# Sustainable Production of Building Blocks by Reusing Stone Waste Sludge
## 4 Conclusions  
This study investigated the possibility of producing cement-based compounds for the production of building elements using SWS and, in particular, artificial stone. Following the characterization of these wastes, the purpose and design guidelines were defined, as well as the flowchart of the production process, which includes after-powder mixing, hydration, and subsequent compaction prior to maturation. After defining the water and cement dosage ranges, the reference particle size melt, and the ideal particle size curve, the aggregates were tested to determine the degree of compaction of the materials. The first experimental activity involved a mixture containing three types of aggregates whose grain size curve best approximated the ideal theoretical curve based on which the change in compressive strength as the amount of water added to the mixture varied. Having determined the optimum amount of water in relation to the corresponding compressive strength, we proceeded to design the optimum mix using two types of aggregates and evaluated the change in mechanical strength of the mix as the SWS increased, even when replacing the cement. The results indicated the following findings:  
The potential of waste materials from stone processing is high and, in particular, they can be extensively reused and returned to the production cycle of building materials;  
The production of artificial stone and mortar allows the use of significant amounts of waste materials (40% on a dry basis is the average contained in the mixtures);  
The designed and tested materials contained very low amounts of both water (13% on a dry basis) and cement (10% on a dry basis on average), which benefits the product economy;  
The designed and tested artificial stone mixes had excellent compressive strength (29.9 N/mm\({}^{2}\) to 13.12 N/mm\({}^{2}\)), and the values found far exceeded the minimum values required by the standards for structural blocks; \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**STONE** & \multicolumn{3}{c}{**LIMESTONE**} & \multicolumn{2}{c}{**BLOCKS CLS**} \\ \hline
**Type** & **Rm \({}^{1}\)** & **Type** & **Rm \({}^{1}\)** & **Type** & **Rm \({}^{1}\)** \\  & **[MPa]** & & **[MPa]** & & **[MPa]** \\ \hline ARENARIA & 105 & MASSAFRA & 3.45 & \multirow{2}{*}{
\begin{tabular}{c} \textgreater{}6.5 \\ \end{tabular} } \\ TRAVERTINO & 101 & CANOSA & 4.1 & \\ TRAN CHIRAO & 194 & GRAVINA & 3.47 & \\ PIETRA DORATA & 512 & FASANO & 3.75 & \\ PIETRA DFI FINALE & 223 & LECCE & 2.06 & \\ \hline \hline \end{tabular} \({}^{1}\) Rm = average compressive strength.  
\end{table} 
Table 10: Characteristic mechanical strengths of stone, Apulian tuff, and concrete blocks for load-bearing masonry in seismic zones in commerce. The mechanical strengths are much higher than materials commonly used for load-bearing masonry (except stone);  
The increased SWS in the mixes resulted in reduced brittleness due to the presence of cement, resulting in large deformation margins before failure;  
The initial observation under a polarized optical microscope showed that the slurries were very cohesive, with little presence of voids, which were of a limited size. The material did not show the formation of canaliculi that could cause the same priming;  
The proposed manufacturing processes are simple, inexpensive, and based on technologies already used in industry. However, further investigation is needed into the possible methods for drying SWS to remove any residual aqueous fraction, and kneading and forming/compacting techniques to make them industrializable. The results proved to be extremely interesting, as they provide a comprehensive overview of the potential of compounds produced according to the identified processes, and showed excellent properties for use as building elements in construction. Further studies should be conducted through further research on the following: water absorption, thermal properties, vapor permeability, fire resistance, and durability through accelerated aging tests.