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PRECAST CONCRETE PAVEMENT
CHAPTER-1
INTRODUCTION
1.1 PRECAST CONCRETE PAVEMENT
Precast concrete is a form of construction, where concrete is cast in a reusable mould
or "form" which is then cured in a controlled environment, transported to the construction site
and lifted into place. In contrast, standard concrete is poured into site specific forms and
cured on site. Precast stone is distinguished from precast concrete by using a fine aggregate
in the mixture so the final product approaches the appearance of naturally occurring rock or
stone.
Precast pavement technology comprises new and innovative construction methods
that can be used to meet the need for rapid pavement repair and construction. Precast
pavement components are fabricated or assembled off-site, transported to the project site, and
installed on a prepared foundation (existing pavement or re-graded foundation). The system
components require minimal field curing time to achieve strength before opening to traffic.
These systems are primarily used for rapid repair, rehabilitation, and reconstruction of bothasphalt and portland cement concrete (PCC) pavements in high-volume-traffic roadways. The
precast technology can be used for intermittent repairs or full-scale, continuous rehabilitation.
In intermittent repair of PCC pavement, isolated full-depth repairs at joints and cracks
or full-panel replacements are conducted using precast concrete panels. The repairs are
typically full-lane width. The process is similar for full-depth repairs and full-panel
replacement. Key features of this application are slab panel seating and load transfer at joints.
Use of precast concrete pavements for reconstruction and rehabilitation is a very
viable alternative to conventional cast-in-place concrete pavement construction, especially in
situations where high traffic volumes and consideration of the delay costs to users due to lane
closures favor reconstruction and rehabilitation solutions that allow expedited opening to
traffic. Precast concrete also offers the advantage of being factory made in a more
controlled environment than cast-in-place construction and thus is potentially more durable
and less susceptible to construction and material variability.
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1.2 PAVEMENT TYPES
Hard surfaced pavements are typically categorized into flexible and rigid pavements:
1.2.1 FLEXIBLE PAVEMENTS:
Those which are surfaced with bituminous (or asphalt) materials. These types of
pavements are called "flexible" since the total pavement structure "bends" or "deflects" due
to traffic loads. A flexible pavement structure is generally composed of several layers of
materials which can accommodate this "flexing".
1.2.2 RIGID PAVEMENTS:
Those which are surfaced with portland cement concrete (PCC). These types of
pavements are called "rigid" because they are substantially stiffer than flexible pavements
due to PCC's high stiffness.
Each of these pavement types distributes load over the subgrade in a different fashion.
Rigid pavement, because of PCC's high stiffness, tends to distribute the load over a relatively
wide area of subgrade. The concrete slab itself supplies most of a rigid pavement's structuralcapacity. Flexible pavement uses more flexible surface course and distributes loads over a
smaller area. It relies on a combination of layers for transmitting load to the subgrade .
This Guide focuses on flexible pavements. In general, both flexible and rigid
pavements can be designed for long life (e.g., in excess of 30 years) with only minimal
maintenance. Both types have been used for just about every classification of road. Certainly
there are many different reasons for choosing one type of pavement or the other, some
practical, some economical, and some political.
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1.3 BENEFITS OF PRECAST PRESTRESSED CONCRETE
PAVEMENT
1.3.1 FASTER CONSTRUCTION:
What do we mean by faster construction? We're not necessarily talking about how
fast the pavement can be constructed, but rather how fast it can be opened to traffic.
Conventional cast-in-place pavement requires several days of additional curing time after the
concrete is placed before it is strong enough to withstand traffic loading. While "fast-setting"
concrete mixtures have been developed for this purpose, these can be cost-prohibitive for
large-scale pavement construction.
1.3.2 REDUCED USER DELAY COSTS:
What are user delay costs? These are costs to the drivers of the roadway that are
directly attributable to congestion caused by construction activities. Increased fuel
consumption, lost work time, increased vehicle wear and tear, and increased air pollution are
just a few of these costs. The savings in user delay costs realized through limiting
construction to only off-peak travel times (at night or over a weekend) can be substantial.
This is where the primary economic benefit of precast pavement will be realized.
