Elsevier

Composite Structures

Volume 234, 15 February 2020, 111675
Composite Structures

Tensile behaviour of carbon fabric reinforced cementitious matrix composites as both strengthening and anode materials

https://doi.org/10.1016/j.compstruct.2019.111675Get rights and content

Abstract

Recently, a promising solution to corroded steel reinforced concrete structures was proposed in which a dual-functional carbon-fabric reinforced cementitious matrix (carbon-FRCM) composite is used for impressed current cathodic protection (ICCP) and structural strengthening (SS); this method is referred to as ICCP-SS. The tensile behaviour of carbon-FRCM must be understood for design purposes. In this study, the tensile characteristics of carbon-FRCM composites with different fabric reinforcement ratios were assessed to determine the strengthening capability of the materials. Then, using the composite as an anode material, the tensile behaviour of carbon-FRCM specimens subjected to anodic polarization in ICCP was evaluated. Direct tensile tests were conducted to obtain the tensile stress-strain behaviour of the carbon-FRCM specimens. By comparing the results from each case, the influences of different parameters on the tensile behaviour of the carbon-FRCM composites were evaluated, and useful information regarding the application of these materials in ICCP-SS was obtained.

Introduction

A promising fabric reinforced cementitious matrix (FRCM) composite composed of fibres in a fabric mesh shape and an inorganic matrix has been investigated for strengthening masonry and/or reinforced concrete (RC) structures [1], [2], [3], [4], [5]. Textile reinforced mortar (TRM) and textile reinforced concrete (TRC) are in the same composite family as FRCM. Unlike the well-known fibre reinforced polymer (FRP) composite, the fabric mesh in an FRCM is typically made of fibres that are individually coated but are not bonded together by a polymeric resin; i.e., FRCMs use “dry fibres” [6]. Compared to an FRP using an organic polymeric resin, an inorganic matrix has better inherent heat resistance, superior compatibility with the substrate and greater long-term durability. These properties have driven researchers who work mainly on the intervention of existing structures to conduct systematic investigations on the strengthening performance of FRCM composites.

Several studies [7], [8], [9], [10], [11] have been conducted on the mechanical characterization of FRCMs combining various types of fabrics, such as carbon, glass, polybenzoxazole (PBO), and basalt fabrics, with different inorganic matrices (cement-based, geo-polymer, lime-based mortar). Arboleda et al. [12] compared the tensile behaviours of PBO-FRCM, carbon-FRCM and glass-FRCM using both clamping grip and clevis grip methods. Their results showed that the stress-strain behaviour was trilinear when using the clamping grip method, whereas the stress-strain behaviour was bilinear when using the clevis grip method. Donnini et al. [13] performed tensile tests with the clevis grip method by changing the bonded length of the metallic tabs used to grip the ends of the specimens. They concluded that a bonded length of 150 mm was suitable for characterizing FRCM composites. The performance and failure modes of FRCMs reinforced with multiple carbon fabric plies were also investigated by Donnini et al. [13]. The tested carbon fabric was coated with epoxy resin and quartz sand in combination with lime-based mortar. Lime-based matrices are generally used for strengthening masonry structures, while cement-based mortar is suitable for strengthening RC structures [7]. Barhum et al. [14] addressed the influence of the dispersing short glass and carbon fibres in cement-based mortar on the tensile behaviour of TRC and the bonding behaviour between yarn and mortar matrix. In their study, the TRC was reinforced by an alkali-resistant (AR) glass fabric with a polymer coating, and improvements in both the tensile strength of the TRC and the bond strength between the yarn and the matrix were achieved. However, a limited number of studies have been performed on carbon-FRCM composites with multiple layers of dry fabric reinforcement and mortar matrix modified by short, dispersed carbon fibres.

