Concrete spalling is a form of deterioration within a reinforced or prestressed concrete system. This type of deterioration for a concrete structural component occurs at the surface where concrete will decompose, often leaving any steel reinforcement visible and open to additional corrosion. Spalling is typically a result of reinforcement corrosion or joint failure, where produced internal expansion forces can “lead to large-scale delaminations” of the surrounding concrete (Transportation Research Board 2004, p. 7).
Proper bridge maintenance techniques can largely relieve any additional adverse effects from initial concrete spalling. Some forms of remediation include: patching, strengthening through composites, concrete sealants, and joint adjustment. A lack of proactive and preventative measures can lead to significant consequences. As an example, one can examine the Lake View Drive Bridge collapse (along I-70 in Pennsylvania), where extensive concrete and reinforcement deterioration ultimately lead to the bridge’s failure.
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Causes of Concrete Deterioration & Spalling
As a form of concrete deterioration, concrete spalling is a serious and common issue within bridge structures. It begins at either the concrete or steel reinforcement level, where chemical-physical effects will occur. Typical forms of reaction include: calcium chloride with concrete, sulfate attack on concrete, chloride penetration to steel, and the carbonation process. Certain environments can exacerbate these phenomena, so appropriate consideration must be taken.
Calcium Chloride & Concrete
Calcium chloride, a typical concrete mix additive, helps speed the rate of concrete curing. With the faster cure rate, the following benefits can be reached: high initial strength, improved workability, and a reduced final set time (among others) (Morris Chemicals, Inc.). Ultimately, a calcium chloride additive is beneficial when environmental factors inhibit curing, such as cold temperatures and excessive humidity. However it is important to regulate the amount used and whether or not it is appropriate for a given structure.
ACI 318-11 provides guidance on the admixture, where it should be avoided for prestressed concrete structures and carefully used when aluminum/steel sheeting & reinforcement are utilized (ACI, p. 50-51). Generally speaking, the consequences of corrosion for prestressed concrete structures are much more significant. Since tendons are typically subjected to stresses up to “70 to 80 percent of their tensile strength”, corrosion weakening the steel “may lead to fracture” (Weyers, p. 18). Since chloride free accelerators exist, calcium chloride shouldn’t be used for prestressed concrete due to a high-susceptibility for “future pitting corrosion” (Weyers, p. 22). Particularly in humid environments, corrosion of supplementary steel (reinforcement/formwork) can become an issue when calcium chloride is used.
Chloride Penetration to Reinforcement Steel
Figure 1: Chloride Penetration [Image Credit: Robert Pirro]
As a leading source of reinforcement (and subsequent concrete) deterioration in bridge structures, chloride corrosion is a key issue to consider in a bridge structure’s design. Penetrating through existing cracks in the concrete, chlorides induce corrosion of the steel reinforcement. Spalling of the concrete will then occur following the expansive forces produced from the corroded steel. For bridge structures, external chlorides can be introduced in the form of sea water (in coastal regions) and deicing salts. Often for marine environments, it is typical for the service life of the structure to be dependent on the level of deterioration due to reinforcement corrosion (Costa, p. 354). Furthermore, widely used chloride based deicing chemicals produce the most damage to a bridge structure, from both mass and strength loss perspectives (Wang, p. 187).
Carbonation Process
Figure 2: Carbonation Process [Image Credit: Robert Pirro]
Concrete carbonation occurs naturally over the service life of a concrete structure, where carbon dioxide reacts with calcium hydroxide within concrete to form calcium carbonate. Carbon dioxide can come from either the atmosphere or from external water sources. It is important to note that the “rate of carbonation depends on the porosity & moisture content of concrete” where water plays a signature role in the carbonation process (Concrete Experts International). While carbonation can increase the strength capacity of concrete, it also reduces its alkalinity. The reduced alkalinity decreases the corrosion protection capabilities of the reinforcement steel, often leading to spalling as a result. Similarly to chloride penetration, the effects of concrete carbonation seem to be exacerbated in marine environments. It has been found that carbonation occurs more rapidly in structures located at the coast as opposed to their inland counterparts. Diffusion into concrete “varies strongly with the moisture content in the concrete pores”, where coastal regions induce this situation (Costa, p. 242).
