I W S C (SSC) S R FRP C - SEACONseacon.um-sml.com/uploads/1/6/7/2/16727926/workshop...environmentally detrimental; desalination of seawater and sea sand is also costly. The use of

Proceedings of the INTERNATIONAL WORKSHOP ON SEAWATER

SEA-SAND CONCRETE (SSC) STRUCTURES

REINFORCED WITH FRP COMPOSITES

13 December 2016

Editors: J.G. Teng, J.G. Dai and G.M. Chen

Organized by: Department of Civil and Environmental Engineering & Research Institute for Sustainable Urban Development

The Hong Kong Polytechnic University

Copyright©2016 Department of Civil and Environmental Engineering & Research Institute for Sustainable Urban Development, The Hong Kong Polytechnic University Authors retain all proprietary rights in any process, procedure, or article of manufacture described in the Work. Authors may reproduce or authorize others to reproduce the Work, material extracted verbatim from the Work, or derivative works for the author’s personal use or for company use, provided that the source is indicated. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission from the publisher. Although all care is taken to ensure the integrity and quality of this publication and the information herein, no responsibility is assumed by the publisher nor the authors for any injury and/or damage to property or persons as a result of operation or use of this publication and/or the information contained herein. ISBN: 978-988-14480-3-3 Published by: Department of Civil and Environmental Engineering & Research Institute for Sustainable Urban Development, The Hong Kong Polytechnic University, Hong Kong, China.

Proceedings of the

International Workshop on Seawater Sea-sand Concrete (SSC) Structures Reinforced with FRP Composites

13 December 2016, Hong Kong, China

Organised by Department of Civil and Environmental Engineering & Research Institute for Sustainable Urban Development


Sponsored by Research Institute for Sustainable Urban Development


Co-sponsored by SEACON Project and Fibrpro International Limited

Organizing Committee

Chair: Professor Jin-Guang TENG, The Hong Kong Polytechnic University

Co-chair: Dr. Jian-Guo DAI, The Hong Kong Polytechnic University Secretariat: Dr. Guang-Ming CHEN, Guangdong University of Technology

Ms. Jan LIEN, The Hong Kong Polytechnic University

International Workshop on Seawater Sea-sand Concrete (SSC) Structures Reinforced with FRP Composites 13 December 2016, Hong Kong, China

i

Preface Coastal cities like Hong Kong rely heavily on their marine/coastal infrastructure (e.g. ports, bridges & artificial islands) for social-economic development. A major challenge for marine infrastructure is its deterioration due mainly to steel corrosion in steel-reinforced concrete structures. Another major challenge for marine infrastructure is the shortage of fresh water and river sand (or crushed stone fines) for making concrete. Apart from the negative environmental effects of consuming great amounts of fresh water and river sand/crushed stone fines, their transportation is both expensive and environmentally detrimental; desalination of seawater and sea sand is also costly. The use of fibre-reinforced polymer (FRP) to replace steel in concrete structures to eliminate the steel corrosion problem has been gaining increasing acceptance over the past two decades. If FRP is used as the reinforcing material, then locally available seawater and sea-sand can be directly used to make concrete instead of freshwater and river sand as FRP is expected to be little affected by the rich chloride content in seawater/sea-sand. The resulting structures, made of FRP and seawater sea-sand concrete (SSC) (i.e., FRP-SSC structures), have the potential to offer many significant advantages, including: cost-effective marine infrastructure with a longer service life, savings in material transportation costs, better protection of rivers due to reduced sand mining, and savings in freshwater which is a scarce resource on the planet. The idea of using SSC with FRP in marine construction was first proposed by the Chair of the present Workshop at a national conference in 2011 held in Hangzhou, China and later promoted internationally on a number of occasions. As a result, a significant number of research projects have since been funded around the world, and a number of publications have appeared on the subject. It is obvious that for this important technology to become widely used in the near future, extensive research is needed to gain an in-depth understanding of and develop design and construction methods for FRP-SSC structures. One key issue to be addressed is the long-term performance of FRP-SSC structures in marine environments. While significant evidence has accumulated that the rich chloride content in seawater/sea-sand has little effect on the performance of FRP composites, they can suffer deterioration due to other factors such as the ingress of moisture. This Workshop was organised to provide the first international forum for in-depth exchanges on FRP-SSC structures and closely related topics (e.g., behaviour of SSC; field exposure tests of FRP bars in marine environments) to achieve the following specific objectives: (1) Examine in detail the advantages and challenges brought about by FRP-SSC structures; (2) Provide a survey of research projects being undertaken or planned around the world on FRP-SSC structures and

closely related topics; (3) Identify key issues to be tackled before FRP-SSC structures can be widely accepted in practice; and (4) Explore opportunities for international collaboration to accelerate research progress in the area. The program of the Workshop included 15 invited presentations on FRP-SSC structures or related topics. Each paper was followed by extensive discussions to achieve the objectives of the Workshop. The Workshop was attended by over 70 participants (including the invited speakers). Many people have contributed to the organization of the Workshop. We would like to thank all invited speakers for sharing their work and insight at the Workshop and all participants for their interest and support for the Workshop and their participation in the discussions. We are also grateful to the two co-sponsors (SEACON, a project funded by Infravation, and Fibrpro International Limited) for their support to the Workshop and to Prof. Tony Nanni for his help and enthusiasm for the Workshop. Over the past few years, we have benefited greatly from exchanges with many researchers on the topic, particularly through the preparation of a research proposal for submission to the Theme-based Research Scheme of the Hong Kong Research Grants Council. We are grateful to all of them for sharing their wisdom and insight with us. Our special thanks go to Dr. Guang-Ming CHEN and Ms Jan LIEN, who provided the much needed secretarial support, covering technical, logistics and all other necessary aspects. Jin-Guang TENG (Workshop Chair) & Jian-Guo DAI (Workshop Co-Chair)


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TABLE OF CONTENTS PREFACE i

TABLE OF CONTENTS ii

WORKSHOP PROGRAMME iii

STUDY ON THE PERFORMANCES OF CONCRETE MADE WITH DREDGED MARINE SAND FROM THE PEARL RIVER MOUTH F. Xing, W. Liu

1

MICROSTRUCTURAL CHARACTERIZATION AND DURABILITY OF GFRP REINFORCING BARS EXPOSED TO CONCRETE ENVIRONMENT AND SALINE SOLUTION B. Benmokrane, A.H. Ali and H. Mohamed

3

LONG-TERM EXPOSURE PERFORMANCE OF FRP COMPOSITES IN MARINE ENVIRONMENTS I. Nishizaki, I. Sasaki and H. Sakuraba

14

DEGRADATION OF FRP COMPOSITES EXPOSED TO SEAWATER G.J. Xian and Z.Y. Lu

16

BEHAVIOUR OF FRP-CONFINED SEAWATER SEA-SAND (SSC) CONCRETE J.F. Chen, G.M. Chen, Z.B. He and J.G. Teng

18

CURRENT RESEARCH AT MONASH UNIVERSITY ON HYBRID CONSTRUCTION USING SEAWATER SEA SAND CONCRETE AND FRP X.L. Zhao

19

BOND BEHAVIOR BETWEEN SEAWATER SEA-SAND CONCRETE AND FRP J.Z. Xiao, C.B. Qiang and Q.T. Zhang

20

EXPERIMENTAL STUDY ON SEAWATER CORAL AGGREGATE CONCRETE FILLED FRP TUBES UNDER AXIAL COMPRESSION Jie Wang and Peng Feng

21

HYBRID STRUCTURES MADE OF SEAWATER SEA-SAND (SSC) CONCRETE AND FRP: CURRENT STATUS AND RESEARCH NEEDS J.G. Teng

22

HOW DO WE DETERMINE THE SUSTAINABILITY OF SEAWATER SEA-SAND CONCRETE AND FIBER-REINFORCED POLYMER COMPOSITE (FRP-SSC) STRUCTURES? Lawrence C. Bank

23

CHEMOMECHANICAL BEHAVIOR OF CEMENT-BASED MATERIALS AND MOLECULAR DYNAMICS MODELING AT INTERFACES F. Sanchez

24

LAYER-BY-LAYER ASSEMBLY OF MULTI-WALLED CARBON NANOTUBES ON LONG-PERIOD GRATING SENSORS FOR MARINE ENVIRONMENTAL MONITORING Y.Q. Ni, S.Q. Ding and H.P. Wang

26

SEACON AND THE HALLS RIVER BRIDGE PROJECT Antonio Nanni

28

CONCRETE DURABILITY AND THE A1 MOTORWAY CULVERT PROJECT L. Bertolini

29

PERSPECTIVE OF A CEMENT MANUFACTURER ON SEAWATER SEA-SAND CONCRETE F. Canonico

30


iii

Workshop Programme Room V312, Floor 3, Jockey Club Innovation Tower (JCIT), PolyU

Time Invited Speaker Title of presentation 8:00-8:30 Registration 8:30-8:40 Opening remarks by Prof. J.G. Teng Session Chair: Professor Xiao-Ling ZHAO 8:40-9:05 Prof. Feng XING

(To be delivered by Prof. Ningxu HAN) Shenzhen University, China

Study on the performance of concrete made with dredged marine sand from the Pear River mouth

9:05-9:30 Prof. Brahim BENMOKRANE University of Sherbrooke, Canada

Microstructural characterization and durability of GFRP reinforcing bars exposed to concrete environment & saline solution

9:30-9:55 Dr Itaru NISHIZAKI Innovative Materials and Resources Research Centre, Public Works Research Institute, Tsukuba, Japan

Long-term exposure performance of FRP composites in marine environments

9:55-10:20 Prof. Gui-Jun XIAN Harbin Institute of Technology, China

Degradation of FRP composites exposed to seawater

Session Chair: Professor Larry C. BANK 10:20-10:40 Coffee Break 10:40-11:05 Prof. Jian-Fei CHEN

Queen’s Univesrity Belfast, UK Behaviour of FRP-confined seawater sea-sand concrete

10:05-11:30 Prof. Xiao-Ling ZHAO Monash University, Australia

Current research at Monash University on hybrid construction using seawater sea-sand concrete and FRP

11:30-11:55 Prof. Jian-Zhuang XIAO Tongji University, China

Bond behaviour between seawater sea-sand concrete and FRP

11:55-12:20 Prof. Peng FENG Tsinghua University, China

Experimental study on seawater coral aggregate concrete filled FRP tubes under axial compression

12:20-14:00 Lunch (Free for all participants) Session Chair: Professor Brahim BENMOKRANE 14:00-14:25 Prof. Jin-Guang TENG

The Hong Kong Polytechnic University, China

Hybrid structures made of seawater sea-sand (SSC) concrete and FRP: current status and research needs

14:25-14:50 Prof. Larry C. BANK City College of New York, USA

How do we determine the sustainability of seawater sea-sand concrete and fibre-reinforced polymer composite (FRP-SSC) structures?

