This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

Three testing methods for predicting the durability of cement-stabilized soils—the tube suction (TS), 7-day unconfined compression strength (UCS), and wetting–drying durability tests—were tested and compared for their correlations and influence factors using a problematic low plastic silt clay from subgrade commonly encountered in Louisiana. A series of samples was molded at six different cement dosages (2.5, 4.5, 6.5, 8.5, 10.5, and 12.5% by dry weight of the soil) and four different molding moisture contents (15.5, 18.5, 21.5, and 24.5%). The test results indicate that the water–cement ratio of cement-stabilized soil had the dominant influence on the maximum dielectric value (DV), 7-day UCS, and durability of stabilized samples tested, although the dry unit weight of cement-stabilized soil could cause the variation of the results. This study confirms that TS, 7-day UCS, and wetting-drying durability tests are equivalent in predicting durability, and tentative charts to ensuring the durability of cement-...

Durability of Cement Stabilized Low Plasticity Soils

Treatment and Improvement of the Geotechnical Properties of Different Soft Fine-Grained Soils Using Chemical Stabilization

Strength and deformation characteristics of compacted silt from the lower reaches of the Yellow River of China under monotonic and repeated loading

Chemical stabilizers are commonly used to improve the performance of problematic soils. Lime, cement, and fly ash are typically used for this purpose. To achieve effective soil stabilization, type and concentration of the stabilizer are usually calculated based on the plasticity and gradation of the material. To achieve the mix design, the optimum stabilizer content is usually based on experience or following time-consuming specifications. New accelerated testing methods are proposed that minimize the time required for soil specimen preparation, curing, and moisture conditioning to complete the design process. Proposed methods were compared to current specifications. A curing time of 2 days and a back-pressure method to complete moisture conditioning are recommended to complete the mix design in 3 days. In addition, a more rigorous soil classification which considers the soil mineralogy is included. For that matter, simple chemical methods to determine the mineralogy of the soil fines are included. Cation Exchange Capacity, Specific Surface Area and Total Potassium could be used to substitute methods such as X-ray Diffraction and Scanning Electron Microscope. Durability and permanency studies on the treated and untreated soils were also evaluated to address the permanency and leachability of the chemical stabilization associated with rainfall infiltration and to simulate seasonal changes. Other important issues that were evaluated are adequate mixing and curing, adequate density and moisture, adequate short-term and long-term strength and stiffness, and proper construction.

Accelerated Stabilization Design of Subgrade Soils

Many areas of Louisiana consist of soils with high silt contents, low strengths, and minimal bearing capacity. Construction traffic in these soils can cause detrimental pumping action in areas with a high water table. These wet subgrades under Louisiana pavements cause both construction and performance problems. Common solutions to the problem include excavation and replacement, lime treatment, or cement stabilization. Special provisions are often included in the contract for chemical additives in lieu of undercutting. The research emphasis of this study was placed on efforts to refine the pumping problem and on the development of guidelines for identifying the problem silt-soils. Secondary importance was given to the identification of alternate methods for stabilization. The study consisted of two phases. Phase 1 documented the field experiences of the Louisiana Department of Transportation and Development (DOTD) districts. Phase 2 consisted of a testing program to investigate the nature of the problem, the character of the silt materials, and their performance with modifying and stabilizing agents. Eight soil samples from four of the DOTD districts were used in the laboratory program. The soils were typical examples of those commonly encountered with a high-silt content. Several were acquired from current projects in which pumping problems were occurring. The basic characteristic-parameters of the natural samples were determined with standard laboratory tests. The response and stability of the silts under compaction and loading with various moisture levels and compaction efforts were also tested. The susceptibility to pumping of the different samples was reviewed in terms of their physical characteristics. In addition to the silt content percentage, the plasticity character was noted as significant during testing. Anomalies were also found to exist between the DOTD's earthwork specifications and the physical properties of the high silt-content soils. The potential for the modification and stabilization of the problem silt soils was also studied. The laboratory tests were selected with respect to construction needs and possible post construction conditions. A limited number of specific additives were proposed with consideration for their ability to dry the subgrade silts sufficiently in order that they be compacted and with the strength to provide a working table for the construction of the base and pavement. The additives selected included hydrated lime, portland cement, and Class C fly ash. Limited tests for evaluating long-period stability of the stabilized silt-subgrade subjected to accelerated curing followed by vacuum-saturation conditions were also conducted.

M. Nataraj

Papers

Identification and stabilization methods for problematic silt soils