Materials selection for concrete overlays : the final report Page: 49
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3.13 Laredo - IH 35
On December 15, 2009, a survey was performed on the Laredo Whitetopping Project on
IH-35. The segment in question is located north of Laredo, near Artesia Wells in LaSalle
County, between mileposts 51 and 52. The IH-35 whitetopping section, placed on the
northbound lanes only, was constructed in December of 2001 and January of 2002, and consists
of a 9-in.-thick layer of continuously reinforced concrete pavement (CRCP) on top of the
existing ACP, from which approximately 3 in. were milled off [35].
This project has been monitored by CTR since its construction. The fact that two other
surveys have been conducted before the current one allows for an evaluation of its performance
over time.
The survey this time consisted of a visual inspection of the outside lane of the mile-long
segment from the shoulder, recording the location of every crack and sign of distress, while
making photographic records of findings. In the next section, some of the details of the overlay
construction are presented.
3.13.1 IH 35 Whitetopping Construction
Being an experimental project, several features related to the design and construction of
the overlay were carefully selected to insure its success over time. The first was the time of
placement for the concrete pavement. Over a number of years of observing PCC pavement
performance using a rigid pavement database system and other studies, it has been found that
pavements constructed under extremely hot conditions have a higher probability of developing
failures, because of the increased climatic stresses, which in turn result in cracking. The adverse
climatic conditions subject the freshly placed concrete to higher evaporation of water from the
pavement surface, which may cause increased plastic shrinkage cracking. Furthermore, placing
warmer PCC on a hot AC surface can lead to excessive thermal restraint stresses resulting from
the large gradient between the PCC at hardening and overnight low temperatures [12].
Therefore, any construction during the summer months was ruled out for this project, and it was
recommended to schedule the construction for the winter months.
In order to provide a structure able to carry the heavy traffic that traverses IH-35, PCC
shoulders were used in lieu of asphalt shoulders. Tied PCC shoulders provide support to the
edge of the slab, where the stress concentration is critical, thus, reducing the stresses and
deflections in the main slab, and decreasing fatigue and damage. Also, the tied PCC shoulders
are better able to carry main lane traffic during construction and maintenance operations.
Excellent performance has been experienced over the state where pavements have been
constructed using coarse aggregates with low coefficient of thermal expansion and lower
modulus of elasticity [54]. Generally, these characteristics are provided by coarse aggregates
from limestone. Hence, considering the availability of aggregates in the area, the specification
required that a limestone source be used, establishing a limit design value of 5.5x10-6 in./in./F
for the coefficient of thermal expansion.
Another critical design feature was the requirement for a carpet drag finish in lieu of
tining. Tining has evolved as the standard finishing for PCC pavements, and has generally been
required by the FHWA since the 1970s. The need for tining originated from efforts to eliminate
hydroplaning on concrete pavements in wet weather conditions. Then it was promoted to help
with skid resistance where concrete pavements had polished to a glass-like finish [55]. In Texas,
at the same time that some early pavements were tined, limestone fines had been eliminated from
use in PCC paving mixtures by the use of an acid insoluble test.49
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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/m1/69/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.