Circular Economy, which it is among the priorities of the European Commission, is defined as an economy in which the value of products, materials and resources is maintained for as long as possible and the production of waste is reduced to minimum. Keeping in mind the impact on the environment caused on the one hand by post-consumer plastic waste and on the other hand by production processes of concrete, it is possible to find a solution able, at least partly, to mitigate these two issues. Following the principles of the circular economy, in fact, it is possible to reuse post-consumer plastic waste as fine aggregates in concrete: in this way, post-consumer plastic from waste becomes a resource; at the same time, the use of other natural resources is limited, such as the minerals traditionally used as aggregates in concrete. However, this virtuous solution still presents some problems to study and solve: this work aims to illustrate some of these issues, and provides indications on the aspects to be analyzed and solved.