Recycling of eps foam and demolition wastes in the preparation of ecofriendly render mortars with thermal-acoustic insulation properties

2.1. Starting materials

General use Portland cement was used, the CDW used in this research were selected and sampled from the waste storage yard of MAECOL®, Materiales Ecológicos de Colombia SAS, located in Yumbo, Colombia. The materials came from various work in building in the city of Cali. Specifically, fired red clay brick waste (BW) and mortar and concrete waste (MW) were used, which underwent crushing in a jaw mill followed by milling in a hammer mill. The resulting material (Figure 1) was sifted through a No. 30 mesh sieve, and the retained material was used for this research.

Expanded polystyrene (EPS) waste was selected and samples taken from a building site in the city of Cali (Constructora Bolívar, Colombia). The EPS was collected in the form of blocks and was used in forming slab caissons. The EPS was sanded in an industrial sander (Trofemarcas, Colombia) at a speed of 330 m/min and with a No. 60 sandpaper. The sanded EPS was sieved in a No. 50 mesh sieve, and the retained material used for this study.

2.2. Tests and characterization techniques

The following characterization techniques were used:

Additionally, application of the optimal mixes was carried out on the surface of a wall to determine the characteristics of material consumption, workability during application, drying time and finally visual monitoring was carried out up to 60 days after application.

3.1. Raw materials

Figure 2 shows the particle size distribution curves for the waste used, BW, MW and EPS. The average particle size for BW and MW was 322.2 µm and 222.3 µm, respectively, and in the case of EPS it was 385.4 µm. The density of Portland cement is provided by the manufacturer technical data sheet, which is 2411 Kg/m³. The apparent density was 2550 Kg/m³ and 1870 Kg/m³ for BW and MW respectively; and the absorption was 2.11% for BW, and 12.35% for MW. The “Unit Weight” for EPS sanded was 140 Kg/m^3.

The Figure 3 presents the SEM images for the waste materials under study. The MW powders (Figure 3a and b) are composed of particles of irregular shapes and different sizes, some less than 100 µm, which corroborates what was found in the laser granulometry for this waste. Also observed in Figure 4a is the presence of cement paste with many micropores adhered to large-sized particles. Other studies have shown that a higher content of adhered mortar influences a greater water absorption and a decrease in the density (34-3634. Ferreira, R.L.S.; Anjos, M.A.S.; Maia, C.; Pinto, L.; Azevedo, A.R.; Brito, J. (2021) Long-term analysis of the physical properties of the mixed recycled aggregate and their effect on the properties of mortars. Constr. Build. Mater. 274, 121796. https://doi.org/10.1016/j.conbuildmat.2020.121796.
35. Bonifazi, G.; Palmieri, R; Serranti, S. (2018) Evaluation of attached mortar on recycled concrete aggregates by hyperspectral imaging. Constr. Build. Mater. 169, 835-842. https://doi.org/10.1016/j.conbuildmat.2018.03.048.
36. Kim, J. (2022) Influence of quality of recycled aggregates on the mechanical properties of recycled aggregate concretes: An overview. Constr. Build. Mater. 328, 127071. https://doi.org/10.1016/j.conbuildmat.2022.127071.
). In Figure 3c and d, the BW powders are shown. These are made up of angular and irregular particles of different sizes, corroborating the broad size distribution previously shown in the Figure 3a. For higher increases in the BW particle (Figure 5d), it is possible to observe an irregular and vitreous surface of the particles due to brick firing temperatures around 800-900 °C.

The lightweight EPS filler, after the sanding process, presented a wrinkled and/or rolled plate-like morphology (Figure 3e and f), which can be attributed to the sanding process at high revolutions. The higher magnification image (Figure 3f) shows that the wall of the initial foam has been modified and after sanding, crushing of the cells was generated. The EDS results indicated in Figure 3b and 3d are shown in Table 1, corroborating the aluminum-silicate nature for BW and MW.

3.2. Mix design

The render mortars were made from 70% by volume recycled fine aggregates (BW, MW and EPS) and 30% by volume matrix (99.7 wt% general use Portland cement and 0.30 wt% methyl hydroxyethyl cellulose powder (Cellueast^TM FM ME 40000) for improving the workability of plaster when applied on a wall. The matrix content remained fixed, and within the 70% that constitutes aggregates, different combinations were used following the EPS/CDW volume proportionality of 70/30 (mix A1), 50/50 (mixes A4, A5 and A6) and 30/70 (mixes A7, A8 and A9) for a total of 7 mixes (Figure 4 and Table 2). Additionally, as a commercial render mortar from IMPADOC® was used, labelled AC1.

