**2. Materials and Methods**

It is important to highlight that for projection application, some mortars characteristics in the fresh state must be different from those used in the conventional application method. The main one being the workability. This can be defined as the material fluidity, i.e., the ability of the mass to flow or spread over the substrate surface [19]. The fluidity required for the projection will depend on the corresponding equipment used. For this purpose, a sample of mortar used by a construction firm in the region of Campos dos Goytacazes, Brazil, was collected and its workability was defined by the consistency index. This test consists of molding a conical trunk with fresh mortar and, after 30 drops on the consistency table, measure its spread [20].

Once this index was determined, the workability was kept constant using the same consistency index in all mixture. Then, the amount of water and proportion of additive, which, each mortar should have as reference consistency index was defined [21].

In addition to develop a mortar suitable for projection without cracks, a mortar with ornamental rock waste and an additive developed at our laboratory, were tested for the creation of a novel and sustainable product. In order to analyze whether the materials are economically viable substitutes for hydrated lime, a cost-effective study was carried out. For that, Table 1 presents a comparison made in three commercial centers at Campos dos Goytacazes to estimate the hydrated lime CH-III price. The only cost related to the

ornamental rock waste is its transportation from the city of Cachoeiro do Itapemirim to Campos dos Goytacazes, both in the southeast of Brazil. mental rock waste is its transportation from the city of Cachoeiro do Itapemirim to Campos dos Goytacazes, both in the southeast of Brazil.

In addition to develop a mortar suitable for projection without cracks, a mortar with ornamental rock waste and an additive developed at our laboratory, were tested for the creation of a novel and sustainable product. In order to analyze whether the materials are economically viable substitutes for hydrated lime, a cost-effective study was carried out. For that, Table 1 presents a comparison made in three commercial centers at Campos dos Goytacazes to estimate the hydrated lime CH-III price. The only cost related to the orna-


**Table 1.** Price of hydrated lime and ornamental rock waste. **Table 1.** Price of hydrated lime and ornamental rock waste.

*Sustainability* **2022**, *14*, x FOR PEER REVIEW 4 of 16

The cement used in this work was the same used as the reference mortar, CPIII-40 RS [22], purchased from the same batch so that there was no variation in the constituents percentage (clinker + calcium sulfate, blast furnace slag and carbonate material). The cement used in this work was the same used as the reference mortar, CPIII-40 RS [22], purchased from the same batch so that there was no variation in the constituents percentage (clinker + calcium sulfate, blast furnace slag and carbonate material).

The small aggregates selected for mortars manufacture came was quartz sand extracted from the bed of the South Paraíba River, with a maximum diameter of 2.4 mm [23]. The small aggregates selected for mortars manufacture came was quartz sand extracted from the bed of the South Paraíba River, with a maximum diameter of 2.4 mm [23].

The ornamental rock waste used (Figure 1a) was collected from Decolores, an ornamental rock processing industry, located at Cachoeiro do Itapemirim. To be applied in this study, the ornamental rock waste was first dried naturally in the sun to remove excess moisture and then placed in a greenhouse (Sterilife brand, Brazil) at 60 ◦C during 72 h. Completely dry, the waste was crushed and passed through the ASTM 50 sieve (Figure 1b). Corinaldesi et al. [17] characterized Italian marble waste and observed that these were mainly composed of calcite (60% calcium carbonate—CaCO3), while Vardhan et al. [24] studied Indian rocks, and concluded that they were composed of 40.73% CaO and 15.21% MgO. This indicates that the waste chemical composition will depend on the region of origin of the rock from which it was extracted [25]. The ornamental rock waste used (Figure 1a) was collected from Decolores, an ornamental rock processing industry, located at Cachoeiro do Itapemirim. To be applied in this study, the ornamental rock waste was first dried naturally in the sun to remove excess moisture and then placed in a greenhouse (Sterilife brand, Brazil) at 60 °C during 72 h. Completely dry, the waste was crushed and passed through the ASTM 50 sieve (Figure 1b). Corinaldesi et al. [17] characterized Italian marble waste and observed that these were mainly composed of calcite (60% calcium carbonate—CaCO3), while Vardhan et al. [24] studied Indian rocks, and concluded that they were composed of 40.73% CaO and 15.21% MgO. This indicates that the waste chemical composition will depend on the region of origin of the rock from which it was extracted [25].

