Learning from Innovation

The construction industry faces an enormous challenge: Cement production accounts for approximately 8% of global greenhouse gas emissions. With concrete being the world's second-most consumed material after water, finding sustainable alternatives has become critical for meeting climate goals. A high-risk, high-gain three-year research project, "Cement Recycling Using Biobased Chemicals," recently concluded its ambitious attempt to revolutionize how we approach concrete waste.

Led by Wageningen Food & Biobased Research and supported by a consortium including Gelderland, Preco, ProRail, TNO, Urban Mine, Rijkswaterstaat, and AMS Institute, this project addressed one of construction's most persistent problems. When concrete structures reach the end of their lifecycle, the cured cement within them typically becomes mere filler material for new concrete or asphalt. The research team envisioned something far more transformative: reactivating this "spent" cement at room temperature using biobased additives derived from agricultural byproducts like starch and pectins.

"This work focuses on recycling of spent material, cement in particular," explains the project coordinator. "If it were possible to recycle the spent cement, it would imply that carbon dioxide emissions would go down significantly." The approach centered on controlling calcium, one of cement's two key strength-providing components alongside silicon, in solution through innovative biobased chemistry.

Recycling cement

The vision extended beyond environmental benefits to economic transformation. "We aim to develop and study breakthrough innovations that can have a big impact on society and create opportunities for Dutch companies to thrive," the researchers explain. This innovation would create an entirely new value chain where biobased materials would find novel applications while simultaneously increasing the value of construction waste.

To understand the challenge, it helps to know the chemical mechanism that makes concrete work. "Concrete is widely used as a building material and basically consists of water, cement, sand, and gravel," the team explains. "Cement in concrete hardens when you mix it with water by forming strong chemical bonds. To recycle the cement, you need to break these bonds so the cement can harden again to 'glue' together the sand and gravel in new concrete."

Unexpected Discoveries Along the Way

The research yielded interesting insights that the team did not expect up front. One of the most significant discoveries was the remarkable stability of biobased additives under cement's harsh, high-pH environment.

This finding opens doors for future applications beyond the original project scope. The team successfully demonstrated that biobased polymers could regulate calcium concentration, a crucial breakthrough that validates the underlying science.

However, the research also revealed unexpected complexities. "Reactivating cement is essentially breaking down the molecules and allowing the calcium and silicon in the solution to create new bonds," the researchers explain. "The idea of doing this seemed to make sense, but it is a wicked problem actually to do it in practice." One challenge was the heterogeneous nature of construction waste itself: "CDW itself is not homogeneous, and the type of cement that is used in the original concrete is usually not known."

Cement Recycling is Extraordinarily Complex

While the project did not achieve its ultimate goal of creating recycled cement with full original strength, it did manage to reach two-thirds of its original strength. This represents significant progress for future applications in pavement tiles for public roads. The research revealed that cement recycling is quite complex, requiring precise control of calcium and silicon components simultaneously.

"The project focused on one part of the cement equation, but it takes two to tango," the team reflected. "Just regulating the calcium concentration is by far not enough to create strong cement." This insight proved invaluable, highlighting that future research should address positively charged calcium and negatively charged silicon components to achieve full cement recycling potential.

The team tried multiple approaches throughout the project. "We tried several biobased additives in different amounts and under different conditions. But we were unable to control the breaking of the bonds and to reactivate the cement neatly," they acknowledge.

Essential Groundwork

Rather than viewing the results as a setback, the research team sees this work as essential groundwork for future breakthroughs. The collaboration with TNO Building Materials and Structures team provided crucial expertise from biobased chemistry and concrete engineering perspectives, a partnership model that will inform future projects.

The team has already identified promising next steps, including investigating how to release silicon components from spent cement structures and exploring alternative applications for biobased polymers in cement stabilization. "The use of biobased polymers instead of polyacrylates will lead to lower greenhouse gas emissions," they note, though significant technical challenges remain before practical applications can be realized.

A Brilliant Failure

This research exemplifies how scientific progress often unfolds through bold hypotheses, rigorous testing, and honest assessment of results. By sharing both successes and challenges openly, the team contributes valuable knowledge to the global effort toward sustainable construction.

The researchers embrace the concept of transforming unsuccessful attempts into valuable learning experiences. "From a technology perspective, yes. We tried a new approach, and it did not succeed, so that is a failure," they acknowledge. However, as Prof. Paul Iske highlights with his Institute of Brilliant Failures, a failure can turn into a Brilliant Failure if you learn from it and share what you have learned."

This approach serves the broader scientific community: "We have learned that our approaches did not work, and we hope that by sharing our results, others may be able to look at our results from a different perspective and come up with new approaches for cement recycling that are more effective and viable."

The construction industry's path to sustainability will require many such innovative attempts. Each provides crucial learning that brings us closer to breakthrough solutions for one of our most pressing environmental challenges.

For the complete research findings and detailed technical analysis, visit the full report on openresearch.amsterdam.