The chapter delves into the integration of phase change materials (PCMs) into cement boards to improve energy efficiency in construction. It highlights the direct incorporation technique as a cost-effective method and examines the effects of varying PCM contents on the physical and mechanical properties of the boards. Key topics include the impact on open pore volume, real and apparent density, total porosity, water absorption, and flexural strength. The study reveals that while PCMs enhance energy storage, they also influence the boards' structural integrity. The findings offer valuable insights for developing sustainable and efficient building materials.
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Abstract
Currently it is necessary to give a new direction to the construction sector, making it essential to change the way that buildings are constructed and rehabilitated, with the aim of obtaining a construction with greater sustainability value. To minimize energy consumption, it is important to take advantage of renewable energy sources like solar power. Phase change materials (PCM) can help reduce building energy consumption due to their energy storage capacity. PCM has been studied in different solutions for walls, ceilings, and floors, essentially using encapsulation techniques. The use of PCM in building materials has social, environmental, and economic benefits, including increased thermal comfort, decreased energy consumption from non-renewable sources, and reduced air conditioning needs and costs. The development of cement boards incorporating PCM brings a new option for the thermal improvement of buildings, which can be used in new buildings and rehabilitation operations. The main objective of this study was the development of cement boards with the incorporation of pure and free PCM, through direct incorporation, consisting of a simple, low-cost, and very promising incorporation technique. The results showed that the technique was easy to use in manufacturing cement boards for interior coatings of building walls and ceilings. It was also possible to observe a decrease in the water/cement ratio with the incorporation of PCM and a consequent decrease in the porosity, which resulted in a slight reduction in its mechanical strengths, without ever compromising the necessary performance for its function.
1 Introduction
Construction is responsible for 40% of energy consumption, carbon dioxide emissions, and natural raw material consumption [1, 2]. Efforts must be made to change the paradigm of construction, which is dependent on-air conditioning systems and building materials with high embodied energy, to a more holistic and sustainable approach [1].
Europe is currently experiencing significant energy supply challenges, which have been exacerbated by recent international conflicts in natural gas and oil producing and exporting countries. As a result, there is an increasing need for European Union countries to explore options for achieving greater energy independence. One potential solution is to invest in renewable energy sources, which could help to reduce reliance on traditional energy sources. Additionally, the incorporation of functional construction materials, such as those with thermal storage capacity, has the potential to enhance energy efficiency and comfort in both residential and commercial buildings.
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The use of phase change materials (PCMs) has been employed as a measure to regulate energy consumption in buildings. PCMs have been studied for building applications due to their thermal storage capacity based on solar energy, with many of the studied applications focused on building interiors [2‐6]. Regarding PCM incorporation into building materials, the encapsulation technique is the most widely used and the most expensive [7, 8]. In this study, the direct incorporation technique of PCM into mortars was used, which is a low-cost technique [3, 9, 10].
The main objective of this study was to develop and characterize interior panels with direct incorporation of PCM. The composition of the panels was based on the composition of the mortars previously developed. Four distinct compositions were developed with different PCM contents (0%, 5%, 10%, and 20%). The behavior of the panels was evaluated in the hardened state, based on open pore volume, real and apparent density, total porosity, water absorption by immersion, water absorption by capillarity, and flexural strength.
2 Experimental Program
2.1 Materials
The cement used was CEM II/B-L 32.5 N with a density of 3030 kg/m3. The fly ash used was produced in a Portuguese coal-fired power plant and had a density of 2420 kg/m3. The aggregate used was composed of two different types of sand (A and B). Sand A has a minimum dimension of 0.125 mm and a maximum dimension of 0.5 mm, with an average particle size of 439.9 μm and a density of 2600 kg/m3. Sand B is composed of particles with a minimum dimension of 0.125 mm and a maximum dimension of 8 mm, with an average particle size of 762 μm and a density of 2569 kg/m3.The PCM used is non-encapsulated, of organic nature, composed of a paraffin with a transition temperature between 20 ℃ and 23 ℃, enthalpy of 200 kJ/kg, solid state density of 760 kg/m3 and liquid state density of 700 kg/m3.
