Karbhari / Lee Service Life Estimation and Extension of Civil Engineering Structures

1. Auflage 2010
ISBN: 978-0-85709-092-8
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 320 Seiten

Reihe: Woodhead Publishing Series in Civil and Structural Engineering

Service life estimation is an area of growing importance in civil engineering both for determining the remaining service life of civil engineering structures and for designing new structural systems with well-defined periods of functionality. Service life estimation and extension of civil engineering structures provides valuable information on the development and use of newer and more durable materials and methods of construction, as well as the development and use of new techniques of estimating service life.Part one discusses using fibre reinforced polymer (FRP) composites to extend the service-life of civil engineering structures. It considers the key issues in the use of FRP composites, examines the possibility of extending the service life of structurally deficient and deteriorating concrete structures and investigates the uncertainties of using FRP composites in the rehabilitation of civil engineering structures. Part two discusses estimating the service life of civil engineering structures including modelling service life and maintenance strategies and probabilistic methods for service life estimation. It goes on to investigate non-destructive evaluation and testing (NDE/NDT) as well as databases and knowledge-based systems for service life estimation of rehabilitated civil structures and pipelines.With its distinguished editors and international team of contributors Service life estimation and extension of civil engineering structures is an invaluable resource to academics, civil engineers, construction companies, infrastructure providers and all those with an interest in improving the service life, safety and reliability of civil engineering structures. - A single source of information on the service life of reinforced concrete and fibre-reinforced polymer (FRP) rehabilitated structures - Examines degradation mechanisms in composites for rehabilitation considering uncertainties in FRP reliability - Provides an overview of probabilistic methods for rehabilitation and service life estimation of corroded structures

Autoren/Hrsg.

Karbhari, Vistasp M.

