Corrosion-Induced Major Tendon

TECHBRIEF Failures in Post-Tension (PT)

Concrete Bridges
FHWA Publication No.: FHWA-HRT-24-148
FHWA Contact: Frank Jalinoos, HRDI-30, 202–493–3082,
frank.jalinoos@dot.gov.
This document is based on Chapter 3 of the FHWA-HRT-22-090
report entitled Corrosion-Induced Durability Issues and
Maintenance Strategies for Post-Tensioned Concrete Bridges.

INTRODUCTION
There are two types of PT tendons—bonded or unbonded—depending on
the timing of installing the duct, tensioning the strands, and filling the duct
with grout. Injected filler materials afford additional corrosion protection by
providing physical barriers to water and air, i.e., oxygen and carbon dioxide.
Cementitious grout can also be beneficial, providing a high-pH environment
to form a protective, passive film (an invisible oxide film) on the steel
surface. However, if the passive film is compromised by aggressive anions
such as chloride ions and sulfate ions, and carbonation of the surrounding
grout occurs (i.e., the pH falls below 9), prestressed steel can corrode.(1)

All the observed PT tendon corrosion problems were linked to water or

moist environments and grout voids, although other issues sometimes
were factors.(2) Water can enter from external sources or can form internally
through the grout bleeding phenomenon. Grout voids can be formed due to
poor-quality grouting, e.g., operations and from bleed water that eventually
evaporates or absorbs into the hardened grout. Once corrosion starts, many
factors control the rate of corrosion: oxygen availability, moisture content,
the grout’s electrical resistance, the degree of carbonation, ion concentrations,
and grout segregation that leads to bleeding and variable water-cement ratios.

A collective protection system provided by concrete cover, ducts, and grout

is the primary defense against any service environment. For grouted external
tendons, prestressed steel is always buried in a grout and duct system. For
grouted internal tendons, prestressed steel is buried in a grout, duct, and
concrete system that makes ongoing corrosion difficult to detect before it is
too late. Deployment of nondestructive evaluation technologies to assess tendon
conditions presents a challenge at some critical locations—anchorage zones,
diaphragms, and deviation blocks—where a heavily reinforced steel network
is enclosed in massive concrete. When inspection is necessary, the semi-invasive
method of drilling small holes for borescope inspection occurs but only for
Research, Development, special situations and only at selected locations due to the destructiveness of
and Technology the process and its high costs.
Turner-Fairbank Highway
Research Center This document summarizes the reported cases of corrosion-induced tendon
6300 Georgetown Pike failures in the United States and foreign countries in chronological order and
McLean, VA 22101-2296 the lessons learned from these tendon failures. The basis for this document is
information from chapter 3 of a Federal Highway Administration (FHWA) report
https://highways.dot.gov/research (FHWA-HRT-22-090). Additional information is available in the full report.(2)
This report also presents information about a failure case that occurred in 2020.
MAJOR TENDON FAILURES Figure 1. Illustration. Bridge locations on the
IN THE UNITED STATES U.S. map, modified by the authors.
Between 1990 and 2020, 6 States—Pennsylvania,
Florida, Virginia, Minnesota, Indiana, and South
Carolina—experienced tendon failures in a total of
10 major PT bridges. Figure 1 shows the approximate
locations of the affected bridges and their main causes.
Also, table 1 summarizes the bridge characteristics and
key corrosion-related information.

The following information briefly discusses tendon

failures for each bridge in table 1.

Walnut Lane Bridge in Pennsylvania (1990)

The Walnut Lane Bridge in Philadelphia, PA, the first
precast, prestressed concrete bridge in the United States
was constructed between 1949 and 1950 and opened to
traffic in late 1950. It had three spans, and each span
consisted of thirteen 79-inch- (2-m-) tall PT I girders.
A conventional grout injected into the ducts protected
the prestressed wires from corrosion. The bridge was Source: Original map: © lesniewski/AdobeStock.com.
replaced in 1990 after nearly 40 yr of service due to Modified by FHWA (see Acknowledgments section).
improper tendon grouting and other detail deficiencies.(3)

Table 1. Summary of tendon failures reported in the United States (1990–2020).

Bridge Year Failure Year Tendon Location Cause Remedial

Name (ID) Opened (Failure Age) Type of Failure of Failure Action
Walnut 1950 1990 (40) Four rectangular Multiple Improper Demolished
Lane internal ducts ducts grouting and
Bridge, PA containing 62 detail deficiencies
0.276-inch (7-mm)
wires in each girder

Niles 1983 1999 (16) 6 external tendons Anchorage Leaked chloride Tendon
Channel in each span; each zone at bearing water replacement
Bridge, FL tendon contains leaking into a void formed
(900117) 19 0.6 inch (15-mm) expansion behind an anchor
7 wire strands joints head

Mid-Bay 1993 2000 (7) 6 external tendons Anchorage A void 11 of 846

Bridge, FL in each span; each zone formed behind tendons replaced
(570091) 2018 (25) tendon contains 19 an anchor head
0.6 inch (15-mm) 2 severely 8 tendons
7-wire strands corroded Corrosion by replaced
tendons in leaking water
one span

Sunshine 1987 2000 (13) 12, 17, and 18 A vertical 11 of 17 strands Many deficiencies in the 76
Skyway 0.5 inch (12.7-mm) tendon in a fractured and high-level approach columns
Bridge, FL 7-wire strands in northbound many other were repaired, and the
(150189) a 3-inch (75-mm) column tendons corroded deteriorated north column was
primary tendon due to leaking rehabilitated by adding mild
water through reinforcing dowel bars into the
poorly sealed support footings and filling the
joints, presence core of the hollow pier with
of voids, and duct concrete poured from the deck
cracking

