Yvonne Mak's Sandbag Castle Floats Low-Carbon Concrete in Eindhoven's Dommel River

Yvonne Mak's Sandbag Castle floats in Eindhoven's Dommel river beside the Van Abbemuseum Café, a five-meter-wide, three-meter-high structure built from hundreds of stacked concrete modules shaped like sandbags. The work confronts cement's environmental footprint by putting low-carbon alternatives on public display. More than ten distinct formulations appear in the piece, among them calcined clay, alternative binders, geopolymer concrete, recycled aggregates and self-healing mixes. TBI served as main partner, working alongside specialized material and technology contributors. Cast concrete sandbag forms echo temporary flood barriers, pointing to how heavily protective infrastructure depends on concrete. Red warning flags sit atop the castle, borrowing the visual language of beach safety signals. Each flag carries a custom coat of arms combining symbols for water, bridges, flora and hands, a reference to where nature, infrastructure and human intervention meet. The project was submitted through designboom's DIY submissions feature and edited by Christina Vergopoulou. Photographs are credited to Yvonne Mak. The installation argues that structural alternatives capable of cutting concrete construction's CO₂ emissions already exist and are still emerging.