*3.4. Hardened State Tests*

A hydrated lime mortar was produced at our laboratory as a reference index's for comparison, and obtained a water absorption by immersion of 15.35%, lower than the three values found in the developed mixtures, although R03 has reached values similar to that of lime [55–57]. From the analysis of this parameter, there was no significant change due to the replacement, a fact explained by the proximity between the granulometries and fine particles found in the rock residue, leading to better packing by the filler effect [17,18,24,58,59].

It is known that the water absorption by immersion and the void index are interconnected. As the absorption tends to increase, the same happens for the void index, evidenced in Table 4. The resulting void indices were compared with that reported by Azevedo et al. [3], and the mixtures developed were below the limit established by these authors. The slight increase in the void ratio was due to the introduction of an inert material replacing one of the mortar's binders. Thus, its contribution is only for the filler effect and not for the development of hydration products [20]. It is known that the water absorption by immersion and the void index are interconnected. As the absorption tends to increase, the same happens for the void index, evidenced in Table 4. The resulting void indices were compared with that reported by Azevedo et al. [3], and the mixtures developed were below the limit established by these authors. The slight increase in the void ratio was due to the introduction of an inert material replacing one of the mortar's binders. Thus, its contribution is only for the filler effect and not for the development of hydration products [20].

Regarding the water absorption by capillarity, it concerns the capillary pores that are on the coating surface, being its determination important since it is the most effective means of pathological and aggressive agents to penetrate the mortar. Fine particles as ornamental rock waste can be used to reduce void-filling, triggering the reduction of water absorption by capillarity [20]. The capillarity coefficient of R03 mixture in Table 4 displays the best result among the three ornamental rock waste mixtures analyzed. Finally, none of the mortars studied were above the limit established by the literature [1,20,37]. Regarding the water absorption by capillarity, it concerns the capillary pores that are on the coating surface, being its determination important since it is the most effective means of pathological and aggressive agents to penetrate the mortar. Fine particles as ornamental rock waste can be used to reduce void-filling, triggering the reduction of water absorption by capillarity [20]. The capillarity coefficient of R03 mixture in Table 4 displays the best result among the three ornamental rock waste mixtures analyzed. Finally, none of the mortars studied were above the limit established by the literature [1,20,37].

In order to optimize the tests time, the mixtures developed were mechanized projected on the substrate and the cracks appearance was observed, as shown in Figure 7. Despite the appearance or not of cracks being one of the acceptance criteria for the mortars developed, all of them were tested in the hardened state, even those that presented this pathology. Thus, it was possible to analyze whether the mortars with cracks also had other properties affected [55,56]. In order to optimize the tests time, the mixtures developed were mechanized projected on the substrate and the cracks appearance was observed, as shown in Figure 7. Despite the appearance or not of cracks being one of the acceptance criteria for the mortars developed, all of them were tested in the hardened state, even those that presented this pathology. Thus, it was possible to analyze whether the mortars with cracks also had other properties affected [55,56].

**Figure 7.** Visualization of cracks presence (red circle). Mixtures: (**a**) R01, (**b**) R02, (**c**) R03, (**d**) Hydrated Lime. **Figure 7.** Visualization of cracks presence (red circle). Mixtures: (**a**) R01, (**b**) R02, (**c**) R03, (**d**) Hydrated Lime.

The samples R01 and R02, Figure 7a,b presented a small incidence of cracks, however their amplitude may cause problems. Mortars composed by hydrated lime showed small cracks in greater quantity, while the R03 mixture did not show cracks at all. Although all mortars have the same workability range, sample R03 has a higher percentage of superplasticizer in its composition, thus reducing the amount of water present. The appearance of most cracks was observed when the coating was not fully hardened, configuring the so-called plastic shrinkage, which occurs by the rapid evaporation of the kneading water before the end of the setting and results in a superficial cracking [57,58]. their amplitude may cause problems. Mortars composed by hydrated lime showed small cracks in greater quantity, while the R03 mixture did not show cracks at all. Although all mortars have the same workability range, sample R03 has a higher percentage of superplasticizer in its composition, thus reducing the amount of water present. The appearance of most cracks was observed when the coating was not fully hardened, configuring the so-called plastic shrinkage, which occurs by the rapid evaporation of the kneading water before the end of the setting and results in a superficial cracking [57,58]. The values found in flexural and compressive strength, Figure 8, were compared