14:50-15:15 A/Prof. Florence SANCHEZ Vanderbilt University,USA

Chemomechanical behaviour of cement-based materials and molecular dynamics modelling at interfaces

15:15-15:40 Prof. Yi-Qing NI The Hong Kong Polytechnic University, Hong Kong, China

Layer-by-layer assembly of multi-walled carbon nanotubes on long-period grating sensors for marine environmental monitoring

15:40-16:00 Coffee Break Session Chair: Dr. Jian-Guo DAI 16:00-16:25 Prof. Antonio NANNI

University of Miami, USA SEACON and the Halls River Bridge project*

16:25-16:50 Prof. L. BERTOLINI (To be delivered by Dr. Federica Lollini) Politechnic of Milan, Italy

Concrete durability and the A1 Motorway culvert project*

16:50-17:15 Dr. F. CANONICO Buzzi Unicem SpA, Italy

Perspective of a cement manufacturer on seawater sea-sand concrete*

17:15-18:00 Discussions (Chair: Prof. Jin-Guang TENG) * Presentation via WebEX

http://www1.ccny.cuny.edu/index.cfm


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STUDY ON THE PERFORMANCES OF CONCRETE MADE WITH DREDGED MARINE SAND FROM THE PEARL RIVER MOUTH

F. Xing and W. Liu College of Civil Engineering, Shenzhen University, Shenzhen, 518060, P. R. China, Email: [email protected]

(F. Xing); [email protected] (W. Liu) ABSTRACT Marine aggregates are naturally occurring sand and gravels found in sea or dredged from seabed. They can be used as aggregate in concrete after appropriate desalting treatments. They are significant marine mining resources. Marine aggregates hold a large proportion of construction sand and gravels in some coastal cities of China due to the shortage of aggregates on land. Unlike river sand, marine sand contains soluble salts and shell which restrict its use in concrete. Particularly, chloride slat content in marine sand makes a larger effect on the properties of concrete, including affecting hydration of Portland cement (Dong et al. 2013), carbonation of concrete (Liu et al. 2016) and causing corrosion of reinforcing bars in concrete (MA et al 2007). In this research, the characteristics of dredged marine sand (DMS) from the Pearl River Mouth were compared with rive sand (RS). Then, the mechanical and durability properties of concrete made with these DMS were studied. The results indicated that the RS surface is rough and matte. In contrast, the surface of DMS is more smooth and lustrous than RS, the DMS and RS possess similar mineral compositions and that their primary minerals are quartz and feldspar (Figure 1). But the DMS has chloride ions attached on the surface of DMS, which is a potential factor for steel bar corrosion (Figure 2). According to comparison studies of DMS concrete and RS concrete between mechanical properties (compressive strength and elastic modulus), and durability (carbonation, and chloride ion penetration), DMS as equal as RS can be employed to manufacture Grade C20 to C80 concrete (Figure 3). Based on the relationship between chloride ion content of DMS and corrosion behavior of rebar embedded in DMS concrete (Figure 4), limit values of chloride ion content for DMS and DMS concrete were suggested. Referring to development trend of limit values of chloride ion content in international standards or codes, when DMS was used for reinforcement concrete (RC) structure under Type I general dry environments, limit value of chloride ion content for DMS shall be less than 0.18%, and whilst the value for DMS concrete shall be less than 0.30%. Moreover, when DMS was used for RC structure under chloride-bearing environments, the value for DMS shall be less than 0.06%, whilst, for DMS concrete, the value shall be less than 0.10%. KEYWORDS Dredged marine sand, Concrete, Durability, Chloride ions REFERENCES Dong Bi-qin, Liu Wei, Xing Feng, et al. (2013). “Electrochemical impedance spectroscopy on the hydration behavior of

the mortar with marine sand”. Journal of Building Materials, 2, 306-309(in Chinese) Wei Liu, Hongzhi Cui, Zhijun Dong, Feng Xing, et al. (2016). “Carbonation of concrete made with dredged marine sand

and its effect on chloride binding”. Construction and Building Materials, 120, 1-9. MA Hong-yan, Xing Feng, Dong Bi-qin, et al. (2007). “Study of electrochemical characteristics for steel corrosion in sea

sand concrete”, Concrete,7, 20-23 (in Chinese)


2

Figure 1 XRD diagrams of RS and DMS Figure 2 EDX test results for DMS

Figure 3 Comparison of mechanical properties and durability of concrete made with DMS concrete and RS concrete

(A: River sand, B: Washed marine sand, C: Marine sand)

a) Ecorr b) icorr

Figure 4 Effect of chloride content on the Ecorr and icorr of rebar embedded in DMS concrete.


3

MICROSTRUCTURAL CHARACTERIZATION AND DURABILITY OF GFRP REINFORCING BARS EXPOSED TO CONCRETE ENVIRONMENT

AND SALINE SOLUTION

B. Benmokrane1, A.H. Ali2 and H. Mohamed2 1NSERC and Canada Research Chair Professor, Department of Civil Engineering,

University of Sherbrooke, Sherbrooke, Quebec, Canada, 2Postdoctoral Fellow, University of Sherbrooke, Sherbrooke, Quebec, Canada,

Email : [email protected] ABSTRACT This study was conducted to investigate the mechanical, microstructural, and durability properties of two types of vinyl-ester / glass-fiber-reinforced-polymer (GFRP) solid and tubular GFRP bars. The testing program aimed to assess the long-term durability characteristics of tubular and solid GFRP bars subjected to a saline solution (simulating seawater) and predicting their long-term tensile strength in such environments. The tubular GFRP bars were filled with cement grout to simulate concrete environment. The study simulated rather aggressive conditions by immersing the tubular and solid GFRP bars in the solution at different elevated temperatures (20ºC, 40ºC, and 50ºC) in climate chambers for different exposure times of 1000, 3000 and 5000 h. Arrhenius plots were applied to the test results, extrapolating the project’s life to 50 years at a mean annual temperature (MAT) of 32ºC (hot marine environment). The results show the very high long-term durability of solid and tubular bars exposed to field conditions. The predicted tensile strength at a MAT of 32oC is 96.8 and 97.3 % for a service life of 50 years for solid and tubular GFRP bars, respectively. Based on the obtained results, the tested GFRP bars were recommended as alternatives to stainless-steel bars for concrete structures in marine environment and to stainless-steel rock bolts as ground control in subsea caverns for gas or oil storage. KEYWORDS Durability, FRP, solid & tubular GFRP bars, aging, saline solution, concrete, tensile strength, modelling, long-term prediction, marine environment, subsea INTRODUCTION The strength of the glass fibers and resin matrix—two GFRP reinforcing bar constituents—can decrease when subjected to wet alkaline or saline environments (Benmokrane et al., 2011). Thus, an adequate durability study of GFRP bars should be performed to gain wide acceptance of their use in the civil-engineering and mining industries. Considerable research has been conducted in the past decade to assess the suitability of GFRP reinforcement in reinforced-concrete structures (Benmokrane et al. 2016; Ali et al. 2015, Robert et al., 2009; Riebel and Keller, 2007; Micelli and Nanni, 2004, Benmokrane et al. 2015). The work of these researchers has highlighted the short-term performance of GFRP-reinforced concrete structures and the durability of GFRP reinforcing bars subjected to aging in alkaline solutions. Some researchers have reported on the durability of GFRP bars embedded in moist concrete, which simulates actual application conditions, and on the adverse effects of cracks and microcracks in GFRP bars on their long-term durability (Robert and Benmokrane, 2010a). Nevertheless, the data on the durability of GFRP bars subjected to saline solutions simulating marine applications are very limited. The resins widely used for GFRP composites include polyester, vinyl ester, and epoxy (ACI 440.1R-15). Weak adhesion of polyester or vinylester can result in serious deterioration when hydroxyl ions penetrate the structure (Coomasaramy and Goodman, 1999). On the other hand, a considerable drawback of epoxy is that it can absorb from 1% to 7% moisture by weight, which plasticizes the matrix, inducing differential swelling stresses and generally degrading physical properties (Soles et al., 1998). In general, the matrix could be damaged through cracking and microcracking due to volume expansion during moisture absorption, whereas its stiffness could be reduced by plasticization. A subsequent mechanism of degradation resulting from the breaking of polymer chains triggered by hydrolysis and the leaching out of low molecular-weight material from the bulk resin could further damage the matrix (Ashbee et al, 1967; Ashbee and Wyatt, 1969). In comparison to the polyester matrix, the matrix formed by vinyl ester—which contains significantly fewer ester units than polyester—remains generally unaffected by hydroxyl ions. Glass fibers are the most susceptible to degradation due to moisture and alkalinity (Benmokrane et al., 2006). Dejke (1999) reported that E-glass fibers are known to degrade in the presence of water, and that moisture can decrease the resin’s glass transition temperature (Tg) and act as a plasticizer, potentially having significant effect on the strength of GFRP materials. The reaction of the GFRP composite with the alkali in concrete is a major durability concern. Typically, concrete environments have high alkalinity, depending on the design mixture and type of cement used (Diamond, 1981;


4

Taylor, 1987). This alkaline environment damages glass fibers through loss in toughness and strength and through embrittlement. Glass fibers are damaged due to the combination of two processes: (1) chemical attack of the glass fibers by the alkaline cement environment and (2) concentration and growth of hydration products between individual filaments (Murphy et al., 1999). Fiber embrittlement results from the nucleation of calcium hydroxide on the fiber surface. Hydroxylation can cause fiber-surface pitting and roughness, which act as flaws, severely reducing fiber properties in the presence of moisture. In addition, calcium, sodium, and potassium hydroxides in the concrete pore solution are aggressive to glass fibers (Benmokrane et al., 2002). Therefore, the degradation of glass fibers depends not only on a high pH level, but also on the combination of alkali salts, pH, and moisture. The deterioration at the fiber–matrix interface involves a much more complex mechanism (Chen et al., 2007). The interface—a nonhomogeneous region about 1 µm thick—is weakly bonded and most vulnerable to deterioration (Chen et al., 2007). The three dominant deterioration mechanisms include matrix osmotic cracking, interfacial debonding, and delamination (Bradshaw and Brinson, 1997). The moisture diffusion into FRP composites could be influenced by the material’s anisotropic and heterogeneous character. Along with diffusion into the matrix, wicking through the fiber–matrix interface in the fiber direction could be a predominant mechanism of moisture ingress (Apicella et al., 1982; Prian and Barkatt, 1999). Nonvisible dissociation between fibers and matrix could lead to rapid losses of interfacial shear strength (Ashbee and Wyatt, 1969). In order to assess the long-term durability performance of GFRP in harsh environments, extensive studies have been conducted to develop accelerated aging procedures and predictive models for long-term strength estimates (Porter et al., 1997; Dejke, 2001; Bank et al., 2003; Chen et al., 2006). These models are based on the Arrhenius model. Research on the effects of temperature on the durability of FRP bars in concrete alkaline environments indicates that an acceleration factor for each temperature difference can be defined using Arrhenius laws. These factors differ for each product, depending on the fiber and resin types and bar size. In addition, these factors are affected by environmental conditions, such as the surrounding solution media, temperature, pH, moisture, and freeze–thaw conditions. Predictive models based on Arrhenius laws make the implicit assumption that the elevated temperature will only increase the rate of degradation without affecting the degradation mechanism or introducing other mechanisms. Bank et al., 2003 indicated that at least three elevated temperatures were necessary to perform an accurate predication based on Arrhenius laws. Moreover, the measured data should be in continuous time intervals. We followed those recommendations for this study. RESEARCH GAP AND STATEMENT OF THE PROBLEM Several studies have addressed the durability of GFRP bars as internal reinforcement of concrete (Robert et al., 2009; Chen at al., 2006). Very limited studies, however, have been conducted on the durability of GFRP bars subjected to saline solutions, which would be of crucial relevance to the marine structures. The properties of the pultruded products (void content, interface quality, and fiber distribution) and the nature of the aggressive environment can lead to important changes in the final product’s behavior and durability. As such, the available knowledge on the durability of GFRP reinforcing bars subjected to typical alkaline solutions as specified by ASTM D7705 may not be directly applicable to GFRP bars subjected to saline solution and high temperature at the same time. In addition, engineers now aim to design structures with service lives of 75 to 150 years, thereby requiring studies that predict the durability and service life of the new GFRP bars, including solid and tubular bars, used for marine concrete structures. Our study aimed at assessing the environmental durability of GFRP bars subjected to a saline solution simulating the marine structures and predicting their long-term behavior in such environments. The study simulated rather aggressive conditions by immersing the GFRP bars in a saline solution (simulating seawater) at different elevated temperatures for 5000 h. Two types of GFRP bars were tested: 1) solid bar, and 2) tubular (or hollow) bar as shown in Figure 1. Tensile strength was considered the primary structural parameter, and was therefore used an indicator of degradation due to exposure. Additional microstructural and physical characterizations were performed, and service-life models were established. TUBULAR VERSUS SOLID GFRP BARS ADVANTAGES Recently, a new developed tubular GFRP bars (with a hollow-core) have been developed and introduced in the market. Compared to bars with equivalent cross-sectional area, the two main advantages tubular bars provide are: a) increase in surface area, yielding higher bond-to-concrete; and b) reduction of shear-lag effect, increasing the effective cross-sectional area of glass fibres carrying load (Claure et al. 2014). Figure 2 presents a schematic drawing for the phenomenon of shear lag for the solid and tubular GFRP bars. The figure indicated that when the FRP bars exhibited to tensile forces, the tensile strength undergoes change caused by the development of higher stress in the outer fibers than in the inner ones due to the shear lag occurring in the section of the bar (Achillides and Pilakoutas 2004).