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Table 1. Summary of tendon failures reported in the United States (1990–2020). (Continued)

Bridge Year Failure Year Tendon Location Cause Remedial

Name (ID) Opened (Failure Age) Type of Failure of Failure Action

Varina-Enon 1990 2007 (17) 19 0.6 inch diameter A tendon Repaired grout 2 tendons replaced
Bridge, VA (15.2-m-diameter) near an
(00000000 2017 (27) 7-wire strands in anchorage Weak grout Tendon replacement and
0010007) a 4-inch (100-mm) zone acoustic emission monitoring
plastic duct); a total of since October 2020
480 external tendons Near a
and 360 PT bars parapet in
main span

Cline 1983 2009 (26) A total of 1,063 Widespread Water seeped Demolished
Avenue tendons corrosion through deck
Bridge, IN problems cracks
(033029)

Plymouth 1983 2010 (27) 19 0.5 inch diameter Internal Chloride-bearing Major repairs, including
Avenue (12.7 mm diameter) tendons in water from the installation of extra external
Bridge, MN 7-wire strands in a the bottom deck corroded tendons
(27611) 3.5 inch (89-mm) slab the bottom
metal duct slab through
the misaligned
drainage pipe
inside the box
girders

Ringling 2003 2011 (8) A total of 132 Upper Segregated grout 17 tendons replaced
Causeway external tendons; horizon
Bridge, FL 2011 (8) 22 0.6-inch (15.2 mm) portion of
(170176) 7-wire strands in a sloped
a 4-inch diameter tendon
(100-mm-diameter)
plastic duct. At an upper
deviator

Wando River 1989 2016 (27) A total of 696 M-1 South Grout void filled Tendon replacement and
Bridge, SC internal and external tendon in with recharging extra external tendons added
(0000000 2018 (29) tendons, including WB structure water; possibly
00008235) 240 external tendons carbonation
in the approach M-5 tendon
span units and 60 in WB
external tendons structure
in the main span (near the
units; Each tendon first failed
has 19 0.6-inch tendon)
(15.2-mm) 7 wire
strands

Roosevelt 1997 2020 (23) Details are not Failed Chloride-bearing Major repairs done
Bridge, FL available tendons water seeped including deck waterproofing
(SB 890151; found in the through segment
NB 890152) first span of joints and
SB structure ducts; elevated
the chloride
concentration
ranging from 12.5
to 25 pcy (7.4 to
14.8 kg/m3) in
grout samples and
30 pcy (17.8 kg/
m3) in concrete

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Niles Channel Bridge in Florida (1999) Figure 2. Photo. Failed tendon in the Niles Channel
The Niles Channel Bridge is a 4,557-ft-long Bridge (main cause: chloride).(4,5)
(1,389-m-long) precast box girder concrete bridge
with a deck width of 38.5 ft (11.7 m) that connects
Summerland Key and Ramrod Key. The bridge was built
in 1983 using a low-level, span-by-span method (the
fourth bridge constructed with this method in Florida).
The bridge has 6 grouted external PT tendons in each
span, and each tendon contains 19 0.6-inch (15.2-mm)
7-wire strands filled with neat cement grout.

In 1999, bridge inspectors discovered that one of 234

external tendons had failed after 16 yr in service due
to intensive corrosion in a grout void formed by bleed
water. Figure 2 shows some of the damaged strands
still attached to the anchor head associated with
the failed tendon.(4,5) © 2002 Florida Department of Transportation (FDOT).

This incident was regarded the first PT tendon failure

caused by corrosion in the United States. The void Figure 3. Photo. Failed tendon in the Mid-Bay Bridge
location was behind an anchor head at an expansion (main cause: chloride).(4)
joint diaphragm. Recharging water contaminated
with airborne chloride in the void was responsible
for the corrosion. Inspectors speculated that the water
leaked through the expansion joints and ran down
the inner faces of the segment diaphragms onto the
anchorage in question.

Mid-Bay Bridge in Florida (2000)(4-7)

The Mid-Bay Bridge is a 19,265-ft-long (5,982-m-long),
precast segmental concrete box girder bridge spanning the
Choctawhatchee Bay between Destin and Niceville, FL.
Like the Niles Channel Bridge, the Mid-Bay Bridge
construction method was span-by-span and used neat
cement grout. Each of its spans has 6 tendons, and each © 2002 FDOT.
tendon has 19 0.6-inch (15.2-mm), 7 wire strands in
the free length of the tendon. Speculation was that the
4-inch (100-mm) polyethylene (PE) ducts. The bridge
penetration of moisture and air through the cracked ducts
opened to traffic in 1993.
appeared to initiate corrosion. The measured chloride
In August 2000, a routine inspection revealed that a concentrations in the grout samples were very low
failed tendon had separated from an expansion joint (0.150 lb/yd3 (89 parts per million (ppm)) to 0.259 lb/yd3
diaphragm due to severe corrosion in the anchorage (154 ppm)) to play a role in the corrosion process.
zone. The strong bond between the grouted steel pipe
These corrosion problems prompted the Florida
and the failed tendon section pulled the steel pipe
Department of Transportation (FDOT) to launch
from the expansion joint diaphragm during the tendon
emergency inspections, including visual crack
rupture (figure 3).
inspections, vibration testing, the sounding of all ducts,
The failure pattern resembled the failed tendon observed and borescope inspections of all 1,728 anchorages.
in the Niles Channel Bridge. This incident was regarded Inspectors subjected each PT tendon to magnetic flux
as the second PT tendon failure by corrosion in the leakage (MFL) testing to locate significant section losses
United States. nondestructively. The MFL testing located potential
corrosion problems and wire fractures in two tendons.
A second deteriorated tendon discovered in another At the end of the inspections, inspectors replaced 11
span was ruptured but was severely damaged. The PE severely corroded tendons of 846 tendons, and regrouted
duct was cracked, and 11 strands were fractured in anchor voids using the vacuum grouting (VG) method.

