Researchers published an innovative finding in the Journal of Cleaner Production: spent coffee grounds (SCG), can be used as a partial replacement for sand in concrete manufacturing, improving its mechanical performance and offering a concrete solution to organic waste management.
The study proposes a sustainable alternative that addresses two critical environmental challenges: organic waste dumping, which generates methane emissions, and the intensive use of natural sand, a resource whose massive extraction is associated with severe ecological impacts.
From organic waste to structural additive: the role of pyrolysis
The technique used is pyrolysis, a thermal process in the absence of oxygen that converts the waste into biochar, a porous material with high carbon content. By treating SCG at 350 °C, a product called 350CBC is obtained, whose properties allow to:
- Replace up to 15% of sand in cement mixes
- Increase concrete compression strength by 29.3%
- Improve internal curing, adhesion, and microstructure
Biochar acts as an internal reinforcement agent: its pores allow the entry of cement and store water that is gradually released, optimizing the setting process.
On the other hand, if coffee is subjected to pyrolysis at higher temperatures (500 °C), the resulting material becomes more brittle and loses structural effectiveness.
Environmental and economic impacts of a circular solution
The use of coffee residues in concrete not only improves the performance of the material but also:
- Reduces pressure on quarries and river ecosystems by decreasing the use of natural sand
- Decreases greenhouse gas emissions by preventing organic waste from degrading in landfills
- Leverages an abundant and recurrent waste, with potential for urban collection
This innovation aims to redefine how urban waste can be transformed into functional inputs for construction, creating new circuits of circular economy.
From coffee shops to infrastructure: scalability and potential application
With a global coffee production exceeding 9 million tons annually, the valorization potential of SCG in the construction industry is significant. If the technique is applied on a large scale, it could:
- Reduce the use of sand in large construction projects
- Decrease logistical and raw material costs
- Integrate into sustainable architecture programs and ecological certifications