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Figure 1. View of GFRP: (a) solid bar, (b) tubular bar, and (c) tubular bar filled with cement grout.

This phenomenon can be attributed to the fact that the stress developed at the fiber located near the surface of the bar is not fully transferred to the fibers located at the core, hence, resulting the nonefficiency of the whole section. Since the shear lag eliminates the central fibers from fully developing their proper performance, a cost-efficient section can be designed using tubular GFRP bars with equivalent cross-sectional area.

Figure 2: Shear lag of solid and tubular GFRP bars EXPERIMENTAL APPROACH

Material Solid (Type K60/25) and tubular (Type J64/28/(12)) GFRP bars manufactured by Firep International AG (Switzerland) were examined and tested at the University of Sherbrooke. The solid GFRP bars (K60/25) had an outer diameter of 25 mm, while the tubular bar (J64/28/(12)) had an outer diameter of 28 mm with an inn diameter of 12 mm. The solid and tubular GFRP bars were designed to have the same cross-sectional area for stress calculation: 350 mm2 as the nominal area and 443 mm2 as the effective cross-sectional area (area by immersion test). All the tensile properties reported in this paper were determined using the nominal area of 350 mm2 for the both GFRP bars. Figure 1 shows a picture of the solid and tubular GFRP bars, which have continuously profiled surfaces. Both the solid and tubular GFRP bars were made of continuous ECR-glass fibers impregnated in a vinyl-ester resin using the pultrusion process, leading to a cure ratio of more than 99%. The mass fractions of glass were 83.0% and 82.5% for the solid and tubular bars, respectively, and were determined by thermogravimetric analysis according to ASTM E1131. Their relative densities according to ASTM D792 were 2.11 and 2.09 for the solid and tubular bars, respectively. All of the bars were cut into 1440 mm lengths to perform tensile testing as specified in ASTM D7205. The GFRP bars were divided into three series: (1) the unconditioned reference samples (solid and tubular), (2) the conditioned solid samples (27 bars) immersed in saline solution, and, (3) conditioned tubular samples (27 bars) filled with cement grout and immersed in saline solution. The cement grout used to fill the tubular GFRP bars consisted of Type I cement according to ASTM C150 and had a water-to-cement ratio (w/c) of 0.40. Test Plan This study used accelerated aging in a saline solution simulating the seawater. The specimens were completely immersed at three different temperatures (22oC, 40oC, and 50oC) and were removed from the water after three different periods of time (1000, 3000, and 5000 h) to lead to predictions about long-term properties.. The pH value of the saline solution was around 6.7. Table 1 presents the complete composition of the saline solution used in this study. The pH of the solution surrounding the cement-grout-filled tubular bars resulted from the pH of the saline solution and from the cement grout absorbing water, thereby releasing alkaline ions into the bar environment. The aging was performed by immersing the GFRP bars in stainless-steel containers specially manufactured for the study (Figure 3). The containers were tightly closed with lids to prevent excessive evaporation of water during conditioning. The bars were spaced apart and from the bottom of the container to allow the solution to freely circulate between and around the bars. Furthermore, the water level was kept constant throughout the study to avoid a pH increase, which could result from decreased water level, and a significant increase of alkaline ions in the solution. The immersion temperatures were chosen to accelerate the

(a) (b) (c)

Solid GFRP bar

Normal stress distribution

Normal stress distribution

Tubular GFRP bar

δverage δmax

δmin δmax

δmax

δmax

δmin δmin


6

degradation effect of aging. They were not so high, however, as to produce any thermal-degradation mechanisms [Robert et al., 2010b]. For predicting long-term properties, three solid GFRP bars and three cement-grout-filled tubular GFRP bars were removed from the saline solution after every time period and tested under tension to compare their tensile-strength retention values to those of the reference specimens. The surface of the GFRP bars (solid or tubular) evidenced no significant changes after specimen immersion.

Figure 3: Stainless-steel container built for aging the GFRP specimens in saline water (simulating seawater):

(a) conditioning at ambient temperature and (b) conditioning at 50ºC

Table 1: Complete composition of the saline solution (simulating seawater) used in this study

Compound Concentration (g/L of distilled water) Ionic Content

Ion Content (ppm) Sodium chloride (NaCl) 26 Cl- 16 760

Potassium sulfate (K2SO4) 0.6 SO42- 2330

Calcium chloride (CaCl2) 1.5 Na+ 10 200 Magnesium sulfate (Mg2SO4) 3.0 Mg2+ 1000

Ca2+ 540 K+ 270

Tensile Tests All of the GFRP bars were tested under tension according to ASTM D7205. The tubular GFRP bars were tested with their cement-grout core centered to avoid any damage to the specimen due to the removal of the cement grout. Due to the brittle nature of GFRP, no yielding occurred and the stress–strain behavior was linear. Arrhenius Relation Equation (1) expresses the Arrhenius relation in terms of the degradation rate (Nelson, 1990)

(1)

where k = degradation rate (1/time); A = constant relative to the material and degradation process; Ea = activation energy of the reaction; R = universal gas constant; and T = temperature in degrees Kelvin. The primary assumption in this model is that only one dominant degradation mechanism of the material operates during the reaction and that this mechanism will not change with time and temperature during the exposure [Chen et al., 2006]. Only the rate of degradation will be accelerated with increased temperature. Equation (1) can be transformed into:

(2)

(3)

From Equation (2), the degradation rate k can be expressed as the inverse of time needed for a material property to reach a given value [Chen et al., 2006]. From Equation (3), one can further observe that the logarithm of time needed for a material property to reach a given value is a linear function of 1/T with a slope of Ea /R [Chen et al., 2006]. Ea and A can be easily calculated by using the slope of the regression and the point of intersection between the regression and the y–axis, respectively.

−=

RTE

Ak aexp

=

RTE

Akaexp11

( )ATR

Ek

a ln11ln −=

(a) (b)


7

Water-Immersion Test The moisture uptake at saturation of the solid and tubular GFRP bars was determined before and after conditioning according to ASTM D570, except that the immersions were performed in tap water instead of distilled water. Scanning Electron Microscopy (SEM) SEM observations and image analysis of the solid and tubular GFRP bars were performed to observe specimen microstructure before and after aging. The samples observed under SEM were the unconditioned specimens and specimens aged for 5000 h in the saline solution at 50oC, which is harsher aging. All specimens observed under SEM were first cut, polished, and coated with a thin layer of gold–palladium with a vapor-deposition process. After the surfaces were coated, microstructural observations were performed on a JEOL JSM-840A SEM. These observations were conducted to determine any potential degradation of the polymer matrix, glass fibers, or interfaces. Differential Scanning Calorimetry (DSC) Twelve-milligram to 15 mg specimens from both unconditioned and aged samples were sealed in aluminum pans and analyzed in a TA Instruments DSC Q10 calorimeter equipped with a refrigerated cooling system. Analysis was conducted on solid and tubular GFRP bars in modulated DSC mode. The specimens were heated from 25°C to 195°C at a rate of 5oC/min. The glass transition temperature (Tg) was determined for both specimens in accordance with ASTM E 1356. Two scans were performed for each specimen. The first scan is useful in determining the difference in Tg between the reference and conditioned specimens. A decrease in Tg for the conditioned samples would indicate a plasticizing effect or chemical degradation. The second scan gives information about the degradation mechanism. A shift to a higher Tg could be observed due to post-curing during the first scan. If the aged sample’s Tg falls within the same range as the Tg of the reference sample after the second scan, then the plasticizing effect due to the moisture absorption is reversible. If the aged sample’s Tg remains lower than that of the reference, the chemical degradation is irreversible. TESTS RESULTS AND DISCUSSION

Tensile-Strength Retention The tensile testing of the unconditioned specimens showed an approximately linear behavior up to failure. All of the specimens failed suddenly, as expected, as the result of fiber rupture. Figure 3 shows the failure mode of representative specimens for each GFRP bar type. All the failures started with splitting and ended with bar rupture. The splitting was accompanied by the delamination of fibers and resin, as shown in Figure 3. The failure initiated at the quarter point of the gauge length and extended to the other side by delamination. This might also be related to the bar’s surface type (continuously profiled surface). A similar mode of failure was observed for the specimens immersed in the saline solution, as shown in Figure 3. Micelli and Nanni (2004) also observed similar tensile-failure modes of GFRP bars. It is also worth mentioning that no chemical deposits were observed on the surface of the conditioned GFRP bars before tensile testing for residual properties. Table 2 shows the experimental results obtained during the tensile tests concerning the longitudinal tensile properties of the solid and tubular aged bars tested after immersion at 23°C, 40°C, and 50oC for 1000 h, 3000 h, and 5000 h. Figure 4 shows the tensile-strength retention of the aged bars according to the duration of immersion at various temperatures. As shown in Table 2, the tensile strength was equal to 1069±33 MPa and 1042±82 MPa for the unconditioned solid and tubular GFRP bars, respectively. Note that the bar tensile strength decreased to 1017±3 MPa and 927±77 MPa for the solid and tubular bars, respectively, after 5000 h exposure to the saline solution at 50°C. Figure 4 shows that no significant decrease of the ultimate tensile strength of solid and tubular bars occurred with increased immersion duration or temperature. It can be seen that, for an immersion duration of 5000 h at 50oC, the strength loss was 2% and 3 % for the solid and tubular GFRP bars, respectively. The slight variation in tensile strength is probably related to the slight increase in moisture absorption over time, leading to plasticizing effects of the polymer matrix [Montaigu et al., 2013]. Effect on Young’s Modulus Figure 5 shows the change in the elastic modulus of the aged bars with immersion time at various temperatures. Indeed, it can be seen from the measured results that, after 5000 h, the loss of elastic modulus was negligible; none of the aged solid and tubular GFRP bars were affected by the higher temperature or exposure to the saline solution. This result shows that the modulus of elasticity of the bars was not affected by aging in the simulated mining environment herein. This result can be explained by the fact that the Young’s modulus of unidirectional GFRP materials relates more to fiber properties, which are not affected by the saline solution (Robert and Benmokrane, 2013).


8

(a) Reference solid bars (b) Reference tubular bars

(c) Solid bars conditioned for 1000 h at 20oC (d) Tubular bars conditioned for 1000 h at 20oC

(e) Solid bars conditioned for 1000 h at 40oC (f) Tubular bars conditioned for 1000 h at 40oC

(c) Solid bars conditioned for 1000 h at 50oC (d) Tubular bars conditioned for 1000 h at 50oC

Figure 3: Typical failure mode of tested specimens subjected to tensile test Results of Water-Immersion Testing Table 3 presents the water uptake at saturation of the solid and tubular GFRP bars before and after conditioning in the saline solution. The results presented in Table 3 are the average values obtained from five test specimens. These results show that the moisture absorption at saturation of the solid and tubular GFRP bars was not affected by aging in the saline solution. The measured moisture uptake at saturation of the solid bars was 0.37% and 0.39%, respectively, before and after immersion in the saline solution for 5000 h at 50oC. For the tubular bars, the measured moisture uptake at saturation was 0.41% and 0.39%, respectively, before and after immersion in the saline solution for 5000 h at 50oC. The slight variation in moisture absorption is related to the precision of the scales used for the measurement.

