MIT Team Cuts Beam Concrete by Two-Thirds Using Sewn Fabric Molds

A 3-meter concrete beam cast in sewn fabric molds used roughly one-third the concrete and half the steel reinforcement of a conventional beam carrying the same load. MIT engineers designed and built the test beam using an automated pattern-making process, and load testing showed deflection within about 2 percent of the team's computer model. The results appear in the Journal of Building Engineering.

Topology optimization, a computational design method, can produce beams that use far less material, but the resulting shapes are usually too complex for conventional rigid molds. The few structures built so far have relied on concrete 3D printers or machine-carved molds — equipment out of reach in regions where construction demand is growing fastest. The MIT team's alternative relies on textile formwork, fabric molds that are inexpensive, lightweight, and fast to produce compared with wood or steel.

How did the team design the beam?

The researchers combined two design methods. Graphic statics, which generates structural designs almost instantly, mapped the path of the steel reinforcement so the bar carries an equal share of the load along its length. Topology optimization, slower but able to place material freely, determined where concrete was needed and where it could be removed.

"Both methods are good at different things, so we tried to combine the strengths of both into a single methodology," said Jackson Jewett PhD '25, a co-author of the study. The result is a beam with a top section, narrow angled legs, and a thin bottom section holding the steel. An automated process translated the 3D design into flat fabric pieces cut and sewn into a mold, with a simple timber frame for support.

Fabric deforms under wet concrete, which has long made final shapes hard to predict. "The key realization was that this flexibility is not just a limitation to manage; with the right computational pattern design, it can become a way to produce optimized structural forms," said Josephine Carstensen, the Gilbert W. Winslow (1937) Career Development Professor in Civil Engineering and senior author of the study.

What did the casting and testing show?

Lead author Mark Hellrich SM '26 tuned the concrete mix for the fabric. Woven cotton lets water seep through, and a runny mix presses harder against the fabric, pushing it off the intended shape. The team chose a moderately wet, sand-rich mix with only small stones so concrete could flow through the narrow legs, then packed it by hand.

"This is where the flexibility of the mold becomes an advantage: you can work the concrete through the interconnected passages without a vibrator, which a rigid mold of this shape would need," Hellrich said.

To gauge sewing precision, the team built three molds for the same design from 36, 56, and 76 fabric pieces. More seams improved local control but also multiplied opportunities for cutting, sewing, and assembly errors. The 56-piece mold offered the best balance of geometry capture and effort.

The load test stacked 36 water-filled buckets on one beam, reaching about 30 percent of design load. All three cast beams were free of wrinkles and creases; the main deviation was a downward sag along the bottom.

Where does the economics work?

Cost depends on geography. In the Global South, where materials cost more relative to labor, all three fabric versions were 10 to 20 percent cheaper than a conventional beam. In the Global North, higher sewing labor made them 16 to 55 percent more expensive. The team sees the strongest case in one-off or small-batch custom components — exposed beams, roof or long-span framing, pedestrian structures, landscape elements — while conventional reusable molds stay cheaper for repetitive rectangular beams where labor is expensive.

The stakes are material. Cement production accounts for roughly 8 percent of human-caused carbon emissions, and the world's building stock is expected to nearly double by 2050, with about 85 percent of that growth in developing countries. "This work addresses concrete's climate footprint primarily by reducing material demand," Carstensen said.

The 3-meter beam, comparable to a short building span, scales up from the team's earlier 1.2-meter version. Larger beams need new designs because self-weight and mold pressure change with length. The next milestone is structural: Carstensen said the team plans "to test multiple beams to failure." Co-authors included Abhinit Sati, Edward Chien, and Emily Whiting of Boston University, with partial support from the U.S. National Science Foundation.