Recyclable Cement – A Dream Come True
Concrete is recognised as the most widely used human-made material in the world. With rapid urbanisation and infrastructure development in recent decades, the production of concrete waste has surged, particularly in developing countries such as South Africa. To recycle concrete addresses waste management issues and contributes significantly to sustainability and environmental conservation. This article explores the environmental impacts of cement production, the conventional methods of recycling concrete, and a groundbreaking recycling method developed by the Green Concrete Lab at the University of the Free State (UFS). This new method promises recycled concrete of equal or higher quality than the original, at a significantly lower cost, aligning with the principles of a circular economy.
Environmental impact
The cement industry is a major contributor to global carbon emissions, responsible for 6-8% of total emissions due to fossil fuel consumption and lime calcination during production. The recycling of old concrete such as that found in building demolition waste can offer significant economic and environmental benefits. These include reducing the volume of construction and demolition waste that ends up in landfills, minimising the environmental impact of cement production, conserving landfill space, and reducing the environmental impact of waste disposal. The production of new concrete is energy-intensive and generates significant carbon dioxide (CO2) emissions. Using recycled concrete can cut CO2 emissions by up to 80% compared to producing new concrete, i.e., a crucial reduction in the combatting of climate change. Moreover, recycled concrete is often cheaper to produce than new concrete, leading to cost savings in construction projects. Furthermore, the proximity of recycled aggregate sources can reduce transportation costs and related emissions.
Conventional methods for recycling concrete
The conventional recycling method involves breaking down old concrete into aggregate, which is then reused in new concrete mixtures. In this approach, only the aggregate component is replaced with recycled concrete aggregate (RCA), while new cement is still required, typically in the form of Portland cement. This is significant because the majority of the costs and environmental impact associated with concrete production stem from the cement, not the aggregate.
Cement production is highly energy-intensive and generates considerable CO2 emissions due to the calcination process and the combustion of fossil fuels. The use of new cement in conventional recycling methods does not fully address these environmental concerns. Typically, a significant portion of recycled aggregate consists of hydrated cement paste bound to fine and coarse aggregate particles. One of the challenges in the use of recycled concrete as an aggregate is related to the presence of hydrated cement paste within the recycled aggregate, which negatively affects the physical and mechanical properties of the new concretes. The hydrated cement paste has relatively lower strength and higher water absorption compared to natural aggregates, resulting in strength loss and lower workability of the concrete mixtures made using recycled concrete aggregates. Therefore, while conventional recycling addresses some waste management issues, it does not fully optimise the potential of recycled concrete in terms of quality and sustainability.
Developing the new recyclable concrete and recycling method
Researchers at the Green Concrete Lab at the University of the Free State have developed a new zero-waste recycling method that allows for the recycling of both aggregate and cement paste from demolished concrete. In the proposed approach, the recycled binder is used as the binder in the new mixtures along with the aggregates. The method employs an alternative recyclable cement instead of Portland cement in the parent concrete, formulated based on vastly available industrial wastes such as coal ash and slag. The new recycling approach consists of a series of activation processes, including thermal, mechanical and chemical activation.
One of the key advantages of the developed method is the simplicity of its processes, which can be easily adopted and implemented at existing recycling plants with minimal costs. This method ensures that the recycled product is of high quality, often matching or even exceeding the performance of new concrete. This includes higher strength, making it a viable option for various construction applications such as roads, pavements and buildings. The production and recycling of concrete through this developed method reduces the need for new ingredients, including Portland cement and natural sands and stones. The new method also offers remarkable economic and environmental benefits by limiting the need for Portland cement production. In addition, by using industrial by-products and waste materials, this innovative approach not only reduces waste but also decreases the demand for virgin raw materials.
A Promising Future Ahead
The adoption of recyclable cement and concrete recycling practices holds profound environmental benefits. By decreasing reliance on virgin materials and reducing greenhouse gas emissions, these practices contribute to a more sustainable construction industry and also align more closely with global sustainability goals and local environmental regulations. Innovations in recyclable cement can drastically reduce CO2 emissions by reducing the CO2 produced during the Portland cement manufacturing process. The concept of recycling concrete furthermore aligns with the principles of a circular economy, where materials are reused and recycled to extend their lifecycle. This approach not only reduces waste but also promotes resource efficiency, which is crucial for sustainable development. The recycling industry has the potential to create numerous job opportunities, from the collection and processing of concrete waste to the manufacturing of recycled concrete products, which can be particularly beneficial in South Africa.
While the benefits of recycling concrete are clear, challenges such as ensuring the quality and consistency of recycled concrete due to contamination and variability in source materials need to be addressed.
Advanced sorting and processing technologies are required to produce paste-rich powder along with clean aggregate. A robust regulatory framework is essential to promote the use of recycled concrete, including policies that mandate or incentivise the use of recycled materials in construction projects and standards to ensure the quality and safety of recycled concrete. Education and awareness campaigns, coupled with successful case studies, can help change perceptions and increase acceptance of recycled concrete. The future of concrete recycling in South Africa looks promising, with increasing awareness and adoption of sustainable practices in the construction industry. Innovations from the Green Concrete Lab at the University of the Free State are paving the way for a greener and more sustainable construction sector.
Recycling concrete is not just an environmental imperative; itʼs an economic opportunity. By embracing sustainable practices and innovations like those of the UFS, South Africa can lead the way in green construction. This shift towards sustainability will not only protect our environment but also bolster the construction industry, making it more resilient and cost-effective. As South Africa continues to grow and develop, the adoption of concrete recycling practices and innovative sustainable materials will be essential in building a greener, more sustainable future.
