Material Preparation

The wood-cement steatite powder (WCSP) mixtures tested in this project were all prepared with the same ratio by weight of wood-binder and SP-binder, where the binder phase is the sum of cement and SP. The wood-binder ratio and SP-binder ratio selected were 0.35 and 0.15 (Table 3—P3). After mixing the materials in the mortar mixer, each particleboard was cast using the same <sup>450</sup> <sup>×</sup> <sup>330</sup> <sup>×</sup> 14 mm<sup>3</sup> wooden mold. The wet mixture was poured into the mold, the surface was then levelled off with a wood screed, and in the end a wooden lid was secured on top of the mold with C-clamps. The particleboard thickness was reduced to 13 mm due to the pressure of the lid. The particleboards were unmoulded at the age of 3 days and stored in a conditioning chamber at 23 ◦C and 60% R.H. The various test specimens were sawn from the particleboard using a 5 mm thick saw blade at the age of 28 days (Figure 3). Particleboards nos. 1, 2, 3, 6, 7 and 8 were tested for bending modulus of rupture (MOR) and modulus of elasticity (MOE), and screw-withdrawal later. Thermal properties and water absorption tests were carried out on particleboards nos. 4 and 5. The reaction to fire was determined on particleboards nos. 9 and 10.

Due to the settling of the SP at the bottom of the panels, this face of the WSCP which was in contact with the mold had a less porous, denser microstructure than at the top. This face is the smoothest and is called front face. The top face of the panel in the mold which is the roughest is referred to as back face throughout this paper (Figure 4) and should be used against the structure when mounting a wall. In Section 2, the front face will be used for reaction to fire testing and nail pull resistance testing, while the three-point bending test is applied on both faces of the WCSPs.

**Figure 3.** Sketch of samples cutting for WCSP (all measurements in mm).

**Figure 4.** Edges and faces of a wood–cement steatite powder particleboard cut with a saw.

#### *2.3. Test Methods*

In this study, the mechanical properties of the investigated particleboards and GB were determined in accordance with ASTM D1037-12 Standard test methods for evaluating the properties of wood-based fiber and particle panel materials [20]. Beside, the nail pull resistance test were determined in accordance with ASTM C473-17 Standard test methods for physical testing of gypsum panel products [21]. In both method, MOR and MOE, screw withdrawal resistance and nail pull resistance were determined using an MTS QTest-5 Universal Test Frame (MTS systems corporation, Eden Prairie, MN, USA) featuring the Elite Modular Control System. All experiments on WCSP test specimens were conducted at the age of 28 days. As shown in Figure 4, the molded WCSP samples have the shape of a panel. Therefore, the determination of density was based on the weight and the average dimensions of the samples.

Water absorption was determined in accordance with ASTM D1037-12. The reaction to fire was tested following the ISO 5660 [22] using a cone calorimeter (Fire testing technology Limited, West Sussex, UK). Thermal capacity, specific heat and thermal conductivity were determined with a FOX 314 Heat Flow Meter (TA instruments-LaserComp Inc., Wakefield, MA, USA) following the ASTM C518 [23]. The sample was placed between the two plates of the heat flow meter at a controlled temperature. The flux meter was attached on each side of sample. The temperature and heat flux could therefore be measured at the board surface. The bottom face of WSCP (in the mold) is the exposed face in the test. The bottom face was exposed directly to the heat flux and spark igniter. The four parameters (two temperatures and two heat fluxes) can then be used to calculate heat capacity and thermal conductivity of the sample.

Finally, solid samples were observed under a Scanning Electron Microscope in order to analyse its microstructure by the JEOL JSM-840A (JEOL USA Inc, Peabody, MA, USA) equipped with an energy dispersive X-ray analysis system (EDS). The specimens were placed on double-sides adhesive tape and coated with a thin alloy of Au-Pd. The operating conditions were set at 15 kV.
