Climate Considerations

The climatic conditions expected during placement and during the service life of the CRCP should be considered during the design stage as they affect the cracking behavior and thus may affect the potential development for punchouts in the long term. For example, the precipitation expected in the region will influence the selection of the drainage system required. CRCP construction in hot climates causes an increase in the concrete heat of hydration and thus the slab temperature at set. Subsequent temperature drops can result in short crack spacings and meandering cracks, increasing the potential for punchout occurrence. In addition, when paving during hot weather, the pavement is more prone to experience excessive moisture loss from the pavement surface, which may result in subsequent spall development. Besides air temperature, low ambient humidity, and high wind speeds can also contribute to higher moisture loss from the concrete surface.

While climatic effects on early-age CRCP behavior will vary based on the project location and time of year of construction, previous investigations of early-age CRCP behavior have demonstrated that the time of day when the pavement is placed can affect the crack pattern. For example, when constructing CRCP in hot weather and placing in the late afternoon and early evening, the concrete heat of hydration will typically occur at a different time than the peak air temperature. This can results in a lower temperature drop in the concrete, and thus more uniform crack spacing.

Although the designer might not have control over the placement time, specifications or special provisions can be used to limit the maximum temperature of the concrete mix [typically 90 to 95ºF (32.2 to 35°C)] during placement of concrete. The heat of hydration and thus maximum temperature in the concrete will be a function of the constituents and proportions of the concrete mix. Therefore, specifications that limit the maximum curing temperature of the concrete rather than the temperature of the mix are more desirable as they provide the designer with a better control of the maximum temperature drop expected. A specification that controls the maximum curing temperature in the concrete has been recently investigated in Texas, and some concepts of this method are provided in Appendix A of the CRSI-FHWA CRCP Design and Construction Guidelines document.

When designing CRCP, adequate selection of the design temperature drop should be made. The design temperature drop is sometimes based on both the average concrete curing temperature after placement and the lowest slab temperature during the year for where the CRCP will be constructed:

\Delta T_{D}= T_{H}-T_{L}

Where:

  • \Delta T_{D} = Design temperature drop (°F or °C)
  • T_{H} = Average concrete curing temperature after placement (°F or °C)
  • T_{L} = Average daily low temperature during the coldest month of the year (°F or °C)

Oftentimes during the design stage, little information on when the pavement will be placed is available. Therefore, the average concrete curing temperature is commonly assumed as the average daily high temperature for the hottest month of the year. Historical climatological records can be obtained from the National Oceanic and Atmospheric Administration (NOAA) to estimate the design minimum temperature. The design minimum temperature is typically taken as the average daily low temperature for the coldest month of the year. It should be noted that if the design temperature drop is being used to estimate the critical crack width, a value of 32°F (0°C) may be considered for TL, since water infiltration is not as much of a concern in sub-freezing temperatures.