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The mechanistic-empirical pavement design guide (M-EPDG) recommends the use of resilient modulus (MR) for characterization of subgrade soils. Subgrade soils may not always have enough strength and stiffness to support the pavement structure. Therefore, a certain type of soil improvement method using cement, lime, or other stabilization techniques is often needed to enhance the strength and stiffness properties of weak subgrade soils. The cement-stabilized soils show brittle behavior under compression loading, which can induce cracking in overlying pavement layers. In general, polymer-treated soils show a semiductile or ductile behavior. It is important to look for combined cement and polymer treatments to address brittle behavior issues as well as moisture susceptibility while maintaining strength and moduli properties. A research study was conducted to understand the strength, resilient, and ductile behaviors of sandy soils treated with cement and a combination of cement and vinyl acetate ethylene (VAE) copolymer. Engineering tests such as unconfined compressive strength (UCS) and resilient modulus tests were conducted on both control and treated soil specimens cured for 7 days. Tests were conducted on specimens before and after immersing in water bath for 4 h to investigate the moisture susceptibility. In these tests, an increase in UCS was observed after cement and cement-VAE treatments as compared to control soil specimens. Results showed that cement-VAE-treated soils exhibited an increase in the axial strain at failure, indicating the semiductile behavior compared to cement-treated specimens. An improvement in the resilient moduli was observed after treatments. Subsequently, two of three-parameter models were used to analyze resilient modulus formulations with stress conditions and determined the regression constants. In conclusion, the study revealed that the use of VAE copolymer improved the stress-strain responses of cement-treated soils and imparted closer to the semiductile behavior, which will reduce cracking in overlying pavement structures. [ABSTRACT FROM AUTHOR]

A research attempt was made to design a controlled low-strength material (CLSM) mix that can be used as bedding and haunch material for a pipeline by using the native soil as fine aggregate. Several CLSM mix designs were attempted using native high-plasticity clay as fine aggregate material. Comprehensive material characterization studies including flowability to strength tests were performed. These results were analyzed to address the applicability of each mix to serve as pipe bedding/backfilling zones in a pipeline construction. Both flowability and density test results are first evaluated, and as a result, several mixes are formulated. These mixes were further subjected to engineering characterization-related studies, and this paper presents these test results. Setting time, strength, and stiffness results as well as excavatability evaluations of these mixtures are covered as a part of these studies. These results indicate that the CLSMs can be produced using native high-plasticity soils with strength properties always matching specified requirements. Certain relaxation on setting time periods could further help in developing economical mix designs. CLSMs that meet project specifications are recommended for field implementation. [ABSTRACT FROM AUTHOR]

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Abstract: Organic soils are mostly composed of decayed plant matter and weathered rock material. Often, these soils are known for their inferior engineering behavior including very high compressibility and low shear strength. In order to improve these properties, organic soils are, by and large, modified with calcium based stabilizers such as lime, cement and fly ash. However, transportation agencies in the United States have mentioned that the anticipated improvements were never achieved or the improvement obtained disappeared quickly with time. Therefore, a research study was initiated to understand the behavioral mechanisms of lime and cement stabilized organic soils. Eight natural expansive soils bearing different organic contents (varying between 2 and 6%) were selected for the present investigation. First, optimum dosages of lime and cement were determined for the selected soils. Then treated and untreated (control) specimens were prepared to study their physical and engineering behaviors of the soil specimens at varied curing periods. There is a drastic increase in unconfined compressive strength (UCS) of lime and cement treated specimens until 28days of curing. Beyond which, a negligible improvement in UCS property was recorded for lime treated specimens and a slight decrease in UCS for cement treated soils was noticed. This reduction in strength for cement treated specimens could be attributed to the reduction in pH concentration with curing as well as the formation of inorganic calcium humic acid at this stage. [Copyright &y& Elsevier]

