Impact of gypsum mortars functionalized with phase change materials in buildings

Journal of Energy Storage 72 (2023) 108608 Available online 8 August 2023 2352-152X/© 2023 Elsevier Ltd. All rights reserved. Research papers Impact of gypsum mortars functionalized with phase change materials in buildings Sandra Cunha * , Jhonny Castro, Jos´ e B. Aguiar CTAC, Department of Civil Engineering, School of Engineering, University of Minho, Campus de Azur´ em, 4800-058 Guimar˜ aes, Portugal ARTICLE INFO Keywords: Gypsum mortars Phase change materials Physical behavior Mechanical behavior Thermal performance Cost analysis ABSTRACT The construction industry needs to adopt raw materials with less environmental impact and functional raw materials. The utilization of phase change materials (PCM) in interior mortars allows the energy efficiency of buildings improvement, based on solar energy, a renewable and clean energy source. On the other hand, the selection of mortars based in binders whose production emits lower carbon dioxide emissions than cement, like gypsum, can be a promising solution in help to minimize carbon dioxide (CO 2 ) emissions and the energy consumption for raw materials production. The main objective of this work was the development and characterization of gypsum-based mortars functionalized with PCM. Four distinct mortars were developed with different contents of pure and non-encapsulated PCM (0 %, 5 %, 10 % and 20 %). The different mortars were tested from a physical and mechanical point of view. The thermal performance of the mortars according to the summer and spring seasons of the north part of Portugal and an economic analysis of the application of these mortars in a typical Portuguese building were also carried out. The results obtained allow to observe that the incorporation of 20 % PCM leads to a decrease in the water absorption by capillarity, water absorption by immersion, flexural and compressive strengths of about 65 %, 30 %, 47 % and 59 %, respectively. However, its applicability has not been compromised. The thermal performance of the PCM mortars was improved, based in the temperature range and heating and cooling needs decrease. Regarding to the summer season it was observed a maximum temperature decrease of 2.3 ◦C, a minimum temperature increase of 2.6 ◦C and a decrease of cooling and heating needs of 13 % and 21 %, respectively. Concerning to the spring season it was verified a maximum temperature decrease of 2.7 ◦C, a minimum temperature increase of 1.9 ◦C and a decrease of cooling and heating needs of 100 % and 16 %, respectively. The cost analysis revealed savings in electricity costs for buildings climatization of around 17 % during the summer season and around 59 % during the spring season. 1. Introduction Nowadays, the construction industry is one the major energy consumers worldwide, especially energy from non-renewable sources, namely fossil fuels. The exploitation of fossil fuels is very polluting, causing serious and irreversible damage to the environment [1]. Thus, it is necessary to find alternative solutions that allows to meet the needs of this sector, mainly based on renewable energy sources and in more efficient and cleaner approaches. Residential buildings are responsible for about 25 % of the global energy consumption and 17 % of the global carbon dioxide (CO 2 ) emissions, especially associated with their demand for heating and cooling, with a significant effect on increasing global warming [2]. In this context, near-zero energy buildings (NZEBs) emerge as a decarbonization factor, which are being developed around the world to reduce global warming, based on the idea of meeting the dynamic demands of buildings based on clean, reversible and low-cost energy from renewable sources [1–4]. Many governments and organizations are setting ambitious targets to reduce greenhouse gas emissions and promote energy efficiency in buildings. The European Union has set a target for all new buildings to be “zero” by 2050. Starting from January 1, 2030, all new buildings should be subject to zero-emission building requirements, and starting from January 1, 2027, all new buildings owned or occupied by public authorities should comply with these requirements [5]. There are mainly three ways to design NZEB buildings, which can be by minimizing the needs of a building, matching loads based on the * Corresponding author. E-mail addresses: [email protected] (S. Cunha), [email protected] (J. Castro), [email protected] (J.B. Aguiar). Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est https://doi.org/10.1016/j.est.2023.108608 Received 11 May 2023; Received in revised form 31 July 2023; Accepted 2 August 2023 Journal of Energy Storage 72 (2023) 108608 2 dynamic demands and increasing the use of local renewable energy sources to supply energy to the building [2]. However, the large variability in the supply of energy through renewable sources due to their inconsistency throughout the day may compromise the viability of this type of buildings. Thus, the use of technologies that allow to store energy for later use becomes very interesting. The use of thermal storage systems allows an efficient utilization of solar energy, as it allow storing the energy provided by the sun to be used when it is no longer available [5–9]. Another important measure for minimizing CO 2 emissions is related to the selection of raw materials for constructive solutions to be adopted for the construction of buildings. The most used binder in the construction industry is the cement, which entails high energy consumption and CO 2 emissions [10–12]. Therefore, it is also necessary start to adopt, whenever it is possible, binders with less environmental impact and functional additives that allows contribute to the energy efficiency of buildings. Zhi et al. [13] indicate that the use of calcium sulfate, or hemihydrate, will provide a reduction