Extending the Service Life of Existing Concrete Structures to Last Beyond 100 Years

. New bridges and other concrete structures are being built using the design concepts presented in SHRP2 R19A (Bridges for Service Life Beyond 100 Years: Innovative Systems, Subsystems, and Components) and FIB Bulletin 34 (Model Code for Service Life Design) to achieve 100+ year service life. Existing concrete structures may not have been built with a specific design service life in mind but the principles of SHRP2 R19A can be used to maintain and extend the service life of existing concrete structures. Application of these principles and methods can extend service life by mitigating corrosion of embedded reinforcing steel by over 80%. Extending the service life of existing reinforced concrete structures provides many benefits to structure owners and society. Direct benefits include cost savings for owners and a general reduction in disruption to the public caused by repair and replacement. Extending service life also provides many indirect benefits including; reduction in the use of materials, reduction in the generation of demolition waste, reduction of environmental emissions, and the protection of sensitive habitat and existing ecosystems. This paper presents case studies which illustrate how the SHRP2 R19A protocol was used to design durable repairs to extend service life of existing concrete structures and the direct and indirect benefits which were achieved. Service life extension of existing reinforced concrete structures is a sustainable practice and should be encouraged.


Introduction
New bridges and other concrete structures are being built using the design concepts presented in the SHRP2 R19A (Bridges for service life beyond 100 years: innovative systems, subsystems, and components) and FIB bulletin 34 (Model Code for Service Life Design) to achieve 100+ year service life.
The principles of SHRP2 R19A can be used to maintain and extend the service life of existing bridges.Application of these principles and methods can extend service life by mitigating corrosion of embedded reinforcing steel and structural cables.
The SHRP2 R19A guide outlines the design of new structures for 100+ year service life with two principles in mind; immunity and avoidance.The guide also discusses the design of repairs to extend the service life of existing structures beyond 100 years.
With the ongoing pressure on owners to stretch their limited infrastructure dollars over an ever-increasing infrastructure deficit, and the pressure to minimize delays and disruptions to the traveling public, extending the service life of existing bridges is an effective option.Extending service life also provides many indirect benefits including; reduction in the use of materials, reduction in the generation of demolition waste, reduction of environmental emissions, and the protection of sensitive habitat and existing ecosystems.
The case studies presented will show how the use of electrochemical treatments can extend the service life of structural components and extend the service life of the entire structure.
2 Design process SHRP2 R19A outlines two basic approaches to design, immunity and avoidance.When designing new structures many strategies can be used to improve the corrosion resistance and durability of new structures.These include: • The use of low-permeability concrete; • The use of increased concrete cover; • The use of improved construction methods such as curing to minimize cracking; • The use of corrosion-resistant reinforcement; • The use of corrosion inhibitors to increase the corrosion initiation threshold; • The use of membranes, coatings, and sealers; • The use of improved design details to keep elements dry and to prevent exposure to chlorides.
Immunity concept refers to the selection of materials or components are immune or insusceptible to particular service life issues.An example of immunity is the use of corrosion resistant reinforcing to protect again corrosion in reinforced concrete.Avoidance eliminates or bypasses a particular service life issue, when avoidance is not practical, mitigation techniques should be implemented to improve service life.When considering the strategies to improve corrosion resistance and durability of new and existing structures all are avoidance techniques.We are providing the corrosion resistance through effecting the environment around the reinforcing not through the specific properties of the reinforcing.
The concept of Avoidance or Mitigation is paramount in the design of maintenance or repair strategies for structures for 100+ year service life.The reality of a repair is that a structure is already in its existing condition.Service life extension starts from the existing condition of the structure.Service life extension focus is generally on "Avoidance".The designer looks to meet the concept of avoidance by either delaying the onset of damage or limiting future damage.
For existing structures, the first part of the design process is to determine the current condition of the structure and specific components that will reduce the overall service life.One of the main factors limiting service life in structures is the corrosion of steel in reinforced concrete.This applies to all types of bridge structures.
A detailed corrosion survey can provide invaluable information to delineate the areas currently showing signs of corrosion or exhibiting potential for future corrosion.It is important to determine the areas that show a high potential for future corrosion so that one does not repair a limited area only to have the area directly adjacent fail after the repair.It is also important to understand the potential for future corrosion if one is trying to determine the viability of extending the service life of the overall structure.
There are typical areas which deteriorate on bridge structures, whether short span or long span.These common areas include, but are not limited to, bridge decks, areas adjacent to expansion joints, areas directly below expansion joints on abutments and pier caps, piers and piling in marine environments, particularly in the tidal and splash zones.
There can be numerous causes for the corrosion of steel in concrete; Chlorides, both cast in place or surface applied; carbonation of dissimilar metals.The rate of corrosion is related to the level of contamination of the concrete, the amount of moisture present and the temperatures.
The selection of the appropriate level of corrosion protection is based on many factors, such as the level of chloride contamination and carbonation, the amount of concrete damage, location of corrosion activity (localized or widespread), cost and design life of the corrosion protection system, and the expected service life of the structure.
The SHRP2 R-19A design guide delineates four levels of corrosion protection for electrochemical corrosion mitigation systems.
The three levels of continuous, active corrosion protection available are cathodic protection, corrosion control, and corrosion prevention.All are similar in that a protective current is provided to prevent or reduce the corrosion activity of the reinforcing steel.Each level is suitable for a given range of applications.They differ in terms of the intensity of the protective current provided to the steel.
Electrical current can be supplied in two ways.Impressed Current Cathodic Protection (ICCP) Systems utilize an external power supply to power the system with permanent anodes embedded in the concrete to be protected.ICCP systems need to be maintained and monitored over their life.Galvanic systems utilize sacrificial anodes connected directly to the reinforcing steel to be protected and corrode preferentially to the reinforcing thus providing the protective current.The current provided by a galvanic system is self-regulating.No ongoing maintenance or attention is required with a galvanic system.
New two-stage systems have been introduced that allow for an initial higher impressed current applied to reestablish alkalinity around the reinforcing steel with a lower galvanic current maintaining the protection over the long term.
Corrosion passivation -electrochemical treatment is a process where a current is applied for a period of time to change the chemical environment around the reinforcing steel to passivate the steel and providing long term protection without ongoing intervention.The majority of damage to concrete structures is caused by corrosion of the reinforcing steel which can occur when salt and water soak into the concrete and get to the rebar.ECE stops corrosion by removing chloride ions (salt) from the concrete before the concrete is damaged beyond repair.Chloride ions are transported out of the concrete by ion migration under the influence of an electric field as illustrated in process schematic, (Figure 2).The process also raises the pH of the concrete surrounding the reinforcement to passivate the reinforcement and prevent further corrosion from taking place.

