High Performance Concrete
ABSTRACT
High Performance Concrete is that concrete
which meets special performance and uniformity requirements that cannot always
be achieved by conventional material, normal mixing, placing and curing practices.
Architects,
engineers and constructors all over the world are finding that using HPC allows
them to build more durable structures at comparable cost. HPC is being used for
building in aggressive environments, marine structures, highway bridges and
pavements, nuclear structures, tunnels, precast units.
This reports
aims to discuss the application of HPC particularly for bridge structures. The
use of HPC was found to have added advantages compared with normal concrete in
areas of strengths, service life, construction time, economy, etc.
An experimental
study on “Behavior of instrumented prestressed high performance concrete bridge
girders” by Hazim M. Dwairi, Mathew C. Wagner, Mervyn J.Kowalsky, Paul Zia is
also discussed as case study.
1. INTRODUCTION
1.1
GENERAL
Concrete is
considered as durable and strong material. Reinforced concrete is one of the
most popular material used for construction around the world. Reinforced
concrete is exposed to deterioration in some regions especially in costal
regions. There for researchers around the world are directing their efforts
towards developing a new material to over come this problem. Invention of large
construction plants and equipments around the world added to the increased use
of material. This scenario led to the use of additive materials to improve the
quality of concrete. As an out come of the experiments and researches cement
based concrete which meets special performance with respect to workability,
strength and durability known as” High Performance Concrete” was developed.
1.2 HIGH PERFORMANCE CONCRETE
High performance
concrete (HPC) is that which is designed to give optimised performance
characteristics for the given set of materials, usage and exposure conditions,
consistent with requirement of cost, service life and durability.
The American
Concrete Institute (ACI) defines HPC ‘‘as concrete which meets special
performance and uniformity requirements that cannot always be achieved
routinely by using only conventional materials and normal mixing, placing, and
curing practices.”
High performance
in a broad manner can be related to any property of concrete. It can mean
excellent workability in the fresh state like self-levelling concrete or low
heat of hydration in case of mass concrete, or very rigid setting and hardening
of concrete in case of sprayed concrete or quick repair of roads and airfields,
or very low imperviousness of storage vessels, or very low leakage rates of
encapsulation containments for contaminating material.
HPC is composed
of the same material as normal concrete, but it has been engineered to achieve
enhanced durability or strength characteristics, or both, to meet the specified
demands of a construction project. The main ingredients of high performance
concrete are cement, fine aggregate, coarse aggregate, water, mineral
admixtures and chemical admixtures.
If the structure
of normal strength concrete (NSC) is compared with high performance concrete
(HPC) one notes several differences: The matrix stiffness of HPC is larger than
NSC and approaches the stiffness of the aggregate, the bond strength between
matrix and aggregate is higher for HPC, matrix tensile strength is higher, Reduced
internal cracking in terms of number of cracks and size of intrinsic cracks
before loading. These aspects show that HPC is more elastic and more brittle
than NSC.
Figure.1 Schematic representation of the
stress-strain curve from a uniaxial test along with the simplified crack
pattern. (C.S Suryawanshi)
HPC has a
greater Young’s modulus than NSC and the post-peak softening branch is steeper.
High Performance Concrete (HPC) is more homogeneous than normal strength
concrete (NSC).
HPC does not
simply mean high strength concrete (HSC), but also includes other enhanced
material properties such as early-age strength, increased flow ability, high
modulus of elasticity (MOE), low permeability, and resistance to chemical and
physical attack (increased durability). HPC is usually high strength concrete
(HSC), but HSC may not always be of high performance.