of about 20 % in CO 2 emissions to the atmosphere, in addition allows to obtain better thermal and acoustic insulation, fire resistance, environmental comfort and cracking prevention. On the other hand, the phase change materials (PCM) are a thermal storage technique, due to their ability to store and release Nomenclature € Electricity electricity price ( € /kWh) A area (mm 2 ) A Building building area (m 2 ) b specimen width (mm) C coefficient of water absorption by capillarity (kg/m 2 . min 0.5 ) C Climatization climatization cost ( € /m 3 ) C Cost climatization cost ( € ) d specimen height (mm) d season duration of the season (days) F max maximum load (N) h Building building height (m) I water absorption by immersion (%) l distance between supports (mm) M 1 sample mass at 10 min of testing (g) m 1 saturated sample mass (g) m 2 hydrostatic sample mass (g) M 2 sample mass at 90 min of testing (g) m 3 dry sample mass (g) N climatization climatization needs per season (kWh/m 3 ) N cooling cooling needs per day (J/m 3 ) N cooling/heating cooling or heating needs (J/m 3 ) N heating heating needs per day (J/m 3 ) R c compressive strength (MPa) R f flexural strength (MPa) T(t) representative function of the temperature curve (K.h) t 0 initial time (min) T G0PCM temperature in the reference small test cell (G0PCM) (◦C) T G5,10,20PCM temperature in the PCM small test cell (G5PCM, G10PCM and G20PCM) (◦C) t i final time (min) Δt time (h) ρ cv volumetric capacity of the air (J/m 3 K) Table 1 Summary of PCM incorporation in mortars. Study Publication year Mortar type PCM classification PCM properties PCM incorporation technique Main achievements Cunha et al. [15] 2020 Cement mortars Paraffin – Organic Temperature transition of 22 ◦C; Enthalpy of 200 kJ/kg; Density of 760 kg/m 3 . Direct incorporation Higher PCM content leads to a decrease in the flexural and compressive strength and in the cooling and heating needs. Cunha et al. [16] 2017 Gypsum and aerial lime based mortars Paraffin – Organic Temperature transition of 24 ◦C; Enthalpy of 150 kJ/kg; Density of 880 kg/m 3 . Encapsulation - Microencapsulation Higher PCM content leads to an increase in the water absorption, a decrease in the mechanical strengths and in the energy needs. Illampas et al. [17] 2021 Cement-based repair mortars Paraffin – Organic Temperature transition of 37 ◦C; Enthalpy of 190 kJ/kg. Encapsulation - Microencapsulation Higher PCM content leads to an increase in the open porosity and a decrease in the flexural and compressive strength and elastic modulus. The thermal performance of the PCM mortars was improved. Lopez-Arias et al. [18] 2023 Cement mortars Paraffin – Organic Temperature transition of 70 ◦C; Enthalpy of 120 kJ/kg; Density of 968 kg/m 3 . Immersion Higher PCM content leads to a higher thermal conductivity and compressive strength. Shadnia et al. [19] 2015 Geopolymeric mortars Paraffin – Organic Temperature transition of 28 ◦C; Enthalpy of 180–195 kJ/kg; Density of 900 kg/m 3 . Encapsulation - Microencapsulation Higher PCM content leads to a decrease in the compressive strength and heat transportation. Aguayo et al. [20] 2016 Cement mortars Paraffin – Organic PCM-M temperature transition of 24.3 ◦C and enthalpy of 100 kJ/kg. PCM-E temperature transition of 23.4 ◦C and enthalpy of 159 kJ/kg. Encapsulation - Microencapsulation Higher PCM content leads to an increase in the compressive and flexural strengths. Cunha et al. [40] 2016 Gypsum, cement, hydraulic and aerial lime based mortars Paraffin – Organic Temperature transition of 24 ◦C; Enthalpy of 150 kJ/kg; Density of 880 kg/m 3 . Encapsulation - Microencapsulation Higher PCM content leads to a decrease in the flexural and compressive strengths and reduction of the energetic consumptions. The gypsum mortars exhibited the better thermal regulation. S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 3 energy from the environment, only based in solar energy. The PCM present a great potential for application in different construction materials, namely interior coating mortars [14–20], concrete [21–24], bricks [25,26], interior coating boards [27,28], carbon based materials [29–31], natural based materials [32–34], functionalized aggregates [35–37] and even solar thermal systems, like photovoltaic panels [38,39]. The application of PCM in construction materials must consider the availability of the application area, for this reason its application on walls is a very interesting solution. Thus, the study and development of mortars for covering interior walls, due to the large area available in buildings and the proximity to the interior environment, becomes one of the most interesting solutions to explore the potential of these functional materials. The development of mortars for the interior coating of buildings has essentially been based on the use of PCM microcapsules. In their research, Illampas et al. [17] utilized PCM microcapsules in cementbased repair mortars, developing a reference mortar (0 % of PCM) and three additional mortars with different contents of PCM (5 %, 10 %, and 20 % by weight of the powder components). The PCM used was a paraffin with temperature transition of 37 ◦C and enthalpy of 190 J/g. The study results indicate that an elevated PCM content in the mortars led to an increase in open porosity and a reduction in flexural strength, compressive strength and elastic modulus, attributed to the lower strength and stiffness of the PCM microcapsules when compared to the aggregate particles. However, the thermal performance of the PCM mortars was improved as a result of the reduced thermal conductivity and thermal diffusivity, increasing the specific heat capacity and contributing to the attenuation of the temperature peaks. Shadnia et al. [19] developed geopolymeric mortars with PCM microcapsules incorporation, observing a decrease in the compressive strength and heat transportation