Used diapers get a second life in concrete

Used nappies at a diaper recycling plant in Spresiano, Italy, August 31, 2018.

Casting bulky items in reinforced concrete is an old fantasy. In the cinema, we remember Jo, a 1971 comedy by Jean Girault, in which Louis de Funès got rid of the corpse of his supposed blackmailer by drowning it in the foundations of a garden gazebo. In study published by the British journal Scientific Reports on May 18, a team based at the University of Kitakyushu, in Japan, made up of three researchers, two Indonesians and a Belgian, analyzes the merits of integrating into the concrete… elements of diapers used disposables. A waste which represents on average, in the world, 2% to 7% of the total volume of domestic household waste (“ Solid and Hazardous Waste Management », Science and Engineering2017) and usually ends up in incinerators or, much more often, in open landfills.

This isn’t the first time the recycling of diapers into concrete has been researched. Already in 2017, theIndian Journal of Science and Technology had reported interesting results obtained in Malaysia, by enhancing the absorbency of diapers “transformed into a gelatinous substance” improving the viscosity of concrete. The new element brought by the article of Scientific Reports is to quantify the proportion of diapers that can improve the quality of concrete, including in the load-bearing elements of buildings.

The experiment was carried out in Indonesia on a low-cost habitat: houses of 36 square meters on the ground, composed only of a ground floor divided into a living room, two bedrooms and a bathroom. Of the total volume of concrete required, 22.79 cubic meters, the three researchers show that the share of diapers, previously washed, dried and shredded before incorporation into cement, aggregates, sand and water, can reach 1.73 cubic meters, without the bearing capacity of the concrete being modified. “This indicates that a maximum of 7.6% disposable diapers can replace fine aggregate in construction”they say, in this case sand.

A full-scale housing prototype, built by the team of researchers based at Japan's Kitakyushu University, in late 2022, Indonesia.  Waste diapers are used for the walls and floor.

The proportion varies according to the elements of the building. In columns and beams, where the compressive strength is set at 10 megapascals, diaper components can replace a maximum of 27% of the weight of sand. In the walls, likely to resist only 2 megapascals, the proportion can go up to 40%. Conversely, in the slab constituting the floor of the dwelling, where 8.5 megapascals are necessary, it is limited to 9%. Diapers are really just one source of superabsorbent polymers (superabsorbent polymersor SAP) that are of interest to research.

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