Jeb S. Tingle

Stabilization mechanisms of nontraditional additives

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 non-traditional 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 of Clay Soils with Nontraditional Additives

A laboratory experiment was conducted to evaluate the stabilization of low- and high-plasticity clay soils with nontraditional chemical or liquid stabilizers. Clay soil specimens were mixed with various stabilization products and compacted using a gyratory compaction machine to approximate ASTM D1557 moisture–density compaction. Each specimen was subjected to wet and dry testing following a 28-day cure. Twelve nontraditional stabilizers were evaluated, including an acid, enzymes, a lignosulfonate, a petroleum emulsion, polymers, and a tree resin. Additional specimens were stabilized with Type I portland cement and hydrated lime for comparison with traditional stabilizers under the same mixing, compaction, and curing conditions. Analysis of the test data consisted of determining the average strength, in terms of unconfined compressive strength, of three replicate specimens of each mixture. The average strength of the three replicates of each additive was compared with the average strength results of the remaining nontraditional additives, the traditional stabilization results, and a series of control specimens that were not stabilized. The experiment results indicate an increased strength of some nontraditionally stabilized specimens when compared with that of both the control series and the traditional stabilization alternatives. Other nontraditional stabilizers did not demonstrate significant increased strength compared with that of the control series for the conditions of this experiment. Many of the stabilized specimens were highly susceptible to moisture, indicating the potential for poor performance when exposed to adverse environmental conditions, whereas a few specimens demonstrated excellent performance when exposed to moisture. Specific product categories are recommended for stabilizing low- and high-plasticity clay soils.

Stabilization of Silty Sand with Nontraditional Additives

A laboratory experiment was conducted to evaluate the stabilization of a silty- sand (SM) material with nontraditional chemical or liquid stabilizers. SM soil specimens were mixed with various stabilization products and compacted using a gyratory compaction machine to approximate ASTM D1557 moisture—density compaction. Each specimen was subjected to wet and dry testing following the designated cure period. Twelve nontraditional stabilizers were evaluated in this experiment, including acids, enzymes, lignosulfonates, petroleum emulsions, polymers, and tree resins. Additional specimens were stabilized with an asphalt emulsion, cement, and lime to provide a comparison with traditional stabilizers under the same mixing, compaction, and curing conditions. The analysis of the test data consisted of determining the average strength, in terms of sustained load, of three replicate specimens of each mixture. The average strength of the three replicates of each additive was compared with the average strength results of the remaining nontraditional additives, the traditional stabilization results, and a series of control specimens that were not stabilized. The results of the experiment indicate increased strength of some nontraditionally stabilized specimens compared with that of both the control series and the traditional stabilization alternatives. Other nontraditional stabilizers did not demonstrate significantly increased strength compared with the control series for the conditions of the experiment. Many of the stabilized specimens were highly moisture susceptible, indicating the potential for poor performance when they are exposed to adverse environmental conditions, whereas a few specimens demonstrated excellent performance when exposed to moisture. Specific product categories are recommended for stabilizing SM soils.

Cyclic Plate Load Testing of Geosynthetic-Reinforced Unbound Aggregate Roads

A laboratory research program designed to investigate geotextile and geogrid reinforcement of the aggregate layer in unbound pavement sections was performed by the U.S. Army Engineer Research and Development Center. The investigations objective was to evaluate the performance of geosynthetic-reinforced aggregate road sections over a very soft subgrade. Standard construction materials were used to construct six aggregate road sections in a large steel box. Each instrumented road section was subjected to cyclic plate load tests to evaluate the performance of the model pavement sections under simulated truck traffic. The mechanistic response and permanent deformation of each instrumented pavement section were monitored periodically during each test. Analysis of the experiment data indicated that the geosynthetics improved the performance of the reinforced pavement sections compared with the unreinforced section in terms of improved load distribution and reduced permanent deformation or rutting. Additional i...

Empirical Design Methods for Geosynthetic-Reinforced Low-Volume Roads

Low-volume road managers are forced to focus their limited resources on higher-capacity infrastructure, with minimal funding for repairing, maintaining, or improving unpaved low-volume roads as a result. Insufficient funding requires road managers to consider the use of innovative stabilization and reinforcement materials to reduce operational costs and minimize maintenance requirements. Geosynthetic materials have been used for many years to improve the quality of low-volume roads in an effort to reduce the amount of aggregate required or to extend the service life of the pavement. The objective of this paper is to review the use of geotextiles and geogrids in unpaved roads, compare common design approaches, discuss advantages and limitations of current design methods, and seek directions for future research efforts to improve the implementation of geosynthetic technologies. This paper summarizes prior research activities to establish the historical performance of geosynthetic-reinforced unpaved roads. Once the performance benefits have been generally supported, current design methods for separation and reinforcement, including advantages and limiting assumptions, are discussed. The sensitivity of the design methods to specific input parameters is examined to provide users with an understanding of the impact of design assumptions on the resulting structural design. Design methods are compared by performing designs with different methods for a variety of site conditions. Finally, the paper discusses the essential requirements for the development of more advanced design methods.

