## 2 Experimental Section  
### Materials  
The raw materials used in this paper were light-burned MgO powder, MgCl\({}_{2}\cdot\)6H\({}_{2}\)O, silica sand, and waste EPP particles. Crushed waste expanded polypropylene came from the aircraft models production. EPP was chosen for the investigation particularly with respect to its thermal and physical properties. In order to reduce the thermal conductivity of MOC cement composites as much as possible and with the knowledge of the high MOC cement binding capacity, it was decided to replace all natural aggregate. Based on the preliminary workability tests of the fresh mixtures [16], for further study the amount of the EPP particles of 150% by volume of natural silica sand was chosen. Magnesium oxide used in this paper was obtained from Styromagnesit Steinische Magnesitindustrie Ltd., Oberdorf, Austria and its chemical composition determined by X-ray fluorescence (EDXRF Spectrometer, ARL QUANTX, Thermo Fisher Scientific, Waltham, MA, USA) is given in Table 1.  
The main physical parameters of MgO powder such as specific density, powder density, and Blain specific surface are summarized in Table 2. The specific density was measured on a helium pycnometry principle using a Pycnomatic ATC (Porotec, Hofheim, Germany). This device is equipped with the real multi volume density analyzer and with the fully integrated temperature control with a precision of \(\pm\) 0.01 \({}^{\circ}\)C. The powder density was calculated from the dry mass of the sample and its volume and the Blain specific surface was accessed in accordance with the standard EN 196-6 [34].  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Substance** & **Mass\%** \\ \hline MgO & 78.6 \\ CaO & 5.7 \\ Fe\({}_{2}\)O\({}_{3}\) & 4.1 \\ SiO\({}_{2}\) & 4.4 \\ Al\({}_{2}\)O\({}_{3}\) & 6.8 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of light-burned MgO powder obtained by XRF.  
The X-ray diffraction analysis of MgO powder was examined at room temperature using Bruker D8 Discoverer (Bruker, Germany) powder diffractometer with parafocusing Bragg-Brentano geometry using CuK\({}_{\alpha}\) radiation (\(\lambda\) = 0.15418 nm, U = 40 kV, I = 40 mA). Data were scanned over the angular range 5-80\({}^{\circ}\) (29) with a step size of 0.019\({}^{\circ}\) (29). Results are shown in Figure 1. In addition to the main phase (magnesia), also some impurities were identified such as calcite, dolomite, and talc. This was in good agreement to XRF data.  
An average particle size (\(d_{50}\)) of used MgO powder measured on a laser diffraction principle using an Annalsyette 22 Micro Tec plus (FRITSCH, Idar-Oberstein, Germany) was approximately 45 \(\upmu\)m. The cumulative and frequency distributions of particle size distribution are for the studied MgO powder introduced in Figure 2. The displayed data were acquired based on three independent measurements.  
\begin{table}
\begin{tabular}{c c} \hline Specific Density (kg\(\cdot\)m\({}^{-3}\)) & 3339 \\ \hline Powder Density (kg\(\cdot\)m\({}^{-3}\)) & 838 \\ \hline Blain Specific Surface (m\({}^{2}\)\(\cdot\)kg\({}^{-1}\)) & 698 \\ \hline \end{tabular}
\end{table}
Table 2: Physical properties of light-burned MgO powder.  
Figure 1: X-ray diffraction pattern of MgO powder.  
Figure 2: Particle size distribution of MgO powder—curative and frequency curves.  
To prepare the magnesium chloride solution, MgCl\({}_{2}\)-6H\({}_{2}\)O of p.a. purity (Lach-Ner Ltd., Neratovice, Czech Republic) was dissolved in the tap water. For our solution we used 120.4 g of MgCl\({}_{2}\)-6H\({}_{2}\)O and 100 g of water.  
The natural aggregate used for preparation of reference MOC cement composites was silica sand of particle size fraction 0-2 mm and specific density 2649 kg\(\cdot\)m\({}^{-3}\). It was provided by Filtracni pisky Ltd., Chlum u Doks, Czech Republic.