The growing focus on environmental sustainability has assumed a central role in the definition of industrial policies and development strategies at the global level. In this context, the circular economy serves as a reference model capable of promoting waste reduction, resource recovery, and the valorization of materials originating from production processes. Within the framework of ecological transition, the reuse of industrial materials emerges as a key strategy to reduce the environmental impact of construction activities. However, the environmental compatibility of these materials must be rigorously evaluated in order to prevent potential negative effects on soil, groundwater, and the surrounding environment. The introduction of the End of Waste concept (European Directive 2008/98/EC) marks a turning point in the approach to waste management, allowing certain waste streams to cease being classified as waste and instead be recognized as products, provided that they meet specific quality and safety criteria. Simultaneously, the classification of materials as by-products, under Article 184-bis of Legislative Decree 152/2006, offers an additional instrument for fostering the responsible use of resources generated by production processes. Nevertheless, the management of such materials in the construction sector requires a systematic approach integrating environmental, technical, and economic assessments. From the perspective of environmental compatibility, the requirements are not clearly delineated; in fact, the EoW criteria specify that “the use of the substance or object will not lead to overall negative impacts on the environment or human health,” while by-product regulations require that “its further use is lawful, meaning that the substance or object meets, for the specific use, all pertinent product, health, and environmental protection requirements and will not lead to overall negative impacts on the environment or human health.” This doctoral thesis examines the characteristics of three types of materials: Recycled Aggregates (RA) from Construction and Demolition Waste (CDW): These are inert materials obtained through the treatment and recovery of debris generated from construction, renovation, and demolition activities involving buildings, infrastructure, and other works. They primarily include concrete, bricks, ceramics, mortars, stones, and asphalt, which undergo crushing, screening, and separation processes to remove impurities and produce reusable materials. Electric Arc Furnace Steel Slag (EAFS): Steel mills currently employ standardized and consolidated procedures for producing pig iron and steel. These processes differ with respect to raw materials used, furnace size, processing duration, and process management, as well as the resulting outputs. In particular, alongside primary raw materials (pig iron or steel), these methods generate by-products such as steelmaking slag. Waste Foundry Sand (WFS): Each year, foundries purchase hundreds of millions of tons of silica sand to form molds and cores that give shape to cast components. After multiple uses, these sands become waste and must be appropriately recovered or disposed of. This dissertation therefore aims to analyze the tools and methodologies employed for assessing the environmental compatibility of materials derived from recovery and reuse processes, with the goal of enabling their safe and effective utilization in the construction sector, especially in unbound applications (i.e., those that do not incorporate binders such as cement or bitumen).