# Sustainable Production of Building Blocks by Reusing Stone Waste Sludge
## 2 Materials and Methods
### Materials  
The materials used in the trial are limestone sand (CS) for the production of mortars, water (W), PC, and finally QLD and SWS as ultrafine materials. The waste was taken from the stone production processes of the marble basin of Apricena. The PC used was of the type, CEM I 42.5 R, conforming to the prescribed composition of UNI EN 197-1:2011 [45];  
The W was as required by UNI EN 1008:2003 [46];  
The CS used was natural standard sand (according to CEN EN 196-1 [47])  
SWS consists of stone processing waste generated in wet stone processing plants, the characterization of which was performed in a previous study [12], the results of which are presented below. Mineralogical analysis was carried out via X-ray diffractometry, and the results show that the main phase is calcite (CaCO\({}_{3}\)), while traces of Dolomite (MgCa(CO\({}_{3}\))) and hematite (\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)) were detected as compounds. The results of TG-DTA show a sample mass loss of 43.30%, and a calcium carbonate content of 98.41% by mass. The experimental data were confirmed via the hydrochloric acid attack performed on two powder samples, and indicate an average value of non-carbonate impurities of 1.56% by mass and a calcium carbonate content equal to 98.44% by mass. The chemical composition of SWS was determined via X-ray fluorescence spectrometry, which was also used to support the XRD analysis carried out quantitatively. The results show that SWS is composed mainly of CaO (55.6%), and all the other components (Fe\({}_{2}\)O\({}_{3}\), Al\({}_{2}\)O\({}_{3}\), SiO\({}_{2}\), Na\({}_{2}\)O, K\({}_{2}\)O, TiO\({}_{2}\), SO\({}_{4}\), CO\({}_{2}\)) were present in amounts less than 0.1% except MgO (0.25%). The results of the eluate analysis show that with reference to the Italian Regulations [48], the SWS was found not to be \"non-hazardous waste\", and can be designated for recovery. The specific gravity is 2.80 g/cm\({}^{3}\). The moisture content of the SWS is equal to 23.5%. The test performed to measure the ISO brightness level showed a very high and almost pure degree of whiteness with a value of 93.5% \(\pm\) 1. The particle size distribution of the solid particles, obtained by using the laser diffraction method, shows that the maximum particle size, expressed as the equivalent diameter, was equal to 77 \(\upmu\)m. Only 8% of the mass  
Figure 1: Production process flowchart. had a particle size between 22.5 \(\upmu\)m and 77 \(\upmu\)m, while the remaining 92% of the mass had a particle size below 77 \(\upmu\)m. Only 8% by mass had a particle size between 22.5 \(\upmu\)m and 77 \(\upmu\)m, while the remaining 92% by mass had a particle size below 22.5 \(\upmu\)m, with 7% by mass having a particle size below 0.5 \(\upmu\)m. The Blaine specific surface area was 9273.79 cm\({}^{2}\)/g. This value confirms the significant fineness of SWS. QLD, derived from stone crushing in the aggregate production process in Crete, was used in the first phase of the study and was analyzed by [PERSON] [PERSON] [36; 37] who compared it with the results obtained for SWS. QLD and SWS have mineralogical compositions that were analyzed using completely similar X-ray directorometers. They consist primarily of calcite (approximately 98% by weight) with traces of other elements such as quartz and dolomite. The chemical compositions are also similar (Table 1), with an absolute prevalence of CaCO\({}_{3}\) present in amounts greater than 98%, with a difference of 0.22% between QLD and SWS. In contrast, the particle sizes of the two types of waste analyzed were slightly different (Figures 2 and 3). Although they are mostly ultrafine materials, it appears that SWS contains the largest amount of ultrafine material, while QLD produced for the production of concrete aggregate tended to be slightly larger in diameter.