SURVEY ON DURABILITY
OF PRESTRESSED CONCRETE
STRUCTURES IN THE
UNITED STATES, CANADA,
AND PACIFIC AND
FAR EASTERN COUNTRIES
Rudolph Szilard, Dr.-Ing.
University of Hawaii
Honolulu, Hawaii
Upon the request of Professor
Franco Levi, President of the Federation Internationale de la Precontrainte, it was decided at the meeting of the FIP Commission on
Durability, held in Milan in February 1968, to form a subcommittee to
investigate the actual performance
of prestressed concrete structures.
The main objectives of this worldwide survey on the durability of prestressed concrete structures were:
1. To obtain an estimate on the
total number of prestressed
.concrete structures built.
2. To determine the prevailing
practice in each country regarding the materials and construction techniques used for
various types of prestressed
concrete structures.
3. To assess the number of prestressed concrete structures
which have shown signs of serious deteriorations or failures.
4. To investigate, if possible, the
causes of the damage and to
recommend preventive measures.
62
The survey used two types of
questionnaires obtained from the
Commission on Durability. The primary purpose of the "short form"
was to compare the number of prestressed concrete structures actually
built with the number of prestressed
concrete structures which have
shown signs of distress. The "long
form" detailed the materials and
techniques used in the construction
of these structures, including their
age, environmental conditions, etc.;
this form obtained more information
on the causes of serious damage or
failure than was obtained in the
short form.
The survey presented herein covers the performance of prestressed
concrete structures in the United
States, Canada, Japan, Australia,
New Zealand, India, Ceylon, and
other Pacific and Far Eastern countries.
RESULTS OF SURVEY
United States. The use of prestressed
concrete is relatively new in the
United States, since the oldest prePCI Journal
The durability of prestressed concrete structures and the prevailing
practice used in their construction were surveyed for the United
States, Canada, Japan, Australia, New Zealand, India, and other
Pacific and Far Eastern countries. It was found that the cases of
distress or failures were exceedingly small, considering the vast
number of prestressed concrete structures actually built. The
analysis of the reported cases of failures indicates that the failures
were caused mostly by improper construction techniques and,
to a lesser degree, by improper design.
stressed concrete structure is approximately 18 years old. Although
the total number of prestressed concrete bridges reported in this survey
was 6280, the author's previous survey^ l> indicates that there are approximately 13,000 prestressed concrete highway bridges in service.
The same survey has shown more
than 90 percent of the prestressed
concrete bridges in the United States
are pretensioned, based on the number of bridges built. It is believed
that this percentage is misleading,
since precast, pretensioned bridges
are used mostly for small spans. A
comparison on the dollar value of
bridges estimates the volume of pretensioned bridges in the neighborhood of 75 percent.
In fabricating bridge girders using
pretensioning techniques, the most
commonly used tendon material is
the uncoated, cold-drawn, stress-relieved single wire conforming to
ASTM Designation A421 (Fig. 1),
followed by seven-wire, stress-relieved strand. The minimum nominal
diameter used in pretensioning varOctober 1969
ies from 0.106 in. to 0.50 in.; the average diameter is % in. The maximum diameter of the tendons varies
from 7/ 6 in. to 0.60 in. Seventy-nine
percent of the fabricators use ½-in.
diameter tendons. The question on
heat-treatment in the questionnaire
Fig. 1. Tendon material for pretensioning (USA)
63
Post—tensioning
System
(s)
2.6
Number of
Firms Using
(1)
Freyssinet
15
(2)
Stressteel
10
(3)
CCL
3
(4)
Anderson
2
(5)
BBRV
2
(6)
PI
2
(7)
Prescon
2
(8)
Atlas
2
(9)
VSL
1
Fig. 2. Use of post-tensioning systems in the United States
was apparently misinterpreted since,
as far as could be determined, steel
companies in the United States supply only cold-drawn prestressing
steel.
The Freyssinet system is the most
widely used for post-tensioning
bridge girders in the United States,
followed closely by the Stressteel
system. The "new" Freyssinet system used 6 to 12 strands, % in. in
diameter. The Stressteel system uti-
lized high-strength alloy bars, V2 in.
to 1 3/s in. in diameter. The popularity of the various post-tensioning
systems is shown in Fig. 2.