The samples R01 and R02, Figure 7a,b presented a small incidence of cracks, however

*Sustainability* **2022**, *14*, x FOR PEER REVIEW 12 of 16

The values found in flexural and compressive strength, Figure 8, were compared with the results of Kamani et al. [36], since the Brazilian standard does not establish minimum limits for these two parameters. Comparing the results obtained with [36], which indicates a minimum of 1 MPa, all the mortars studied showed results above the minimum established, although the R01 and R02 mortars reached the lowest values, the others compositions presented acceptable results. Analyzing the compressive strength, mortars R02 and R01 showed close averages, followed by the hydrated lime and finally, mortar R03. The mixtures containing 1.3% of additive, R03, are above the expected average [7,36,59]. with the results of Kamani et al. [36], since the Brazilian standard does not establish minimum limits for these two parameters. Comparing the results obtained with [36], which indicates a minimum of 1 MPa, all the mortars studied showed results above the minimum established, although the R01 and R02 mortars reached the lowest values, the others compositions presented acceptable results. Analyzing the compressive strength, mortars R02 and R01 showed close averages, followed by the hydrated lime and finally, mortar R03. The mixtures containing 1.3% of additive, R03, are above the expected average [7,36,59].

According to NBR 13529 [41], to be used as an external coating, the minimum bond strength that mortar must have is 0.30 MPa and as internal, 0.20 MPa. Therefore, observing Figure 8, only the mixtures R03 and hydrated lime can be used as an internal and external coating, since the other two are below the value of 0.30 MPa, thus they can be used only as internal coating. In the mortars with ornamental rock waste, the flexural strength remained practically constant, as well as the tensile bond strength, while the compressive strength improved in the R03 mix and decreased in the R01 and R02 mortars. The only variation between the developed mortars is the amount of water in the mixture, thus it was responsible for the variation found in the strength. According to NBR 13529 [41], to be used as an external coating, the minimum bond strength that mortar must have is 0.30 MPa and as internal, 0.20 MPa. Therefore, observing Figure 8, only the mixtures R03 and hydrated lime can be used as an internal and external coating, since the other two are below the value of 0.30 MPa, thus they can be used only as internal coating. In the mortars with ornamental rock waste, the flexural strength remained practically constant, as well as the tensile bond strength, while the compressive strength improved in the R03 mix and decreased in the R01 and R02 mortars. The only variation between the developed mortars is the amount of water in the mixture, thus it was responsible for the variation found in the strength.

**Figure 8.** Average flexural strength, compression strength and tensile bond strength. **Figure 8.** Average flexural strength, compression strength and tensile bond strength.

Due to the existence of cracks, the dimensional variation test [42] was performed, and the curve with its results was plotted in Figure 9. Ornamental rock waste mortars reached 90% of their total retraction at 14 days, while the curve stabilization of hydrated lime occurred around 9 days. The shrinkage found in the dimensional variation test can be correlated to the appearance of cracks in recent aging times observed in the coatings [60]. Due to the existence of cracks, the dimensional variation test [42] was performed, and the curve with its results was plotted in Figure 9. Ornamental rock waste mortars reached 90% of their total retraction at 14 days, while the curve stabilization of hydrated lime occurred around 9 days. The shrinkage found in the dimensional variation test can be correlated to the appearance of cracks in recent aging times observed in the coatings [60].

**Figure 9.** Dry shrinkage (mm/m) x age (days). **Figure 9.** Dry shrinkage (mm/m) x age (days).

#### **4. Conclusions 4. Conclusions**

The material characterization showed that ornamental rock waste () is an advantageous substitute for hydrated lime, since its granulometry is closer to the lime as well as its microstructural composition. Concerning the mechanized projected mortars, workability is a fundamental characteristic for this process to occur correctly, being fixed in this specific case, according to the consistency index, at 310 ± 5 mm. It is influenced by the amount of water and additive in the mixture, incorporated air content and water reten-The material characterization showed that ornamental rock waste () is an advantageous substitute for hydrated lime, since its granulometry is closer to the lime as well as its microstructural composition. Concerning the mechanized projected mortars, workability is a fundamental characteristic for this process to occur correctly, being fixed in this specific case, according to the consistency index, at 310 ± 5 mm. It is influenced by the amount of water and additive in the mixture, incorporated air content and water retention.