1.3.3 IMPROVED DURABILITY AND PERFORMANCE:
Precast concrete has a proven track record as a durable high-performance product for
bridge and commercial building construction. This is the result of a high degree of quality
control that can be achieved at a precast fabrication plant. High strength, low permeability
concrete mixtures with a low water-cement ratio and uniform aggregate gradation are used
routinely by precast fabrication plants. At most plants concrete batching and quality control
is done on-site and the concrete is transported only a short distance from the batch plant to
the forms, minimizing changes in concrete properties between the mixing and placing
operations. What's more, precast fabrication plants offer tremendous flexibility over the
curing operation. Precast concrete elements can be fabricated indoors, they can be wet-mat
cured, steam cured, and curing can be maintained as long as necessary after casting.
Problems that can plague cast-in-place pavement construction such as surface strength loss,
"built-in" curling, and inadequate air entrainment, can all be eliminated with precast concrete
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1.3.4 WHY PRESTRESSED PRECAST PAVEMENT?
Prestressing has a proven track record for enhancing the performance and durability
of concrete structures. And though it has seen very limited use in pavements, there are
clearly benefits of prestressed concrete pavement, such as...
1.3.5 REDUCED CRACKING:
While conventional pavements are "designed" to crack at specific locations or at
regular intervals, in general cracking is not desirable. Cracks can spall, they can permit water
to penetrate the underlying base, they can fault, and they can eventually lead to severe
pavement failures such as punch outs. Prestressing helps to minimize or even eliminate
cracking. By putting a pavement in compression there is less likelihood of cracking due to
tensile stresses. What's more, the so-called "elasto-plastic" behavior of prestressed concrete
will help keep any cracks that do form tightly closed.
1.3.6 REDUCED SLAB THICKNESS:
While the underlying pavement structure is also a factor, the primary controlling
factor in pavement thickness design is the magnitude and number of wheel load repetitions on
the pavement over its expected design life. For a given pavement support structure and a
given wheel load, tensile stresses in a thinner pavement will be higher than those in a thicker
pavement. These higher stresses wear out or fatigue a concrete pavement faster. Prestressing
can be used to reduce the tensile stresses in a thinner pavement slab to those of a much
thicker pavement slab, increasing the design life of the pavement.
1.3.7 BRIDGING CAPABILITY:
Prestressing gives the pavement a certain "bridging" capability that permits the
pavement slab to span small voids and "soft" base materials beneath the pavement. This is
critical for pavement removal and replacement operations that are limited to short
(overnight) construction windows when it is often not possible to recondition or replace the
underlying base material.
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CHAPTER-2
PRECAST PAVEMENT CONCEPT
The basic precast prestressed pavement concept consists of a series of individual
precast panels that are post-tensioned together in the longitudinal direction after installation
on site. Each panel can be pretensioned in the transverse direction (long axis of the panel)
during fabrication, and ducts for longitudinal post-tensioning are cast into each of the panels.
The basic features (typical) of the PPCP system are as follows:
1. Panel size: up to 38 ft (11.6 m) wide, typically 10 ft (3 m) long, and 7 to 8 in. (178
to 203 mm) thick (or as per design).
2. Panel types: a. Base, joint, and central stressing panels (as originally developed).
b. Base and joint stressing panels (as installed at a demonstration project in Missouri).
3. Tongue-and-groove transverse epoxied joints.
4. Post-tensioning details:
a. 0.6-in. (15 mm) diameter 7-wire monostrand tendons typically spaced at 24 in.
(600 mm).
b. Tendon load: 75 percent of ultimate tendon load, typically.
c. Prestress force: sufficient to ensure about 150 to 200 lbf/in2 (1.0 to 1.4 MPa)
residual prestress at the mid-point of each series of prestressed panels.
d. Grouted post-tensioning ducts.
5. Expansion joint spacing: ~ 250 ft (76 m), typically.
6. Base type:
a. Hot-mix asphalt concrete base with polyethylene sheet over base or asphaltconcrete interlayer in the case of an overlay application.
b. Permeable base (as used in the Missouri demonstration project).
c. Lean concrete base (as used in the California demonstration project).
d. Aggregate base (as used in the Iowa demonstration project).