Water content was adjusted to achieve a constant workability among all mixes, which was similar to that required during the application of the commercial render mortar AC1. The total water to cement ratio (w/c) for the mortars was defined as that required for obtaining a consistency (measured on flow table) similar to AC1 (94 mm). Table 3 shows the water content needed for each mix. The high-water requirement is related to the morphology (pronounced angularity), higher absorption and more porous surface for recycled aggregates particles after the crushing process (1818. Silva, R.V.; Brito, J.; Dhir, R.K. (2016) Performance of cementitious renderings and masonry mortars containing recycled aggregates from construction and demolition wastes. Constr. Build. Mater. 105, 400-415. https://doi.org/10.1016/j.conbuildmat.2015.12.171.
) which will be observed later in the microscopy images. Previously, has been reported that mortar with EPS required a higher content of mixing (2828. Fernández, D.; Yedra, E.; Morón, C.; Zaragoza, A.; Kosior-Kazberuk, M. (2022) Circular building process: reuse of insulators from construction and demolition waste to produce lime mortars. Buildings. 12 [2], 220. https://doi.org/10.3390/buildings12020220.
). In general, the high-water requirement in the mixes caused a slow setting process, which led to the decision to leave the mixes hardening at ambient laboratory conditions (relative humidity 70%, temperature 25 °C).

3.3. Mechanical and physical performance of the render mortars produced

In Figure 5a, the compressive strength results for the proposed mixes are shown. The UNE EN 998-1-2018 standard classifies the render mortar according to compressive strength at 28 days (CS), and water capillary (W). The mortar for interior render application, do not required permeable specification (W0), and compressive strength must be: CS I (0.4-2.5 MPa), CS II (1.5-5.0 MPa), CS III (3.5-7.5 MPa), CS IV (> = 6 MPa). Mixes A1, A5 and A6 did not reach the minimum value of 0.4 MPa contemplated in the standard to be classified as an interior render mortar. In those mixtures, the results show that increasing the EPS content directly affects the mechanical properties of the mix, due to the strength close to zero of the EPS particles and their high compressibility. Different authors have shown that, on using EPS, microcracks are generated in the interfacial transition zone (ITZ) between the aggregate particles and the cement paste, further weakening the mixes (11. Duan, P.; Song, L.; Yan, C.; Ren, D.; Li, Z. (2017) Novel thermal insulating and lightweight composites from metakaolin geopolymer and polystyrene particles. Ceram. Int. 43 [6], 5115-5120. https://doi.org/10.1016/j.ceramint.2017.01.025.
, 3737. Sayadi, A.A.; Tapia, J.V.; Neitzert, T.R.; Clifton, G.C. (2016) Effects of expanded polystyrene (EPS) particles on fire resistance, thermal conductivity and compressive strength of foamed concrete. Constr. Build. Mater. 112, 716-724. https://doi.org/10.1016/j.conbuildmat.2016.02.218.
). It is important to clarify that other researchers have produced render mortars with compressive strengths between 2.5-14.5 MPa using different percentages of recycled aggregates (1616. Miranda, L.F.R.; Selmo, S.M.S. (2006) CDW recycled aggregate renderings: Part I - Analysis of the effect of materials finer than 75 μm on mortar properties. Constr. Build. Mater. 20 [9], 615-624. https://doi.org/10.1016/j.conbuildmat.2005.02.025.
, 1818. Silva, R.V.; Brito, J.; Dhir, R.K. (2016) Performance of cementitious renderings and masonry mortars containing recycled aggregates from construction and demolition wastes. Constr. Build. Mater. 105, 400-415. https://doi.org/10.1016/j.conbuildmat.2015.12.171.
, 2828. Fernández, D.; Yedra, E.; Morón, C.; Zaragoza, A.; Kosior-Kazberuk, M. (2022) Circular building process: reuse of insulators from construction and demolition waste to produce lime mortars. Buildings. 12 [2], 220. https://doi.org/10.3390/buildings12020220.
) employing EPS-recycled filler can achieve compressive strength between 2.3-2.9 MPa for hydraulic lime mortars.