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Hartt and Venugopalan carried out a field investigation deposit were observed mostly in the top half of the
on the Mid-Bay Bridge’s failed tendon and other tendon; evaporation or reabsorption of bleed water into
tendons.(6) Although the duct cracking problem was the the grout resulted in a void at the anchorage zone; and
primary focus of Hartt and Venugopalan’s investigation, moisture and air penetrated the cracked ducts, resulting
some of their findings were related to segregated grout, in depassivation and corrosion of the strands.
which contributed to severe corrosion of the PT tendons.
Specifically, they observed a white powdery deposit, Eventually, grout carbonation, segregated grout,
a sign of grout segregation, along a void channel on a and excessive bleed water were collectively
tendon and speculated that the channel was formed by responsible for rapid tendon corrosion in the presence
air and bleed water during the grout segregation process. of oxygen, carbon dioxide, and moisture, irrespective
The quantity of white powdery deposit was directly of chloride concentration.
proportional to the cross-sectional area of the void
In 2018, a biennial bridge inspection discovered
channel. The two investigators observed the channels
recurring corrosion problems on seven tendons in the
and a white powdery deposit mostly in the top half of
Mid-Bay Bridge. A follow-up investigation in 2019
the tendon, but, in some cases, the channels and deposits
revealed that two corroded tendons were close to each
also extended along the underside of individual strands
other in the same span, a situation that forced FDOT to
or several closely grouped strands. White chalky grout
close the bridge for 8 d whether the 2000 investigations
was also found in an 8-ft-long (2.4-m-long) section of
failed to detect ongoing corrosion problems or if new
a tendon. However, the grout in the lower half of the
corrosion had started post inspection. Going forward,
tendon was typically dark gray, well consolidated, and
FDOT planned to conduct condition assessments of all
showed no signs of segregation.
tendons using a hammer-sounding method every 6 mo.
The investigators concluded that grout segregation
occurred along the tendon in the presence of excess Sunshine Skyway Bridge in Florida (2000)(8,9,10)
bleed water. Eventually, evaporation or reabsorption of The Sunshine Skyway Bridge is a 29,040-ft-long
bleed water into the grout resulted in a void at the exit (8,851-m-long), precast segmental box girder
anchorage area. The Hartt and Venugopalan investigation bridge across Tampa Bay in Florida. The bridge was
is credited with reporting the first domestic case of grout constructed using the span-by-span method and opened
segregation-related problems, which were limited to to traffic in 1987. The high-level approaches are
isolated areas with no significant physical deficiencies. supported by nearly elliptical, hollow precast segment
columns with a mix of internal and external tendons. The
The grout in two tendons revealed high pH values except
vertical tendons holding the column segments together
within a thin top layer (16 mil (0.4 mm)). The white
are bonded internally within the thick wall region and
powdery deposit at the top of a tendon had a pH in the
run externally along the upper inner walls. The 3 tendons
range of 8 ± 1 before cleaning with a wire brush. The
are composed of 12, 17, and 18 0.5-inch-diameter
lowest pH was 6. After cleaning, the pH increased to
(12.7-mm-diameter) strands housed in a 3-inch primary
12 ± 1. At the bottom, the 0.25-inch-thick (6.4-mm-thick)
duct. This bridge uses a neat cement grout. The upper
grout was carbonated with a pH of 8 ± 1. Investigators
ends of these tendons are anchored in the cap and form
found the broken wires in this layer. The deeper grout,
a u-loop configuration in the footing. In the thick wall
which exhibited a dark gray color, had a pH of 12 ± 1.
region, the 3-inch-diameter (76-mm-diameter) primary
The investigators noted that the bleed water could be duct is inside a 5-inch-diameter (127-mm-diameter)
corrosive when it was carbonated and that adding an corrugated PE secondary duct cast inside a precast
expansive admixture reduced its pH. Moreover, the segment wall. The bridge opened for traffic in 1987.
carbonated grout (i.e., pH 8 ± 1) severely corroded four
wires in the presence of oxygen and moisture. They also During a special inspection of the bridge in September
speculated that strand corrosion within grout voids and 2000, inspectors discovered severe corrosion in a tendon
carbonated grout would reinitiate during periods of high housed in a northbound column: 11 of 17 0.5-inch
humidity and that strand corrosion would also reinitiate (12.7-mm) strands were fractured at 2 ft (0.6 m) below
in condensed water that previously was absorbed into a column cap. As a result, inspectors performed further
the grout during occasional temperature drops below inspections on all the other high-level approach columns
the dew point. (including comprehensive destructive testing on about
10 percent of the columns), the superstructure, and
Also, investigators also noted that grout segregation the cable anchorage of the main span. Figure 4 shows
occurred along the tendon in the presence of excessive the locations of corrosion problems and illustrates
bleed water; the bleed channels and a white powdery construction of the precast segmental columns.