The survey indicates that the use
of portland cement (ASTM C150) is
predominant (Fig. 3) ; gravel mixed
with sand is the most commonly
used aggregate (Fig. 4). The watercement ratio is approximately 0.35 to
0.45 by weight (Fig. 5), which can
be considered quite favorable re-
D—fl,.^a rg ment ASTM C150
)ther
C. ASTM C175
Fig. 3. Use of various types of cement (USA)
64
PCI Journal
fished stone
Fig. 4. Aggregates for pretensioned
girders (USA)
garding the durability of prestressed
concrete structures (2)• Most construction firms (55 percent) use some type
of admixture, such as ryater reducers
and retarders. Vibrating the concrete
mix and curing the concrete are universal practices. The 28-day concrete
strength is always above the r<equred 5000 psi. The author's previous survey' > ' indicates that the quality of concrete used in the United
States for pretensioned and post-tensioned bridge structures is high.
Portland cement conforming to
ASTM Designation C150 is used almbst exclusively for grouting. The
average water-cement ratio of the
grout is 0.35 to 0.45 by weight. In
the majority of cases, no aggregate is
used. The grouting technique varies
with the post-tensioning system.
While the ; survey shows that the
quality of the grout materials is excellent, the author believes that certain improvements in the grouting
techniques would be highly desirabfe. In less than 4 percent of the
bridges, unbonded prestressing steel
is used. All major post-tensioning
systems used in the United States
have provisions for' unbonded posttensioning techniques, utilizing various types of coatings or grease for
October 1969
corrosion protection.
Although the above results have
been obtained for prestressed concrete bridges', in the author's opinion they can be considered characteristic for the prevailing practice of
the prestressed concrete, industry in
the United States since, in the majority of cases, the very same firms are
engaged in producing other ` types of
prestressed concrete structures. The
only notable exceptions are the construction of prestressed concrete
tanks and pipes which, require circular rather than linear prestressing'
The most serious case of corrosion
-damage of the tendons in prestressed
concrete bridges was reported by the•
State of Washington( 3 >. The damage,
occurred in a floating bridge over
Code No.
Water-Cement
( 1 ),
W
(2)
0.3
(3)
0.35
(4)
0.4
(5)
0.45
(6)
0.5
Fig.
C
<
0.3
W
<
0.35
W
<
0.4
W
<
0.45
5
W
C
<
0.5
5
W
C
C
<
C
C
5. Water-cement ratios (USA)
65
Table 1. Condition survey of prestressed concrete structures
CD
o)
Country
U.S.A.
v
C,
0
Bridges
13,000
23*
it
Buildings
13,533
3*
it
Tanks
Industrial
structures
2,700
27*
2t
3,100
42*
358
11
5
Canada
15,000
4*
420
288
Japan
Australia
1,380
3*
30
80
New
Zealand
250
50
Republic
of China
(Taiwan)
3,000
1*
No report
2,559
106
Wharves,
piers,
quays
Airport
runway
Roads
Other
71
1*
1
0
114
1
0
0
35
Number of distressed
conditions not identified
with type of structures
129*
4t
2*
1t
Combined
with
buildings
0
0
0
0
small*
50
10
0
0
3
small*
50
150
20
0
0
20
0
0
0
0
0
0
116
3*
2t
8
1
6
0
0
1
6
India
Ceylon
300
5
0
0
0
0
0
0
Guam
0
25
1*
0
0
0
0
0
0
* Indicates number of damaged structures including local failures
t Indicates number of major failures (collapse)
0
small*
seawater. Both Michigan and New
York States reported spalling of the
concrete over prestressing wires as a
result of pitting type of corrosion.
Three other states—California, Pennsylvania, and Maryland—reported
rust stains on prestressed concrete
girders but no serious deterioration.
Of the approximately 2700 prestressed concrete tanks in service in
the United States, two have failed.
