Pavement Deflection Data as a Tool for the Prediction of Freeze/Thaw Response

Winter pavement overload permits and spring load restrictions are important to maximize pavement life. In cold regions freeze and thaw conditions have a great effect on the bearing capacity of asphalt concrete (AC) pavement and its sublayers. Studying AC surface deflections from falling weight deflectometer (FWD) tests assists in determining the condition of the surface, base, and subgrade layers of a pavement system. FWD test results are taken from the LTPP Information Management System (IMS). FWD data deflection basin indices can be calculated to analyze AC pavement at different seasonal conditions. This data will aid in determining times when load permits and restrictions should be applied.

Seasonal effects on AC pavements significantly affect the strength of the AC sublayers. In freezing temperatures the AC pavement and its sublayers become much stronger, where overload permits can be granted. However, when the system thaws the layers become extremely weak. Pavement is subject to damage and FWD tests show significant increases in surface deflection. When this happens spring load restrictions should be utilized to preserve the pavement. An in depth study of FWD data can be used to recommend the best times to enforce winter overload permits and spring load restrictions. Using the BISAR computer program, AC pavement can be modeled to represent FWD behavior at various times during the year. BISAR is a layered, linear elastic modeling program that can be used to redevelop asphalt concrete conditions at FWD testing periods. Assumed base and subgrade modulus values will be used for the frozen and thawed AC conditions. Mid depth temperature verses modulus relationships obtained from the LTPP database will be used to model the AC layers. This information will also be used to represent AC condition at a given seasonal time to predict times where overload permits and load restrictions will be enforced. Pavement systems modeled from FWD data and BISAR can be used to successfully to accomplish determining winter increases and spring restrictions.