5
 Figure 4. Schematic and photos. Column structure and locations of tendon corrosion (main cause: chloride).

© 2006 FDOT.

Varina-Enon Bridge in Virginia (2007)(11-15) adjacent to the anchor plates could be formed in a typical
The Varina-Enon Bridge, the only cable-stayed bridge 150-ft-long draped tendon. Field inspections also found
in Virginia, opened to traffic in 1990 and carries three issues. First, tendons were not appropriately sealed
Interstate 295 over the James River between the counties at metal straps used to connect a HDPE duct to steel
of Chesterfield and Henrico. The bridge is 4,680 ft pipe at diaphragms and bulkheads. Second, the seals on
(1,426 m) in length and consists of two parallel approach some vent tubes were incorrect. Third, previously holes
structures (southbound and northbound bridges) and a had been drilled randomly in the HDPE ducts to check
single structure on the cable-stayed main span. It has a for voids. However, inspectors considered inadequate
total of 480 grouted external tendons and 360 PT bars. corrosion protection was limited to an isolated area.
Each box has eight external tendons, and each tendon Following the discovery of the voids, the Virginia DOT
has 19 0.6-inch (15.2-mm) strands encased in a 4-inch, (VDOT) carried out vacuum regrouting in 2003–2004 to
high-density polyethylene (HDPE) duct. The bridge fill the grout voids in 55 percent of the tendons.
opened to traffic in 1990.
In May 2007, a routine inspection discovered one
In 2001, field inspectors found grout voids in many failed tendon in the southbound bridge. Even though
tendons, but the strands did not appear corroded. At the tendon was regrouted in 2004, it still failed due to
that time, they also estimated that grout bleeding was corrosion at the bridge age of 17 yr. Figure 5 shows the
approximately 4 percent in properly batched grout failed tendon: a short section attached to the diaphragm
(water-cement ratio <0.42). This estimation meant that (figure 5-A) and the opposite section to the ruptured
two 3-ft-long (0.9-m-long) voids at the high points section fell onto a deviation block (figure 5-B).

6
 However, well-hydrated grout filled the bottom portions
Figure 5. Photos. Failed tendon in Varina-Enon Bridge
(main cause: defective grout).
of the strands. The top section of the exposed grout
appeared porous, weak, and covered with white powdery
grout. The defective grout condition indicated that grout
segregation occurred during grouting.

Laboratory analysis revealed that all grout samples

taken from the failed tendon had less than 0.003 percent
acid-soluble (total) chloride by weight of cement, which
was well below the corrosion threshold. On the other
hand, the repair grout contained an elevated level of
sulfate ions. Based on the analyst’s findings, VDOT
concluded that excessive sulfate in the repair grout might
be responsible for such a rapid corrosion failure.

The original gray grout was an unsanded neat paste

of ordinary portland cement and water. The estimated
water-cement ratio was from 0.45 to 0.55 or greater
(possibly greater than 0.65). Where the grout was
A. Section attached to the diaphragm.
medium to dark gray, the water-cement ratio was low.
Where the grout was soft and pale gray, the water-cement
ratio was high. Some settled dark cement lumps along
the bottom end of the HDPE duct suggested that the
grout had high water content and experienced bleeding
before setting.

The repair grout material was found in the portion of the

tendon next to the zone of strand failure (trailed off within
a 4-ft (1.2-m) section of the failed area). It appeared to
have been placed in the tendon after the original gray
grout. The tendon in question had a 20-mil- (0.51-mm-)
thick layer of sanded gypsum grout at the top surface.
The repair grout contained minor amounts of a soft
and whitish paste consisting of abundant cement paste,
moderate amounts of clear siliceous sand, and minor
amounts of small non-entrained air voids. The pH values
B. Opposite section on a deviation block. of the samples were somewhat lower than that of normally
hardened grout. The total sulfur (SO3) content of the
Source: FHWA. white grout samples ranged from about 29 to 32 percent,
which was substantially higher than expected for the
Corrosion also damaged another tendon due to ponding portland cement-only grout. Additional free calcium
water near a clogged drain hole in the bottom slab of sulfate, likely in the form of gypsum, was present as the
a box girder. Both tendons were replaced in 2007. In major binder component.
late 2007, MFL testing conducted on approximately
17 mi (27 km) of external tendons (approximately 3,200 In 2017, a transverse tendon also failed because of
sections) identified a severely corroded tendon. corrosion near the parapet in the main span. A follow-up
investigation assessed the condition of transverse
Additional inspections were conducted after removing tendons in two cable-stayed spans (98 tendons per span)
2-ft-long duct sections from the selected 20 tendons. The using the impact echo technique and inspection holes,
inspection discovered incomplete regrouting and broken visual inspections of over 20 tendons confirmed that
wires in two tendons in the northbound bridge. After many locations were fully grouted but contained weak
opening the selected tendon sections, inspectors also grout. Vertical tendon inspections of the superstructure
found large longitudinal grout voids between the 3 and 9 and substructure in 72 locations found 43 voids and
clock orientation (tendon top is 12). Some strands were 24 tendons (16 at the top of the pier anchors and 8 in
partially exposed without any recognizable corrosion. the box anchors) exhibited significant corrosion.