with the presence of a higher PCM content. Aguayo et al. [20] developed the incorporation of two different PCM microcapsules in cementitious composites. The two selected PCM’s were paraffin, with temperature transitions between 23 and 24 ◦C and enthalpy between 100 and 159 J/g. Based in their study it was possible to conclude that a higher PCM content leads to an increase in the compressive and flexural strengths until a certain replacement level of PCM. Cunha et al. [16,40] developed mortars based in different binders (cement, aerial lime, hydraulic lime and gypsum) activated with higher contents of PCM microcapsules. The results revealed a decrease in the mortars flexural, compressive strengths, maximum temperature, energy needs and an increase the minimum temperatures. It is important to note that between all the binders analyzed, the gypsum-based mortars showed the most interesting behavior. The use of other techniques for incorporating PCM in mortars has not been much explored. However, the use of microencapsulated PCM has very high costs. The utilization of a pure PCM, based in direct incorporation technique or immersion can be an alternative since the use of a non-encapsulated PCM causes a decrease in the production cost of the mortars. Lopez-Arias et al. [18] used the immersion technique to add PCM to the hardened structure of the mortars, with different porosities. The samples were subjected to vacuum application for different periods of immersion (15 min, 1 h, and 4 h). The results showed that the mortars with higher porosity and exposed to the immersion period, and consequently higher absorbed PCM content, showed a better thermal conductivity and compressive strength. Cunha et al. [15] developed cement mortars incorporating pure and nonencapsulated PCM, a paraffin, using the direct incorporation technique. The results demonstrated a decrease in compressive strength with increasing PCM content due to the delay in the cement hydration process. However, an improvement in the thermal behavior was achieved. On the other hand, it was proved that the PCM remains contained inside the mortar pores and coats mortar matrix, without damage risk. Table 1 summarizes the main information about the bibliographical review related to the mortars with PCM incorporation. The binder selection to be used for the development of interior coating mortars, in addition to the environmental aspects related to the CO 2 emission and energy consumption, must also consider its applicability in new constructions and rehabilitation works. In Portugal, around 50 % of existing buildings were built before 1991, with major deficiencies in terms of energy efficiency and only around 3 % of buildings are <10 years [41]. The gypsum mortars for interior coating are a solution that easily adapts to new construction and rehabilitation operations, an important measure for Portuguese built park. M’hamdi et al. [42] use phase change materials in different buildings envelopes and different climates in order to define the optimum solutions. Based in their simulation work, the obtained results showed an environmental and economic reduction of 10 % in the energy cost and 707 kg/year of CO 2 emissions. Lamnatou et al. [43] investigated the environmental potential and the life-cycle assessment of different options of solar thermal systems for a Mediterranean climatic conditions. A system without PCM using only rock wool as insulation and a system with PCM and rock wool were studied. The life-cycle results revealed 0.08 KgCO 2 equivalent/kWh for the PCM configuration. Sovetova et al. [44] developed the incorporation of PCM in buildings, through simulation processes, evaluating different climates (Abu-Dhabi, Dubai, Faisalabad, Mecca, Jodhpur, Nouakchott, Cairo and Biskra). The results demonstrating that the PCM presence could save the energy demand in about 6 % and reduce the CO 2 emissions in 1 % in hot desert climate. Taking into account the above, the main objective of this work consisted in the development and characterization of gypsum-based mortars functionalized with non-encapsulated PCM for application inside buildings, whether new constructions or rehabilitation operations. Four distinct compositions were developed, being a reference composition, without PCM (0 % PCM) and three compositions functionalized with PCM in 5 %, 10 % and 20 % of aggregate volume. The behavior of the developed mortars was tested from a physical, mechanical and thermal point of view, taking into account the Portuguese climate. Finally, an economic analysis was carried for a typical building in Portugal. Fig. 1 shows the distribution of the 4,142,581 existing buildings in Portugal according to 2021 data, considering their usable area [45]. The incorporation of non-encapsulated PCM is still an undeveloped area, with great potential of energetic savings for the buildings at lowcost, due to the lower PCM cost acquisition compared to other PCM incorporation techniques. The application of the direct incorporation technique has never been carried out for gypsum-based mortars and the thermal performance of these mortars was never studied before. On the other hand, the economic analysis, resulting of the application of these types of mortars is also an underdeveloped area with great research Fig. 1. Accommodation distribution in Portugal by usable area in 2021 [45]. S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 4 needs. The most part of the existent research works usually presented the constructive solutions impact per cubic meter, in this paper it was developed a cost analysis evidencing the effective saving cost resulting of the application of functionalized PCM gypsum-based mortars for a typical Portuguese summer and spring. Considering the impact of this research work it is possible to addresses the follow United Nations Sustainable Development Goals: - SDG 1: End energy poverty; - SDG 7: Affordable and clean energy; - SDG 9: Resilient, sustainable and innovative infrastructures; - SDG 11: Sustainable cities and communities; - ODS 13: Combat climate change and its impacts. 