Pranshoo Solanki

Resilient Modulus of Clay Subgrades Stabilized with Lime, Class C Fly Ash, and Cement Kiln Dust for Pavement Design

The effects of different percentages of one traditional additive—hydrated lime—and two by-products—Class C fly ash (CFA) and cement kiln dust (CKD)—on the resilient modulus (Mr) of four different clay subgrades were investigated. It was found that at lower application rates (3% to 6%), the lime-stabilized soil specimens showed highest enhancement in the Mr values. At higher application rates (10% to 15%), however, CKD treatment provided maximum improvements. Three log-log and one semi-log stress-based models were evaluated. Validation of selected models was conducted by using additional soil data. Overall, a semi-log deviatoric and confining stress model was found to show the best acceptable performance. Additional analyses were performed to develop correlations of Mr with compacted specimen characteristics and soil and additive properties. To illustrate the application of the semi-log model, the AASHTO flexible pavement design methodology was used to design asphalt concrete pavement sections.

Laboratory Performance Evaluation of Subgrade Soils Stabilized with Sulfate-Bearing Cementitious Additives

A laboratory study was conducted on both raw and stabilized soil specimens to evaluate the performance of two subgrade soils stabilized with three different additives, namely, hydrated lime (or lime), class C fly ash (CFA), and cement kiln dust (CKD). Lime, CFA, and CKD have low sulfate (

Evaluation of Resilient Moduli of Pavement Layers at an Instrumented Section on I-35 in Oklahoma

ABSTRACT Resilient Modulus (Mr) is an important material property for pavement design and evaluation. The Mr values can be estimated in the laboratory by measuring materials response under simulated field loading conditions. It can also be determined from nondestructive tests such as the falling weight deflectometer. Some previous studies have shown, however, that the Mr values determined from laboratory testing can differ significantly from that determined from the backcalculated resilient moduli using FWD data. This paper presents the results of a site-specific comparison of the Mr values determined through laboratory testing and backcalculation of FWD data. Both laboratory and FWD data are related to an instrumented pavement section on I-35 in central Oklahoma. Unlike most previous studies that focused on FWD testing on the top of asphalt concrete, in the present study FWD tests are conducted on different layers namely, natural subgrade, stabilized subgrade, aggregate base and asphalt concrete. The study indicated increase in backcalculated Mr values due to the construction of overlying layers. For natural subgrade and aggregate base layer, backcalculated Mr values were found higher than corresponding laboratory determined Mr values. In addition, FWD tests were also performed on top of the asphalt strain gauges and earth pressure cells and strains and pressure data were collected simultaneously. A comparison of the pavement response between the predictions from a multilayer elastic program, KENPAVE, and the in-situ sensors was made.

Engineering Behavior and Microstructure of Soil Stabilized with Cement Kiln Dust

A laboratory study was undertaken to evaluate the effectiveness of different percentages of cement kiln dust (CKD) as a soil stabilizer, relative to the implementation of new Mechanistic-Empirical Pavement Design Guide (MEPDG). Cylindrical specimens were compacted and cured for 28 days in a moist room having a constant temperature and controlled humidity. After curing specimens were tested for resilient modulus (Mr), modulus of elasticity (ME) and unconfined compressive strength (UCS). The study revealed that the values of Mr, ME and UCS for the CKDstabilized specimen increased with CKD amount. Reaction products due to chemical reactions are clearly observed in the soil voids based on the micrographs obtained using scanning electron microscope (SEM), and they are responsible for the increase in modulus and strength.

Regression and Artificial Neural Network Modeling of Resilient Modulus of Subgrade Soils for Pavement Design Applications

A combined laboratory and modeling study was undertaken to develop a database for common subgrade soils in Oklahoma and to develop relationships or models that could be used to estimate resilient modulus (MR) from commonly used subgrade soil properties in Oklahoma. Sixty-three soil samples from 14 different sites throughout Oklahoma are collected and tested for the development of the database and models. Additionally, thirty-four soil samples from 3 different sites, located in Rogers and Woodward counties, are collected and tested to evaluate the developed models. The routine material parameters selected in the development of the models include moisture content (w), dry density (γ d ), plasticity index (PI), percent passing No. 200 sieve (P200), and unconfined compressive strength (Uc). Bulk stress (θ) and deviatoric stress (σ d ) are used to identify the state of stress. A total of four, two regression models, namely, Polynomial and Factorial, and two feedforward-type artificial neural network (ANN) models, namely, Radial Basis Function Network (RBFN) and Multi-Layer Perceptrons Network (MLPN) are developed. A commercial software, STATISTICA 7.1, is used to develop these models. The strengths and weaknesses of the developed models are examined by comparing the predicted MR values with the experimental values with respect to the R2 values. An evaluation of the four models indicate that for the combined development and evaluation datasets, the MLPN model is a good model for evaluating MR from the selected routinely determined properties. In order to illustrate the application of the developed model, the AASHTO flexible pavement design methodology is used to design asphalt concrete pavement sections.

