# Assessment of Lightweight Concrete Thermal Properties at Elevated Temperatures
## 5 Conclusions  
This research focuses on the thermal properties of three types of structural lightweight concrete. In order to study specific heat and thermal conductivity, three techniques were used. The main conclusions of this work can be summarized in the three sections below:  
1. General conclusions: 1. Porosity and bulk density of LWCs show an inverse relationship at low temperatures: the higher the porosity, the lower the bulk density. LWC-1 has the highest porosity, 28%, and the lowest bulk density, 1740 kg/m\({}^{3}\). True density is defined as the relationship between the mass and volume of the concrete, including the pores in the material. Taking into account this relationship, the true density of the three LWCs is similar: between 1.3 and 1.4 times higher than the bulk density. 2. The structural LWCs studied have significantly lower thermal conductivity than normal concrete, reducing heat losses. Thermal conductivity of LWC is highly affected by moisture content, which depends on porosity and temperature. In this sense, at low temperatures, the higher the porosity, the higher the thermal conductivity; however, at high temperatures, the higher the porosity is, the lower the thermal conductivity is. The results of the tests reveal this variability in the thermal conductivity of LWCs. 3. This research shows interesting differences in the performance of samples manufactured with different dosages of aggregates. This demonstrates the importance of a preliminary phase of material characterization. The standard ISO10456 must be updated to adapt the conversion coefficients when expanded clay is used as the main aggregate. This research work proposes a conversion factor between 6 and 14 for all the LWC mixes with densities between 1700 and 1900 kg/m\({}^{3}\). 4. The current Eurocodes 2 and 4 used for evaluating the fire resistance of elements assume that specific heat for LWC can be simplified with a constant value of 840 J/kg\({}^{\circ}\)C. However, the results of this research work sug  
Figure 11: Comparison of the experimental and proposed thermal conductivity: (**a**) LWC-1; (**b**) LWC-2; (**c**) LWC-3. gest a change to the Eurocodes as temperature has a significant influence on specific heat. 2. Thermal techniques: i. The results of this work show the efficiency of combining MTPS and LFA techniques to measure thermal conductivity in a wide temperature range. The MTPS technique measures thermal conductivity from ambient temperature up to 160 \({}^{\circ}\)C. Although LFA tests with ground particles have inherent limitations due to partial-cle contact, above 160 \({}^{\circ}\)C, at which there is practically no water in the concrete, the values obtained by LFA could be considered valid. Both techniques are complementary, as demonstrated by the equality of the thermal conductivity values at 160 \({}^{\circ}\)C. The MTPS technique requires a stabilization time longer than 1 h to reduce the moisture content of the samples. ii. The MTPS and DSC techniques show that temperature is an influential parameter and must be taken into account to calculate the specific heat. Both techniques show that the specific heat for LWC is higher than the values specified in Eurocodes 2 and 4. Specific heat is affected by decomposition reactions, as shown in the DSC results. For this reason, the MTPS technique should take into account the loss of mass caused by water vaporization to provide an adjusted value of specific heat. Therefore, in order to use the MTPS technique to obtain an adjusted value of the specific heat at elevated temperatures, the density of the material must be measured as a function of the test temperature, and Equation (4) should be applied to make the corresponding adjustments. 3. Proposed equations: i. The proposed equations for specific heat are based on experimental data and dependent on temperature and fitting the experimental values. Although Eurocodes 2 and 4 assume a constant value for specific heat, this research work shows that this assumption has numerous drawbacks.