Plastic mold compaction devices are used to prepare cylindrical test specimens and help with pavement design and quality control in construction. Soil is compacted in a plastic mold with approximately a 2:1 height-to-diameter ratio using a Proctor hammer. One advantage of a PM device is the ability to connect chemically stabilized materials in pavement design. The Mississippi Department of Transportation has been an advocate of this technology and wanted to use it to test construction using Mississippi materials and MDOT practices. Testing was performed on a large-scale controlled project at the National Center for Asphalt Technology test track, which was built with traditional practices. 

Researchers Leigh E. W. Ayers, W. Griffin Sullivan, Isaac L. Howard, and Ashley S. Carey identified three objectives for the study. First, confirm that AASHTO PP92-19 protocols are suitable to measure chemically stabilized soil mechanical properties; second, compare the mechanical property performance of laboratory and field-mixed PM device specimens; and third, analyze the NCAT test track variability with that of other projects using the PM device. In “Characterizing Lime- and Cement-Treated Soil with the PM Device at a Full-Scale Pavement Test Track,” the authors report on the 124 field-mixed specimens and 270 laboratory-mixed specimens they fabricated to evaluate, in a controlled construction environment, the variability of chemically stabilized soils (i.e., soil–cement and soil–lime). This first-of-its-kind research using lime-treated subgrade and comparing mechanical properties from both PM device and beam specimens can be found in the Journal of Materials in Civil Engineering, at The abstract is below.


In this paper, the plastic mold compaction device (PM Device) was used successfully during full-scale construction of lime- and cement-stabilized pavement layers for which strict quality control measures were taken, such as multiple spread rate calibration, frequent moisture contents, and close attention to compaction timing and density measurements. Even with these precautions to minimize variability, there was quantifiable variation in density, unconfined compressive strength (UCS), and elastic modulus () for soil–cement and soil–lime mixtures. Over the 61-m test section, density varied by 5.2% for soil–cement and by 5.0% for soil–lime, UCS varied by 861 kPa for soil–cement and by 246 kPa for soil–lime, and varied by 2,628 MPa for soil–cement and by 1,036 MPa for soil–lime. There also were noticeable differences in PM Device density and measurements compared with nuclear gauge and falling weight deflectometer–calculated modulus. This paper also serves as the first known and documented use of the PM Device with lime-stabilized material, and is the first known and documented comparison of PM Device specimens and beams compacted with a Proctor hammer. Compared with other field projects in which the PM Device was implemented, the variability of density and UCS in this project was lower than in other typical Mississippi Department of Transportation (MDOT) projects. When using the data collected at the National Center for Asphalt Technology (NCAT) test track as a baseline for soil–cement materials, variability likely will be no less than 5% for density as a percentage of the target density and 75% for UCS as a percentage of the average UCS value when using current MDOT construction protocols.

See how these finding could affect how you design the soil layers beneath your pavement in the ASCE Library: