**1. Introduction**

Brazil stands out for having large mineral deposits, such as ornamental stones, which are transformed into products that can replace ceramic coverings and floors. In the Brazilian national territory, the state of Espírito Santo is known as a major producer of ornamental stones, such as marble and granite [1].

The ornamental stone industry is responsible for moving significant volumes in the national and international markets [2,3]. The Brazilian exports of natural stone materials totaled USD 1.34 billion and 2.40 Mt in 2021, an improvement of 35.5% and 11.4%, respectively, compared to 2020. Revenue and annual variation surpassed the historical records recorded

**Citation:** Moreira, P.I.; de Oliveira Dias, J.; de Castro Xavier, G.; Vieira, C.M.; Alexandre, J.; Monteiro, S.N.; Ribeiro, R.P.; de Azevedo, A.R.G. Ornamental Stone Processing Waste Incorporated in the Production of Mortars: Technological Influence and Environmental Performance Analysis. *Sustainability* **2022**, *14*, 5904. https:// doi.org/10.3390/su14105904

Academic Editor: Antonio Caggiano

Received: 30 March 2022 Accepted: 6 May 2022 Published: 13 May 2022

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in 2013 (USD 1.30 billion and 22.8%). The processed stone export activities were responsible for USD 1.077 billion, about 80% of total revenue in 2021 [4]

The observed growth consumption of the ornamental stone industry, in the national and international marketS, is directly linked to the amount of waste from the processing stages of this material. It is estimated that of the total natural stones available for processing, about 41% becomes tailing. Thus, in 2021, internal processing activities in Brazil generated 3.276 million tons of tailing [4]. The tailings obtained in the beneficiation phase form a sludge.

When drying, this sludge turns into non-biodegradable solid ornamental stone processing waste (OSPW) classified as class IIA waste—non-inert and non-hazardous [5]—which often receives inadequate final disposal, having its impacts reflected on human health and depletion of the environment [6]. The OSPW can be classified as non-biodegradable, from the particle's point of view. Due to the strong presence of quartz in its crystalline phase, it resembles the waste glass previously studied [7], which corroborates that this class of waste, produced in increasing volumes, owing to the lack of adequate landfills for packaging, contributes to the intensification of pollution and ecosystem degradation, impacting factors such as water and soil. It is noteworthy that the glass residue, in its X-ray diffraction analysis, presents a quartz peak, and the remainder in the form of an amorphous halo [7].

The expressive volume of OSPW has a great potential for reuse in civil construction, being compatible with cement matrices, and can be applied as a filler in mortars and concrete, positively influencing the stability of the material [8–11].

The processing of ornamental stone has the objective of transforming the blocks, extracted in the mining phase, into final or semi-finished products. In the mining phase, the blocks are extracted in large dimensions, while in the primary processing, the blocks are prepared and sawn into sheets of variable thickness, usually two or three centimeters. Thus, they are subjected to a surface finish, with or without resin, which can be a simple grinding, polishing, brushing and flaming [1,12].

For the production of concrete and mortars incorporated with ornamental stone waste obtained in the processing phase, it is relevant to study the waste chemical characterization, since elements such as magnesium can generate expandability in the hardened state, reflecting in fissures when used in coatings and paving. In addition, the fineness of the residue and the SiO<sup>2</sup> content associated with the production process might dislodge high reactivity, resulting in the occurrence of alkali-aggregate reactions [13,14]. Aiming at better technological performance of the mortar, in addition to prolonging its durability, some researchers evaluated the addition of OSPW, obtained in the processing phase, which is characterized as a non-plastic and non-biodegradable by-product. The study considered particles with a grain size between 2 µm and 60 µm, with chemical characteristics similar to the sand from the same region [15].

The OSPW, derived from granite and marble whose predominant minerals are calcite and dolomite, can be used as raw material in the production of mortar, presenting itself as an alternative that guarantees satisfactory technological performance, in addition to contributing to the reduction in the environmental impact associated with this industrial activity. Thus, investing this waste is mainly justified by the possibility of mitigating the environmental impact associated with the proper disposal of this waste [16,17].

Several studies of mortars incorporated with residues directed their objectives towards characterization and technological evaluation. However, issues from an environmental perspective and their impacts are still incipient [18]. According to Sánchez et al. [19], one of the main inputs for the production of mortar is cement, which, according to its composition and production process, contributes between 5 and 8% to CO<sup>2</sup> emissions in a global context.

The life cycle assessment (LCA) can be understood as a systematic methodology of analysis capable of contributing to the quantification and identification of environmental impacts and protection areas associated with productive activities. This applies to the construction industry, allowing characteristic and comparative analyses of conventional and alternative products. The principle of LCA is to evaluate the basic flows of processes and products, being able to consider such steps as extraction, production, transport, useful life and disposal [20,21].

