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The breakwaters of the entrance of the North Sea Channel at IJmuiden (The Netherlands) protect the port against wave attack. The breakwaters consist of regularly placed 2x2m concrete blocks. The surface of the blocks, and cracks and spaces between these blocks are habitats for a diversity of marine flora and fauna like algae, insects, crabs, shellfish, fish and birds. Because of this, it is important that after renovation of the breakwaters, the ecological system will recover quickly. This can be stimulated by the use of special concrete blocks.

Building with Nature Design Traditional Design

Concrete blocks with eco-friendly surfaces, roughened with various textures and geometric shapes, that stimulate fast and diverse colonization by macro-algae and macro-fauna


Traditional concrete blocks with relative smooth surfaces.

    General Project Description


    Title: Eco-concrete
    Location: IJmuiden Harbour
    Date: 2008-2009
    Companies: Deltares, Ecoconsult, BAM DMC, RWS Noord Holland, Microbeton, C-Fix
    Abstract: Stimulate re-growth and biodiversity with eco-concrete in exposed environment
    Topics: Concrete, breakwater, biodiversity

    Project Objective

    Figures 1 & 2. Weathered concrete blocks provide diverse habitats for many species.
    The breakwaters of the entrance of the North Sea Channel at IJmuiden (The Netherlands) protect the port against wave attack. The breakwaters consist of concrete blocks. The surface of the blocks, and cracks and spaces between these blocks are habitats for a diversity of marine flora and fauna like algae, insects, crabs and shellfish, fish and birds (including a red list species). Because of this, it is important that during and after renovation of breakwaters, the affected hard substrate habitats will recover quickly. This can be stimulated by the use of special concrete blocks, which is investigated in this pilot study.

    Figures 3 & 4. New durable smooth concrete blocks provide poor habitat opportunities for species.

    Project Solution

    In order to stimulate the growth of marine species on the breakwaters, the aim of this pilot study was to test slabs with various textures and geometric shapes attached to the concrete blocks (see Figure 1) for algal and macro-faunal colonisation. Consequently this will contribute to the requirement of maintaining feeding habitat area for a red list bird species, which could be crucial for Natura 2000 legislation of a good ecological condition (EU Water Framework Directive).

    The design and construction of eco-slabs was a co-production of Deltares eco-engineers with construction specialists of BAM DMC and engineers from the Ministry of Public Works - Rijkswaterstaat. In an inter-disciplinary workshop session possible structures were designed.

    Figure 5. Eco-slab with various textures and geometrical shapes covered with marine growth. Mussels prefer artificial cracks as habitat, provided as eco-structure in the left side of the slab

    Governance context

    In 2011 a renovation of the breakwaters of IJmuiden Harbour was planned. To stimulate the recovery of the ecological system at the breakwaters, the IJmuiden Port Authority had interest in using eco-concrete.

    Costs and benefits

    The additional costs for the production of eco-concrete is only marginal with respect to the costs of 'smooth' concrete blocks. Eco-concrete stimulates the settlement of a diversity of marine flora and fauna like algae, insects, crabs and mussels. These species serve as food source for birds such as the Calidris maritima 'Purple Sandpiper'. Besides, given their filter capacity, filter-feeders such as mussels are known to decrease the fine sediment concentrations in the water column and in this way increase the amount of light in the water column (e.g. Dolmer, 2000). Moreover, mussels are known to improve the water quality by retaining toxics (e.g. Strogyloudi et al., 2006).

    Planning and Design



    A pilot study was set-upto investigate the possibility to increase the settlement of algal and macro-faunal colonization by testing various textures and geometrical shapes on the concrete blocks of one of the breakwaters ('Zuiderhavenpier') of IJmuiden harbour in 2008-2009.



    The project was proposed by Deltares, based on funding by Rijkswaterstaat Innovation Program (WINN). Various parties such as Ministry of Public Works - Rijkswaterstaat and BAM DMC contributed to the project by providing materials, transport and additional funding.

    Detailed design

    The eco-slabs have a size of 75 cm x 50 cm and have six different textures/shapes of 25 cm x 25 cm at the top surface. The eco-slabs were attached both horizontally and vertically to the concrete blocks (see Figures 2). The textures and geometrical shapes for the vertically placed slabs were slightly different from for the horizontal ones (See Figure 3).

    The table below lists the six textures/shapes for both the horizontal and vertical slabs.


    vertical slabs


    horizontal slabs


    vertical grooves


    fine and smooth surface structure


    small holes


    cup (45% of surface)


    fine surface structure


    horizontal grooves


    horizontal grooves


    smooth surface structure


    medium-fine surface structure


    small holes


    smooth surface structure


    vertical grooves

    Table 1. Applied textures/shapes at the slabs

    In addition eco structures topping (surface layer) were placed on 15 large size X-blocks (2x2m). These blocks were placed along the Zuiderhavenpier.

