saturating, R.H. values of near-surface regions rapidly increased with time, but expansions in the regions were found to be very small. However, in the middle portions, of which R.H. values were kept 80% ~ 90% R.H. in the drying process, expansion actively progressed, resulting in further development of surface cracks in the re-saturating process.

Key Words
alkali-aggregate reaction; massive concrete; humidity; expansion; cracks detection

Address
Hiroyuki Kagimoto: Wakamatsu Operations & General Management Office, Electric Power Development Co., Ltd., 1,Yanagasaki, Wakamatsu-ku, Kitakyushu, Japan

Yukihiro Yasuda: JPower design Co.,Ltd, Chigasaki, Kanagawa, Japan

Mitsunori Kawamura: Kanazawa University, Kakuma, Kanazawa, Ishikawa, Japan

Abstract
Tailing Material (TM) and Fly Ash (FA) are obtained as waste products from the mining and thermal industries. Studies were carried out to explore the possibility of utilizing TM as a part replacement to fine aggregate and FA as a part replacement to cement, in concrete mixes. The effect of replacing fine aggregate by TM and cement by FA on the standard sized specimen for compressive strength, split tensile strength, and flexural strengths are evaluated in this study. The concrete mix of M40 grade was adopted with water cement ratio equal to 0.40. Concrete mix with 35% TM and 65% natural sand (TM35/S65) has shown superior performance in strength as against (TM0/S100, TM30/S70, TM40/S60, TM50/S50, and TM60/S40). For this composition, studies were performed to propose the optimal replacement of Ordinary Portland Cement (OPC) by FA (Replacement levels studied were 20%, 30%, 40% and 50%). Replacement level of 20% OPC by FA, has shown about 0-5% more compressive strength as against the control mix, for both 28 day and 56 days of water curing. Interestingly results of split tensile and flexural strengths for 20% OPC replaced by FA, have shown strengths equal to that of no replacement (control mix).

Key Words
iron ore tailings; fly ash; blended concrete; strengths

Address
Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal, PO: Srinivasanagar, Mangalore-575025, Karnataka, India

Abstract
In order to investigate the feasibility and advantage of tuff used as pozzolan in cement-based composite, the representative specimens of tuff were collected, and their chemical compositions, proportion of vitreous phase, mineral species, and rock structure were measured by chemical composition analysis, petrographic analysis, and XRD. Pozzolanic activity strength index of tuff was tested by the ratio of the compression strength of the tuff/cement mortar to that of a control cement mortar. Pozzolanic reaction degree, and the contents of CH and bond water in the tuff/cement paste were determined by selective hydrochloric acid dissolution, and DSC-TG, respectively. The tuffs were demonstrated to be qualified supplementary binding material in cement-based composite according to relevant standards. The tuffs possessed abundant SiO2+Al2O3 on chemical composition and plentiful content of amorphous phase on rock texture. The pozzolanic reaction degrees of the tuffs in the tuff/cement pastes were gradually increased with prolongation of curing time. The consistency of CH consumption and pozzolanic reaction degree was revealed. Variation of the pozzolanic reaction degree was enhanced with the bond water content and relationship between them appeared to satisfy an approximating linear law. The fitting linear regression equation can be applied to mutual conversion between pozzolanic reaction degree and bond water content.

Key Words
cement; tuff; pozzolan; content

Address
Lehua Yu, Shuangxi Zhou and Wenwu Deng: School of Civil Engineering, East China Jiaotong University, Nanchang 330013, China


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