Lee, L S

Leseproben

2 Using fibre reinforced polymer (FRP) composites to extend the service life of corroded concrete structures
K. Soudki,     University of Waterloo, Canada Abstract:
This chapter discusses the use of fibre reinforced polymers (FRP) to repair deterioration of concrete structures caused by corrosion of their steel reinforcement. The chapter reviews the effects of corrosion on the serviceability and strength of a corroded structure. It then discusses the effects of FRP repair on the serviceability and the strength of a corroded structure. Models for assessing the service life of a corroded structure are given. The chapter concludes with field applications for FRP repair of corroded structures. Key words corrosion bond flexure fatigue repair and rehabilitation FRP reinforcement 2.1 Introduction
Many concrete structures in adverse environments experience an unacceptable loss in serviceability or safety far earlier than anticipated due to the corrosion of their reinforcing steel, and thus need replacement, rehabilitation, or strengthening. Tuutti (1980) proposed a service life model with two distinct periods of deterioration caused by corrosion (Fig. 2.1). The first one is the initiation period, which represents the time required for CO2 or Cl-ions to diffuse to the steel-to-concrete interface and activate corrosion. The second is the propagation period, which represents the time between corrosion initiation and corrosion cracking. If corrosion cracking can be prevented or delayed, structural strength will be maintained for a longer time in a corroding reinforced concrete member. 2.1 Service life model of corroded structures (Tuutti, 1980). The use of fibre reinforced polymer (FRP) composites in civil engineering has recently emerged as an alternative to the traditional methods used for rehabilitation or reinforcement of structures. FRPs are of interest to rehabilitation engineers because of their high strength-to-weight ratio, high fatigue resistance, ease of installation and the fact that they do not corrode (ACI Committee, 2007). There are structural benefits obtained when externally bonded FRP laminates are used to repair corrosion damaged RC elements (Soudki and Sherwood, 2000; Bonacci and Maalej, 2001; Masoud et al., 2001; Masoud and Soudki, 2006, El Maaddawy et al., 2007). In addition, wrapping a corroded element with FRP laminates may reduce the corrosion activity because a FRP wrap acts as a low-permeability barrier to the further ingress of water and oxygen into concrete, which are required for corrosion reactions to continue (El Maaddawy et al., 2006; Debaiky et al., 2002; Soudki and Sherwood, 2000). The physical confinement may also impede the dispersion of corrosion products and thus stifle the corrosion reaction itself. Wrapping a concrete section with FRP laminates provides external confinement that resists the internal displacement caused by the expansion of the corrosion products and thus decreases corrosion and bond splitting cracks. Hence, the structural strength of corroding reinforced concrete beams is improved if they are repaired with FRP laminates. Figure 2.2 illustrates the benefits of using FRP repair for corroded RC elements. 2.2 Benefits of using FRP in repairing corroded structures. 2.2 Corrosion in reinforced concrete
The alkaline environment of the concrete provides a natural protection for the steel reinforcement against corrosion through the formation of a passive film of iron oxides. Passivation of steel can be destroyed by carbonation or by chloride attack. Once the passive film breaks down, corrosion will start, in the presence of moisture and oxygen (ACI Committee, 2002). Corrosion of steel is described as an electrochemical process involving (Fig. 2.3): (i) an anode where iron, Fe2 + is removed from the steel, (ii) a cathode where hydroxyl ions OH– are produced, (iii) an electrical conductor for electrons transfer, and (iv) an electrolyte for ion transfer. The released hydroxyl ions at the cathode travel through the electrolyte to react with the ions at the anode, producing rust (Fig. 2.4a). The corrosion rate is controlled by many factors, including availability of dissolved oxygen and the concrete resistivity around the steel. Rust formation may occupy up to ten times the volume of the original steel (Broomfield, 1997). The increase in volume causes tensile stresses in the concrete that lead to longitudinal cracking and spalling of the concrete (Fig. 2.4b). For example, corrosion crack width as a function of degree of corrosion can be seen Fig. 2.5. Cracks facilitate ingress of oxygen, moisture and chlorides, and increase the rate of bar corrosion by ten times or more (Bentur et al., 1997). In addition to cracking, the loss in bar section, in combination with bond loss between the steel and concrete, leads to a reduction of the capacity and an increase in deflection of the structural member. 2.3 Corrosion process. 2.4 (a) Corrosion deterioration: section loss of the steel reinforcement, (b) Corrosion deterioration: concrete cracking (Bentur et al., 1997). 2.5 Corrosion crack width versus steel mass loss relationship (El Maaddawy, 2004). 2.2.1 Effect of corrosion on bond strength
Experimental studies reported in the literature on the effect of corrosion on the bond behaviour of reinforced concrete beams showed that, at a low corrosion rate (about 0.04 mA/cm2), the bond strength initially increased, as corrosion increased, as shown in Fig. 2.6 (FIB Bulletin, 2000). This increase was attributed to the fact that the rust produced before cracking would cause a rough surface around the bar, hence increasing the friction force on the interface between the reinforcing steel and the concrete. Once the concrete was cracked due to corrosion, the bond stresses between the reinforcing steel and the concrete significantly decreased and the slip of the reinforcing bar relative to the concrete increased. A decrease in the bond leads to a decrease in the load carrying capacity and an increase in the deflection of the structure (ACI Committee, 2003). 2.6 Variation of bond strength with corrosion (FIB Bulletin, 2000). 2.2.2 Effect of corrosion on flexural strength
Research on the effect of corrosion on the flexural strength of concrete beams showed that corrosion leads to a decrease in the capacity of the member. The reduction in strength was found to be proportional to the reduction in the steel cross-sectional area, due to corrosion. When anchorage zones were corroded, there was bond splitting, with an increase in the deflection (Uomoto et al., 1984; Lee et al., 1997; Mangat and Elgarf, 1999; El Maaddawy et al., 2005). A schematic of the corrosion deterioration for flexural strength is shown in Fig. 2.7. 2.7 Variation of member capacity with corrosion (Uomoto et al., 1984). 2.2.3 Effect of corrosion on fatigue strength
Masoud et al. (2005) investigated the fatigue of corroded reinforcement in concrete and found that it has a significant effect on shortening the service life. Al-Hammoud et al. (2010) investigated the effect of corrosion on the flexural strength. They reported that the decrease in flexural fatigue was not proportional to the corrosion level; for example, a 12% mass loss reduced the fatigue strength on average by 25%, compared with that of uncorroded specimens. It was concluded that the reduction in fatigue life is proportional to the increase in the fatigue notch factor. A strain life approach using the fatigue notch factor was implemented to predict the fatigue life of the corroded beams. Rteil (2007) studied the effect of corrosion on the bond behaviour of reinforced concrete beams under repeated loading. He reported that fatigue had a more pronounced effect on the bond of corroded reinforcement. For example, corrosion levels of 5% and 9% decreased the fatigue bond strength on average by 19%. 2.3 Fibre reinforced polymer (FRP) repair for corrosion damage
2.3.1 Application of FRP repair
It is recommended to follow proper concrete repair procedures as per current practice before and during any FRP repair. The application of the FRP repair should be done in accordance with the procedures provided by the FRP manufacturer and repair guides. Figure 2.8 shows examples of FRP repairs on beam and column specimens in the laboratory. Prior to FRP repair, the reader should consult the relevant documents such as those published by the American Concrete...