Microgravity's Influence on the Hydration of Tricalcium Aluminate and Gypsum Pastes
Open Access
- Author:
- Collins, Peter
- Graduate Program:
- Civil Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 08, 2019
- Committee Members:
- Aleksandra Z Radlinska, Thesis Advisor/Co-Advisor
Farshad Rajabipour, Committee Member
Sven G Bilen, Committee Member
Barry Earl Scheetz, Committee Member
Richard N Grugel, Committee Member
Patrick Joseph Fox, Program Head/Chair - Keywords:
- tricalcium aluminate
gypsum
microgravity
cement
hydration
International Space Station - Abstract:
- The hydration of cement is well known to be a complex, multiphase process that continuously transpires. A variable that has not been discussed in-depth to date is the influence of gravity on the kinetics of the hydration process. It is envisioned that humans will embark on space exploration missions for extended periods of times which leads to the need for resilient habitats and other pieces of infrastructure. Specifically, as part of the Artemis program, a sustained human presence on the Moon is set for 2028 and it is likely that a cement-like binder from in-situ materials will be used for space habitats. Consequently, the kinetics of cement hydration in extraterrestrial context needs to be better understood as it will likely be different than on Earth. As a first step, various samples were sent to the International Space Station to mix and hydrate in the microgravity environment (10-6 g relative to Earth’s gravity). The lack of gravity minimizes transport phenomena due to gravity such as fluid convection and buoyancy. Consequently, this leads to a diffusion-controlled hydration process. At early ages, this promotes enhanced concentration of the reaction products about the decomposing phases. This phenomenon is evident when tricalcium aluminate (C3A) and gypsum samples hydrated in microgravity are compared to an otherwise identical Earth-based samples. In microgravity, the gypsum experiences morphological differences during dissolution and ettringite is seen to grow on the gypsum along with adjacent pockets of monosulfate. C3A and gypsum make up a minor part of portland cements but play a substantial role in the early age kinetics. The addition of gypsum to portland cements hinders the rapid reaction of the C3A with water, effectively negating a flash set. Gypsums phenomenon in hindering the reaction of C3A is what allows for concrete to be mixed, transported, placed, and finished before setting on Earth. Such a phenomenon needs to be understood as a function of gravity in order to lead toward effective mixture designs for a cement-like binder using in-situ planetary materials. Here it is noted that the amount of gypsum within the mixture plays a substantial role in the microstructural development in microgravity as compared to a terrestrial gravity sample.