7. Injection of bedding grout to firmly seat panels (after post-tensioning).
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Figure 2.1. Cross section of the precast panels
Figure 2.2. PPCP design details and panel types.
Figure 2.2 illustrates the design concept underlying this precast pavement technology.
The base panels make up the majority of the post-tensioned pavement section and are placed
between the joint panels and central stressing panels, if used. All of the panels havecontinuous tongue-and-groove keyways along the transverse face of the panels (see figure
2.3). The joint panels are located at the ends of each post-tensioned section of pavement. The
joint panels contain dowelled expansion joints that allow the expansion and contraction
movements of the post-tensioned section. The joint panels also contain the post-tensioning
anchorage for the longitudinal post-tensioning tendons. The anchors are cast into the joint
panels on either side of the expansion joint. Block outs or pockets cast into the joint panels
provide access to the post-tensioning anchors. Figure 2.4 shows the placement of a panel on
a prepared base.
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Figure 2.3. Tongue-and-groove keyway. Figure 2.4. PPCP panel being placed over
polyethylene sheet placed over a base.
When the central stressing panels are used, the post-tensioning strands are fed into the
ducts at the large block outs cast into the central stressing panels. Strands are fed in either
direction from each block out down to the anchors in the joint panels. The strands from
either side of the block out are then coupled together and tensioned. The post-tensioning canalso be applied at the joint panels without use of the central stressing panels.
2.1 PANEL ASSEMBLY:
The basic precast prestressed pavement concept consists of a series of individual
precast panels that are post-tensioned together in the longitudinal direction after installationon site. Each of the panels are pretensioned in the transverse direction (long axis of the
panel) during fabrication, and ducts for longitudinal post-tensioning are cast into each of the
panels. The basic panel layout consists of three types of panels.
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2.2 BASE PANELS:
Base panels make up the majority of the post-tensioned pavement section and are
placed between the joint panels and central stressing panels. All of the panels have
continuous tongue and groove keyways along the edges of the panels. The pretensioning
strands extend along the length (long axis) of the panels, and the post-tensioning ducts are
oriented across the width (short axis) of the panels.
Figure 2.5. Base Panel
2.3 JOINT PANELS:
The joint panels are located at the ends of each post-tensioned section of pavement.
The joint panels contain dowelled expansion joints which "absorb" the expansion and
contraction movements of the post-tensioned section. Each half of the joint panel is tied to
the panels on either side of the actual expansion joint. The joint panels also contain the post-
tensioning anchorage for the longitudinal post-tensioning tendons. The anchors are cast into
the joint panels on either side of the expansion joint. Block outs or pockets cast into the joint
panels provide access to the post-tensioning anchors.
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2.4 CENTRAL STRESSING PANELS:
Post-tensioning is completed at the central stressing panels. The post-tensioning
strands are fed into the ducts at the large block outs cast into the central stressing panels.Strands are fed in either direction from each block out down to the anchors in the joint
panels. The strands from either side of the block out are then coupled together and tensioned.
Figure 2.6. Joint Panels
2.5 PANEL JOINTS:
As described above, tongue and groove keyways are cast into the edges of the precast
panels. These keyways help ensure vertical alignment between panels as the panels are
installed. The keyways also provide temporary load transfer between panels prior to post-
tensioning. It should be noted that the panels are not match-cast. The tolerances of the
keyway dimensions are such that the panels can be fabricated on a long-line casting bed
without the need to match-cast. What's more, match-casting requires the panels to be
installed in a very specific sequence, whereas "standard" panels can be utilized for long-line
fabrication.
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A highly viscous epoxy is normally applied to the keyways prior to assembling the
panels. The epoxy acts as a lubricant during panel installation and also seals the joints
between panels to prevent the intrusion of water and incompressibles. The epoxy also bonds
the panels together so that they act as a continuous slab after post-tensioning.
Figure 2.7 Panel Joints
2.6 EXPANSION JOINTS:
As described above, the joint panels contain the expansion joints at the end of each
post-tensioned section of pavement. Up to four inches of movement can be expected at the
expansion joints, so they must be robust and able to withstand repeated heavy wheel loading.
