Investigation of Geopolymer Based Soil Stabilization Methods for Expedient Airfield Pavement Surfaces
Date of Award
Master of Science (MS)
Dr. Prasad Rangaraju
Dr. Nadarajah Ravichandran
Dr. Ronald Andrus
The United States Air Force (USAF) has the unique capability of being able to interdict superior airpower anywhere, at any time. However, superior airpower is only as effective as the amount of time an aircraft can spend in a particular area. The closer an aircraft can get to the mission need, the more time that can be spent in the air, or the less time that must be spent moving in and out of the operational area. Through the use of skilled and experienced men and women, the USAF is able to apply expedient and unsurfaced airfield paving techniques that can provide the means to launch and a recover an aircraft from remote and austere locations. This keeps aircraft in the fight longer and keeps aircraft closer to where they are needed. The current techniques for providing these unsurfaced and expedient airfields, typically involve soil stabilization, and often require the use of Portland cement, a material that is in growing demand each day, and already has a significant carbon footprint. This research was performed to understand the possibility of more environmentally sound, cost effective, and better performing materials to replace Portland cement as the go-to material. In order to fully understand the processes of stabilizing an unstable soil, an in-depth look into the civilian sector’s research on soil stabilization, and the military’s history of expedient and unsurfaced airfields was taken. Doing this showed that there were potential prospects in ground glass fibers (GGF), ground granulated blast furnace slag (slag), and metakaolin for replacing Portland cement as the stabilizing agent of choice. Due to the nature of these materials being geopolymers, or materials that require alkali activation in order to create their strength, testing was done to determine the ideal solution normality in which the peak reaction occurred for these three materials. From the testing, it was determined that activator solutions of 8N NaOH for geopolymers based on GGF and 5N NaOH for slag would be used. The concentration of the NaOH alkali activator solution needed for metakaolin to react and geopolymerize was determined to be too high for this research. Once the proper solution normality was determined, soil-cement testing was done using five, ten, and fifteen percent replacement values of the geopolymers in the soil to create three-inch by six-inch cylinders. These cylinders were made using the slurry mix method commonly used in soil stabilization. These cylinders were compressed using a universal testing machine (UTM) to create stress-strain plots. These plots provided an elastic modulus of each soil-cement cylinder, and a California bearing ratio (CBR) value that was empirically derived from the elastic modulus. These values were used in the USAF standard evaluation software P-CASE to determine the viability of the materials as an airfield base course, and surface course. The materials were tested to determine the number of allowable passes and the allowable loads of a C-17A Globemaster III, and a C-130J Hercules aircraft on the airfield surface. Based on tests conducted using slurry mix method, it was determined that both slag and GGF showed the potential to be viable options that could eventually replace Portland cement as a soil stabilizing agent, however, neither material performed as well as Portland cement in the slurry mix method. From a test batch made during the research, it was shown that the dry mix method also commonly used in soil stabilization may produce significantly better results for slag and GGF compared to the slurry mix method and should be further researched. By implementing parts of this research, and conducting further testing, there is potential for cost savings, and to more effectively be able to project superior airpower.
Albertson, Brett, "Investigation of Geopolymer Based Soil Stabilization Methods for Expedient Airfield Pavement Surfaces" (2022). All Theses. 3942.