Many studies direct their efforts to study the incorporation of waste in the elaboration of new materials, mainly evaluating their results based on technological tests in accordance with current standards. However, in addition to the technological feasibility provided by the standards, it is necessary to evaluate the environmental impacts obtained in the elaboration of these new materials.

Additionally, it should be noted that compliance with the standards represents the minimum parameter for the use of construction materials in the industry, which stimulates the development of new materials. In addition to mitigating the environmental impacts associated with their production, it also results in technological performance that is superior to that expected by the norm. Thus, the present research represents a starting point for studies related to the incorporation of OSPW in the production of mortar, aiming at reducing environmental impacts and improving the technological performance of these new materials, considering the chemical composition of this residue and its positive effects on the formation of mortar.

This study aims to analyze the technological and environmental effects of replacing sand with OSPW in the production process of mortars used in civil construction. Three types of cement were considered for the production of mortar, namely Portland Cement II (CPII), Portland Cement III (CP III), and Portland Cement V (CPV) according to ABNT NBR 16697 [22].

#### **2. Materials and Methods** *Sustainability* **2022**, *14*, x FOR PEER REVIEW 4 of 26

Figure 1 presents the methodological flow established for the execution of tests and analyses in this research.

**Figure 1.** Schematic diagram of the methodological flow.

#### **Figure 1.** Schematic diagram of the methodological flow. *2.1. Selection and Characterization of Materials*

Santo.

*2.1. Selection and Characterization of Materials*  To produce the mortar and carry out the technological tests, the selection stage con-To produce the mortar and carry out the technological tests, the selection stage consisted of obtaining the raw materials sand and OSPW (Figure 2). The sand extraction region

The aforementioned materials were taken to an oven at a temperature of ±105 °C for a period of 24 h. After drying, the OSPW passed through a 30 min milling process, using a ball mill just to ensure the homogenization of the sample particle size. To finish the preparation of the materials the sand and the residue went through the sieving process in a 20 mesh sieve. The analysis of the particle size of the ornamental stone waste was de-

termined following ABNT 7181 [23] by the sieving and sedimentation method.

sisted of obtaining the raw materials sand and OSPW (Figure 2). The sand extraction region was the city of Campos dos Goytacazes, Brazil, with the selection of 50 kg of sand.

**Figure 2.** The ornamental stone processing waste sample.

was the city of Campos dos Goytacazes, Brazil, with the selection of 50 kg of sand. The OSPW, on the other hand, was obtained in the same amount, in Cachoeiro de Itapemirim, Brazil, the main ornamental stone producing city in the state of Espirito Santo. The OSPW, on the other hand, was obtained in the same amount, in Cachoeiro de Itapemirim, Brazil, the main ornamental stone producing city in the state of Espirito Santo.

To produce the mortar and carry out the technological tests, the selection stage consisted of obtaining the raw materials sand and OSPW (Figure 2). The sand extraction region was the city of Campos dos Goytacazes, Brazil, with the selection of 50 kg of sand.

Fresh State Hardened State Environment analisys

*Sustainability* **2022**, *14*, x FOR PEER REVIEW 4 of 26

Selection and characterization of materials

Preparation of Samples

Capillary Absorption

LCA

Tensile Strength in Flexion and Compression

**Figure 2.** The ornamental stone processing waste sample. **Figure 2.** The ornamental stone processing waste sample.

**Figure 1.** Schematic diagram of the methodological flow.

*2.1. Selection and Characterization of Materials* 

Consistency Index

Squeeze Flow

Mass Density

Water Retention

Calorimetry

X-Ray Diffractometry

The aforementioned materials were taken to an oven at a temperature of ±105 °C for a period of 24 h. After drying, the OSPW passed through a 30 min milling process, using a ball mill just to ensure the homogenization of the sample particle size. To finish the preparation of the materials the sand and the residue went through the sieving process in a 20 mesh sieve. The analysis of the particle size of the ornamental stone waste was de-The aforementioned materials were taken to an oven at a temperature of ±105 ◦C for a period of 24 h. After drying, the OSPW passed through a 30 min milling process, using a ball mill just to ensure the homogenization of the sample particle size. To finish the preparation of the materials the sand and the residue went through the sieving process in a 20 mesh sieve. The analysis of the particle size of the ornamental stone waste was determined following ABNT 7181 [23] by the sieving and sedimentation method.

#### termined following ABNT 7181 [23] by the sieving and sedimentation method. *2.2. Preparation of Samples*

Together with the preparation of the materials, the composition of the samples according to the raw materials was adopted in the proportion 1:6 cement/sand. For its dosage, Portland cement types CP II, CP III and CP V (ABNT 16697) [22] were used, and the sand was replaced by 10%, 30% and 60% of OSPW. To compare the results, the reference trace was prepared with 0% substitution, as shown in Table 1.


**Table 1.** Samples composition.
