The material recycling options and current research activities for the circular use of the construction composite concrete

Construction materials account for a large fraction of materials handled by humans, and a correspondingly large footprint, ranging from extraction/mining of raw materials, embodied CO2 through materials production /refinement, and waste of construction activities and demolition. Concrete, after water the second most used material globally, is a staple when it comes to infrastructure in general. It is a composite material made from cement, sand, gravel water, and possibly other admixtures and additives, and their recipes/proportions can be as complex as their value chains. Concrete can be understood as man-made geology as it is an artificial stone, which is ideally tailored to its functionality, but its components may differ in chemical composition and therefore have different properties. Additionally, the material may change according to its environmental conditions, which may reduce the circular economy (CE) options for reuse and recycling. Integrating CE principles in the construction sector would ideally lead to the material reuse of construction elements as this provides the biggest CO2 benefit. However, the material properties and their possible determine the lifetime, maintenance costs, and risk for owners, operators, investors, and construction activities. Reduce, reuse, and recycle, for example, have all different meanings for the design, maintenance, and end-of-life of concrete structures depending on the type of composite/concrete and the proposed reuse strategy. It is then crucial to understand concrete properties at the end of life so we can define appropriate CE avenues (reuse, recycle, etc). This manuscript explains the most common resources (cement, sand, gravel water, and other admixtures and additives) used, and their influence on the CE-relevant design choices which ultimately also define the possible reuse or recycling routes. Additionally, a literature overview of current research topics will be provided that allows insight into reuse and recycling options for concrete. This becomes increasingly interesting as the traditional linear economy practices are threatening the supply chain of seemingly abundant materials such as sand and water as well. Hence the transition from a linear to a circular economy might not only help with reducing CO2 emissions but resource uses, even though additional work/energy/CO2 will be required to produce first-grade recycling materials that can replace virgin materials 1:1