**Figure 1.** Ornamental Rock Waste (**a**) in the ornamental rock industry with humidity, (**b**) dry and passed at #50. **Figure 1.** Ornamental Rock Waste (**a**) in the ornamental rock industry with humidity, (**b**) dry and passed at #50.

Figure 2 shows a flowchart that demonstrates the experimental steps of this research.

Figure 2 shows a flowchart that demonstrates the experimental steps of this research.

**Figure 2.** Experimental flowchart of the steps developed. **Figure 2.** Experimental flowchart of the steps developed.

To increase the mortars workability without adding large proportions of water, and thereby decrease the likelihood of cracking, a superplasticizer additive was developed at our Laboratory of Non-Conventional Materials of the State University of the North Fluminense, in Campos dos Goytacazs), to be added in ornamental rock waste mortars, in order to create an entirely new material. Due to the percentage of fine particle size, which allows the waste to act as a filler and improve packing by reducing the voids left by the other two components, the requirement of water increases as the amount of ornamental rock waste in samples is enhanced [26]. Therefore, superplasticizers are used to achieve the required workability [23], since it is a projected mortar, and workability needs to be superior to the conventional ones. To increase the mortars workability without adding large proportions of water, and thereby decrease the likelihood of cracking, a superplasticizer additive was developed at our Laboratory of Non-Conventional Materials of the State University of the North Fluminense, in Campos dos Goytacazs), to be added in ornamental rock waste mortars, in order to create an entirely new material. Due to the percentage of fine particle size, which allows the waste to act as a filler and improve packing by reducing the voids left by the other two components, the requirement of water increases as the amount of ornamental rock waste in samples is enhanced [26]. Therefore, superplasticizers are used to achieve the required workability [23], since it is a projected mortar, and workability needs to be superior to the conventional ones.

First of all, the ornamental rock waste characterization was carried out using granulometric analysis [27], dispersive energy X-ray fluorescence (EDX), X-ray diffraction (DRX) and scanning electron microscopy (SEM). The EDX aims to determine the oxides percentages present in the analyzed materials using a Shimadzu EDX-700 equipment. The DRX determines the crystal atomic and molecular structure, in samples using a Rigaki MiniFlex 600. The SEM reveals the particle morphological analysis in a Shimadzu SSX-50 Superscan equipment, Japan. These tests were made concurrently with the consistency First of all, the ornamental rock waste characterization was carried out using granulometric analysis [27], dispersive energy X-ray fluorescence (EDX), X-ray diffraction (DRX) and scanning electron microscopy (SEM). The EDX aims to determine the oxides percentages present in the analyzed materials using a Shimadzu EDX-700 equipment. The DRX determines the crystal atomic and molecular structure, in samples using a Rigaki MiniFlex 600. The SEM reveals the particle morphological analysis in a Shimadzu SSX-50 Superscan equipment, Japan. These tests were made concurrently with the consistency test [28], to determine the ideal amount of water for the desired workability.

test [28], to determine the ideal amount of water for the desired workability. Once the components have been characterized, their dosage was set for the reference mortar, with design mix of 1:1:4, obtained at the aforementioned construction site, have shrinkage cracks after drying. It contributes to find the consistency index determination to be used to maintain a fixed workability of 310 ± 5 mm. As mentioned before, this is one of the most important characteristics in a mechanized projected mortar, as it allows the material to flow through the projection pump hose without clogging or disaggregation Once the components have been characterized, their dosage was set for the reference mortar, with design mix of 1:1:4, obtained at the aforementioned construction site, have shrinkage cracks after drying. It contributes to find the consistency index determination to be used to maintain a fixed workability of 310 ± 5 mm. As mentioned before, this is one of the most important characteristics in a mechanized projected mortar, as it allows the material to flow through the projection pump hose without clogging or disaggregation between the paste and aggregates.

between the paste and aggregates. With this in mind, the reference mortar was subjected to the consistency test [28], where it was molded in a conical trunk. After performing 30 drops the spreading was With this in mind, the reference mortar was subjected to the consistency test [28], where it was molded in a conical trunk. After performing 30 drops the spreading was measured. The more fluid the material, the greater this spread and consequently the consistency index. The value found was 310 ± 5 mm, which is higher than the limit established by NBR

13276 [28]. However, the standard value must be disregarded, considering that it applies only to conventional mortars.

With the known spread, it was possible to determine the amount of water and the percentage of additive that would be used in each mix, as shown in Table 2.


