University of Tokyo Turns Food Scraps Into a Concrete-Beating Building Material

University of Tokyo researchers have turned dried, powdered food scraps — including banana peels, orange rinds, onion skin, pumpkin peel, cabbage and seaweed — into rigid building-material prototypes by pressing the powder under heat, without adding any petroleum-based resin.

The process had four stages: the researchers cut and dried the food scraps, pulverised them into a powder, mixed the powder with water or edible seasonings, and compressed it inside a heated mould. They tested temperatures from 60 to 180 degrees Celsius and pressures from 6 to 50 megapascals; a common baseline was 100 degrees, 50 megapascals and 10 minutes.

The best-performing sample, made from Chinese cabbage, reached about 17.7 megapascals of flexural strength, its resistance to bending, in three-point bending tests, compared with the researchers' benchmark of 5 megapascals for ordinary concrete. Materials engineer Yuya Sakai, who worked on the project with Kota Machida, said the strength comes from sugars in the food scraps softening under heat and filling the gaps between plant fibres, then hardening into a binder as the material cools.

The original 2021 paper described the result as "more than three times stronger" than the concrete benchmark; a later University of Tokyo account rounded the comparison to "four times." Pumpkin peel alone fell short of the concrete benchmark, but blending it with 25% Chinese cabbage raised its flexural strength to about 10 megapascals.

The work was published as a conference paper and preprint rather than a peer-reviewed structural study, and flexural strength alone does not show the material can replace concrete, which is normally valued for carrying loads under compression rather than bending. The researchers tasted the untreated samples themselves and reported no visible mould, rot or insects after four months at room temperature, but the prototypes lost strength when wet and have not undergone formal food-safety testing.