## 1 Introduction
It improves the durability of concrete, notably its resistance to sulfates and chloride penetration, and reduces the carbon footprint of concrete [20; 21]. SCMs offer promising opportunities for reducing the carbon footprint of cementitious matrices. For example, a 22% reduction in CO\({}_{2}\) emissions has been observed for a 40% replacement of cement by fly ash in a cementitious paste [22]. Similarly, replacing 15% of cement with silica fume in concrete results in a 12% reduction in CO\({}_{2}\) emissions [23]. In the case of metakaolin, a 20% substitution results in around 17% reduction [24]. GGBS can reduce emissions by up to 47% with a substitution rate of 70% in concrete [25]. These results demonstrate the potential of SCMs to significantly reduce the environmental impact of cementitious materials. At present, research is focusing on optimizing the substitution rates of these SCMs, assessing their impact on the mechanical and durability properties of concrete and analyzing the life cycle of the materials. However, major gaps remain, notably concerning the variability of the chemical composition of these wastes and their long-term effects on concrete structures. Further study is needed to better understand these effects and improve SCM design and application practices in the concrete industry. By judiciously exploiting SCMs, the concrete industry can reduce its carbon footprint while optimizing the technical performance of its products, thus contributing to a more sustainable future for the construction sector. The use of concrete industry waste as SCM is a rapidly expanding field. The current research focuses on optimizing substitution rates, assessing impacts on mechanical and durability properties and life-cycle analysis. However, there are still significant gaps concerning the variability of the chemical composition of these wastes and their long-term effects on concrete structures. Some of these studies have explored recycling concrete industry waste as SCM. For example, the reuse of finesfrom washing ready-mix concrete has been studied, showing a reduction in compressive strength but an improvement in durability [26]. Similarly, recycled concrete fines obtained by mechanosynthesis have been valorized for construction material production [27]. Among the promising new sources of SCMs, washing fines represent a particularly interesting and innovative opportunity. These fines are waste products from the cleaning operations of concrete plants and truck-mixers after the production of ready-mix concrete. Composed mainly of fine silica and calcium particles, these wash fines are often considered non-value-added waste and simply disposed of, generating additional costs and undesirable environmental impacts. However, their incorporation into mortar and concrete formulations as a partial substitute for Portland cement offers a significant double advantage. On the one hand, it would reduce cement consumption and, consequently, the CO\({}_{2}\) emissions associated with its energy-intensive production. On the other hand, it would transform a previously unused waste product into a valuable resource, reclaiming these washing fines and reducing the environmental impact associated with their management and disposal. The use of washing fines as an alternative SCM fits perfectly with the concrete industry's strategy to reduce its carbon footprint while promoting a more sustainable circular economy. The judicious recovery of this waste not only reduces waste management costs but also reduces demand for Portland cement, the production of which is particularly energy-intensive and emits greenhouse gases. This innovative approach represents a further step towards a more environmentally friendly concrete industry by fully exploiting the potential of all available by-products and waste as valuable alternative resources. Wash fines, once considered a worthless waste product, could play a key role in the transition to more sustainable construction.