Construction start-up CircuBrick officially launched the ARC-300, a precast cylindrical building block that turns the familiar rectangular brick on its side—literally. Measuring 300 mm in diameter and 600 mm in height, each hollow-core unit locks together without mortar, forming columns, arches and load-bearing walls up to 20 m tall while cutting embodied carbon by 38 % compared with standard CMUs.

The breakthrough lies in geometry. By extruding high-strength geopolymer concrete into a perfect cylinder, engineers distribute compressive forces evenly around 360°, eliminating corner stresses that typically crack conventional blocks. “A circle has no weak joints,” explained CircuBrick co-founder Dr. Lea Hartmann during a live demo at BAU 2025. “Each ARC-300 carries 1.8 MN—roughly the load of 30 passenger cars—yet weighs only 16 kg thanks to a 40 % void ratio.”

That void is not wasted space. A central 110 mm conduit accepts rebar, electrical conduit or hydronic piping, allowing MEP trades to thread services vertically without drilling. When grout is pumped through the same cavity, the block behaves like a reinforced concrete column, satisfying Eurocode 6 without additional steel cages or complex formwork. The result is a hybrid system: modular speed on day one, monolithic strength for the building’s life.

Installation is fast. Interlocking tongue-and-groove rings on the top and bottom faces self-center each block to within ±1 mm, enabling a two-person crew to erect 30 m² of wall per hour using nothing more than a rubber mallet and a laser level. Because the units stack in a helix, wall curvature can be introduced or straightened on the fly by rotating each successive block two degrees—ideal for amphitheaters, silos and modernist façades alike.

Sustainability is baked in. The geopolymer mix replaces 70 % of Portland cement with fly ash and ground-granulated blast-furnace slag, slashing CO₂ emissions to 95 kg per m³ versus 240 kg for conventional concrete. Pigmentation is achieved with natural iron oxides, removing the need for paint over the block’s 100-year design life. At end-of-life, the cylinders can be unscrewed, cleaned and reused; CircuBrick pledges buy-back at 50 % of original cost.

Early adopters are enthusiastic. Dutch firm Van Wijnen is using 18 000 ARC-300 units to build a circular parking garage in Utrecht, eliminating expansion joints and saving an estimated 12 weeks of schedule. In Nairobi, the NGO BuildX has trained 30 local masons to assemble a 120-seat school hall in five days—proof, says director Kioni Mwangi, that advanced geometry need not require advanced machinery.

Pricing starts at €4.90 per block delivered ex-works in northern Europe, competitive with premium clay bricks once labor savings are included. CircuBrick has secured €12 million in Series A funding to expand production from 5 000 to 50 000 units per day by Q2 2026, with licensing agreements already signed in North America and Southeast Asia.

As cities race to decarbonize and densify, the humble cylinder may prove more revolutionary than any algorithm. “We didn’t invent concrete,” Hartmann noted. “We just gave it a better shape.”