The A4 mortar (with the same total proportion of BW and MW) gave the highest compressive strength (0.48 MPa) from 35% EPS group. Similarly, for the group of mixes with 21% EPS (A7, A8, A9), the A7 mortar was found to have the highest compressive strength (1 MPa); like A4, it has the same proportion of BW and MW waste in its composition. These results can be explained: (i) via a better balance in the particle size distributions, exhibited increased packing, where the MW waste contributes a greater amount of fine particles with d (0.5) = 69.1 µm, while the brick waste BW provides coarser particles with d (0.5) = 197 µm, similar results have been shown previously (1818. Silva, R.V.; Brito, J.; Dhir, R.K. (2016) Performance of cementitious renderings and masonry mortars containing recycled aggregates from construction and demolition wastes. Constr. Build. Mater. 105, 400-415. https://doi.org/10.1016/j.conbuildmat.2015.12.171.
). Also, (ii) the equal distribution in volume between the BW and MW wastes in the A4 and A7 mixes; the finest fraction of the BW could also be contributing pozzolanic activity, by reacting with the portlandite from OPC hydration process of the matrix, a behavior that has been previously reported (1818. Silva, R.V.; Brito, J.; Dhir, R.K. (2016) Performance of cementitious renderings and masonry mortars containing recycled aggregates from construction and demolition wastes. Constr. Build. Mater. 105, 400-415. https://doi.org/10.1016/j.conbuildmat.2015.12.171.
, 3838. Zawrah, M.F.; Gado, R.A.; Feltin, N.; Ducourtieux, S.; Devoille, L. (2016) Recycling and utilization assessment of waste fired clay bricks (Grog) with granulated blast-furnace slag for geopolymer production. Process Saf. Environ. Prot. 103, 237-251. https://doi.org/10.1016/j.psep.2016.08.001.
). Nevertheless, the compressive strength results for the mixes proposed in this study were lower than for the commercial sample, AC1 (3.05 MPa). In general, the strength of the mortars decreases up to 50% with the replacement of the aggregate due to the high absorption capacity in mixtures with recycled aggregates (2020. Ferreira, R.L.S.; Anjos, M.A.S.; Nóbrega, A.K.C.; Pereira, J.E.S.; Ledesma, E.F. (2019) The role of powder content of the recycled aggregates of CDW in the behaviour of rendering mortars Constr. Build. Mater. 208, 601-612. https://doi.org/10.1016/j.conbuildmat.2019.03.058.
, 3939. Fernández-Ledesma, E.; Jiménez, J.R.; Ayuso, J.; Corinaldesi, V.; Iglesias-Godino, F.J. (2016) A proposal for the maximum use of recycled concrete sand in masonry mortar design. Mater. Construcc. 66 [321], e075. https://doi.org/10.3989/mc.2016.08414.
, 4040. Fernández-Ledesma, E.; Jiménez, J.R.; Ayuso, J.; Fernández, J.M.; Brito, J. (2015) Maximum feasible use of recycled sand from construction and demolition waste for eco-mortar production - Part-I: Ceramic masonry waste. J. Clean. Prod. 87 [1], 692-706. https://doi.org/10.1016/j.jclepro.2014.10.084.
). Additionally, the values of compressive strength in this study are similar to values for EPS-gypsum composites (3030. Oliveira, K.A.; Oliveira, C.A.B.; Molina, J.C. (2021) Lightweight recycled gypsum with residues of expanded polystyrene and cellulose fiber to improve thermal properties of gypsum. Mater. Construcc. 71 [341], e242. https://doi.org/10.3989/mc.2021.07520.
, 4141. Bumanis, G.; Pavils, P.; Sahmenko, G.; Mironovs, D.; Rucevskis, S.; Korjakins, A.; Bajare, D. (2023) Thermal and sound insulation properties of recycled expanded polystyrene granule and gypsum composites. Recycling. 8 [1], 19. https://doi.org/10.3390/recycling8010019.
), and vermiculite-gypsum composites (2626. Gencel, O.; Coz Diaz, J.J.; Stcu, M.; Koksal, F.; Alvarez, F.P.; Martinez-Barrera, G.; Brostow, W. (2014) Properties of gypsum composites containing vermiculite and polypropylene fibers: Numerical and experimental results. Energy Build. 70, 135-144. https://doi.org/10.1016/j.enbuild.2013.11.047.
), and higher than vermiculite-gypsum-sunflower stalk fiber composites (2727. Binici, H.; Aksogan, O.; Dıncer, A.; Luga, E.; Eken, M.; Isikaltun, O. (2020) The possibility of vermiculite, sunflower stalk and wheat stalk using for thermal insulation material production. Therm. Sci. Eng. Prog. 18 [21], 100567. https://doi.org/10.1016/j.tsep.2020.100567.
).