7
As part of the corrosion mitigation effort, in 2015 spans, span numbers 1, 2, 4, and 5 were cast in place on
VDOT injected four tendons with an impregnated falsework, MnDOT constructed the 260-ft (79-m) main
type of corrosion inhibitor. Also, an acoustic emission span (span 3) using form travelers in unidirectional,
monitoring system was recently installed on the bridge cast-in-place cantilever construction. Each internal
as the most economical technology for detecting tendon contains 19 0.5-inch-diameter (12.7-m-diameter)
real-time wire breaks and making decisions concerning 7-wire strands in a 3.5-inch (89-mm) metal duct.
tendon replacement. The system monitors some
longitudinal external tendons, transverse internal During an annual inspection in 2010, inspectors
tendons, the cable stays, the piers, and the towers. In observed slab cracking and rust stains in the box girders.
operation since October 2020, the system has had no A follow-up inspection revealed significant cracking,
wire breaks reported as of April 2021. rust stains, and corrosion of internal continuity tendons
buried in the bottom slab under the delaminated
Cline Avenue Bridge in Indiana (2009)(16,17) concrete. Figure 6 shows the damaged bottom slab.
The Cline Avenue Bridge is a 6,600-ft-long
(2,012-m-long), cast-in-place concrete box girder bridge Figure 6. Photos. Plymouth Avenue Bridge’s severely
over the Indiana Harbor and Ship Canal in Indiana. It damaged bottom slab (main cause: chloride).(5)
opened to traffic in 1983. A routine inspection identified
significant longitudinal and transverse cracking in
the bridge deck and more cracking in the webs and
diaphragms. Indiana Department of Transportation
(INDOT) was concerned enough about the condition of
the PT tendons to conduct a field investigation in 2003.

Of 1,063 total tendons in the bridge, inspectors used

drilling and borescope on 277 tendons (26 percent).
Inspectors found a total of 33 voids at high points. Eight
of them exposed the strands, but none was corroded.
After the borescope inspection, INDOT filled the voids
using the VG method. The investigators concluded that
most of the PT system functioned with little corrosion
(no section loss). The exception was at a few couplers,
where significant duct voids resulted in some cross
section losses. A. Interior condition.

However, a later year routine inspection revealed

significant corrosion of PT tendons and reinforcing
steel bars caused by water seeping through cracks in
the bridge deck. INDOT determined that the level of
corrosion compromised structural integrity beyond
viable repairs. Consequently, the bridge permanently
closed in November 2009 after 26 yr of service.

Plymouth Avenue Bridge in

Minnesota (2010)(5,18,19)
The Plymouth Avenue Bridge is the first cast-in-place
segmental box girder PT bridge constructed in Minnesota
and opened in 1983. It consists of two parallel twin
concrete box girders with varying depths of 10 to
13 ft (3 to 4 m) and carries Plymouth Avenue over the
Mississippi River on the north side of Minneapolis,
B. Exterior condition.
MN. This bridge has a total length of 943 ft (287 m)
with a deck width of 75.5 ft (23 m) for four lanes
© 2012 MnDOT.
of traffic and two pedestrian sidewalks. Among five

8
The bridge was closed for nearly 1 yr to carry out bridge is the first constructed with segmental duct
detailed inspections, subsequent repairs, and the couplers and prepackaged non-bleed/thixotropic grout
installation of five additional external tendons in each in Florida. Each of the external tendons contains 22
box girder to strengthen the bridge. Each new tendon 0.6-inch (15.2-mm) 7-wire strands in a 4-inch-diameter
contains 12 0.6-inch (15.2-mm) strands. The new (100-mm-diameter) HDPE duct.
tendons were installed through new concrete deviation
blocks attached to the bottom slab and anchored in the Figure 7 shows corrosion failure of an external tendon
concrete blisters (anchor blocks) newly formed at the was discovered in January 2011, and another external
girder ends. tendon failed in July 2011 after less than 8 yr of service.
The figure shows the as-discovered condition when the
The 2010 investigation also determined that the failed tendon fell to the girder floor. The inset image
chloride-bearing water from the deck that leaked through shows the complete separation of entire strands due to
the misaligned drainage pipe sections inside the box severe corrosion.
girders and deicing salts accumulated in the bottom slab
triggered corrosion of the internal tendons and adjacent Figure 7. Photos. Ringling Causeway Bridge’s first failed
reinforcing steel. tendon (main cause: defective grout).(21)

The bottom slab had large, patched areas over the

base concrete. Delaminating the patches allowed
direct ingress of moisture, chloride, and oxygen to the
tendons and structural reinforcing bars. Investigators
observed that the totally corroded metal duct and
grout and corrosion products mingled with severely
corroded strands such that individual wires could not be
distinguished. Nearby concrete contained a high level of
acid-soluble chloride concentration (nearly 0.8 percent
by weight of grout) at 0.8 inches (20 mm) deep.