A Comparative Evaluation of Various Additives Used in the Stabilization of Sulfate Bearing Lean Clay

A laboratory study was conducted on both raw and stabilized clay specimens to evaluate short- and long-term performance of three different additives, namely, hydrated lime, class C fly ash (CFA), and cement kiln dust (CKD), for providing better treatment of sulfate rich lean clay. Short-term performance evaluation experiments included Atterberg limits, resilient modulus (Mr), modulus of elasticity (ME), and unconfined compressive strength (UCS), after 28 days of curing. Long-term performance was evaluated in terms of moisture susceptibility (tube suction test) and three-dimensional swell during 120 days of capillary soaking. At the end of 120 days, specimens were also tested for Mr, ME, and UCS, as additional indicators to long-term pavement performance. Short-term performance evaluation projected 15 % CKD with highest improvement, while long-term performance evaluation showed 15 % CFA providing maximum enhancements after 120 days of capillary soaking. The study further indicated swelling of specimens stabilized with lime and CKD; however, CFA helped in reducing the swelling. All the percentages of additives used in the study helped in reducing the moisture susceptibility of clay. Mineralogical studies such as scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction were also used to verify research findings observed from the macro test results.

Evaluation of Mechanistic-Empirical Design Guide Input Parameters for Resilient Modulus of Subgrade Soils in Oklahoma

Resilient modulus ( M r ) of subgrade soil is a key input parameter in all three hierarchical levels of the new mechanistic-empirical pavement design guide (MEPDG). A successful implementation of the MEPDG requires a comprehensive evaluation of M r database(s) for local subgrade soils and its assessment to determine desired input parameters. To this end, a database containing subgrade M r values, index properties, standard Proctor, and unconfined compressive strengths for 712 soil samples from 39 different counties in Oklahoma was developed. A total of five stress-based regression models were evaluated using a statistical software package (“SPSS,” Version 17), and material constants (k1, k2, and k3) for these soils, categorized in accordance with the American Association of State Highway and Transportation Officials Classification system, were determined. The goodness of fit and the significance of these models were ranked with respect to their R2 and F values, respectively; the MEPDG recommended octahedral model was found to outperform the others. Furthermore, reasonably good correlations of material constants with routine soil properties were established for Level 2 analysis and design. Typical M r values of common Oklahoma soils for Level 3 analysis and design were also estimated. The findings of this study are expected to help the implementation of the MEPDG in Oklahoma.

Characterization of Subgrade Resilient Modulus for Pavement Design

Resilient modulus (Mr) of subgrade soil is a key design parameter in all three hierarchical levels of the new mechanistic-empirical pavement design guide (MEPDG). A successful implementation of the MEPGD requires a comprehensive Mr database for local subgrade soils and its assessment to determine desired input parameters. To this end, a database containing subgrade Mr, index properties, standard Proctor, and unconfined compressive strengths for 713 soil samples from 39 different counties in Oklahoma was developed. The Mr data was randomly divided into two datasets: (i) a “development” dataset to develop statistical models, and (ii) a “evaluation” dataset to validate these models. A total of five stress-based regression models were evaluated using a statistical software (“SPSS”; Version 17), and pertinent material constants (k1, k2 and k3) were determined for these soils categorized in accordance with the AASHTO classifications. The goodness of fit and the significance of these models were ranked with respect to their R2 and F values, respectively; the MEPDG recommended octahedral stress-based model was found to outperform the others. Furthermore, reasonably good correlations of material constants along with Mr with routine soil properties were established. The findings of this study are expected to help the implementation of the MEPDG in Oklahoma.

Effect of Wet-Dry Cycling on the Mechanical Properties of Stabilized Subgrade Soils

A comparative laboratory study was conducted to evaluate the durability of two different subgrade soils stabilized with hydrated lime, class C fly ash (CFA) and cement kiln dust (CKD). Cylindrical specimens were compacted at optimum moisture content (OMC) and cured for seven days in a moist room having a constant temperature and controlled humidity. After curing, the specimens were subjected to different wet-dry (W-D) cycles and tested for unconfined compressive strength (UCS) or resilient modulus (M r ). The UCS and M r values after W-D cycling were compared with those of the raw soil specimens to determine the influence of soil and additive type on durability. The UCS and M r values revealed that the addition of cementitious additive increased the durability of stabilized specimens against W-D cycles. The extent of improvement in durability, however, was dependent on the characteristics of both soil and additive and number of W-D cycles.

Evaluation of Mechanistic-Empirical Design Guide Input Parameters for Resilient Modulus of Stabilized Subgrade Soils

Resilient modulus (Mr) of stabilized subgrade soil is a key input parameter in all three hierarchical levels of the mechanistic-empirical pavement design guide (MEPDG). This study evaluated Mr test data of 139 samples from four types (i.e., Carnasaw, Port, Kingfisher, and Vernon series) of soils in Oklahoma modified with different amounts of lime, class C fly ash (CFA), and cement kiln dust (CKD). Regression analyses of five selected stress-based models were conducted by using a statistical software (“SPSS”, Version 17), and material constants (k1, k2 and k3) for these soils were determined. The goodness of fit and the significance of these models were ranked with respect to their R 2 and F values, respectively. A significant increase in Mr values was observed for the selected additives. However, the extent of increase in the Mr value depends on the type of soil, and type and amount of additive. Among the selected models, the octahedral model was found to outperform the others. Furthermore, correlations of material constants with routine soil parameters were established. The findings of this study are expected to help the implementation of the MEPDG in Oklahoma and can be extended to soils from any other locations.