The results of adherence test for mixtures is shown in Figure 5b. Mixes A4, A5 and A6 with EPS content of 35% had a lower adherence compared to A7, A8, A9 (21% EPS), which indicates that there is an inverse proportional relationship between the EPS content in the mix and the adhesive strength the material can acquire once applied. It can also be seen that the adhesive values change markedly in the group of mixes A7, A8, and A9, depending on the variation in the content of BW and MW wastes, adhesive strength found to be greater in A7 (equal volumes of BW and MW waste), followed by mix A9 (a higher volume of MW) compared to mix A8. Just as was explained previously, by eliminating the fine material adhered to the coarse particle, this could contribute to the improved performance in adhesive strength. Adhesive strength values of 0.25 to 0.7 MPa have been found in render mortar by utilization of recycled sand (16-1816. Miranda, L.F.R.; Selmo, S.M.S. (2006) CDW recycled aggregate renderings: Part I - Analysis of the effect of materials finer than 75 μm on mortar properties. Constr. Build. Mater. 20 [9], 615-624. https://doi.org/10.1016/j.conbuildmat.2005.02.025.
17. Braga, M.; Brito, J.; Veiga, R. (2012) Incorporation of fine concrete aggregates in mortars. Constr. Build. Mater. 36, 960-968. https://doi.org/10.1016/j.conbuildmat.2012.06.031.
18. Silva, R.V.; Brito, J.; Dhir, R.K. (2016) Performance of cementitious renderings and masonry mortars containing recycled aggregates from construction and demolition wastes. Constr. Build. Mater. 105, 400-415. https://doi.org/10.1016/j.conbuildmat.2015.12.171.
, 4040. Fernández-Ledesma, E.; Jiménez, J.R.; Ayuso, J.; Fernández, J.M.; Brito, J. (2015) Maximum feasible use of recycled sand from construction and demolition waste for eco-mortar production - Part-I: Ceramic masonry waste. J. Clean. Prod. 87 [1], 692-706. https://doi.org/10.1016/j.jclepro.2014.10.084.
, 4242. Saiz Martínez, P.; González Cortina, M.; Fernández Martínez, F.; Rodríguez Sánchez, A. (2016). Comparative study of three types of fine recycled aggregates from construction and demolition waste (CDW), and their use in masonry mortar fabrication. J. Clean. Prod. 118, 162-169. https://doi.org/10.1016/j.jclepro.2016.01.059.
). (1717. Braga, M.; Brito, J.; Veiga, R. (2012) Incorporation of fine concrete aggregates in mortars. Constr. Build. Mater. 36, 960-968. https://doi.org/10.1016/j.conbuildmat.2012.06.031.
) and (2020. Ferreira, R.L.S.; Anjos, M.A.S.; Nóbrega, A.K.C.; Pereira, J.E.S.; Ledesma, E.F. (2019) The role of powder content of the recycled aggregates of CDW in the behaviour of rendering mortars Constr. Build. Mater. 208, 601-612. https://doi.org/10.1016/j.conbuildmat.2019.03.058.
) have found that the use of CDW with an average size smaller than 150 µm increases the shrinkage in mortars by 44% compared to that in mortars made with natural aggregates, and this increases their cracking, affecting the mechanical strength. These results follow other previous studies where the adherence strength between 0.13-0.23 MPa employing EPS-recycled filler (2828. Fernández, D.; Yedra, E.; Morón, C.; Zaragoza, A.; Kosior-Kazberuk, M. (2022) Circular building process: reuse of insulators from construction and demolition waste to produce lime mortars. Buildings. 12 [2], 220. https://doi.org/10.3390/buildings12020220.
). From the above, it is concluded that the higher the EPS content in the mix, the lower the mechanical properties, in agreement with various authors (11. Duan, P.; Song, L.; Yan, C.; Ren, D.; Li, Z. (2017) Novel thermal insulating and lightweight composites from metakaolin geopolymer and polystyrene particles. Ceram. Int. 43 [6], 5115-5120. https://doi.org/10.1016/j.ceramint.2017.01.025.
, 3737. Sayadi, A.A.; Tapia, J.V.; Neitzert, T.R.; Clifton, G.C. (2016) Effects of expanded polystyrene (EPS) particles on fire resistance, thermal conductivity and compressive strength of foamed concrete. Constr. Build. Mater. 112, 716-724. https://doi.org/10.1016/j.conbuildmat.2016.02.218.
). From ANOVA (Table 4) analysis for adherence test show differences between the mixtures. The ANOVA concludes that there is significant evidence that every mixtures influences the levels of adherence. This is how the contrasts showed differences in the combinations of A4-A7, A4-A8, A4-A9, A7-A8, and A7-A9 mixtures-opposite case between mixes A8 and A9. Mixes A7, A8 and A9 presented the most outstanding results, reaching values between 0.044 and 0.085 MPa. The Figure 6. shows specimens A6, A7 and AC1 after the adhesive test. The A6 mixture had an adhesive mode failure, indicating little adhesion between the render mixture and the substrate. While the A7 mixture had a cohesive mode failure, indicating that the render mixture had satisfactory adhesion to the substrate. AC1 has a mixed type failed.

