2023 Undergraduate Research Showcase

Document Type

Student Presentation

Presentation Date

4-21-2023

Faculty Sponsor

Dr. Nick Hudyma

Abstract

Coquina is a weak sedimentary limestone composed of shell and shell fragments that have been cemented together. It is most often found in coastal regions, such as the Anastasia Formation along the east coast of Florida. Coquina is a historically significant building material, with the best-known example being the Spanish Castillo de San Marcos in St. Augustine, Florida. It has withstood cannonball fire during battles and centuries of weathering yet is still structurally sound. Although coquina is very important historically, not much is known about its properties. Preliminary studies have shown the orientation of the shells impacts tensile strength. Additionally, larger specimens tended to have lower tensile strength. Building on previously performed tests, I will further investigate how the orientation of shells impacts coquina’s tensile strength, as well as how specimen size affects tensile strength. I predict the specimens cored in the vertical direction will have a higher tensile strength because the shells will be oriented horizontally. The larger specimens will have a lower tensile strength because there is a greater number of existing fractures within the larger specimens. Indirect tension testing will be performed on the specimens. Compression on the top of the puck-shaped specimens will cause failure in tension. I will use acoustic emission monitoring to measure microcracking events during testing, specifically looking for the beginning of unstable crack growth. Unstable crack growth is a precursor to ultimate failure, where microcracks coalesce and form a macroscopic failure plane.

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