1.2.1 HIGH PERFORMANCE CONCRETE CHARACTERISTICS
High-performance
concrete characteristics are developed for particular applications and
environments; some of the properties that may be required include:
• High strength
• High early
strength
• High modulus
of elasticity
• High abrasion
resistance
• High
durability and long life in severe environments
• Low
permeability and diffusion
• Resistance to
chemical attack
• High
resistance to frost and deicer scaling damage
• Toughness and
impact resistance
• Volume
stability
• Ease of
placement
• Compaction
without segregation
• Inhibition of
bacterial and mold growth
1.2.2 PREPERATION OF HPC
High-performance
concretes are made with carefully selected high-quality ingredients and
optimized mixture designs; these are batched, mixed, placed, compacted and cured
to the highest industry standards. Typically, such concretes will have a low
water-cementing materials ratio of 0.20 to 0.45. Plasticizers are usually used
to make these concretes fluid and workable. Table 1 lists materials often used
in high-performance concrete and why they are selected.
Table.1 Materials used in High Performance
Concrete
|
Material
|
Primary
contribution/Desired property
|
|
Portland cement
|
Cementing
material/durability
|
|
Blended cement
|
Cementing material/durability/high strength
|
|
Fly ash
|
Cementing
material/durability/high strength
|
|
Slag
|
Cementing material/durability/high strength
|
|
Silica fume
|
Cementing
material/durability/high strength
|
|
Calcined clay
|
Cementing
material/durability/high strength
|
|
Metakaolin
|
Cementing
material/durability/high strength
|
|
Calcined shale
|
Cementing material/durability/high strength
|
|
Super plasticizers
|
Flowability
|
|
High-range water reducers
|
Reduce
water to cement ratio
|
|
Hydration control
admixtures
|
Control
setting
|
|
Retarders
|
Control
setting
|
|
Accelerators
|
Accelerate
setting
|
|
Corrosion inhibitors
|
Control steel corrosion
|
|
Water reducers
|
Reduce
cement and water content
|
|
Shrinkage reducers
|
Reduce
shrinkage
|
|
ASR inhibitors
|
Control
alkali-silica reactivity
|
|
Polymer/latex modifiers
|
Durability
|
|
Optimally graded aggregate
|
Improve
workability and reduce paste demand
|
1.3
HIGH PERFORMANCE CONCRETE BRIDGES
High performance
concrete bridges include two key elements: total precast bridge systems that
can dramatically improve construction speed and high performance concrete that
can improve durability and structural efficiency. In HPC bridges, these
improvements are achieved at no cost premium and often at a reduced initial
cost.
Designing with
HPC components can drastically reduce construction time because various precast
components can be combined to allow a truck-to-structure systems approach
without waiting for site forming and curing. Full depth precast decks are being
used on both new and rehabilitated bridges. The cost for this approach can
result in overall savings due to more efficient designs that permit longer
spans or fewer girders and/or piers. HPC can be used effectively in virtually
all bridge components to aid in minimizing construction and future maintenance.
HPC components can include piles and pile caps, piers and column bents,
abutments, decks, and rails and barriers. HPC uses the same materials as
typical concrete but is engineered to provide higher strength and better
durability. These attributes can be varied to align with the design’s needs.
They will be affected by environmental and geographic conditions and the
specific bridge components (that is, substructure, beams or deck).
Figure.2 Cross section of
the pier elevation shows the main components of a bridge system.
1.3.1 ADVANTAGES OF HPC BRIDGES
Overall, the
advantages accruing from higher durability and/or additional strength include a
variety of benefits:
• Longer service
life thanks to higher durability and lower chloride penetration. When needed, bridge
life can extend to 100 years or even more.
• Lower
maintenance and inspection requirements, especially since the bridge requires
no painting or rust protection. This savings grows with the bridge’s longer
service life.
• Longer spans,
which can reduce costs by eliminating piers or allowing the use of concrete
beams instead of steel beams.
• Wider beam
spacing, reducing the number and cost of beams.
• Shallower
beams due to higher concrete strength.
• Improved
mechanical properties such as greater tensile strength.
• Rapid
construction due to the ability to factory-cast components while site work is
underway and the ability to erect pieces upon delivery. These benefits cut the
time necessary for disruptions to local traffic.