3.4. Density, water absorption, and porosity properties

The low density, higher angularity, and surface roughness of recycled aggregate particles compared to natural crushed ones play an important role in reducing the density and poorer workability of concrete mixtures (1111. Şimşek, O.; Pourghadri H.; Gökçe, H.S. (2022) Performance of fly ash-blended Portland cement concrete developed by using fine or coarse recycled concrete aggregate. Constr. Build. Mater. 357, 129431. https://doi.org/10.1016/j.conbuildmat.2022.129431.
, 1515. Garg, N.; Shrivastava, S. (2022) A review on utilization of recycled concrete aggregates (RCA) and ceramic fines in mortar application. Mater. Today Proc. 73, 64-73. https://doi.org/10.1016/j.matpr.2022.09.226.
, 3535. Bonifazi, G.; Palmieri, R; Serranti, S. (2018) Evaluation of attached mortar on recycled concrete aggregates by hyperspectral imaging. Constr. Build. Mater. 169, 835-842. https://doi.org/10.1016/j.conbuildmat.2018.03.048.
). The results of density, water absorption and porosity are shown in Table 5. The high-water absorption of the mortars under study stands out, reaching values between 56.2% and 103.5%. A directly proportional relationship was found between the increase in EPS content and water absorption. High water absorption and high porosity in recycled aggregates results in a significant decrease in compressive strength in mortars, as previously has been observed (2020. Ferreira, R.L.S.; Anjos, M.A.S.; Nóbrega, A.K.C.; Pereira, J.E.S.; Ledesma, E.F. (2019) The role of powder content of the recycled aggregates of CDW in the behaviour of rendering mortars Constr. Build. Mater. 208, 601-612. https://doi.org/10.1016/j.conbuildmat.2019.03.058.
, 4343. Patra, I.; Al-Awsi, G.R.L.; Hasan, Y.M.; Almotlaq, S.S.K. (2022) Mechanical properties of concrete containing recycled aggregate from construction waste. Sustain. Energy Technol. Assessments. 53, 102722. https://doi.org/10.1016/j.seta.2022.102722.
). The group of mixes A4, A5, A6 thus had a greater absorption compared to mixes A7, A8, A9. The porosity in the mixes was higher to the extent that the EPS, MW and BW waste (highly porous waste) was incorporated, which is associated with different phenomena such as: (i) the greater demand for water in the mixes (Table 3) to achieve adequate workability (as explained in the Methodology section) as the EPS was increased. Moreover, as is known, the water that does not react with the OPC matrix is ​​finally released during drying, leaving behind porosity, which in turn is reflected in the greater water absorption for the mixes with 35% EPS compared to the samples with 21%EPS. In addition, it is possible that during the test, the water was trapped inside the channels of the EPS waste, which were observed to be deep and flattened (SEM, Figure 3e and 3f), and inside the pores of the recycled MW and BW aggregates (Figure 3 a, b, c, d), phenomena that have been reported by other authors (1919. Jesus, S.; Maia, C.; Brazão Farinha, C.; Brito, J.; Veiga, R. (2019) Rendering mortars with incorporation of very fine aggregates from construction and demolition waste. Constr. Build. Mater. 229, 116844. https://doi.org/10.1016/j.conbuildmat.2019.116844.
, 2020. Ferreira, R.L.S.; Anjos, M.A.S.; Nóbrega, A.K.C.; Pereira, J.E.S.; Ledesma, E.F. (2019) The role of powder content of the recycled aggregates of CDW in the behaviour of rendering mortars Constr. Build. Mater. 208, 601-612. https://doi.org/10.1016/j.conbuildmat.2019.03.058.
). Finally, the higher the EPS content, the lower the density of the mixes, and in all cases the density was lower than that of commercial AC1.

The densities of mixes A4, A5, A6 are close to the density of water (1000 Kg/m³), and during the test they initially floated in water, similar to that reported by materials based on gypsum. For a render mortar, a low density can become a technical advantage, since it gives less weight to the packed material, which favors transport, workability, as well as a possible lower consumption of material compared to traditional mortars, which is discussed later in Section 3.8. (1515. Garg, N.; Shrivastava, S. (2022) A review on utilization of recycled concrete aggregates (RCA) and ceramic fines in mortar application. Mater. Today Proc. 73, 64-73. https://doi.org/10.1016/j.matpr.2022.09.226.
, 4040. Fernández-Ledesma, E.; Jiménez, J.R.; Ayuso, J.; Fernández, J.M.; Brito, J. (2015) Maximum feasible use of recycled sand from construction and demolition waste for eco-mortar production - Part-I: Ceramic masonry waste. J. Clean. Prod. 87 [1], 692-706. https://doi.org/10.1016/j.jclepro.2014.10.084.
) have found a linear fall of the density of hardened mortar as the replacement ratio of recycled sand increased, which was due to the lower density of recycled aggregate. The density values are lower than EPS-lime mortars (2828. Fernández, D.; Yedra, E.; Morón, C.; Zaragoza, A.; Kosior-Kazberuk, M. (2022) Circular building process: reuse of insulators from construction and demolition waste to produce lime mortars. Buildings. 12 [2], 220. https://doi.org/10.3390/buildings12020220.
) and similar to EPS-plaster mortar (4444. Fernández, D.; Álvarez, M.; Saiz, P.; Zaragoza, A. (2022) Experimental study with plaster mortars made with recycled aggregate and thermal insulation residues for application in building. Sustain. 14 [4], 2386. https://doi.org/10.3390/su14042386.
).

According to the previous results of mechanical and physical properties, mixes A4, A7, and A9 were selected for the next part of the study to determine their thermal and acoustic properties.

