Elsevier

Corrosion Science

Volume 141, 15 August 2018, Pages 1-13
Corrosion Science

Durability of fiber reinforced polymer (FRP) in simulated seawater sea sand concrete (SWSSC) environment

https://doi.org/10.1016/j.corsci.2018.06.022Get rights and content

Highlights

  • Moisture uptake of FRPs (except BFRP) followed: NC > SWSSNC > DW > HPC > SWSSHPC.

  • The presence of NaCl in simulated concrete led to a less FRPs moisture uptake.

  • Simulated high performance concrete solution leads to less degradation of FRP.

  • Greater basalt fiber degradation in SWSSC might due to the reaction of Al, Fe, and Mg with alkali and Cl ions.

  • CFRP exhibited the best durability in SWSSC, followed by GFRP and then BFRP.

Abstract

This paper presents an experimental investigation on the degradation of carbon/glass/basalt fiber reinforced polymer (i.e., CFRP/BFRP/GFRP) exposed to simulated seawater sea sand concrete environments (SWSSC) at 25, 40 and 60 °C for 6 months. The presence of NaCl in simulated concrete environment was found beneficial for the moisture uptake of CFRP and GFRP. The greater fiber degradation of BFRP was attributed to its high aluminium, iron and magnesium contents on fibers. Further, FRPs showed greater degradation resistance in high performance concrete solutions that have a lower alkaline content. Thus, CFRP exhibited the best durability to simulated SWSSC environments, followed by GFRP and BFRP.

Introduction

According to a report by United Nations, global population is expected to increase by 2.4 billion by 2050 [1], placing huge demand on the infrastructure, and hence, on their construction materials. As a result, there will be increasing shortage of fresh water and river sand, the two main ingredients of conventional concrete. In addition, there has been an increasing need of additional coastal infrastructures due to the rising sea level [2], requiring large quantities of river sand and fresh water transported from inland to the site. The potential use of seawater and sea sand concrete (SWSSC) is a hugely attractive proposition as substitute for conventional concrete that requires fresh water and river sand.

Though SWSSC offers enormous benefits, it may be nearly impossible to use the traditional carbon steels to act as external confinement or internal reinforcement that will suffer sever corrosion due to very high Cl content of seawater and sea sand. ‘Concrete Cancer’, which is spallation and cracking of concrete due to enhanced corrosion of steel reinforcement by Cl ions, and hence a serious concern even for conventional concrete, will only be highly accelerated in the presence of seawater and sea sand. A series of studies investigating the corrosion of steels in SWSSC concrete has been summarised in [3]. To mitigate the critical problem of unacceptably high corrosion rate of steels in SWSSC, fiber reinforced polymer (FRP) is proposed as a potential alternative material for SWSSC reinforcements, given their superior corrosion resistance and competent mechanical properties.

Given the distinct potential advantages of FRPs over steels as external confinement or internal reinforcement material, it is mandatory to ascertain their durable performance in the relatively new environment of SWSSC. A number of studies have explored pre-exposure of FRPs to simulated conventional concrete environments, followed by mechanical testing to characterise deterioration in mechanical properties as a result of the pre-exposure [[4], [5], [6], [7], [8], [9], [10]]. It has been found that concrete environment, the most common source of alkali, is detrimental to the mechanical properties of FRPs while the salt content only has a marginal effect [4,6,8,10,11]. For instance, Chen et al. [6] reported that GFRPs that were exposed to simulated seawater at 60 °C for 70 days exhibited highest tensile strength retention (i.e., 74%), followed by those exposed to distilled water (71%) and then highly alkaline solution (64%), while CFRP retained 96% of its tensile strength after exposure to the most aggressive environment, i.e., the highly alkaline solution at 60 °C. Similar results were reported by [11] for GFRP, BFRP and CFRP after 60 days of immersion in seawater, alkaline solution and distilled water. To explain the difference in the extent of the reported mechanical property losses in the three solution types, some studies have looked into the degradation specifically at fiber, resin and interface during exposures to these solutions. It was reported in [12] that vinylester resin of GFRP plasticized during exposure to distilled water, simulated concrete solution and concrete leachate solution. Hydrolytic degradation and fiber degradation were enhanced particularly in the alkaline solution. Similar findings were also reported for epoxy-based BFRP [11]. However, there are very few studies on the durability of FRPs exposed to SWSSC environment, which has a mix of alkali and chloride. El-Hassan et al. [13] found matrix hydrolysis, increasing void content, weakening of fiber/matrix interface but no detectable fiber degradation on GFRP bars that were embedded in seawater-contaminated concrete for 15 months. On the other hand, Wang et al. [14] observed chemical attack of fiber in the cross sections of both GFRP and BFRP bars pre-exposed to simulated SWSSC solutions and a greater degradation of fiber/matrix interface in the case of BFRP than GFRP upon exposure to the highly alkaline solution at 55 °C for 63 days. However, it is argued that the degradation at the fiber/matrix interface seen in this study [14] might have been caused (or accentuated) by grinding of cross-section during specimen preparation. Therefore, there might be a need for examining such degradation by an alternative approach.

This study aims to systematically investigate the degradation mechanism of three different types of filament-wound FRPs (i.e. CFRP, GFRP, BFRP) exposed to simulated seawater and sea sand concrete (SWSSC) environments and simulated conventional concrete environments. The results will provide a critical understanding of FRP degradation in SWSSC that will enable a suitable reinforcing material selection.

Section snippets

Materials and specimens

Filament-wound CFRP, BFRP and GFRP tubes with a nominal outer diameter of 50 mm and wall thickness of 3.5 mm were procured from CST Composites Australia. The winding pattern is 20% 15° + 40% 45° + 40% 75°, and the epoxy resin in each FRP was a bisphenol A and bisphenol B blend with an amine hardener. Inductively coupled plasma- atomic emission spectroscopy (ICP-AES) was used to determine the chemical composition of intact E-glass and basalt fibers. Table 1 provides the chemical compositions of

Visual observation

As seen from Fig. 1, after 6-month immersion at 60 °C, the colour and luster of exposed CFRP specimens remained largely unchanged, irrespective of the solutions they were exposed to. On the other hand, the colour of the GFRP and BFRP specimens immersed in simulated concrete solutions (i.e., NC, HPC, SWSSNC, SWSSHPC) turned brighter, and their surface texture became rough, whereas the specimens exposed to distilled water showed only slight colour change with little change in luster. Those

Conclusion

This study investigated the degradation behaviour of three types of filament wound FRPs (i.e. CFRP, GFRP, BFRP) exposed to simulated SWSSC and other concrete solutions. Key findings can be summarised as following:

  • 1

    Moisture uptake of FRPs (except BFRP at 60 °C) during exposure to various environments followed a trend: NC > SWSSNC > DW > HPC > SWSSHPC

  • 2

    Degradation of resin and fibers, particularly basalt and glass fibers, in the simulated high performance concrete solutions that have considerably

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