Both armored joints (similar to those used for bridge decks) and plain dowelled joints have
been utilized on projects to date. The type of joint will depend on the expected traffic loading
and movement of the pavement slab. Regardless of the type of joint used, dowels across the
joint are essential for providing load transfer.
CHAPTER-3
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PANEL FABRICATION
3.1 PROCEDURE
The precast panels are fabricated at an established precast plant, preferably as close as
possible to the installation site. For larger jobs, particularly in remote locations, it may be
possible to set up a temporary precast bed near the jobsite. The concrete mixtures used are
similar to those utilized for other precast prestressed elements and are not be restricted to
"paving" mixtures. Steam curing, wet mat curing, or membrane curing are all options for
precast pavement panels.
The panels were fabricated on a wide flat steel casting table which was long enough
to produce up to two panels end to end. Steel sideforms and bulkheads were custom made
for the panels. The pretensioning strands extended through both panels, anchored at
bulkheads at either end of the self-stressing casting bed. Bulkheads between the precast
panels, bolted down to the casting bed, were used to hold the pretensioning strands at the
proper elevation at the ends of the precast panels. Steel chairs were used to harp the strands
within the precast panels to match the strand profile provided in the panel detail drawings.
Figure.8 shows the forms as the pretensioning strands are threaded through the forms.
In general, two base panels were cast each day. Panels were normally stripped from
the forms in the morning and the bed was cleaned and set up for an afternoon pour. Joint
panels required additional form set-up time due to the anchor blockouts and additional
reinforcement and post- tensioning anchors. Joint panels were each cast in two halves on
separate days.
A separate sideform was used to hold the dowel bars in place and form the recess
for the header material at the expansion joint. The first half of the joint panel was cast and
steam cured, but the pretensioning strands were not released until after the second half had
been subsequently cast and cured.
3.2 PANEL TREATMENT
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3.2.1 REINFORCMENT
Minimal mild-steel (non-prestressed) reinforcement was provided in the base
panels. As the panel detail drawings in the Appendix show, only perimeter steel at the
top and bottom of the panel was provided for the base panels. Joint panels also had
perimeter steel, but were heavily reinforced with stirrups around the stressing pockets
and post-tensioning anchors. Epoxy-coated grade 60 No. 4 deformed bars were specified
for all non-prestressed reinforcement. For the joint panels abutting the existing cast-in-
place pavement, the half of the panel not post-tensioned was reinforced with mild steel in
the longitudinal direction. No. 6 epoxy-coated reinforcing bars spaced at 200 mm (8inches) on center provided approximately 0.65 percent steel for this portion of the
precast panel. Figure 3.1 shows the reinforcement for the non-post-tensioned half of a
joint panel prior to concrete placement.
Figure 3.1. Reinforcement for the non-post-tensioned joint panel.
3.2.2 PRETENSIONING
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All pretensioning steel was 13 mm (0.5 inch) diameter, Grade 270 low relaxation 7-
wire strand. For the base panels, eight strands were required. The strands were spaced
evenly across the width of the base panels and alternated above and below the post-
tensioning ducts to minimize any prestress eccentricity. For the joint panels, the
pretensioning strands were concentrated in the outer edges and along the expansion joint to
avoid crossing through the post-tensioning blockouts. Twelve strands were specified for the
joint panels for to provide additional flexural strength for handling panels with post-
tensioning blockouts. For both the base panels and joint panels, the strands were
maintained at a constant depth over the portion of the panel which was 200 mm (8 inches)
or thicker (traffic lanes). However, in the shoulder regions of the panels, it was necessary to
harp the strands slightly to follow the top surface of the panels.