The collapse of a ten-year old tank is
attributed to an abnormally corrosive environment( 4 ) which produced
stress corrosion in the prestressing
wires. Poor concrete mix, insufficient
depth of cover, unsuitable prestressing wires, improper design, and severe environmental conditions were
the principle causes of severe deterioration. The long delay between
prestressing and grouting, coupled
with corrosive environmental factors, produced failures in the wires
of the post-tensioned cables in the
Richmond Reservoir in California(5).
The late Mr. Lyman, Executive
Director of the Prestressed Concrete
Institute, estimated the total number
of incidents of deterioration (varying
from minor problems to failure conditions) to be less than 10 percent of
the prestressed concrete structures
used for buildings. According to Mr.
Lyman's estimate, the total number
of serious deterioration is less than
1 percent.
If we assume that the number of
distress conditions not identified
with a specific type of structure,
given in the last column of Table 1,
refers to buildings, and all distress
conditions are failures, then the survey tends to verify the above estimate. Since these assumptions are
quite severe, it is safe to say that
the total number of serious deteriorations is less than I percent of the
total number of structures built.
October 1969
The total number of reporting
agencies in the United States was
slightly more than 100. Approximately 90 percent of the distress
conditions reported (most of which
are repairable) can be grouped as
follows:
1. Local failures during the construction stage resulting from
—improper connections
—shear failures of ledger beams.
2. Damage during service life
caused by
—improper details of connections restraining, volume
change movements due to
creep, shrinkage and temperature
—loss of camber resulting from
errors in the design or design
assumptions.
Because of the more favorable environmental conditions, corrosion of
the prestressing steel is rarely a
problem in prestressed concrete
building construction.
Canada. This survey received excellent cooperation from Canadian government agencies and private firms
engaged in design and construction
of prestressed concrete structures.
Twenty-five agencies replied to the
FIP questionnaires. The results of
the replies to the short form questionnaires are given in Table 1.
As the responses to the long form
questionnaires indicate, the prevailing Canadian practices in design
and construction of prestressed concrete structures are similar to those
used in the United States. Probably
the most notable exception is in the
configuration of bridges. In the
United States, the use of simplysupported, standard AASHO girders
with span lengths 40 to 100 ft. prevails; in Canada, the geometrical
configurations, coupled with the
structural systems, show considerably
67
Fig. 6. Structural systems used for bridges in Canada
more variation (Fig. 6). Most of the
prestressed concrete structures were
built during the last ten years. The
age of the oldest reported bridge is
approximately 14 years. As Table 1
indicates, prestressed concrete structures are used more for bridges than
for all other types of structures combined.
The environmental conditions of
the cold winters in Canada are more
severe than in most parts of the
United States, especially in the case
of bridges, where excessive application of de-icer salts (e.g. calcium
chloride) on the roadway creates a
highly corrosive environment. This
is most probably responsible for the
more than 1 percent distress condition reported.
68
In such a highly corrosive environment, the deterioration of prestressed concrete bridges can be
sub-divided into three different processes:
1. Alterations in the physical
properties of the concrete.
2. Increased permeability.
3. Chemical alteration of the concrete which destroys its anticorrosive mechanism.
It has been found that prefabricated, pretensioned concrete structures are predominant in Canada,
but the use of the various post-tensioning systems is considerably
higher than in the United States.
The Freyssinet system is the most
popular followed by the BBR,
Stressteel, and Magnel-Blaton sysPCI Journal
tems. More than 90 percent of the
post-tensioned systems use grout for
the protection of the tendons. Where
no grout is used, protective coatings
(e.g. asphalt) are applied to prevent
corrosion.
For pretensioned and post-tensioned systems alike, an almost exclusive use of portland cement has
been reported. The favorite aggregate is gravel and sand. The average
water-cement ratio is in the vicinity
of 0.4 by weight. The reported 28day cylinder strengths is always
above 5000 psi. Pneumatically
placed concrete containing non-hydroscopic retarding admixtures is
used for prestressed concrete tanks.
The survey shows that, in spite of
the apparent lack of strict field inspections, the concrete used for prestressed concrete structures in Canada is of high quality.
Two collapse conditions of prestressed concrete structures built in
Canada could be analyzed closely.
