# Assessment of Lightweight Concrete Thermal Properties at Elevated Temperatures
## 3 Results and Discussion
### MTPS Results  
Four tests were performed for each sample block to determine thermal conductivity and specific heat. The average of the four measurements was calculated. The initial moisture content of the LWC samples is calculated using Equation (5). The initial moisture content is between 3% and 8% and, at the end of the tests (160 \({}^{\circ}\)C), the moisture content is lower than 1%, which means a reduction in bulk density. \[\text{{MC}}=\frac{V_{water}}{V_{concrete}}=\left(\frac{m_{1}-m_{2}}{m_{1}} \right)\times 100 \tag{5}\]  
where _MC_ is the percentage of moisture content, _m\({}_{1}\)_ is the mass of the sample at ambient temperature in kg, and _m\({}_{2}\)_ is the mass of the sample in dry conditions in kg. Figure 4: Thermal conductivity for LWC-1 at different pressures (100, 240, and 290 N/cm\({}^{2}\)). Figure 5: Thermal conductivities for all LWC types. Thermal conductivity at ambient temperature was measured before starting the heating curve. The results are shown in Table 3. The LWCs studied present high values of porosity, as well as high water content, and they are susceptible to changes in thermal conductivity due to a variation in moisture content [12]. The dependence of LWC thermal conductivity on moisture content is due to the replacement of the air phase by a water phase in the concrete pores. Water-accessible porosity is the key parameter that influences the increase in LWC thermal conductivity with moisture content. In addition, porosity affects thermal conductivity at elevated temperatures; the higher the LWC porosity, the lower its thermal conductivity. Due to samples having different moisture contents, in this work, a moisture content of 7% was set to study thermal conductivity. According to ISO 10456 [40], a thermal conductivity value related to specific conditions can be transformed to a different value in different conditions. The conversion of thermal values from a set of conditions (\(k_{1}\)) to another set of conditions (\(k_{2}\)) is carried out in accordance with Equation (6) [40]:  
\[k_{2}=k_{1}\times F_{T}\times F_{m}\times F_{a} \tag{6}\]  
where \(k_{1}\) is the thermal conductivity for the first set of conditions (W/mK), \(k_{2}\) is the thermal conductivity for the second set of conditions (W/mK), \(F_{T}\) is the conversion factor for temperature, \(F_{m}\) is the conversion factor for moisture content, and \(F_{a}\) is the conversion factor for aging. In the present work, it is assumed that there is no influence from temperature and aging. However, a conversion factor of moisture content was applied, since different moisture content conditions were analyzed. The ISO 10456 establishes a conversion factor (\(F_{mi}\)) for the moisture content as a function of the moisture content per unit mass for the \(i\)-th set of conditions, \(u_{i}\), through the conversion coefficient, \(f_{u}\). Following the research work of [PERSON] et al. [6], Equation (6) can be transformed into Equation (7). \[k(\phi)=k_{amb}\times e^{f_{u}(u_{i}(\phi)-u_{amb})} \tag{7}\]  
where \(\phi\) is the relative humidity, \(k_{amb}\) is the thermal conductivity at ambient temperature, \(f_{u}\) is the conversion coefficient of moisture content, \(u_{i}\) is the moisture content for the \(i\) conditions, and \(u_{amb}\) is the moisture content for ambient conditions. The conversion of thermal conductivity of LWCs from experimental conditions to reference set conditions is carried out in accordance with Equation (7). Following previous works [6], a conversion coefficient (\(f_{u}\)) of 14 was used for LWC-1, while, for LWC-2 and LWC-3, this value was 6. Least-squares fitting was calculated by minimizing the root-mean