1. Experimental Design 1.1. Materials The mortars developed in this study were produced with a gypsum with a density of 2509 kg/m 3 , produced by a Portuguese company (Sival). Two different siliceous sands were adopted (sand 1 and sand 2) with the aim to obtain a more extensive granulometric curve. Sand 1 presents a minimum dimension of 0.063 mm and maximum dimension of 0.5 mm, a D10 of 105 μ m, a D50 of 310 μ m, a D90 of 480 μ m and a density of 2600 kg/m 3 . Sand 2 presents a minimum dimension of 0.125 mm and maximum dimension of 4 mm, a D10 of 162.5 μ m, a D50 of 0.7 mm, a D90 of 2.8 mm and a density of 2569 kg/m 3 . The superplasticizer used was a polyacrylate, produced by Germany company (BASF), with a density of 1359.7 kg/m 3 . The PCM used was a commercial and nonencapsulated paraffin, produced by a Germany company (Rubitherm), with a temperature transition of 22 ◦C, a density in the solid state of 760 kg/m 3 , a density in the liquid state of 700 kg/m 3 and an enthalpy of 200 kJ/kg. 1.2. Mix design The development of the study was based on four different formulations (Table 2), considering previous works developed by the research team [14,15]. It was developed a composition without PCM incorporation (reference mortar - G0PCM) and three compositions with addition of 5 %, 10 % and 20 % of PCM (G5PCM, G10PCM and G20PCM). The PCM content was fixed in relation to the volume of aggregate. The aggregate mixture used in these mortars was constituted by 50 % of sand 1 and 50 % of sand 2. The mortars water/binder ratio was fixed in 0.45 and the workability of the mortars was adjusted by the dosage of superplasticizer. All the mortars were prepared using a standard mixer, according to a pre-established manufacturing procedure. Initially, all the liquid material (water, PCM and superplasticizer) were mixed, for 60 s, thus an emulsion was created able to receive the solid materials. Finally, all the solid materials (gypsum, sand 1 and sand 2) were added to the emulsion and mixed for 90 s, allowing obtain a homogeneous mortar. The mortar workability was evaluated according the European standard EN 1015-3 [46]. The test was only considered valid when the scattering diameter was 155 ±5 mm. If the spreading diameter was not achieved, a new mortar formulation was carried out with an adjusted amount of superplasticizer. Thus, the determination of mortar consistency is an iterative process. 1.3. Sample manufacturing The preparation, curing and conditioning of the test specimens were carried out in accordance with European standard EN 1015-11 [47]. Thirty-six prismatic samples measuring 40 ×40 ×160 mm 3 were molded, with the fresh mortars. The molds were covered with polyethylene film and the samples were demolded after 48 h and wrapped in polyethylene bags for more 5 days, remaining at a temperature of about 20 ◦C and a relative humidity of about 95 %. Posteriorly, the samples were unwrapped and stored for 21 days in controlled laboratory conditions at a temperature of about 20 ◦C and a relative humidity of about 65 %. These samples were used for the water absorption by capillarity, water absorption by immersion, flexural strength and compression strength tests. Four small scale tests cells with interior dimensions of 200 ×200 × 200 mm 3 constructed with extruded polystyrene boards with 3 cm of thickness were coated inside with a mortar layer of 1 cm of thickness. The mortars were covered with polyethylene bags for 7 days and stored at a temperature of about 20 ◦C and a relative humidity of about 95 %. During the following 21 days, the walls that constituted the small-scale test cells remained at a temperature of about 20 ◦C and a relative humidity of about 65 %. These small-scale test cells were used for the thermal performance evaluation. 2. Methods The mortars workability was performed based in the flow table test method in accordance with European standard EN 1015-3 [46]. The method consists of filling the truncated conical mold with two layers of mortar of roughly the same height and compacting each layer with 10 short strokes. Subsequently, the truncated conical mold must be removed vertically and 15 short strokes applied to the mortar, so that it spreads on the table top, making it possible to measure the spreading diameter in two perpendicular dimensions. The water absorption by capillarity test was performed based in the European standard EN 1015–18 [48]. Initially, the samples were dried in an oven at a temperature of 60 ◦C, until constant mass, i. e. when two consecutive weight measurements with 24 h of time difference, did not differ >0.2%wt. Posteriorly, the lateral surfaces of the samples were covered with silicone, to ensure that the contact with the water happened only on the inferior face of the sample. The test started when the samples were placed in contact with a water layer of 10 mm. A weighing plan was established (Table 3), starting with the dry mass and interrupted with two consecutive constant measurements. Based on measurements taken at 90 min and 10 min, it was possible to determine the coefficient of water absorption by capillarity according to Eq. (1): C=0.1× (M2−M1)(1) Table 2 Mortars formulations (kg/m 3 ). Composition Gypsum Sand 1 Sand 2 Superplasticizer PCM Water G0PCM 600 601 601 27 0 270 G5PCM 600 557.8 557.8 21 30 270 G10PCM 600 513.8 513.8 15 60 270 G20PCM 600 422.8 422.8 6 120 270 Table 3 Weighing plan of the water absorption by capillarity tests. Measurement Time (hours) Time (minutes) Measurement Time (hours) Time (minutes) 1 0.0 0 10 3.0 180 2 0.017 1 11 4.0 240 3 0.083 5 12 5.0 300 4 0.167 10 13 6.0 360 5 0.333 20 14 7.0 420 6 0.5 30 15 24.0 1440 7 1.0 60 16 48.0 2880 8 1.5 90 17 120.0 7200 9 2.0 120 18 144.0 8640 