# Reutilization of Recycled CDW Sand in Mortars, Paving Blocks, and Structural Concrete
## 1 Introduction  
The reutilization of construction and demolition waste (CDW) as recycled aggregates (RAs) has been paid considerable attention in recent years for its potential to address environmental concerns and to enhance resource efficiency in the construction industry. Global urbanization and industrialization have led to an increasing demand for infrastructure and housing, which results in the generation of vast quantities of CDW. Over 3 billion tons of CDW waste are generated globally each year [1, 2], and in the European Union,CDW constitutes about one-third of the total waste produced annually [3]. According to [PERSON] et al. [4], the construction industry is responsible for approximately 36% of the global solid waste found in landfills. CDW can be classified into waste generated during the construction phase, and that generated during demolition, which typically accounts for over 50% of the total waste produced by the construction industry [5]. Additionally, the construction sector is a major consumer of natural resources, accounting for approximately 50% of all extracted materials, including metals, stones, gravel, sand, or wood. It is also responsible for the release of approximately 6 billion tons of CO\({}_{2}\) into the atmosphere [6]. Consequently, the development of sustainable practices to reduce the sector's environmental footprint is imperative. In this context, disposing of CDW in landfills is becoming increasingly unsustainable and necessitates the development of innovative waste management solutions that align with circular economy principles. These solutions should prioritize the reuse of CDW in higher-value-added applications, such as employing it as raw material in the production of new building materials, rather than restricting its use to lower-value applications like road sub-bases. To mitigate the environmental impact of CDW, researchers such as [PERSON] et al. [2] developed a sustainable bioleaching method to reduce the volume of concrete in CDW. This innovative approach offers an efficient and environmentally friendly strategy for CDW management, facilitating its reuse in the production of new building materials. The RAs that derive from CDW are a promising alternative to natural aggregates (NAs) in construction applications, including recycled aggregate concrete (RAC), road construction, and embankments. Apart from reducing the volume of waste disposed in landfills, reusing CDW as RAs helps to keep natural resources and to mitigate the environmental impacts associated with resource extraction, habitat destruction, water pollution, and carbon emissions [7; 8; 9; 10]. Although RA use can result in cost savings by decreasing the demand for natural materials and lowering waste disposal costs, the initial investment in processing facilities and equipment can be substantial. As highlighted by [PERSON] et al. [11], the implementation of landfill taxes could be crucial in promoting RA use by offsetting initial processing costs and improving the competitiveness of recycled materials compared to NAs. The properties and performance of RAs have been extensively researched [12; 13; 14]. Recent studies have shown that, when appropriately processed, the properties of RAs can be comparable to those of NAs, which makes them a viable substitute in many structural and non-structural applications [13; 14; 15; 16; 17; 18]. [PERSON] and [PERSON] [12] observed that the impact of RAs on concrete strength is influenced more by the recycled material quality than by its quantity. Some studies have reported a reduction in compressive strength when NAs are replaced with RAs [8; 19; 20; 21], but other research works have indicated that mechanical properties remain largely unaffected or even improve with the incorporation of RAs [22; 23; 24; 25; 26]. This variability in material properties, in addition to the perception of reduced quality compared to NAs, poses challenges of widespread RA adoption.