Browsing by Author "Roy H. Borden, Committee Co-Chair"

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Investigation of the Effect of Lime on Performance of Hot Mix Asphalt using Advanced Testing and Modeling Techniques
(2008-08-21) Lee, Sangyum; Kimberly S. Weems, Committee Member; Murthy N. Guddati, Committee Member; Roy H. Borden, Committee Co-Chair; Y. Richard Kim, Committee Chair
The benefits of using hydrated lime as an additive in asphalt concrete are well known. When added to asphalt concrete mixtures hydrated lime shows the beneficial effects of filler, while also improving resistance to moisture damage. This study presents findings from four studies into the impact of hydrated lime, the impact of lime introduction method on the volumetric optimums, and the performance evaluation of unmodified and lime-modified hot mix asphalt (HMA) mixtures at varying asphalt contents using Simple Performance Tests developed from the NCHRP projects 9-19 and 9-29 and the viscoelastic continuum damage (VECD) finite element analysis. The performance characteristics evaluated in this study include fatigue cracking and rutting behavior in both dry and moisture-conditioned states. Test methods adopted in this evaluation are: the dynamic modulus test for stiffness characterization; the triaxial repeated load permanent deformation test for rutting characterization, and the direct tension test for fatigue cracking characterization. From the experimental investigation it is found that the method of lime introduction can have an important effect on the optimum volumetric asphalt content. Regarding dynamic modulus it is found that hydrated lime has a minimal impact on the mixtures in this study. However, the findings from this study support conventional understanding of the effects of asphalt content, lime modification, and moisture conditioning on the fatigue cracking and rutting performance of HMA mixtures. That is, as asphalt content increases, the resistance to fatigue cracking improves and rutting performance worsens. Another accepted fact is that lime modification reduces the susceptibility for moisture damage in terms of both fatigue cracking and rutting. The contribution of this paper, therefore, is to demonstrate advanced test methods and models that can be used in the performance evaluation of various mixtures. With additional validation and calibration, the comprehensive methodology described in this paper may serve as the foundation for a performance-based HMA mix design and performance-related HMA specifications.
Long-Term Performance Assessment of Asphalt Concrete Pavements Using the Third Scale Model Mobile Loading Simulator and Fiber Reinforced Asphalt Concrete
(2004-03-14) Lee, Sugjoon; Roy H. Borden, Committee Co-Chair; Hechmi Hamouda, Committee Member; Jon P. Rust, Committee Co-Chair; Y. Richard Kim, Committee Co-Chair; Murthy N. Guddati, Committee Member
Long-term pavement performance such as fatigue and rutting is investigated using the third scale Model Mobile Loading Simulator (MMLS3). Prediction algorithms are proposed that can account for the loading rate of MMLS3 and temperature variation along the depth of pavement. In a separate study, influence of fibers on the fatigue cracking resistance is studied. In this research, laboratory asphalt pavement construction technique, sensor instrumentation, and test conditions are evaluated to establish effective test protocols for fatigue cracking and rutting evaluation using the MMLS3. The investigated results present that: (1) the MMLS3 with wheel wandering system can induce the realistic fatigue (alligator pattern) cracks; (2) using wavelet correlation method (WCM), fatigue damage growth and microdamage healing are observed; (3) the algorithm for the fatigue life prediction of laboratory pavement is established using the indirect tension testing program and linear cumulative damage theory; (4) the MMLS3 performs a rapid assessment of the rutting potential under controlled conditions; (5) the predictive algorithm predicts rutting performance of asphalt pavements loaded by the MMLS3 using the repetitive cyclic triaxial compression testing program. It was found that fiber inclusion can improve the mechanical properties of asphalt concrete. Single nylon fiber pullout test was used to investigate debonding and pulling behavior. As for indirect tension strength tests, asphalt concrete containing nylon fibers showed the potential of improving fatigue cracking resistance by an increase of the fracture energy.
A Numerical Investigation of the Effects of Loading Conditions on Soil Response
(2009-03-27) Zhao, Xueliang; T. Matthew Evans, Committee Chair; Roy H. Borden, Committee Co-Chair; Mohammed A. Gabr, Committee Member; M. Shamimur Rahman, Committee Member; Murthy N. Guddati, Committee Member; C. C. David Tung, Committee Member
All three principal stresses play a part in the stress-strain-strength response and volumetric behavior of solids and granular materials. In geotechnical engineering, conventional triaxial compression (CTC), plane strain (PS), and direct shear (DS) are the three most commonly used laboratory tests to simulate the field conditions. It is natural to assume that specimens subjected to different loading conditions will show different responses and behaviors. In reality, many soil problems involving shear strength approximate to PS loading conditions in the field (e.g., earth dam, embankment, and retaining wall). However, CTC or DS test is typically used to measure the stress-strain-strength parameters for design because of their simplicity and versatility compared with the complexity and difficulty of the PS test, even though they might not closely mimic the field condition. The current research focuses on the numerical analysis of effects of different loading conditions (e.g., CTC, PS, and DS) on the macro- and micro-behaviors of granular materials using discrete element method (DEM). Analytical, statistical, and stereological approaches are employed. It is the first work to compare the results under the three most common loading conditions (PS, CTC, and DS) in DEM modeling. Models of the CTC, PS, and DS tests are developed. A new method to simulate the membrane behavior is proposed. Parametric analyses to qualitatively assess the effects of the specific parameter on the macroscale response of the specimen are performed. Macroscale responses of sets of simulations of assemblies under PS, CTC, and DS loading conditions are studied. Small-strain responses, shear strengths, and volumetric behaviors of the assemblies under different loading conditions are investigated. Microscale analyses on the assembly behaviors (e.g., void ratio and coordination number) and particle behaviors (e.g., particle rotation and displacement) are conducted. Particle orientation and contact properties (e.g., contact normal and contact force) are investigated using statistical analysis method. An algorithm to generate numerical slicing images which is to simulate the way in laboratory experiments is proposed. The local void ratio distribution analysis and particle orientation distribution analysis are performed using stereological method. Integrating macro-, micro-, and stereological methods, some issues such as strain localization, critical state, and principal stress direction rotation of DS test are investigated.