**Table 2.** Consistency index and water/dry materials ratio.

As the aim of this work was to develop a mortar with ornamental rock waste to be applied in a mechanized projected way and within the parameters of the Brazilian standard, it was tested in the fresh and hardened state. With the amount of water and superplasticizer known, the mortars were molded following the NBR 13276 [28] procedures and tested by the fresh state for squeeze flow [29], mass density in the fresh state and the incorporated air content [30] as well as water retention [31]. Like the consistency index, the squeeze flow test is used to determine workability. It was carried out in a universal EMIC press, and consists of compressing the sample between an upper plate, which will apply load to the material and has the same diameter as the initial sample, and a lower plate, which has at least twice the sample initial diameter. The sample is placed and spread when the test is started [32,33].

The mass density test in the fresh state is applied to determine the mortar weight at the application moment. This test is important in situations where the mortar is mechanized projected into the substrate and also to determine the incorporated air content. This characteristic affects its workability, and corresponds to the amount of air existing inside the mortar, expressed as a percentage [34]. The water retention property is related to the mortar's ability to retain water in the fresh state, maintaining its workability or consistency when subjected to conditions that cause water loss [35]. Properties such as mechanical strength, adhesion and durability are influenced by this characteristic [36].

For hardened state parameters, the mortars were molded according to NBR 13279 [37] and their parameters analyzed. These were water absorption by immersion and voids index [38] as well as water absorption by capillarity [39], tensile bond strength [40] and determination of dimensional variation [41]. In addition the flexural and compressive strength, were both obtained in the universal EMIC press. The speeds to perform each test, flexural and compressive strength, was respectively, 50 ± 10 N/s and 500 ± 50 N/s. The compressive strength is statistically associated with the ability to resist surface abrasion, traction, impact and shear, being representative of the others. The water absorption tests by immersion and capillarity are related to coating durability. The first simulates exposure to rain, excessive humidity, and action from coating washing and cleaning. While the capillarity absorption is related to the pores present on the coating surface. The tensile bond strength is the mortar's ability to remain fixed to the substrate when normal and tangential stresses are imposed, without breaking. Its test consists of using a continuous load application equipment to pull the mortar paste from the coating. The shrinkage determination in the mechanized projected mortars is important due to the more fluid consistency of this material and its greater propensity to cracks appearance. The drying shrinkage begins on the coating surface and moves towards its interior, generating tensions and, at the moment when the humidity begins to decrease, the drying rate is not uniform [42].

### **3. Results and Discussion 3. Results and Discussion**

#### *3.1. Physical Characterization 3.1. Physical Characterization*

Granulometric curve, presented in Figure 3, shows that ornamental rock waste grain size curve, in red, had 95% of its fraction smaller than 0.075 mm, similar to the characteristics of hydrated lime, pink curve, (97% fines content), facilitating the substitution by this material. The specific mass was also defined, using NBR NM 52 [43], resulting in a value of 2.48 g/cm<sup>3</sup> for the ornamental rock waste, approximately equal to that found by Vardhan et al. [24], 2.60 g/cm<sup>3</sup> , meanwhile the results found for hydrated lime were 2.27 g/cm<sup>3</sup> . Granulometric curve, presented in Figure 3, shows that ornamental rock waste grain size curve, in red, had 95% of its fraction smaller than 0.075 mm, similar to the characteristics of hydrated lime, pink curve, (97% fines content), facilitating the substitution by this material. The specific mass was also defined, using NBR NM 52 [43], resulting in a value of 2.48 g/cm³ for the ornamental rock waste, approximately equal to that found by Vardhan et al. [24], 2.60 g/cm³, meanwhile the results found for hydrated lime were 2.27 g/cm³.

**Figure 3.** Granulometric curves: hydrated lime in pink, ornamental rock waste in red and sand in purple. **Figure 3.** Granulometric curves: hydrated lime in pink, ornamental rock waste in red and sand in purple.

#### *3.2. Chemical and Microstructural Characterization 3.2. Chemical and Microstructural Characterization*

By the chemical characterization it was observed the presence of 76.34% of SiO<sup>2</sup> and 12.49% of CaO in the ornamental rock waste, close to those found in the literature [16,44– 46], while lime is mostly composed of CaO, around 93.43%. In the mineralogical analysis of ornamental rock waste, the predominant minerals were quartz and dolomite, showing good correlation between the chemical analysis performed and studies previously carried out on these materials [8,12,18,20,24,45]. Lime is predominantly composed of portlandite and calcite [46]. Thus, based on chemical and mineralogical characterization, the ornamental rock waste might be an effective substitute hydrated lime. By the chemical characterization it was observed the presence of 76.34% of SiO<sup>2</sup> and 12.49% of CaO in the ornamental rock waste, close to those found in the literature [16,44–46], while lime is mostly composed of CaO, around 93.43%. In the mineralogical analysis of ornamental rock waste, the predominant minerals were quartz and dolomite, showing good correlation between the chemical analysis performed and studies previously carried out on these materials [8,12,18,20,24,45]. Lime is predominantly composed of portlandite and calcite [46]. Thus, based on chemical and mineralogical characterization, the ornamental rock waste might be an effective substitute hydrated lime.

