Trr No. 1377 Pavement Design, Management, And Performance, pp. 26-35
In seasonal frost areas, a frozen pavement structure undergoes a complex change in its ability to support traffic as the subgrade and base thaw. In an attempt to quantify this change, several test sections of various cross sections were built in the Frost Effects Research Facility at the Cold Regions Research and Engineering Laboratory. These test sections were subjected to freeze-thaw cycles, and changes in their structural capacity were monitored. The performance of only on of these, TS1, is discussed. The structural capacity during the thaw cycles was characterized nondestructively using a falling weight deflectometer (FWD). Other measurements, such as frost ang thaw depths, were obtained from subsurface temperature and resistivity gauges. The Corps of Engineers computer program WESDEF was used to backcalculate layer moduli from the FWD data. On the basis of temperature and resistivity gauge measurements, the pavement layers were appropriately subdivided to reflect the thawed and frozen layers. The backcalculated moduli were used to calculate the horizontal strains at the bottom of the asphalt concrete layer and the vertical strain at the top of the subgrade. These results were compared with those of similar strains obtained when the thawed and frozen layers were combined into a single composite layer. It was found that the thickness of the frozen and thawed layers were critical in backcalculating layer moduli and damage to pavement structures. Larger errors were introduced between measured and theoritical deflection basins when the frozen and thawed layers were considered as a single composite layer. The horizontal strains at the bottom of the asphalt layer were not greatly affected by ignoring the thwed layer. The damage to pavements with respect to vertical strains was grossly underestimated when the thawed and frozen layers were not considered separately.