Sulfate Attack
Sulfate chemicals can be introduced into bridge concrete structures through either the form of external solutions or in components of the concrete’s mix. With external factors as the most common cause, “an overall loss of concrete strength” can occur due to the sulfates effects on the concrete “composition and concrete structure”. External sources can include: seawater, groundwater, and oxidation of sulfide minerals into concrete. Sulfate can also be presented internally, through components such as sulfate-rich aggregates or gypsum (WHD Microanalysis Consultants). Generally where sulfate corrosion is a concern, admixtures can be included (ACI, p. 60).
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Structural Design Philosophy
Throughout design, a variety of steps can be taken to limit the possibility of deterioration within the structure. Preventative design can be done in both the material properties and structural configuration. ACI 318-11 provides building requirements in both aspects, where design is completed in accordance to environmental and site conditions. Additionally, adequate drainage for the structure is particularly important. Especially in regions where abrasive deicing salts are used, it is critical to have proper water flow in the structure to preserve its integrity.
Concrete Mix Design
Beyond maintaining acceptable levels for typical concrete mix components, a variety of admixtures can be included in interest of deterioration perspective. For instance, ACI 318-11 specifies that concrete structures facing “moderate or severe sulfate exposures” can be protected through “the use of fly ash, natural pozzolans, silica fume, or ground-granulated blast-furnace slag” (ACI, p. 60).
Fly ash, for example, can be used as an admixture in concrete and partial replacement for Portland cement. It can result “in an increase in strength” and “decrease in corrosion activity” for up to a content level of 35% (Weyers, p. 150). Furthermore, fly ash protects the structure via: binding with free lime making it unavailable for sulfate reaction, reducing concrete permeability, and reducing the amount of reactive aluminates available for sulfate reaction (Headwaters Resources). However, despite the power of certain admixtures, concrete can be best protected through quality design and placement. With “appropriate cement content, air-entraining admixture, and proper placement”/construction, concrete will be able to sustain an acceptable service life (PCA).
Epoxy Coated Steel
Since the 1970’s, epoxy coated steel has been used as a form of reinforcement for bridges exposed to corrosive environments. Particularly in areas where deicing solutions are used or marine environments, epoxy coated steel can be a good protection against long term steel corrosion and deterioration for a bridge structure. According to FHWA, epoxy-coated reinforcement in conjunction with sufficient concrete cover can drastically “reduce the likelihood of a concrete deck failure” (Chavel, p. 21). Due to reduced long-term maintenance costs, they have been shown to decrease the overall “life-cycle costs on concrete bridge decks” (CRSI). Just like normal reinforcement steel, it is important to properly fabricate, handle, and implement the epoxy coated steel to avoid any premature deterioration.
Adequate/Proper Drainage & Joint Configuration
Standard bridge drainage systems come in the form of deck drains and gutter systems, as well as attention to roadway elevation and grade. Properly detailed drainage components are critical for ensuring adequate water flow and protection of the structure (particularly from deicing solutions). In general, it is important to consider drainage from the early stages of the structural design in order to successfully avoid any related future concerns.
Furthermore, “it is important to locate drainage and connecting elements in regions of the superstructure where, if they become clogged with debris, they will cause the least damage” (Chavel, p. 12). It may also be advantageous to “make the steel super structure continuous and eliminate the expansion joints”, removing the source of concern (Chavel, p. 12). If joints are included in the bridge structure, it is critical to note the material compatibility of the “parent material” (i.e. bridge girders) and the “joint material” (i.e. shear keys, etc.). If compatibility is overlooked, the joints primary role of transferring moment and shear while remaining water tight can be hard to achieve (leading to possible deterioration) (Aktan, p. 22).
Figures 3-5 below illustrate the importance of a proper joint location. Due to the location of the joint above the overpass bridge pier, significant deterioration has occurred. Likely attributed to the corrosive effects of deicing salts, damage could have been avoided with an alternative placement (or complete absence).
