National Academies Press: OpenBook

Nondestructive Testing to Identify Concrete Bridge Deck Deterioration (2012)

Chapter: Chapter 2 - Common Defects of Concrete Bridge Decks

« Previous: Chapter 1 - Background
Page 7
Suggested Citation:"Chapter 2 - Common Defects of Concrete Bridge Decks." National Academies of Sciences, Engineering, and Medicine. 2012. Nondestructive Testing to Identify Concrete Bridge Deck Deterioration. Washington, DC: The National Academies Press. doi: 10.17226/22771.
×
Page 7
Page 8
Suggested Citation:"Chapter 2 - Common Defects of Concrete Bridge Decks." National Academies of Sciences, Engineering, and Medicine. 2012. Nondestructive Testing to Identify Concrete Bridge Deck Deterioration. Washington, DC: The National Academies Press. doi: 10.17226/22771.
×
Page 8
Page 9
Suggested Citation:"Chapter 2 - Common Defects of Concrete Bridge Decks." National Academies of Sciences, Engineering, and Medicine. 2012. Nondestructive Testing to Identify Concrete Bridge Deck Deterioration. Washington, DC: The National Academies Press. doi: 10.17226/22771.
×
Page 9
Page 10
Suggested Citation:"Chapter 2 - Common Defects of Concrete Bridge Decks." National Academies of Sciences, Engineering, and Medicine. 2012. Nondestructive Testing to Identify Concrete Bridge Deck Deterioration. Washington, DC: The National Academies Press. doi: 10.17226/22771.
×
Page 10
Page 11
Suggested Citation:"Chapter 2 - Common Defects of Concrete Bridge Decks." National Academies of Sciences, Engineering, and Medicine. 2012. Nondestructive Testing to Identify Concrete Bridge Deck Deterioration. Washington, DC: The National Academies Press. doi: 10.17226/22771.
×
Page 11

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

7C h a p t e r 2 Reinforced concrete structures such as bridge decks and pil- lars, highways, and other infrastructure facilities experience loss of integrity over time because of poor initial quality, damage from deicing salts, overloading, freeze–thaw cycle- induced stresses, fatigue, and, above all, corrosion of rebars (Figure 2.1). According to the Federal Highway Administra- tion (FHWA), the cost of repairing and replacing deteriorat- ing highway bridges in the United States is approximately $100 billion (Lemieux et al. 2005; El-Safty 2008). The differ- ent kinds of deterioration observed in reinforced concrete structures are outlined in the following sections. The most frequent deterioration phenomena identified by Bien et al. (2007) are the following items: • Corrosion; • Carbonation; • Alkali-silica reaction; • Crystallization; • Leaching; • Oil and fat influence; • Salt and acid actions; • Creep; • Fatigue; • Influence of high temperature; • Modification of founding conditions; • Overloading; • Shrinkage; and • Water penetration. Common Deterioration types in Bridge Decks The deterioration of steel-reinforced concrete structures can be caused by the corrosion of steel or degradation of con- crete. These deterioration processes are complex and often prompt one another. Among all the deterioration phenom- ena listed above, four deterioration mechanisms are of the highest concern to bridge engineers and are the focus of this project. Those include the following: • Rebar corrosion; • Deck delamination; • Vertical cracking; and • Concrete degradation. Each of the deterioration mechanisms is briefly discussed in the following sections. Rebar Corrosion Reinforcing steel embedded in concrete is naturally protected from corrosion by the high alkalinity of the cement-based materials and an adequately thick concrete cover. High alka- linity can cause the formation of a passive and noncorroding protective oxide film on the steel surface. ACI 222R-01 (2001), which was reapproved in 2010, describes the process of metal corrosion in concrete. During this process, concrete allows electrolytic conduction and the flow of ions from anodes to cathodes. Once the oxide film is destroyed, an electric cell is formed along the steel or between steel bars, and the electro- chemical process or corrosion begins. Some areas along the bar become anodes discharging current in the electric cell, and iron goes into the solution with oxygen. Other steel areas receive current resulting in the formation of hydroxide ions known as cathodes. A major contributor to this problem is chloride diffusion. Chlorides are derived primarily from the application of roadway deicing salts. Corrosion of steel rein- forcement in a bridge deck can directly reduce the structural capacity of the deck. Furthermore, the corrosion process can cause internal stresses, cracking, delamination or surface fracture planes, and eventually spalling in concrete at, or just above, the level of the reinforcement (Figures 2.2 and 2.3). The two most common steel corrosion processes are chloride-induced pitting corrosion and carbonation. Bridge Common Defects of Concrete Bridge Decks

8engineers can often visually distinguish the two corrosion types. The locally confined, chloride-induced pitting corro- sion leaves blackish rust marks, whereas red or brownish rust stains indicate carbonation-based corrosion. The rate of cor- rosion is dependent on numerous factors, including the com- position of the metal, as well as humidity, temperature, water pH, and exposure to pollution and salt. Wet and dry cycles accelerate the corrosion process. Studies have shown that the corrosion rate is highest during the spring season and lowest during the winter. These rates can vary by a factor of about four or five during the year (Smith and Virmani 1996; Page et al. 1996). Deck Delamination Delamination or horizontal cracking caused by corrosion of embedded reinforcing steel is a serious form of deterioration in concrete bridge decks. Reinforcing steel expands as it corrodes. Such expansion may create a crack or subsurface fracture plane in the concrete at or just above the level of the reinforcement, as illustrated in Figure 2.4. Delamination may be localized or may extend over a substantial area, especially if the concrete cover is thin. It is possible that in a given area, delamination can occur along different planes between the concrete surface and the reinforcing steel. Delamination is not visible on the concrete surface; however, if repairs are not made in a timely fashion, the delamination progresses to open spalls. With continued corrosion, this process will even- tually affect the structural integrity of the deck. Vertical Cracking In addition to rebar corrosion, many other factors can cause cracking in bridge decks. These factors include plastic shrink- age, hydration heat, ambient temperatures, geometric con- straint as the deck concrete cures, traffic load, and freeze–thaw Figure 2.1. Deck deterioration. Figure 2.2. Corrosion process.