The investigation included spot checks at high points

of the tendon ducts in the box girder webs and other
areas of interest, i.e., areas with moisture present on the
web surface. Investigators also observed a good quality
grout without moisture. The grout contained 0.075
percent acid-soluble chloride concentration by weight © 2011 FDOT.
of grout, which explained its corrosion-free condition.
The conclusion was that the web tendons were in good These tendon failures were the first incident involving a
condition and appeared fully grouted with a normal prepackaged grout product in the United States, originally
(nonsegregated) grout. Although the grout used in the thought to be a solution to grout-related problems.
Plymouth Avenue Bridge would likely be neat cement
grout (i.e., a nonthixotropic), the overall quality of the The first tendon failure occurred in the upper horizontal
grout was considered very good. portion of a sloped tendon section adjacent to an upper
deviator. This tendon exhibited severe corrosion mostly
Ringling Causeway Bridge in concentrated on the strands in the upper portion of
Florida (2011)(20,21,22) the failed tendon. Except for the heavily corroded
The Ringling Causeway Bridge is a 3,094-ft-long strands, the failure mode of the remaining strands
(943-m-long), 106-ft-wide (32-m-wide) precast appeared ductile, as evidenced by necking signs at the
segmental box girder bridge spanning Sarasota Bay ruptured ends of the wires. The corroded-in-two wire
and the Intracoastal Waterway of the Gulf of Mexico tips suggested that the failed tendon must have been
in Florida. Completed in 2003, the bridge consists of exposed to a very corrosive environment for some time.
11 spans supported by 4 fixed and 5 expansion piers Also observed was corrosion in the upper portion of the
plus 2 abutments. The box girders have a three-cell galvanized steel pipe in the upper deviator. Although
configuration with a variable depth from 8.85 to there is no initial photograph of the pipe’s condition, two
16.4 ft (2.7 to 5.0 m) held by internal and external distinctive rust lines on the interior wall indicated that
tendons. Half of the span between piers consists of there likely was water or watery grout up to the rusty
12 12-ft-long (3.7-m-long) precast segments. This watermarks for an unknown duration after grouting.

9
The strands in the upper horizontal region of the tendon were significant amounts of soft and wet grout adjacent
were not fully embedded in grout, and the cross section to both sides of the upper deviator, where investigators
in some locations appeared more than half empty. The first saw the duct separation. The segregated grout had a
grout filled into the bottom was well consolidated and strong odor resembling ammonia. Stratification of silica
hardened with a thin white chalky layer at the grout and fume particles and intermixing of the white chalky grout
void interface. Cementitious residues on the upper part were also observed. The sedimentation did not directly
of the strands suggested that the tendon might have been cause grout segregation and stratification as evidenced
initially filled to that level. by different forms of segregated grout interspersed
within the cross-section. Severe corrosion typically
The grout in other sections filled the duct, but strands occurred in the wet plastic grout area.
were partially exposed in the voids. Tight confinement
of the strands against the HDPE duct wall appeared After the second tendon failure occurred, field
to create some voids. Most voids in the sloped tendon investigations occurred on all 132 external draped
sections were still associated with a continuous tendons. The scope of the investigations included
longitudinal groove (bleed channel) at the 12 clock understanding why and how such rapid tendon failures
orientation. An upward movement of liquid and gases occurred; characterizing the grout’s consistency; locating
and subsequent severe grout segregation in a plastic segregated grout, voided areas, and corroded strands;
state might have contributed to forming the large voids, and repairing or replacing the affected tendons.
segregated grout, and imprints of bubbles. As a result,
the grout was moist and soft throughout. Unlike brittle Segregated grout characteristics were the clay-like
and easily breakable grout found in the upper horizontal consistency of soft and wet (moisture content 50–80
region, the segregated grout in this region remained percent), a sedimented black layer with silica fume,
claylike. It changed its color from dark gray to white and a white chalky (moisture content 20–50 percent)
upon drying in laboratory air. appearance. During inspections of other tendons, soft
and wet grout was present at numerous locations and
Also in 2011, the second failed tendon occurred at sometimes present in large regions. Other characteristics
the west face of an upper deviator. Severe corrosion included high corrosion rate (CR), high pH, high
damage was not as localized as it was in the first failed sulfate concentration, other soluble ionic contents, and
tendon. Instead, corrosion and strand fracture were no significant chloride concentration. In addition to
observed at several locations within a 20-ft (6.1-m) different material properties, the segregated grout and
section. The remaining strands showed a ductile normally hardened grout exhibited different colors. For
fracture with necking. Severe corrosion of the strands instance, the segregated grout tended to have a white or
within the galvanized steel pipe in the upper deviator light gray color contrasted with the normally hardened
was also observed. grout’s dark gray color.

Also observed throughout the region of corrosion Even though it was not clearly understood how the
failure was segregated soft/wet grout. At the low point segregation process of the identical prepackaged grout
anchorage zone, a large amount of segregated grout was product could produce such distinctively different grout
also observed wherein severe corrosion of the anchor textures and material properties, the observed corrosion
head and strands occurred. problems were mainly associated with segregated grout.

While the hardened grout adhered to the anchor head’s Wando River Bridge in South
upper and lower areas, severe corrosion was observed in Carolina (2016)(23-27)
the middle area between them. A lack of adhered grout The Interstate 526 Wando River Bridge (formerly the
there suggested that the area was initially occupied by James B. Edwards Bridge), completed in 1989, connects
a mixture of air and bleed water before corrosion took Mount Pleasant and Daniel Island over the Wando
place in the absence of protective grout. River in Charleston, SC. It is the only segmental box
Unlike the first failed tendon, large voids were not girder bridge in the State and was constructed using a
present in the second failed tendon. Instead, highly span-by-span method for the two approach units and
segregated, poor-quality grout material filled significant a balanced cantilever method for the main span. The
portions of the tendon. Some tendon segments had minor bridge has two 7,900-ft-long (2,408-m-long) parallel
void spaces caused by a closely packed strand bundle structures carrying eastbound and westbound traffic.
against adequate grout flow in the HDPE duct. Also, Each structure consists of 51 precast, segmental PT
investigators observed stratification of the black layer box girder spans and contains 696 longitudinal internal
and signs of gas venting at the grout’s top surface. There and external tendons, including 240 external tendons in

