Date on Master's Thesis/Doctoral Dissertation

12-2014

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Civil and Environmental Engineering

Committee Chair

Sun, Zhihui

Committee Co-Chair (if applicable)

Mohsen, J. P.

Committee Member

Kim, Young Hoon

Committee Member

Sunkara, Mahendra

Committee Member

Sumanasekera, Gamini

Subject

Portland cement; Concrete--Chemistry; Cement--Additives

Abstract

Our current knowledge on cement hydration during setting is based on the discrete observation of hydrated paste. An advanced micro/nano-level technique which can perform the in-situ observation on the continuous hydration of cement paste is demanded. In this study, Raman spectroscopy (RS) was chosen as such a method to continuously investigate wet pastes. The objective of this research is to explore the hydration process and microstructural development of fresh pastes with this technique. This research was conducted in three phases. First, the RS analysis was used to continuously observe the cement hydration from 20 minutes after mixing to 9 hours. Based on the analysis, it was found that RS was able to characterize both the cement ingredient (C3S, C2S, C3A, and gypsum) and hydration products (C-S-H gel, CH, ettringite, and monosulfate). The evolution of these components during the setting period was also detected by RS. The obtained Raman signals can indicate the end of the dormant period and initial setting in the cement paste. The RS was then expanded to study the differences in the hydration mechanisms of hardened ordinary cement paste and ultra-high performance concrete (UHPC). The silica fume included into the UHPC was found to react quickly during the first two weeks. The content changes of calcium silicates, calcium hydroxide (CH), and ettringite were different in the ordinary paste and UHPC. In the third phase, Raman chemical mapping was implemented on the hardened cement paste to explore the microstructure developments during the hydration process. A mapping protocol was developed. The obtained maps were able to correctly reflect the distributions and connections of the different paste components. From the mapping study on the cement paste, it was found that ettringite tended to locate on the surface of calcium silicates, while CH was apt to concentrate and localize in the pores as big crystals.

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