In recent years, the nevada department of transportation has observed cases of severe rutting during the first warm weather following a chip seal application. Cores from these pavements have shown evidence of severe stripping. Sealing the surface appears to accelerate moisture damage by trapping moisture that wouldotherwise escape in the pavement layers. This observation led to the hypothesisthat rutting was occurring in the asphalt concrete layer owing to a loss of cohesion and shear trength as a result of moisture damage. To test this hypothesis, a preliminary study was undertaken to determine if moisture susceptibility wasrelated to permanent deformation. Samples from behind the paver were collected from 20 nevada construction projects during 1985 and 1986. These materials were compacted, and a preliminary creep test described by astm was performed to determine the permanent strain. Samples from each of these projects were moisture conditioned, and a strain ratio (i.E., Conditioned percent strain divided by unconditioned percent strain) was developed to relate unconditioned to conditioned results. Conclusions from this research were that moisture conditioning appears to play a significant role in permanent deformation. A preliminary multiple regression equation was developed by using strain ratio and daily 18, 000-lb equivalent single-axle loads (esals) to predict average project rut depth. This equation yielded a correlation coefficient of 0.70. This paper appears in transportation research record no. 1259, Chip seals, friction courses, and asphalt pavement rutting 1990.
Abstract