Materials selection for concrete overlays : the final report Page: 4
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be more deteriorated than for UTW requirements. The overlay relies on existing
pavement to carry some of the load by monolithic behavior through a good bond
between overlay and substrate. TWTs are generally used when moderate traffic is
present.
* Conventional whitetopping (CWT): CWT is typically 9 in. or thicker and is used
when the existing pavement is in a severely deteriorated condition. CWT design
assumes an unbonded condition, so the existing pavement is only expected to serve
as a subbase. The new overlay will carry the entire traffic load. CWTs are
generally used when heavy traffic is anticipated.
Performance Factors
The following factors determine the performance of whitetoppings:
* Effectiveness of bond: For whitetoppings that rely on existing pavement to carry
load through bonding, properly achieved bond will promote monolithic behavior.
This behavior is crucial in ensuring that the stiffness of the rehabilitated pavement
(overlay and existing pavement) will carry the traffic load as one structure.
* Existing pavement condition: Since UTWs and TWTs rely on the existing
pavement to assist in carrying the traffic load, the condition of the existing
pavement affects the performance of the rehabilitated pavement. Proper repairs or
upgrades should be made to the substrate to provide adequate support as required
by design.
* Proper joint spacing: If joints are required, proper joint spacing helps to reduce
curling stresses and bending stresses due to traffic loads. This is especially true for
UTW and TWT because of their thinness.
Common Modes of Failure
The following failure modes are commonly seen in whitetoppings:
* Loss of bond: The bond between the overlay and the existing pavement can be lost
due to lack of quality control in surface preparation or placement.
* Rapid transition zone failure: Accelerated deterioration in the transition zones can
occur at the interface between asphalt and the concrete overlay. Thicker concrete
overlay sections are recommended in these areas [1].
2.2.2 Bonded Concrete Overlay
A bonded concrete overlay (abbreviated "BCO") is a relatively thin concrete layer that is
used to resurface an existing concrete pavement. This type of overlay is typically 2 to 4 in. thick
and its performance depends on good bond to the existing pavement.
Purposes and Uses
The purpose of the BCO is to rehabilitate deteriorating concrete pavements to increase
load capacity and ride quality. A BCO is recommended when the existing pavement is
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Kim, Dong H.; Fowler, David W.; Ferron, Raissa P.; Trevino, Manuel M. & Whitney, David P. Materials selection for concrete overlays : the final report, report, July 2012; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth303706/m1/24/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.