Because of the high cost of quality construction materials, transportation engineers are often forced to seek alternative designs using substandard materials, commercial construction aids, alternative pavement materials, and innovative design practices. Nontraditional soil stabilization additives are being marketed as viable solutions for stabilizing marginal materials as a low-cost alternative to traditional construction materials. Nontraditional additives are diverse in their composition and the way they interact with soil. Unfortunately, little is known about their interaction with geotechnical materials and their fundamental stabilization mechanisms. The objective of this research was to advance current understanding of the chemical and physical bonding mechanisms associated with selected nontraditional stabilizers. The research consisted of conducting qualitative analyses of hypothesized stabilization mechanisms, examining historical literature for supporting documentation, and performing laboratory experiments to improve the understanding of how these nontraditional additives stabilize soils. Laboratory experiments included image analyses, physical characterization, and chemical analyses to determine the primary constituents of the mineral, soil, stabilizer, and stabilized soil composite. The focus of this effort was to provide insight into the proposed mechanisms by using the laboratory data to examine proposed mechanisms from the historical literature and to provide additional hypotheses for the interaction between nontraditional additives and different soil types.

Stabilization Mechanisms of Nontraditional Additives

The aim of this study was to characterise the technical and environmental implications of non-traditional treatments of a low-plasticity compacted silt (PI = 14) and to investigate their actions both at the micro- and macro-structural scales. Three non-traditional additives derived from industrial vegetal by-products were studied. These additives are classified as an acid solution, an enzymatic solution (ES) and calcium lignosulfonate (LS). The first step was to characterise the effects of these treatments on Proctor compaction, bearing capacity, unconfined compressive strength and stiffness. The index properties of the treated samples were also measured to assess changes in the interaction between soil minerals and the additives. These experimental results showed that the 0.002 % ES and 2.0 % LS treatments were the most effective at improving the soil dry density and allowing the soil to reach optimum density using 3 % less water or 25 % less compaction energy. In a second step, the mechanisms involved in the treatment were investigated. A microscopic study was conducted including scanning electron microscopy and mercury injection porosity tests; measurements of the surface tension of non-traditional additives mixed with water completed the study and demonstrated that the ES treatment has the same surfactant properties as sodium dodecyl sulphate, a common surfactant. Compaction tests confirmed that the behaviours of the soil after ES and sodium dodecyl sulphate treatments were similar.

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Soil treatment with organic non-traditional additives for the improvement of earthworks

: Personnel of the U.S. Army Engineer Research and Development Center (ERDC), Vicksburg, MS, and Navy Environmental Health Center (NEHC), Portsmouth, VA, evaluated the environmental fate and effects of six commercially available dust stabilizer products. As part of the evaluation, a relative risk comparison was made of the six materials to other materials that have been used historically to control dusts (i.e., diesel, crude oil, fuel oil). Data for this evaluation were obtained primarily through literature review, communication with the manufacturers of the products, and through some limited analytical chemistry. Data gaps and uncertainties were also identified and described. Conclusions were derived from the results of the evaluation, with each stabilizer group presented separately along with general conclusions applicable to all stabilizers studied.

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Environmental Evaluation of Dust Stabilizer Products

The U.S. Army Engineer Research and Development Center (ERDC) was tasked to develop a method for the in situ evaluation of unsurfaced Portland cement-stabilized soil airfields. The ability of portable in situ strength and stiffness measuring devices to determine the material properties of stabilized soils was investigated using the Clegg hammer, dynamic cone penetrometer, soil stiffness gauge, portable falling-weight deflectometer, and portable seismic property analyzer. Regression and correlation analyses were performed to develop relationships between the in situ test device measurements and the unconfined compressive strength, modulus of rupture, repeated-load elastic modulus, and falling-weight deflectometer backcalculated elastic modulus of representative materials. Relationships proposed in previous studies were found ineffective, and a precise relationship for the determination of cement-stabilized soil material properties was not discovered. As a result of this study, it has been determined that further research is required for the development of an accurate cement-stabilized soil performance model.

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In Situ Evaluation of Unsurfaced Portland Cement-Stabilized Soil Airfields

During the period March through October 2016, research was conducted at the U.S. Army Engineer Research and Development Center in Vicksburg, MS, to develop alternative backfill materials for rapid airfield damage repairs using a variety of commercially available products. The performance of a variety of additives, including 15 traditional and nontraditional materials, and a control comprised the test matrix of stabilization additives. The types of additives included cement, polymer, polyurethane, petroleum emulsion, and silicates. This report presents the technical evaluation of the laboratory and field performance of alternative backfill materials used in the subgrade of concrete repairs using Rapid Set Concrete Mix®. The additive performance criteria focused on bearing capacity, unconfined compressive strength at 2 hr and at 7 days, and durability of the specimen when partially submerged in water. Laboratory testing included mixing silty, clayey sand soil with each of the additives at specified application rates; compacting; curing; and conducting unconfined compressive strength and California Bearing Ratio testing. For the field evaluation, a repair consisted of preparing the subgrade with a selected additive and overlaying it with Rapid Set Concrete Mix®. Passesto-failure rates for each repair were determined by using an F-15E load cart at a maximum of 3,500 passes. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. ERDC/GSL TR-18-33 iii

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Laboratory evaluation of next-generation backfill materials and methods for airfield damage repair

: Personnel of the U.S. Army Engineer Research and Development Center (ERDC), Vicksburg, MS, conducted a series of laboratory experiments designed to characterize the constitutive properties of selected soil minerals and nontraditional stabilization additives. The results of these experiments were analyzed and included in this report to document the baseline characteristics prior to mixing the stabilizers and individual soil minerals. Analyses of the potential of individual stabilization products to reinforce specific soil types were conducted and reported. Additionally, an experimental modeling approach for describing the reinforcement mechanisms of individual stabilization agents was developed.

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John F. Peters

Papers

Constitutive Analyses of Nontraditional Stabilization Additives