Figure 3: I-81 Virginia Overpass, Butt Hollow Rd. [Photo Credit: Christopher Friend]
Figure 4: I-81 Overpass Deterioration 1 [Photo Credit: Christopher Friend]
Figure 5: I-81 Overpass Deterioration 2 [Photo Credit: Christopher Friend]
Sufficient Concrete Cover
Generally speaking, increasing the concrete cover (over steel reinforcement) can be used as an approach to limit possibility of steel corrosion. Especially in environments prone to corrosive conditions, ensuring adequate concrete cover can drastically increase the service life of the structure. ACI 318-11 provides guidelines for proper cover, including specific recommendations for areas with certain types of exposure (ACI, Chapters 4, 7). Lastly, proper “detailing and subsequent installation of reinforcement will have a significant effect on the behavior and long-term performance” of the bridge structure (Chavel, p. 37). While a particular cover depth may have been desired for a design, poor detailing can lead to faulty construction implementation and leave the reinforcement “susceptible to corrosion” (Chavel, p. 37).
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Maintenance and Rehabilitation
Beyond structural design, a proactive approach must be made in order to limit any of the effects from concrete spalling. Investigation through non-destructive methods can provide information early on so a preemptive response can be conducted. Examples of non-destructive methods include ground penetrating radar (GPR) and infrared analysis. Ultimately, a regular inspection schedule is crucial for proper care of any bridge structure.
Depending on the severity of deterioration, a number of rehabilitation methods exist. To initially limit deterioration, deck sealants and overlays can thwart a significant amount of damage. After damage is discovered, patching and structural strengthening (through composites) can relieve any structural weaknesses.
Preventative Maintenance
Preventative measures to limit extent of deterioration come from regular inspection/investigation schedules and addressing present deterioration. Forms of investigation can come in the form of non-destructive analysis, electrochemical testing, and various lab procedures among others. Non-destructive testing (NDT) can include ground penetrating radar (GPR) and infrared thermography (IRT), where a subsurface perspective on the reinforcement steel is provided. Furthermore, electrochemical testing in the field can provide insight on the rate of concrete corrosion and a prediction for future damage (Venugopalan). Following any inspection/investigation, it is important to address any concerns. Through sufficient bridge cleaning, a variety of deck overlays (see Figures 6-7), and crack sealants, the extent of damage can be drastically reduced.
Figure 6: Bridge Epoxy Overlay [Photo Credit: Park Thompson]
Figure 7: Bridge Concrete Overlay [Photo Credit: Park Thompson]
Rehabilitation Strategies
For more severe cases, extensive rehabilitation techniques may be necessary in order to preserve the integrity of the structure. In addition to sealants and overlays, additional remediation can come through patching, joint removal, and strengthening through composites. Patching, the most common form of rehabilitation, involves removing any compromised concrete and replacing it with a “rapid-curing protective treatment” (Sprinkel).
Joint removal also is a major form of remediation, particularly in areas above abutments and piers providing structural support. Joint removal can eliminate a source of corrosive chemicals to a structure, avoiding drainage and respective deterioration issues. Removal of the joint includes extra reinforcement and concrete placement to produce a continuous structure (see Figures 8-9). Joint closures are also often complemented by an additional epoxy overlay (Sprinkel).
For structures requiring additional strengthening following increased loads & levels of deterioration, composite materials can be utilized. External attachment of composites can include fiber reinforced polymers (FRP) and carbon fiber reinforced plastics (CFRP), which are light weight and resistant to corrosion (Grantham, p. 377). While FRP materials themselves present a high upfront cost, their low weight “helps to reduce labor costs” through “ease in handling the material on construction sites” (Grantham, p. 377).
