Date on Master's Thesis/Doctoral Dissertation

12-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Civil and Environmental Engineering

Degree Program

Civil Engineering, PhD

Committee Chair

Sun, Zhihui

Committee Member

Kim, Young Hoon

Committee Member

Ghasemi Fare, Omid

Committee Member

Sathitsuksanoh, Noppadon

Author's Keywords

Alkali-silica reaction; hydrophobic materials; ionic transport mechanisms; concrete durability; silane aggregate coating; chloride permeability testing

Abstract

Alkali-silica reaction (ASR) causes extensive damage to concrete infrastructure worldwide, with traditional mitigation strategies increasingly constrained by supplementary cementitious material (SCM) supply limitations. This dissertation investigates an innovative approach to ASR prevention through strategic application of hydrophobic materials to modify moisture and ionic transport pathways in cement mortars. The research employed a comprehensive three-objective experimental program using highly reactive aggregates and three hydrophobic materials: hexamethyldisilazane (HMDS)-treated fumed silica, silane-based emulsion, and silane-based crème. The first objective demonstrated the feasibility of hydrophobic aggregate surface modification, achieving 46% and 38% reductions in ASR expansion for washed and non-washed hydrophobic aggregates, respectively. Microstructural analysis revealed that hydrophobic coatings effectively reduced alkali transport to reaction sites while delaying crack initiation. The second objective compared varied hydrophobic materials application methods in mortar and fly ash replacement. Results showed that while hydrophobic fumed silica coatings provided superior ASR expansion reduction, silane crème coating demonstrated better transport resistance. However, 20% fly ash replacement remained most effective overall. Scanning electron microscopy revealed that interfacial integrity is critical, as powder-based coatings created gaps that enhanced ionic transport under electrical fields. The third objective focused on fundamental transport mechanisms using rapid chloride permeability testing and pore solution analysis. Results revealed that fly ash modification achieved significantly lower diffusion coefficients than control mortars, while hydrophobic treatments exhibited ion-specific behaviors. Silane crème aggregate coating emerged as the most promising hydrophobic method. This research demonstrates that hydrophobic materials offer a viable complementary approach to ASR mitigation when properly applied, providing new insights into transport mechanisms in modified cementitious systems and establishing guidelines for implementing hydrophobic treatments in concrete durability design.

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