In the first case, failures in the wires
of a dome roof of a sprinkling filter
unit were attributed to the calcium
chloride used in the pneumatically
placed concrete( 6 >. In the second
case, serious failure occurred duri-,g
the line tests of prestressed concrete
pipes( 7 ). This failure has been attributed partially to the manufacturing process which caused stress
corrosion in the prestressing wires.
Other fairly serious distress conditions are attributed to production
problems such as:
1. Use of unwashed aggregates.
2. Inadequate storing and handling of tendons.
3. Improper curing techniques.
Faulty design of connections and
inadequate allowance for volumetric
changes (creep, shrinkage and temperature) caused more than 50 percent of the minor failures.
Japan. Detailed information on the
status of the prestressed concrete industry in Japan has been obtained
from the Prestressed Concrete Engineering Association, Tokyo.
The first prestressed concrete
bridge in Japan was built in 1952.
900
900
800
800
Buildings
700
700 ,,,
\
CC
° 600
I
0 w 500
/
600 " +
\ /
•H
500
Bridges
o0
400 ai °
gc 400
300
300
1'
f"
Pa 6
200
200 F'
100
100
52
53 54
55
56 57
58
59 60
Years
61 62
63
64
65 66
67
Fig. 7. Growth of the prestressing industry in Japan
October 1969
69
Table 2. Total production of prestressed concrete structures in Japan up to 1968
Type of structure
Total
Prestressing
technique
Highway bridges
Length:
1.53 x 10 6 ft.
2.02 x 10 6 ft.
Pretensioned
Post-tensioned
Railroad bridges
Length:
2.08 x 10 3 ft.
254.0 x 103 ft.
Pretensioned
Post-tensioned
Buildings
Tanks
Area:
Number:
Thus, the use of prestressed concrete
is also relatively new in this highly
industrialized country. During the
last years, however, the use of prestressed concrete structures has
gained a considerable momentum.
This impressive growth is shown in
Fig. 7. Based on the total number of
prestressed concrete structures, Japan is currently second after the
United States in the countries surveyed by the author (Table 1). As
Table 2 indicates, more than 60 percent of the prestressed concrete
bridges are post-tensioned, while in
all other countries surveyed the pretensioning technique is prevailing.
The average length of prestressed
concrete bridges is 160 ft. A highway
bridge has been built with an impressive span length of 530 ft.
The Freyssinet system is the most
popular post-tensioning system in
Japan, as in the other countries surveyed. The second place is occupied
by the BBRV, followed by Dywidag.
Unbonded tendons are not used for
any structure of importance. In pretensioning the most commonly used
tendon is the uncoated, cold-drawn,
stress-relieved wire, followed by the
seven-wire strand. It should be
noted that heat-treated wires were
also fabricated and used before
70
3.6 x 106 sq. ft.
Not reported
288
Not reported
the year 1959.
The use of portland cement is predominant for prestressed concrete
structures as well as for the grout.
The average water-cement ratio is
0.35 to 0.45 by weight, and the 28day cylinder strength of the concrete
is always above 5500 psi. Consequently, the concrete used in Japan
for prestressed concrete structures
is of high quality. Generally, no
aggregate is used in the grout. Water
reducing, retarding, and other type
admixtures are frequently added to
the grout.
In 1959, the fractures of heattreated prestressing wires were observed at two construction sites. In
both cases the wires failed during
storage before prestressing had been
applied. These prestressing wires
had been delivered in coils of 5 ft.
diameter, producing high initial
bending stresses. Prestressing wires
were exposed to excessive salt water
spray at one construction site during
a typhoon. Approximately 20 percent of the wires failed shortly after
the coils were exposed to this highly
corrosive environment. The author
believes that these failures were
caused by stress corrosion (3 ). About
3 percent of the same type of prestressing wires failed at another conPC] Journal
struction site, although they were
not exposed to any known corrosion
environment. In both cases the 7-mm
wires failed transaxially. After these
failures, heat-treated wires were not
used in Japan for prestressed concrete structures of importance.
Some failures of cold-drawn wires
during the prestressing operation
were also reported. Investigations
indicated that defects acquired during the manufacturing process
caused these conditions.
