ESTABLISHING A CONSTRUCTION CUTOFF DATE FOR PLACEMENT OF AGGREGATE-LIME-POZZOLAN

Aggregate-lime-pozzolan has been, for the most part, successfully used as a base course and shoulder material in flexible pavement construction in Pennsylvania. However, a number of recent failures associated with late season construction have occurred. These failures prompted the Pennsylvania Department of Transportation to impose a construction cutoff date for the placement of the material. In this paper, failure criteria based on attained tensile strengths and the probabilities of attaining these tensil strengths before the freezing season are established. Total probabilities of failure of a typical 3 percent lime, 15 percent fly ash, and 82 percent limenstone aggregate (regular mix) are determined and plotted against placement dates. An acceptable failure probability is chosen, and the corresponding placement date is designated as the cutoff data for placement of the typical aggregate-lime-pozzolan material. Two field demonstration projects were monitored for one freezing season to verify the chosen cutoff date.