Materials selection for concrete overlays : the final report Page: 18
xviii, 192 p. : col. ill. ; 28 cm.View a full description of this report.
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2.5.1 Environmental Limitations
Weather conditions prevailing during concrete overlay construction can be critical to the
performance; environmental variables that play a key role in the behavior of the concrete overlay
are temperature, moisture surrounding the concrete. Hot and dry climates pose the most
problematic conditions for concrete overlay placement, because these conditions favor the loss of
moisture from fresh concrete. Excessive water evaporation from the concrete can cause plastic
shrinkage cracking, which reduces the integrity of the concrete surface and may lead to reduced
durability.
A combination of high wind velocity, high air temperature, low relative humidity, and
high concrete temperature is the most harmful for paving conditions, because it results in high
water evaporation. Placing during low temperature months, i.e., December and January, can
minimize climatic stresses and cracking [35].
Caution must be taken in hot, dry, and/or windy climates to avoid excessive evaporation
of water from concrete and produce plastic shrinkage cracking. Weather stations should be used
to monitor the weather conditions and the ACI 503R nomograph should be used to determine the
evaporation rate. The following adverse conditions must be monitored in construction [4, 36]:
* Surface of the existing pavement should not exceed 125 OF immediately before
placement.
* Temperature differential in the 24 hours after the placement must be less than 25
F.
* Evaporation rates should not exceed 0.2 lb/ft.2/hr based on the ACI 503R
nomograph and may need to be lower depending on mixture constituents.
If any of the adverse conditions mentioned above occurs during the placement of
concrete, the placement should be avoided unless the following conditions can be achieved [4,
36]:
* Cooling the aggregate or concrete.
* Special curing methods (See section 2.5.7).
* Use of fly ash as cement replacement to lower the heat of hydration.
2.5.2 Surface Preparation
Surface preparation encompasses the operations conducted on the existing pavement
surface to enhance it in such a way that the new concrete layer can behave as designers intended.
The level of surface preparation will determine to a significant extent the longevity of a concrete
overlay. Surface preparation is crucial for any type of concrete overlay [28].
For BCOs
It is not an overstatement to say that the longevity of a BCO is mainly determined by the
effectiveness of bond at the interface. This statement is truer the thinner BCOs because thin
BCOs rely on the existing pavement to carry the traffic load; thus good bond is the most
important factor.18
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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/m1/38/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.