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

Lime or cement stabilizations have been used to modify wet and soft roadbed soils so that the roadbed can carry the load of construction vehicles without excessive rutting. Lime stabilization is recommended for fine-grained and high plasticity soils, and cement stabilization is recommended for coarse-grained and low plasticity soils. The durability and structural benefits of the stabilized road bed soils have been investigated in this study through four tasks. First, the in-situ conditions of stabilized subgrade were investigated using the Dynamic Cone Penetrometer (DCP) test. The results show that the moduli of stabilized soils are generally higher than non-stabilized soils several years after construction. The second task investigated the durability and strength characteristics of stabilized soils through laboratory tests. Unconfined compressive strength, California Bearing Ratio, and resilient modulus of stabilized soils are all higher than non-stabilized soils. After freezing and thawing cycles, the stabilized soils retain more strength and modulus than the non-stabilized soils. The third task evaluated the conditions of 4 test sections on State Route 2 in Erie County, with subgrade stabilized with 6% cement, 5% lime, 3% lime with 3% cement, respectively, and a control section with no stabilization. Pavement deflection measurements were taken during different stages of construction and for each of the 3 years after construction. The backcalculated subgrade moduli show that stabilization increases the subgrade modulus, with the cement treated soil being the strongest initially, followed by the 3% lime plus 3% cement section. However, the lime stabilized subgrade continues to gain strength three years after construction. The cement stabilized section has sandy soils, while the other sections have clayey soils. The fourth task developed a design procedure to quantify the increase in strength and modulus as an "effective" subgrade modulus in order to include the structural benefit of stabilized subgrade in the current pavement thickness design procedure.

Structural support of lime or cement stabilized subgrade used with flexible pavements

The use of various slags as by-products of steel industry is well established in civil engineering applications. However, the use of BOS slag in the area of soil stabilization has not been fully researched and developed despite having similar chemical composition and mineralogy to that of Portland cement. This paper reports on efforts to extend the use of BOS slag to soil stabilization by determining possible beneficial effects it may have on compressive strength and durability. Results of laboratory tests conducted on kaolinite samples stabilized with lime and treated with various percentages of BOS slag are presented. Tests determined strength development of compacted cylinders, moist cured in a humid environment at 35° C and durability by freezing and thawing method. Results showed that additions of BOS slag to kaolinite samples singularly or in combination with lime increased unconfined compressive strength and durability. These characteristics were significantly enhanced by the concurrent use of lime and BOS slag for stabilization of kaolinite.

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Effects of basic Oxygen steel slag (BOS) on strength and durability of kaolinite

Lime stabilization is used worldwide to enhance the engineering properties of problematic clayey soils; however, exposure to moisture has a detrimental impact on the longevity of lime-stabilized soils. A research study was designed and conducted to investigate the impact of stabilizer dosage and curing time before moisture intrusion on the durability and recuperative properties of lime-treated expansive soils. The soil was treated at optimum and optimum + 2% lime dosages. The stabilized soils’ behavior, before and after capillary soaking, was studied based on the strength and volume change properties of the specimens cured for 0 (6 h), 3, 7, and 28 days. The unconfined compressive strength tests were performed to study strength characteristics after moisture exposure. Furthermore, the soaked specimens were air-dried to pre-soaking moisture contents, cured again, and then tested for strength properties to study the stabilized soils’ recuperative properties. These results were also corroborated by supplementary mineralogical and microstructural studies. Test results indicate that the stabilized soils were able to completely recover from the moisture-induced damage only when exposed to moisture intrusion within a specific time window after treatment, the duration of which was governed by the stabilizer dosage. 

Durability and Recuperative Properties of Lime Stabilized Soils

A laboratory test has been developed for the evaluation of the mechanisms governing soil/geotextile drainage systems. The test is orientated toward applications that involve radial flow toward geotextile wrapped drainage pipes. The influence of any given soil, geotextile or drainage pipe combination can thus be studied. A description of the test apparatus and procedures is given. The results of a test program show that filtration behaviour is dependent on soil compaction conditions and the onset of a soil filter at the soil/geotextile interface. A comparison of various grades of a non woven geotextile showed only marginal variations in their performance. The impact of various drainage pipes were assessed and found to have minimal effect on the filtration system as a whole. The results are compared with data obtained from tests on geotextile discs located in a modified permeameter and good agreement was obtained. The validity of various retention and filtration design criteria was checked against test results and good agreement was observed (a). For the covering record of the conference, see IRRD no 808936.

A laboratory study of the retention and filtration characteristics of geotextile wrapped drainage pipes --14th arrb conference, 28 august - 2 september, 1988, canberra, act, australia; proc. parts 1 - 8

In recent years, lime stabilization of poor quality subgrade soils to upgrade quality or provide acceptable subbase material has increased in popularity as a construction alternative. However, in many situations, specifications relative to cutoff dates for lime stabilization construction have rendered the alternative unfeasible. Previous studies have revealed that soil-lime mixtures cured prior to subjection to freeze-thaw conditions undergo autogenous healing that resulted in continued strength gain. The purpose of this study was not to evaluate the ramifications of autogenous healing of soil-lime mixtures but to evaluate the behavior of soil-lime mixtures subjected to cold weather stabilization. The basic premise involved in this study was that soil-lime mixtures subjected to freeze-thaw conditions immediately after compaction would not undergo pazzolanic reactions until favorable curing conditions were attained. Soil-lime reaction that would not occur during cold weather treatment would then be renewed under favorable conditions to produce latent strength gains. The scope of this study involved the investigation of the behavior of only one soil subjected to cold weather lime stabilization. The selected soil was evaluated at only one lime content, which was established as the stabilization lime content for that soil.

Cold weather lime stabilization

The purpose of this study was to investigate the behavior of a nonwoven fabric filter in subdrainage applications. Experiments were restricted to a single fabric, Mirafi 140. Conventional aggregate filters were tested under compatible conditions to provide a basis of performance behavior. Experimental results indicate that the nonwoven fabric provides desirable performance under a relatively wide range of soil conditions. Hypotheses that relate to mechanisms controlling the behavior of the nonwoven fabric in subdrain applications are discussed. These mechanisms are, in turn, related to induced filtration and internal grading of the soil near the soil-fabric contact surface.

B Dan Marks

Papers

Cold weather lime stabilization

Investigation of filtration characteristics of a nonwoven fabric filter