Table 2: Test matrix and longitudinal tensile properties of reference and conditioned specimens

Immersion Time (h)

Temperature (oC)

Number of

Specimens

Mean Tensile Strength (MPa)

Modulus of Elasticity (GPa)

Ultimate Strain (%)

Solid COV (%) Tubular COV

(%) Solid COV (%) Tubular COV

(%) Solid COV (%) Tubular COV

(%) 0 23 5 1069±33 3 1042±82 8 60.8±1.7 2.8 62.8±1.5 2.3 1.76±0.1 4.6 1.66±0.1 5.9

1,000 23 3 1066±29 3 1084±21 2 55.1±3.3 5.9 63.4±0.7 1.1 1.94±0.1 4.1 1.71±0.1 1.5 40 3 1037±41 4 1045±7 1 56.1±0.9 1.5 63.4±1.1 1.7 1.85±0.1 4.3 1.65±0.1 1.8 50 3 1047±21 2 1006±152 5 59.6±0.9 1.6 62.0±1.0 14 1.76±0.1 3.54 1.62±0.2 14

3,000 23 3 1053±40 4 1059±5 1 57.4±2.9 5.0 62.2±0.6 0.9 1.84±0.1 4.9 1.70±0.1 1.0 40 3 1023±29 3 1051±93 9 56.1±1.7 3.0 61.9±1.4 2.2 1.82±0.1 4.2 1.70±0.1 6.6 50 3 1029±30 4 977±43 4 59.3±0.9 1.5 60.5±1.9 3.1 1.74±0.1 4.4 1.61±0.1 1.3

5,000

23 3 1084±18 2 1023±72 7 57.5±2.9 5.0 61.9±1.8 3.0 1.89±0.1 3.33 1.65±0.1 4.6 40 3 1012±28 3 965±16 2 57.8±2.6 4.4 62.1±0.7 1.1 1.76±0.1 7.10 1.56±0.1 2.6 50 3 1017±3 1 927±77 8 58.7±1.8 3.0 62.9±1.1 1.7 1.73±0.1 2.73 1.47±0.1 6.8


9

Figure 4: Tensile-strength retention of conditioned GFRP bars aged in saline solution at 22°C, 40°C, and 50°C for (a)

solid bars and (b) tubular bars.

Table 3: Water absorption at saturation before and after conditioning in the solution

Conditioning Temperature (oC)

Duration (hours)

Moisture Uptake (%) Solid Tubular

Unconditioned 0.37 0.41 Immersed in the saline solution 50 5000 0.39 0.39

Figure 5: Elastic moduli of reference and conditioned GFRP bars aged in saline solution at 23°C, 40°C, and 50°C for

(a) solid bars and (b) tubular bars. Microstructural Effects The visual and microstructural observations showed no significant damage after 5000 h of immersion in the saline solution simulating the seawater water at the highest temperature (50oC). The micrographs in Figures 6 and 7 show the fiber–matrix interface of the solid and tubular GFRP bars, respectively, for the unconditioned bars and for the bars aged in the saline solution for 5000h at 50oC. Observation of these interfaces and microstructure, in general, demonstrate that the conditioning of the solid and tubular GFRP bars in the saline solution did not affect the microstructural properties of the GFRP bars and that the presence of saturated cement grout in the tubular bars did not lead to any significant effects. This is in agreement with what Robert and Benmokrane (2013) reported when similar cement-mortar-wrapped GFRP bars used for internal reinforcement of concrete were immersed in salt water (3% NaCl). This phenomenon clearly illustrates the fact that the tested GFRP bars were not significantly affected by accelerated aging. Micrographs of External and Internal Surfaces of the GFRP Bars Figure 8 provides micrographs of external surfaces of the reference and conditioned solid GFRP bar specimens. The micrographs in Figure 9 show the external and internal surfaces of the tubular GFRP bars for unconditioned and aged in the saline solution for 5000 h at 50oC. Comparing these micrographs shows no significant damage to the external surfaces of the aged solid and tubular GFRP bars (Figure 8b and 9b). Similarly, the micrograph of the internal surface of the tubular bar (Figure 9d) shows that the aging in the saline solution at 50oC for 5000 h did not lead to any significant damage.

0153045607590

105120

1000 3000 5000

Tens

ile st

reng

th re

tent

ion

(%)

Exposure time (hours)

22 40 50

0153045607590

105120

1000 3000 5000

Tens

ile st

reng

th re

tent

ion

(%)


22 40 50

0

10

20

30

40

50

60

70

1000 3000 5000

Mod

ulus

of e

last

icity

(GPa

)


ref 23 40 50

0

10

20

30

40

50

60

70

1000 3000 5000

Mod

ulus

of e

last

icity

(G

Pa)


ref 23 40 50


10

(a) (b)

Figure 6: Micrograph (X4000) of solid GFRP bars for (a) unconditioned bar and (b) aged in saline solution at 50°C for 5000h.

(a) (b)

Figure 7: Micrograph (X4000) of tubular GFRP bars for (a) unconditioned bar and (b)aged in saline solution at 50°C for 5000h.

(a) (b)

Figure 8: Micrographs of external surfaces of solid GFRP bar specimens for (a) unconditioned reference bar and (b) bar aged in saline solution at 50oC for 5000 h.

Prediction of Long-Term Behavior Following the procedure proposed by Bank et al. (2003), the natural logarithm of time to reach a set of levels of normalized performances versus 1/T, expressed as the inverse of absolute temperature (1000/K), was used to predict the service life at the mean annual temperature (MAT=32oC) in hot marine applications. While a coefficient-of-determination (R2) value close to 1 is desired. ASTM procedures recommend a minimum value of 0.80 for acceptability, and the


11

obtained R2 values were between 0.96 and 0.99. The service-life time necessary to reach the established tensile-strength retention levels (PR) can be extrapolated for any temperature from the Arrhenius plot. Consequently, predictions were made for tensile-strength retention as a function of time for immersion at 32°C, and the general relation between the PR and the predicted service life at the average temperature of 32oC can be drawn (Figure 10). The predicted time to reach the determined tensile-strength retention level (PR) for the solid and tubular GFRP bars aged in the saline solution simulating the seawater at an isotherm temperature of 32oC is approximately 100 years for a PR of more than 96%. Moreover, the predicted service life of the GFRP bars aged in the saline solution at an isotherm temperature of 32oC with a PR of less than 95% can be estimated as being infinity. These predictions show that the solid and tubular GFRP bars tested in this study are durable with respect to the saline environment encountered in hot marine applications, since the saline solution used herein closely simulates the seawater.

(a) (b)

(c) (d)

Figure 9: Micrographs of surfaces of tubular GFRP bar specimens for (a) external surface of unconditioned reference bar, (b) external surface of bar aged in saline solution at 50oC for 5000 h, (c) internal surface of unconditioned

reference bar, and (d) internal surface of bar aged in saline solution at 50oC for 5000 h.

Figure 10: General relation between the PR and the predicted service life at a mean annual temperature of 32oC


12

CONCLUSIONS Based on the results of this study, the following conclusions may be drawn about the tested products: • The change in tensile strength of the tested GFRP bars was minor even at high temperatures (50oC), making for a

more aggressive environment (highly concentrated saline solution). • No significant microstructural changes were observed after 5000 h of immersion of the GFRP bars in the saline

solution at 50oC. The interfaces between the resin and fibers appeared unaffected by moisture absorption and high temperature.

• The polymer matrix was not affected by moisture absorption or high temperature: no changes in the glass transition temperature occurred, as observed by differential scanning calorimetry. FTIR did not show any significant changes in the polymer’s chemical structure, i.e., degradation.

• Predictions of the long-term behavior of the conditioned GFRP bars were made using a method based on the Arrhenius relation. These predictions provide information about long-term tensile-strength retention. In order to use the Arrhenius relation, we assumed that the mechanisms of degradation would remain the same during bar service life, but that they would be accelerated by aging.

• According to the long-term predictions, the tensile-strength retention of the solid and tubular GFRP bars immersed in the saline solution will decrease by 4% after 100 years at an isotherm temperature of 32°C. It was shown that the bar service life with a tensile-strength retention of less than 95% at 32oC should be infinite.

• Civil engineers currently aim at designing structures with service lives of up to 100 years. According to the predictions, even after a service life of 100 years, the tensile-strength retention of the tested GFRP bar would still be higher than 95% for a mean annual temperature (Singapore) of 32°C, which is higher than the design tensile strength according to ACI 440 (guaranteed tensile strength multiplied by the environmental reduction factor = CE × ffu

*). ACKNOWLEDGEMENTS This research was supported by the National Science and Engineering Research Council (NSERC) of Canada, and Firep International AG (Switzerland). The authors would like to thank the technical staff at the Department of Civil Engineering, University of Sherbrooke (Sherbrooke, Quebec, Canada) for their assistance in fabricating and testing the specimens. REFERENCES Achillides, Z., and Pilakoutas, K., (2004) “Bond behavior of fiber reinforced polymer bars under direct pullout conditions,”

Journal of Composites for Construction, 8(2), pp. 173–181. Ali, A. H., Mohamed, H. M., ElSafty, A., and Benmokrane, B. (2015). “Long-term durability testing of Tokyo rope

carbon cables.” 20th International Conference on Composite Materials, (ICCM20), Copenhagen, Denmark, 19-24th July, 2015.

American Concrete Institute (ACI). (2015). “Guide for the design and construction of structural concrete reinforced with FRP Bars.” ACI 440.1R-15, Farmington Hills, Michigan.

Apicella, A., Migliaresi C., Nicodemo L., Nicolais L., Iaccarino L., and Roccotelli S. (1982). “Water sorption and mechanical properties of a glass-reinforced polyester resin.” Composites. 13(4), 406–410.

Ashbee, K, and Wyatt R. (1969). “Water damage in glass fibre/resin composites.” Proc R Soc. London, Ser. A. 312(1511), 553–564.

Ashbee, K, Frank F, and Wyatt R. (1967). “Water damage in polyester resins.” Proc R Soc. London, Ser. A. 300(1463), 415–419.

ASTM C150 (2005). “Standard specification for portland cement.” American Society for Testing and Materials. ASTM D570 (2010). “Standard test method for water absorption of plastics.” American Society for Testing and Materials. ASTM D7205 (2011). “Standard test method for tensile properties of fiber reinforced polymer matrix composite bars. ”

American Society for Testing and Materials. ASTM D7705 (2012).“Standard test methods for density and specific gravity (Relative Density) of plastics by

displacement.” American Society for Testing and Materials. ASTM D792 (2008). “Standard test methods for density and specific gravity (Relative Density) of plastics by

displacement.” American Society for Testing and Materials, Conshohocken, USA. 6 pp. ASTM E 1356 (2003). “Standard test method for assignment of the glass transition temperature by differential scanning

calorimetry.” American Society for Testing and Materials. ASTM E1131 (2003). “Standard test method for compositional analysis by thermogravimetry.” American Society for

Testing and Materials. Bank, L.C, Gentry, T.R, Thompson, B.P, and Russel, J.S. (2003). “A Model specification for composites for civil

engineering structures.” Construction and Building Materials, 17(6-7), 405-437. Benmokrane, B., El-Salakawy, E., and Ahmed, E. (2011). “Durability and sustainability of fibre reinforced polymer (FRP)

composites for construction & rehabilitation.” Proceedings of the Fourth International Conference (CDCC 2011), July 20-22, 2011, Quebec City (Quebec), 687 p.

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Benmokrane, B., Wang, P., Pavate, T., and Robert, M. (2006). “Durability of FRP composites for cvil infrastructure applications, Chapter 12, durability of FRP composites for civil infrastructure applications.” Whittles Publishing, Scotland, 300-343.

