McKay Creek Plaza EarthCache
Before You Go:
This earthcache will take you to McKay Creek Plaza within Florida Botanical Gardens. The Gardens are open from 7 to 5 PM daily, excluding selected holidays.
There is no fee for admission. Leashed pets are allowed. All paths should be ADA accessible.
Entrances are located at 12520 Ulmerton Road and 12211 Walsingham Road.
Logging Tasks
You will be observing shellcrete, a geological material that has a deep connection to the local geology and history of Florida's coast. Send answers using the message center. Please do not post the answers in your log.
- -From the Lesson provided: What is the main component of shellcrete? What is at least one benefit and one disadvantage to shellcrete?
- -On-Site Observation Compare and Contrast: Select a section of the shellcrete walkway and describe two distinct observations you can make about its texture, color, or visible shell fragments. Using the photo provided, compare the shellcrete and coquina. Describe one key difference you can observe in the natural rock and man-made material. (ex. Shellsize, overall color)
With the given information and by visually inspecting the shellcrete in the plaza, does it support or contradict the stated benefits of shellcrete (ex, non-slip, heat-resistant, durable) mentioned in the lesson.
- Photo 📸 As proof of your visit and to complete the logging requirement, post a photo You do not need to be in the photo, but it must be taken at the GZ or in the Gardens with something you enjoyed. Please note spoilers.
Shellcrete and Pinellas County Geology
The walkway beneath your feet at McKay Creek Plaza is an example of shellcrete. Shellcrete is a type of concrete where a portion of the aggregate (the gravel or stone) has been replaced with seashells. It is a man-made building material, often found in coastal regions, like Pinellas County where shells are plentiful.
While modern shellcrete is a man-made geological material, it is closely related to a naturally occurring rock called coquina (Koh-KEE-na) A spanish word for “cockle or “shellfish”
(Close up photo of a piece of coquina)
Coquina’s Cousin
Coquina is a type of sedimentary rock composed of shell fragments and sea creatures. It is held together by calcium carbonate or calcite. It forms when waves break up the shells and redeposit them near the shore. Over time, these fragments become cemented into a porous rock that is then harvested for building purposes.
Shellcrete mimics this natural process but on a human timescale. Historically, settlers in coastal areas, like St. Augustine harvested coquina and used a basic cement (like lime from burning shells) to bind it, creating a durable building block. Shellcrete takes local seashells and combines them with portland cement and water.
(Modern Process for Shellcrete)
Both materials are composed of bioclastic sediment (broken seashells). The shells make the surface light and porous, like a sponge. Shellcrete and coquina are primarily made of calcium carbonate, the chemical compound that shells are made of. The walkway you are on is a shellcrete mix. It demonstrates how builders adapt and utilize the geology of an area to create modern, beautiful structures.
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Shellcrete
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Coquina
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Origins
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Man-made modern engineering composite
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An ancient natural sedimentary rock
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Cement “glue”
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Portland cement and water
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Calcite from seashells
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Formation Process
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A few hours to days
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Can take years
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Geological Classification
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Composite material (concrete)
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Type of sedimentary limestone
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Shellcrete Benefits
This Shellcrete creates an environmentally friendly, durable, non-slip surface. It is naturally resistant to heat and has a visually pleasing coastal look. It utilizes recycled natural materials; the shells are often a byproduct of dredging or waste shells from local seafood industries. This combination of shells and concrete creates a hard-wearing surface that can withstand various weather conditions, resistant to cracking and abrasions from weathering. Because of its light color and texture, it reflects the sun’s heat. Finally, the embedded shells give the walkway a unique, beach-like appearance and a slip resistant surface.
Shellcrete Disadvantages
While shellcrete has many advantages, there are a few disadvantages when it comes to utilizing shellcrete as a building material. Shells are naturally full of tiny holes, and cause it to be more porous. This allows for water to soak in quickly. Also shells are more susceptible to chemical weathering from acid rain. Lastly, while shellcrete is resistant to general cracking and abrasions from wind and sand, it is less load-bearing.
Much thanks to the Florida Botanical Gardens Foundation and Pinellas County Parks and Conservation Resources Department for granting permission for this earthcache.
References
Bryan, J., Scott, T., Means, G, 2008 , Roadside Geology of Florida: Mountain Press Missoula.
Jones, D., Randazzo, A., The Geology of Florida : University Press of Florida, Gainesville.
Concrete shell - Wikipedia https://share.google/jtxOiUPrllBsNA8TG
https://localworksstudio.com/projects/shellcrete-transforming-sea-shells-into-low-carbon-materials
The Florida Botanical Gardens-https://www.flbgfoundation.org/?hl=en-US
https://oceanservice.noaa.gov/facts/coquina-tabby.html?hl=en-US
Washed Shell Aggregate - Barclay Earth Depot https://share.google/XwXgkx5y4j7K5onPo
https://www.publicgardens.org/wp-content/uploads/2015/11/The-Florida-Botanical-Gardens-From-Vision-to-Reality.pdf?hl=en-US
Al Disclamer: AI was used for researching purposes, to check sources, help with art and review against plagiarism.