CENTER FOR TRANSPORTATION RESEARCH
THE UNIVERSITY OF TEXAS AT AUSTIN
Project Summary Report 0-1405-S
Center for Durability Design of Post-Tensioned Bridge Substructure Elements
The University of Texas at Austin Authors: Ruben M. Salas, Andrea J. Schokker, Jeffrey S. West,
John E. Breen, and Michael E. Kreger
Center for Transportation Research, The University of Texas at Austin
Durability Design of Post-Tensioned Bridge
Substructure Elements: Summary
Corrosion protection for when using advanced techniques superstructures. This information
bonded internal tendons can be to assess localized voids or active allowed the scope of the
very effective. Within the corrosion, since in these cases experimental portion of the project
elements, internal tendons can be the analysis is limited to specific to be narrowed.
well protected by the multilayer areas in selected bridge elements, Component 2 was developed
protection system— including a overlooking grout voids or even and implemented under TxDOT
sound design taking away the corrosion of prestressing steel in Project 0-1264 and transferred to
surface water, surface treatments, other member locations. TxDOT Project 0-1405 for long-
high quality concrete, plastic or term testing. A total of thirty-
galvanized duct, sound cement What We Did... eight macrocell specimens were
grout, coatings and other internal used to investigate the corrosion
barriers in the prestressing steel, After an extensive literature protection of internal tendons at
and good anchorage protection review, the project was divided segmental joints. See Figure 1(a).
measures. However, potential into the following main Half of the specimens were
weak links exist when, among components: autopsied after four and a half
other conditions, the following 1. Literature Review and Survey years of highly aggressive
hold true: (1) the concrete has of Existing Bridge Substructure exposure. The second half of the
high permeability; (2) the concrete Inspection Reports specimens were autopsied with
has cracking; (3) the ducts are not (BRINSAP), over eight years of very
adequately spliced or adequately 2. Investigation of Corrosion aggressive exposure. The
protected by impermeable Protection for Internal variables included: joint type,
concrete; (4) the Portland cement Prestressing Tendons in duct type, grout type, and level of
grout has voids, bleed water, and Precast Segmental Bridges, joint compression.
cracks; and/or (5) the prestressing 3. Development of Improved Component 3 consisted in
steel is not adequately protected Grouts for Post-Tensioning, testing numerous grouts in three
and handled during construction. 4. Long-Term Corrosion Tests phases to develop a high
One of the major problems with Large-Scale Post- performance grout for corrosion
that agencies face today is the Tensioned Beam and Column protection. The testing phases
difficulty of providing good Elements, and included fresh property tests,
monitoring and inspection 5. Development of accelerated corrosion tests, and a
techniques for bonded post- Recommendations and Design large-scale clear draped parabolic
tensioned structures. Condition Guidelines for Durable Bonded duct test that allowed observation
surveys are often limited to visual Post-Tensioned Bridges. of the grout under simulated field
inspections for signs of cracking, conditions. See Figures 1(b) and
spalling and rust staining, which Component 1 included 1(c). Two grout mixes were
can often overlook the literature review of a substantial recommended and have already
deterioration of prestressing steel amount of relevant information become widely used in practice.
and fail to detect the potential for that could be applied to the Component 4 included
very severe and sudden durability of post-tensioned testing of twenty-seven large-
collapses. Similar limitations exist bridge substructures and scale beam specimens, which
Project Summary Report 0-1405-S –1–
were constructed in two phases. See years of exposure). Partial autopsies Figure 1(e). Variables included column
Figure 1(d). Phase I beams (16 were performed on two Phase I beams. to foundation connection, loading,
specimens) were used to investigate Full autopsies for the remaining concrete type, prestressing bar
the effect of prestressing levels, crack specimens will be performed at a coatings, and post-tensioning ducts.
widths, and high performance grout. future date under TxDOT Project Full autopsies were performed at the
Phase II beams (11 specimens) were 0-4562. Component 4 also included end of testing, after six and a half
used to investigate duct splices, grout testing of five non-prestressed and years.
type, concrete type, strand type, duct five post-tensioned column specimens
type, and end anchorage protection. to investigate corrosion mechanisms
and chloride ion transport (“wicking
What We Found...
