Soil–Cement Laboratory Mixture Design That Interfaces with Pavement Design and Construction Quality Control

A growing need among agencies is the ability to interface soil–cement pavement layer thickness design, laboratory mixture design, and field quality control/quality assurance (QC/QA) operations. This need has existed for some time, but in recent years implementation of the Mechanistic–Empirical Pavement Design Guide (MEPDG) has reinforced the need for a more unified system for materials, design, and construction. As part of a Mississippi Department of Transportation (DOT) study, equipment referred to as the plastic mold (PM) device was developed to help meet this need. This paper’s objective is to present alternative soil–cement laboratory mixture design concepts that use the PM device to bring continuity between pavement layer thickness design, laboratory mixture design, and construction QC/QA. More than 1,100 soil–cement specimens were tested to evaluate unconfined compressive strength (UCS) development over time, wheel-tracking performance, and variability. Data presented confirmed the design cement content levels being used by the Mississippi DOT are reasonable and that the most needed advancement is interconnection of mix design with other soil–cement activities. UCS variability results revealed that the PM device and Proctor specimens have approximately the same amount of variability, and increasing the number of replicates could benefit the design procedure by increasing design reliability. Overall, the PM device has been shown to be as effective in selecting an optimum cement content as standard Proctor equipment, but the PM device has added advantages relative to interfacing with MEPDG input needs and QC/QA activities. The Mississippi DOT is evaluating the proposed mix design procedures for implementation.