Finding low-cost, sustainable building materials is important for the environment and providing access to affordable housing. Researchers have created a composite building material by replacing sand in concrete and mortar with a common, non-degradable waste product: used disposable diapers.
Access to affordable, appropriate housing is a basic human right. This is a growing issue, especially in many low-income countries where supply and demand are mismatched.
Building materials are often the most expensive component in home-building, accounting for up to 80% of the costs. While using materials such as natural fibers, earthen materials, and industrial building waste has been explored, concrete remains the mainstay of house construction – indeed, any construction – because of its strength and durability. But concrete can leave a large carbon footprint.
Researchers from the University of Kitakyushu, Japan, looked for a way of maintaining the benefits of concrete but making it more environmentally friendly and cheaper to produce. They turned to a common non-degradable waste product: the disposable diaper.
In undertaking this study, the researchers were driven by a desire to tackle Indonesia’s significant population growth and demand for low-cost housing. Accompanying any population growth is an increase in waste. In 2019, total waste in Indonesia was 29.21 million tons; this figure rose to 32.76 million tons in 2020.
According to Maritime Fairtrade, Indonesia is ranked sixth globally for disposable diaper usage. Many used diapers are tossed in the country’s rivers and waterways, causing pollution through leeched chemicals and microplastics. This research could address two important issues: cleaning up the environment and providing a low-cost construction alternative.
The researchers prepared concrete and mortar samples by combining washed, dried, and shredded used disposable diapers with cement, sand, gravel, and water. The samples were cured for 28 days. Curing is the process of maintaining adequate moisture in concrete within a temperature range that aids cement hydration, the chemical reaction between cement and water that contributes to its strength and durability.
Mixes containing different proportions of disposable diaper waste were tested to see how much pressure they could withstand before breaking. The researchers then calculated the maximum amount of sand that could be replaced with diaper waste to safely construct a house with a floor plan of 43 square yards (36 square meters).
They found they could replace 10% of the sand with disposable diaper waste in the concrete needed to form columns and beams in a three-story house. In a single-story house, that proportion increased to 27%. In terms of the mortar used to create partition walls, the researchers could replace up to 40% of sand with diaper waste. For the formation of floors and garden paving, 9% of sand could be replaced. They found that exceeding these proportions resulted in concrete unfit for construction.
Overall, the researchers found that up to 8% of the sand in all concrete and mortar structures needed to build a single-story house with a floor plan of 36 m sq could be replaced with disposable diaper waste. That equates to 60 cubic feet (1.7 cubic meters) of waste.
“This research has concluded that adding used diapers to concrete does not significantly diminish its strength,” the team stated. “It demonstrates that using diapers to create composite materials is feasible, particularly concerning the development of environmentally friendly and cost-effective materials.”
The researchers consider their disposable diaper concrete has wide applications outside of creating housing in Indonesia. This is important because disposable diapers are the third largest contributor to landfills globally. Across the globe, more than 18 billion disposable diapers end up in landfills each year.
“Concerning this paper’s social and economic advantages, the development of materials can be accessed from low to high technology,” they said. “The procedures are relatively easy to conduct and low-cost.”
The researchers know the current limitations of using waste diapers as a construction material. For one thing, it would require engagement with waste treatment facilities to collect used diapers from households and sanitize them. Secondly, machines that shred the used diapers would be needed on a large scale.
Nonetheless, the research highlights the potential for using non-degradable waste as a building material, addressing sustainability issues and providing low-cost housing.
The study was published in the journal Scientific Reports.
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