The microstructural characterization, Figure 4, also reveals similarity between hydrated lime and ornamental rock waste. Both ornamental rock waste and hydrated lime have grains of similar texture in terms of particle size and pore size. Although the shape of its grains is a little different, the lime presents rounder and more homogeneous particles while the waste elongated and irregular grains due to the industrial processing [3,47]. Furthermore, the ornamental rock waste presented a rough surface in many of its particles, as also observed by Lozano-Lunar et al. [48]. The fact that sizes and shapes of hydrated lime and ornamental rock waste are similar, it is believed that the replacement of lime by the ornamental rock waste will not impair at the mortars properties, as could be seen in the following tests. The microstructural characterization, Figure 4, also reveals similarity between hydrated lime and ornamental rock waste. Both ornamental rock waste and hydrated lime have grains of similar texture in terms of particle size and pore size. Although the shape of its grains is a little different, the lime presents rounder and more homogeneous particles while the waste elongated and irregular grains due to the industrial processing [3,47]. Furthermore, the ornamental rock waste presented a rough surface in many of its particles, as also observed by Lozano-Lunar et al. [48]. The fact that sizes and shapes of hydrated lime and ornamental rock waste are similar, it is believed that the replacement of lime by the ornamental rock waste will not impair at the mortars properties, as could be seen in the following tests.

**Figure 4.** SEM of: (**a**) hydrated lime, (**b**) ornamental rock waste. **Figure 4.** SEM of: (**a**) hydrated lime, (**b**) ornamental rock waste.

#### *3.3. Fresh State Tests 3.3. Fresh State Tests*

The results obtained in the squeeze flow test [30] are presented in graphs of load x displacement. For this purpose, they are first compared with the reference graph presented in Figure 5. This graph is divided into 3 regions or phases. In region I the material behaves as a solid and has linear elastic deformation. In region II there are intermediate displacements, and the material will flow with plastic or viscous deformation. In phase III there is a significant increase in the load to continue with the material deformation, characterizing the restricted flow of the material, because the frictional forces are predominant, being this stage of great deformations. The results obtained in the squeeze flow test [30] are presented in graphs of load x displacement. For this purpose, they are first compared with the reference graph presented in Figure 5. This graph is divided into 3 regions or phases. In region I the material behaves as a solid and has linear elastic deformation. In region II there are intermediate displacements, and the material will flow with plastic or viscous deformation. In phase III there is a significant increase in the load to continue with the material deformation, characterizing the restricted flow of the material, because the frictional forces are predominant, being this stage of great deformations.

**Figure 5.** Typical profile load x deformation a squeeze flow test [19]. **Figure 5.** Typical profile load x deformation a squeeze flow test [19]. **Figure 5.** Typical profile load x deformation a squeeze flow test [19].