On December 27, 2005, the Lakeview Drive Bridge collapsed along I-70 in Pennsylvania. Significant structural deterioration and deficiencies ultimately lead to the bridge’s failure. Failure occurred when “the fascia girder supporting the east-side parapet wall of the third span failed under the action of dead load” (Harries, p. 78). Sources of the failure relate to: the “concrete cover to the lower layer was less than prescribed”, the prestressing steel’s “poor resistance to corrosion”, and extensive drainage issues (particularly demonstrated by significant deterioration of the bridge’s shear keys) (Harries, p. 91).
Ultimately, proper damage response and inspection/rating techniques for the bridge could have reduced the likelihood of failure. For an in-depth analysis of the collapse, see “Structural Testing of Prestressed Girders from the Lake View Drive Bridge” (Kent Harries).
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Annotated Bibliography
American Concrete Institute (ACI) (2011). Building Code Requirements for Structural Concrete (ACI 318M-11) and Commentary. American Concrete Institute, Farmington Mills, MI. P. 50-51
Design Manual: Contains code requirements and commentary for concrete structural design.
Aktan, Haluk et al. (2009). “Condition Assessment and Methods of Abatement of Prestressed Concrete Box-Beam Deterioration.” MDOT Research Report, RC-1527. Michigan Department of Transportation. P. 22
Technical Report: Provides insight on strength capacities for box-beam bridges and techniques for adequate maintenance and repair.
Chavel, Brandon and Yadlosky, John (2011). “Framework for Improving Resilience of Bridge Design.” FHWA Report, FHWA-IF-11-016. Federal Highway Administration. P. 12, 21, 37
Technical Report: Discusses bridge issues that result in closure, collapse, or major repairs. It presents on how to minimize these problems.
Cope, R.J. (2004). Concrete Bridge Engineering: Performance and Advances, Elsevier Applied Science Publishers LTD, Essex, England. P. 39.
Book: Provides pertinent details behind concrete bridge engineering, from preliminary design to maintenance strategies.
Costa, A. and Appleton, J. (1998). “Chloride Penetration into Concrete in Marine Environment – Part II: Prediction of Long Term Chloride Penetration”. Materials and Structures, Scientific Reports. P. 354
Technical Report: Provides insight on how chloride penetration plays a role in concrete deterioration.
Costa, A. and Appleton, J. (2001). “Concrete Carbonation and Chloride Penetration in a Marine Environment”. Concrete Science and Engineering, Scientific Reports. P. 242
Technical Report: Provides insight on how carbonation and chloride penetration affect concrete in a marine environment.
Grantham, Mike et al. (2009). Concrete Solutions, CRC Press, Leiden, The Netherlands. P. 377
Book: Contains detailed information on the most common forms of concrete deterioration in the UK & US. Provides effective inspection and rehabilitation strategies.
Harries, Kent (2009). “Structural Testing of Prestressed Concrete Girders from the Lake View Drive Bridge.” J. Bridge Eng. 2009.14:78-92. DOI: 10.1061/ASCE1084-0702(2009)14:2(78). P. 78, 91
Technical Report: Provides a report for an example failure due to excessive concrete & steel deterioration. Discusses the forensic investigation following the bridge’s failure.
Morris Chemicals, Inc. (2011). “Concrete and Calcium Chloride”. Morris Chemicals, Inc. and South Eastern Road Treatment, <http://www.calciumchloride.com/concrete.shtml> (Dec. 10, 2013).
Website: Provides background on calcium chloride and concrete.
Pirro, R. (2013). "Concrete Deterioration and Repair". Professional lecture, Oct. 3, 2013.
Presentation: This presentation was given by R. Pirro, P.E. on modes of concrete deterioration and rehabilitation/maintenance strategies.
Website: Presents strategies in an effort to “prevent, delay or reduce deterioration of bridges or bridge elements” due to corrosion effects (which can cause spalling).
Wang, Kejin et al. (2005). “Damaging effects of deicing chemicals on concrete materials”. Cement & Concrete Composites. Elsevier Ltd. P. 187
Technical Report: Discusses the effects of deicing chemicals on concrete.