tion. The visual cracks analysis showed that among the three mortars developed; only one did not present this pathology, the sample that had the lowest water/dry material ratio. This shows that, although water increases the workability, in excess it affects others properties, such as the coating durability. From the results of dimensional variation, it was The visual cracks analysis showed that among the three mortars developed; only one did not present this pathology, the sample that had the lowest water/dry material ratio. This shows that, although water increases the workability, in excess it affects others properties, such as the coating durability. From the results of dimensional variation, it was observed that all mortars showed a similar process of retraction, although R03 with 1.3% ornamental rock waste had the smallest retraction.

observed that all mortars showed a similar process of retraction, although R03 with 1.3% ornamental rock waste had the smallest retraction. There was an increase in the mass density in the fresh state, of approximately 16%, in all developed mortars with ornamental rock waste in relation to hydrated lime mortars. There was an increase in the mass density in the fresh state, of approximately 16%, in all developed mortars with ornamental rock waste in relation to hydrated lime mortars. The incorporated air content was around 9% and the water retention above 90%, following to the adopted values from literature [36].

The incorporated air content was around 9% and the water retention above 90%, following to the adopted values from literature [36]. In relation to the hardened state parameters, the R03 mortar presented a greater performance than the other two mortars, R01 and R02, mainly in the mechanical strength, being approximately 50% above the obtained values. Regarding the capillarity water absorption test, the three mortars, presented good coefficients, close to the values found for the hydrated lime mortar of 6.800 g/dm²·min1/2. For the void index and water absorption In relation to the hardened state parameters, the R03 mortar presented a greater performance than the other two mortars, R01 and R02, mainly in the mechanical strength, being approximately 50% above the obtained values. Regarding the capillarity water absorption test, the three mortars, presented good coefficients, close to the values found for the hydrated lime mortar of 6.800 g/dm<sup>2</sup> ·min1/2. For the void index and water absorption by immersion, the ornamental rock waste incorporated mortar presented values that were approximately the same as lime mortar.

by immersion, the ornamental rock waste incorporated mortar presented values that were approximately the same as lime mortar. Therefore, it can be said that among the developed mortars, the one that presented the best performances, did not show any cracks, and its workability was in accordance with that required by the projection equipment, was the R03. Thus, with all the arguments presented, the ornamental rock waste studied at this work can replace hydrated lime by mechanized projected mortars in a satisfactory way. These results corroborate other studies on the feasibility of using this waste in mortars for coating. Moreover, they fills an important gap regarding the validation of the condition of mechanized projected application, giving a strong reduction of time, cost and waste in civil construction, contributing to make mortars more sustainable. Thus, this research complements other studies in the Therefore, it can be said that among the developed mortars, the one that presented the best performances, did not show any cracks, and its workability was in accordance with that required by the projection equipment, was the R03. Thus, with all the arguments presented, the ornamental rock waste studied at this work can replace hydrated lime by mechanized projected mortars in a satisfactory way. These results corroborate other studies on the feasibility of using this waste in mortars for coating. Moreover, they fills an important gap regarding the validation of the condition of mechanized projected application, giving a strong reduction of time, cost and waste in civil construction, contributing to make mortars more sustainable. Thus, this research complements other studies in the literature and advances clearly in this field, aiming at a real and practical application for the industries of the sector.

**Author Contributions:** Conceptualization: J.A. and G.d.C.X.; methodology: A.L.P.; formal analysis: A.L.P.; data curation: A.L.P.; writing—original draft preparation, A.L.P.; writing—review and editing: S.N.M.; supervision: A.R.G.d.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by State University of the Northern Fluminense (UENF), partial financed by CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brazil) and provided additional financial CNPq (Coordenação Nacional de Pesquisa) Code 309428/2020-3. The participation of A.R.G.A. was sponsored by FAPERJ through the research fellowships proc. no: E-26/210.150/2019, E-26/211.194/2021, E-26/211.293/2021, andE-26/201.310/2021 and by CNPq through the research fellowship PQ2 307592/2021-9.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors acknowledge the Brazilian governmental research agencies CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), and FAPERJ (Fundação de Amparo à Pesquisa do Estadodo Rio de Janeiro).

**Conflicts of Interest:** The authors declare no conflict of interest.