Each developed mortar in Figure 6 has a specific and unique curve, and comparing them and Figure 5, it is possible to define the most workable ones. The lower the load obtained to reach the same displacement, the less viscous the material is, i.e., the more workable [49]. So, it can be said that these mortars have a predominant stage II. The test was performed at a displacement 3 mm/s speed, with a stop criterion of either 1000 N or 9 mm of displacement, whichever came first. Observing the graphs of Figure 6, for the displacement of 4 mm, the mortar R01 needed a larger load than the others to reach this mark. Therefore, it is considered the least workable among the studied mixtures. All the mortars developed presented curves similar to hydrated lime, concluding that their workability showed also be close. Therefore, it is possible to be replace lime by ornamental rock waste. Of the three regions that are presented in the typical curve of Figure 5, these mortars in Figure 6 have a significant stage II, which means that they will have a higher deformation without a significant increase in strength [50,51]. Each developed mortar in Figure 6 has a specific and unique curve, and comparing them and Figure 5, it is possible to define the most workable ones. The lower the load obtained to reach the same displacement, the less viscous the material is, i.e., the more workable [49]. So, it can be said that these mortars have a predominant stage II. The test was performed at a displacement 3 mm/s speed, with a stop criterion of either 1000 N or 9 mm of displacement, whichever came first. Observing the graphs of Figure 6, for the displacement of 4 mm, the mortar R01 needed a larger load than the others to reach this mark. Therefore, it is considered the least workable among the studied mixtures. All the mortars developed presented curves similar to hydrated lime, concluding that their workability showed also be close. Therefore, it is possible to be replace lime by ornamental rock waste. Of the three regions that are presented in the typical curve of Figure 5, these mortars in Figure 6 have a significant stage II, which means that they will have a higher deformation without a significant increase in strength [50,51]. Each developed mortar in Figure 6 has a specific and unique curve, and comparing them and Figure 5, it is possible to define the most workable ones. The lower the load obtained to reach the same displacement, the less viscous the material is, i.e., the more workable [49]. So, it can be said that these mortars have a predominant stage II. The test was performed at a displacement 3 mm/s speed, with a stop criterion of either 1000 N or 9 mm of displacement, whichever came first. Observing the graphs of Figure 6, for the displacement of 4 mm, the mortar R01 needed a larger load than the others to reach this mark. Therefore, it is considered the least workable among the studied mixtures. All the mortars developed presented curves similar to hydrated lime, concluding that their workability showed also be close. Therefore, it is possible to be replace lime by ornamental rock waste. Of the three regions that are presented in the typical curve of Figure 5, these mortars in Figure 6 have a significant stage II, which means that they will have a higher deformation without a significant increase in strength [50,51].

**Figure 6.** Load x displacement curve of the mixtures developed in this study. **Figure 6.** Load x displacement curve of the mixtures developed in this study. **Figure 6.** Load x displacement curve of the mixtures developed in this study.

As discussed by Ashish [52] and required by the ASTM standard [53,54], when a material is replaced by another with a larger specific surface, such as cement for ornamental rock waste, the workability of the material decreased, due the specific surface of the waste be higher than that of the cement, generating greater friction between the grains. On the As discussed by Ashish [52] and required by the ASTM standard [53,54], when a material is replaced by another with a larger specific surface, such as cement for ornamental rock waste, the workability of the material decreased, due the specific surface of the waste be higher than that of the cement, generating greater friction between the grains. On the As discussed by Ashish [52] and required by the ASTM standard [53,54], when a material is replaced by another with a larger specific surface, such as cement for ornamental rock waste, the workability of the material decreased, due the specific surface of the waste be higher than that of the cement, generating greater friction between the grains. On the contrary, when a material with a low specific surface is replaced by one with a smaller

surface, as sand being replaced by waste, the workability increased, due to fine filler effect of ornamental rock powder. Therefore, the workability was not affected by the incorporation of the ornamental rock waste replacing the hydrated lime, since their grains have similar morphology, and also their specific surface.

Table 3 provides some results of properties of the different mortars in the fresh state. Mortars composed of ornamental rock waste presented a higher mass density when compared to those produced with lime. This result was already expected, considering that the mass density of the residue found was around 2.49 g/cm<sup>3</sup> , which is higher than the hydrated lime, 2.27 g/cm<sup>3</sup> , according to results mentioned in the literature [7,8,30,36].


**Table 3.** Fresh state parameters for the developed mortars and hydrated lime.

The incorporated air content is a property with a direct influence on workability. The higher this parameter, the greater the workability and the greater the time the material remains workable, resulting in less effort to handle the mortar, and higher productivity. Therefore, comparing Figure 6 with Table 4, it can be said that the more viscous the mortar the less is the incorporated air content, although the values found are close to each other. Thus it is difficult to say how much this property influenced the others. Knowing that the Brazilian standard does not establish a range of incorporated air content, this result was compared to the literature [53], which indicates that it should be between 2% and 7%, so all the values found are slightly above the recommended by the bibliography. Nonetheless only this result is not enough to validate or discard the mixtures.

**Table 4.** Results of water absorption by immersion, voids content and capillarity coefficient for the developed mortars and hydrated lime.


Regarding water retention, a property that prevents excessive water loss, guaranteeing the workability and complete cement hydration, the Brazilian standard does not stipulate a minimum value. Thus, 90% was adopted according to ASTM C270 [54] and Azevedo et al. [21], reaching the conclusion that the replacement of lime by ornamental rock waste did not influence this characteristic [36].