3.5. Microstructure

The A7 mortar presented the best results in terms of mechanical properties, which indicates a better internal cohesion between the aggregates that compose it and the cement matrix. In Figure 7a an EPS particle can be seen adhered to the mortar, and in Figure 7b the interface between the EPS particle and the cement paste can be seen, indicating that it is of good quality, dense, without presence of microcracks, and in this study the anchoring mechanical type is favored owing to the morphology of the EPS particle. This is in contrast with other studies in which, when EPS with rounded morphology and sizes from 2.0 mm were used, a weak interface and the appearance of microcracks were reported (11. Duan, P.; Song, L.; Yan, C.; Ren, D.; Li, Z. (2017) Novel thermal insulating and lightweight composites from metakaolin geopolymer and polystyrene particles. Ceram. Int. 43 [6], 5115-5120. https://doi.org/10.1016/j.ceramint.2017.01.025.
, 2929. Villaquirán-Caicedo, M.A.; Perea, V.N.; Ruiz, J.E.; Mejía de Gutiérrez, R. (2022) Mechanical, physical and thermoacoustic properties of lightweight composite geopolymers Propiedades mecánicas, físicas y termoacústicas de geopolímeros compuestos aligerados. Ingen. Compet. 24 [1], 1-21
, 3737. Sayadi, A.A.; Tapia, J.V.; Neitzert, T.R.; Clifton, G.C. (2016) Effects of expanded polystyrene (EPS) particles on fire resistance, thermal conductivity and compressive strength of foamed concrete. Constr. Build. Mater. 112, 716-724. https://doi.org/10.1016/j.conbuildmat.2016.02.218.
). In this investigation, a quality and dense interface was found, associated with the fineness, and elongated morphology that the EPS particles retained after mechanical polishing. The mechanical anchoring of the EPS particle to the matrix, added to the use of a polymer-based additive, to improve adherence and dispersion in the formulation, allows a better anchoring of the EPS.

Table 6 shows the chemical composition results by EDS for mix A7 according to the position were EDS analyses were carried out in Figure 7b. The EDS for point 1 and 2, correspond to the elements that constitute the compounds formed in the hydration of the cement and its reaction with the compounds of silica, aluminum and iron present in the waste of mainly ceramic origin (SiO₂, Al₂O₃, and Fe₂O₃), which upon contact with calcium hydroxides (Portlandite, Ca(OH)₂), a product of cement hydration, form compounds such as calcium silicate hydrates (CSH) and calcium aluminates (C₃A). In point 3, meanwhile, located between the junction of the EPS particle and the matrix, the constituent elements are C, O and Ca, which indicates the presence of portlandite, and also the carbon from the EPS.

Assessment of the physical and mechanical properties made it possible to define mixes A4, A7 and A9 as optimal. The A7 mix was selected for having the best mechanical properties. In the adherence test, however, no significant differences were found between mixes A8 and A9, which both have 21% EPS content. Mix A9 was therefore selected from these two mixes, which had slightly better performance in mechanical properties. Mix A4 was considered for the next stage due to its high content of EPS (35%), which is expected to favor thermal and acoustic performance.

3.6. Thermal properties

Since the EPS has low conductivity (0.030 W/m·K) (4444. Fernández, D.; Álvarez, M.; Saiz, P.; Zaragoza, A. (2022) Experimental study with plaster mortars made with recycled aggregate and thermal insulation residues for application in building. Sustain. 14 [4], 2386. https://doi.org/10.3390/su14042386.
), it is to be expected that render mortars with higher EPS proportion will have the lowest thermal conductivity. Table 7 presents the results of thermal conductivity, where the proposed mixes A4, A7, A9 had a lower thermal conductivity than commercial mix AC1. In turn, as expected, mix A4 (35% EPS) was found to have the lowest conductivity values. On comparing the conductivity values of the proposed mixes with AC1, a decrease in this property was found of 79.5%, 62.3% and 71.7% for A4, A7 and A9 respectively. Mixes A4 and A9 gave lower thermal conductivity when compared to other thermal insulating materials with EPS particles (2828. Fernández, D.; Yedra, E.; Morón, C.; Zaragoza, A.; Kosior-Kazberuk, M. (2022) Circular building process: reuse of insulators from construction and demolition waste to produce lime mortars. Buildings. 12 [2], 220. https://doi.org/10.3390/buildings12020220.
, 2929. Villaquirán-Caicedo, M.A.; Perea, V.N.; Ruiz, J.E.; Mejía de Gutiérrez, R. (2022) Mechanical, physical and thermoacoustic properties of lightweight composite geopolymers Propiedades mecánicas, físicas y termoacústicas de geopolímeros compuestos aligerados. Ingen. Compet. 24 [1], 1-21
, 4444. Fernández, D.; Álvarez, M.; Saiz, P.; Zaragoza, A. (2022) Experimental study with plaster mortars made with recycled aggregate and thermal insulation residues for application in building. Sustain. 14 [4], 2386. https://doi.org/10.3390/su14042386.
, 4545. Villaquirán-Caicedo, M.A.; Mejía de Gutierrez, R.; Sulekar, S.; Davis, C.; Nino, J. (2015) Thermal properties of novel binary geopolymers based on metakaolin and alternative silica sources Appl. Clay Sci. 118, 276-282. https://doi.org/10.1016/j.clay.2015.10.005.
). The thermal conductivity in this research are similar to EPS-gypsum composites 0.18-0.24 W/m·K (3030. Oliveira, K.A.; Oliveira, C.A.B.; Molina, J.C. (2021) Lightweight recycled gypsum with residues of expanded polystyrene and cellulose fiber to improve thermal properties of gypsum. Mater. Construcc. 71 [341], e242. https://doi.org/10.3989/mc.2021.07520.
, 4141. Bumanis, G.; Pavils, P.; Sahmenko, G.; Mironovs, D.; Rucevskis, S.; Korjakins, A.; Bajare, D. (2023) Thermal and sound insulation properties of recycled expanded polystyrene granule and gypsum composites. Recycling. 8 [1], 19. https://doi.org/10.3390/recycling8010019.
), vermiculite-gypsum composites-sunflower stalk composites (2727. Binici, H.; Aksogan, O.; Dıncer, A.; Luga, E.; Eken, M.; Isikaltun, O. (2020) The possibility of vermiculite, sunflower stalk and wheat stalk using for thermal insulation material production. Therm. Sci. Eng. Prog. 18 [21], 100567. https://doi.org/10.1016/j.tsep.2020.100567.
); and is lower than mortar elaborate with vermiculite-gypsum (2626. Gencel, O.; Coz Diaz, J.J.; Stcu, M.; Koksal, F.; Alvarez, F.P.; Martinez-Barrera, G.; Brostow, W. (2014) Properties of gypsum composites containing vermiculite and polypropylene fibers: Numerical and experimental results. Energy Build. 70, 135-144. https://doi.org/10.1016/j.enbuild.2013.11.047.
), 100% glass particles wastes (0.5 W/m·K) and recycled concrete aggregate (0.9-1.3 W/m·K) (4646. Chindaprasirt, P. (2022) Thermal insulating and fire resistance performances of geopolymer mortar containing auto glass waste as fine aggregate. J. Build. Eng. 60, 105178. https://doi.org/10.1016/j.jobe.2022.105178.
).

