Materials selection for concrete overlays : the final report Page: 23
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2.5.5 Placement
The following are general considerations for placement of concrete overlays:
* To prevent water loss in concrete due to absorption by the existing pavement, the
prepared surface ahead of the paving machine should be dampened with water to
achieve SSD condition [11, 18, 39].
* Tracking of dirt or debris ahead of paving machine should be prevented.
* Bonding agents should not be used unless under special circumstances. With a
properly prepared surface in SSD condition, a bonding agent, such as epoxy, is not
required. If bonding agents are used improperly, they may act as bond breakers.
(See section 3.8).
* For BCOs, reinforcements can be directly placed on top of existing pavement.
Laboratory studies have shown that reinforcement placed at the interface develops
the same bond as reinforcement placed in the middle of the overlay. Placement of
the reinforcement at the interface also eliminates the risk of concrete honey
combing and poor consolidation beneath the steel [4].
* The grading machine must be adjusted to achieve the required thickness of the
concrete overlay.
* The steel fibers at the surface of the pavement can become entangled with burlap
and can be pulled out along with other fibers and coarse aggregates. An un-
weighted carpet drag can be a substitution to provide a satisfactory interim surface
finish on the pavement [23, 24].
* Finishing of the new concrete overlay surface should follow the same practices used
to finish any concrete pavement [4].
2.5.6 Jointing
To reduce the edge and corner stresses, longitudinal joints should not be placed in the
wheel path. Heavy loads concentrated near the edge of the thin panels should not exceed their
load capacity [40, 41]. The following are recommendations for jointing:
* The timing of joint sawing is critical. Sawing too early can cause excess raveling,
and sawing too late can result in shrinkage stress causing uncontrolled random
cracking.
* ACPA recommends that joint spacing be about 12 to 15 times the slab thickness.
* Joint spacing has a significant effect on the rate of corner cracking. Short joint
spacing, common on thin concrete overlays, reduces load-related stresses, because
the slabs are not long enough to develop as much bending moment [8]. The joint
location is also important to avoid concentrated loads. For example, 4-ft. by 4-ft.
panels on a 12-ft.-wide lane would put truck tires on the edge of the panels, and
significant distress would occur if the thin concrete overlays became de-bonded
from the existing pavement [9]. Figure 2.10 is a good example of failed joints in
wheel paths.23
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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/m1/43/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.