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									                                                            CENTER FOR TRANSPORTATION RESEARCH
                                                              THE UNIVERSITY OF TEXAS AT AUSTIN


                                                                                 Project Summary Report 1517-S
   Center for                                                     Project 9-1517: Feasibility of Precast Slabs in PCC Pavements
   Transportation Research
          The University of Texas at Austin                           Authors: David K. Merritt, B. Frank McCullough, Ned H. Burns,
                                                                                         and Anton K. Shindler
                                                                                              February 2001

                                              Feasiblility of Precast Prestressed
                                                Concrete Panels for Expediting
                                                 PCC Pavement Construction
REPORT




                        The ever-increasing number                          Such scheduling will signifi-    project. The expert panels con-
                    of vehicles on America’s road-                          cantly reduce traffic congestion sisted of various professionals
                    ways is causing pavements to                            resulting from construction ac-  from transportation agencies,
                    deteriorate faster, requiring                           tivities, which in turn will     the precast industry, and the
                    major rehabilitation or replace-                        greatly reduce user delay costs  concrete paving industry.
                    ment. Rehabilitation or con-                            while also ensuring a durable,       The third objective of the
                    struction of new pavements,                             high-performance pavement.       research was to perform a fea-
                    however, can cause significant                                                           sibility analysis on the possible
                    traffic congestion, leading to a                        What We Did...                   concepts that were generated
                    substantial increase in user                                The first objective of the   through the literature review
                    costs.                                                  research was to determine the    and expert panel meetings. The
                        Under this premise, and                             current state of the art in pre- feasibility analysis examined
SUMMARY




                    owing to the success of precast                         cast pavement technology         the possible concepts from the
                    concrete technology in the                              worldwide, as well as in the     standpoint of design, construct-
                    bridge and commercial build-                            precast concrete and concrete    ibility, economics, and durabil-
                    ing industries, the Texas De-                           paving industries in general.    ity. Finally, once a feasible
                    partment of Transportation                              This was accomplished prima- concept for precast pavement
                    (TxDOT) and the Federal                                 rily through a comprehensive     was established, the final ob-
                    Highway Administration                                  literature review. The second    jective of the research was to
                    (FHWA) commissioned re-                                 objective was to identify possi- make recommendations for fu-
                    search to investigate the feasi-                        ble concepts for a precast pave- ture implementation and guide-
                    bility of using precast concrete                        ment. As the amount of litera-   lines for performance monitor-
                    panels for pavement construc-                           ture and experience with         ing of future precast pavement
                    tion.                                                   precast pavements was very       test sections.
                        Pavement construction that                          limited, possible concepts were
                    makes use of precast concrete                           generated primarily through      What We Found...
                    panels can take place during                            two expert panel meetings, one       The proposed concept for a
PROJECT




                    off-peak travel times, such as                          at the beginning of the project  precast pavement consists of
                    at night and over weekends.                             and one near the end of the      full-depth precast, prestressed




                          (a)                                                  (b)                                           (c)

                                                                                                           Ducts for                                                Ducts for
                                                                                                           Post-tensioning                                          Post-tensioning
                                                          Ducts for
                                                          Post-tensioning
                                                                                                           Continuous                                             Continuous
                                                                                                           Shear Key                                              Shear Key
                                                         Continuous
                                                         Shear Key                                   Stressing Pockets
                                                                                                                                                       Expansion Joint Detail
                                              Pretensioning Strands                         Pretensioning Strands                  Pretensioning Strands


                                                Figure 1. Three types of panels used for a precast pavement:
                                               (a) base panel, (b) central stressing panel, and (c) joint panel.

