Civil Engineering ETDs

Publication Date

9-12-2014

Abstract

Calcium Silicate Hydrate (C-S-H) is the primary binding agent that is responsible for setting and hardening, strength, dimensional stability, and durability of Portland cement paste. Although Portland cement hydration produces C-S-H, Calcium hydroxide (CH), ettringite, and other hydration products are also acquired from this process and make it difficult to characterize C-S-H exclusively. C-S-H was first synthesized by mixing calcium oxide (CaO), created by calcining calcium carbonate (CaCO3) that was heated to 950 \xbaC for 24 hours with fumed silica (SiO2) and deionized water (H2O) under nitrogen which produced the synthetic gel-like C-S-H slurry. This composition mixture of synthetic C-S-H was mixed continuously for 7 days with a constant speed and transferred to a filtration system for removal of excess water. The C-S-H gel was then transferred to a drying unit and purged in nitrogen for 5 weeks with a relative humidity (RH) of 11% using Lithium Chloride (LiCl) for 5 weeks. Specimens were obtained by compacting the dried C-S-H powder at 500 MPa. These compacted samples were tested for identifying its mechanical properties on macro, micro, and nano-scale levels. Nanoindentation was used to identify creep compliance and the reduced elastic modulus of C-S-H. Nanoindentation tests confirmed the 0.7 C/S ratio is stiffer (higher elastic modulus) than C-S-H with 1.5 C/S ratio. Furthermore, C-S-H with 0.7 C/S ratio has a lower creep compliance compared with C-S-H with 1.5 C/S ratios. Microstructural investigations using 29Si nuclear magnetic resonance (NMR) and Transmission Electron Microscopes (TEM) were performed on C-S-H specimens. This work shed light on the significance of silicate polymerization in C-S-H on elastic and creep behavior of cement and concrete. This work might lead to developing alternative cements for concrete structures with time-dependent critical applications.

Keywords

Calcium Silicate Hydrate, Nanoindentation, Dynamic Modulus Analyzer, Mechanical Properties, Microstructure

Sponsors

National Science Foundation

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Maji, Arup

Second Committee Member

Matteo, Edward

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