Past experience in Kentucky indicated that thickness designs using portland cement concrete best agreed with criterion used in the Portland Cement Association's design method for 2 or 3 million EAL's or less. For EAL's greater than 3 million, past experience best agreed with criterion developed from the AASHO Road Test.

Research reported herein indicates the two criteria become asymptotic at approximately 2.5 million EAL's. The merger of the criteria is presented, and the combined criterion is coupled with the principal of equal work as defined in classical physics to produce thickness design curves for portland cement concrete pavements. Research has indicated that a general conic equation can be used to satisfactorily estimate the work, as calculated by the Chevron N-layered program, at the bottom of the portland cement concrete slab under an 18-kip single axleload. The transition from a tensile strain to a work criterion is presented.

The thickness of portland cement concrete varied up to a maximum of approximately 0.15 inch for the same CBR and design EAL when the thickness of crushed-stone base was varied from 3 to 6 inches. Therefore, the design thickness of the portland cement concrete slab is relatively insensitive to changes in thickness of the crushed-stone base. Resulting thickness design curves are presented for a concrete elastic modulus of 4.2 million psi (typical of Kentucky conditions).

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The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, of the Kentucky Transportation Cabinet, nor of the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.