Corps of Engineers Design of Geosynthetic-Reinforced Unpawed Roads

U.S. Army Corps of Engineers design procedure was reviewed to validate the existing criteria for geotextile-reinforced unpaved roads and to modify the criteria for the addition of stiff biaxial geogrids. Geogrid stiffness here refers to products demonstrating good torsional rigidity and aperture stability. The theoretical basis for the existing design procedure was reviewed to ensure that appropriate assumptions were used to derive the current design method. Historical test section results were used to validate the empirical bearing-capacity factors, Nc used for unreinforced and geotextile-reinforced base materials. In addition, an empirical bearing-capacity factor for geogrid reinforcement was derived to modify the existing design procedure for both geotextile and geogrid use. The relevant theory used in the development of the existing design method to establish the basis for the analyses is described. Previously unpublished test section results are presented and used to calculate experimental bearing-capacity factors, and the calculated factors are compared with the theoretical values used in the existing procedure. The results of the analyses support the use of the existing design procedure’s bearing-capacity factor for unreinforced sections; the existing bearing-capacity factor for geotextile-reinforced unpaved roads appears to be unconservative for the conditions of the full-scale test section presented. Finally, a bearing-capacity factor for the use of a geogrid and geotextile combination is recommended for modification of the existing Corps of Engineers design procedure.

Full-Scale Evaluation of Geosynthetic-Reinforced Aggregate Roads

A full-scale test section was constructed and trafficked by the U.S. Army Engineer Research and Development Center to evaluate the performance of geosynthetic reinforced aggregate road sections constructed with marginal base materials over a typical subgrade. Eight instrumented aggregate road sections–-including three different aggregate base materials and two different geosynthetics–-were constructed. The mechanistic response and permanent surface deformation of each pavement section were monitored at selected intervals during trafficking, and the data were analyzed to determine the benefit of using geotextiles or geogrids to reinforce aggregate roads. The test sections results indicated that the geosynthetics improved the performance of the reinforced pavement sections compared with unreinforced sections for all aggregate base materials. The mechanistic response in terms of surface deflection, deflection at the top of the subgrade, and vertical stress at the top of the subgrade was favorably consistent with the observed permanent deformation of the individual test items.

Evaluation of Products and Application Procedures for Mitigating Dust in Temperate Climates

An evaluation of commercial dust palliatives was conducted to determine their effectiveness in mitigating fugitive dust on roads in temperate climates. Several types of dust palliatives were tested, including polymer emulsions, a polysaccharide solution, a calcium chloride solution, and synthetic fluids. Each product was placed in an individual test section; application rates ranged from 1.8 to 3.6 L/m2 with a topical or an admix construction method (grade, spray, till, compact, spray). Water-soluble products were diluted by using one part product and three parts water. Test sections were constructed and observed for 220 days to monitor product performance. Test sections were located along training routes at Ft. Leonard Wood, Missouri, and were subjected to heavy military truck and tracked vehicle traffic. Data from stationary and mobile particle collectors were analyzed to determine the ability of each product to suppress dust for extended periods. Nuclear density tests were performed to monitor soil moisture content and density. Several products are recommended for use on roads in temperate climates as a result of this evaluation.

Full-Scale Evaluation of Geogrid-Reinforced Thin Flexible Pavements

A full-sale test section was constructed and subjected to traffic loading at the U.S. Army Engineer Research and Development Center to evaluate the performance of a geogrid that was used for base reinforcement in a thin flexible pavement. Three test items—a geogrid-reinforced test item and two unreinforced control test items—were constructed under controlled conditions. The test pavements were subjected to accelerated traffic loading to evaluate the relative performance of the pavement structures. Pavement stiffness and permanent surface deformations were measured periodically throughout the testing. The study results showed that the geogrid-reinforced pavement performed better than the unreinforced control pavements did. The results were used to develop traffic benefit ratios and effective base course structural coefficients to enable comparison of the pavement structures.

Full-Scale Accelerated Testing of Multi-axial Geogrid Stabilized Flexible Pavements

Abstract : The U.S. Army Engineer Research and Development Center (ERDC) constructed a full-scale test section to evaluate the performance of geogrid-stabilized highway pavements. The test section consisted of two pavements composed of 3 in. of hot mix asphalt over a crushed limestone base course over a 6 CBR subgrade. One section was stabilized with Tensars TX5 multi-axial geogrid, and the second section was stabilized with a developmental geogrid referred to as TX8. Each section was instrumented with moisture probes, pore-water pressure probes, temperature probes, earth pressure cells, and asphalt strain gauges. Simulated truck traffic was applied using a heavy vehicle simulator (HVS) to evaluate the rutting performance and collect instrumentation response data. This report summarizes the material characterization and construction techniques, instrumentation response, and performance response of each section under simulated truck traffic. Comparisons are drawn to previous sections constructed and trafficked at ERDC without geogrids utilizing similar construction techniques and material properties.