Reformative Coral Habitats - Rethinking Artificial Coral Reef structures through a robotic clay printing method

Abstract

In 2018 after Typhoon Mangkhut hit Hong Kong, the city lost around 80% of its existing corals (Acropora, Platygyra and Pavona corals). As a consequence, a team consisting of marine biologists and architects is currently developing a series of performative structures that will be deployed on three sites intending to aid new coral growth. The present research focuses on means of creating 3D printed ceramic artificial reef structures, designed to optimize this growth. Australian design firm Reef Design Lab has recently developed their 3D Printed Reefs for an oyster restoration project in the North Sea. French firms XtreeE and Seaboost also developed the underwater structure “rexcor artificial reef” with the same purpose. However, both projects utilize concrete as a printing material. Concrete is still a material that has one of the highest environmental impacts during production, and the key question is how to reduce this impact. Clay, on the other hand, though it needs to be fired has a much lower impact on the environment than concrete. It’s a building material that has been around for thousands of years, due to its properties: plasticity, porosity, and vitrification. It’s a material which could potentially be harvested locally, leading even more to a lower degree of ecological footprint. Furthermore, the characteristics of the material prove much more potential, ceramic being similar to the calcium carbonate found in real coral reefs. As a solution to the problems mentioned above, 3D printing using clay holds the potential of creating a more viable habitat for corals. In addition to these material parameters, the printing language in this project has been optimized according to a series of factors. The overall design of the project is based on a strategy that combines a traditional gridded bottom part as a structural platform with a second layer on top that follows an approach of bio-mimicry and serves as the primary surface to attach corals. Several parameters have informed the computational design strategy. Since the structure will be placed underwater and has to accommodate coral growth, local conditions needed to be taken into consideration. For example, the geometry cannot be a full, solid block, but needed to be perforated so that there is no sediment deposition possible, which could potentially suffocate the corals. For the same reason, the geometry needed to be based on ridges and trenches are created alongside the surface of the geometry – the ridges act as anchors for the corals, while trenches direct sedimentation. To avoid bivalves nesting into empty spaces and to outgrow the initial area, the distances between the ridges needed to be carefully calibrated. The grid cells of the lower part are calibrated so that there is enough perforation to avoid sedimentation, to ensure the shortest possible toolpath and to tense the entire structure, in order to prevent it from cracking. All of the above had to be addressed through a novel robotic printing method that will be explained in this paper. The 3D printed alphabet of design parameters has been calibrated, optimized, and tested within dry-land conditions. The artificial coral reef structures account for machinic, material, and speculated environment behavior, but further research potential will be generated by the on-site assembly, with the possibility of monitoring underwater situations.