Benmokrane, B., Wang, P., Ton-That, T., Rahman, H., and Robert, J. (2002). “Durability of glass fibre reinforced polymer reinforcing bars in concrete environment.” J. Compos. Constr., 6(2), 143–153.

Benmokrane, B., Ali, A. H., Mohamed, H. M., Robert, M., and ElSafty, A. (2016). “Durability performance and service life of CFCC tendons exposed to elevated temperature and alkaline environment.” J. Compos. Constr., 10.1061/(ASCE)CC.1943-5614.0000606 , 04015043.

Benmokrane, B., Ali, A.H., Mohamed, H.M., and ElSafty, A. (2015). “Durability of Tokyo Rope carbon cables in alkaline environment.” 7th International Conference on FRP Composites in Civil Engineering International Institute for FRP in Construction, 22-24th August, Vancouver.

Bradshaw, R. D., and Brinson, L. C. (1997). “Physical aging in polymers and polymer composites, An analysis and method for time-aging time superposition.” Polymer Engineering and Science. 1, 31.

Chen, Y., Davalos, J. F., and Ray, I. (2006). “Durability prediction for GFRP bars using short-term data of accelerated aging tests.” J. Compos. Constr., 10(4), 279-286.

Chen, Y., Davalos, J. F., Ray, I., and Kim, H. Y. (2007). “Accelerated aging tests for evaluation of durability performance of FRP reinforcing bars reinforcing bars for concrete structures.” Composite Structures. 78(1), 101-111.

Claure, G., De Caso Y Basalo, F., and Nanni, A. (2014). “GFRP hollow-core bars as reinforcement of concrete beams.” In CAMX 2014 - Composites and Advanced Materials Expo: Combined Strength. Unsurpassed Innovation. The Composites and Advanced Materials Expo (CAMX), Orlando, US.

Coomarasamy A., and Goodman S. (1999). “Investigation of the durability characteristics of fiber reinforced plastic (FRP) materials in concrete environment.” J of Thermoplastic Composite Materials. 12(3), 214-226.

Dejke, V. (1999). “Durability of fibre reinforced polymers (FRP) as reinforcement concrete structures.” Publication P-98:18, Chalmers University of Technology, Goteborg, Sweden, 69 p.

Dejke, V. (2001). “Durability of FRP reinforcement in concrete-Literature review and experiments.” Thesis for the Degree of Licentiate of Engineering, Department of Building Materials, Chalmers University of Technology, Göteborg, Sweden, 225 p.

Diamond, S. (1981). ‘‘Effects of two Danish flyashes on alkali contents of pore solutions of cement fly ash pastes.’’ Cem. Concr. Res., 11, 383 – 394.

Micelli, F., and Nanni, A. (2004). “Durability of FRP rods for concrete structures.” Construction Builing Materials, 18(7): 491–503.

Montaigu, M., Robert, M., Ahmed, E. A., and Benmokrane, B. (2013). “Laboratory characterization and evaluation of durability performance of new polyester and vinylester E-glass GFRP dowels for jointed concrete pavement.” J. Compos. Constr., 17(2): 176-187.

Murphy, K., Zhang, S., and Karbhari, V. M. (1999). ‘‘Effect of concrete based alkaline solutions on short term response of composites.’’ Proc., 44th Int. SAMPE Symposium and Exhibition, L. J. Cohen, J. L. Bauer, and W. E. Davis, eds., Society for the Advancement of Material and Process Engineering, Long Beach, Calif., 2222–2230.

Nelson, W. (1990). “Accelerated testing—statistical models, test plans, and data analyses.” Wiley, New York. Porter, M. L., Mehus, J., Young, K. A., O’Neil, E. F., and Barnes, B. A., (1997). “Aging for fiber reinforcement in

concrete,” Proc. of the Third International Symposium on Non-Metallic (FRP) Reinforcement for Concrete Structures, Sapporo, Japan, Vol. 2, 59-66.

Prian L., and Barkatt A. (1999). “Degradation mechanism of fiberreinforced plastics and its implications to prediction of long-term behavior.” J of Material Science. 34(16), 3977–3989.

Riebel, F., and Keller T. (2007). “Long-term compression performance of a pultruded GFRP element exposed to concrete pore water solution.” J. Compos. Constr., 11(4): 437-447.

Robert, M., and Benmokrane B. (2010a). “Physical, mechanical and durability characterization of preloaded GFRP reinforcing bars.” J. Compos. Constr., 14(4):368-375.

Robert, M., and Benmokrane, B. (2013). “Combined effects of saline solution and moist concrete on long-term durability of GFRP reinforcing bars.” Construction and Buiding Materials. 38: 274-284.

Robert, M., Cousin, P., and Benmokrane B. (2009). “Durability of GFRP reinforcing bars embedded in moist concrete.” J. Compos. Constr., 13(2): 66-73.

Robert, M., Cousin, P., Wang, P., and Benmokrane B. (2010b). “Temperature as an accelerating factor for long-term durability testing of FRPs: should there be any limitations?” J. Compos. Constr., 14(4): 361-367.

Soles C. L., Chang F. T., Bolan B. A., Hristov H. A., Gidley D. W., and Yee A. F. (1998). “Contributions of the nanovoid structure to the moisture absorption properties of epoxy resins.” J of Polymer Science: Part B: Polymer Physics, 36, 3035-3048.

Taylor, H. F. W. (1987). ‘‘A method for predicting alkali ion concentration in cement pore water solutions.’’ Adv. Cem. Res., 1(1), 5–16.

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http://www.sciencedirect.com/science/article/pii/S0950061812006046

http://www.sciencedirect.com/science/article/pii/S0950061812006046


14

LONG-TERM EXPOSURE PERFORMANCE OF FRP COMPOSITES IN MARINE ENVIRONMENTS

I. Nishizaki1, I. Sasaki2 and H. Sakuraba3 1 Innovative Materials and Resources Research Center,

Public Works Research Institute, Tsukuba, Japan. Email: [email protected] 2 Innovative Materials and Resources Research Center,

Public Works Research Institute, Tsukuba, Japan. Email: [email protected] 3 Innovative Materials and Resources Research Center,

Public Works Research Institute, Tsukuba, Japan. Email: [email protected] ABSTRACT In order to confirm the durability of FRP composites in marine environments, the authors have carried out the exposure tests for 6 types of FRP cables (re-bars) including CFRP, AFRP and GFRP under severe marine environment in Japan for up to 17 years. Table 1 shows the type of cables used in this study and Figure 1 show the exposure conditions. The exposure environments during the tests have a variety of conditions such as with/without direct sunshine or tension. Figure 2 shows the results of residual strength of CFRP specimens. The result suggests that tested CFRP have a good durability in marine environment. AFRP also showed similar results, however the results suggest the requirement of careful confirmation on durability for GFRP and VFRP. The authors also show the results of creep performance and chemical analysis in the report. KEYWORDS FRP cables, marine environment, durability, exposure test, residual strength, creep performance REFERENCES Iwao Sasaki and Itaru Nishizaki (2015), "TENSILE LOAD PROPERTIES AND POLYMER DETERIORATION OF

FRP CABLES DURING LONG-TERM EXPOSURE", Proceedings of the ConMat'15 Conference. Iwao Sasaki, Itaru Nishizaki (2012), "TENSILE LOAD RELAXATION OF FRP CABLE SYSTEM DURING LONG-

TERM EXPOSURE TESTS, "Proceedings of the 6th International Conference on FRP Composites in Civil Engineering, Paper No. 691.

Itaru Nishizaki and Iwao Sasaki (2010), "Long-Term Durability of FRP Cables under Maritime Conditions", Proceedings of the 5th International Conference on FRP Composites in Civil Engineering (CICE2010), Vol. 1, pp.372-375.

Table 1 FRP cables used in the exposure tests

Code CFRP1 CFRP2 AFRP1 AFRP2 GFRP VFRP

Shape Strand Rod Rod Braided Rod Rod

Fiber type Carbon Carbon Aramid Aramid E-glass Vinylon

Matrix resin Epoxy Epoxy Vinyl ester Epoxy Vinyl ester Epoxy

Vf (%) 64 65 66 65 65 72

Diameter (mm) 12.5 8.0 6.0 8.0 6.0 6.0

Ultimate load (kN) 141 70.6 52.4 65.7 36.3 19.6

Modulus (GPa) 145 168 55.6 62.1 52.9 28.6

Anchor system Adhesive Wedge Adhesive Adhesive Adhesive Adhesive


15

(a) Exposure station (b) FRP specimens under exposure test

Figure 1 Conditions of the exposure tests

Figure 2 Results of the residual strength of exposed CFRPs

after 17years exposureInitial load (×Pu) 0.8 0.6 0.8 0.6 0.8 0.6 0.8 0.6 ial

Direct sunlight rec With Without With WithoutCFRP1 CFRP2

0

50

100

150

Tens

ile ru

ptur

e lo

ad(k

N)

after 3.5years exposureafter 17years exposureMax. Min. in variationInitial average strengthMin. in variation


16

DEGRADATION OF FRP COMPOSITES EXPOSED TO SEAWATER

G.J. Xian1 and Z.Y. Lu2 1 School of Civil Engineering, Harbin Institute of Technology

Harbin 150090, China. Email: [email protected] 2 School of Civil and Transportation Engineering, Guangdong University of Technology

Guangzhou 510006, China. Email: [email protected] ABSTRACT Unlike steel bars, fiber reinforced polymer (FRP) bars are not expected to be corroded in seawater. Due to this, it is may be feasible that the seawater and sea-sand can be used for the FRP bar reinforced concrete. This means FRP bars could find wide application in marine structures. However, as found in some research works, even for the carbon fiber based FRPs, degradation occurred when FRPs were exposed to seawater environments (Kafodya, Xian et al. 2015). Therefore, it is necessary to study the evolution of the properties of the FRP bars in seawater. In the present study, two kinds of FRP bars, glass and basalt based FRP bars (GFRP and BFRP, respectively) with the same epoxy resin matrices of 8 mm in diameter were exposed to water or seawater at 20, 40 and 60oC, and the water uptake and mechanical properties were tracked with immersion time. The study aims to reveal the degradation of FRP bars in seawater, and encourage the safe application in marine environments. After 6 month immersion of the FRP bars, the water uptake increases with immersion temperatures, and BFRP shows more water uptake (Figure 1). For examples, at 60oC for 6 months, the water uptake of BFRP is 0.89%, while that of GFRP is 0.60%. The higher water uptake of the BFRP bar is attributed to the higher void contents and possible weak fiber-resin bond. It is worth noting that no obvious difference of the water immersion and seawater immersion on the water uptake for both GFRP and BFRP bars. The immersion in seawater brings in the degradation of the tensile strength of both bars. However, GFRP bars shows better resistance to the immersion (Figure 2). Almost no degradation is found for GFRP bars immersed in 20 and 40oC seawater in a period of 6 months, while about 30% decrease in tensile strength occurred at 60oC. In addition, the immersed bars were dried and tested again. As found, drying bars showed higher tensile strength, while the values were still lower than those of unaged samples, especially at higher temperatures. This indicates the un-recovered damage occurred during immersion, such as fiber debonding, hydrolysis of the resin etc. The internal shear strength of FRP bars showed the degradation of the fiber-resin bond. FRP bars were also exposed to the natural sea environments (mainly immersion in seawater). The results coincided with the laboratory testing results. Based on the above testing results, it is concluded that degradation of the FRP bars will occur in seawater environments, and the fiber-resin bond of the FRP bar play a key role on the degradation rate. KEYWORDS FRP bar, Basalt Fiber, Glass Fiber, Seawater, Durability ACKNOWLEDGEMENTS This work was financially supported by NSFC (China) with Grant No.51478145, and the National Key Basic Research Program of China (973 Program) with Grant No.2012CB026200. REFERENCES Kafodya, I., Xian G. and Li H. (2015). "Durability study of pultruded CFRP plates immersed in water and seawater under

sustained bending: Water uptake and effects on the mechanical properties." Composites Part B-Engineering 70, 138-148


17

(a) BFRP bars (b) GFRP bars

Figure 1 Water uptake of BFRP (a) and GFRP (b) bars immersed in seawater (SW) or distilled water (DW). Note, 20-SW means immersed in seawater at 20oC.