Full autopsies were performed on six
effect”) in various column connection High-Performance Grouts and
Phase I beams (after four and a half
years of exposure) and also on six configurations and to evaluate Grouting Procedures
Phase II beams (after three and a half corrosion protection measures. See • A 30% fly ash grout with a 0.35 w/c
(water content) had excellent
performance in horizontal
WE • A 2% anti-bleed grout with 0.33 w/c
had excellent performance in vertical
• The standard TxDOT grout had
CE - Counter Electrode
WE - Working Electrode
RE - Reference Electrode
below average performance.
• Grout voids, due to entrapped air,
bleed water, incomplete grout filling
or lack of grout fluidity were found
(a) (b) to be detrimental not only to the
2.4 m Vent 2.9 m prestressing strand, but also to the
X X X X
galvanized duct, as shown in
A X X G
B C X E
F H I J 0.9 m Figure 2.
X D X X • Grout is not prestressed and grout
0.9 m 0.9 m 0.9 m 0.9 m
1.2 m 1.2 m 0.6 m cracks were often found under
Inlet service loading.
• Calcium Nitrite corrosion inhibitor
4.62 m (15' 2")
Section 16 mm PT Bar Cross Section
added to the grout did seem to
5/8 in. PT Bar Ponded Salt Cross Section:
(5/8 in.) Solution 18
610 provide some enhanced long-term
(18 x 24 in.)
strand corrosion protection.
Reaction Ducts for Internal Post-Tensioning
• Galvanized steel ducts performed
poorly (see Figure 2). Plastic ducts
4.5 m 1.37 ft
4.5 m 4.5 m
(4.5 ft) (4.5 ft) (4.5 ft) were superior.
• The use of completely filled epoxy
joints with unspliced plastic ducts
showed very good protection.
4 PT bars
Cracking and Joints
6 dowels: rubber
• Transverse cracking due to loading
had a definite effect on corrosion
cover gasket coupler
damage. Larger crack widths and
crack density were the cause of very
Dow eled Joint Post-Tensioned Joint No Dowel severe localized and uniform
(e) reinforcement corrosion activity.
Figure 1. (a) Macrocell Specimen, (b) Schematic of ACTM Station, (c) Large-
Scale Clear Draped Parabolic Duct Test, (d) Beam Test Setup, (e) Column-
Project Summary Report 0-1405-S –2–
• Duct gaskets in epoxy joints
should be avoided.
• Mixed reinforcement members
should be used in aggressive
exposures only if special
provisions are made to seal
cracks and to prevent concrete
Figure 2. Bleed Water Voids and Galvanized Duct Corrosion
exposure to chlorides.
• Longitudinal or splitting cracks Post-Tensioning Bars or Strands • Fully prestressed members are
always indicated very severe • PT bar coatings showed recommended in aggressive
corrosion within the member. enhanced general corrosion environments.
• Dry joints and incompletely filled protection, in comparison to plain
. • High performance concrete
epoxy joints in the macrocell PT bars. However, under very (w/c=0.29) is recommended in
specimens showed very poor severe localized attack, as in a aggressive environments.
performance. crack or joint location, corrosion • Fly ash (Class C) concrete
activity was severe. (w/c=0.44) may also be
Levels of Post-Tensioning considered when the environment
• As the level of post-tensioning or Exposure Testing Methods is less aggressive.
concrete precompression • After using half-cell potential • Development of better duct
increased, the corrosion readings, chloride content splicing systems should be a high
protection increased. Lower determinations and corrosion priority.
permeability due to increased current readings, only the first • Inspection of in-service bridges
precompression also provided two showed some degree of should identify potential
better resistance to wicking correlation with forensic reinforcement corrosion from any
effects. examination results. noted longitudinal or splitting
Concrete Type The Researchers • A minimum of 2-inch cover to
• High performance concrete any reinforcement should be used
appears to be effective in
• For PT Tendons with small rises in any post-tensioning design.
minimizing the chloride • Fully plastic chairs to ensure
penetration through concrete. under severe exposure conditions,
the following grout should be proper concrete cover are
used: 0.35 w/c, 30% fly ash recommended to eliminate
(Class C) replacement and corrosion damage, instead of
• Small concrete cover was clearly
4 ml/kg superplasticizer. chairs made out of steel.
shown to be detrimental to
• For PT Tendons with large rises • Column elements should be
under severe exposure conditions, prestressed to improve spiral and
Galvanized Duct Splices the following grout should be rebar corrosion protection in very
• Neither the industry standard used: 0.33 w/c and 2% anti-bleed aggressive environments.
splice (duct taped) nor the heat- admixture. • Galvanized steel bars or epoxy
shrink splices appear to be • Plastic ducts should be used in all coated are susceptible to severe
satisfactory to prevent moisture situations where even moderate localized corrosion.
and chloride ingress. aggressive exposure may occur. • Bar coatings can be used when
• Epoxy joints should always be positive sealing of cracks or joints
Gaskets for Post-Tensioning used with internal prestressing is attained.