It was found that the selected mixes A4, A7 and A9 have a lower specific heat than commercial mix AC1, which means that in the proposed mixes a lower supply of heat energy is required to increase their temperature. The higher specific heat of the A4 mix compared to the other mixes is directly related to the higher content of EPS in the mix, since this has a higher specific heat than natural or recycled aggregates, which in turn allowed a lower thermal conductivity in A4. However, the heat transfer through the thickness of the material is slower in the proposed mixes than in AC1, due to the lower thermal diffusivity of the produced mixes, A9 being the one with the lowest thermal diffusion among the proposed mixes, which is related to the low density of the mix. The proposed mixes have a lower thermal inertia compared to mortar AC1, which indicates that their temperature can increase faster on the surface during an outbreak of fire. However, when compared with materials commonly used in interior construction, plasterboard (386 J/m² s^1/2K), cellular concrete (372,7 J/m² s^1/2K), and chipboard (226 J/m² s^1/2K) show close values (47, 48). Based on UNE-EN-998-1 render mortar A4 and A7 could be classified as type T2 (thermal conductivity < 0.2 W/m·K).

Figure 8 correlates the results of thermal conductivity vs apparent density of the material. A directly proportional relationship can be observed between the density of the material and the thermal conductivity. As the density of the material decreases, its thermal conductivity decreases. This is directly related to a greater volume of pores that the use of recycled aggregates gives the material, which in turn causes a decrease in density and greater water absorption. The thermal conductivity in a ceramic material decreases as its density decreases (4949. Gregorová, E.; Pabst, W.; Sofer, Z.; Jankovský, O.; Matějíček, J. (2012) Porous alumina and zirconia ceramics with tailored thermal conductivity. J. Phys. Conf. Ser. 395, 012022. https://doi.org/10.1088/1742-6596/395/1/012022.
) therefore, the percentage of water absorption increases, and the pore volume increases which means a higher content of air that acts as a heat flow barrier due to its low thermal conductivity (0.026 W/m·K).

3.7. Acoustic properties

Figure 9a shows the results of sound pressure level (SPL) measurement relative to full scale (dBFS) for the mixes evaluated and the direct sound source, for frequencies between 250 - 4000 Hz. It must be made clear that, since the measurement is recorded relative to full scale (dBFS), the values ​​are negative. The more the value is increased, this signifies a lower SPL. It was found in relation to the SPL of the direct sound source, the greatest reduction was achieved in general for the frequencies of 2000 Hz and 4000 Hz. A significant reduction was achieved for the frequency of 250 Hz. In contrast, for the frequencies of 500 Hz and 1000 Hz, in general, the mixes evaluated did not register a significant decrease in SPL. Figure 9b presents the results for the absorption coefficient of the developed render mortars. The A9 mix achieved the highest acoustic absorption coefficient for the frequencies of 250 Hz and 4000 Hz (0.39 and 0.91 respectively), while the A4 and A7 mixes achieved the highest acoustic absorption coefficient for the frequencies of 500 Hz (0.15 for both) and 2000 Hz (0.74 and 0.75 respectively). Among the proposed mixes, in general the acoustic absorption coefficient was low for frequencies of 500 Hz and 1000 Hz. In contrast, (2929. Villaquirán-Caicedo, M.A.; Perea, V.N.; Ruiz, J.E.; Mejía de Gutiérrez, R. (2022) Mechanical, physical and thermoacoustic properties of lightweight composite geopolymers Propiedades mecánicas, físicas y termoacústicas de geopolímeros compuestos aligerados. Ingen. Compet. 24 [1], 1-21
) reported acoustic absorption coefficients close to 0.7 for frequencies of 300 at 500 Hz and close to 0.5 for a frequency of 1000 Hz, for a geopolymeric cement incorporating 4% (weight) EPS with a particle size of 2.35 mm. In general, the proposed samples had a higher acoustic absorption coefficient compared to the commercial mix AC1 for frequencies of 250, 500, 2000 and 4000 Hz. This is related to the higher permeable pore volume percentage and low density of the proposed mix samples compared to AC1 (5050. Moretti, E.; Belloni, E.; Agosti, F. (2016) Innovative mineral fiber insulation panels for buildings: Thermal and acoustic characterization. Appl. Energy, 169, 421-432. https://doi.org/10.1016/j.apenergy.2016.02.048.
).

