3.3.1. Prefabricated Blocks

A possible use of these plaster mortars is the production of prefabricated blocks for construction. This section presents the results obtained after the tests carried out on blocks of 29 × 11.5 × 11.5 cm, where the alveoli to lighten weight have been made by incorporating two recycled soft drink cans with a diameter of 6.5 cm and a height of 11.5 cm. The template and test blocks used are shown in Figure 5.

**Figure 5.** (**a**) Mould for the elaboration of prefabricated blocks; (**b**) type prefabricated block; (**c**) test of resistance to compression of the blocks.

The capillarity water absorption tests are shown in Table 15 for the different blocks produced.

**Table 15.** Initial rate of water absorption by capillarity according to the guidelines of the UNE-EN 722-1: 2011 standard.


As can be seen in Table 15, the incorporation of sand in plaster material reduces the water absorption coefficient compared to the reference material E.08. Mortars with the incorporation of RAmix presented the highest absorption coefficient [63], and, in all cases, the incorporation of thermal insulation residues has reduced this absorption coefficient.

Figure 6 shows the results obtained after the compressive strength test on mortar blocks.

**Figure 6.** Results of compressive strength test on prefabricated blocks.

As can be seen in Figure 6, all plaster mortar blocks exceeded in their mechanical capacity the compressive strength of the reference block E0.8. The results are in accordance with those presented in Figure 3, where mortars made with natural aggregate have higher resistance than mortars made with RAcon, and these in turn have higher resistance than those made with RAmix. It is also observed how the incorporation of thermal insulation residues reduces compressive strength, especially in the case of expanded polystyrene with graphite. Finally, it should be noted that in all the cases tested, plaster mortar presented good adherence to the cans used to make the alveoli, even so, in all the blocks the effect of the breakage in the core of the precast was observed, coinciding with these alveoli that are the most fragile areas and therefore the preferred points of breakage.

#### 3.3.2. Prefabricated Plates

This section includes the results derived from the tests on 50 × 30 × 2 cm mortar plates. Figure 7 shows the test method used.

These tests on plates and panels are of special importance to study the behaviour of plaster mortars made in prefabricated pieces with dimensions close to the real ones used in the study, as well as to evaluate their deformation capacity under possible alterations of the structure [64]. The results obtained for the different types of plates made in this study are shown in Figure 8.

**Figure 7.** Flexural strength test on prefabricated panels. (**a**) Plate before the test; (**b**) plate after assay.

**Figure 8.** Results of flexural strength test on prefabricated plates.

Figure 8 shows how flexural strength is reduced in plates and panels with dimensions close to reality, in comparison with standardized RILEM 4 × 4 × 16 cm specimens studied in Section 3.1. Likewise, it is observed how flexural strength is increased by incorporating aggregates in the matrix of plaster material. In addition, and as expected, mortars that incorporate mineral wool fibres have a greater resistance to bending and are more suitable for the manufacture of prefabricated panels and plates. On the other hand, mortars with the incorporation of expanded polystyrene residue with graphite showed lower flexural strengths, and mortars made with RAmix–EPS show strengths below the reference E0.8 plaster.

The results obtained in this research should be understood as a characterization of materials tested. If these materials were to be used in real on-site prefabricated elements, mechanical tests should be carried out on pieces with the specific geometry of the slabs and panels in order to consider the size effect. In addition, it is recommended to use these materials in interiors and not as cladding mortars on external facades. However, it would be advisable in future studies to carry out research that considers the durability of these materials, such as: humidity and drying cycles, total water absorption, thermal shock, etc. Thus, a future line of research to improve the technical performance of these materials involves the incorporation of reinforcement fibres in plaster matrix.

#### **4. Conclusions**

From the results obtained in this work, it can be concluded that recycled aggregates and thermal insulation residues for the elaboration of plaster mortars can be applied in building and are more respectful to the environment. In particular, the following conclusions were reached:


In general, it can be seen how plaster mortars have good technical performance for their application in building, and how the incorporation of recycled aggregates and thermal insulation residues improves the mechanical and physical properties of traditional plasters. The performance of this type of study is in line with the Sustainable Development Goals set by the United Nations Organization, supporting a more efficient use of natural resources and a decrease in the consumption of raw materials.

**Author Contributions:** Conceptualization, D.F. and M.Á.; methodology, D.F.; software, D.F. and P.S.; validation, P.S., D.F. and A.Z.; formal analysis, D.F. and P.S.; investigation, D.F. and M.Á.; resources, D.F.; data curation, D.F. and P.S.; writing—original draft preparation, D.F. and A.Z.; writing—review and editing, M.Á.; visualization, A.Z.; supervision, D.F.; project administration, D.F.; funding acquisition, D.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by URSA Ibérica Aislantes, S.A., grant number P2054090068.

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

**Informed Consent Statement:** Not spplicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to acknowledge the collaboration of the company URSA Ibérica Aislantes, SA, through the project P2054090068 "Thermo-acoustic solutions in housing renovation, simulation, and monitoring", which has served as a support and initiative framework for the realization of this research.

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