Temperature of pavementis one of the most influencing factor in both Asphalt pavements and rigidpavements. The stiffness, or modulus, of AC isextremely sensitive to temperature. Deflection testing is used to evaluatevariety of pavement characteristics, including axle or vehicle load capacity,structural life, and uniformity. Deflection test results are dependent onseasonal variation. To get correct deflection results it should be adjustedaccording to temperature values. Temperature and moisture affectdeflection response of both flexible pavements (asphaltic concrete) and rigidpavements (Portland Cement Concrete).
The stiffness (rigidity) of asphaltconcrete (AC) is very sensitive to temperature changes occurring over both longterm (seasonal) and short term (hourly) periods. As the temperature of thepavement increases, the magnitude of deflection from a given impulse load willincrease if all other factors remain the same. Therefore, deflections measuredon a hot summer day will be larger than the deflections measured during acooler period. Also, changes in temperature with depth (vertical temperaturegradients) influence stresses in the AC layer. The influence of verticaltemperature gradients becomes more pronounced as the thickness of the ACincreases. 5 Therefore, Temperature has a vital rolein predicting pavement characteristics.
The temperature values for the state ofTEXAS can reach up to 110 F. These temperature values have profound effects onthe test that are done on test sections. The report uses several temperaturevalues to predict temperature at various depths. The surface temperature of thepavement is measured during the FWD testing using IR sensors. TheFWD computer automatically records the information. Associated informationincludes the site number, date of test, and time of test.
Air temperature isanother important parameter that contributes to the temperature at variousdepth of the pavement. Several instruments are used to record temperature.Thermistors, a type of resistor whose resistance is dependent on temperature isused at various depths to record temperatures. Manual in-depth pavementtemperature measurements from holes drilled at each end of test section tospecified depth in the pavement. Temperatures are measured at two locations,generally about a meter before and after the test section. The in-depthtemperature is measured manually with a hand-held digital thermometer.
Thetemperatures are measured about every half hour and hand recorded on a form,along with information about the station and site number, time and date of themeasurement, depth of the hole. 2 Linear interpolation is atechnique that is used to find temperature at various depths as temperaturefollows linear trend and the interpolated values are compared with the manuallyrecorded temperatures. The temperature data are obtained from LTPP (Long TermPavement Performance) database and Seasonal Monitoring Program (SMP) sections.