• Predictable
performance and close tolerances for precast members due to the high quality
achieved through PCI certification and casting under controlled conditions in
the plant.
In general, HPC
components can produce lighter, longer precast pieces and smaller-diameter
columns that creep less. This means span lengths can be lengthened and under
clearances can be maximized.
2.1 GENERAL
In this study
work done by Hazim M. Dwairi, Matthew C. Wagner, Mervyn J. Kowalsky, Paul Zia
on the “Behaviour of instrumented high performance concrete bridge girders” is
discussed
A comprehensive
monitoring of the behavior of four prestressed high performance concrete (HPC)
bridge girders, with higher compressive strength, during construction and while
in-service, is presented. The monitoring program covered instrumentation and
monitoring of a series of four girders during the casting operation, after
construction, under the effects of traffic and thermal loads, as well as under
controlled
load conditions.
Figure.3 shows
the bridge for three southbound lanes under construction, which forms the basis
for the work described in this paper. Figures.4 and 5 show the plan of the
bridge and a typical cross section respectively.
Figure.3 US
401 Southbound Bridge over the Neuse River , Raleigh ,
NC
Figure.4 US 401 Southbound Bridge over the Neuse River
Figure.5
Typical cross-section of Southbound
Bridge
2.2 OBJECTIVE AND SCOPE
The objective of
the research presented in this paper is to develop an understanding of the
behavior of HPC in bridge structures. This objective was achieved through a
comprehensive monitoring program including: (1) characterization of the actual
HPC utilized in the construction of the bridge, (2) extensive instrumentation
and monitoring of a series of four girders in the bridge during the casting
operation, and (3) monitoring of the bridge structure after construction under
the effects of traffic and thermal loads, as well as controlled load
conditions.
2.3 PROPERTIES OF HPC
For the HPC used
in the US 401 Bridge, selected performance criteria are shown in Table.1. Tests
were conducted on the material to evaluate its compressive strength, flexural
strength, modulus of elasticity (MOE), modulus of rupture (MOR), creep, shrinkage,
thermal properties, and chloride permeability. In all cases, the concrete
samples were taken from batches of material used in four instrumented bridge
girders. Two were AASHTO (American Association of State Highway and
Transportation Officials) Type IV girders (designated as A4 and B4) and two
were AASHTO Type III girders (designated as C4 and D4) as shown in Figure.4.
Table.2 HPC target performance criteria. (
Hazim M. Dwairi et al.)
|
Material characteristic
|
Target value
|
|
Compressive strength at 28 days
Modulus of elasticity
Shrinkage
Target slump before/after
addition of plasticizer
Air content (range)
Creep
Freeze–thaw durability (x =
relative
dynamic modulus of elasticity
after 300 cycles)
Chloride permeability (x =
coulombs)
Scaling resistance (x = visual
rating of surface after 50 cycles)
Abrasion resistance (x = average depth of
wear in inches)
Resistance to internal chemical
attack (x = alkali in cement)
|
69 < x< 76 MPa
41 < x <52 GPa
x < 400 micro strain
0/203 mm
%3–5
45 < x > 30/MPa
x< 80%
800 < x <2000
x = 2.3
x < 0.02
x < 0.4%
|
2.3.1 MATERIAL TESTING
Numerous 102 *
203 mm cylinders, six 76 * 76 *286 mm prisms, and six 152 * 152 *508 mm prisms
were cast for the material testing. The specimens were cured along side with
the girders to keep the curing temperatures for the specimens as close as
possible to those of the actual girders. Table.3 shows the mix proportion of
the concrete that was used for the girders. The test results of compressive
strength, modulus of elasticity, shrinkage, creep, etc. met the performance
criteria.
Table.3 HPC mix proportion. ( Hazim M.
