Coffee Pulp Concrete Can Make Concrete 30% Stronger!

Coffee, which has been part of our lives for approximately 500 years and is consumed during ceremonies, holidays, special occasions or simply for pleasure, has become an indispensable beverage in our culture. Coffee, said to have beneficial effects on human health, holds a unique and ancient place in our culture due to its history, the structures named after it, its brewing method, the way it is served and consumed, and the tools used in its preparation. Because of its rich cultural foundation, it was included in 2013 by UNESCO in the Representative List of the Intangible Cultural Heritage of Humanity. However, in this article we will discuss its industrial applications rather than its cultural value.

^{A Cup of Coffee (Generated by Artificial Intelligence)}

Considering the vast scale of the coffee industry and the billions of cups of coffee consumed worldwide, it is estimated that millions of tons of coffee waste are generated annually.

Coffee grounds from filtered coffee, Turkish coffee or any other type brewed from coffee beans can be utilized in many areas such as compost, animal feed, energy production and skincare products. In addition, various initiatives are being carried out through local waste management practices, sustainability efforts and waste recycling projects to reduce the impact of such waste.

A new study suggests that replacing a portion of the sand in concrete with used coffee grounds can increase the concrete’s strength by approximately 30 percent. Thus, thermally treated used coffee grounds enhance the compressive strength of concrete.

According to the UK Coffee Association, two billion cups of coffee are consumed worldwide every day. However, according to the new study, most coffee grounds are discarded in landfills where they slowly decompose and produce methane, a greenhouse gas 21 times more potent than carbon dioxide.

Researchers in Australia may have found an effective recycling solution for all this coffee waste by replacing part of the sand in concrete with coffee grounds. The research team noted that the construction industry typically extracts sand from rivers, lakes and deltas, and that altering its composition could help preserve ecosystems worldwide. They found that concrete partially made from coffee grounds is stronger than traditional concrete.

For studies published in the Journal of Cleaner Production, researchers collected used coffee grounds from local cafés in Melbourne and investigated how different proportions and pre-treatments of these coffee wastes affect the properties of concrete. They found that replacing 15 percent of the sand with processed coffee grounds increased compressive strength.

Holmer Savastano Junior, a civil engineer at the university, explained that ordinary concrete consists of a cementitious binder (a mixture of cement and water), sand and coarse aggregate such as gravel, in well-designed proportions depending on the intended application. Aggregate refers to the mixture of sand and gravel that forms the raw materials of concrete. A person from São Paulo, Brazil, not involved in the study, stated that a complex series of hydration reactions between compounds in the water-cement mixture cause concrete to harden, but sand also plays a vital role in this process.

The researchers also noted that sand and other aggregates are generally classified as inert materials—that is, they do not chemically interact or participate in hydration reactions. However, these materials are responsible for the stability, integrity and macrostructural performance of concrete, roughly comparable to skeletal elements in the human body.

In the new study, researchers quickly found that raw coffee grounds significantly weakened the resulting concrete. They explained that untreated used coffee grounds may release chemicals into fresh concrete mixtures and disrupt the chemical hydration reactions responsible for cement hardening. Accordingly, the research team improved the properties of these coffee wastes using a chemical process known as pyrolysis and transformed the coffee into a suitable substitute for sand, which they named “biocoal.”

Pyrolysis involves heating a material to high temperatures (between 350 and 500 degrees Celsius) to break down its molecules into smaller chemical components. This thermal treatment increased the stability of coffee grounds and prevented the release of chemicals that inhibit hydration reactions.

Coffee biocoal has several important structural advantages. Civil engineer Holmer Savastano Junior noted that coffee biocoal retains the porosity and permeability of the original waste material. These characteristics play a crucial role in mechanical performance and therefore in the strength of cement-based materials such as concrete.

The porous structure enhances adhesion between cement and coffee particles and traps moisture within the biocoal’s pores. This allows the coffee biocoal to gradually release moisture back into the surrounding concrete, enabling the vital hydration reactions to continue and preventing premature drying and cracking of the concrete.

The research team concluded that replacing 15 percent of the sand in concrete with coffee biocoal produced at high temperatures yielded the best improvement in strength. They are now investigating other properties such as long-term performance, water absorption, freeze-thaw resistance and electrical resistance, and hope to collaborate with local councils to test this new material in real-world applications.