# Development of Passive Fire Protection Mortars
## 2 Materials and Methods
### Experimental Testing System and Procedure  
The experimental testing system (Figure 7) used in thermal analysis of steel plates consisted of a cylindrical oven with internal dimensions 400 mm in height and 250 mm in diameter, capable of reaching a maximum temperature of 1200 \({}^{\circ}\)C (a) and the respective oven controller (b). A Datalogger TDS-530 was used as a data acquisition system (c) to record the temperature readings. Regarding the test procedure, after sealing all the existing unions and holes of the oven with rock wool, a 8 cm thick rock wool blanket with a circular opening of 210 mm in diameter was also placed on the top of the oven (e), which allows the passage of heat from the interior of the oven to the specimen. Subsequently, the specimen (d) was placed on the top of the oven, i.e., on the rock wool blanket and centred with the barycentric axis of the oven.  
Figure 6: Distribution of thermocouples (**a**) and fabrication of specimens, preconcreting (**b**), concreting on the short steel columns (**c**), and concrete specimen without formwork (**d**).  
Figure 7: Experimental setup: (**a**) cylindrical oven (**b**) oven controller (**c**) data acquisition system (**d**) specimen (**e**) rock wool.  
In all tests, the specimens were placed in a suitable position to ensure perfect accommodation with the rock wool and thus avoid heat losses between the specimen and the oven. The specimen was heated at a heating rate of 15 \({}^{\circ}\)C/minute until reaching the desired temperature level (900 \({}^{\circ}\)C). Temperatures inside the specimen and the oven were measured every 5 s. When the target temperature in the specimen was reached, it was maintained uniform during 3 h and after, the test was given as concluded.  
The experimental layout for the short steel columns (SSC) under fire conditions (Figure 8) consisted essentially of a reaction steel frame (A) to apply the serviceability load on the specimen, a support steel frame (B), a hydraulic jack (C), and an electric furnace (H).  
This steel frame was defined by HEB 500 columns and a HEB 600 beam (A), with a stiffness capable of minimizing possible displacements of this steel structure during the tests. Additionally, a support 3D steel frame consisting of two frames (B) with HEB 300 columns and HEB 400 beams accommodate the testing specimen to similar actual boundary conditions. Regarding the test equipment, a 3 MN hydraulic jack (C) and its controller (J), a 3 MN load cell (D), and a 1 MN load cell (E) were used for measuring the compression forces. Ten linear variable displacement transducers were used for displacements measurements (F), a Datalogger (G) for data acquisition, and an electric furnace (H) to heat up the steel columns (I).  
Figure 8: Experimental system used in the laboratory to test SSC. The letters in this figure are defined in the following text.  
A hydraulic jack controlled by a servo-controlled central was used, and a preload of 50% of the design value of the loadbearing capacity of the columns at ambient temperature (ULS) was applied (727.8 kN) to simulate a service load on the specimen. After stabilising this loading in the specimen, the furnace was switched on and the specimen heated according to the temperature evolution established by the ISO 834 standard fire curve [41].  
Due to the increase in temperature during the test, significant thermal elongation was generated in the specimen. The test was stopped based on the axial contraction criterion defined by ISO 834-1:1999 [42], which defines a limit shortening of the specimen according to its initial length, i.e., when the specimen could no longer support the initial applied load subjected to high temperatures. Thus, the final value of vertical deformation considered was 12.5 mm. Finally, the degree of detachment of the protective mortar and the failure mode in each specimen were observed.