9Figure 2.3. Corroded rebar in an excavated deck (top) and extracted core (bottom left), and delamination in a drill hole in a deck (bottom right). Figure 2.4. Delamination observed in extracted cores.

10 cycles. The progression of rebar corrosion can further exag- gerate these cracks. Vertically oriented cracks and load-related cracks will be the primary focus of the validation testing. Concrete Deterioration A reduction in concrete strength or modulus is considered to be a form of concrete degradation. It may be the result of micro- cracking and macrocracking and other phenomena, such as alkali–silica reaction (ASR), delayed ettringite formation (DEF), plastic shrinkage, and freeze–thaw cycles. Each of the phenomena is briefly described in the following paragraphs. The alkali–silica reaction is a reaction between reactive sil- ica phases in aggregates and alkali hydroxides in the concrete pore solution. This reaction produces a silica gel that swells in the presence of water, causing internal and external cracking. The expansion of concrete resulting from ASR can cause two main problems: (1) the deformation of the structure, thereby impairing the serviceability, and (2) the development of a crack network through the structure (Figure 2.5). Delayed ettringite formation is perceived as a form of inter- nal sulfate attack. DEF is believed to be a result of improper heat curing of the concrete where the normal ettringite forma- tion is suppressed. The highly concentrated sulfate in the pore (a) (b) Source: ASR photograph courtesy of Dr. Moon Won, Texas Tech University. DEF damage photograph courtesy of Texas Department of Transportation Bridge Division. Source: Photographs courtesy of Dr. Ken Maser. Figure 2.5. (a) ASR and (b) DEF damage.

11 liquid may eventually react with calcium- and aluminum- containing phases of the cement paste to form the hydrated calcium sulfoaluminate mineral, ettringite. The formation of ettringite causes the concrete to expand, and empty cracks (gaps) may form around aggregates (see Figure 2.5) Plastic shrinkage (volume reduction) can cause cracks in concrete. These cracks often occur on plane structures such as deck slabs, with no preferential crack orientation. Freeze–thaw can increase the hydraulic pressure in con- crete. The concrete will rupture once the pressure exceeds the tensile strength of the concrete. The exposure of concrete to repeated freeze–thaw cycles will ultimately cause extensive deterioration in the form of cracking, scaling, or crumbling. Overlay Debonding Some old bridge decks are overlaid with asphalt concrete or portland cement concrete (PCC). In such bridge decks, the overlay can debond from the existing concrete decks. Once an overlay debonds, moisture and chlorides may enter the debonded region, further promoting deterioration. If repairs are not made, debonded overlay regions can eventually dete- riorate into open spalls, which affect the ride quality of the deck and compromise the structural integrity of the deck. Furthermore, bonded and debonded overlays contribute to the complexity of the analysis of NDT methods and may impede their effectiveness.

Next: Chapter 3 - Candidate Methods for Deterioration in Concrete Bridge Decks »
Nondestructive Testing to Identify Concrete Bridge Deck Deterioration Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s second Strategic Highway Research Program (SHRP 2) Report S2-R06A-RR-1: Nondestructive Testing to Identify Concrete Bridge Deck Deterioration identifies nondestructive testing technologies for detecting and characterizing common forms of deterioration in concrete bridge decks.

The report also documents the validation of promising technologies, and grades and ranks the technologies based on results of the validations.

The main product of this project will be an electronic repository for practitioners, known as the NDToolbox, which provides information regarding recommended technologies for the detection of a particular deterioration.

An e-book version of this report is available for purchase at Amazon, iTunes, and Google

As part of the project that developed SHRP 2 Report S2-R06A-RR-1, a series of videos were produced that show various nondestructive testing technologies being demonstrated by teams from industry and academia. Technologies highlighted in the videos include electrical resistivity (Rutgers); galvanostatic pulse measurement (Olson Engineering); ground penetrating radar (3D Radar, IDS-Italy, NDT Corp, Aladdin System, Olson Engineering/IDS, and Rutgers); half-cell potential (Rutgers); impact echo (University of Illinois, NDT Corp, Olson Engineering, Rutgers, University of Texas at Austin, and Germann Instruments); impulse response (Germann Instruments); infrared thermography (FHWA and the University of Texas at El Paso); ultrasonic pulse echo (University of Texas at El Paso); and ultrasonic surface waves (Rutgers).

Renewal Project R06A is one of seven follow-on projects to SHRP Renewal Project R06 that produced SHRP 2 Report S2-R06-RW: A Plan for Developing High-Speed, Nondestructive Testing Procedures for Both Design Evaluation and Construction Inspection, which examines existing and emerging nondestructive evaluation technologies and their current state of implementation to satisfy the NDE needs for highway renewal.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!