A new “spitball-throwing” robot, developed by a team at ETH Zurich led by Lauren Vasey, could reshape sustainable building practices. This technology, known as impact printing, shoots out a clay-based material at high speed, allowing for quick construction without the need for cement or curing time—a leap forward in reducing construction’s carbon footprint.

The building sector faces mounting pressure to curb CO2 emissions, especially from materials like concrete, which is slow to 3D-print and heavily dependent on cement. “The building sector needs to dramatically decrease our CO2 emissions from new construction and move towards more circular supply chains,” Vasey explained in a video introduction to the technology.

Impact printing works as a high-powered form of 3D printing, where a machine fires a clay composite at 10 meters per second, bonding each layer on impact. The robot can construct walls and columns up to two stories high, and it’s equipped with a smoothing arm that refines the material, giving it a polished appearance rather than a “bunch of blobs,” as described by New Atlas. The material mix includes clay, silt, and a commonly available waste product sourced from Eberhard AG, a partner on the project. Customizable mixes offer flexibility for various structures and load requirements.

Vasey said the aim of impact printing is “to decrease dependency on scarce skilled labor and increase construction speed, making it cost-competitive with modern building materials.” The team is further developing reinforcement capabilities, which will allow the robot to build stronger structures with minimal human intervention.

This innovation sidesteps the need for cement, a material that, while comprising just 10-15% of concrete, contributes up to 90% of its pollution. Cement alone is responsible for 7% of global emissions, only slightly trailing iron and steel (8%) and surpassing even the oil and gas industry in carbon footprint.

Other green building alternatives, such as Rebetong—a fully recycled concrete—and glass bricks, are also in development, pointing to a future with a wider array of sustainable building materials.

By Impact Lab