Date of Graduation

12-2020

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Murray, Cameron D.

Committee Member

Hale, W. Micah

Second Committee Member

Fairey, Julian L.

Keywords

concrete; air content; air entrainment admixture (AEA); portland cement concrete

Abstract

Air is purposefully entrained into concrete primarily to improve resistance to freeze-thaw deterioration while saturated with water. Air entraining admixtures (AEAs) are chemical admixtures designed to entrain air into the concrete to provide adequate resistance to the effects of freezing and thawing. One of the challenges associated with air entrainment in concrete is the interaction of an AEA with supplementary cementitious materials present in the concrete, particularly fly ash. Fly ash is a by-product of the coal fired electrical generation industry, and often contains residual unburned carbon and other components that can increase the AEA demand of a particular concrete mix. Properly estimating the amount of AEA required to reach the specified air content in a concrete containing fly ash is of utmost importance to the ready mix concrete supplier, as an insufficient air content may lead to job site rejection and the resultant monetary losses.

This study aimed to better relate fly ash and concrete properties obtainable prior to final concrete placement, to direct measures of concrete durability obtainable only after the concrete has set and been put into service. A new device known as the Super Air Meter (SAM) was studied concurrently to better examine the relationship between its System Air Metric number (SAM number) and hardened concrete durability properties. Generally, fly ashes with higher foam index values and surface areas required higher dosages of AEAs to reach a specified air content value. No such relationship could be determined with the more commonly available loss on ignition percentage of the fly ash. The SAM number correctly predicted an acceptable spacing factor in 9 out of 12 different concretes tested, although all of the concretes tested displayed poor performance in freeze-thaw durability. These results demonstrate that air content testing alone is not necessarily sufficient to ensure high quality, durable concrete structures.

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