Level of protection Description
Chloride extraction is accomplished by applying an electric field between the reinforcing steel and an externally mounted temporary anode.The temporary anode is embedded in a conductive media (sprayed on mixture of potable water and cellulose fiber), (Figure 3).Wires are connected between a temporary power supply, the reinforcing steel and the temporary anode and the structure is wrapped in plastic.Once the chloride (salt) content has been reduced to acceptable levels the temporary anode and conductive media that now contains the chlorides are removed from the structure.
In 2002, in conjunction with the National Research Council (NRC), Vector Construction Ltd. and MIT completed a project to evaluate Impressed Current Cathodic Protection (ICCP) on the The (SU-3) of the PTH 75-PTH 100 interchange.ICCP systems are another type of electrochemical corrosion mitigation system.ICCP systems utilize anodes and a permanent DC power supply as illustrated in ICCP System Schematic, (Figure 4).
The ICCP system installed on SU-3, received periodic maintenance for the first five years of its service life, and  there are no records indicating any ongoing maintenance after that time.The power supply was not operated and the system was no longer operating at the time of the major rehabilitation in 2013-2014.This is one of the disadvantages of this type of system.For the system to provide its full effectiveness it must be maintained and remain energized for the life of the structure.If the system breaks down or loses its power, the corrosion protection ceases, as happened in this case.This data illustrates the fact that corrosion of steel in concrete is not a linear process, but is exponential.
The actual area requiring concrete repair during the 2013/2014 rehabilitation totaled 330 m 2 (3,552 sq.ft) and correlates directly to whether the pier was treated or not.Pier SU-4 (Untreated Control), total concrete repairs required were ~250.0 m².(2,691 sq.ft) 100% of the surface area of the control pier required concrete repair in the 2013/2014 major rehabilitation.The condition of the control pier prompted a contract change to complete replacement of the substructure unit above the footing.This was determined to be a less expensive option than the repair and corrosion mitigation.
The ECE treated pier (SU-2) performed the best and required the least repair (repair area was less than 4% of the area of the pier).The ICCP treated pier (SU-3) also performed significantly better than the Control Pier (repair area was 28% of the area of the pier).This case study shows the benefit of the ECE treatment.If implemented before damage is too great, ECE can extend the service life and reduce the extent of future repairs.
The ICCP treated pier also performed better than the Control pier.The problem encountered with this system was the lack of on-going maintenance.When considering options, a structure owner must assess whether they are likely to perform long-term maintenance.If the commitment to maintenance and monitoring cannot be made, the owner should choose a system which requires little or no long-term maintenance.
Finally, with the Control Pier, the damage to the structure due to corrosion increased exponentially over time.

