Browsing by Subject "Thickness"

Now showing 1 - 3 of 3

Increased Single-Lift Thicknesses for Unbound Aggregate Base Courses
(1998-10) Allen, John J.; Bueno, Jaime L.; Kalinski, Michael E.; Myers, Michael L.; Stokoe, Kenneth H.
A study was conducted to evaluate the feasibility of compacting unbound aggregate base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of material types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone. Three crushed granite test sections were built as part of a road widening project in Georgia, and two test pads were constructed of uncrushed and partially crushed gravel with loess fines at a gravel production facility near Memphis, Tennessee. Single-lift thicknesses varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of-Surface-Waves (SASW) technique, was used to evaluate stiffness profiles within the compacted lifts. Cyclic plate load tests were accomplished by means of the Rolling Dynamic Deflectometer (RDD), modified for this static application. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.
Optical characterization of emerging electronic and ferroelectric materials and structures
(2019-04-05) Cho, Yujin; Downer, Michael Coffin; Demkov, Alexander A.; Lai, Keji; Zhou, Jianshi; Sitz, Greg O.
My Ph. D. work is on altering material properties to improve or apply in device applications and probing the manipulated properties through linear/ nonlinear optical methods. I focused my study on three types of structural modifications. First, in Chapter 2, I applied strain on a 3D integrated silicon circuit structure and BaTiO₃ thin film. Silicon, well-understood bulk material and most popular semiconductor platform, acquires new electronic and optical properties under strain. In addition, one can significantly control the ferroelectric and electro-optic properties of BaTiO₃ thin film, a traditional perovskite ferroelectric, by applying strain via a piezoelectric substrate, as shown in Chapter 5. Second, I engineered well-characterized bulk materials into thin films, as thin as 1 nm. In Chapter 4, I measured retention time of ferroelectric polarization on BaTiO₃ film thicknesses in the range of 10-20 nm. In addition, the thickness of the layers of a 2D material, e.g. In₂Se₃, introduces variations in bandgaps, dielectric functions, and/or absorption, which will be shown in Chapter 6. Lastly, I characterized the displacive and disorder-to-order transitions in ferroelectric materials. For example, in Chapter 3, we discovered order-disorder ferroelectric mechanism in double perovskites synthesized by Spark-plasma-sintering method and studied their Curie temperatures. Through these projects, I discovered new ways of controlling material properties and studied their underlying origins of the emerging phenomena using optical methods
A Study on the Feasibility of Compacting Unbound Graded Aggregate Base Courses in Thicker Lifts Than Presently Allowed by State Departments of Transportation
(1998-10) Bueno, Jaime Luis; Stokoe, Kenneth H.; Allen, John J.
A study was conducted to evaluate the feasibility of compacting unbound aggregates base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of materials types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone, and three crushed granite test sections were built as part of a road widening project in Georgia. Single-lift thickness varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of Surface-Waves (SASW) techniques, was used to evaluate stiffness profiles within the compacted lifts. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.