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

Abstract

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.

Case Study of Interstate 269 Corridor through Mississippi Focusing on Chemically Stabilized Pavement Layers

“…The I-269 Mississippi corridor construction was divided into 10 contracts (seven earthwork/grading, three paving) with a total price of approximately $423 million. The work required approximately 11.8 million yd 3 of earthwork, 3.1 million yd 2 of soil-cement mixing (near equal split between subgrade and base layers), 190,000 yd 3 of concrete, and one million tons of asphalt. Construction began in 2011 and the last portion of construction is envisioned to be completed in late 2018.…”

“…The PM Device is a metal mold which allows specimens to be compacted into an interior plastic mold with a Proctor hammer. There are two versions: one produces specimens 3 inches in diameter by 6 inches tall which has been documented ( 1 – 3 ); the other produces specimens 4 inches in diameter by 8 inches tall and was first used in the field on I-269. These two versions are denoted hereafter as PM3x6 and PM4x8, respectively.…”

“…Second, the Mississippi Department of Transportation (MDOT) is a heavy user of chemically stabilized soil, exampled by its average annual usage of roughly 30 million yd 2 of soil-cement, in addition to lime stabilization ( 1 ), and is considering changes to stabilization practices, so this project could be viewed as a baseline of sorts. Third, the plastic mold compaction device (PM Device) ( 2 , 3 ), is envisioned to be a key part of MDOT’s updated soil stabilization practices and it was utilized on-site during this project for assessment of current practices and to gain knowledge on how to incorporate protocols more fully into design and construction with this new specimen preparation and testing philosophy.…”

Performance Evaluation for Polymer-Stabilized Soils

“…This observation is also in accordance with the results shown in Figure 3a, where the curing scenario was evaluated. Conversely, and typically for the expected performance of cement, Howard et al showed that the strength increase is tangible after approximately one year of specimen preparation, although a slight drop is visible in the case of specimens with C w = 3.4% (27). From this comparison, it could be estimated that a total polymer content on the order of 15% to 20% should produce an outcome similar to that found with cement-stabilized specimens, with C w approximately 3.2% to 4.3%.…”

“…To benchmark the UCS results against published data, the work of Howard et al was selected (27), and a comparison is illustrated in Figure 7. It should be noted that the cited results are reported on the basis of the average of various cases with the same design cement content by dry mass of soil (C w ).…”