Figure 2 Tensile strength of BFRP (a) and GFRP (b) bars as a function of immersion time in seawater (SW) or distilled

water (DW).


18

BEHAVIOUR OF FRP-CONFINED SEAWATER SEA-SAND (SSC) CONCRETE

J.F. Chen1,2, G.M. Chen3, Z.B. He3 and J.G. Teng4 1 College of Civil Engineering and Architecture, Wenzhou University, China 2 School of Natural and Built Environment, Queen’s University Belfast, UK

3 School of Civil and Transportation Engineering, Guangdong University of Technology, China 4 Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, China

ABSTRACT In rapidly developing coastal regions in many countries such as China, the huge demand of sand for use in concrete construction has led to an acute shortage of river sand. Abuse of sea-sand in concrete has also been common in some regions, leading to many quality problems for reinforced-concrete structures. In offshore construction, transporting river sand and freshwater from an onshore site is costly. Therefore, many benefits can be derived if sea-sand and seawater can be directly used in concrete structures in a safe manner. Against this background, a project has recently been funded by the National Natural Science Foundation of China (NSFC) to investigate the behaviour of FRP-confined seawater sea-sand concrete (SSC) structures with internal FRP reinforcement. In such FRP-SSC structures, the use of steel reinforcement is completely avoided, eliminating the corrosion problem of steel in seawater and sea-sand. This presentation reports the preliminary test results from the NSFC-funded project. Concrete cylinder specimens, with or without FRP confinement, were tested at the ages of 7 and 28 days. The concrete specimens were cast with a) normal concrete with river sand and freshwater, b) sea-sand concrete where river sand is replaced by sea-sand, c) seawater concrete where fresh water is replaced by sea water, and d) SSC where river sand and freshwater are replaced respectively by sea-sand and seawater. The effects of these factors on the 7 and 28-day strengths and stress-strain behaviour for specimens with or without FRP confinement are discussed in this presentation. Keywords: Fibre-reinforced polymer (FRP), seawater concrete, sea-sand concrete, seawater sea-sand concrete (SSC), confinement, Acknowledgement The research presented here was supported by the National Natural Science Foundation of China (Project No. 51578423).


19

CURRENT RESEARCH AT MONASH UNIVERSITY ON HYBRID CONSTRUCTION USING SEAWATER SEA SAND CONCRETE AND FRP

X.L. Zhao Department of Civil Engineering,

Monash University, Clayton, VIC 3800, Australia. Email: [email protected] ABSTRACT This presentation gives a summary of current research at Monash University on hybrid construction using seawater sea sand concrete (SWSSC). It forms part of an Australian Research Council (ARC) Discovery Project through collaboration among Monash University, The Hong Kong Polytechnic University and Southeast University, China. This presentation contains four major parts: (1) Properties of seawater and sea sand concrete (SWSSC): Alkali activated slag concrete with seawater and sea sand was used in this research. The 3% (percentage weight of slag) sodium meta-silicate activator, which is composed of 47% SiO2 and 36% Na2O, was pre-blended with slag in the dry form before mixing. Material properties measured include modulus of elasticity, compressive strength, bending strength at ambient temperature as well as elevated temperature. (2) Long-term behavior of fiber reinforced polymer (FRP): Filament-wound FRP tubes were adopted in this research. Three types of fibres were used, namely glass, carbon and basalt fibres. Tensile coupons and split-disk rings were used to determine the longitudinal and hoop strength of FRP tubes. Coupon specimens were designed to investigate the three different types of FRP (GFRP, CFRP, BFRP) in simulated SWSSC environment, whereas tube specimens were used to investigate the degradation mechanism/damage pattern of these materials when used as confining tubes that are exposed to different environment internally and externally. Exposure temperatures include 25, 40, 60˚C with exposure time varies from 1 month to 12 months. Various techniques will be utilized to gather evidence, such as Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC) and X-Ray scanning. (3) SWSSC-filled FRP and SS stub columns: A total of 62 stub columns, including hollow sections and SWSSC fully filled tubes or double-skin tubes, were tested under axial compression with the load applied to concrete and tubes simultaneously. The stress-strain curves of the core concrete indicate that concrete strength and ductility is enhanced due to the confinement effect. The effects of some key parameters (e.g., tube diameter-to-thickness ratio, cross-section types, outer tube types, and inner tube types) on the confinement effects were also discussed. Comparisons were made among CFRP, BFRP and GFRP in terms of confinement to SWSSC. Capacity formulae are proposed to estimate the load carrying capacity of SWSSC filled FRP tubes. (4) Durability of FRP bars in SWSSC environment: Accelerated corrosion tests were conducted on FRP bars using two types of SWSSC solutions at different pH and temperatures, and for different durations. Scanning electrical microscopy (SEM), X-ray computed tomography (CT) and energy dispersive X-ray spectroscopy (EDS) results were utilized to explain the damage mechanism. The long-term behaviour of BFRP and GFRP bars under the service construction condition was also predicted using Arrhenius degradation theory.


20

BOND BEHAVIOR BETWEEN SEAWATER SEA-SAND CONCRETE AND FRP

J.Z. Xiao 1, C.B. Qiang 2 and Q.T. Zhang 3

1 Department of Structural Engineering, Tongji University, Shanghai 200092, China. Email: [email protected]



ABSTRACT The numerous consumption of concrete around the world, especially in developing countries like China and India, demands huge amount of raw materials like coarse/fine aggregates and fresh water, but the extraction of aggregates and usage of fresh water have raised serious environment problems. Urge for environmental protection and sustainable development of concrete construction industry has promoted the researches in the application of recycled coarse aggregate (RCA), sea-sand and seawater as raw materials for concrete and the practicability has been proved by existing investigations. For solving the abundance of Cl- in seawater and sea-sand, using fiber reinforced polymer (FRP) bars, such as glass fiber reinforced polymer (GFRP), instead of traditional steel reinforcements in concrete with seawater and/or sea-sand may be a good solution. The bond behavior between FRP and concrete is the fundamental performance for the combined action of FRP and concrete, thus the bond behavior between seawater sea-sand concrete (SSC) and FRP is necessary to be investigated considering the difference between sea-sand/seawater and river-sand/freshwater. The basic mechanical properties of concrete with different raw materials including seawater, sea-sand and RCA were experimentally studied based on 288 cubes and 96 prisms. It is found that seawater sea-sand recycled aggregate concrete (SSRAC) has better mechanical properties than ordinary recycled aggregate concrete (RAC). For the 28d cube compressive strength, SSRAC is up to 10% higher than RAC for strength grade C50, but a little inferior compared to natural aggregate concrete (NAC). The splitting tensile strength shows tiny difference between RAC and SSRAC. Furthermore, a total of 21 pull-out tests were conducted to examine the effect of varying parameters (the raw materials and strength grade of SSRAC) on their bond characteristics. All the specimens failed with the splitting of concrete and some specimens appeared the shear failure of glass fiber reinforced polymer (GFRP) bar ribs. The bond-slip development between GFRP ribbed bars and concrete, which including NAC, RAC, seawater sea-sand natural aggregate concrete (SSNAC) and SSRAC with the same water/cement ratio, is lightly influenced by the change of the raw materials in concrete, and shares the similar ascending stage of the bond-slip curve. But the bond strength of SSC is lower than that of NAC. For SSRAC, with concrete strength grade varying from C20 to C50, the bond strength of SSRAC increases with the rise of the strength grade. The ascending stage of bond-slip curve between GFRP ribbed bars and SSRAC is studied and compared with some typical models, i.e., BPE (mode proposed by Eligehausen et al.), Malvar’s mode and CMR modes (proposed by Cosenza et al.). Modification of existing models is proposed for the bond-slip development between SSRAC and GFRP ribbed bars with the consideration of the effect of raw materials and concrete strength. Finally, some recommendations are put forward for further investigation on the bond behavior between SSRAC and FRP bars, mainly refers to the influence of existence for seashell particles in sea-sand. KEYWORDS Seawater sea-sand concrete (SSC), recycled coarse aggregate (RCA), mechanical property, glass fiber reinforced polymer (GFRP) bars, bond behaviour, pull-out test


21

EXPERIMENTAL STUDY ON SEAWATER CORAL AGGREGATE CONCRETE FILLED FRP TUBES UNDER AXIAL COMPRESSION

Jie Wang1 and Peng Feng2 1Department of Civil Engineering, Tsinghua University, Beijing 100084, China.

Email: [email protected] 2Department of Civil Engineering, Tsinghua University, Beijing 100084, China.

Email: [email protected] ABSTRACT The use of sea water coral aggregate concrete (SCAC), instead of ordinary aggregate concrete (OAC), in CFFT members is highly attractive, due to the beneficial effect of fiber-reinforced polymer (FRP) has the good resistance to salt can effectively counteract the biggest shortcomings of the containing chloride ions in SCAC. Especially, as the development of marine construction, SCAC filled FRP tubes are potentially to be an attractive alternative for piles and columns applications in corrosive marine environments. The axial compressive behavior of SCAC filled FRP tubes (SCFFTs) was firstly experimentally investigated and compared with OAC filled FRP tubes (OCFFTs) in this study. Also, the used CAs and SCAC were systematically prepared and tested, including materials test on coral aggregates (CAs), the uniaxial loading test on SCAC and microstructure analysis on SCAC. CAs were found to have many characteristics compared to ordinary aggregates (OAs). Their porous nature and low strength led to a different and brittle failure mechanism of SCAC under uniaxial loading, also led to delay in rapid expansion of concrete and activation of confinement in SCFFT. As a result, the axial load of SCFFT experienced a slight drop in the transition zone for the range axial strains approximately between 0.002 and 0.004. The non-homogeneity and brittleness of SCAC led to a non-uniform hoop strain distribution in SCFFT under compression, and hence discount the effective of confinement, eventually the ultimate load of SCFFT is just about 60% of its OCFFT counterpart. The key elements and basic frame to predict FRP-confined SCAC under axial compression was illustrated through a comparison of experimental results of SCFFTs with predicting results from an existing analysis-oriented model for FRP-confined OAC. KEYWORDS: Coral aggregate (CA), Sea water, Sea water coral aggregate concrete (SCAC), FRP tube, Axial compression


22

HYBRID STRUCTURES MADE OF SEAWATER SEA-SAND (SSC) CONCRETE AND FRP: CURRENT STATUS AND

RESEARCH NEEDS

J.G. Teng Department of Civil and Environmental Engineering & Research Institute for Sustainable Urban Development

The Hong Kong Polytechnic University, Hong Kong, China. ABSTRACT Marine infrastructure is constructed mainly of steel-reinforced concrete, which means the consumption of large amounts of fresh water and river sand/crushed stone fines each year; in addition, steel corrosion in steel-reinforced concrete structures poses a great challenge to the service life of marine infrastructure. To address these challenges, it has recently been proposed that a new type of reinforced concrete structures made of corrosion-resistant fibre-reinforced polymer (FRP) and seawater sea-sand concrete (SSC) be developed to replace steel-reinforced concrete structures in marine construction. The author was the first to propose the use of FRP bar-reinforced SSC structures for marine infrastructure at a national conference in 2011 held in Hangzhou, China (Teng et al. 2011) and later promoted it internationally on a number of occasions including CICE 2014 (8th International Conference on FRP Composites in Civil Engineering, Vancouver, Canada, August 2014) and ACMSM 23 (23rd Australasian Conference on the Mechanics of Structures and Materials) (Teng 2014). The idea has since attracted some significant attention, and subsequently, a number of research projects have been funded in China, Australia, the US and Europe on the topic. A small number of publications have also appeared on the subject. For FRP-SSC structures to become widely used, extensive research is needed to gain an in-depth understanding of their behaviour and to develop design and construction methods. The author has recently led a multi-disciplinary team of researchers to formulate a major research proposal for possible financial support by the Theme-based Research Scheme of the Hong Kong Research Grants Council. The proposed research programme aims to: (1) develop new steel-free structural forms for marine construction; (2) understand and model the short- and long-term behaviours of FRP-SSC structures at both material and structural levels; (3) establish monitoring methods for field performance evaluation; (4) create engineering tools for practical use; and (5) facilitate practical implementations through knowledge transfer This paper presents a summary of the understandings gained from the preparation of the above-mentioned research proposal and provide a brief exposition of the proposed research programme. A strong emphasis will be placed on the need to understand and predict the long-term performance of FRP-SSC structures in a marine environment; a multi-scale multi-physics approach is believed to be needed for the modelling of material and structural deterioration to predict the life-cycle performance of FRP-SSC structures. Keywords: Fibre-reinforced polymer (FRP), seawater sea-sand concrete (SSC), long-term performance, durability References Teng, J.G., Yu, T., Dai, J.G. and Chen, G.M. (2011). “FRP composites in new construction: current status and

opportunities”, Proceedings, 7th National Conference on FRP Composites in Infrastructure (Supplementary Issue of “Industrial Construction”) (Abstract), Hangzhou, China, 2011.