It should be noted that the pretensioning strands were only tensioned to 75 percent of
theirultimate strength, rather than 80 percent assumed during the design process. While this
will reduce the effective prestress in the panels, the lump-sum prestress loss assumed in the
design calculations is likely very conservative anyway. Based on actual lifting and handling
of the precast panels, the pretensioning level was clearly adequate to prevent cracking
3.2.3 POST-TENSIONING
Monostrand post-tensioning ducts with an inside diameter of 23 mm (0.9 inches)
were used for the longitudinal post-tensioning tendons. The ducts were developed
specifically for monostrand post-tensioning and are made of corrosion-proof polyethylene
material. The ducts are ideal for monostrand bonded tendons, with ribs to facilitate bond
with the concrete and two continuous channels along the length of the duct to facilitate the
flow of grout. The ducts are flexible and required adequate chairing and the use of bar
stiffeners inserted in the ducts during concrete placement to prevent sagging and bowing of
the duct under the mass of fresh concrete.
Encapsulated monostrand anchors were used for the post-tensioning anchors. The
anchors were cast into the joint panels and bolted to the post-tensioning blockout formers.
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Grout ports were located just in front of the anchors and in every 5th base panel along the
length of each post- tensioned section of pavement. Trumpeted openings and recesses for the
foam gaskets were formed at the ends of the post-tensioning ducts in each panel using
machined steel recess formers. Figure 3.2 shows the post-tensioning duct, anchor, and
blockout former used in the joint panels.
Figure 3.2. Post-tensioning duct, anchor, and blockout former in a joint panel.
3.2.4 CONCRETE PLACEMENT, FINISHING, AND CURING
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The concrete mixture was transported from the batch plant to the forms. Concrete
was placed in the forms in two lifts; the first filling the forms to the level of the post-
tensioning ducts, and the second, immediately following the first, filling the forms to the top
surface. The flowable nature of the mixture required only minimal vibration to consolidate
the concrete around the reinforcement, ducts, and blockouts.
A hand screed was used to initially strike off the concrete surface, flowed by a
vibratory screed to achieve a uniform, smooth surface. An intermediate curing compound
was sprayed over the surface between the hand screed and vibratory screed to minimize
moisture loss from the large surface area of the fresh concrete. Immediately following the
vibratory screed, a light broom texture was applied along the length of the panels (transverse
to the direction of traffic flow). A carpet drag texture was specified in the original Job
Special Provisions, but was changed to a broom finish after problems were experienced with
the carpet drag. Figure 3.3 show the screeding and texturing operations.
.
Figure 3.3. Application of the light texture to the panel surface.
After application of the surface textures,the panels were covered with tarps and
steam cured overnight. The steam was generally turned off by 5 am at which time strength
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was checked. If the strength was adequate for release, the tarps were removed and the
pretensioning strands de-tensioned. If strength was not adequate, the steam was turned
back on for 1-2 hours until adequate strength had been achieved. While steam curing was
used to achieve the necessary release strength overnight, some additional form of curing
on the top surface and sides of the panels was required for a minimum of 72 hours after
concrete placement or until the 28-day strength had been achieved. This requirement was
satisfied by covering the panels with wet burlap and plastic sheeting for an additional 24
hours after they were moved from the forms to the storage area, as shown in Figure 3.4.
Figure 3.4. Curing and Storage.
CHAPTER-4
PAVEMENT CONSTRUCTION
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4.1 BASE PREPARATION
The reconstructed base beneath the PPCP section consisted of 100 mm (4 inches) ofpermeable asphalt treated base over 100 mm (4 inches) of dense graded granular base. To
better ensure that the precast panels would be properly supported and the polyethylene
sheeting used as friction-reducing material beneath the precast panels was rolled out just
prior to placement of each panel. Figure show the construction of the permeable base and
the final surface.
Figure 4.1. Construction of the permeable asphalt treated base.
4.2PANEL INSTALLATION
4.2.3 TRANSPORTATION AND STAGING
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Delivery of the precast panels to the site is a critical aspect of the installation process.
Enough delivery trucks must be available to meet the required installation rate. Care must be
taken during the delivery process to ensure that the panels are not damaged in any way during
shipment
The panels were transported to the job site on flat bed tractor trailers truck. The
crawler crane used for panel installation was positioned on the base in front of the panel
installation. Panel delivery trucks lined up on the existing pavement south of the project, then
pulled onto the shoulder next to the PPCP section where the crane picked the panels off the
truck and lowered them into place, as shown in Figure 4.2.
