Application of Cementitious Materials and Fiber Reinforcement to Enhance Lime Stabilization for Nebraska Shale Soils

Soil stabilization is a process that the engineering properties of a weak soil are enhanced permanently with lime or cement. Stabilized soils outperform non-stabilized soils when materials, design, and construction are properly considered. Furthermore, when the stabilized soil layer is incorporated into the structural design of the pavement, the subsequent layers can be thinner resulting in sizable cost savings. Not only for properties related to strength or stiffness but also stabilized soils form a solid monolith that decreases permeability, which in turn reduces the shrink/swell potential and the harmful effects of freeze/thaw cycles. Stabilization in clay soils results from two distinct chemical processes caused by the stabilizing agent. One is the cation exchange and immediate flocculation effects, and the other is the pozzolanic and hydration effects which are time-dependent. To stabilize clay soils within the time constraints usual in the field, the fast reaction provided by cation exchange and flocculation processes plays a vital role. Lime has been popularly used in clayey soil stabilization applications, which uses pozzolans, which are naturally present in clay soils, to generate cementitious bonds that permanently strengthen a soil. Pozzolans such as silica and alumina react with calcium, supplied by the lime, and water to form calcium-silicate-hydrates (C-S-H) and calcium aluminate-hydrates (C-A-H). A pozzolanic reaction produces stable calcium silicate hydrates and calcium aluminate hydrates as the calcium from the lime reacts with the aluminates and silicates solubilized from the clay. However, lime can be not active when there is less alumina in the soil. Therefore, some concerns exist for the performance and durability of lime stabilization associated with fewer silica and alumina soils (or high sulfur compounds) and other conditions such as poor drainage, freezing, and thawing. In this case, cement as a stabilizing method can be used to increase the strength of weak soils by mixing it with cement and water. The water hydrates the cement, generating reactions that create a matrix between the soil particles and give the soil strength. Cement stabilization is especially useful in coarse-grained soils. But the cost of cement is expensive than lime, thus the appropriate amount of mixing should be known depending on site-specific conditions. Also, the mixing ratio between lime and cement can be uncertain depending on the soil properties and environmental factors such as pH or moisture contents. As an alternative, previous studies on discrete fiber-reinforced natural and chemically stabilized soils have generally shown improvements in soil shear strength, bearing capacity, ductility, toughness, and resistance to rutting. Accordingly, the microfiber reinforcement could be promising for enhancing the performance of the subgrade as an alternative to lime stabilization. Gray and Ohashi (1983) reported that the failure mechanism of a fiber-reinforced soil depends on the acting average effective stress. Failure occurs through slippage of fibers up to critical stress and, as the stresses increase, failure is governed by the tensile strength of the fiber element reported that in unconfined compressive strength tests, the fiber-reinforced soil yielded higher shear strengths due to the development of tension in the fibers with increasing strains. Consoli et al. (2003) indicated that the fiber content, the orientation of fibers concerning the shear surface, and the elastic modulus of the fibers influence the contribution of the reinforcement to the shear strength. In Iowa loess, Hoover et al. (1982) found that the inclusion of fibers decreased freeze-thaw volumetric changes on the order of 40% compared to soil with no fibers. Lime and cement can be mutually complementary. Lime alone has been ineffective in stabilizing several specific soils in Nebraska. In particular, lime has not been effective at stabilizing shale soils in northeast Nebraska. However, previous studies have found that by combining lime with fly ash, cement, or fiber reinforcement they can control shrinkage and swelling as well as increase strength and stiffness. This method of combining an additive with lime enhances the performance of the stabilization. However, NDOT has not tried varying proportions of additives with lime that provisions can be written, and construction practices developed for use in the field. Thus, a systematic study is warranted to help NDOT facilitate its usage for subgrade stabilization. It is needed to identify the effectiveness of mixing cementitious materials and fiber reinforcement to enhance lime stabilization and to prepare the design practice in Nebraska.

    Language

    • English

    Project

    • Status: Active
    • Funding: $142,129.00
    • Sponsor Organizations:

      Nebraska Department of Transportation

      1500 Nebraska 2
      Lincoln, NE  United States  68502
    • Project Managers:

      Halsey, Lieska

    • Principal Investigators:

      Eun, Jongwan

      Kim, Seunghee

      Song, Chung

    • Start Date: 20220701
    • Expected Completion Date: 20240531
    • Actual Completion Date: 0

    Subject/Index Terms

    Filing Info

    • Accession Number: 01849039
    • Record Type: Research project
    • Source Agency: Nebraska Department of Transportation
    • Files: RIP, STATEDOT
    • Created Date: Apr 19 2022 9:40AM