In an attempt to solve two environmental problems at once, researchers from Kitakyushu University in Japan have found that the shredded layers can be used to replace between 9 and 40% of the sand used in the manufacture of concrete without reducing its strength. . Disposable diapers are a growing source of non-recyclable waste, and cement production is responsible for almost 7% of global greenhouse gas emissions and consumes around 50 billion tonnes of sand each year.
Layer-infused concrete was used to build a small house in Indonesia, to demonstrate how this type of waste could 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 teaching at the Bandung Science Technology Institute near Jakarta. Although the population of rich countries often plateaus and declines, that of Indonesia and other low- and middle-income countries will continue to grow, leading to more babies, more nappies, and more demand for low-cost housing. .
“It all depends on the availability of resources,” says Zuraida. “As the population grows, diaper waste will also increase. It’s difficult, so we thought it would be part of our contribution to recycling this waste.
Single-use diapers are typically made from wood pulp, cotton, and super-absorbent polymers, small amounts of which have been shown to improve the mechanical properties of concrete. With funding from a Jakarta-based waste management company called Awina, Zuraida set out to determine how much sand could be swapped for shredded layers to create useful concrete and mortar.
Close to the house
Initially, the researchers sourced the diapers locally – Zuraida has a toddler herself. After the layers 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 hardening, the samples were pressure tested to determine the breaking point of the composite material. From these measurements, Zuraida and his colleagues calculated the maximum proportion of diaper waste that could meet the needs of building components.
The more layer waste in the concrete, the lower the compressive strength. Structural components such as columns and beams therefore required a smaller proportion of shredded layers than architectural elements, such as walls and concrete blocks. For their prototype one-story house, the researchers calculated that 27% of the sand could be replaced by waste diapers. But if the house had three floors, the proportion should drop to 10%.
In architectural components, up to 40% of the sand could be replaced by waste layers, with the highest proportion in concrete wall panels. In floor and garden coverings, which must be stronger than walls to meet construction standards, only 9% of the sand could be replaced by layers.
The house that the diapers built
The researchers then used their layer-infused 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 spaces. To speed up the construction process, the researchers used layered 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 represents about 8% of the total volume of composite materials.
As a way to extract value from non-degradable waste, “it’s a nice and really useful piece in a step-by-step process,” says Christof Schröfl, a chemist who studies sustainable building materials at the University of Technology in Dresden in Germany.
But he warns that transporting diaper waste to treatment plants or construction sites could “generate quite long transport routes”, and that if the team wanted to increase the environmental friendliness of their home at low price, it could opt for walls made of wood-composite materials based on concrete.
Zuraida agrees that separating the layers of the waste stream would be the hardest part of translating his work into the real world. Indonesia generated 20 million tons of waste in 2021, of which around 10% of plastics were recycled. “There is no support system in municipal waste management to separate the layers,” Zuraida said. “Plastic bottles are being separated at the moment because they recycle quite easily, but diapers usually go through the incineration process.”
This article is reproduced with permission and has been first post May 20, 2023.