Weyers, Richard (1994). Concrete Bridges in Aggressive Environments, American Concrete Institute, Detroit, Michigan. P. 18, 22, 150
Book: Discusses environmental factors involved in concrete deterioration/corrosion
Key Words: concrete deterioration, bridge deterioration, spalling, calcium chloride, chloride, sulfate, carbonation, concrete mix, epoxy coated steel, concrete cover, bridge rehabilitation, bridge maintenance, Lake View Drive
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Introduction
Table of Contents
Proper bridge maintenance techniques can largely relieve any additional adverse effects from initial concrete spalling. Some forms of remediation include: patching, strengthening through composites, concrete sealants, and joint adjustment. A lack of proactive and preventative measures can lead to significant consequences. As an example, one can examine the Lake View Drive Bridge collapse (along I-70 in Pennsylvania), where extensive concrete and reinforcement deterioration ultimately lead to the bridge’s failure.
__
Causes of Concrete Deterioration & Spalling
As a form of concrete deterioration, concrete spalling is a serious and common issue within bridge structures. It begins at either the concrete or steel reinforcement level, where chemical-physical effects will occur. Typical forms of reaction include: calcium chloride with concrete, sulfate attack on concrete, chloride penetration to steel, and the carbonation process. Certain environments can exacerbate these phenomena, so appropriate consideration must be taken.Calcium Chloride & Concrete
Calcium chloride, a typical concrete mix additive, helps speed the rate of concrete curing. With the faster cure rate, the following benefits can be reached: high initial strength, improved workability, and a reduced final set time (among others) (Morris Chemicals, Inc.). Ultimately, a calcium chloride additive is beneficial when environmental factors inhibit curing, such as cold temperatures and excessive humidity. However it is important to regulate the amount used and whether or not it is appropriate for a given structure.ACI 318-11 provides guidance on the admixture, where it should be avoided for prestressed concrete structures and carefully used when aluminum/steel sheeting & reinforcement are utilized (ACI, p. 50-51). Generally speaking, the consequences of corrosion for prestressed concrete structures are much more significant. Since tendons are typically subjected to stresses up to “70 to 80 percent of their tensile strength”, corrosion weakening the steel “may lead to fracture” (Weyers, p. 18). Since chloride free accelerators exist, calcium chloride shouldn’t be used for prestressed concrete due to a high-susceptibility for “future pitting corrosion” (Weyers, p. 22). Particularly in humid environments, corrosion of supplementary steel (reinforcement/formwork) can become an issue when calcium chloride is used.
Chloride Penetration to Reinforcement Steel
As a leading source of reinforcement (and subsequent concrete) deterioration in bridge structures, chloride corrosion is a key issue to consider in a bridge structure’s design. Penetrating through existing cracks in the concrete, chlorides induce corrosion of the steel reinforcement. Spalling of the concrete will then occur following the expansive forces produced from the corroded steel. For bridge structures, external chlorides can be introduced in the form of sea water (in coastal regions) and deicing salts. Often for marine environments, it is typical for the service life of the structure to be dependent on the level of deterioration due to reinforcement corrosion (Costa, p. 354). Furthermore, widely used chloride based deicing chemicals produce the most damage to a bridge structure, from both mass and strength loss perspectives (Wang, p. 187).
Carbonation Process
Concrete carbonation occurs naturally over the service life of a concrete structure, where carbon dioxide reacts with calcium hydroxide within concrete to form calcium carbonate. Carbon dioxide can come from either the atmosphere or from external water sources. It is important to note that the “rate of carbonation depends on the porosity & moisture content of concrete” where water plays a signature role in the carbonation process (Concrete Experts International). While carbonation can increase the strength capacity of concrete, it also reduces its alkalinity. The reduced alkalinity decreases the corrosion protection capabilities of the reinforcement steel, often leading to spalling as a result. Similarly to chloride penetration, the effects of concrete carbonation seem to be exacerbated in marine environments. It has been found that carbonation occurs more rapidly in structures located at the coast as opposed to their inland counterparts. Diffusion into concrete “varies strongly with the moisture content in the concrete pores”, where coastal regions induce this situation (Costa, p. 242).