The use of reclaimed asphalt pavement (RAP) materials in road construction has been proven to reduce both the amount of construction debris disposed of in urban landfills and the rate of depletion of natural resources. However, source-dependent product variability, federal and local environmental regulation, and deficient strength-stiffness characteristics often limit RAP applications in road bases. These limitations have led to new research efforts aimed at exploring novel, cost-effective, chemical and/or mechanical stabilization methods to treat RAP materials before their reuse in pavement construction. In this work, a series of tests were performed on RAP aggregate materials treated with different dosages of portland type I/II cement and with alkali-resistant glass fibers. Tests include permeability, leachate, unconfined compression, and small-strain shear moduli through resonant column testing. Leachate tests include pH, total and volatile dissolved solids, total and volatile suspended solids, and turbidity. Test results confirm the potential of cement-fiber-treated RAP material as an environmentally and structurally sound alternative to nonbonded materials for base and subbase applications in pavement engineering. A companion paper presents the results from a comprehensive repeated-load triaxial test program to investigate the resilient modulus characteristics of cement-treated RAP. [ABSTRACT FROM AUTHOR]

The use of reclaimed asphalt pavement (RAP) aggregate materials in road construction reduces natural resource depletion and promotes the recycling of RAP materials for other applications. However, product variability and low resilient moduli characteristics often limit RAP applications in road bases. Stabilization of RAP materials with cement was hence attempted in a research study to evaluate the effectiveness of cement treatments in enhancing resilient characteristics of RAP aggregates. The present paper describes the results from a series of resilient modulus tests that were conducted in a laboratory environment using a repeated load triaxial test setup. The effects of three different cement dosages and various confining and deviatoric stress levels on the resilient modulus (MR) response of treated RAP materials were studied. MR values of untreated and cement-treated RAP aggregates ranged from 180 to 340 MPa and 200 to 515 MPa, respectively, which reveal the enhancements with cement treatment. Regression modeling analyses of MR test results, by using two- and three-parameter models, are also presented. The analyses show that both models are reasonably capable of capturing the effects of stress levels on treated RAP resilient properties. Test results were also analyzed to determine structural coefficients for pavement design purposes, which ranged from 0.16 to 0.22, suggesting a greater structural support of cement-treated RAP layers when compared with untreated aggregates. [ABSTRACT FROM AUTHOR]

This paper presents the process and results of a quality management program performed during and immediately after the construction of two deep soil mixing (DSM) test sections. The quality management program consisted of laboratory, in situ, and mineralogical tests to address the effectiveness of the treatment during and after construction. In situ investigations including the down-hole seismic and spectral analysis of surface waves (SASW) test methods were performed to evaluate the degree of improvement achieved through the measurement of compression and shear-wave velocities of the columns and surrounding soils. Scanning electron microscopy and electron dispersive x-ray analysis were performed on raw, laboratory treated and field-treated specimens for qualitative understanding of the degree of mixing achieved in the field and the compounds formed at particle level during stabilization, respectively. Laboratory tests results on field cores indicated that both field stiffness and strength are about 20 to 40% less than the corresponding laboratory prepared soil samples. The down-hole seismic and SASW tests showed considerable improvement in stiffness in and around the DSM columns. Mineralogical studies indicated the formation of silica and alumina hydrates along with interwoven structure of lime-cement treated clay particles in both laboratory and field specimens, suggesting adequate mixing of the soil and binder in both environments. [ABSTRACT FROM AUTHOR]

Performance of pavements has been affected by heave distress problems caused by sulfate rich soils treated with calcium-based stabilizers. A research study was conducted to address the effectiveness of sulfate resistant cement stabilizers Types I/II and V, for providing better treatment of sulfate rich soils. Experiments were designed and conducted on both control and cement treated sulfate soils to investigate compaction relationships, Atterberg limits, linear shrinkage and free swell strain potentials, unconfined compressive strength, and low strain shear moduli properties. This paper presents a comprehensive summary and analysis of these test results. Test results were statistically analyzed to study the potentials of sulfate resistant cement stabilization methods for significant enhancements to the strength and stiffness properties as well as reductions in swell and shrinkage strain potentials of natural sulfate rich soils. Mineralogical studies were used to verify research findings observed from the macro test results. [ABSTRACT FROM AUTHOR]

The authors respond to comments on their research "Studies of Sulfate-Resistant Cement Stabilization Methods to Address Sulfate-Induced Soil Heave," previously published in the "Journal of Geotechnical and Geoenvironmental Engineering." They would like to thank the discussers for their positive remarks and would like to offer the following explanations for the comments raised on their paper. Overall, these comments can be summarized into three areas: 1) sulfate soil selections in the treated soils; 2) sulfate measurement procedural steps; and, 3) sulfate mineral formed during chemical treatment.