Civil Engineering ETDs

Author

Emilia Foley

Publication Date

8-30-2011

Abstract

Calcium Silicate Hydrate (C-S-H) constitutes two-thirds of hydrated cement paste by volume. Having a better understanding of the mechanical properties of C-S-H will significantly aid in future effort for making concrete by design' for specific applications such as blast resistance. C-S-H is an amorphous compound whose chemical structure has been debated by researchers for years. It has been found that C-S-H can form with a wide variety of calcium to silicate (C/S) ratios, and it is the intent of this thesis to determine the effect of the C/S ratio on mechanical properties, most specifically elastic modulus of C-S-H. By varying the calcium and silicate ratios as well as the density of the material, relationships can be formulated between these properties and the mechanical properties of the material. As C-S-H is an amorphous substance, its chemical composition can vary widely depending on the ratio of the raw materials mixed and the water-cement ratio. Here, C-S-H is synthesized at room temperature and atmospheric pressure by producing calcium oxide (CaO) using calcium carbonate and then mixing it with fumed silica (SiO2) and enough deionized water to make slurry. The slurry was continuously mixed for 7 days, after which the excess water was removed. C/S ratios of 1.5, 1.2, and 0.9 were synthesized. In addition, C-S-H with a C/S ratio of 1.5 was synthesized under high temperature (80\u25e6C) and pressure (10 MPa, 98.7 atm). The resultant C-S-H was dried to a set water level using two standard techniques known as D-drying and equilibration to 11% relative humidity (RH). The C-S-H was then chemically and mechanically characterized. The dried powders were characterized using thermogravimetric analysis (TGA), x-ray diffraction analysis (XRDA), and 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The characterization confirmed the formation of C-S-H with high purity. It also identified the level of silicate polymerization and its correlation to the stiffness of C-S-H. The powders were then compacted to create specimens with porosities similar to C-S-H in cement. The specimens underwent nanoindentation experiments to mechanically characterize C-S-H. These experiments provide insight on the nanoscale mechanical characteristics of C-S-H. We then try to establish some links between the C-S-H composition and its mechanical properties.'

Keywords

Calcium silicates--Mechanical properties, Hydrates, Cement.

Sponsors

Defense Threat Reduction Agency

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Advisor

Taha, Mahmoud

First Committee Member (Chair)

Maji, Arup

Second Committee Member

Juenger, Maria

Third Committee Member

Taha, Mahmoud

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