During field trials at Yerseke, blocks of Xiriton placed on tidal flats were inundated twice daily. "After a year, every block was around 70 per cent covered with life such as oysters, mussels and algae," said PhD candidate Victoria Mason.
"This indicates that Xiriton blocks are not only cheap, sustainable and practical to manufacture on a large scale, but also suitable for use in enhancing settlement and potentially restoring biodiversity. By adjusting the lifetime of the material, it can also break down naturally into harmless substances once a reef can sustain itself, instead of remaining permanently in the ecosystem."
The team used locally sourced cordgrass (Spartina anglica) and Elephant grass (Miscanthus giganteus) to manufacture the blocks, though other grasses could also serve as input as long as they are sustainably harvested. Xiriton's final strength is determined by drying time and the amount of binding component, with five weeks of curing producing the highest material strength. Mason added, "With a pH value of 8 to 9, it is much more neutral than standard concrete, which is more alkaline. Concrete has a pH of around 13, which can be unfavourable for organisms that need to settle on it."
Mechanical durability was confirmed via erosion tests, which exposed Xiriton blocks molded in coffee cups to strong currents for over two months. Xiriton's resistance was found on par with Roman cement alternatives. "We used those coffee cups to place the material in the flow instead of having the flow go over the structure, like with tiles," reported Jente van Leeuwe, formerly a master's student at Wageningen University and now completing doctoral work at NIOZ.
Mason described the requirements for restoration materials as environmental safety, flexible construction geometry, temporary presence, and cost-effectiveness. "They must be flexible in terms of what shapes we can build, and temporary, so they don't require expensive removal or leave harmful products in the environment. As well as that, they need to be inexpensive enough to be upscaled to larger projects and different areas."
A prospective study is planned to assess the material's potential for wave-breaking and large-scale marine structures. Adjusting the Xiriton mixture could control lifetime so that reef scaffolding decomposes after ecosystem recovery.
The concept was originally developed by Frank Bucher of Stiens, Friesland. Bucher emphasized the flexibility of the material: "All buildings up to three stories high, for example. But you don't have to bake it and you don't need clean drinking water. You can make it with ditch or sea water." He highlighted that wood can reinforce Xiriton and vice versa, enabling novel building concepts, particularly for hydraulic engineering. The construction sector has yet to broadly adopt the material, but coastal restoration is drawing increasing attention, and research has expanded to Van Hall Larenstein University of Applied Sciences.
Senior researcher Jim van Belzen commented, "The built world now weighs more than all the biomass on Earth. If we really want to reduce our footprint, we need to radically rethink the way we build. New biobased concepts - where nature, circularity and regeneration are central - are not a luxury, but a necessity. The technology is still in its infancy, but biodiversity will not wait." He noted that Xiriton demonstrates the characteristics needed for nature-friendly marine protection, serving as an option for breakwaters, artificial reefs, and seawalls with reduced impact compared to conventional concrete. "The future of water safety? It could well be greener than stone and concrete."
Research Report: Using local materials for scalable marine restoration: Xiriton as a nature-enriching, low impact building material
Related Links
Royal Netherlands Institute for Sea Research
Space Technology News - Applications and Research
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