No actual collapse of structures in
service have been reported. The
relatively small number of distress
conditions can be attributed to:
1. Improper details of connections.
2. Cracking of grout due to freezing.
3. Inadequate placing of tendons.
4. Inadequate reinforcement of
the concrete at the anchorage.
Of considerable interest is the report obtained on the performance of
prestressed concrete structures during severe earthquakes. The typical
distress conditions produced by
large seismic motions were:
1. Spalling of the ends of girders
produced by "hammering".
2. Development of cracks (vertical and horizontal) at the top of
concrete abutments or piers
supporting girders when the
motion of the girders was prevented by shear dowels.
3. "Hammering" of rocker bearings against the neighboring
concrete surfaces.
4. Settlement of supports due to
liquidation of the foundation
materials, such as sand and silt.
Australia and New Zealand. Information pertinent to Australia has
been obtained from the Australian
Prestressed Concrete Institute, the
Main Roads Department, and two
other agencies. The reports indicate
October 1969
that prestressed concrete structures
are used mostly for bridges. The
average span lengths are 30 ft. to 140
ft. In Australia, prestressed concrete
has almost superceded other forms
of construction for highway bridges
and is extensively used for railroad
bridges. No failure or severe damages have been reported. The minor
distress conditions are mainly due to
inadequate construction techniques.
In New Zealand, the conditions
are similar in many respects to those
in Australia, as reported by the N. Z.
Portland Cement Association. The
construction techniques in both
countries generally follow the
British and American practices
rather than the European construction methods.
Republic of China (Taiwan). During
the last ten years, a considerable
number of prestressed concrete
highway bridges have been constructed in Taiwan. The average
span length used in multispan
bridges is approximately 120 ft. No
major failures have been reported.
One detailed report by the Taiwan
Highway Bureau on a distress condition indicates extensive cracks in
the 126 ft. girders before prestressing has been applied. The cracks
have been caused by excessive settlement of the formwork. The use of
portland cement is predominant.
The leading post-tensioning system
is the Freyssinet system. The 28-day
cylinder strength of the concrete is
always over 5000 psi. No report has
been obtained on the use of prestressed concrete structures for
buildings and other types of structures.
India. Although the number of prestressed concrete structures built in
India is comparatively small, the
data obtained from the Concrete
Association of India are quite de71
tailed. The details of prestressed
concrete structures were also received from five major contracting
firms.
Table 1 indicates that, in India
also, most of the prestressed concrete structures actuall y built are
bridges. The prevailing tendency in
India is the utilization of prestressed
concrete for major bridge structures
with quite respectable span lengths
up to 257 ft. This partially explains
the almost exclusive use of the
Freyssinet system for precast and
cast-in-place girders. The average
diameter of the wires is 7 mm with a
smooth surface. All reported structures were built during the last ten
years. The climatic conditions to
which the structures are exposed
vary from a tropical climate with
high humidity and temperatures to a
coldclimate. Other environmental
conditions show similar extremes
such as partially-immersed and
open-air conditions.
The exclusive use of portland cement is reported. The average watercement ratio of the concrete is in the
vicinity of 0.40 by weight. Crushed
stone (granite) was reported as the
primary choice for aggregate, followed by gravel plus sand. The 28day cylinder strength of the concrete
•was always above 5000 psi. All posttensioned structures are grouted.
The analyses of the two maior reported failures show that one was
caused by flood and, consequently,
no inadequate design or construction
method could be blamed for it. The
other major failure was due to the
inadequate design provisions of all
standard codes which do not have
provisions to eliminate torsional instability during the launching of the
prestressed concrete girder. The rotational movement of the girder
created vertical cracks along the
72
web, resulting in complete collapse.
Minor failures are attributed to;
1. Faulty placement of tendons.
2. Settlement of temporary supports.
3. Cement used was subjected to
weathering during transport
and/or storage.
Other countries. The Office of the
Chief Bridge Engineer in Ceylon reports no failures. Prestressed concrete structures in Ceylon are used
predominantly for bridges. Guam
reports minor damages due to premature detensioning. In American
Samoa and the Philippines, no prestressed concrete structures have
been built to date. No reports have
been obtained from Korea, Vietnam,
Pakistan, Thailand, and mainland
China. Although all Latin American
countries have been contacted, no
reply has been obtained to date.