In accordance with the classification of the ISO 11654-1997 standard, the proposed mixes have an Absorbent (Class D) behavior for frequencies of 250 Hz, Slightly absorbent (Class E) for 500 Hz, Reflective for 1000 Hz, and Highly absorbent (Class C) for frequencies of 2000 Hz and 4000 Hz. Only for mix A9 is it Extremely absorbent (Class A) for a frequency of 4000 Hz. This can be related to the fact that, at high frequencies, the waveform lengths are smaller, so they can more easily enter the pores of the material, which is why the materials can better absorb sounds.

3.8. Application of render mortars

Application of the proposed mixes A4, A7 and A9 along with the commercial mix AC1 was carried out. In Table 8 the results of the estimated consumption of material to cover a section on a brick wall of 0.40 m x 0.50 m to two layers approximately 1 mm thick each are presented (Figure 10). It is known that the lower density contributes to the enhanced workability for the similar consistency of concrete mixtures (1111. Şimşek, O.; Pourghadri H.; Gökçe, H.S. (2022) Performance of fly ash-blended Portland cement concrete developed by using fine or coarse recycled concrete aggregate. Constr. Build. Mater. 357, 129431. https://doi.org/10.1016/j.conbuildmat.2022.129431.
). It was found that mix A4 had the lowest consumption of material and the highest demand for water. Mixes A7 and A9 had a similar consumption. The commercial mix AC1 had a higher consumption and waste of material, compared to a lower consumption of water. The proposed mixes allow a reduction in material consumption of at least 51% compared to AC1. This is associated with the results of the apparent density test, in which it was shown that the proposed mixes have a lower density than the commercial mix. In addition, there is a directly proportional relationship between the apparent density of the material and consumption during application. The use of EPS waste allows, in addition to reducing the density of the material, lowering the consumption of material during application, which constitutes a technical and possibly economic advantage for the end user of the material, compared to the use of a traditional render mortar, corroborating what was reported by (2020. Ferreira, R.L.S.; Anjos, M.A.S.; Nóbrega, A.K.C.; Pereira, J.E.S.; Ledesma, E.F. (2019) The role of powder content of the recycled aggregates of CDW in the behaviour of rendering mortars Constr. Build. Mater. 208, 601-612. https://doi.org/10.1016/j.conbuildmat.2019.03.058.
).

From the proposed mixes, the best workability (lower sliding resistance by the applicator trowel and better surface quality) during application was for A9. However, difficulties arose during the dispersion of the mix on the brick surface. The best workability in mix A9 can be related to the high MW content in this mix compared to A4 and A7. MW, according to the results of the particle size distribution, had a bimodal distribution of particles (Figure 4b), thus providing a better distribution between the fine and coarse particles, allowing the finer ones to fill the spaces between the coarse particles, resulting in better dispersion during application to the surface. According to Weymouth’s gradation theory, in order to obtain adequate workability in mortars and concretes, grains of a single size must have enough space to move within the space left by grains of the subsequent larger size. When this occurs, the particles can move freely and are better distributed in the mortar, making it extremely workable (1616. Miranda, L.F.R.; Selmo, S.M.S. (2006) CDW recycled aggregate renderings: Part I - Analysis of the effect of materials finer than 75 μm on mortar properties. Constr. Build. Mater. 20 [9], 615-624. https://doi.org/10.1016/j.conbuildmat.2005.02.025.
).

Comparing the data reported for initial drying with those reported for initial setting time (standardized method for cement), it was found that, during the actual application of the material, the initial drying time is less than the initial setting time. This is associated with the fact that the render of applied material are a few millimeters (2 mm), which allows a faster evaporation of water compared to the experimental procedure of the Vicat needle setting time test. In the case of the final drying time compared to the final setting time, the differences are more evident. During the drying time test, in the external application the proposed mixes took a maximum of 240 minutes to dry, while in the final setting time test, they took more than 24 hours, even 50 hours (mix A4). There is evidently a directly proportional relationship between the initial setting time and the EPS content in the mix, since the higher the EPS content, as in the case of mix A4 (35%), the greater the initial setting time versus mixes A7 and A9 (21%).