## 3 Studies of PCMs Incorporated in Passive Systems
### Experimental Studies
#### 3.1.1 At the Composite Scale  
[PERSON] et al. [19] incorporated a paraffin PCM (RT22 HC) into a mortar made from Portland cement. Four different compositions were tested from the fresh to the 28-day aged state: the reference mortar (0 wt% PCM) and three other mortars composed of 5 wt%, 10 wt% and 15 wt% PCM. The different mortar formulations were tested in terms of physical properties (workability, density, water absorption by capillarity and immersion), mechanical properties (compressive and tensile strength) and thermal behavior. The thermal test was conducted in a climatic chamber of 0.008 m\({}^{3}\) simulating the summer (11-44 \({}^{\circ}\)C) and winter (12-29 \({}^{\circ}\)C) climatic conditions of a region in Portugal. The results show an improvement of the liquid binder ratio but a reduction for superplasticizer with the PCM fraction was observed. Moreover, the incorporation of 5 wt% of PCM leads to a reduction of the water absorption coefficient by capillarity of 34%. The mechanical properties varied little with the addition of PCM up to 20 wt% where reductions of 8% and 19% were observed for the compressive and tensile properties. On the other hand, the mortar with 20 wt% PCM exhibited the best thermal performance due to a reduced peak temperature of 5 \({}^{\circ}\)C and was delayed by 48 min in time. In a similar study, [PERSON] and [PERSON] [51] analyzed and compared the thermal performance of direct incorporation of PCMs into mortar. Five different PCMs with phase change temperatures in the range of 17-33 \({}^{\circ}\)C were used in this study: two inorganic PCMs, HS24 and HS29, and three organic PCMs, OM29, which is a commercially available organic PCM, n-Butyl stearate (n-BS) and polyethylene glycol-600 (PEG-600). The cement in the mortar is partially replaced by the PCMs in proportions of 5 wt% to 15 wt%. To ensure proper retention of the liquid phase of the PCM in the mortar, a leakage test was conducted. The compression test showed a reduction in compressive strength with the addition of PCM. For inorganic PCMs, there was no effect on the mechanical strength at all ages up to 10 wt% incorporation rate compared to organic PCMs where a drastic reduction in mechanical properties is observed at all incorporation levels regardless of ages. All PCM compositions showed high thermal stability after 750 and 1000 cycles. Thermal conductivity measurement performed by the guarded hot plate method for several days shows an increase in thermal conductivity with age and a decrease with the addition of PCM. The formulation of 10 wt% inorganic PCM in the mortar was selected as optimal because it \begin{table}
\begin{tabular}{c c c c} \hline
**Techniques** & **Advantages** & & **Disadvantages** \\ \hline \multirow{8}{*}{Shape-stabilized} & - & Simple and inexpensive techniques & - & PCMs can diffuse to the surface and be progressively lost if the process is not optimized \\  & - & Containment of the liquid phase & - & More contact between the PCM and the environment, which can lead to corrosion or adverse reactions \\  & - & Wide variety of support materials & \\  & - & Increased thermal conductivity & \\  & - & Possibility to encapsulate a large fraction of & \\  & PCMs (10–100\%) & & \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._does not affect the mechanical strength properties and has good thermal performance with a reduction in peak temperature of 3-5\({}^{\circ}\)C.  
[PERSON] et al. [52] conducted an experimental and numerical study of the characteristics of a bio-sourced composite material by direct impregnation of a vegetable non-cocoa oil in an insulating material made of clay and cellulose fibers with an incorporation rate of 56% by volume of PCM. The temperatures, heat of fusion, and solidification of the composite material are measured by differential scanning calorimetry (DSC) and have values of 34.83 \({}^{\circ}\)C, 22.34 \({}^{\circ}\)C, and 60.41 J g\({}^{-1}\), 62.39 J g\({}^{-1}\), respectively.