    Project delivery

    The eco-slabs have been constructed using moulds and are made of various types of concrete. They were attached to one of the breakwaters (Zuiderhavenpier) of IJmuiden harbour in April 2008 (see Figure 6). The breakwater consists of concrete blocks of 22 and 30 metric ton embedded in asphalt. In total, 20 slabs have been placed from low water to high water mark; 10 werep laced in wave exposed locations and 10 at sheltered locations. The aim of this variation is to determine the optimum position for the various textures with respect to water level. The slabs were placed using a crane. The slabs were mounted to the concrete blocks using bolts and nuts.

    Operation and Maintenance


    Analysis of the photographs taken of the sections on the slabs showed that the sections on the slabs with a fine or coarse surface were colonized more rapidly by small green algae (Ulothrix flacca and Urospora penicilliformis) than those with a smoother surface. The geometric structures, cup and holes, which retained water longer during low tide favored the initial colonization by larger green algae (Ulva intestinalis). As succession proceeded the differences in algal density between the sections on the slabs became less obvious. All sections of the slabs in the mid and low tidal zone of both locations where rapidly overgrown by barnacles (Elminius modestus). Mussels (Mytilus edulis) were only found in the 9 sections with grooves, holes and cup, and developed best within the grooves (Figure 5). Both grooves and holes where used by periwinkles (Littorina littorea) for shelter at low tide. These results were in line with results found in the Azores (Martins et al., 2010), where pits with varying densities and sizes were drilled in a seawall, resulting in higher number of algae and macrobenthos within those pits.

    The table below shows the flora (algae) and fauna that was found on the eco-slabs after well over a year of deployment. It was found that 9 algae species were growing on the eco-slabs.


    flora species


    fauna species


    Urospora penicilliformis


    Elminius modestus


    Ulothrix flacca


    Littorina littorea


    Blidingia minima


    Mytilus edulis


    Ulva intestinalis


    Actinia equina


    Gayralia oxyspermum



    Porphyra umbilicalis



    Fucus vesiculosus



    Ceramium rubrum



    Bangia atropurpurea


    In conclusion, small adaptations of both texture and structure of concrete constructions within the intertidal zone of the marine environment lead to better settlement and growth conditions for algae and macrobenthos to settle and grow. Thus primary and secondary production is enhanced, without decreasing the safety level of the port. Given the 'scale-concept', these small scale adaptations can provide benefits for groynes and revetments as sources of enhanced productivity and habitat diversity on the meso scale.

    The costs for the production of the eco-slabs for the pilot study were €50 per piece (total production of 10 slabs?). The construction costs (of 10 slabs) were about €6000.

    For (possible future) large-scale production, it is recommended to apply the special textures and geometrical shapes directly on the concrete blocks instead of working with slabs. The estimated additional costs of such eco-blocks are expected to be about 2-3% of the costs of the normal concrete blocks.

    Lessons Learned

    • Use of certain types of textures and geometrical shapes on the concrete blocks of a harbour breakwater has a positive impact on the amount of biomass at the breakwater.
    • The additional costs of eco-friendly concrete blocks are only in the order of a few percent of the costs of concrete blocks.
    • One can control the settlement of certain species by applying a certain texture or geometrical shape; mussels prefer grooves, periwinkles settle mainly in the grooves and holes, etc.



    Almada-Villela, P.C. 1984. The effects of reduced salinity on the shell growth of smallMytilus edulis L. Journal of the Marine Biological Association of the UK., 64: 171-182.

    Dolmer, P., 2000. Feeding activity of mussels Mytilus edulis related to near-bed currents and phytoplankton biomass. Journal of Sea Research 44, 221-231.

    Joschko, T.J., Buck, B.H., Gutow, L., Schroder, A., 2008. Colonization of an artificial hard substrate by Mytilus edulis in the German Bigth. Marine biology research 4, 350-360.

    Kamermans, P. & Smaal, A. 2008. Evaluatie van de mosselzaadinvang (MZI- Mussel Seed Capturing Installations): proefperiode 2008. Rapport C022/09 (in dutch).

    Kautsky, N. 1982. Growth and size structure in a Baltic Mytilus edulis population. Marine Biology, 68: 117-133.

    Korringa, P. 1976. Economic aspects of mussel farming. Proc. FAO Tech. Conf. on Aquaculture held in Kyoto, Japan, 26 May – 2 June 1976.

    Strogyloudi, E., Giannakourou, A., Legrand, C., Ruehl, A., Graneli, E., 2006. Estimating the accumulation and transfer of Nodularia spumigena toxins by the blue mussel Mytilus edulis: An appraisal from culture and mesocosm experiments. Toxicon 48, 359-372.

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