2.2 Test Methods
Regarding the characterization of the boards with incorporation of PCM, they were evaluated considering their physical and mechanical behavior. Considering the absence of specific harmonized standards for this type of material, it was decided to adapt the standards for natural stone boards, NP EN 1469 [11]. The physical behavior was based on real and apparent density, total and open porosity, and water absorption by capillarity and immersion. The mechanical behavior was based on flexural strength. The determination of real and apparent density, and total porosity was performed according to the specification NP EN 1936 [12]. The determination of real density and total porosity was carried out according to the Le Chatelier method described in the specification NP EN 1936 [12]. Water absorption by immersion was performed according to the specification NP EN 13755 [13], and water absorption by capillarity was determined according to NP EN 1925 [14].Finally, the flexural behavior of the boards with the incorporation of PCM was determined based on the specification NP EN 12372 [15] with load control and a speed of 50 N/s.
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2.3 Boards Prototype
The determination of the geometry and dimension of the prototype of the PCM-enhanced boards was based on market research, which revealed a wide availability of natural stone boards and composites with different dimensions suitable for various project needs. Therefore, it was decided to follow the geometrical indications provided in specification NP EN 12372 [15], considering a geometry that allows for easy handling and industrial production, with a prismatic geometry of dimensions 100x100x20 mm3 selected.
2.4 Formulations
The development of these formulations was based on previous works carried out by the authors regarding the incorporation of phase change materials (PCMs) into mortars for interior coatings [3, 9, 10]. Four different compositions of cement mortars were developed by incorporating different levels of unencapsulated PCMs (Table 1). A reference mortar was produced without the addition of PCM (C0PCM), and three mortars with varying incorporation levels of 5% PCM (C5PCM), 10% PCM (C10PCM), and 20% PCM (C20PCM) relative to the mass of the aggregate. The binder used comprised 500 kg/m3, consisting of 40% cement and 60% fly ash, while the aggregate consisted of a mixture of 50% Sand A and 50% Sand B. The aggregates were used in dry form.
Table 1.
Mortars composition (kg/m3).
Composition
Cement
Fly ash
Sand A
Sand B
PCM
Water
C0PCM
200
300
684.9
684.9
0
280
C5PCM
200
300
583.6
583.6
58.4
275
C10PCM
200
300
519.1
519.1
103.8
260
C20PCM
200
300
423.7
423.7
169.5
240
3 Test Results and Discussion
3.1 Open Pores Volume
The results presented in Fig. 1 indicate that the presence of a higher content of phase change material (PCM) in the composite board leads to an increase in the open pore volume. Comparison with reference boards, which did not incorporate PCM, revealed that the incorporation of 5% PCM resulted in a more than 30% increase in the open pores volume. This behavior can be attributed to the geometry of the PCM composite board prototype, which has a larger exposed surface area, facilitating water evaporation during the curing process. Moreover, PCM exhibits a higher tendency to migrate towards the surface, which also contributes to an increase in the open pore volume. In this case, PCM can move from its initial location, but the quantity of PCM involved in this effect is not significant. This phenomenon is known as the “board effect”.
Fig. 1.
Open pores volume of the developed mortars.
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3.2 Real and Apparent Density
The results of Fig. 2 indicates that the incorporation of higher PCM content into the mortars led to a decrease in both apparent and real density. Specifically, a decrease of over 11% in apparent density was observed with the incorporation of 5% PCM, compared to the reference boards. In contrast, the decrease observed in real density was less significant, around 5%.
The behavior of apparent density is strongly influenced by the volume of open pores, as higher values of open pores volume (Fig. 1) lead to lower values of apparent density. In contrast, the behavior of real density can be explained by the lower density of PCM compared to the sand used. Additionally, this behavior could also be observed due to the decrease in the water/binder ratio in the mortars that was demonstrated in previous works [3, 9, 10].
Fig. 2.
Boards density: (a) Apparent density; (b) Real density.