FRCM strengthening is a potential method for rehabilitating and upgrading aged RC structures [15], [16], [17], [18]. Babaeidarabad et al. [19] investigated the feasibility of using FRCMs for strengthening RC members, and they considered the effect of multiple layers of dry fibre fabric in FRCMs. Yin et al. [20] investigated the compressive performance of TRC-strengthened concrete columns containing steel reinforcement with chloride-induced corrosion. The load-bearing capacity and ductility of RC columns increased with an increasing number of textile layers; however, both the load-bearing capacity and the ductility decreased after chloride wet-dry cycling due to the corrosion effect of chloride ions. It is expected that the load-bearing capacity of FRCM-strengthened RC structures could be continuously reduced from the persistent chloride-induced corrosion of the steel reinforcement in the concrete. Impressed current cathodic protection (ICCP) has been shown to be one of the most efficient methods for addressing the chloride-induced corrosion of steels in concrete [21], [22]. Therefore, Zhu et al. [23], [24] proposed a promising solution (ICCP-SS) to increase the load-bearing capacity of aged RC structures and to control the corrosion of steels in concrete by using a dual-functional carbon-FRCM composite. The carbon fabric mesh embedded in the carbon-FRCM has a superior conductivity characteristic with a reasonable and acceptable cost in comparison with normal anode material, meanwhile, it also has an advanced light weight – high strength and a strong resistance to corrosion characteristics comparing with traditional steel plate for strengthening. The ICCP technique is compatible with structural strengthening (SS) when using carbon-FRCM, which serves as the anode material for the ICCP and as a strengthening material in SS; the combined approach forms the ICCP-SS intervention system.

The mechanical and anodic performance of the dual-functional carbon-FRCM composites are essential to the ICCP-SS intervention system. Nguyen et al. [25] investigated the performance of carbon fibre fabric as an ICCP anode in saturated calcium hydroxyl solution (Ca(OH)2). They reported that the weight loss of the carbon fabric after anodic polarization in ICCP was 2.69%. Hence, it is necessary to understand the durability of anode materials in ICCP. However, studies have not yet clarified the durability issues of carbon-FRCMs, such as the degradation in the tensile behaviour and anodic performance of the materials, due to the influence of anodic polarization in ICCP.

In this paper, 21 tensile tests using the clevis grip method were conducted in two series. For the first series, 9 tensile tests were performed on carbon-FRCM specimens reinforced with 1, 2, and 4 carbon fabric layers (three specimens for each configuration) to investigate the influence of the fabric reinforcement ratio on the tensile behaviour. For the second series, carbon-FRCM specimens reinforced with 2 layers of carbon fabric mesh were used as anode materials in an ICCP procedure. Then, 12 tensile tests (four anodic polarization cases and three specimens for each case) were conducted on carbon-FRCM specimens to investigate the influence of anodic polarization in ICCP.

Section snippets

Cement-based mortar matrix

A cement-based mortar matrix composition for carbon-FRCM composites is shown in Table 1. The binder was Portland cement type 52.5 R, and the water-to-cement ratio was 0.35. Quartz sand with different particle sizes was used; the fine size ranged from 0.1 mm to 0.5 mm, and the moderate size was smaller than 1.0 mm. The weight ratio between fine and moderate sand was 0.5. The mortar contained 0.75 wt% (measured as a percent of the cement weight) short, dispersed carbon fibres with a nominal

Results overview

Fig. 5(a) shows the stress-strain behaviour of the carbon-FRCM coupons regarding the overall cross-sectional area of the carbon fabric mesh. The stress in the vertical axis of the carbon-FRCM coupon was calculated with Eq. (4), in which the tensile force (F) was divided by the nominal cross-sectional area of the carbon fibre mesh (Acfm). The strain in the horizontal axis of the carbon-FRCM was the deformation measured within the 200-mm gauge length of the extensometer.σcf=F/Acfm

As expected, the

Results of the ICCP procedure

Fig. 9 shows the results of the feeding voltage (Efeed) between the carbon-FRCM anode and the steel cathode, the anode potential (Ean), and the steel potential (Ecat) as a function of the testing time. The instant-off steel potentials (Ecat) in all specimens were more negative than −800 mV with respect to the Ag/AgCl RE. According to BS EN 12696–2000 [31], the results of Ecat in the present paper meet the criteria for successful protection of steels in concrete, which indicates the efficiency

Conclusions

Carbon-FRCM composites are a promising dual-functional material in ICCP-SS intervention systems, in which these composites can be used for SS and as the anode materials in ICCP systems. The influences of the carbon fabric reinforcement ratio and anodic polarization in ICCP on the tensile behaviour of multiple layers of carbon-FRCM were investigated. The tensile strength, deformation, crack pattern and stiffness based on the stress-strain curves obtained from direct tensile tests were analysed

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The research described in this paper was supported by the National Natural Science Foundation of China (51538007, 51778370), the Natural Science Foundation of Guangdong (2017B030311004), and the Shenzhen Science and Technology Project (JCYJ20170818094820689).

Data availability statement

The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

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