Dwairi et al.)
|
Materials used to produce the mix
Water/cementitious materials 0.305
Cement, Type I/II (kg/m3) 518
Coarse aggregate78 m (kg/m3) 892
Coarse aggregate 67 m (kg/m3) 259
Fine aggregate (kg/m3) 521
Water (kg/m3)
1000/1
AEA, micro-Air (kg/m3)
0.223
HRWR (kg/m3)
3.0
Retarder (kg/m3) 1.334
|
2.4 GIRDER BEHAVIOR DURING CASTING
2.4.1 OVERVIEW OF INSTRUMENTATION PLAN
A single line of
girders was instrumented in order to monitor temperature and strains within the
girders, as shown in Figure.4. There are five girder lines, each with four
spans: 28.0, 28.0, 17.5, and 17.5 m. The longer spans use AASHTO Type IV
girders and the shorter spans use AASHTO Type III girders. The instrumented
girders are designated A4, B4, C4, and D4.
The use of the
HPC mix eliminated one line of girders and increased transverse girder spacing
from the original design using the conventional concrete. The strength
requirement for the girders was 69.0 MPa to 76.0 MPa at 28 days, and the average strength of the
tested cylinders met the requirements as shown in Table.2.
In order to
monitor the temperature gradients within the girders both during the curing
period and the long-term testing, a total of 22 thermocouples (Omega FF-K-24)
were placed at five cross sections of each of the four girders. Ten
thermocouples were placed at mid-span, three at 1/4 L, three at 3/4 L, and
three at a distance of L/ 50 from either end (where L is the girder span. To
measure strains in the concrete, a series of Vibrating Wire ages (VWGs)
(Roctest EM-5) were placed at the center of gravity of the prestressing strands
at mid-span and 1.524 m for girders C and D, and 1.219 m for girders A and B,
in either side from mid-span to measure long-term strains. Prestressing force
was measured with load cells and transfer length was determined from strains
measured by using an embedded steel bar with attached strain gages.
2.4.2. PRESTRESS FORCE
Load cells
(Strainsert model PC-50 with 220 kN capacity) were placed at the dead end of
the casting bed to measure the prestressing force after tensioning, as well as
after curing, and immediately prior to detensioning of the strands. The load
cells were placed on four strands on each of the casting beds (Type III and
Type IV). Tables 4 and 5 summarize the load cell readings at various times
after tensioning.
Table.4 Load cell reading for Type III
girders, kN. ( Hazim M. Dwairi et al.)
|
Time
|
Temp
|
Strand ID
|
|
|
|
|
|
|
|
1
|
2
|
3
|
4
|
Average
|
|
Initial
|
16.7
|
190.4
|
189.9
|
189.0
|
190.8
|
189.9
|
|
24h
|
15.6
|
182.4
|
183.7
|
181.9
|
187.3
|
183.7
|
|
48h
|
15.6
|
176.1
|
177.0
|
175.3
|
178.8
|
177.0
|
|
55h
|
21.1
|
189.5
|
192.2
|
189.0
|
192.6
|
190.8
|
Table.5 Load cell rading for Type IV
girders, kN. ( Hazim M. Dwairi et al.)
|
Time
|
Temp
|
Strand ID
|
|
|
|
|
|
|
|
1
|
2
|
3
|
4
|
Average
|
|
Initial
|
29.4
|
187.7
|
189.5
|
183.3
|
185.5
|
186.4
|
|
17h
|
15.6
|
195.3
|
194.4
|
188.6
|
192.2
|
192.6
|
|
40h
|
15.6
|
194.4
|
194.4
|
188.6
|
192.2
|
192.6
|
|
64h
|
15.6
|
188.2
|
188.2
|
181.9
|
185.9
|
185.9
|
2.4.3. TRANSFER LENGTH
The transfer
length of prestressing strands at the ends of the girders was determined by
measuring the strains in a ‘‘strain gage bar” (SGB) embedded in each girder.
