Testing Modular Artificial Reef Units: Concrete vs Engineered Cementitious Composite

Researchers evaluated a modular artificial reef unit, known as the MMFAR, using two material options: reinforced concrete (RC) and engineered cementitious composite (ECC). Each unit was manufactured to a standardised geometry, with a cubic envelope of roughly 650 mm per side, limb cross‑sections of 150 mm by 196.5 mm and a central bulb radius of about 300 mm. The maximum design weight was set at 150 kg per module, a figure intended to facilitate handling and deployment in marine settings.

The study employed 3D‑printed moulds to cast the reef units, a step aimed at reducing fabrication costs while ensuring repeatable dimensional accuracy. Full‑scale structural tests were carried out in November 2025, including bending, uniaxial compression and mini slump assessments. These tests were conducted under the guidance of DNV‑RP‑C205 and ISO 19903:2006 standards, with reference to Eurocode EN 1993‑1‑8:2011 for structural evaluation.

Mechanical results revealed that the RC configuration outperformed the ECC variant in several key metrics. The concrete unit exhibited a compressive strength of 38.97 MPa and a Young’s modulus of 27.87 GPa, whereas the ECC unit recorded 2.96 MPa and 2.71 GPa respectively. Variation in concrete stiffness was limited to 2.71 % and strength variation to 1.02 %, indicating a high degree of material consistency across specimens.

Load‑capacity tests showed that the RC unit could sustain higher loads before failure, and it also displayed greater deformation capacity. Initial stiffness measurements confirmed the concrete module’s advantage, reflecting its higher modulus. Failure analysis highlighted differing mechanisms: the concrete unit cracked at the central bulb and experienced reinforcement lashing, while the ECC unit failed by separation of the loaded limb, a behaviour linked to its lower tensile capacity.

The authors—Fábio Cruz, Isabel B. Valente, Tiago Miranda and Eduardo B. Pereira—interpreted these outcomes as evidence that material choice markedly influences reef module performance. While concrete offers superior strength and stiffness, ECC provides a more ductile response, potentially beneficial in environments subject to dynamic loading. Both materials, however, meet the basic criteria for artificial reef deployment, such as weight limits and dimensional stability.

Beyond the mechanical findings, the research underscored broader challenges in reef engineering. The mechanical behaviour of artificial reef structures remains insufficiently documented, and standardized protocols for characterising such elements are lacking. The study’s methodology, grounded in established civil‑engineering standards, aims to fill part of this gap and offers a reproducible framework for future investigations.

Looking ahead, the team plans to leverage these insights to refine reef designs, aiming for more efficient and sustainable construction. By integrating additive manufacturing with proven material systems, they anticipate reducing ecological footprints while enhancing habitat complexity for marine organisms.

The work contributes to the growing body of knowledge on engineered reef habitats, supporting efforts to restore degraded reef ecosystems and bolster biodiversity. While the tests focused on structural performance, subsequent studies are expected to examine ecological colonisation and long‑term durability in marine conditions.