S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 5 The water absorption by immersion was performed adapting the Portuguese specification LNEC E 394 [49]. The samples were dried in an oven at 60 ◦C until constant mass, in other words, when two 24 h consecutive weight measurements did not differ >0.1%wt. The samples were immersed in water at a temperature of about 20 ◦C, at atmospheric pressure. The samples were saturated until the constant mass. After, the hydrostatic mass was determined, weighing the sample in water. The mortars water absorption by immersion was determined according to Eq. (2): I= ((m1−m3)/(m1−m2) ) × 100 (2) The flexural and compressive strengths of the mortars were performed in accordance with the European standard EN 1015-11 [47]. Initially, it was performed the flexural tests with resource to a universal testing machine, with load control at a speed of 50 N/s. The samples were placed into a flexion assembly with an upper bearer and two inferior roller supports spaced 100 mm. After the samples failure the compressive strength tests were performed by loading the six resulting half prisms, with load control at a speed of 150 N/s. The flexural strength and compressive strength were determined according to Eqs. (3) and (4). Rf=1.5×((Fmax ×l)/(b×d2)) (3) Rc=Fmax ×A(4) The mortars thermal behavior was analyzed based in real temperature laws. Real temperature data were collected using a meteorological station, installed on the Campus of Azur´ em, of the University of Minho in Guimar˜ aes, Portugal, for 12 months. The temperature law was selected for the most representative day of the summer and spring season (Fig. 2), for the northern region of Portugal, and these temperature laws were subsequently applied to a climatic chamber. The temperature law used for simulate the summer season ranged from a minimum of 11 ◦C and a maximum of 44 ◦C. The temperature law used for simulated the spring season ranged from a minimum of 12 ◦C and a maximum of 29 ◦C. The simulation of each season was carried out by carrying out 7 test cycles, with each test cycle having a duration of 24 h. The first 4 test cycles were disregarded, as they were used for climate chamber calibration, while the remaining 3 test cycles were used for the results treatment. Each small-scale test cell was coated with a different mortar and instrumented with a thermocouple, type K inside, in the central area, connected to a data acquisition system (Agilent 34970A). The temperature inside each small-scale test cell was collected each minute, as well as the temperature inside the climatic chamber. The temperature laws selected for the summer and spring seasons allowed the phase transition of the PCM, allowing the observation of its ability to absorb and release energy from the environment. 3. Physical performance 3.1. Workability The tests were developed in order to obtain the same workability in all developed mortars, measured by the obtained spreading diameter (Table 4). According to Fig. 3 it was possible verify that the superplasticizer content decreases with the presence of a higher PCM content. However, the liquid-binder ratio showed an increase with the incorporation of a higher PCM content. The incorporation of 5 % of PCM leads to a decrease in the superplasticizer content higher than 22 % and an increase in the liquid-binder ratio higher than 11 %. This behavior can be explained by the fact that the PCM is added do the mortar mixture in its liquid state. Therefore, the liquid PCM has the ability to act as an enhancer for creating a well-workable and homogeneity mortar, replacing part of the water in its function. These results are in agreement with other works performed through the direct incorporation of PCM in mortars based in other binders [15,50]. However, the use of other PCM incorporation techniques, namely microencapsulation, leads to opposite results, resulting in a higher superplasticizer or water content in order to obtain the same workability, due to higher specific surface area of the PCM microparticles [16,17,51]. 3.2. Water absorption by capillarity The water absorption by capillarity is influenced by the PCM presence, since the incorporation of a higher PCM content leads to a decrease in the amount of water absorbed (Fig. 4) and in the capillarity water coefficient (Fig. 5). Regarding to Fig. 4 it was possible to verify that the reference mortar (G0PCM) showed a higher capacity to absorb water by capillarity, which can be related to the mortar matrix contain a larger number of micropores. However, a lower capacity to absorb water by capillarity was observed for the mortars functionalized with PCM, due to the accommodation of the pure and free PCM in the mortar pores, as referenced in other works, developed with cement-based mortars [15,50]. The identified behaviors allow verifying that the pure PCM, even incorporated directly, is trapped in the mortar matrix, limiting its absorption capacity. Thus, it was also possible indicate that the PCM did not move from the matrix mortar after the application, making this technology very promising, due to its lower cost, since PCM does not have any kind of initial processing, such as encapsulation (macroencapsulation or microencapsulation). In Fig. 5 it was observed the water absorption by capillarity coefficient. It was possible to observe that the presence of a higher PCM content leads to a lower water absorption by capillarity coefficient, in accordance with the water by capillarity capacity (Fig. 4) of the mortars doped with PCM. The incorporation of 5 % of pure and nonencapsulated PCM causes a decrease higher than 21 % in the water absorption by capillarity coefficient. Once again, this behavior can be associated with the PCM occupation in the mortar pores, which can indicate that the mortar pores are saturated with non-encapsulated PCM, as referenced in other research works [15,50]. In addition, the PCM presence also creates a hindrance to water evaporation. As a result, Fig. 2. Summer and spring temperature laws. Table 4 Mortars spreading diameter. Composition Spreading diameter (mm) G0PCM 154 G5PCM 155 G10PCM 155 G20PCM 154 S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 6 mortars with a higher PCM content demonstrate a lower water absorption by capillarity coefficient. 