                    Project Summary Report 1517-S                                        –1–
concrete panels. The panels will                       Neoprene Seal
all be pretensioned in the trans-
                                                                                                        1/2" Ø Nelson
verse direction during fabrication                                                                      Deformed Bars
and post-tensioned together in the                                                                      (~ 2' in length)
longitudinal direction after place-      6"            Weld
ment. The advantage of using pre-
stressed panels is a significant in-                                                                    11/4" Ø Stainless
                                                                                                        Steel Dowel
crease in the durability of the
pavement, with a significant re-
duction in required pavement             2"                   Asphalt Concrete Layer                    Dowel Expansion
thickness. For example, an 8 in.                                                                        Sleeve
thick precast, prestressed pave-
                                                               Existing Pavement
ment can be designed for the same
design life as a 14 in. thick contin-
uously reinforced concrete pave-         Figure 2. Expansion joint detail to be cast into the joint panels.
ment by simply adjusting the pre-
stress level in the pavement. This      of the panels to self-locking,             mize the amount of voids beneath
adjustment will not only result in      spring-loaded post-tensioning an-          the panels. A single layer of poly-
significant material cost savings       chors cast into the joint panels.          ethylene sheeting will also be
but will also allow for more flexi-     The use of self-locking anchors            placed over the asphalt leveling
bility when pavements are con-          will allow the strands to simply be        course to reduce the friction be-
structed in areas with overhead         pushed into the anchors from               tween the leveling course and the
clearance restrictions, such as un-     some point along the pavement,             precast panels.
der bridges.                            most likely from small pockets                 Through the feasibility study
    The proposed concept consists       cast into the joint panels.                described above, the researchers
of three different types of panels,         After the post-tensioning              developed a feasible concept for a
as shown in Figure 1. The base          strands are tensioned from the             precast concrete pavement. This
panels (Figure 1a) are the “filler”     central stressing pockets, the             concept should meet the require-
panels between the joint panels         pockets will be filled with a fast-        ments for both expedited con-
and central stressing panel(s). The     setting concrete, which will have          struction and increased durability,
central stressing panel (Figure 1b)     sufficient strength by the time            which will result in both tremen-
is a panel similar to the base pan-     traffic is allowed back onto the           dous savings in user costs and an
el, with the addition of pockets        pavement. The strands will then            increased design life.
cast into the panel. These pockets      be grouted in the ducts via inlets/            With respect to expedited con-
will allow the post-tensioning          vents located at the expansion             struction, the proposed concept
strands to be stressed at the center    joints and at the stressing pockets.       has many features that will allow
of the slab, rather than at the an-     The intermediate joints between            for construction to take place dur-
chorage, which will be cast into        the individual panels will then be         ing overnight or weekend opera-
the joint panels. The joint panels      sealed with a low-viscosity, liquid        tions. First, the asphalt leveling
(Figure 1c) will contain an expan-      sealant. If needed, the pavement           course can be placed well in ad-
sion joint detail (Figure 2), similar   can then be diamond-ground to              vance of the precast panels. This
to that of bridge expansion joints,     smooth out any major irregulari-           will allow for the entire asphalt
which will absorb the significant       ties, and any major voids beneath          leveling course to be placed at one
expansion and contraction move-         the pavement can be filled by              time, rather than just prior to the
ments of the pavement with daily        standard grout injection or expan-         placement of the precast slabs.
and seasonal temperature cycles.        sive polyurethane foam.                    Traffic on the leveling course
    A typical panel assembly is             To obtain a smooth riding sur-         should not have a detrimental ef-
shown in Figure 3. The slab length      face over the assembled pave-              fect as long as the panels are
(between expansion joints) will be      ment, continuous shear keys will           placed within a reasonable amount
varied by an increase in the num-       be cast into the panel edges, as           of time after the leveling course.
ber of base panels between the          shown in Figure 1, to ensure exact         Second, neither the stressing
joint panels and central stressing      vertical alignment of the panels as        pockets nor the post-tensioning
panels. After all of the panels are     they are set in place. Additionally,       ducts must be filled or grouted
set in place, the post-tensioning       the panels will be placed over a           prior to exposure to traffic. The
strands will be inserted into the       thin, 1 to 2 in. thick, asphalt level-     pockets can simply be temporarily
ducts via the central stressing         ing course, which should provide           covered and the strands can be
pockets and threaded through all        a smooth, flat surface on which            grouted during a subsequent con-
                                        the panels can be placed to mini-          struction operation. Finally, tem-

Project Summary Report 1517-S                           –2–
        Joint Panel      Base Panel          Central         Base Panel         Joint Panel
                       (Variable Number) Stressing Panel   (Variable Number)