Teng, J.G. (2014). “Performance enhancement of structures through the use of fibre-reinforced polymer (FRP) composites”, Proceedings, 23rd Australian Conference on Mechanics of Structures and Materials (ACMSM23), Lismore, Australia (Abstract), 2014.


23

HOW DO WE DETERMINE THE SUSTAINABILITY OF SEAWATER SEA-SAND CONCRETE AND FIBER-REINFORCED POLYMER COMPOSITE (FRP-SSC)

STRUCTURES?

Lawrence C. Bank Department of Civil Engineering, The City College of New York,

160 Convent Ave, 103 Steinman Hall, New York, NY 10031, USA. Email: [email protected] ABSTRACT The focus of this presentation is on how the proposed research will achieve its stated mission of contributing “to the development of a sustainable built environment” in the context of the HK Research Grants Council (RGC) call which states that proposals should “focus on enhancing the sustainability of the built environment, especially issues relating to the provision of high quality working and living environments, green buildings, and the social, economic and environmental impact of urban development.” The presentation will include a brief history of Sustainable Development, Environmental Life-Cycle Assessment, Social Life-Cycle Assessment, Life-cycle Cost Assessment, Eco-systems Design and the Cradle-to-Cradle/Circular Economy philosophy. This includes a discussion of the current frameworks for sustainability assessment and how sustainability is currently evaluated for the products and manufacturing systems. Since the proposed research deals with a manufactured product the presentation will discuss how the sustainability of these manufactured products - fiber-reinforced polymer (FRP) composite reinforcing products and the seawater sea-sand (SSC) composite concrete products - can be assessed. The presentation will present examples of other product systems for which sustainability frameworks have been developed and see how they can be applied to FRP-SSC. Particular attention will be paid to where the topics of durability, life-cycle performance and service-life prediction fall into the hierarchy of sustainability assessments.


24

CHEMOMECHANICAL BEHAVIOR OF CEMENT-BASED MATERIALS AND MOLECULAR DYNAMICS MODELING AT INTERFACES

F. Sanchez Department of Civil and Environmental Engineering,

Vanderbilt University, Nashville, Tennessee 37235, USA. Email: [email protected] ABSTRACT Nano/microfiber (steel, carbon, or polymer) reinforced cement-based materials are an important class of materials that can be tailored for specific applications. These materials have shown improved mechanical properties and structural performance, including enhanced fracture toughness, impact resistance, fatigue strength, endurance, and energy adsorption capacity (Banthia et al. 1996; Lange et al. 1996; Li 2003). Fiber reinforcements provide additional, unique properties, including low electrical resistivity, self-sensing capabilities (carbon and steel) (Chung 2002), high ductility, self-healing, and self-control of cracks (polymer) (Li 2003). These multifunctional materials are thus promising solutions to the problem of infrastructure deterioration with potentially lower total life cycle costs. Whereas, a large number of studies have been conducted to examine the structural and mechanical properties provided by the fibers and explain their reinforcement mechanisms (Lange et al. 1996; Li 2003), the interfacial bonding characteristics and underlying mechanisms are not well understood. As a result, the design of fiber reinforced cement-based composites still remains essentially based on empirical approaches and testing. Among the various phenomena that influence fiber reinforced cement-based materials, interfacial interactions between the solid matrix phases, the reinforcement, and any surrounding liquid are important in controlling the overall mechanical response and damage mechanisms of the composites. In particular, characteristics such as strength and fracture toughness are strongly dependent upon the structure and properties of the reinforcement–matrix interfaces. While the role of these interfaces on the overall material performance is well recognized, little is known about the underlying reinforcement mechanisms. Interactions at the reinforcement–matrix interfaces are highly dependent on local molecular structure and bonding and must be accurately characterized to provide a fundamental understanding of the complex, interfacial interactions and interface load-transfer mechanisms that, in turn, provide the building blocks for models of macroscopic constitutive behavior. This requires investigation into the behavior of the interfaces at the nanometer length scale. At the molecular level, interactions between the reinforcing structure and the base material are controlled by the chemical structure of and the interactions between solid phases, the reinforcing structure, and any surrounding liquid and may act through chemical bonds, electrostatic attraction, hydrogen bonding, and van der Waals forces (Sugama et al. 1989; Zhandarov et al. 2005) (Figure 1). Probing molecular-scale effects at interfaces using current experimental characterization techniques in-situ is difficult and, generally, provides macroscale data from which the nanoscale behavior must be deduced. Molecular dynamics modeling can provide molecular-scale information of surface and interfacial phenomena. Molecular dynamics modeling has been successfully employed to provide insight into the structure of calcium-silicate-hydrate (C-S-H), the main phase of cement-based materials (Faucon et al. 1997; Pellenq et al. 2009) and how water and solutions behave with the surface of cement phases (Kalinichev et al. 2002) as well as to simulate the interaction between surface functionalized graphitic structures, C-S-H, and electrolyte solutions (Sanchez et al. 2008; Sanchez et al. 2010). Figure 2 shows results of molecular dynamics simulations of the effect of hydroxyl functionalization on the fracture pattern of single layer graphene under tension. This paper will discuss current work that is directed at developing a fundamental understanding of the chemo-mechanical behavior of multi-scale, environmental weathering of cement-based materials through an integrated experimental and computational program focusing on how molecular level, chemical phenomena at internal interfaces influence long-term, bulk material performance. A summary of recent research on molecular dynamic modeling of the interaction between reinforcing structure, liquid phase, and solid matrix phase interfaces will be provided. KEYWORDS Fiber reinforced cement-based materials, molecular dynamics modeling, reinforcement-cement interfaces, surface functionalization, mechanical properties ACKNOWLEDGEMENTS The research program described above is being supported by the National Science Foundation NSF CMMI 1462575. The simulations presented in Figure 2 were conducted by Mr Baig AL MUHIT.


25

REFERENCES Banthia, N. and J. Sheng (1996). "Fracture toughness of micro-fiber reinforced cement composites." Cement and

Concrete Composites 18(4): 251-269. Chung, D. D. L. (2002). "Composites get smart." Materials Today 5(1): 30-35. Faucon, P., J. M. Delaye, J. Virlet, J. F. Jacquinot and F. Adenot (1997). "Study of the structural properties of the C-S-

H(I) by molecular dynamics simulation." Cement and Concrete Research 27(10): 1581-1590. Kalinichev, A. G. and R. J. Kirkpatrick (2002). "Molecular Dynamics Modeling of Chloride Binding to the Surfaces of

Calcium Hydroxide, Hydrated Calcium Aluminate, and Calcium Silicate Phases." Chem. Mater. 14(8): 3539-3549. Lange, D. A., C. Ouyang and S. P. Shah (1996). "Behavior of cement based matrices reinforced by randomly dispersed

microfibers." Advanced Cement Based Materials 3(1): 20-30. Li, V. C. (2003). "On engineered cementitious composites (ECC) - A review of the material and its applications." Journal

of Advanced Concrete Technology 1(3): 215-230. Pellenq, R. J.-M., A. Kushima, R. Shahsavari, K. J. V. Vliet, M. J. Buehler, S. Yip and F.-J. Ulm (2009). A realistic

molecular model of cement hydrates. Proceedings of the National Academy of Sciences 106.38 (2009): 16102-16107. © 2009 National Academy of Sciences.

Sanchez, F. and L. Zhang (2008). "Molecular dynamics modeling of the interface between surface functionalized graphitic structures and calcium-silicate-hydrate: Interaction energies, structure, and dynamics." Journal of Colloid and Interface Science 323(2): 349-358.

Sanchez, F. and L. Zhang (2010). "Interaction energies, structure, and dynamics at functionalized graphitic structure-liquid phase interfaces in an aqueous calcium sulfate solution by molecular dynamics simulation." Carbon 48(4): 1210-1223.

Sugama, T., L. E. Kukacka, N. Carciello and D. Stathopoulos (1989). "Interfacial reactions between oxidized carbon fibers and cements." Cement and Concrete Research 19(3): 355-365.

Zhandarov, S. and E. Mader (2005). "Characterization of fiber/matrix interface strength: applicability of different tests, approaches and parameters." Composites Science and Technology 65(1): 149-160.

Figure 1 Solid-solid and solid-liquid interfacial interactions in fiber reinforced cement-based materials

Figure 2 Fracture patterns for (a) pure graphene sheet, (b) functionalized graphene sheet with 50% –OH functional

groups preferentially oriented along the X-direction, and (c) functionalized graphene sheet with 50% –OH functional groups preferentially oriented along the Y-direction. [Red: carbon-atoms, blue: oxygen-atoms, and green: hydrogen-

atoms]

Bulk base material

Interfacial Zone

Fiber-base material interface

Liquid Phasewith Ions

Fiber

Ca

OHOH

O OHC

OH

O

C

Ca

O

OH

O

Ca

OC

Ca

O

O

Ca

OH

R R R

C

O

Molecular scale§van der Waals§Electrostatics§Chemical bonds

Ca++- - - - -

Micro-scale§Interfacial shear stress§Debonding

Strength of interfacial interaction

(density of interfacial bonds, bond energies)

= fCO OH

SO42-

Cl-

PO43-

Na+

Ca2+

Mg2+

R= { Si SiO ••• 2-

PO43-

Solid Phase

Interface cohesive traction-separation relationships

(a)

Carbon

Oxygen

Hydrogen

(b) (c)


26

LAYER-BY-LAYER ASSEMBLY OF MULTI-WALLED CARBON NANOTUBES ON LONG-PERIOD GRATING SENSORS FOR MARINE ENVIRONMENTAL MONITORING

Y.Q. Ni1,2, S.Q. Ding1,2 and H.P. Wang1 1 Department of Civil and Environmental Engineering,

The Hong Kong Polytechnic University, Hong Kong, China. Email: [email protected] 2 Research Institute for Sustainable Urban Development,

