Multiscale assessment of freezing-heating effects on fine-grained geomaterials
Abstract
The overall objective of this project is to explain the evolution of critical macro-scale properties of fine-grained geomaterials (i.e., clays) due to freeze-heat cycles using thermally-induced microstructural changes. Earth surface materials are naturally subjected to temperature cycles ranging from below freezing to elevated temperatures. These temperature cycles alter the behavior of earth materials with the most critical effects occurring in slow-drainage soils such as clays. Such effects include strength loss and excessive volume changes, which can lead to catastrophic landslides, debris flows, coastal cliffs failures, excessive deformations in highways, or water/power lines breakages. Furthermore, the design of robust mobility systems for conventional and driverless vehicles requires a basic understanding of the response of earth materials, including clays, to extreme loading and weather conditions. Additionally, the development of new clay-based sealing compounds and clay-based hydrogels for various industrial and military applications requires understanding the response of these materials when subjected to the temperature cycles expected during operation. Despite this critical need for understanding the behavior of clay-rich materials subjected to freeze-heat cycles, such knowledge is currently absent mainly due to difficulties relating the clay responses at freezing temperatures to those at elevated temperatures. In this project, it is argued that identifying the changes in the microstructure of saturated clays resulting from full freeze-heat thermal cycles will facilitate explaining the evolution of various clay macro-scale critical properties over these thermal cycles including volume changes and softening yield) stress. This project adopts a multi-scale testing approach to examine the impacts of freeze-heat cycles on the clay microstructure and, consequently, their macroscale responses. The proposed research activities consider macro-scale tests and microstructural characterization experiments in four interrelated specific aims. These aims focus on determining the effects of freeze-heat cycles on volume changes and yield stress of saturated clays and identifying the underlying causes of these effects by studying the freeze-heat effects on the clay pore structure, fabric, and adsorbed water. The methods that will be employed in this project include the use of a a state-of-the-art thermo-hydro-mechanical triaxial cell capable of freezing and heating soil samples under confining pressures; and (b) bench-top microstructure characterization techniques such as Mercury Intrusion Porosimetry (MIP to measure any thermally-induced changes in the distribution of the pore sizes, gas adsorption to measure thermally-induced changes in the surface area, and various in-situ synchrotron experiments at the National Synchrotron Light Source-II (NSLS-II at Brookhaven National Laboratory BNL). The expected outcome of the proposed research is a clear understanding of the evolutions of the clay microstructure over continuous thermal cycles from freezing to elevated temperatures and the effects of these evolutions on clay behavior. This contribution will advance our understanding of the thermo-hydro-mechanical behavior of earth surface materials under cycles of extreme temperatures. Such advancements will allow incorporating temperature effects on the design of the national infrastructure. Furthermore, these outcomes will facilitate the development of new, and improve current, clay-based sealing compounds and hydrogels. Additionally, the results will facilitate increasing the effectiveness of the tires, chains, and supports of air-and-ground vehicles, which will ensure the land power dominance of the Army of 2030.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 09, 2020
- Source ID
- W911NF2010238
Entities
People
- Sherif Lotfy Abdelaziz
Organizations
- Army Contracting Command
- United States Army
- Virginia Tech