3.3. Water absorption by immersion According to Fig. 6, a decrease in the capacity of water absorption by immersion was observed with the addition of PCM in mortars. Notably, the inclusion of 5 % non-encapsulated PCM resulted in a decrease in water absorption by immersion of about 18 %, being more expressive for higher PCM contents. This phenomenon, as previously described in the absorption of water by capillarity (Figs. 4 and 5), can be attributed to the complete or partial filling of mortar pores by the pure and free PCM, distributed in the mortar matrix [15,50]. However, this behavior is contradictory to presented by mortars activated with PCM through other incorporation techniques, namely microencapsulation, whose water absorption by immersion increases with the presence of a higher PCM content [16]. 4. Mechanical performance 4.1. Flexural strength The flexural behavior of the developed mortars was observed in Fig. 7. The addition of up to 10 % of PCM content does not lead to a Fig. 3. Superplasticizer and liquid-binder ratio of the developed mortars. Fig. 4. Capillary water absorption of the developed mortars. S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 7 significant effect on the flexural strength, since the addition of 5 % of PCM and 10 % of PCM caused an increase of 4 % and a decrease of about 3 % in the flexural strength, respectively. However, the results for an addition of a higher content, 20 % of PCM, showed a more expressive decrease in the flexural strength, about 47 %. The low influence of the incorporation of non-encapsulated PCM up to an incorporation content of 10 % has already been demonstrated by the research team in previous studies carried out in mortars based on other binders [15,50]. The factors underlying this behavior are the higher liquid-binder ratio and the total or partial PCM occupation of the mortar pores, which decreases the porosity of the mortars, as can be observed by the decrease in water absorption by capillarity (Fig. 4) and by immersion (Fig. 6), which affects the curing process of mortars, since as reported in studies for mortars based in other binders [50]. Fig. 5. Coefficient of water absorption by capillarity of the developed mortars. Fig. 6. Water absorption by immersion of the developed mortars. S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 8 4.2. Compressive strength Fig. 8 shows the results obtained for the compressive strength. In this case it was possible verify a greater influence of the PCM incorporation in the compressive strength. Since only up to 5 % of PCM addition, the influence on the compressive strength was not significant, having verified a decrease of about 5 %. However, the addition of 10 % PCM and 20 % of PCM led to a more significant decrease in compressive strength of approximately 19 % and 59 %, respectively. This greater influence is justified not only by the total or partial PCM occupation of the mortar pores, negatively affecting the mortar curing process, but also by the fact Fig. 7. Flexural strength of the developed mortars. Fig. 8. Compressive strength of the developed mortars. Table 5 Compressive strength classification according to specification NP EN 998-1. Class Compressive strength range (MPa) CSI 0.4 to 2.5 CSII 1.5 to 5.0 CSIII 3.5 to 7.5 CSIV ≥6.0 S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 9 that PCM has a lower resistance compared to the natural aggregate. The decrease in the mechanical strength of mortars with a higher content of non-encapsulated PCM incorporation, as previously mentioned, has already been demonstrated in previous studies [15,50]. However, it is important to note that, contrary to other properties, the incorporation of PCM according to other incorporation techniques, such as microencapsulation, also caused losses in the compressive strength of mortars based in different binders and concretes [14,16,21,22]. The standard NP EN 998-1 [52] allows the classification of gypsum mortars according to their compressive strength. Table 5 shows the different strength classes and the compressive strength range used for each one. Even knowing that the developed mortars, as they are interior coating mortars, will not have a structural function, it was decided to obtain a minimum classification of CSII, in order to apply and use the mortars with more security. According to Table 6, it was possible to verify that all the developed mortars presented a compressive strength classification superior or equal to CSII, which indicate an appropriate mechanical behavior. 5. Thermal performance The thermal performance of the developed mortars was based in the study of two different seasons (summer and spring). In this way, a hot season and a mild season were tested. During these tests, situations with temperatures below 20 ◦C were identified, defined as situations with heating needs (heating situation) and situations with temperatures above 25 ◦C, defined as situations with cooling needs (cooling situation). 