Limiting Base Moduli to Prevent Premature Pavement Failure

Density criterion for base materials is the most common practice in quality control and quality assurance for pavement construction. However, cases in which the base material has met the density requirement but turned out to be the cause of a premature failure exist. It means meeting the density requirements would not prevent the premature failures from occurring. Field studies indicated that these base materials are found to be either too weak to provide sufficient base support or too brittle, which causes cracks in base layers which in turn leads to secondary damage in other pavement layers. This paper documents the pavement layer moduli obtained from eight forensic investigations spanning 10 years. Falling-weight deflectometer and dynamic cone penetration tests were conducted to determine the layer moduli on sections that were either too weak or too brittle. In some cases, laboratory tests were performed to evaluate the base materials’ reactions to the stabilizers (lime or cement) and base susceptibility to moisture. On the basis of the analysis results, the following ranges of base moduli are recommended for flexible pavements with more than 2.5 million equivalent single axle load design traffic: greater than 345 MPa (50 ksi) for unbound aggregate base; and from 1,033 MPa (150 ksi) to 3,445 MPa (500 ksi) for stabilized bases. Because currently no construction control requirements to limit the base modulus exist, threshold values for base moduli established from the forensic studies described in this paper will be beneficial to minimize potential premature failure.