## 2 Experimental Section
### Experimental Methods
#### 2.3.2 MOC Cement Composites Testing Methods  
The workability of the fresh composites was investigated immediately after the production of individual mixtures according to the standard EN 12350-5 [38]. For the measurement of the flow diameter, three samples of each mixture were used. For the hardened lightweight MOC composites, basic structural characteristics, mechanical parameters, thermal properties, water- and water vapor transport parameters were investigated. SEM/EDS and XRD analyses were also conducted. The testing was carried out on a minimum of five samples of the particular studied material. The reaction products in the MOC composites were identified by X-ray diffraction (the same parameters and device as described above). Scanning electron microscopy (SEM) with a FEG electron source (Tescan Lyra dual beam microscope) was used for the characterization of the morphology and microstructure of MOC composites. Elemental composition and mapping were performed using an energy dispersive spectroscopy (EDS) analyzer (X-MaxN) with a 20 mm\({}^{2}\) SDD detector (Oxford instruments) and AZtecEnergy software. To conduct the measurements, the samples were placed on a carbon conductive tape. SEM and SEM-EDS measurements were carried out using a 10 kV electron beam. The measurements of compressive and flexural strength as well as the assessment of the dynamic Young's modulus of elasticity were conducted on 28 days cured samples. For measurement of the flexural strength, prisms with dimension of 40 mm \(\times\) 40 mm \(\times\) 160 mm were used. On the remains of samples from flexural strength measurement, the compressive strength was evaluated; the loading area was 40 \(\times\) 40 mm. Figure 4: Used aggregate: silica sand (**a**); crushed waste expanded polypropylene (EPP) (**b**). Scale bar is in centimeters. Both strength tests were performed in accordance with the standard EN 14016-2 [35] and their relative expanded uncertainty was 1.4%. The measurement of the dynamic Young's modulus of elasticity was conducted on a pulse ultrasonic principle using an ultrasonic pulse velocity tester 58-E4800 UPV (Controls, Milan, Italy). Based on the measured wave velocity \(v\) (m-s\({}^{-1}\)) and bulk density \(\rho_{\mathrm{b}}\) (kg\(\cdot\)m\({}^{-3}\)), the dynamic Young's modulus was calculated using Equation (1):  
\[E_{d}=\rho_{b}v^{2} \tag{1}\]  
The expanded combined uncertainty of this measurement method was 3.1%. In order to evaluate the bulk and specific density of the hardened composites, the specimens were first dried in a vacuum drier until the changes in their mass were \(<\)0.1%. For the bulk density measurement, the test was based on a gravimetric principle according to the standard EN 12390-7 [39] and the cubic samples were employed. The expanded combined uncertainty of bulk density test was 2.4%. The specific density was accessed on the fragments from the strength tests using the helium pycnometry (see above). The expanded combined uncertainty of the specific density test was 1%. The porosity of MOC composites was then calculated using the bulk and specific density values. The relative expanded combined uncertainty of the porosity determination was 3.5%. For the assessment of thermo-physical parameters of MOC cement composites, i.e., the thermal conductivity \(\lambda\) (W\(\cdot\)m\({}^{-1}\).K\({}^{-1}\)) and the volumetric heat capacity C\({}_{\mathrm{p}}\) (J\(\cdot\)m\({}^{-3}\).K\({}^{-1}\)), apparatus thermal constant analyzer hot disk TPS 1500 (Hot Disk AB, Gothenburg, Sweden) was applied. The apparatus works on a transient plane source method based on the use of a transiently heated plane sensor consisting of double spiral shape nickel-metal wire with diameter 10 \(\upmu\)m embedded between two thin special foils keeping it electrically insulated. The measuring range of the thermal conductivity of TPS 1500 device was from 0.03 to 500 W\(\cdot\)m\({}^{-1}\).K\({}^{-1}\) with the measuring accuracy \(\pm\)5% and reproducibility \(\pm\)2%.