Reefs are fractal. They display complex shapes at scales from millimeters to tens of meters that provide a myriad of niches for other animals and plants from microscopic diatoms to large sharks. Artificial reef designs have found it difficult to mimic this range of structural complexity… until now. The photographs below document the concept development for an artificial reef structure that is stable provides numerous internal voids, has a highly irregular external shape consisting of calcium carbonate rock, and is easily mass-produced. A half-scale test module (~1m diameter) in the water just off of Lanikai Beach, Oahu since 2016, displays natural recruitment of macro-algae, corals, and fish, and is indistinguishable from the surrounding natural reef.
Click on the photos to enlarge them
Rather than design the reef structure, we began by designing the structure of the holes internal to the reef. This is a soft plastic 3D printed matrix that accounts for about 50% of the internal volume of the shape.
The void mold was placed into a tight-fitting wooden box and mortar was poured near the surface of the void mold. Coral gravel was pressed into the surface of the mortar between the exposed ends of the plastic mold branches.
The soft plastic was dissolved away with alcohol leaving the concrete structure with 50% internal voids. This structure was designed with a 45o front face to act as a wave-absorbing seawall.
To build a larger (~1/2 scale) reef module a support framework of dowels was constructed to hold the vertical void columns
Each Dowel was wrapped with corn-starch foam.
Additional dowels were added to support horizontal void structures.
The completed void mold held by Dr. Mike Folley.
A 1+-meter diameter hole was excavated and lined with calcium carbonate reef rocks, each ~10cm in diameter. On 6/13/16 the void mold was inverted and inserted into the hole with all of the void arm tips touching the reef rocks lining the hole and the hole was filled with wet concrete (nine 50-lb bags).
After curing for 14 days, the reef module was lifted from the ground with the assistance of Hugo de Vries’ forklift and inverted onto a pallet.
The corn-starch foam was dissolved with water and the dowels removed.
The resulting structure can be seen to have a highly irregular shape, with exposed calcium carbonate rocks on the surface and plentiful internal spaces.
Photo from above shows the location of several of the vertical void columns.
When the concrete was fully cured, it was loaded onto the back of a pickup truck, and transported to Lanikai.
It was carried by a dozen volunteers out into the water. The module was floated off the pallet with a 50-gallon drum,
and pushed out into a sand patch roughly 25m off shore and surrounded by a natural reef at a depth of approximately 3m.
The half-scale test module (~1m diameter) is shown here in the water just off of Lanikai Beach, Oahu. Since 2016, it displays the natural recruitment of macro-algae, corals, and fish, and is indistinguishable from the surrounding natural reef.
This is a video of the reef taken in January 2022.