Sulfate Attack
Sulfate chemicals can be introduced into bridge concrete structures through either the form of external solutions or in components of the concrete’s mix. With external factors as the most common cause, “an overall loss of concrete strength” can occur due to the sulfates effects on the concrete “composition and concrete structure”. External sources can include: seawater, groundwater, and oxidation of sulfide minerals into concrete. Sulfate can also be presented internally, through components such as sulfate-rich aggregates or gypsum (WHD Microanalysis Consultants). Generally where sulfate corrosion is a concern, admixtures can be included (ACI, p. 60).__
Structural Design Philosophy
Throughout design, a variety of steps can be taken to limit the possibility of deterioration within the structure. Preventative design can be done in both the material properties and structural configuration. ACI 318-11 provides building requirements in both aspects, where design is completed in accordance to environmental and site conditions. Additionally, adequate drainage for the structure is particularly important. Especially in regions where abrasive deicing salts are used, it is critical to have proper water flow in the structure to preserve its integrity.Concrete Mix Design
Beyond maintaining acceptable levels for typical concrete mix components, a variety of admixtures can be included in interest of deterioration perspective. For instance, ACI 318-11 specifies that concrete structures facing “moderate or severe sulfate exposures” can be protected through “the use of fly ash, natural pozzolans, silica fume, or ground-granulated blast-furnace slag” (ACI, p. 60).Fly ash, for example, can be used as an admixture in concrete and partial replacement for Portland cement. It can result “in an increase in strength” and “decrease in corrosion activity” for up to a content level of 35% (Weyers, p. 150). Furthermore, fly ash protects the structure via: binding with free lime making it unavailable for sulfate reaction, reducing concrete permeability, and reducing the amount of reactive aluminates available for sulfate reaction (Headwaters Resources). However, despite the power of certain admixtures, concrete can be best protected through quality design and placement. With “appropriate cement content, air-entraining admixture, and proper placement”/construction, concrete will be able to sustain an acceptable service life (PCA).
Epoxy Coated Steel
Since the 1970’s, epoxy coated steel has been used as a form of reinforcement for bridges exposed to corrosive environments. Particularly in areas where deicing solutions are used or marine environments, epoxy coated steel can be a good protection against long term steel corrosion and deterioration for a bridge structure. According to FHWA, epoxy-coated reinforcement in conjunction with sufficient concrete cover can drastically “reduce the likelihood of a concrete deck failure” (Chavel, p. 21). Due to reduced long-term maintenance costs, they have been shown to decrease the overall “life-cycle costs on concrete bridge decks” (CRSI). Just like normal reinforcement steel, it is important to properly fabricate, handle, and implement the epoxy coated steel to avoid any premature deterioration.Adequate/Proper Drainage & Joint Configuration
Standard bridge drainage systems come in the form of deck drains and gutter systems, as well as attention to roadway elevation and grade. Properly detailed drainage components are critical for ensuring adequate water flow and protection of the structure (particularly from deicing solutions). In general, it is important to consider drainage from the early stages of the structural design in order to successfully avoid any related future concerns.Furthermore, “it is important to locate drainage and connecting elements in regions of the superstructure where, if they become clogged with debris, they will cause the least damage” (Chavel, p. 12). It may also be advantageous to “make the steel super structure continuous and eliminate the expansion joints”, removing the source of concern (Chavel, p. 12). If joints are included in the bridge structure, it is critical to note the material compatibility of the “parent material” (i.e. bridge girders) and the “joint material” (i.e. shear keys, etc.). If compatibility is overlooked, the joints primary role of transferring moment and shear while remaining water tight can be hard to achieve (leading to possible deterioration) (Aktan, p. 22).
Figures 3-5 below illustrate the importance of a proper joint location. Due to the location of the joint above the overpass bridge pier, significant deterioration has occurred. Likely attributed to the corrosive effects of deicing salts, damage could have been avoided with an alternative placement (or complete absence).
