Lori Tunstall successfully presented her Final Public Oral defense of her thesis on Friday, May 13. Her thesis, entitled "A study of surfactant interaction in cement-based systems and the role of the surfactant in frost protection” addressed four main topics: (1) interaction of air-entraining agents (AEA) with ions in solution; (2) adsorption of AEA onto cement, fly ash, and carbon contaminants; (3) strains during freezing of cement containing AEA; (4) strains during freezing of cement containing carbon-contaminated fly ash and AEA. Her work demonstrated distinct differences in the behavior of 4 commercial AEA, and showed that AEA exhibiting the strongest tendency to self-association are most effective in protecting against frost damage. She explained the mechanism by which carbon contamination interferes with air entrainment, which resolved decades of contradictory reports in the literature. Her measurements of strain during freezing revealed that the microstructure of the shells around air voids is a critical factor in the frost protection provided by the AEA. In summary, her thesis clarifies the mechanisms by which AEA work, how carbon contamination interferes with AEA, and how the molecular structure of the AEA influences the microstructure of the voids that provide frost protection in concrete.