Field and Lab Investigations of Prematurely Cracking Pavements

A forensic study was conducted to identify the cause of the premature cracking on three recently completed projects that were built with the same design. Nondestructive [ground penetration radar, falling weight deflectometer (FWD), GeoGauge, and Portable FWD], nuclear density gauge, dynamic cone penetration, and extensive laboratory tests were performed. It was found that the initial stiffness of the treated base was found to be excessively high by FWD backcalculation. Some sections of the backcalculated base moduli were over $20.7\mathrm{GPa}$ . This indicates that the layer is excessively brittle for a base material, similar to lean concrete. Six specimens (that were made without a mellowing period) exhibited cracks. There was no cracking for six specimens that had two days of mellowing. It was concluded that the culprit of the transverse cracking in the main lanes was the shrinkage of lime treated base layers. The longitudinal cracks are related to the edge drying and the transverse cracks are related to the insufficient mellowing period. Based on the findings of this study, the District implemented a $2\text{-}\text{day}$ mellowing period for Quicklime treated caliche base. Three newly constructed pavements (age 8, 5, and $2\text{months}$ ) were surveyed. No cracking can be observed so far, and the District thinks the cracking problem has been mitigated by the $2\text{-}\text{day}$ mellowing period. Without the mellowing period, cracking had normally occurred $1\text{to}2\text{months}$ after construction.