Case study -Ohio DOT
This Ohio DOT bridge substructure repair project was completed in July 2005 with a galvanic encasement.The ODOT bridge substructure repair included the removal of delaminated concrete and refacing the abutments of multiple bridges with self-consolidating concrete (SCC) and distributed embedded galvanic anodes as shown in Figure 6, Figure 7 and Figure 8.
The embedded galvanic anodes were designed to provide cathodic protection.The bridge was monitored as part of ODOT technology evaluation program from May 2005 to 2010.This repair strategy is now commonly used to extend the service life of bridge abutments and columns across Ohio.
The monitoring program included the installation of data loggers for monitoring the current flowing from the galvanic anodes to the reinforcing steel as well as embedded thermocouples to measure the temperature of the concrete in Error!Reference source not found.situ.Manual measurements of current corrosion potentials and polarization were obtained when personnel visited the bridge.
Galvanic current data collected at regular intervals can be integrated to calculate the consumption of the galvanic anodes.The service life of the installed anodes system is calculated to be over 40 years.
The performance data indicates that the installed galvanic cathodic protection system is performing well.The following NACE SP0216 cathodic protection criteria are satisfied: • Cathodic polarization formation shift exceeds 100 mV, • The polarized instant-off potential is more negative than -720 mV vs CSE The abutment is in very good condition 15 years after the galvanic encasement was completed, as indicated in the photos below.Prior to completing this galvanic encasement, this type of abutment was being repaired every 5 to 7 years.
The performance of this galvanic encasement installation verifies the system has been providing galvanic cathodic protection for over 15 years, and that there is sufficient zinc supplied to provide corrosion protection for over 40 years.The scope of work for the pile protection included the removal of existing steel jackets and the installation of a galvanic pile jacket system.
NYSDOT specified activated distributed anode strips in conjunction with stay-in-place fiberglass reinforced polymer (FRP) jackets filled with a flowable concrete.
The galvanic jackets consisted of a 6 ft.high FRP shell, FRP bottom form and 8 Galvanic anode strips (two per face).During 2006, the system was installed to protect 764 precast concrete piles.Embedded galvanic anodes were included in concrete repairs to extend the service life of any spot patch repairs above the jackets.
The initial design of the pile protection system was to achieve a 35-year service life.A representative sample of the piles are being monitored.Based on the most recent data collected, the system is performing very well with 24-hour depolarization exceeding the Nace 100 mV cathodic protection criterion (averaging 297 mV).The anode service life is estimated to be over 50 years, well in excess of the initial design criteria.