Sufficient Concrete Cover
Generally speaking, increasing the concrete cover (over steel reinforcement) can be used as an approach to limit possibility of steel corrosion. Especially in environments prone to corrosive conditions, ensuring adequate concrete cover can drastically increase the service life of the structure. ACI 318-11 provides guidelines for proper cover, including specific recommendations for areas with certain types of exposure (ACI, Chapters 4, 7). Lastly, proper “detailing and subsequent installation of reinforcement will have a significant effect on the behavior and long-term performance” of the bridge structure (Chavel, p. 37). While a particular cover depth may have been desired for a design, poor detailing can lead to faulty construction implementation and leave the reinforcement “susceptible to corrosion” (Chavel, p. 37).__
Maintenance and Rehabilitation
Beyond structural design, a proactive approach must be made in order to limit any of the effects from concrete spalling. Investigation through non-destructive methods can provide information early on so a preemptive response can be conducted. Examples of non-destructive methods include ground penetrating radar (GPR) and infrared analysis. Ultimately, a regular inspection schedule is crucial for proper care of any bridge structure.Depending on the severity of deterioration, a number of rehabilitation methods exist. To initially limit deterioration, deck sealants and overlays can thwart a significant amount of damage. After damage is discovered, patching and structural strengthening (through composites) can relieve any structural weaknesses.
Preventative Maintenance
Preventative measures to limit extent of deterioration come from regular inspection/investigation schedules and addressing present deterioration. Forms of investigation can come in the form of non-destructive analysis, electrochemical testing, and various lab procedures among others. Non-destructive testing (NDT) can include ground penetrating radar (GPR) and infrared thermography (IRT), where a subsurface perspective on the reinforcement steel is provided. Furthermore, electrochemical testing in the field can provide insight on the rate of concrete corrosion and a prediction for future damage (Venugopalan). Following any inspection/investigation, it is important to address any concerns. Through sufficient bridge cleaning, a variety of deck overlays (see Figures 6-7), and crack sealants, the extent of damage can be drastically reduced.Rehabilitation Strategies
For more severe cases, extensive rehabilitation techniques may be necessary in order to preserve the integrity of the structure. In addition to sealants and overlays, additional remediation can come through patching, joint removal, and strengthening through composites. Patching, the most common form of rehabilitation, involves removing any compromised concrete and replacing it with a “rapid-curing protective treatment” (Sprinkel).Joint removal also is a major form of remediation, particularly in areas above abutments and piers providing structural support. Joint removal can eliminate a source of corrosive chemicals to a structure, avoiding drainage and respective deterioration issues. Removal of the joint includes extra reinforcement and concrete placement to produce a continuous structure (see Figures 8-9). Joint closures are also often complemented by an additional epoxy overlay (Sprinkel).
For structures requiring additional strengthening following increased loads & levels of deterioration, composite materials can be utilized. External attachment of composites can include fiber reinforced polymers (FRP) and carbon fiber reinforced plastics (CFRP), which are light weight and resistant to corrosion (Grantham, p. 377). While FRP materials themselves present a high upfront cost, their low weight “helps to reduce labor costs” through “ease in handling the material on construction sites” (Grantham, p. 377).
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Related Failures
Lake View Drive Bridge Collapse
On December 27, 2005, the Lakeview Drive Bridge collapsed along I-70 in Pennsylvania. Significant structural deterioration and deficiencies ultimately lead to the bridge’s failure. Failure occurred when “the fascia girder supporting the east-side parapet wall of the third span failed under the action of dead load” (Harries, p. 78). Sources of the failure relate to: the “concrete cover to the lower layer was less than prescribed”, the prestressing steel’s “poor resistance to corrosion”, and extensive drainage issues (particularly demonstrated by significant deterioration of the bridge’s shear keys) (Harries, p. 91).Ultimately, proper damage response and inspection/rating techniques for the bridge could have reduced the likelihood of failure. For an in-depth analysis of the collapse, see “Structural Testing of Prestressed Girders from the Lake View Drive Bridge” (Kent Harries).
