_Isla Rhizolith

Isla Rhizolith | Rhizolith Island - A Floating Concrete Breakwater is a concept and prototyping project that investigates the potential for high performance, floating concrete structures to revitalize Colombian shorelines along vulnerable sites with ongoing flooding in urbanized areas. Due to the devastating depletion of mangrove forests that naturally control sediment and shorelines from erosion, the installation and speculative urban proposals aim to achieve a new urban infrastructure through emphasis on newly developed concrete materials, formal expression, and performance.

The project is a collaboration between APTUM and CEMEX Research Group (CRG). The exhibition was part of the RC 2016 (Reunion del Concreto), an international Expo and Academic Conference on Concrete held last week in Cartagena. 

What (part 1 – incubator islands):

Rhizoliths are root systems that have been encased in mineral matter and are created through the process of chemical weathering, decomposition, and cementation. Rhizolith Island is a breakwater system comprised of ‘root-like’ concrete elements and planted mangroves that together act as an artificial and natural Rhizolith. Once aggregated and growing, the structure acts as a breakwater as well as a “seed” for the revitalization and protection of substrate for new mangroves. Continual urban growth, agriculture, and storm surges all contribute to devastating amounts of vegetation and habitat loss, as well as annual flooding along the shoreline of Colombia. The exhibition reflects on the current state of our coastal cities but also what can be done to reverse these unfortunate consequences and create a safer, more resilient infrastructure for our cities to thrive.

What (part 2 – floating concrete!): The elements are constructed out of two individual pieces; a head and a fin, both made with proprietary concrete mixes and casting techniques. The head is made from a concrete mixture that is lighter than water (the elements float because of this and not due to displacement). The concrete mixture guarantees that the island floats even if there are holes in the shell. In addition, the weaker mixture of the lightweight concrete permits the roots of the mangroves to grow through the concrete over time. The Fin, on the other hand, is made from UHPC (ultra high performance concrete). It’s weight and strength stabilizes the elements in the water and provides a basis for the development of a marine habitat by offering shelter and surfaces for barnacles to grow. To protect the elements from each other, a rubber ring is cast into the top of the head. Steel grommets embedded in the rubber allow the elements to be sewed together with rope into larger aggregations.

How (part 1 - urban acupuncture): The Rhizolith Island is a fragment of a larger breakwater that can be deployed along the shoreline in an “acupuncture” strategy in locations most affected by depleting mangroves and annual flooding. The system uses the porosity of the concrete as well as its form to dissipate the force of the water during a storm surge. As the first phase, the mangroves are planted and protected by split encasement tubes to stabilize the mangrove seedlings. The tubes are anchored into the substrate in top of the concrete elements and designed with voids to allow the roots of the maturing mangrove to grow and spread beyond the elements. Simultaneously, the element fins serve as stabilizers and create pockets of space with voids puncturing the surfaces to create inviting ecosystems, similar to leaf litter and decomposing debris, for flora and fauna to inhabit the structure.  

How (part 2 - urban expansion): In the second phase, the mangrove trees continue to grow on the floating elements, as well as on shore, as newly deposited sediment slowly accumulates; allowing for further growth of mangrove trees along the shoreline. In the final phase, the floating elements eventually moor into the seabed and further work as a type of Rhizolith breakwater system to reduce additional erosion of the sediment. This system establishes a local restoration and expansion of the mangrove forest.

Where (future locations): Two site locations chosen for further development were Cienaga de la Virgen Lagoon and Isle Grande. Both site strategies reflect the long-term goals of restoring the shoreline over time (5-10 years), using the concrete island as an incubator for the mangroves to grow and thrive. Eventually the roots of mangroves break through the concrete and take over to be a permanent, natural buffer to soak up water and reduce flooding during storms.

Collaborator: CEMEX Research Group, Biel Switzerland