Characterization and Modeling of Unbound and Cementitiously Stabilized Materials for Structural Analysis of Multilayer Pavement Systems
The incorporation of cement for soil improvement is a sustainable solution for utilizing marginal materials in the construction of new pavements and the rehabilitation of existing roadway systems. To effectively design and assess the performance of pavement structures, it is crucial to determine the strength and resilient properties of cementitiously stabilized aggregates. Accurate determination of the Unconfined Compressive Strength (UCS), tensile strength, and Resilient Modulus (Mr) is of utmost importance for thoroughly characterizing the structural capacity of pavement layers through a mechanistic approach. The tensile strength of stabilized materials can be assessed in a laboratory setting through the implementation of two widely employed testing techniques: the flexural beam test and the Indirect Diametrical Tensile (IDT) strength test. Previous studies have shown that the split tensiontype testing setup is a more reliable method compared to the traditional bending beam test due to its practicality, consistency of results, adherence to theoretical principles, ease of specimen preparation, and uniform distribution of the stabilizer (Wang & Huston 1972, Kennedy & Hudson 1973, Dempsey et al. 1984, Thompson 1965a, Piratheepan & Gnanendran 2008, Gnanendran & Piratheepan 2010, Ashtiani & Tarin 2016). The resilient characteristics of stabilized materials can be evaluated through stress-path laboratory testing, which is a complex, time-consuming, and costly procedure. The testing involves exposing specimens to uniform static confining stresses and axial cyclic loading within a triaxial chamber, while monitoring stresses and strains to determine the resilient behavior of the cement-treated samples (Lee et al. 1997, Hossain & Kim 2015). Due to the increasing demand for accelerated mixture design methods and the resource-intensive nature of conducting a full set of laboratory tests, many transportation agencies do not conduct all of the recommended tests to accurately determine the material properties required for design input parameters. As a result, pavement engineers often rely on past experiences or readily accessible correlation equations to design and analyze cementitiously stabilized layers. This dissertation sheds light on the relationship between the IDT strength and the UCS, as well as the correlations between the Mr and the UCS of cementitiously stabilized virgin and reclaimed materials from various aggregate sources, under varying stabilizer content and moisture susceptibility conditions. The results of this study will prove valuable for engineers and design agencies as they aim to enhance their predictions of the IDT strength and Mr of virgin and reclaimed materials stabilized with cement. A parallel aspect of this dissertation is related to the laboratory preparation of cementtreated specimens. Proper compaction of these specimens is essential for obtaining accurate and reliable strength and resilient property measurements of both unbound and cementitiously stabilized materials. The commonly used method for preparing specimens in the laboratory is a variation of the Proctor compaction procedure, which is widely adopted by design practitioners and pavement agencies (Browne 2006, Cerni & Camilli 2011, Arabali et al. 2018, Yaghoubi et al. 2018). Despite some variations in details such as mold geometry, hammer weight, number of layers, and number of blows per layer (Du et al. 2018), the fundamental mechanism of Proctor compaction, which involves the application of loads imparted by an impact hammer, remains consistent across different pavement design agencies. It is widely acknowledged that laboratory compaction procedures, which involve the use of impact energy, diverge greatly from the traditional compaction methods employed in the field (Sebesta & Liu 2008). The compaction of pavement layers during construction is accomplished through a combination of kneading, vibration, and static pressure (Browne 2006). However, the Proctor compaction method in the laboratory imitates field compaction by dropping a hammer from a specified height (Cerni & Camilli 2011). The aim of this dissertation is to explore the effect of laboratory compaction methods on the pore structure and strength properties of cementitiously stabilized materials. The homogeneity, quality, and distribution of pores in laboratory-compacted specimens can greatly impact the reliability of data used for the design and analysis of pavement structures. To address this issue, the study focuses on the examination of virgin and reclaimed aggregates stabilized with cement from various sources. The investigation aims to determine the interaction between material type, cement content, and compaction energy on the orthogonal strength properties of the cementitiously stabilized mediums. The main final aspect of this dissertation is concerned with the study of the structural behavior of a particular type of multilayer pavement system known as inverted pavement, which comprises a cementitiously stabilized layer within its structure. This type of multilayer pavement structure consists of an asphalt-wearing course, an unbound aggregate layer at the bottom, and an underlying cement-treated layer placed on top of the subgrade soil. Unlike traditional pavements, where the stiff layer is located near the surface, the location of the cement-treated layer in an inverted pavement system results in unique interaction between layers of varying rigidity when subjected to traffic-induced stress paths and environmental conditions. To fill the gap in the limited number of studies about the design, mechanical response, and performance of inverted pavement structures, this dissertation presents and analyzes the nondestructive in-situ test results from full-scale inverted pavements constructed on Bull Run Route 659 in Virginia. Ground Penetrating Radar (GPR) was utilized to verify the layer thicknesses, while Dynamic Cone Penetrometer (DCP) and Falling Weight Deflectometer (FWD) testing was performed to analyze and compare the deformation characteristics of inverted and conventional pavement structures loaded under controlled conditions. Moreover, the stiffness properties of the unbound granular layer of the inverted layered system were studied based on the DCP results. In addition to the DCP and FWD testing, the inverted section and adjacent conventional road segment were instrumented with different sensing devices embedded within the pavement structures. The instrumentation plan aimed to monitor the mechanical responses of the layers under controlled traffic loading conditions at certain critical depths. Lastly, a backcalculation analysis was carried out, using the deflection values obtained from the in-situ FWD testing to calculate the modulus values of each layer of the inverted pavement. The collected data from the in-situ testing was used to conduct a finite element (FE) numerical analysis that compared the mechanical response of the Virginia inverted pavement section to an equivalent conventional design, where the order of the two layers located beneath the asphalt concrete layer was switched. The numerical simulations performed based on the Virginia inverted pavement were replicated on another inverted pavement section built on State Highway SH-123 in Texas, which had a different layer arrangement and unique material characteristics. The layer thicknesses were obtained through in-situ GPR testing and the Modulus values of each pavement layer were estimated from FWD test outcomes. The Texas inverted structure was compared to an equivalent conventional design obtained by rearranging the order of the two layers located below the bituminous superficial layer of the inverted pavement. Two distinct loading scenarios were considered for the Texas inverted pavement section: conventional heavy vehicles and Super Heavy Loads.
Civil engineering|Materials science
Rodriguez Velasquez, Edgar Daniel, "Characterization and Modeling of Unbound and Cementitiously Stabilized Materials for Structural Analysis of Multilayer Pavement Systems" (2023). ETD Collection for University of Texas, El Paso. AAI30424697.