                                        Figure 3. Typical panel assembly.
porary precast ramps can simply         prevented. This will reduce, if not       ing construction with a very mini-
be placed at the end of the slab to     eliminate, spalls and punchouts           mal impact on traffic, such as cer-
provide a transition for traffic onto   during the design life of the pave-       tain frontage roads or rest area
and off the new pavement. These         ment. Prevention of cracking will         roads. Any necessary laboratory
ramps can then be reused during         also protect the post-tensioning          testing should be completed prior
subsequent operations.                  strands in the pavement. The cast-        to the construction of the pilot
    User delay costs can be sub-        in-place prestressed pavement             projects to ensure the viability of
stantially reduced by limiting con-     constructed in 1985 on Interstate         certain aspects, such as the spring-
struction to an overnight or week-      35 in McLennan County, Texas, is          loaded anchors and strand place-
end timeframe. As an example,           a testament to the increased dura-        ment procedures.
the computer program QUEWZ              bility of prestressed pavements.              The pilot projects will be fol-
was used to compute and compare         Finally, because the precast pan-         lowed by rural implementation,
user delay costs for precast pave-      els will generally be thinner than        wherein the construction process
ment construction and for conven-       conventional pavements, and be-           will be further streamlined under
tional pavement construction. For       cause there will be a great deal of       simulated time constraints. As
conventional pavement construc-         control over the temperature gra-         with the pilot projects, rural imple-
tion, wherein traffic is diverted       dient in the precast panels during        mentation should be undertaken
through the construction zone for       casting, “built-in curl” will be sig-     on pavements that will not have a
24 hours per day until construc-        nificantly reduced, if not eliminat-      very significant impact on traffic if
tion is complete, the user delay        ed. This will greatly reduce tem-         problems occur during construc-
costs were computed as approxi-         perature curling stresses in the          tion. Rural implementation should
mately $383,000 per day. On the         pavement.                                 take place, however, on a road that
other hand, precast pavement con-                                                 will experience significant traffic
struction, wherein traffic is only      The Researchers                           loading, such as a rural interstate.
diverted from 8 p.m. to 6 a.m. dai-                                                   Finally, after rural implementa-
ly, results in user delay costs of      Recommend...                              tion, urban implementation will
only $1,800 per day. Although it            The proposed concept appears          present the most challenges to pre-
may not be possible to place as         to be a feasible method for expe-         cast pavement construction. Urban
much precast pavement as con-           diting construction of portland           implementation should take place
ventional pavement during one           cement concrete (PCC) pave-               on an urban intersection or major
day, the savings in user costs far      ments. However, the true feasibil-        arterial where road closure must
outweigh any additional construc-       ity of this concept will be realized      be limited to overnight or weekend
tion time.                              only through actual implementa-           operations. By the time urban im-
    In addition to expedited con-       tion. Therefore, a staged imple-          plementation is undertaken, how-
struction, precast pavement also        mentation strategy is recommend-          ever, the construction process
offers enhanced durability. First,      ed for testing these concepts and         should be fully streamlined to ac-
the panels will be cast in a con-       slowly introducing this new con-          commodate strict time constraints.
trolled environment at a precast        struction technique into current              Implementation will ultimately
yard. This will allow for flexibili-    practices.                                determine the feasibility of the
ty with the concrete mix, making            Staged implementation will            precast concrete pavement con-
the use of lightweight, high per-       begin with small pilot projects           cepts presented in this report. In
formance, and other concretes           aimed at refining the proposed            the end, a simple concept that is
possible. Second, because pre-          concepts and streamlining the             easily adaptable to existing tech-
stressing will be incorporated,         construction process. The pilot           niques yet not restricted by current
cracking in the pavement can be         projects should be constructed on         practices will ensure the viability
                                        pavements that can be closed dur-         of precast concrete pavements.
Project Summary Report 1517-S                          –3–
     For More Details …
        Research Supervisor:    B. Frank McCullough, Ph.D., P.E., phone: (512) 232-3141,
                                email: bfmccullough@mail.utexas.edu
        TxDOT Project Director: Gary Graham, P.E., phone: (512) 467-5926,
                                email: ggraham@dot.state.tx.us

        The research is documented in the following report:
        Report 1517-1, The Feasibility of Using Precast Concrete Panels to Expedite Highway
        Pavement Construction, Draft January 2001

        To obtain copies of the report, contact: CTR Library, Center for Transportation
        Research, phone: (512) 232-3138, email: ctrlib@uts.cc.utexas.edu.




                           TxDOT Implementation Status
                                    July 2001
            The precast, post-tensioned pavement developed under this research project is being
    implemented with IPR 5-1517. This IPR covers the construction of two sections at the
    frontage road of IH-35 north of Georgetown. One section has a length of 1,230 LF with 36
    foot wide panels and the second has a length of 1,000 LF with 20 and 16 foot wide panels.
    These sections will be used to complete the feasibility study of this type of pavement
    construction. The Austin District is the Office of Primary Responsibility (OPR) for this
    project.
            For more information, please contact Dr. German Claros, P.E., Research and
    Technology Implementation Office (512) 467-3881 or email at gclaros@dot.state.tx.us.

                            Your Involvement is Welcome!



                                          Disclaimer
         This research was performed in cooperation with the Texas Department of Transportation and
the U. S. Department of Transportation, Federal Highway Administration. The contents of this report
reflect the views of the authors, who are responsible for the facts and accuracy of the data presented
herein. The contents do not necessarily reflect the official view or policies of the FHWA or TXDOT.
This report does not constitute a standard, specification, or regulation, nor is it intended for
construction, bidding, or permit purposes. Trade names were used solely for information and not for
product endorsement. The engineer in charge was Dr. B. Frank McCullough, P.E. (Texas No. 19914).

Project Summary Report 1517-S                   –4–

								
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