Assessing Rutting Susceptibility of Cement-Treated Base Material under Early Trafficking with Heavy Clegg Impact Soil Tester

Abstract

To avoid the occurrence of early-age damage, cement-treated base (CTB) materials must be allowed to cure for a period of time before the pavement can be opened to early trafficking. As an alternative to specifying a set curing duration, a field-testing method was developed. The specific objectives of the project were to examine correlations between Clegg impact values (CIVs) determined using a heavy Clegg impact soil tester and rut depths measured in newly constructed CTB and to subsequently establish a threshold CIV at which unacceptable rutting should not occur. From data collected in the field and laboratory, one may conclude that successive wheel passes each cause less incremental rutting than previous passes and that rutting should be absent when the CIV exceeds 35. The maximum measured rut depth did not exceed 0.35 in. in this research, probably because of the high-quality limestone base material used to construct the CTB. In identifying a recommended threshold CIV at which CTB layers may be opened to early trafficking, researchers proposed a maximum tolerable rut depth of 0.10 in. for this project, which corresponds to a CIV of approximately 25. Because a CIV of 25 is also achievable within a reasonable amount of time under normal curing conditions and is consistent with earlier research, this threshold is recommended as the minimum average value that must be attained by a given CTB construction section before it can be opened to early trafficking.