The Hong Kong Polytechnic University, Hong Kong, China. ABSTRACT Deterioration in structural performance due to rebar corrosion is a major threat to the durability of seawater sea-sand reinforced concretes (SSC) in marine environment. Decrease in alkaline resistance (pH-value) and increase in relative humidity would accelerate the corrosion process. Therefore, it is of great significance to monitor the variation of pH-value and relative humidity inside SSC structures. Recognising the advantages of small size, lightweight, immunity to electro-magnetic interference, resistance to corrosive and hazardous environments, and sensitivity to the refractive index of surrounding medium of optical fibre long-period gratings (LPG), LPG-based sensors are developed for the detection of the above two environmental parameters. Figure 1 illustrates the fundamental characteristics of LPG. To enhance the sensitivity of LPG sensors to pH-value and relative humidity, carbon nanotubes (CNTs) are utilised as coating material deposited on the bare LPG. CNT is one of the most promising thin film materials in biological and chemical sensing fields, due to its hollow structure with a very large surface area and aspect ratio. It is suitable for either physisorption or chemisorption. In addition, considering its high refractive index and superior chemical and mechanical stability, CNT can be adopted to develop LPG sensors for multi-parameter monitoring. A simple approach to assemble dispersed CNTs into thin-films is by layer-by-layer (LBL) assembly, which consists of the repeated, sequential immersion of a substrate into aqueous solutions of complementarily functionalised materials. This technique can control the refractive index and the thickness of CNT thin films at the nanometer scale, thus precisely tailoring film properties and functionality. Multi-walled CNTs (MWCNTs) functionalised with carboxylic acid groups (i.e. MWCNT-COOH) and with amine groups (i.e. MWCNT-NH2) can be treated as polyanions and polycations. Figure 2 shows the fabrication process of MWCNT-coated LPG sensors. The sensing mechanism of the developed sensors relies on the change of refractive index of the CNT thin film in response to the environmental pH-value and relative humidity. It is shown in the present study that the MWCNT-coated LPG sensors can favourably monitor the variations of pH value and relative humidity and can be applied for corrosion monitoring of SSC structures in marine environment. KEYWORDS LPG sensor, CNTs, LBL assembly, enhanced sensitivity, relative humidity, pH-value, marine environment

(a) Coupling of core and cladding modes (b) Transmission response of a typical LPG

Figure 1. Characteristics of bare LPG


27

Figure 2. Fabrication of MWCNT-coated LPG sensor


28

SEACON AND THE HALLS RIVER BRIDGE PROJECT

Antonio Nanni Department of Civil, Architectural & Environmental Engineering,

University of Miami, Coral Gables, FL, 33146. E-mail: [email protected] ABSTRACT This presentation covers the goals and objectives of an international collaborative project named ‘SEACON’ that aims at demonstrating the safe and durable utilization of seawater and salt-contaminated aggregates (natural or recycled) for a sustainable concrete production when combined with noncorrosive reinforcement. Seawater and salt-contaminated aggregates use in reinforced concrete (RC) is currently prohibited by building codes due to corrosion of the steel reinforcement. To this end, the concrete made with seawater and salt-contaminated aggregate is combined with noncorrosive reinforcement including Glass-Fiber-Reinforced-Polymer (GFRP) or stainless steel bars. The project also includes the construction of demonstration structures in the US and Italy. In particular, this presentation provides some details of the US demonstrator: The Halls River Bridge. Construction of this five-span bridge in central Florida will start January 9, 2017. Many bridges in Florida are in operation along coastlines. The selected structure is intended to replace an existing bridge in Citrus County. The existing bridge is functionally obsolete; thus, the purpose of new bridge is to increase capacity and improve safety of the existing transportation facility. The proposed bridge total length is 56.5 m consisting of five 11.3 m simply supported spans. The proposed bridge section provides two 3.6-m traffic lanes with 2.4 m outside shoulders, 1.5-m wide sidewalk with standard traffic barrier and bridge pedestrian/bicycle railing on each side. Both superstructure and substructure are classified as extremely aggressive due to Halls River’s chloride concentrations and the close proximity of the superstructure to the water. The use of non-corrosive bars and stirrups is an efficient method to address the long-term issues and they will be used in cast-in-place concrete bulkhead caps, pile caps, wing-walls, back-walls, deck, traffic barriers, and approach slabs. KEYWORDS Bridge; chloride limits, corrosion, reinforced concrete, sustainability


29

CONCRETE DURABILITY AND THE A1 MOTORWAY CULVERT PROJECT

L. Bertolini Department of Chemistry, Materials, and Chemical Engineering “Giulio Natta”,

Politecnico di Milano, Milan, Italy. Email: [email protected] ABSTRACT Use of chloride-contaminated raw materials is prohibited by international standards dealing with reinforced concrete (RC) structures durability. Beside possible effects on the early stages of cement hydration and the long-term development of strength, the primary reason of the interdiction is corrosion of black steel reinforcement. In fact, it is well known that chlorides, by destroying the passive film, make steel susceptible to pitting corrosion. Thus, design standards aim at limiting the use of chloride-contaminated materials. However, the use of chloride-contaminated raw materials for the production of concrete would be advantageous from a sustainability point of view, since it would allow saving natural resources, such as fresh water, leading to enhanced environmental sustainability. In the framework of a research project financed by the Infravation Program (Advanced systems, materials and techniques for next generation infrastructure), an experimental study named SEACON (http://seacon.um-sml.com) is been undertaken and it is aimed at demonstrating the safe utilization of seawater and salt-contaminated aggregates (natural or recycled) for a sustainable concrete production when combined with non-corrosive reinforcement to construct durable and economical concrete infrastructures. Laboratory tests are carried out to investigate the performance of concrete made with seawater and salt-contaminated aggregate. Comparison with concrete made with traditional constituents allows the assessment of the role of chloride-contaminated raw materials on the fresh and hardened properties of the concrete. Corrosion behaviour of ordinary carbon steel embedded in concretes made with chloride-contaminated raw materials is studied and it is compared with the behaviour of bars of different grades of stainless steel. Electrochemical measurements of corrosion potential and corrosion rate (with the technique of linear polarization) are carried out on 250x50x100 mm prismatic concrete specimens, with embedded bars of: carbon steel, two austenitic stainless steels (1.4307 and XM-28) and two duplex stainless steels (1.4362 and 1.4462). The concrete was made with water/cement ratio of 0.52, 335 kg/m3 of Portland-limestone cement, 30 kg/m3 of carbon coal fly ash, 1824 kg/m3 of siliceous aggregate and 175 l/m3 of water, respectively deionized and seawater. Tests are also carried out on concrete made with chloride-contaminated recycled-concrete aggregates (RCA). Parallel tests are carried out at the University of Miami on specimens reinforced with GFRP bars. The final objective of the study is to demonstrate the feasibility of using chloride-contaminated concrete combined with appropriated types of FRP or stainless steel bars from a technical point of view and evaluate its impact on the sustainability of RC structures based on a life cycle assessment approach. During this presentation, the results of the first year of laboratory tests will be described; the role of seawater and other chloride-contaminated raw materials on the corrosion of steel will be discussed. Based on the results of laboratory tests two field demonstration projects that include the use of sea-concrete reinforced with both GFRP and SSR bars are being designed, constructed and monitored. In this presentation the field demonstration project that has been started in Italy will be described. This consists on a reinforced concrete culvert along the Milan-Rome A1 motorway, which in winter collects salt-contaminated water. The culvert is divided in different lengths, characterised by the use of reference-concrete, seawater-concrete or RCA-concrete. In the seawater concrete, both ordinary carbon steel bars, two types of stainless steel bars and GFRP bars have been considered. Specifically designed probes have been embedded in each part of the culvert, characterised by a combination of concrete and reinforcement, for monitoring the durability performance in time. KEYWORDS Seawater, corrosion, recycled concrete aggregates, stainless steel, GFRP, durability.


30

PERSPECTIVE OF A CEMENT MANUFACTURER ON SEAWATER SEA-SAND CONCRETE

F. Canonico Buzzi Unicem SpA,

Via L.Buzzi 6 15033 Casale (AL) Italy Email: [email protected]; ABSTRACT Portland Cement (OPC) is one of the most important building materials worldwide mainly used for the production of concrete. Portland cement is manufactured by inter-grinding Portland clinker (the main constituent of Portland cement) together with a sulfate carrier (gypsum or anhydrite) and other inorganic components (supplementary cementitious materials (SCMs), limestone filler). The process of production of OPC is highly energy-intensive, in particular the grinding of the raw materials, the burning of the clinker at 1500°C and the final grinding of cement, and is responsible for the emission of CO2 that occurs due to the calcination of the limestone and from the burning of fossil fuels. Global average gross CO2 emissions per ton of clinker are about 866 kg CO2 (1). Over the last 20 years the cement industry has achieved significant targets with regard to the reduction of CO2 emissions per ton of clinker thanks to several mitigation strategies: 1) the improved efficiency of the cement plants; 2) the increased use of alternative fuels in the burning of the clinker; 3) the use of SCMs as clinker replacement in cement. SCMs are hydraulic inorganic materials that develop mechanical strengths by pozzolanic reaction or by latent hydrauliticy. The pozzolanic reaction is based on the chemical reaction of the SCMs with the Ca(OH)2 developed during the hydration of cement while the latent hydraulicity is an intrinsic property of some building materials (such as blast furnace slag) that can develop strength after activation. Both these approaches lead to cement with low porosity and excellent resistance against chemical attack, but are characterized by weaker performance compared to OPC in terms of carbonation resistance. In fact the amount of Ca(OH)2 released during the hydration of Portland cement is the main cause of the buffering potential of the cement paste pore solution and therefore of its protection against CO2 penetration, that is known to be one of the most relevant requirements for the protection of the steel reinforcement in concrete. A number of innovative low-carbon clinkers are also currently being developed by cement companies, such as Calcium Sulphoaluminate Clinker (CSA) (2), and Belitic clinker. They are produced in a smaller amount compared to OPC and commercially used in niche applications. Buzzi Unicem has also obtained the CE label, valid at European level for structural concrete application, on three formulations of CSA formulation in 2013. These innovative CSA and Belitic clinkers are also being developed following the concept of reducing the amount of CaO in the raw materials. In addition, these cements show interesting properties such as high early strength, good durability performance and low shrinkage but also a weaker carbonation resistance compared to OPC. Is this innovative process going on at cement industry level exploitable together with the seawater and sea-sand in concrete? There are several arguments to support this idea, and probably the most interesting is that the innovative cements mentioned above develop a pore solution characterized by a lower pH compared to that actually used Portland cement, giving an environment benefit for the durability of the glass fiber reinforced polymer (GFRP) reinforcement, moreover the faster carbonation of this system is not a barrier for the GFRP reinforcement but a desired condition. Further research is required in order to better understand the hydration behavior of this innovative binder also in presence of high chloride conditions especially with regards to the influences on the phase assemblage of the hydrated cements, on the release of minor elements, on the stability of the phase and on the other performance factors of the concrete that could be influenced by the “osmotic exchange” between the concrete and the atmospheric environment (shrinkage, creep, freeze thaw resistance etc…). A last comment, valid for both Portland and the innovative cements, is that the European cement industry is forced to fulfill the criteria of the standard EN 197-1 regarding the chloride content in cement. The chloride in cement must be below 0.1% in order to avoid the risk of corrosion of the black steel rebar in concrete. This regulation limits the amount of chloride that can be employed in the cement manufacturing and for example the amount of chloride containing cement dust that can be added during the grinding of cement. Higher limits regarding chloride would enable the use of higher amounts of alternative fuels, raw materials and alternative SCMs at the moment and could be from an economic and environmental point of view convenient.


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Figure 1 CO2 penetration of mortar made with different cements

KEYWORDS Innovative cements, Calcium sulfoaluminate cements, supplementary cementitious materials ACKNOWLEDGEMENTS ERA-NET Plus Infravation Program and the members of the SEACON project REFERENCES Data for 2006, “The cement sustainable initiative” www.wbcsdcement.org/ http://www.buzziunicem.it/online/it/Home/Prodotti/Legantispeciali/BuzziUnicemNext.html

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