Case study -Gardiner Expressway, Toronto, Ontario
The Gardiner Expressway is 11.2 miles long (18 km) and is an elevated expressway for 4.2 miles (6.8 km).This municipal Expressway is 8 to 10 lanes wide.It was built in segments between 1955 and 1964.It now serves as one of the busiest pathways to the center of the city.The Expressway, in particular the elevated structure, is a critical link in the city's transportation infrastructure.The effects of age, heavy usage, weather and salt have taken their toll on the structure.The city considered numerous options for the replacement of the structure including tunneling.It was determined that the most viable option was rehabilitation.To that end a 10-year rehabilitation plan is being implemented.
The scope of that rehabilitation plan includes the replacement of the superstructure utilizing Accelerated Bridge Construction Techniques and rehabilitation of the substructure.A number of options were considered for the rehabilitation of the substructure.The extensive damage and need for repairs to the piers and pier caps precluded the use of Electrochemical Treatment as a cost-effective option.The repair option selected is to jacket or overbuild the existing piers and pier caps.This option allows for the addition of additional reinforcing to the structure.The existing concrete is heavily contaminated with chlorides, generally well above threshold levels.Impressed current cathodic protection system was considered but was not pursued due to the maintenance requirements over the life of the system.The option incorporated into the design was the use of a Galvanic Cathodic Protection/Corrosion Prevention system embedded in new concrete jackets.The requirement of the system is to provide active corrosion protection to the reinforcing steel for a minimum of 35 years.This rehabilitation will extend the service life of the 60+ year-old structure to over 100 years.The first phase of the repair was removal of all delaminated and unsound concrete.Sound concrete was not removed all around the reinforcing bars or stirrups as per ICRI guidelines but is left in place so that shoring of the structure is not required.Galvanic anodes are installed in the concrete overbuild and directly connected to the existing reinforcing steel to provide corrosion protection.The size and spacing of the galvanic anodes are designed to provide the level of current required to provide the corrosion protection desired for the years of specified service life.
Once continuity is confirmed and the galvanic anodes have been installed galvanized welded wire mesh is installed for reinforcement and crack control.Forming is completed and the Self -Consolidated Concrete (SCC) is placed to jacket that portion of the substructure.The encapsulation with SCC concrete completes the protective system and provides the concrete repair required to extend the service life of the structure to 100 years +.
The Gardiner Expressway case study also allows us to discuss sustainability.In addition to keeping existing structures in service, shortening construction time and keeping the traveling public happier, we reduce demand for concrete and other construction materials by extending the service life of existing structures.While this is a challenge, it is possible if we make it a priority.
Concrete is the most widely used man-made building product in the world with over 6,000,000,000 tons produced per year.Concrete is a huge consumer of materials and energy.Despite the environmental impact, concrete is one of the most environmentally friendly materials available if it is used properly.Concrete is extremely durable and has ability to last for many years.Keeping existing concrete in service is very beneficial.The Gardiner Expressway Accelerated Bridge Repair project will extend the service life of the structure by 35+ years.In doing so 70,450 yd.³ (53,865 m³) of concrete will be maintained in service.Keeping these qualities concrete in service will reduce CO2 emissions by 35,225 tons (equivalent to the annual emissions of 7045 people.)

Conclusion
The case studies demonstrate how corrosion protection utilizing design protocols presented in SHRP2 R19A (Bridges for Service beyond 100 Years: Innovative Systems, Subsystems, and Components) and NFIB bulletin 34 (Model Code for Service Life Design) can contribute to extending the service life of existing structures to over 100 years..These systems are capable of providing effective, long-term corrosion protection to substructure elements, common areas of deterioration on long span bridges limiting their overall service life.
Case studies on galvanic protection using embedded distributed anodes for the repair and protection of reinforced bridge elements exposed to both marine and non-marine environments were presented.Long term monitoring of distributed and discrete anode systems indicates a high level of corrosion protection performance for over 20 years.Structures treated with Electrochemical Extraction have documented service life extensions of over 30 years.
The service life extension of critical bridge components, particularly substructures can provide significant benefits to owners, the traveling public and the environment.
These benefits include reduced maintenance and lifecycle costs as well as environmental benefits.
by changing the chemistry of the concrete around the steel 3 Case study -PTH 75 -PTH 100 Interchange A project completed by Manitoba Infrastructure and Transportation) in 1998 provides an excellent platform to compare the effectiveness of Electrochemical Extraction (ECE) versus Impressed Current Cathodic Protection (ICCP) and o a control.This project allows one to compare the performance of various systems in identical environments over time.The 1998 project used Electrochemical Chloride Extraction (ECE) treatment process to remove chlorides adjacent to the reinforcing steel and to halt corrosion of the Western Pier (SU-2) of the PTH 75 -PTH 100 Interchange.

The
East Pier received no corrosion mitigation treatment and remained as a Control until the major rehabilitation in 2013-2014.Manitoba Infrastructure and Transportation (MIT) have inspection reports for the substructure units in 2005, 2008 and 2010.While the information from the inspection reports are not specific to each individual substructure unit (i.e.SU-2, SU-3, and SU-4), they provide insight into the overall concrete condition of the substructure piers.The defective areas rated fair and poor (areas which require concrete repair work) increased significantly between 2005 and 2010 as shown in Table2.

Fig. 10 .
Fig. 10.Anode installation, Temporary forms to support FRP Jackets during concrete placement, and Completed Pile encapsulation

Fig. 11 .
Fig. 11.Condition of Structural Elements Prior to Rehabilitation

Table 2 .
Inspection Reports for the Substructure Units

Case study -New York State DOT Pile Protection The
Robert Moses Causeway is part of the north-south corridor from Sunken Meadow State Park in Kings Park to Robert Moses State Park at the western tip of Fire Island.The causeway was built over a 10-year period from 1954 to 1964.In 2005, the New York State DOT (NYSDOT) embarked on a major project to rehabilitate the superstructure and repair and protect the 24-inch square precast concrete piles exposed to saltwater environment.