Materials selection for concrete overlays : the final report Page: 20
xviii, 192 p. : col. ill. ; 28 cm.View a full description of this report.
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Removal Principle Depth Important advantages Important disadvantages
method behavior action
(mm)
Water-jetting High pressure Yes Effective (especially on Water handling, removal in
(hydro water jet from a horizontal surfaces), frost degrees; costs for
demolition) unit with a selective, does not damage establishment.
movable nozzle reinforcement or concrete,
improved working
environment.
Depth of scarification and type of aggregate of the existing concrete may dictate the type
of surface preparation to use. Cost is also a factor to take into consideration. Typically
shotblasting is the most inexpensive option and produces better prepared surfaces [29].
The scarification depth and texture should be specified for each project, depending on
economic considerations as well as the materials properties, both of the existing pavement and
the new overlay. For instance, if the existing pavement grout paste is relatively soft and the
coarse aggregate is especially hard, a light shotblasting will be sufficient to remove the paste to
reach the specified depth, leaving the aggregate intact, resulting in a good surface texture.
Typically, the depth of surface removal is about 0.25 in. into the coarse aggregate [42]. It
can also be specified in terms of some standardized texture test method, such as the sand patch
test (ASTM E 965) or circular track meter (CT Meter). Typical texture readings from this test
are between 0.050 in. and 0.099 in.
For Whitetopping/Unbonded Concrete Overlay (UBCO)
If surface distortions on the existing asphalt pavement are excessive (greater than 2 in.),
either milling or a leveling course may be necessary to provide proper grading. The milling
process should be controlled by a string line to prevent concrete quantity overruns [9].
Typically, milling is used to scarify the existing pavement to roughen up the surface.
For UBCO placements, the existing pavement acts as a base, and a separation layer is
placed on top to separate the UBCO and the existing pavement to prevent cracks from reflecting
through. Since the existing pavement serves only as a base, no special preparation is needed.
Usually, a thin layer of asphalt is used to act as a separation layer, so if there are any asphalt
patches on the existing pavement there is no need to remove them.
White pigmented curing can be used to cool the existing pavement prior to pouring. This
curing compound reflects heat and prevents heat build-up in the dark surface, reducing shrinkage
cracking in the concrete and potential paving problems due to a soft surface [8, 24]. Water
fogging is another method that can reduce the asphalt temperature. Figure 2.7 shows a way to
cool down the prepared surface by spraying with water. It is good practice to water fog if the
asphalt surface heat makes it uncomfortable to touch with an open palm [37]. It was found that
mix water in the fresh concrete overlay was absorbed into the dry substrate, reducing the amount
of water available to fully hydrate the cement paste at the bonding interface [38].20
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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/m1/40/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.