Bars used in girders C4, D4, and B4 had eight strain gages, while the bar used
in girder A4
had nine strain
gages. The gages were read with a standard strain gage indicator after the
concrete had cured and just before detensioning, in order to obtain the initial
readings. The gages were then read immediately after detensioning. The change
in strain for each gage is plotted in relation to its distance from the end of
the girder in Figs. 10 and 11. The average strain is also plotted in these
figures. To determine the transfer length from the measured strains, a method
similar to that proposed by Oh and Kim was followed to establish the strain
plateau, which was obtained by drawing a horizontal line at 95% of the maximum
value of the plotted average strains. The transfer length is taken as the
horizontal distance from the origin (i.e. the end of the girder) to where the
horizontal line intersects the plotted average strain profile (see Figs. 10 and
11). For the Type III girder, a transfer length of 0.711 m was estimated, while 0.660 m was estimated for the Type IV girder.
Figure.6
Transfer length for Type III girder. ( Hazim M. Dwairi et al.)
Figure.7 Transfer length for Type IV girder. ( Hazim M. Dwairi et al.)
2.4.4. THERMAL GRADIENTS DURING CASTING
Figures.8 and 9
represent a sample of the girder curing temperatures along with the ambient
temperature.
Figure.8 Thermocouples 1–5 for girder C4 at mid-span. ( Hazim M. Dwairi
et al.)
Figure.9 Thermocouples 6–10 for girder C4
at mid-span. ( Hazim M. Dwairi et al.)
2.4.5. CONCRETE STRAINS DURING CASTING
Concrete strains
were recorded by using embedded VWGs. A typical result is shown in Figure.10
for a series of vibrating wire gages. It is noticed that the strain values
change as the heat of hydration develops.
Figure.10 VWG strains for girder D4. (
Hazim M. Dwairi et al.)
2.4.6. PRESTRESS LOSSES
Table.6 shows
that the prestress loss due to elastic shortening based on the strain
measurement is less than predicted, especially for the Type III Girder. It is
suspected that the gages failed to record the entire compressive strain during
detensioning; this could be due to some reasons such as inadequate consolidation
of concrete around the embedded gages or failure of the gage itself. By using
the predicted loss due to elastic shortening, it appears that the total
prestress loss for the Type IV Girder given in Table.7 is slightly
overestimated.
Table.6 Measured vs predicted prestress loss due to
elastic shortening. ( Hazim M. Dwairi et al.)
|
|
Loss in prestress
|
|
|
|
|
|
Girder A4
|
Girder B4
|
Girder C4
|
Girder D4
|
|
Measured
|
88.3
|
98.6
|
4.1
|
2.8
|
|
Predicted
|
124.8
|
124.8
|
82.7
|
82.7
|
|
% Difference
|
29%
|
21%
|
95%
|
97%
|
Table.7 Prestress loss, MPa. ( Hazim M.
Dwairi et al.)
|
Cause of loss
|
Type
|
|
|
Elastic shortening
|
82.7
|
124.8
|
|
Crep
|
87.6
|
120.7
|
|
Shrinkage
|
9.0
|
16.5
|
|
Total loss
|
179.3
|
262
|
2.5 IN-SERVICE BRIDGE BEHAVIOUR
As previously
noted, only girder-line 4 shown in Figure.11 was instrumented.
Figure.11 Bridge over the Neuse River
In this phase of
research three types of instruments were utilized in this phase, twelve
previously installed thermocouples were retained and an additional two
thermocouples were placed in the deck at a distance of L/4 from the supports in
spans A and D, as shown in Figure.13. Twelve of the previously installed EM-5
Vibrating Wire Gauges (VWGs), were retained and additional VWG’s were placed in
the deck at supports. Finally, one additional LVDT was used at each abutment
and two extra LVDT’s were used at the expansion joint to measure the
longitudinal movement of the girder. All instruments were connected to CR23X
Campbell scientific data-loggers, placed at bent diaphragms under the bridge
and powered by solar panels. Two data-loggers were used one for spans A and B,
and the other for spans C and D. The data was recorded every 4 h over a period
of four month under normal traffic loading, at each period the data-logger
recorded the instruments readings for five minutes. The data-logger records up
to 1500 readings per second. The monitoring of the bridge started two months
after it was opened for traffic. Figure. 12 shows span C and D end
displacements due to thermal effects in addition to differential displacements
measured by LVDTs during the four month period.
