Next: Summary Up: Example Results Previous: Concrete Surface Temperature vs.

Time-of-Wetness and Time-of-Freezing Predictions

The wetting and freezing events for 12 representative geographical locations are summarized in Tables 2 and 3. It is easily observed that there is considerable variability in time-of-wetness and number of freeze-thaw cycles across the United States. Of the 12 locations investigated to date, Tucson, AZ is the driest with the concrete pavement being wet only 128 h per year. Conversely, Seattle, WA is the wettest climate with the pavement being wet 1698 h per year. Obviously, the time-of-wetness and number of freeze-thaw cycles will have a significant influence on the durability of concrete pavements and bridge decks in any given geographical location. This influence will be further developed in the sorptivity-based service life models for sulfate attack and freeze-thaw deterioration [1] currently being developed as one of the final stages of this research project.

For freezing events, there are always more freeze-thaw cycles for the bridge decks than for the pavements (in agreement with the ubiquitous posting of road signs indicating that "bridge freezes before roadway"). Not surprisingly, Tampa, FL experiences the fewest freeze-thaw cycles, with only the bridge decks experiencing any cycles in a representative year. Cheyenne, WY experiences the most freeze-thaw cycles, with over 125 cycles for both the pavements and bridge decks being observed in a representative year. In comparing bridge decks to pavements, Baltimore, MD exhibits the greatest difference, with the bridge deck concrete experiencing 21 more freeze-thaw cycles per year than a comparable pavement. This is most likely due to the somewhat moderate winter climate in Baltimore, with the ambient often near 0 ºC, so that the bridge decks often experience freezing while the nearby pavements are just above the freezing point.


 
Table 2: Wetting and Freezing Events for Concrete Pavements


U.S. City NREL code Number of Total h/yr Average RH Number of
    wetting events wet before wetting F-T cycles
Kansas City, MO 03947 173 448 83.7 79
Tampa, FL 12842 244 613 86.0 0
Lubbock, TX 23042 138 348 83.6 61
Tucson, AZ 23160 78 128 66.3 9
Cheyenne, WY 24018 117 224 71.5 126
Pierre, SD 24025 117 190 85.3 92
Seattle, WA 24233 407 1698 81.6 25
Fresno, CA 93193 139 393 86.2 14
Baltimore, MD 93721 238 948 84.7 83
Bridgeport, CT 94702 229 835 87.2 90
Alpena, MI 94849 218 680 86.1 102
Waterloo, IA 94910 209 551 86.7 72





 
Table 3: Wetting and Freezing Events for Concrete Bridge Decks


U.S. City NREL code Number of Total h/yr Average RH Number of
    wetting events wet before wetting F-T cycles
Kansas City, MO 03947 179 490 84.1 81
Tampa, FL 12842 268 639 86.8 4
Lubbock, TX 23042 148 413 84.3 71
Tucson, AZ 23160 78 141 66.3 16
Cheyenne, WY 24018 125 252 72.9 131
Pierre, SD 24025 123 229 85.7 100
Seattle, WA 24233 413 1812 81.7 34
Fresno, CA 93193 161 521 87.0 20
Baltimore, MD 93721 254 972 85.3 104
Bridgeport, CT 94702 229 860 87.0 104
Alpena, MI 94849 239 758 86.8 107
Waterloo, IA 94910 212 623 86.8 86





Next:
Summary Up: Example Results Previous: Concrete Surface Temperature vs.