The Mississippi corridor of Interstate 269 (I-269) is located in northwest Mississippi and construction of this corridor encompassed approximately 27 miles of new Interstate. This study documents I-269 as a case study of the chemically stabilized soil pavement layers. The evaluation comprises pre-construction activities (material selection, mixture design, pavement design, contract information), construction activities (processes, specifications, as-built quality), and an assessment of three cement stabilized base sections. Detailed assessment included on-site specimen preparation using the plastic mold compaction device (PM Device), core drilling, and subsequent laboratory testing for density, unconfined compressive strength, and elastic modulus. This project was able to document and quantify density variability within current Proctor and nuclear gauge practices to the point where there was noticeable agency and contractor risk. Variability is known to exist in large construction projects, but quantifiable measurements over a large project, as presented in this paper, are more valuable than general expectations for basing future decisions. This paper provides evidence that a construction quality control program where nuclear gauge and Proctor compaction practices are interconnected with mechanical property measurements taken on specimens fabricated with the PM Device is worth considering for implementation. The PM Device fared well for construction, mixture design, and pavement design activities when benchmarked relative to the density, strength, and modulus of the several dozen cores taken and assessed from I-269.

In current soil-cement practice there exists a disconnection between laboratory mixture design, pavement layer thickness design, and construction quality control. A device was developed to integrate all three aspects by allowing compaction of soil-cement into single-use plastic cylinder molds. The device is a metal split mold design that surrounds the slightly modified plastic mold to prevent distortion of the specimen during compaction. Compaction was performed by two methods: 1) a custom-built compaction frame (similar concept to ASTM D 1632 device), and 2) a manual modified proctor hammer. This paper's objective is to demonstrate the feasibility of using this device to produce suitable specimens and provide discussion of possible applications. Over 750 soil-cement specimens were compacted under laboratory conditions using the new device. Specimens were analyzed for final dimensions (e.g. diameter, height), unconfined compressive strength variability, and elastic modulus. Analysis showed that the device can produce acceptable test specimens with unconfined compressive strength variability similar to traditional Proctor specimen variability, and specimen elastic modulus values were observed to be similar to those found in literature. Currently, the Mississippi Department of Transportation is working towards incorporating this new compaction device into their soil-cement practices. Sullivan et al. 2

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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.

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