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- This Ph.D. dissertation compiles studies that are part of the Microgravity Investigation of Cement Solidification (MICS) research project. The goal of MICS is to explore how cement solidifies in the absence of gravity by conducting experiments aboard the International Space Station (ISS). For the first time, the initial contact between cement and water, and the entire hardening process took place in a microgravity (g) environment, which corresponds to 10-6 of the terrestrial gravity (1g). After 6-10 weeks from initial hydration, the samples returned to Earth for a microstructural characterization and a comparison to the ground-control samples.The characterization of the hardened cement paste consisted of utilizing advanced experimental techniques to obtain qualitative and quantitative data on the microstructure of ground- and space-processed cement pastes. The observed microstructural differences between space and ground specimens are those formed through physical mechanisms dominated by gravity. The hypothesis states that upon minimizing gravity-driven phenomena, such as buoyancy, sedimentation, and thermosolutal convection, cement forms its skeletal structure through a diffusion-controlled mass transport, in case of diluted paste. In case of concentrated cement paste, colloidal forces dominate over diffusion and over gravity forces, regardless of being under terrestrial gravity or microgravity, all of it happening prior to setting.The benefits promoted by isolating hydration from the complications caused by gravity are twofold. It can empower the understanding on how terrestrial gravity affects the microstructure of cement-based materials. In particular, this research addresses bleeding in cement pastes in absence and presence of chemical admixture. Understanding and minimizing bleeding in cement-based materials improve their efficiency and durability, which ultimately promotes sustainability. As importantly, this research provides fundamental knowledge about materials processing in absence of gravity, which is a prerequisite for long-duration space missions.In addition to the MICS cement solidification endeavor, efforts have also been made to characterize a lunar regolith simulant - JSC 1A as a construction material. A thorough investigation of the material from a construction point of view was necessary for a more comprehensive understanding of JSC-Portland cement blended mixtures. Ultimately, the study will assist with the choice of an appropriate precursor to activate and bind JSC 1A with in-situ extraterrestrial resources.The topics presented and discussed throughout this manuscript are subdivided in four chapters, as follows:Chapter 1: IntroductionIt provides background about the cement and its main constituents, as well as describes the main concepts discussed throughout this dissertation. Chapter 1 also presents the research objectives and research motivation.Chapter 2: Microgravity Effect on Microstructural Development of Tri-calcium Silicate (C3S) Paste Made with High Water-to-Cement RatioThis chapter covers the most pronounced differences and similarities in the microstructure of g hydrated C3S paste in comparison to the 1g-control. Relevant observations led by the presence or absence of gravity, including bleeding effect, density, and crystallography are also presented and discussed in detail.Publications: Moraes Neves, J., Collins, P, Wilkerson, R.P., Grugel, R.N., and Radliska, A. (2019). Microgravity Effect on Microstructural development of Tri-calcium Silicate (C3S) Paste. Frontiers in Materials - Structural Materials Vol. 6, Article 83, P.1-12. Juliana Moraes Neves, Aleksandra Radliska, Richard Grugel and Barry Scheetz. (2019) Experimental Investigation of Cement Hydration in Gravity-free Environment. Proceedings on the 15th International Conference on the Chemistry of Cement (ICCC). Paper ID: 269.Chapter 3: The Role of Water-to-cement Ratio and Superplasticizer on the Microstructure of Cement Paste Hydrated in Microgravity:The analysis of three portland cement-based sets of samples were carried out in a similar fashion as the C3S paste, discussed in Chapter 2. In addition to the gravity level, this research presented a more comprehensive comparison among the mixtures by varying the amount of mixing water and addition of a superplasticizer. New insights on bleeding effect are presented, which can advance the understanding of its influence on the microstructure of hardened paste. Chapter 4 Characterization, Mechanical Properties, and Microstructural Development of Lunar Regolith Simulant-Portland Cement Blended Mixtures This chapter describes JSC-1A, a lunar regolith simulant similar to samples brought back from the Moon by Apollo 14, 16, and 17, as a potential construction material. The chapter advances the critical, prerequisite knowledge for the construction of shelters on the Moon, in support of longer extraterrestrial missions, such as Artemis. Submitted as a journal paper to the Construction and Building Materials journal, under review.Chapter 5: Conclusions This Chapter summarizes the main findings and their implications, as well as elucidations of future research.
- Dissertation Note:
- Ph.D. Pennsylvania State University 2020.
- Technical Details:
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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