Mr. Ben C. Lerwick, Tr., FIP representative of PCI, called the author's attention to a serious distress
condition "at San Nicolas Bay, Peru,
where prestressed concrete piles
made and driven about 1959 or 1960
are disintegrating. These were made
on the site, which is a coastal desert,
using local aggregates and standard
Types I and II cement, and were
pretensioned. About one year ago
extensivecracking was discovered
along the corners. This has been
found to extend from mean tide to
sea bottom. Attempts to coat the
piles with epoxy mortar have been
unsuccessful. The problem is believed due to a combination of unsound aggregates and alkali-aggregate reactivity."
CONCLUSIONS AND
RECOMMENDATIONS
In all of the countries surveyed,
the use of prestressed concrete strucPCI Journal
tures is relatively new. Prestressed
concrete is used largely for bridge
structures, followed closely by
buildings. In most countries surveyed, with the notable exception
of Japan, pretensioning dominates.
The large number of prestressed
concrete tanks is surprising, since
these require a special prestressing
technique and an exceptionally high
quality, impervious concrete. Considering the large number of prestressed concrete structures actually
built, the total number of distress
conditions, varying from minor
damages to complete collapse, is
exceedingly small. Distressed conditions are caused mostly by improper construction techniques and,
to a lesser degree, by improper design and use of faulty materials.
Noteworthy are the recommendations of the Prestressed Concrete
Engineering Association of Japan
for proper aseismic design which includes the exclusive use of bonded
tendons. Furthermore, it is recommended that seismic forces should
be transmitted by the most direct
path. For this reason the use of
rubber buffers or other devices between the individual simply supported girders of adjacent spans is
encouraged in bridge construction.
For buildings, the monolithic construction should be emphasized;
consequently, special attention
should be paid to connection details.
The author finds a pronounced
need for detailed international specifications covering all phases of design and construction, including extensive specifications for all materials
used in prestressed concrete structures. Furthermore, the introduction
of strict field inspection and quality
control tests could have virtually
eliminated the small number of failures that do exist at the present time.
October 1969
The use of heat-treated prestressing
steel is not recommended.
ACKNOWLEDGMENT
The author wishes to express his
gratitude to his numerous colleagues
in the United States and abroad for
their active cooperation in the survey. Special appreciation is due to
Mr. K. G. Tamberg, Bridge Research Engineer, Department of
Highways, Ontario, Canada, to the
late Mr. R. J. Lyman, Executive Director of the Prestressed Concrete
Institute (U.S.A.), and to Dr. Shuji
Inomata, Prestressed Concrete Association (Japan), for their vigorous
support of this work.
REFERENCES
1. Szilard, R., "Present Practice Regarding
Corrosion Protection of Tendons in Prestressed Concrete Bridges in the
U.S.A.," University of Denver, DRI Interim Report No. 952-6705-I, May 1967.
2. Szilard, R. and Wallevik, 0., "Effectiveness of Concrete Cover in Corrosion
Protection of Prestressing Steel," paper
presented at the meeting of the Commission on Durability of Prestressed
Concrete Structures (F.LP.) held Feb.
22-23, 1968, in Milan, Italy.
3. Szilard, R., "Corrosion and Corrosion
Protection of Tendons in Prestressed
Concrete Bridges," Journal of American
Concrete Institute, January 1969, pp.
42-59.
4. "Corrosion Destroys Prestressed Tank,"
Engineering News-Record, January 25,
1962, p. 6.
5. "Wires Break in Prestressed Reservoir,"
Engineering News-Record, June 2, 1955.
6. Bouvy, J. J., "Some Problems Concerning High Tensile Steel from the User's
Point of View," Proceedings of the Second F.I.P. Congress, Amsterdam, 1953,
Cement and Concrete Association, London. 1955, pp. 164-177.
7. Legget, R. F., "Failure of Prestressed
Concrete Pipe in Regina, Saskatchewan," Paper No. 6587, Proceedings of
Institute of Civil Engineers, Canada,
1962, pp. 11-20.
73