Materials selection for concrete overlays : the final report Page: 30
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Even though in some segments the delamination was extensive, it did not continue to
deteriorate over time and did not appear to significantly affect performance [49]. Relatively
recent condition surveys conducted on this segment in November 2000 and June 2006 revealed
that, in spite of the heavy traffic, after 20 years of service, the BCO was still in excellent shape,
presenting a minimal number of distresses [18, 50].
3.5 Evaluation Study of Third BCO in Texas
The third BCO rehabilitation in Texas was also implemented on the IH-610 Loop in
Houston. In this case, the rehabilitated section was located on the southeast quadrant of the
urban interstate loop. Important lessons learned in the IH-610 North project were applied in the
construction of this rehabilitation project. TxDOT implemented new construction controls, such
as monitoring evaporation rates in real time with a portable electronic weather station and
limiting paving to periods when the evaporation rate during construction was less than 0.2
lb/ft.2/hr, and concrete placement was allowed only when the predicted temperature differential
during the 24 hours following placement was less than 250F. They were motivated to implement
these concepts, since the adverse environmental conditions surpassing these limits were
identified as the primary triggers of the IH-610 North BCO delaminations.
The 8-in.-thick CRCP section is about 4 miles long, and it included the aforementioned
BCO built in 1983. The approximate rehabilitation project limits are from just east of SH 288, to
just west of Telephone Rd. [30]. This project started in 1989 and was completed in 1990. It
consisted of a 4-in.-thick BCO placed on 112 lane miles. The reinforcement was wire mesh and
the coarse aggregate was limestone. Portland cement grout was used as the bonding agent [5,
30].
The BCO included ten experimental sections, each 400-ft. long and four lanes wide, in
which several combinations of bonding agents, reinforcement types, and surface treatments were
implemented for performance comparisons [36]. Substantial early delaminations occurred in the
sections where a latex modified portland cement grout was used as a bonding agent, and this
prompted the removal of the overlay shortly after construction. The reason for the delamination
was that the grout was being sprayed too far ahead of the paving machine, allowing much of the
grout to dry. Before the concrete overlay was placed the contractor applied fresh grout over the
dried grout, in which the solid latex at the interface behaved as a bond-breaking layer. The BCO
was replaced within 30 days, after the newly prepared (debonded overlay material removed)
sections received the same treatment as the control sections (cold milling and PC grout). Aside
from dismissing the use of latex as a bonding agent, another important lesson learned is that the
bond failures were induced at relatively low stresses (under 50 psi), while the overlay was still in
its early age. The experimental results also emphasized the importance of good surface
preparation.
3.6 Houston - SH 146 and SH 225
On June 8, 2010, a field trip was made to visit two bonded concrete overlay (BCO)
projects in the Houston area. The purpose of the trip was to perform visual condition surveys on
the BCOs on SH 146 and SH 225.
Unfortunately, only one of the overlay surveys could be done as planned; just at the time
of setting up for the survey, it was found that the 4.25 mi long BCO segment on SH 225, from
the IH-610 Loop to Redbluff has been resurfaced with asphalt, making it impossible to perform
the survey on this section.30
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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/m1/50/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.