# Development of Passive Fire Protection Mortars
## 2 Materials and Methods
### Preparation of the Specimens  
The manufacturing process, shape, and dimensions of the SP and moulds were defined to measure the thermal gradient generated between the inner surface of the steel plate exposed to high temperatures and the exposed surface of the fire protection mortar. Thus, a suitable mould was designed and manufactured for these tests (Figure 1). This mould assigns the desired geometric shape to the specimen, was easy to transport and clean, was reusable for many experimental tests, and was easy to assemble and disassemble when concreting and removing the specimen. During the fabrication of mortars, a balance accurate to 0.1 g, a graduated beaker, Ho \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Different Types of Tested Columns** & **Specimens** & **Number of Repetitions** & **Total No. of Specimens** \\ \hline Columns without passive & SSC1 & 2 & \\ fire protection & SSC2 & & \\ \hline Columns coated with CM & SSC3 & 2 & \\  & SSC4 & & \\ \hline Column coated & Without MS and NS & SSC5 & 2 & \\ with DCM & With MS and NS & SSC11 & 2 & \\ \hline Column coated & Without MS and NS & SSC7 & 2 & \\ with DGMP & With MS and NS & SSC12 & 2 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Experimental program on short steel columns. Figure 1: Mould used in the manufacture of SP: (**a**) mould components; (**b**) mould assembly. of capacity and a stainless-steel lab spatula were used. The procedure adopted in the fabrication of mortars was as follows:  
1. The raw materials were weighed and placed inside the mixer container. 2. Then, the mixer was put into operation for 5 min at a slow speed (136 rotations per minute). At the same time, the corresponding amount of water was added, with a constant flow rate to guarantee the homogeneous addition of water in the whole mortar. 3. After this procedure, the mortar was manually kneaded with a spatula to remove parts of the mortar that were on the walls of the container and thus homogenize the mixture, then returning the container to the mixer for another 2 min. 4. The mortar was placed inside the mould (Figure 2). In the production of mortars, the same procedure was followed to ensure that the different properties of the mortars were only dependent on their composition. To minimize possible effects that temperature and humidity might have on the properties of each mortar composition, all mixtures of each composition were manufactured on the same day and placed in a room with controlled environmental conditions. It is well known that the moisture content greatly influences the fire behavior of mortars at elevated temperatures [39, 40], in the same way as in the concretes. About 48 h after casting the SP in the moulds described above, they were demoulded and placed in the curing process (Figure 3a) for 28 days in the laboratory environment with controlled temperature (25 \({}^{\circ}\)C) and a relative humidity (RH) of 55%. The specimens were tested with 6 months of age. The specimens comprised a S355 steel plate with a square section of 250 mm of edge and a thickness of 5 mm; and 10 mm thick fire protection mortar on one side of the steel plate (Figure 3b). The temperature measurement in the SP was carried out by placing  
Figure 3: (**a**) Specimens in the process of curing; (**b**) specimen schematic representation and respective dimensions. Figure 2: Manufacture of specimens: (**a**) Hobart N50 mixer; (**b**) fresh mortar in the mixer container; (**c**) steel plate with thermocouples applied; (**d**) specimen in the process of curing during the first 48 h.  
4 type K thermocouples. The thermocouples were placed at different depths across the specimen (Figure 4). With this distribution of thermocouples, it was possible to determine the thermal gradient between the surface of the mortar exposed to high temperatures (ESMHT--thermocouple 3) and the unexposed surface (USMHT--thermocouple 2), as well as the temperature on the inner surface of the steel plate (ISSP--thermocouple 1) and its external surface (ESSP--thermocouple 4).