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3.3 Total Porosity
The Fig. 3 depicts the total porosity of the PCM composite boards, and it is evident that the total porosity increases with the incorporation of higher PCM contents. Comparing the board without PCM incorporation (0% PCM) to the board with 5% PCM incorporation, a significant increase in total porosity of 48% was observed. Furthermore, the increase in total porosity was 65% and 76% for an incorporation of 10% and 20% of PCM, respectively. The observed increase in total porosity can be attributed to the higher ease of water evaporation, resulting from the higher exposed surface area of the boards, which is associated with the “board effect” described earlier. This effect mainly affects the macroporosity of the boards.
Fig. 3.
Total porosity of the developed mortars.
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3.4 Water Absorption by Immersion
The presented results in Fig. 4 show the water absorption by immersion of the developed boards. It was observed that the water absorption tends to increase with the presence of higher PCM contents. An increase of approximately 3%, 7%, and 21% in water absorption by immersion was observed for boards with 5%, 10%, and 20% PCM incorporation, respectively. This behavior could also be explained by the increase in the liquid/binder ratio in the mortars that was demonstrated in previous works [3, 9, 10]. Also, due to the increase in open pore volume (Fig. 1) and total porosity (Fig. 3) in the boards with PCM incorporation. This increase in pore volume and total porosity is associated with the presence of a higher macroporosity in the boards.
Fig. 4.
Water absorption by immersion of the developed mortars.
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3.5 Water Absorption by Capillarity
The capillary absorption coefficient of the boards provides information about their microporosity. Figure 5a shows the capillary absorption coefficient of the developed boards. The boards with 5% and 10% PCM incorporation had a similar capillary water absorption coefficient. However, for boards with 20% PCM incorporation, there was a decrease of about 25% in the water absorption coefficient by capillarity. Figure 5b shows the amount of water absorbed by capillarity. The incorporation of higher PCM content led to lower water absorption. This behavior can be explained by the more compact microstructure of the mortars with PCM incorporation, which leads to a decrease in the microporosity of the mortars [9] and consequently of the boards.
Fig. 5.
Water absorption by capillarity: (a) Capillary absorption coefficient; (b) Water absorption by capillary for each PCM composite board.
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3.6 Flexural Strength
Based on Fig. 6, a decrease in the flexural strength of the boards was observed with the incorporation of PCM. The inclusion of 5% of non-encapsulated PCM resulted in a decrease in flexural strength of over 15%. This reduction in strength is attributed to the increase in liquid content in the mortars [3, 9, 10] and higher macroporosity, which is caused by the greater ease of water evaporation due to the “board effect” explained in this study.
Fig. 6.
Flexural strength of the developed mortars.
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4 Conclusions
This study demonstrates that it is possible to use mortars with the incorporation of non-encapsulated PCM to produce boards. However, the incorporation of non-encapsulated PCM in mortars and boards alters their physical and mechanical properties. Regarding the characterization of the boards, the following aspects were observed:
The volume of open pores, total porosity, and water absorption by immersion decrease with the incorporation of a higher content of PCM. This behavior can be justified by the geometry of the board, since the exposed surface during the curing process is larger than the surface exposed in mortar specimens, facilitating the evaporation of chemically uncombined water, a phenomenon known as the “board effect”.
The apparent and real density decreased with the incorporation of PCM, which can be attributed to the higher macroporosity of the boards caused by the presence of PCM and the “board effect”.
The capillary water absorption decreased with the incorporation of PCM due to the existence of a more compact microstructure of PCM mortars with respect to smaller pores.
The flexural strength decreased with the incorporation of non-encapsulated PCM, which is associated with an increase in the liquid/binder ratio in mortars and the higher macroporosity caused by the “board effect” described in this study.
In summary, the behavior of boards with PCM incorporation is largely influenced by the properties of the mortars that originate them. However, in terms of mechanical behavior, the performance of the boards was not affected by their geometry, which proves that the selected dimensions constitute a possible solution for the prefabrication of construction materials obtained based on functional mortars.
Acknowledgements
This work was supported by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Centre for Territory, Environment and Construction (CTAC) under reference UIDB/04047/2020.
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