Sensitivity analysis of mathematical models for final product properties: Link to DTG curve

Compressive strength and water absorption of fired heavy clay products varies with firing temperatures, but not entirely according to linear function, as it is mostly reported in literature. Also, differential thermo-gravimetric curve shows many turnovers in all the samples tested, within observed temperature range (820–920 °C). The aim of this research was to find a cause for such behaviour. Except derivative weight (DW), compressive strength (CS) and water absorption (WA) are chosen as outputs that represent properties of the fired samples. These parameters can be calculated using second order polynomial models (SOPs), on the basis of content of major oxides and firing temperature, as shown in our previous research. Sensitivity analysis was used as the effective approach in testing changes observed in the SOP outputs, due to the variation of content of major oxides for +1% or −1% of their nominal value. This study reveals in more detail the most significant influence of inputs (SiO2, Al2O3, Fe2O3 and CaO content) over the outputs (DW, CS and WA) in every observed firing temperature. Addition or lowering of content of major oxides can both increase and decrease all the observed outputs, as revealed using sensitivity analysis.