10
the approach span units and 60 external tendons in the chalky grout. These bands were indications that
main span units. Each tendon has 19 0.6-inch (15.2-mm) grout segregation occurred during construction.
7-wire strands. The bridge also has 84 additional tendons
composed of segments of concrete foundation. Based on the investigation findings, investigators
concluded that the unusual occurrence of two factors
Discovered in September 2016, the first external tendon in an isolated area contributed to corrosion: poor
failed when the M 1-South tendon loosened in the quality grout void and exposure to recharged water
main span of the westbound structure. However, the (or moist air). These unfavorable conditions led to
bridge had other issues since its completion in 1989; severe strand corrosion and, eventually, to tendon
since 2010, the bridge underwent several indepth rupture. Nearby strands encased in poor-quality
inspections. A routine biennial inspection in May 2010 grout also experienced corrosion damages, even
and a subsequent walk-through in August 2010 noted without chloride. Strands completely encased
many deficiencies related to inadequate corrosion in good quality grout showed no corrosion.
protection of the PT tendons. Following the cursory
walk-through inspection in 2010, a comprehensive Investigators discovered another failed tendon (M-5)
field investigation occurred in 2011. The following in the westbound structure near the first failed tendon
information summarizes the key findings. during a weekly routine walk-through inspection in
May 2018. This tendon failure led to an emergency
The 2011 investigation inspected various locations on closure of the westbound structure for nearly 3 w.
31 tendons. The primary inspection used the visual Examination of the fractured strands revealed 107 wires
inspection method with the help of a borescope on the (80.5 percent) ruptured by corrosion and the remaining
external tendons. Even though there were grout voids, 26 wires (19.5 percent) ruptured by overstressing in the
no strands were visible inside the voids. Also, there was presence of reduced cross-sectional areas. During the
a significant amount of corrosion products, presumably replacement of the damaged tendon, workers added two
from a metal duct. extra external tendons to increase structural redundancy.

Water droplets observed in the anchorage area indicated Roosevelt Bridge in Florida (2020)(28)
that water was responsible for the active corrosion of The latest corrosion problem was in the internal PT
that area. Most of the locations selected for investigation tendons on the Roosevelt Bridge crossing the St. Lucie
exhibited white-colored deposit material at pour-backs, River in Stuart, FL, in 2020 after approximately 23 yr
unsealed holes in PE ducts, and duct connections of service. This concrete bridge construction used the
adjacent to deviator blocks and diaphragms. In some precast segmental box girder technique consisting
cases, inspectors observed active water leakage. The of 2 separate structures carrying 3-lanes southbound
main composition of the white-colored material was and 3-lanes northbound on Highway 1 (US–1). The
calcium carbonate, which accumulated after water northbound structure is 4,566 ft (1,392 m) long, and
that had infiltrated the PT system evaporated. One the southbound structure is 4,487 ft (1,368 m) long.
confirmed water source was an open grout vent tube Both structures have a deck width of 61 ft (19 m) and a
in a diaphragm that extended up to the deck. There maximum clearance above the water of 65 ft (19.8 m).
might be more locations where the grout vent tubes Surrounding the strands in the internal PT tendons
were partially filled or filled with poor-quality grout. are cementitious grout and galvanized metal ducts.
The failed tendons were in the southbound structure’s
Other factors conducive to corrosion included
span number 1.
incomplete grouting; extensive grout carbonation; and
defective grout exhibiting excessive porosity, cracks, Laboratory analysis of the grout samples revealed
and absorption. Galvanic coupling of the tendons and samples contaminated with excessive chloride
dissimilar metals in the anchorage zone may also have concentrations ranging from 12.5 to 25.0 pounds per
increased corrosion. cubic yard (lb/y3), 7.4 to 14.8 kilogram per cubic
meter (kg/m3) of the sample weight. Furthermore, the
A laboratory investigation inspected 6 strand sections
concrete’s chloride content obtained in the vicinity of
retrieved from the failed tendon and 10 5-ft tendon
the failed tendons was around 30 pcy (17.8 kg/m3).
sections from a span far away from the failure location.
The grout samples contained low levels of sulfate ions
A visual evaluation of the grout revealed that, for the
(<96 parts per million (ppm)).
full lengths of all the tendon sections, the exposed
grout was typically gray to dark gray with a good, Field investigations confirmed that water containing
hard consistency, except for segments of horizontal chloride ions penetrated through some of the segment
bands that contained porous, loose grout or white, joints and metal ducts and evaporated in time. As a