Figure.12 End displacements due to thermal
effect and traffic loading (a) Girder C, and (b) Girder D. ( Hazim M. Dwairi et
al.)
Thermal effects
were calculated in reference to the lowest temperature, these thermal effects
were calculated based upon the temperature gradients obtained from
thermocouples number 3, 4, and 5 for Girder D4 and thermocouples number 6, 7,
and 8 for Girder C4 as shown in Figure. 13
Figure.13
Retained thermocouples of girder cross-sections along girder-line 4 and locations
in each girder cross-section. ( Hazim M. Dwairi et al.)
The differential
displacements represent the difference between the LVDT’s reading at anytime
and its reading when the lowest temperature was recorded. The displacements
measured by the LVDTs placed at the end of the girders show additional end
displacements due to traffic loading; however, maximum girder end than 0.0064
m. End displacement of girders caused by end rotations due to temperature
gradient along the depth of the girder cross-section was found to be minimal
and it has insignificant effect on total end displacements. displacement due to
thermal effects and traffic loading was less.
2.6. CONTROLLED LOAD TESTING
Two static live
load tests were conducted on this bridge, the first test took place before the
bridge was opened for traffic and the second test was eight months after the
bridge was put in-service. In both tests, a five-axle truck was used (Type 3S2
AASHTO designation), loaded roughly to full capacity in one run and to half
capacity in the second; the truck and it is total weight are shown in Figure. 14.
Figure.14 Configuration and weights of the
truck used in live load tests.
( Hazim M. Dwairi et al.)
The truck was
positioned on 10 different locations as shown in Figure.15 to maximize moment
at mid-spans and supports, and to estimate load distribution factors by
positioning the driver’s wheel on Girder-4 in one run and the passenger’s wheel
on the adjacent girder in another.
Figure.15
Truck loading positions. ( Hazim M. Dwairi et al.)
In addition to
the internal gages already embedded in the girder (VWG’s and LVDT’s), two
temporary string potentiometers were placed under the bridge at mid-span D and
mid-span A to record maximum deflections. The live load tests were performed by
placing the loaded five-axle truck on the desired location, when the truck and
trailer came to rest at the designated loading position, instruments readings
were recorded for a period of 30 s. The truck was then moved to next position
without
unloading the
bridge, and then readings were recorded in the previous manner.
Figure.16 Strain distribution versus
cross-section depth, for girder Type-IV at the support between span A and B due
to different loading positions.
( Hazim M. Dwairi et al.)
Figure. 16 represent
the strain distribution at the support between span A and B due to the
different loading positions. It is clear that strains due to half-loaded truck
are approximately half of the strains due to the fully loaded truck, which
indicates that the girder behaved elastically as expected. Load versus strain
for both tests is shown in Figure.17. Strain is measured at mid-span D due to
loading position 1 and at the mid-depth of deck-slab at support between spans C
and D due to loading position 2. The strains recorded in the second live load
test are larger than those recorded in the first live load test, possibly
indicating some minor softening of the system due to micro cracking in the
tension zone.
Figure.17 Load versus strain for both live
load tests; (a) strain measured at mid-span D. (b) strain measured at support
between span C and D.
( Hazim M. Dwairi et al.)
A comparison
between experimental and calculated strains is shown in Figs.18 and 19. A
simplified model was used for strain calculations; every two spans were assumed
to be a continuous beam, although, joints constructed between spans do not
guarantee full rigidity. Load distribution factors were obtained according to
AASHTO provisions and axle loads were distributed accordingly.
Figure.18 Experimental and calculated
strain values due to half-full and full trucks. ( Hazim M. Dwairi et al.)
