# Sustainable Production of Building Blocks by Reusing Stone Waste Sludge
## 1 Introduction  
The construction industry involves activities with some of the highest consumption of raw materials and significant waste generation [1, 2, 3, 4, 5, 6, 7, 8]. According to the European Commission, it requires large quantities of resources, accounting for about 50 percent of all the materials extracted and accounting for more than 35 percent of the EU's total waste production [9]. Among the various activities, particularly incidental is the production of natural stone building components and the production of cement mortars and concretes. In relation to the production of mortars and concretes, according to the data from the Global Cement and Concrete Association, global concrete production amounts to about \(14\times 10^{13}\) m\({}^{3}\)/year. This massive use leads to the predominant extraction of raw materials for cement and concrete aggregates, making them the most mined mineral resources globally [10, 11]. The quarrying and processing of stone involves two primary mechanical processes that generate a significant amount of waste of various types: large waste and debris, granules, dust, and stone waste sludge known as marttola (SWS). The waste generated from the cutting and processing of stone can range from a minimum of 35 percent to a maximum of 75 percent of the stone product, and on average, the SWS is 22.5 percent of the raw material processed [12]. Such waste is now a serious environmental problem because, if it is dumped on the ground, it can reduce the filtration rate of rainwater and degrade soil fertility, and if it is dumped into rivers, streams, and oceans, it contaminates the water [13]. Consequently, the need to reduce the extraction from nonrenewable sources, as well as the amount of products going to landfill, becomes an essential imperative to safeguard natural ecosystems for future generations [13; 14; 15]. To date, the main use of SWS is landfilling, but there are numerous studies and research conducted for their reuse in so many areas. These approaches consider the life cycle of the material and adopt circular economy principles. For example, the potential applications include the use of SWS as a neutralizing agent for acidic wastewater in the glass industry [16], as a heavy metal removal agent for industrial wastewater [17], and in flue gas desulfurization in high-power industrial burners using both dry and wet technologies [18; 19; 20]. Within the construction industry, numerous studies highlight the use of stone processing waste as a secondary raw material in the formulation of innovative materials for the production of tiles [21], cement [22; 23; 24], mortar [25; 26; 27; 28], concrete [29; 30; 31], and bricks [32; 33; 34]. In these formulations, SWS can replace or supplement cement and/or fine aggregate at different percentages. Its high fineness provides good mix cohesion, increases its workability, and reduces concrete's permeability. In many cases, such experiments also involve the use of both organic and inorganic additives. In addition to the cement matrix, other studies involve the use of SWS in lime-based products [12], polymer matrix materials, and 3D printing materials [35]. In the literature, some reviews are available about the use of stone waste in concrete, studying the effect of the partial substitution of aggregates and cement in concrete. Some of them [36] carried out a portfolio of the state of the art on the reuse of ornamental stone and have investigated more the strengths and weaknesses of using stone waste in polymer composites, providing a waste stream classification. Others [37] have reviewed scientific contributions about the use of marble, including mining and processing waste, focusing on the impact of replacing traditional components with waste on the technological performance of concrete in its fresh and hardened state, such as its mechanical properties and durability. The results show that with the use of marble powder, with a replacement rate of 10%, the cement does not reduce the performance of concrete and mortars.