Materials selection for concrete overlays : the final report Page: 14
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Figure 2.5. Spraying grout immediately ahead ofpaver
There are reports that grout does little to improve bond strength [28]. However, if used
properly with a clean, textured surface, good bond can be achieved [29]. Nevertheless, placing
grout is an additional step that will slow the paving process and adds to the cost. The BCO
placed in Houston, on the South Loop [36], showed that dry grout could act as a bond breaker
between the existing pavement and the overlay: the experimental sections where the grout was
used and allowed to dry prior to the paving of the overlay caused early delaminations. The
overlay in those sections had to be removed shortly after construction. Because grout is not
needed when the surface preparation and cleaning are adequate, its use is not recommended, as it
could cause debonding.
Epoxy
Where the substrate has been treated by a less expensive surface cleaning procedure and,
therefore, is not rough enough to ensure an adequate bond, liquid epoxy materials have been
reported to provide extremely high bonding strengths in the laboratory (higher than 5000 psi)
[30]. When epoxy is used, it is very important to apply the epoxy immediately ahead of paving.
If not, the epoxy will harden and act as a bond breaker, which will lead to delamination.
Shear Connectors or "Jumbo Nails"
Use of shear connectors or "jumbo nails" can effectively control development of the
overlay drying shrinkage cracks at early age [31]. These nails are installed along the pavement
edges and longitudinal saw cuts- the areas more susceptible to debonding. Nails are installed on
the original pavement prior to the overlay placement. Installation consists of a three-step
process: drilling, drill-hole cleaning, and nail driving. The high-strength steel nails are driven
into the predrilled holes in the existing pavement by an actuator that makes use of an explosive
charge. The top part of the nail remains out of the existing pavement to be covered by the
concrete overlay when the new concrete is cast.
Similar to shear connectors, curb-type reinforcement bars epoxied into the existing
pavement surface have been used successfully to prevent edge curling and warping [29]. Usage14
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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/m1/34/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.