5.1. Summer season It can be observed in Fig. 9 the thermal performance of the mortars doped with PCM (G5PCM, G10PCM and G20PCM) compared to the reference mortar (G0PCM). It was perceived that the PCM mortars exhibited a lower maximum temperature and a higher minimum temperature, which would subsequently result in decreased requirements for cooling and heating needs in buildings. In opposition, it was also apparent that all PCM mortars displayed a comparable response when the temperature inside the test cells approached the comfort Table 6 Compressive strength classification of the developed mortars. Composition Compressive strength (MPa) Class G0PCM 7.65 CSIV G5PCM 7.29 CSIV G10PCM 6.18 CSIV G20PCM 3.12 CSII Fig. 9. Thermal behavior of the developed mortars - summer season. S. Cunha et al. Journal of Energy Storage 72 (2023) 108608 16 for glass greenhouses, Case Stud. Therm. Eng. 44 (2023), e102895, https://doi. org/10.1016/j.csite.2023.102895. [9] C. Lai, R. Chen, C. Lin, Heat transfer and thermal storage behaviour of gypsum boards incorporating micro-encapsulated PCM, Energy Build. 42 (2010) 1259–1266, https://doi.org/10.1016/j.enbuild.2010.02.018. [10] E. Benhelal, G. Zahedi, E. Shamsaei, A. Bahadori, Global strategies and potentials to curb CO 2 emissions in cement industry, J. Clean. Prod. 51 (2013) 142–161, https://doi.org/10.1016/j.jclepro.2012.10.049. [11] L. Tosti, A. Zomeren, J.R. Pels, R.N.J. Comans, Technical and environmental performance of lower carbon footprint cement mortars containing biomass fly ash as a secondary cementitious material, Resour. Conserv. Recycl. 134 (2018) 25–33, https://doi.org/10.1016/j.resconrec.2018.03.004. [12] E.R. Teixeira, A. Cam˜ oes, F.G. Branco, Synergetic effect of biomass fly ash on improvement of high-volume coal fly ash concrete properties, Constr. Build. Mater. 314 (Part A) (2022), e125680, https://doi.org/10.1016/j. conbuildmat.2021.125680. [13] Z. Zhi, B. Ma, H. Tan, Y. Guo, Z. Jin, H. Yu, S. Jian, Effect of competitive adsorption between polycarboxylate superplasticizer and hydroxypropylmethyl cellulose on rheology of gypsum paste, J. Mater. Civil Eng. 30 (2018), e04018141, https://doi. org/10.1061/(asce)mt.1943-5533.0002346. [14] S. Cunha, J.B. Aguiar, V. Ferreira, Eco-efficient mortars with incorporation of phase change materials, J. Build. Phys. 41 (2018) 469–492, https://doi.org/ 10.1590/s1517-707620190002.0682. [15] S. Cunha, P. Leite, J.B. Aguiar, Characterization of innovative mortars with direct incorporation of phase change materials, J. Energy Storage. 30 (2020), e101439, https://doi.org/10.1016/j.est.2020.101439. [16] S. Cunha, J.B. Aguiar, V.M. Ferreira, Mortars with incorporation of phase change materials for thermal rehabilitation, Int. J. Archit. Herit. 11 (2017) 339–348, https://doi.org/10.1080/15583058.2016.1222464. [17] R. Illampas, I. Rigopoulos, I. Ioannou, Influence of microencapsulated Phase Change Materials (PCMs) on the properties of polymer modified cementitious repair mortar, J. Build. Eng. 40 (2021), e102328, https://doi.org/10.1016/j. jobe.2021.102328. [18] M. Lopez-Arias, V. Francioso, M. Velay-Lizancos, High thermal inertia mortars: new method to incorporate phase change materials (PCMs) while enhancing strength and thermal design models, Constr. Build. Mater. 370 (2023), e130621, https://doi.org/10.1016/j.conbuildmat.2023.130621. [19] R. Shadnia, L. Zhang, P. Li, Experimental study of geopolymer mortar with incorporated PCM, Constr. Build. Mater. 84 (2015) 95–102, https://doi.org/ 10.1016/j.conbuildmat.2015.03.066. [20] M. Aguayo, S. Das, A. Maroli, N. Kabay, J.C.E. Mertens, S.D. Rajan, G. Sant, N. Chawla, N. Neithalat, The influence of microencapsulated phase change material (PCM) characteristics on the microstructure and strength of cementitious composites: experiments and finite element simulations, Cement Concr. Compos. 73 (2016) 29–41, https://doi.org/10.1016/j.cemconcomp.2016.06.018. [21] K. Cellat, F. Tezcan, B. Beyhan, G. Kardas ¸, H. Paksoy, A comparative study on corrosion behavior of rebar in concrete with fatty acid additive as phase change material, Constr. Build. Mater. 143 (2017) 490–500, https://doi.org/10.1016/j. conbuildmat.2017.03.165. [22] A. D’Alessandro, A. Pisello, C. Fabiani, F. Ubertini, L.F. Cabeza, F. Cotana, Multifunctional smart concretes with novel phase change materials: mechanical and thermo-energy investigation, Appl. Energy 212 (2018) 1448–1461, https:// doi.org/10.1016/j.apenergy.2018.01.014. [23] Z. Dong, H. Cui, W. Tang, D. Chen, H. Wen, Development of hollow steel ball macro-encapsulated PCM for thermal energy storage concrete, Materials (Basel) 9 (1) (2016), e59, https://doi.org/10.3390/ma9010059. [24] H. Cui, J. Zou, Z. Gong, D. Zheng, X. Bao, X. Chen, Study on the thermal and mechanical properties of steel fibre reinforced PCM-HSB concrete for high performance in energy piles, Constr. Build. Mater. 350 (2022), e128822, https:// doi.org/10.1016/j.conbuildmat.2022.128822. [25] R. Vicente, T. Silva, Brick masonry walls with PCM macrocapsules: an experimental approach, Appl. Therm. Eng. 67 (2014) 24–34, https://doi.org/10.1016/j. applthermaleng.2014.02.069. [26] H.M. Abbas, J.M. Jalil, S.T. Ahmed, Experimental and numerical investigation of PCM capsules as insulation materials inserted into a hollow brick wall, Energy Build. 246 (2021), e111127, https://doi.org/10.1016/j.enbuild.2021.111127. [27] A. Oliver, Thermal characterization of gypsum boards with PCM included: thermal energy storage in buildings through latent heat, Energy Build. 48 (2012) 1–7, https://doi.org/10.1016/j.enbuild.2012.01.026. [28] F. Kuznik, J. Virgone, K. Johannes, In-situ study of thermal comfort enhancement in a renovated building equipped with phase change material wallboard, Renew. Energy 36 (2011) 1458–1462, https://doi.org/10.1016/j.renene.2010.11.008. [29] J. Zeng, Y. Chen, L. Shu, L. Yu, L. Zhu, L. Song, Z. Cao, L. Sun, Preparation and thermal properties of exfoliated graphite/erythritol/mannitol eutectic composite as form-stable phase change material for thermal energy storage, Sol. Energy Mater. Sol. Cell. 178 (2018) 84–90, https://doi.org/10.1016/j. solmat.2018.01.012. [30] M. Mehrali, S.T. Latibari, M. Mehrali, T.M.I. Mahlia, H.S.C. Metselaar, Preparation and properties of highly conductive palmitic acid/graphene oxide composites as thermal energy storage materials, Energy 58 (2013) 628–634, https://doi.org/ 10.1016/j.energy.2013.05.050. [31] L. Yang, N. Zhang, Y. Yuan, X. Cao, B. Xiang, Thermal performance of stearic acid/ carbon nanotube composite phase change materials for energy storage prepared by ball milling, Int. J. Energy Res. 43 (2019) 6327–6336, https://doi.org/10.1002/ er.4352. [32] C. Wang, C. Cheng, T. Jin, H. Dong, Water evaporation inspired biomass-based PCM from daisy stem and paraffin for building temperature regulation, Renew. Energ. 