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Expansive Soil Mitigation for Transportation Earthworks by Polymer Amendment

Expansive soils pose prevalent problems to transportation infrastructure throughout much of the Northern Great Plains region of the western United States (Nelson and Miller 1992). Pavements are particularly susceptible to damage from the shrink-swell behavior of expansive soils due the combination of low ground pressures and large surface areas. The pervasiveness of expansive soils in the northern-mountain-plains region is illustrated in Figure 1. When transportation infrastructure cannot be routed to avoid expansive soils, subgrade treatments are often used to mitigate damaging shrink-swell behavior. Traditional subgrade soil treatments are based on methods and technologies primarily developed and refined in the 1950s to 1980s (Petry and Little 2002), and do not incorporate state-of-the-art (i.e., nontraditional) expansive soil stabilizers (for example, refer to the practices described in the Colorado Department of Transportation 2015 Pavement Design Manual, CDOT 2015). Stabilizers used to mitigate shrink-swell behavior of expansive soils can be divided into three categories, traditional stabilizers (lime, portland cement, and fly ash), byproduct stabilizers (cement kiln dust, lime kiln dust, ect.), and nontraditional stabilizers (sulfonated oils, potassium compounds, polymers, etc.) (Petry and Little 2002). Shrink-swell reductions with traditional and byproduct stabilizers are mechanistically based on calcium exchange (swell reducing) and pozzolonic (cementing) reactions. Nontraditional stabilizers, rely on alternative methods for stabilization. For example, potassium-based stabilizers rely on the penetration of potassium ions into the inter-clay-platelet galleries of high swelling smectite clay to form (relatively) lower swelling illite clays. Use of traditional stabilizers for expansive soil mitigation in transportation earthworks is relatively straightforward, but requires careful design of a soil-specific treatment program (heterogeneous site conditions must be accounted for in the design), and rigorous quality assurance during implementation. The design program will determine the optimum combination of additive (percent by mass), soil compaction, and soil moisture content to attain required engineering properties. This program will then be implemented in the field by pulverizing the native expansive soil to a prescribed maximum clod size and to a prescribed depth, in-place mixing of a prescribed mass-percent of additive in slurry form, 24-48 hour (or more) in-place curing if using lime, and soil compaction to a prescribed range of densities (Little et al. 2000, Petry and Little 2002). Unfortunately, the effectiveness of traditional stabilizers decreases as soil activity increases, becoming ineffective for highly expansive soils (with a plasticity index ≥ 50; Petry and Little 2002). Traditional soil stabilizers are also ineffective (or even swell causing) in clayey soils containing sulfate salts or with potentially soluble sulfates in response to changes in pH or redox conditions (e.g, soils containing gypsum or pyritic sulfur) (Petry and Little 2002). Numerous nontraditional stabilizers have been previously proffered, and some of these stabilizers have been demonstrated to be effective for specific soil-additive combinations (Petry and Little 2002). The current state-of-the-art in nontraditional stabilizers is polymer based additives; these polymer stabilizers include Global Road Technologies GRT7000 Soil based stabilizers are touted in the manufactures literature to be “effective and green”, “sustainable”, and “cost effective” alternatives to existing soil stabilization technologies. However, adoption of these stabilizers, as is always the case of nontraditional stabilizers (Petry and Little 2002), is hindered by both a lack of un-biased information on their effectiveness, and a lack of understanding of the mechanisms by which these materials function. Understanding mechanisms if fundamental to predicting soil conditions were a specific additive might be effective, and to forecasting long-term behavior in real-world conditions. Polymer-based stabilization of expansive soils, including stabilization of high swelling sodium montmorillonite, has been demonstrated (e.g., Inyang et al. 2007, Mohammed and Vipulanandan 2012, Mousavi et al. 2014). Additionally, extensive scientific literature is available examining the mechanisms of clay-polymer interactions, including mechanisms that reduce or eliminate shrink-swell behavior (e.g., Theng et al. 2015). However, independent demonstration of the effectiveness (or ineffectiveness) of commercially available polymer stabilizers for expansive soils, and identification of the specific mechanisms through which these stabilizers function, is minimal to nonexistent. The proposed project will evaluate if recently developed and commercialized polymer-based stabilizers are a viable option for future transportation earthwork construction that involves expansive soil problems. The proposed project will enhance the ability of transportation practitioners to improve highway conditions and performance via innovative technologies. The current lack of independent assessment inhibits the adoption of potentially valuable materials, as does a lack of information on the mechanisms underpinning stabilization. The proposed project will provide a basis for moving forward on expansive soil mitigation techniques for transportation infrastructure via review of relevant technical literature to summarize the current state-of-art and state-of practice in expansive soil mitigation, and by providing an independent laboratory evaluation of expansive soil-polymer composites. Laboratory testing will be used to assess treatment effectiveness relative to traditional stabilization methods, and to describe mechanistic behavior of polymer modification to aid in creating improved practices for construction of transportation infrastructure. The proposed project will also create a methodology for independent evaluation of future polymer-stabilization technologies.

Language

  • English

Project

  • Status: Active
  • Funding: $120000
  • Contract Numbers:

    DTRT13-G-UTC38

  • Sponsor Organizations:

    Research and Innovative Technology Administration

    University Transportation Centers Program
    1200 New Jersey Avenue
    Washington, DC  United States  20590
  • Project Managers:

    Kline, Robin

  • Performing Organizations:

    Colorado State University

    Department of Civil and Environmental Engineering
    Campus Delivery 1372
    Fort Collins, Colorado  United States  80523
  • Principal Investigators:

    Scalia, Joseph

    Bareither, Christopher

  • Start Date: 20160426
  • Expected Completion Date: 20180731
  • Actual Completion Date: 0
  • Source Data: MPC-509

Subject/Index Terms

Filing Info

  • Accession Number: 01598864
  • Record Type: Research project
  • Source Agency: Mountain-Plains Consortium
  • Contract Numbers: DTRT13-G-UTC38
  • Files: UTC, RiP
  • Created Date: May 5 2016 12:52PM