Figure 4.2. Staging of delivery trucks and the installation crane.
4.3 INSTALLATION PROCEDURE
Prior to lifting each panel from the delivery truck, epoxy (segmental bridge adhesive)
was applied to the mating faces of the panels, and the compressible foam gaskets were
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installed in the recess around each post-tensioning duct on the recessed keyway side of the
panel. After the polyethylene sheeting was rolled out each panel was installed. In general,
two precast panels were installed before moving the crane.
A laser was used to align the precast panels to the centerline of the pavement. The
laser was set on the panels already in place and aligned to nail heads marking the
pavement centerline, pre- surveyed into the base. An alignment guide was installed in the
post-tensioning duct at the centerline of each precast panel, and aligned the laser. Figure
36 shows the alignment laser and the alignment guide installed in a panel.
After two consecutive panels were installed, two temporary post-tensioning strands,
located approximately at the quarter points, were fed through the panels. Post-tensioning
rams were then used to temporarily post-tension the panels together from the face of the
newly installed panels.
Figure 4.3. Laser and alignment guide used to align the precast panels.
4.4 POST- TENSIONING
4.4.1 STRAND INSTALLATION
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Both armored joints (similar to those used for bridge decks) and plain dowelled joints have
been utilized on projects to date. The type of joint will depend on the expected traffic loading
and movement of the pavement slab. Regardless of the type of joint used, dowels across the
joint are essential for providing load transfer.
4.4.4 FILLING POCKETS
After completion of final longitudinal post-tensioning, the stressing pockets and mid-
slab anchor sleeves were filled and finished flush with the pavement surface using a pea
gravel concrete mixture. Subsequent diamond grinding of the pavement surface removed
any roughness associated with the stressing pockets.
4.5 TENDON GROUTING
Grouting of the post-tensioning tendons was essentially the final step in the
construction process, and was completed following post-tensioning and filling of the
stressing pockets. The post-tensioning system used for precast prestressed pavement is a
bonded post-tensioning system. Grouting not only provides an additional layer of corrosion
protection for the post-tensioning strands, but also bonds the tendons to the pavement so that
if it is necessary to remove a precast panel at a later time, the post-tensioning system will
remain intact.
In addition to tendon grouting, underslab grouting may also be required to fill any
voids beneath the pavement. Grout ports can either be cast into the panels or drilled on site.
Underslab grouting is essentially a "gravity" fed process as applying pressure can actually lift
the pavement.
Similarly to post-tensioning, grouting can be completed during a subsequent
construction operation if time constraints do not permit grouting immediately following panel
placement. Grouting should not be completed, however, until all post-tensioning tendons are
stressed and the pockets in the joint panels are filled.
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4.6 DIAMOND GRINDING
Diamond grinding to meet Interstate Highway smoothness requirements was
expected. While the finished pavement surface was smooth enough to open to traffic ifnecessary, it did not meet smoothness specifications for concrete pavement. Diamond
grinding was used to bring the pavement surface back into specification.
No major surface repairs were required for the finished pavement. While a number of
minor spalls were observed at the joints between panels, diamond grinding removed many of
these spalls. Deeper spalls will be monitored over time so that repairs can be made if needed.
Figure 4.5. Final pavement surface after diamond grinding.
4.7 OPEN TO TRAFFIC:
Precast pavement can be opened to traffic as soon as the panels are installed. Post-
tensioning and grouting operations can be completed during a subsequent operation if
necessary. The surface will be smooth enough to open to traffic and can be diamond ground
during a subsequent operation if necessary.
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4.8 RECOMMENDATIONS FOR FUTURE CONSTRUCTION
This demonstration project showed once again the adaption of PPCP technology to
specific project needs. Future projects should focus on applying PPCP technology under
circumstances where lane closures for construction are severely limited, such as busy urban
corridors. This type of project will require very careful planning and preparation to ensure
that none of the issues encountered on this initial demonstration project will occur during
short construction window projects.
Figure 4.6. Finished precast pavement after opening to traffic.
CHAPTER-5
CASE STUDIES
CASE STUDY-1
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5.1 THE TEXAS PILOT PROJECT
Figure 5.1 Georgetown PPCP project layout.
The first PPCP project was constructed in Georgetown, Texas, during 2001 (Merritt
2001). Texas DOT placed approximately 2,300 ft (700 m) of two-lane pavement (plus
shoulders) on the frontage road along I-35. The project layout and panel systems used are
shown in figure 6.1. The project details are as follows:
Constructed: Fall 2001
Project location: Northbound I-35 frontage road near Georgetown, Texas
Project length: 2,300 ft (701 m) (2 lanes plus shoulders)
Panel dimensions: 10 ft x 36 ft (3.1 m x 11.0 m), 10 ft x 20 ft (3.1 m x 6.1 m), and 10
ft x 16 ft (3 m x 4.9 m)
Panel thickness: 8 in. (200 mm)
Number of panels: 339
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Number of post-tensioned sections: 7 at 250 ft (76.2 m), 1 at 225 ft (68.6 m), 1 at
325 ft (99.1 m)
Panel installation rate: 25 panels/6 hours
Features: Both full-width and partial-width construction. Project was the first
application of precast prestressed concrete pavement on a large scale.
For this project, it was decided to use both full-width (36 ft [11 m]) and partial-width
(16 ft and 20 ft [5 m and 6 m]) panels for the frontage road to test the concept for partial-
width panel construction. The partial-width panels were tied together transversely through
post-tensioning with an additional post-tensioning duct cast into each of the partial-width
panels. The precast, pretensioned panels were placed over a well-finished hot-mix asphalt
leveling course overlain with polyethylene sheets and then post-tensioned together in the
longitudinal direction. The tongue-and-groove connection at the transverse joints ensured
satisfactory vertical alignment during installation.
As the contractor became more familiar with the construction process, approximately
25 panelsequaling 250 ft (76 m) of pavementwere installed
Figure 5.1 Georgetown PPCP project layout. in a 6-hour period. Texas DOT found
that post-tensioning, completed after the panels were installed, generally took just a few
hours for each section of pavement. Aside from demonstrating the efficacy of placing the
slabs on grade, the Georgetown project demonstrated the viability of post-tensioning the
panels together in place. The project also showed that match-casting, which is commonly
used for precast segmental bridge construction, was not required to ensure a tight fit
between panels and to align the post-tensioning ducts. Because match casting is not
necessary, the manufacturer can fabricate the panels faster, and shipment and installation
are simplified.
The Georgetown pilot project presented many challenges for precast pavement
implementation (Merritt 2001). The most difficult aspect of the project was considered to be
the meshing of precast concrete and concrete pavement specifications.
This required flexibility on the part of both the precast supplier and Texas DOT. This
pilot project also represented unknown territory for the contractor, precast supplier, and
Texas DOT. Flexibility and a willingness to develop new techniques on the part of all parties
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were essential for the success of this project. After almost 7 years (as of November 2008), the
project is performing well and no maintenance-related issues have been reported.
Figure 5.2. Installation of the precast prestressed concrete pavement system in
Georgetown, Texas.
CASE STUDY-2
6.2 THE CALIFORNIA DEMONSTRATION PROJECT
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The Caltrans demonstration project used the PPCP system as a part of the widening
project on I-10 to provide high-occupancy vehicle lanes and reduce traffic congestion. Most
of the construction work was completed at night. The construction added 27 ft (8 m) of traffic
lanes and 10 ft (3 m) of shoulder to the existing lanes on the eastbound direction. The project
details are as follows:
Constructed: April 2004
Project location: Eastbound I-10, El Monte, California
Project length: 248 ft (76 m) (2 lanes plus shoulder)
Panel dimensions: 8 ft x 37 ft (2.4 x 11.3 m)
Panel thickness: 10 to 13 in. (254 to 330 mm)
Number of panels: 31
Number of post-tensioned sections: 2 at 124 ft (37.8 m)
Panel installation rate: 15 panels/3 hours
Features: Nighttime construction. Change in cross slope cast into the panel surface.
