# Application of Artificial Neural Networks to Predict Insulation Properties of Lightweight Concrete
## 4 Discussion  
Based on the results of LWC laboratory tests, it can be concluded that the porosity and strength of the LWA grains have a significant impact on the physical properties of the LWC, such as: density, porosity, compressive strength and thermal conductivity. In the case of using of two different types of LWA, the grain structure has the main influence, especially the volume of open and closed pores in the grain volume. GAA grain has a higher crushing strength, although the porosity of GAA grain (37%) is similar to that of GEGA grain (37-42%). However, the pore structure and arrangement of the pores in the grain matrix of lightweight aggregate are completely different. The presence of GAA aggregate with increased strength has a significant positive effect on the compressive strength of the LWC. The higher the content of GAA, the higher the compressive strength of LWC. However, the highest strength was achieved with a ratio of GAA 8 mm to GEGA 2 mm of 1.3, because it is necessary to fill the space between the grains aggregate of a size with a diameter 8 mm. Beneficial values of LWC compressive strength were obtained with the use of aggregate GEGA 2 mm in the amount of 25% of the total volume of the aggregate was and if the share of GAA was 75%. If the GAA share was 100%, a 12.6% decrease in compressive strength LWC was noted. This is due to the impossibility of maximum content of aggregate grains with the diameter of 8 mm and construction of a porosity skeleton (20.8%). In the other use of GEGA 4 mm grains in the amount of 25% instead of GEGA 2 mm of 25% resulted in an increase in porosity about 7.9% in LWC (43%) and a decrease in compressive strength about 58.2%. This replacement also did not have a positive effect on the thermal insulation of the lightweight composite. The lowest thermal conductivity coefficient (0.17 W/m\(\cdot\)K) was obtained when GAA aggregate was not used, but only a mixture of GEGA 2 mm (75%) and GEGA 4 mm (25%) aggregates. Summarizing the analysis, it can be concluded that the highest compressive strength is achieved by cement lightweight composites containing 50, 75 and 100% GAA 8 mm and a maximum of 25% GEGA 2 mm. Lower compressive strength test results were observed for samples containing aggregates with the highest porosity and the lowest compressive strength when using 50%, 75% or 100% GEGA 4 mm. It can be concluded that a higher GEGA content with a grain size greater than 4 mm will reduce the compressive strength of the LWC. The higher the proportion of GEGA with a grain size greater than 4 mm, the higher the porosity and the lower the thermal conductivity. For a detailed analysis of LWC properties in the context of using the optimize of mixing ratio of light aggregates with different properties, trained ANN can be used with very good results. The results can be saved as a formula or a graph (Figure 4a-c). For example, it is possible to make a proposal  
Figure 7: Graphical presentation of the relationship between the thermal conductivity coefficient and density of the LWC based on: (**a**) laboratory test results; (**b**) ANN prediction. LWC composition of minimum thermal conductivity for a range of density or porosity as shown in Figure 4g,h. The analysis of the selection of the LWA mixing ratio with the use of ANN confirmed that the participation of GAA 8 mm had the greatest influence on mechanical properties of the lightweight composite, as presented the Figure 4f. While the content of GEGA aggregates in various proportions had an influence on the physical properties such as porosity and thermal conductivity and this presented on Figure 4c,d,g,h. On the Figure 4a,b it is visible that the greatest density values were located around the point (0,0), which means, those with a low content of GEGA 2 mm and GEGA 4 mm. Figure 5 presents the relationship between density and porosity of the LWC based on laboratory test results and ANN prediction, respectively. This dependence is valid only to LWC with GEGA and GAA additives.