Date of Award

2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

First Advisor

Picornell, Miguel Dr.

Abstract

The mechanical strength of cement paste is the property of the material that is most obviously required for structural use. The strength of mortar or concrete depends on the cohesion of the cement paste and its adhesion to the aggregate particles. Cement paste consists of two parts, cement and water. When water is added to cement, it reacts with the cement in what is known as the hydration process. The scope of this study is to determine the mechanical properties of hydrated cement paste with respect to the degree of hydration for different water-to-cement ratios, for developing a molecular macroscopic model for numerical simulations at the nano-scale. Hydration, compression, elastic modulus, flexure and direct tension tests were performed to complete this study. Vacuum-sealed dry curing was chosen for the specimens in this experiment. Results showed that with increased degree of hydration, there was an overall increase in the compressive strength. However, for the tensile strength, there was an overall decrease in both flexure and direct tensile strength. This may be the result of the phenomenon called ‘autogenous’ shrinkage from the method of vacuum-sealed dry curing. This curing method robs the interstitial water in the pores of the cement gel. The loss of pore water results in an increase of the capillary tension in the pores. This increase in the capillary tension causes autogenous shrinkage. To accommodate this shrinkage, the gel cracks or existing cracks extend, resulting in the loss of tensile strength for increasing curing time. Microscopic observations were made on the failure planes of beam A.3 to identify any cracking. The cracks observed show that they have an association with some air void present in the failure plane. Future research must be conducted for better understanding of this mechanical behavior.

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