PAVEMENT CRACKING IN WEST TEXAS DUE TO FREEZE-THAW CYCLING

Freeze-thaw contraction of the base course material used in west Texas is considered an important element in pavement deterioration. Samples from two compactive efforts were frozen in a biaxial closed system. Suction and temperature within the samples were monitored and volume changes after each freeze-thaw period were recorded. Coefficients of thermal activity were calculated from the dimension measurements. These coefficients showed a relationship with the as-compacted total soil moisture suction, which was similar for all materials. Finite element studies of the thermal strains that develop in a typical pavement showed that the thermally induced tensile stresses in the base course are far in excess of typical tensile strengths for initially intact pavements. The surface course did not develop excessive stress levels. Freeze-thaw cycling produced plastic deformations in all samples, and the permanent expansion or contraction was related to the as-compacted total soil moisture suction. These permanent deformations from freeze-thaw cycling imparted a residual tensile stress to the asphalt concrete. During a freeze, suction in the sample showed a marked increase, often 10 to 20 times the initial value. The suction then dropped below the initial value during the thaw cycle. This drop was consistent regardless of the thermal activity of plastic deformation. This indicated a reorganization of the moisture in the sample, which may be related to strength losses caused by freeze-thaw cycling. The data in this study give new insight into the mechanism of freeze-thaw in pavement deterioration.