Photographs of the installation are shown in Figure 6. The project was located on a
section of the Interstate that had no change in vertical curvature and very minimal horizontal
curvature. The longitudinal geometry of the pavement was simple, but the pavement cross
section was more complex, with a change in cross slope from 1.5 percent in the traffic lanes
to 5 percent in the shoulders, which required variable thickness in the panel.
CASE STUDY-3
6.3 THE MISSOURI DEMONSTRATION PROJECT:
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The Missouri DOT evaluated the feasibility of using the PPCP as an alternative
solution for rapid pavement construction and rehabilitation. The project details are as follows:
Completed: December 2005
Project location:Northbound I-57 near Sikeston, Missouri (~ 10 mi (16 km) north of
I-55/I-57 interchange)
Project length: 1,010 ft (307.9 m) (2 lanes plus shoulders)
Panel dimensions: 10 ft x 38 ft (3.0 m x 11.6 m)
Panel thickness: 5.7511 in. (146280 mm)
Number of panels: 101
Number of post-tensioned sections: 4 at 250 ft (76.2 m)
Panel installation rate: 12 panels/6 hours
Features: Pavement crown cast into the panel surface. Non continuous keyways
between panels
The existing pavement was a jointed reinforced concrete pavement with 61.5-ft (18.8
m) joint spacing. The cross section consisted of an 8-in. (203 mm) slab resting on a 4-in.
(102 mm) granular base. The new PCPP cross section consists of a concrete slab of variable
thickness ranging from 10.9 in. (275 mm) at the peak crown to 7 in. (178 mm) at the edge of
the inside shoulder and 5.6 in. (142 mm) at the edge of the outside shoulder. The variable
thickness was necessary to accommodate the 2 percent crown. The PCPP slab rests on a 4-
in. (102 mm) permeable asphalt base. The panels were fabricated in Memphis and
transported to the project site, a distance of over 200 miles (320 km). Two panels were
fabricated each day. Figure 7 illustrates the construction process of the precast panels.
A few panels exhibited full-depth hairline longitudinal cracking at the fabrication
plant. It is believed that the panels may have experienced thermal shock during removal of
the panels from the forms. The temperature and strain data collected during the fabrication
process did indicate high and rapid changes in concrete temperature during fabrication.
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CHAPTER-6
CONCLUSION
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1. As discussed above, precast concrete pavement technology is ready for
implementation, excellent concrete quality with respect to strength and durability and
with respect to continuous applications.
2. The short-term performance of the installed PPCP systems indicates that PPCP
systems can provide rapid reconstruction and rehabilitation that will be durable.
3. The quality of the concrete used for the precast panels appears to meet the
expectations for durable concrete and there is no evidence of early age concrete
failures.
4. Precast pavements may have a higher first cost, the rapid installation that minimizes
lane closures and the long-term durability can easily offset the higher initial costs.
5. It is expected that innovations in this technology will ensure a permanent place for the
application of the precast concretepavement technology for durable, rapid repair and
rehabilitation of existing pavements and will help reduce the cost of panel fabrication
and installation.
6. Rapid construction techniques can significantly minimize the impact on the driving
public, as lane closures and traffic congestion are kept to a minimum.
CHAPTER-7
REFERENCES
1. FHWA Concrete Pavement Technology Program Update:
Precast Prestressed Concrete Pavement - CPTP Project Update.
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2.FHWA Concrete Pavement Technology Program.
3. MoDOT/FHWA Precast Prestressed Concrete Pavement Showcasing Workshop update.
4. Shiraz Tayabji, Dan Ye, and Neeraj Buch.,Precast concrete pavements Technology
overview and technical considerations Journal.
5. Tinu Mishra, Phil French, and Ziad Sakkal., Engineering a better road: Use of two-way
prestressed precast concrete pavement for rapid rehabilitation journal.
6. Shabbir Hossain and Celik Ozyildirim., Evaluation of Concrete Pavement Repair Using
Precast Technology Journal.
7. Shiraz Tayabji and Neeraj Buch., Precast Concrete Pavement Technology Journal.
http://www.fhwa.dot.gov/pavement/concrete/index.cfmhttp://www.fhwa.dot.gov/pavement/concrete/index.cfm