Masters Theses

Date of Award

8-2025

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

Z. John Ma

Committee Members

Baoshan Huang, Nicholas Wierschem

Abstract

Traditional structural concrete mixes focus on individual aggregate sizes which leads to suboptimal mixtures that require excessive paste content, resulting in increased costs, higher carbon footprint, and potential durability issues. There is limited research on the workability challenges and solutions associated with these mixtures to find the optimal balance when paste content is reduced after optimization. So, there is a need for a systematic approach to find the optimal balance between aggregate optimization and paste content reduction while enhancing or maintaining workability, strength, and durability. Also, understanding the effects of different aggregate types on optimization techniques is needed to help engineers and concrete producers make more informed decisions when selecting materials for specific applications while using optimization techniques. This study investigates the effects of reduced paste content on the performance of optimized concrete mixtures for structural applications, while also examining the influence of different aggregate types on optimization techniques. Four different coarse aggregates (two granite, one limestone, and one gravel) and two fine aggregates (manufactured sand and natural sand) were used for optimized concrete using tarantula curve and coarseness factor chart methods. Optimized mixes were designed with 0%, 10%, and 20% reductions in cementitious content and compared to non-optimized control mixes. The study found that the optimization process led to improved freeze-thaw durability, higher compressive strengths, and better resistance to chloride ion penetration. However, there were some trade-offs, such as increased drying shrinkage due to partial replacement of coarse aggregates with intermediate aggregates. The results also indicate that while natural sand demonstrates superior performance compared to manufactured sand in terms of workability and durability, gravel and granite outperformed other coarse aggregate types by providing better compressive strength. While optimized mixes with a 20% reduction in paste content exhibited acceptable properties, a 10% reduction is recommended. This is due to the significantly higher demand for admixtures required in the 20% reduction mixes to maintain adequate workability. The 10% reduction strikes a better balance between sustainability, performance, and cost-efficiency, making it a more practical choice for structural concrete applications.

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