• The use of gaskets in the joints to tendons. • Half-cell potential readings and
avoid epoxy filling of the ducts in • Stringent inspection and chloride content determinations
segmental construction, or the construction practices should be could be used to assess to some
use of rubber gaskets to seal the enforced to guarantee complete degree the service condition of
duct ends at column joints, were grouting and good epoxy filling at the specimens. Better corrosion
detrimental to the performance of the joints in segmental assessment methods should be
the specimens. construction. developed and evaluated.
Project Summary Report 0-1405-S –3–
For More Details...
Research Supervisor: John E. Breen, P.E., (512) 471-4578, firstname.lastname@example.org
TxDOT Project Director: Bryan Hodges (TYL), (903) 510-9127, email@example.com.
The research is documented in the following reports:
− Research Report 0-1405-1, State of the Art Durability of Post-Tensioned Bridge Substructures, October 1999.
− Research Report 0-1405-2, Development of High-Performance Grouts for Bonded Post-Tensioned Structures, October 1999.
− Research Report 0-1405-3, Long-Term Post-Tensioned Beam and Column Exposure Test Specimens: Experimental
Program, October 1999.
− Research Report 0-1405-4, Corrosion Protection for Bonded Internal Tendons in Precast Segmental Construction, October 1999.
− Research Report 0-1405-5, Interim Conclusions, Recommendations and Design Guidelines for Durability of Post-
Tensioned Bridge Substructures, October 1999.
− Research Report 0-1405-6, Final Evaluation of Corrosion Protection for Bonded Internal Tendons in Precast Segmental
Construction, October 2002.
− Research Report 0-1405-7, Long-Term Post-Tensioned Beam Exposure Test Specimens: Final Evaluation, August 2003.
− Research Report 0-1405-8, Long-Term Post-Tensioned Column Exposure Test Specimens: Final Evaluation, August 2003.
− Research Report 0-1405-9, Conclusions, Recommendations and Design Guidelines for Corrosion Protection of Post-
Tensioned Bridges, August 2003.
To obtain copies of the above reports, contact the Center for Transportation Research, The University of
Texas at Austin, (512) 232-3126, firstname.lastname@example.org.
TxDOT Implementation Status
Results from research project 0-1405 have substantially impacted the design and construction of post-tensioned
structural elements for bridges, and have been implemented both within Texas and on a national level. For example,
the TxDOT specifications for grout materials were changed based on this research, and prepackaged grouts are now
commercially available. A national grouting certification program has been implemented through the American
Segmental Bridge Institute for construction personnel, and galvanized metal ducts are no longer specified for post-
tensioning applications in corrosive environments in Texas. Epoxied segment joints are now an industry standard.
Post-tensioning bar and prestressing strand coatings (epoxy, galvanized, and other) show enhanced corrosion
protection and are being conclusively evaluated under ongoing TxDOT research project 0-4562.
For more information please contact Tom Yarbrough, P.E., RTI Research Engineer, at (512) 465-7403 or email at
Your Involvement Is Welcome!
This research was performed in cooperation with the Texas Department of Transportation and the U. S. Department of
Transportation, Federal Highway Administration. The contents of this report reflect the views of the authors, who are responsible
for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official view or policies of the
FHWA or TxDOT. This report does not constitute a standard, specification, or regulation, nor is it intended for construction,
bidding, or permit purposes. Trade names were used solely for information and not for product endorsement. The engineers in
charge were John E. Breen, P.E. (Texas No. 18479), and Michael E. Kreger, P.E. (Texas No. 65541).
The University of Texas at Austin
The University of Texas at Austin
Center for Transportion Research
3208 Red River, Suite #200
Austin, TX 78705-2650