__Annotated Bibliography
American Concrete Institute (ACI) (2011). Building Code Requirements for Structural Concrete (ACI 318M-11) and Commentary. American Concrete Institute, Farmington Mills, MI. P. 50-51
Aktan, Haluk et al. (2009). “Condition Assessment and Methods of Abatement of Prestressed Concrete Box-Beam Deterioration.” MDOT Research Report, RC-1527. Michigan Department of Transportation. P. 22
Chavel, Brandon and Yadlosky, John (2011). “Framework for Improving Resilience of Bridge Design.” FHWA Report, FHWA-IF-11-016. Federal Highway Administration. P. 12, 21, 37
Concrete Experts International (2006). “Carbonation of Concrete”. Concrete Experts International, < http://www.concrete-experts.com/pages/carb.htm> (Dec. 10, 2013).
Concrete Reinforcing Steel Institute (CRSI) (2013). “Epoxy-Coated Reinforced Bars”. < http://www.crsi.org/index.cfm/steel/epoxy> (Dec. 10, 2013)
Cope, R.J. (2004). Concrete Bridge Engineering: Performance and Advances, Elsevier Applied Science Publishers LTD, Essex, England. P. 39.
Costa, A. and Appleton, J. (1998). “Chloride Penetration into Concrete in Marine Environment – Part II: Prediction of Long Term Chloride Penetration”. Materials and Structures, Scientific Reports. P. 354
Costa, A. and Appleton, J. (2001). “Concrete Carbonation and Chloride Penetration in a Marine Environment”. Concrete Science and Engineering, Scientific Reports. P. 242
Grantham, Mike et al. (2009). Concrete Solutions, CRC Press, Leiden, The Netherlands. P. 377
Harries, Kent (2009). “Structural Testing of Prestressed Concrete Girders from the Lake View Drive Bridge.” J. Bridge Eng. 2009.14:78-92. DOI: 10.1061/ASCE1084-0702(2009)14:2(78). P. 78, 91
Headwaters Resources (2005). “Class F Fly Ash Increases Resistance to Sulfate Attack”. < http://www.flyash.com/data/upimages/press/TB.7%20Class%20F%20Fly%20Ash%20Increases%20Resistance%20to%20Sulfate%20Attack.pdf> (Dec. 10, 2013)
Morris Chemicals, Inc. (2011). “Concrete and Calcium Chloride”. Morris Chemicals, Inc. and South Eastern Road Treatment, <http://www.calciumchloride.com/concrete.shtml> (Dec. 10, 2013).
Pirro, R. (2013). "Concrete Deterioration and Repair". Professional lecture, Oct. 3, 2013.
Portland Cement Association (PCA) (2013). “Concrete Technology”. < http://www.cement.org/tech/faq_spalling.asp> (Dec. 10, 2013)
Sprinkel, Michael et al. (2005). “Preventative Maintenance for Concrete Bridge Decks.” Virginia Department of Transportation, <http://www.virginiadot.org/business/resources/bu-mat-OPT7S-CBCPreventMaintConcDecks.pdf> (Oct. 2, 2012).
Venugopalan, Siva. “Corrosion Strategies to Extend the Service Life of Concrete Structures.” Virginia Department of Transportation, <http://www.virginiadot.org/business/resources/Materials/Virginia_Concrete_Presentations/2012/5B_-_Corrosion_Strat.pdf> (Oct. 2, 2012).
Wang, Kejin et al. (2005). “Damaging effects of deicing chemicals on concrete materials”. Cement & Concrete Composites. Elsevier Ltd. P. 187
Weyers, Richard (1994). Concrete Bridges in Aggressive Environments, American Concrete Institute, Detroit, Michigan. P. 18, 22, 150
WHD Microanalysis Consultants Ltd. (2013). “Sulfate Attack in Concrete and Mortar”. < http://www.understanding-cement.com/sulfate.html> (Dec. 10, 2013).
- Website: Discusses sulfate attack in concrete
__Additional Resources and References
Transportation Research Board (2004). Concrete Bridge Deck Performance, National Cooperative Highway Research Program, Washington, D.C. P. 7.