11
result, the chloride ions accumulated in the affected In South Korea during routine walk-through inspections,
grout or concrete over time. Sealing the bridge deck with bridge inspectors of the Seoul Metropolitan Facility
an overlay to reduce the water recharge on the bottom Management Corporation discovered failed external
slab tendons is complete. Nonetheless, the conclusion tendons due to corrosion in two precast segmental box
was that the existing chloride-contaminated grout and girder PT bridges: (38)
water or moisture trapped in the PT system could lead
to severe corrosion and possible failure of additional • Cheong-Rung Creek Bridge, opened to traffic in 1999,
tendons in the future. lost one external tendon due to chloride-bearing water
seeping through an opened air vent from the deck.
TENDON FAILURES IN FOREIGN COUNTRIES
• Seo-Ho Bridge, opened to traffic in 1997, experienced
European countries started experiencing PT tendon tendon failures of two external tendons mainly due to
corrosion problems earlier than the United States. Some the segregated grout.
Asian countries also reported corrosion-induced tendon
failures. The following paragraphs present notable In Hong Kong, the Highway Department staff discovered
failure cases observed in Europe and Asia. a ruptured external tendon on the Shenzhen Bay Bridge
in February 2019.(39) It is a 6-lane bridge connecting Lau
In the United Kingdom, the Bickton Meadows Fau Shan, Hong Kong, and Shekou in Shenzhen, China,
Footbridge, a precast segmental bridge, collapsed and opened to traffic in 2007. Investigators concluded
in 1967 due to the corrosion of prestressing steel. that three factors that occurred during the grouting
In 1985, a single-span segmental bridge, the operation contributed to the failure of the tendon: the
Ynys-y-Gwas Bridge, also suddenly collapsed due segregation of grout due to excessive water in the duct,
to the corrosion of internal tendons. In Belgium, low pumping pressure, and the partial blockage of the
the Melle Bridge collapsed in 1992 due to hidden grout vent tube at the failed anchor head that formed an
corrosion damage on the prestressing steel.(29-33) air pocket behind the anchor head.
In France, several bridges also experienced LESSONS LEARNED
tendon failures:(34)
Constructing a durable PT bridge and maintaining it
• A prestressed concrete bridge built in 1986 over the throughout its service life can be achieved if every
Durance River experienced a tendon failure near an step during the construction and maintenance is
anchorage in 1994. performed correctly. If stringent requirements to ensure
satisfactory performance are not met in any of the
• The Saint-Cloud Viaduct over the Seine River critical steps, corrosion can develop in localized areas
that opened to traffic in 1974 suffered from one containing deficiencies and eventually compromise
tendon failure at the lowest point between two the durability of the entire bridge. In many instances,
deviators in 1998. corrosion-induced tendon failures and near-failure
conditions have led to serious consequences, including
• The Riviere d’Abord Bridge that opened to traffic in
temporary closures of the affected bridges during
1991 experienced one external tendon failure at an
emergency repairs or tendon replacements.
anchor zone in the upper part of a pier segment in 2001.
Even though grout voids and exposed strands were
In Italy, at least three PT bridges experiencing
reasonably common in the hardened grout, the
serious corrosion problems or structural failure
probability of severe corrosion in the PT tendons has
were reported: (35,36,37)
been relatively low. However, when an aggressive
• External tendons in an unidentified bridge failed environment—chloride ions, sulfate ions, and grout
less than 2 yr after construction due to a whitish carbonation—initiates intensive corrosion in local
unhardened paste exhibiting high pH. areas within a tendon, strand fracture can occur after
a relatively short period, and, subsequently, the whole
• One span of the Petrulla Viaduct in Sicily built tendon can fail between 2 and 30 yr of service.
in the mid-80s collapsed due to a lack of grout in
the internal tendons and improperly sealed grout As the PT bridges get older, more durability problems will
vent tubes. surface, and corrosion of PT tendons will likely continue
to be a primary cause. Accordingly, the introduction of
• One ramp of La Reale Viaduct collapsed in 2017 improved quality control and quality assurance practices
due to a lack of sufficient grout protection at the to materials and construction processes would be desirable
collapsed joint. for building more durable PT bridges.

12
ACKNOWLEDGEMENT 9. Theryo, T. S. 2016. “Durability Issues and
Improvement Strategy of Post-Tensioned Bridges
The original map is the copyright property of
in the United States.” Presented at the 3rd
lesniewski/AdobeStock and can be accessed from
International Conference on Sustainable Civil
https://stock.adobe.com. The map overlays show the
Engineering Structures and Construction Materials.
names of 10 major bridges that experienced tendon
Bali, Indonesia.
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the failure was chloride ions; blue stars signify the cause Bridge Post-Tensioned Vertical Tendon Corrosion
of the failure was defective grout. Investigation: Summary of Findings.” Segmental
Bridges Issue No. 57, Volume XIX, Number 1.
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15
Researchers—This study was conducted by FHWA’s Office of Infrastructure Research and Development.
The research was led by Frank Jalinoos from FHWA Coatings and Corrosion Laboratory and conducted by a
researcher, Seung-Kyoung Lee, under contract DTFH61-17-D-00017.

Distribution—This TechBrief is being distributed according to a standard distribution. Direct distribution is being
made to the FHWA divisions and Resource Center.

Availability—This TechBrief may be obtained at https://highways.dot.gov/research.

Key Words—Corrosion, segregated grout, chloride ions, sulfate ions, carbonation, post-tensioned tendon,
tendon failure.

Notice—This document is disseminated under the sponsorship of the U.S. Department of Transportation in
the interest of information exchange. The U.S. Government assumes no liability for the use of the information
contained in this document.

Non-Binding Contents—Except for the statutes and regulations cited, the contents of this document do not have
the force and effect of law and are not meant to bind the States or the public in any way. This document is intended
only to provide information regarding existing requirements under the law or agency policies.

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Recommended citation: Federal Highway Administration,

Corrosion-Induced Major Tendon
Failures in Post-Tension (PT) Concrete Bridges FHWA-HRT-24-148
JULY 2024 (Washington, DC: 2024) https://doi.org/10.21949/1521593 HRDI-30/07-24(WEB)E

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