Materials selection for concrete overlays : the final report Page: 28
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* The debris and contamination was generated by the slab sawing operations in which
contaminants were carried to the prepared surface by surface water prior to concrete
placement.
* The debris accumulated just ahead of the paving machine.
The following recommendations were made in the forensics report:
* Monitor for severe weather conditions contributing to excessive evaporation rate or
temperature limits.
* Follow specifications for proper surface preparation and cleaning.
* Ensure the prompt application of curing compound.
* Be prepared for special curing, if necessary, when adverse weather conditions
warrant it.
3.3 Evaluation Study of First BCO in Texas
The first BCO project in Texas was implemented in 1983, in Houston on IH-610 (south
loop). The project was an experimental BCO on a 1000-ft. continuously reinforced concrete
pavement (CRCP) segment, built in July and August of 1983. It consisted of five 200-ft. test
segments, with several combinations of reinforcement (no reinforcement, welded wire fabric,
and steel fibers) and BCO thicknesses (2 and 3 in.), all constructed on the four eastbound lanes,
between Cullen Blvd. and Calais St. The surface was prepared by cold milling and sandblasting;
portland cement grout was used as a bonding agent for the vast majority of the sections. The
following lists the findings from the construction report [47]:
* Adding an overlay to an aged pavement improves the structural quality of the
pavement as measured by the reduction in (falling weight) deflection both at cracks
and at mid-span positions.
* Overlaying on dry surface results in better bond strength at the interface than
overlaying on a wet surface. Specifically, overlaying when the surface is wet
resulted in the weakest interface bond strength. Under this condition, it is advisable
to apply a grouting agent or to dry the surface before overlaying. If the surface is
dry, there is no need for using a grouting agent.
* Roughening the surface by milling or scarifying helps produce a better bond.
* The effect of positioning overlay reinforcements at different heights versus the
interface bond strength is insignificant. Hence reinforcing bars can be placed on the
original surface in the interest of cost saving.
* (Steel) fiber reinforced overlays are a good alternative to plain or bar-reinforced
concrete overlays.
The following lists the findings from an evaluation report after two years of service [4]:
* In BCO construction, a mixture of water, cement, and plasticizer is an adequate
bonding agent.28
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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/m1/48/?rotate=90: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.