In an effort to solve two environmental problems at once, researchers at Japan’s Kitakyushu University have found that shredded diapers can be used to replace between 9 and 40% of the sand used in concrete making without sacrificing strength to reduce it. Disposable diapers are a growing source of non-recyclable waste and cement production is responsible for nearly 7% of global greenhouse gas emissions and consumes about 50 billion tons of sand annually.
The diaper-soaked concrete was used to build a tiny house in Indonesia, demonstrating how this type of waste can be diverted from landfills to build more affordable housing in low- and middle-income communities.
Siswanti Zuraida, a civil engineer at Kitakyushu University, started the project while giving a lecture at the Bandung Science Technology Institute near Jakarta. While population numbers in rich countries tend to stagnate and decline, those in Indonesia and other low- and middle-income countries will continue to grow, leading to more babies, more diapers and more demand for low-cost housing.
“It’s all about resource availability,” says Zuraida. “As the population grows, diaper waste will also grow. It is challenging, so we thought this would be part of our contribution to recycling this waste.”
Disposable diapers are usually made from wood pulp, cotton and superabsorbent polymers, small amounts of which have been shown to improve the mechanical properties of concrete. With funding from Awina, a Jakarta-based waste management company, Zuraida set out to find out how much sand could be traded for shredded diapers to make usable concrete and mortar.
Close to home
Initially, the researchers bought the diapers locally – Zuraida has a toddler of her own. After the diapers were washed, dried and shredded, the resulting material was combined with cement, sand, gravel and water. The team tested different mixes, replacing up to 40% of the sand in the concrete.
After one month of curing, the samples were pressure tested to determine the breaking point of the composite material. From these measurements, Zuraida and her colleagues calculated the maximum proportion of diaper waste that could meet the needs of building components.
The more diaper waste in the concrete, the lower the compressive strength. Structural components such as columns and beams therefore required a smaller proportion of shredded diapers than architectural elements, such as walls and concrete blocks. For their prototype single-storey house, the researchers calculated that 27% of the sand can be replaced by diaper waste. But if the house were three stories high, the share should drop to 10%.
In architectural components, up to 40% of sand can be replaced by diaper waste, with the highest share in concrete wall panels. In floors and garden paving, which must be stronger than walls to meet building standards, only 9% of the sand can be replaced by diapers.
The house that built diapers
The researchers then used their diaper-soaked concrete to build their experimental home to Indonesian building standards. The house was small; the floor plan totaled only 36 square meters, the size of about 2.5 parking space. To speed up the construction process, the researchers used diaphragm concrete for the architectural components and metal beams for the structural components.
In total, the house used about 1.7 cubic meters of diaper waste, which made up about 8% of the total volume of composite material.
As a way of extracting value from non-degradable waste, “it’s a beautiful and really rewarding piece within a step-by-step process,” says Christof Schröfl, a chemist who researches sustainable building materials at the Technical University of Dresden in Germany. .
But he cautions that transporting the diaper waste to processing plants or construction sites “could generate quite long hauls,” and that if the team wants to increase the eco-friendliness of their low-cost home, it could opt for walls made from wood-composite materials instead of concrete. .
Zuraida agrees that separating diapers from the waste stream would be the most challenging part of translating her work into the real world. Indonesia produced 20 million tons of waste by 2021, of which about 10% of the plastic was recycled. “There is no support system in municipal waste management to separate diapers,” Zuraida said. “They now separate plastic bottles because they recycle fairly easily, but the diapers usually end up in the incineration.”
This article is reproduced with permission and was first print on May 20, 2023.