Figure. 18a and
b show measured and calculated strains at mid-spans D and A, respectively.
Calculated strains were higher than measured strains for both spans and for
different loading values and positions. As a result, one can conclude that the
load distribution factors given by AASHTO are higher than the actual load
distributions.
Figure.19 Experimental and calculated
strain distribution along girder Type IV at middle support between spans A and
B due to loading position 5.
( Hazim M. Dwairi et al.)
Figure. 19 shows
the strain distribution along the cross-section depth at the middle support
between spans A and B. Note that the calculated neutral axis depth was found to
be smaller than the actual one. The slight drop in the neutral axis depth
between live load test one and two could be attributed to minor cracking in the
bridge deck and diaphragm. Another comparison can be made in terms of middle
span deflection. Fig. 20a and b shows measured and calculated deflections at
middle spans D and A, respectively. Again, the calculated deflections were
found to be higher than the actual recorded values.
Figure.20 Experimental and calculated
deflections due to half-full truck (250 kN). ( Hazim M. Dwairi et al.)
3. DISCUSSION
This research
examined the material properties and behavior of four prestressed HPC girders
during casting and initial curing as well as during service. Based on this
research, the following conclusions can be drawn:
. 1. During
concrete curing, the temperature measured by the embedded thermocouples showed
that peak temperatures occurring 7–8 h after casting never reached more than 
Therefore, there was no danger
of thermal cracking.
Therefore, there was no danger
of thermal cracking.
2. Based upon
the load cell readings, practically there were no changes of the initial
prestressing force up to the time of detensioning. Therefore the measurement
suggested that there was no loss of prestress due to strand relaxation prior to
detensioning.
3. Upon
detensioning, the transfer lengths for the 0.015 m strand were found to be
0.711 m and 0.660 m respectively, for Type III and Type IV girders. These
values are slightly less than the standard design value of 50 times the strand
diameter or 0.762 m.
4. The
calculated prestress loss due to elastic shortening was 82.7 MPa for the Type
III girders and 124.8 MPa for the Type IV girders. Total prestress loss was
179.3 MPa), i.e. 12.9%, for the Type III girders and 262.7 MPa, i.e. 19.1%, for
the Type IV girders.
5. The predicted
camber compared closely with the measured camber. The close prediction was
possible because the use of load cells at the anchoring end of the prestressing
bed provided a more accurate value of the prestressing force at
transfer than
the normally assumed prestressing force based on estimated loss of prestress.
6. Girder end
displacements were caused mainly by thermal effects with small effect due to
traffic loading, while displacements due to end rotations could be neglected,
however, maximum total girder end displacement was less than a quarter an inch.
7. The
calculated strains and deflections based on AASHTO load distribution factors
were found to be higher than actual recorded data.
REFERENCES
1. B.H.
Bharatkumar, R. Narayanan, B.K. Raghuprasad, D.S. Ramachandramurthy(2000) “Mix
proportioning of high performance concrete” Cement & Concrete Composites 23
(2001) 71-80
2. D. Cusson, Z.
Lounis, L. Daigle(2010) “Benefits of internal curing on service life and
life-cycle cost of high-performance concrete bridge decks – A case study”
Cement & Concrete Composites 32 (2010) 339–350
3. Hazim M. Dwairi,
Matthew C. Wagner, Mervyn J. Kowalsky, Paul Zia(2010) “Behavior of instrumented
prestressed high performance concrete bridge girders” Construction and Building
Materials 24 (2010) 2294–2311
4.C.S.
Suryawanshi (March 2007) “Structural significance of high performance concrete”
THE INDIAN CONCRETE JOURNAL
5. Design and
Controll of Concrete Mixtures*EB001 “CHAPTER 17 High-Performance Concrete”
6. Guest Article
“Group Promotes Benefits Of High Performance Concrete Bridges” ASCENT,WINTER
2001 by Basile G. Rabbat
Comments