194 (2022) 211–219, https://doi.org/10.1016/j.renene.2022.05.107. [33] S. Cunha, A. Campos, J. Aguiar, F. Martins, A study of phase change material (PCM) on the physical and mechanical properties of compressed earth bricks (CEBs), Malays. Constr. Res. J. 38 (2022) 1–19. [34] R. Wen, Y. Liu, C. Yang, X. Zhu, Z. Huang, X. Zhang, W. Gao, Enhanced thermal properties of stearic acid/carbonized maize straw composite phase change material for thermal energy storage in buildings, J. Energy Storage. 36 (2021), e102420, https://doi.org/10.1016/j.est.2021.102420. [35] A. Sarcinella, J. Aguiar, M. Lettieri, S. Cunha, M. Frigione, Thermal performance of mortars based on different binders and containing a novel sustainable phase change material (PCM), Materials 13 (9) (2020), e2055, https://doi.org/10.3390/ ma13092055. [36] P.K.S. Rathore, S. Shukla, Improvement in thermal properties of PCM/expanded vermiculite/expanded graphite shape stabilized composite PCM for building energy applications, Renew. Energy 176 (2021) 295–304, https://doi.org/ 10.1016/j.renene.2021.05.068. [37] M. Frigione, M. Lettieri, A. Sarcinella, J. Aguiar, Sustainable polymer-based phase change materials for energy efficiency in buildings and their application in aerial lime mortars, Constr. Build. Mater. 231 (2020), e117149, https://doi.org/ 10.1016/j.conbuildmat.2019.117149. [38] A. Hasan, J.S. McCormack, J. Sarwar, B. Norton, Increased photovoltaic performance through temperature regulation by phase change materials: material comparison in different climates, Sol. Energy 115 (2015) 264–276, https://doi. org/10.1016/j.solener.2015.02.003. [39] S. Sharma, A. Tahir, K.S. Reddy, T.K. Malick, Performance enhancement of a building-integrated concentrating photovoltaic system using phase change material, Sol. Energy Mater. Sol. Cells 149 (2016) 29–39, https://doi.org/10.1016/ j.solmat.2015.12.035. [40] S. Cunha, J. Aguiar, A. Tadeu, Thermal performance and cost analysis of mortars made with PCM and different binders, Constr. Build. Mater. 122 (2016) 637–648, https://doi.org/10.1016/j.conbuildmat.2016.06.114. [41] Pordata. https://www.pordata.pt/portugal/edificios+construidos+segundo+os+ censos+na+decada+antecedente+(percentagem)-3790, 2023 (accessed 5 May 2023). [42] Y. M’hamdi, K. Baba, M. Tajayouti, A. Nounah, Energy, environmental, and economic analysis of different buildings envelope integrated with phase change materials in different climates, Sol. Energy 243 (2022) 91–102, https://doi.org/ 10.1016/j.solener.2022.07.031. [43] C. Lamnatou, F. Motte, G. Notton, D. Chemisana, C. Cristofari, Cumulative energy demand and global warming potential of a building-integrated solar thermal system with/without phase change material, J. Environ. Manag. 212 (2018) 301–310, https://doi.org/10.1016/j.jenvman.2018.01.027. [44] M. Sovetova, S.A. Memon, J. Kim, Thermal performance and energy efficiency of building integrated with PCMs in hot desert climate region, Sol. Energy 189 (2019) 357–371, https://doi.org/10.1016/j.solener.2019.07.067. [45] Portada. https://www.pordata.pt/portugal/alojamentos+segundo+os+censos+ total+e+por+area+util-3759, 2023 (accessed 3 May 2023). [46] European Committee for Standardization (CEN), EN 1015-3:2004, Methods of Test for Mortar for Masonry-Part 3: Determination of Consistence of Fresh Mortar (By Flow Table), 2004. [47] European Committee for Standardization (CEN), EN 1015-11, Methods of Test for Mortar for Masonry–Part 11: Determination of Flexural and Compressive Strength of Hardened Mortar, 1999. [48] European Committee for Standardization (CEN), EN 1015-18, Methods of Test for Mortar for Masonry–Part 18: Determination of Water Absorption Coefficient due to Capillary Action of Hardened Mortar, 2002. [49] National Laboratory of Civil Engineering (LNEC), Specification E 394, Concrete–Determination of Water Absorption by Immersion, 1993 (in Portuguese). [50] S. Cunha, M. Lima, J.B. Aguiar, Influence of adding phase change materials on the physical and mechanical properties of cement mortars, Constr. Build. Mater. 127 (2016) 1–10, https://doi.org/10.1016/j.conbuildmat.2016.09.119. [51] S.G. Sanfelix, I. Santacruz, A.M. Szczotok, L.M.O. Bello, A.G. De la Torre, A. L. Kjøniksen, Effect of microencapsulated phase change materials on the flow behavior of cement composites, Constr. Build. Mater. 202 (2019) 353–362, https:// doi.org/10.1016/j.conbuildmat.2018.12.215. [52] Portuguese Institute for Quality (IPQ), NP EN 998-1:2010. Specification for Masonry Mortars -Part 1: Plastering Mortars for Interior and Exterior, 2010 (in Portuguese). [53] A. Jayalath, R.S. Nicolas, M. Sofi, R. Shanks, T. Ngo, L. Aye, P. Mendis, Properties of cementitious mortar and concrete containing micro-encapsulated phase change materials, Constr. Build. Mater. 120 (2016) 408–417, https://doi.org/10.1016/j. conbuildmat.2016.05.116. [54] S. Cunha, A. Sarcinella, J. Aguiar, M. Frigione, Perspective on the development of energy storage technology using phase change materials in the construction industry: a review, Energies 16 (2023), e4806, https://doi.org/10.3390/ en16124806. [55] G.P. Panayiotou, S.A. Kalogirou, S.A. Tassou, Evaluation of the application of Phase Change Materials (PCM) on the envelope of a typical dwelling in the Mediterranean region, Renew. Energy 97 (2016) 24–32, https://doi.org/10.1016/ j.renene.2016.05.043. [56] Portada. https://www.pordata.pt/europa/precos+da+eletricidade+para+utilizad ores+domesticos+e+industriais-1477, 2023 (accessed 3 May 2023). S. Cunha et al.