# Effect of Different Gradings of Lightweight Aggregates on the Properties of Concrete
## 4 Evaluation of the Properties of Concretes with Different Aggregate Gradings
### Mechanical Property Evaluation  
The mechanical properties, elastic modulus and compressive strength, are evaluated. For the experiments, the mechanical loading tools that satisfy the German (elastic modulus) and European (compressive strength) standards are used. The numerical properties are also computed using the ABAQUS package and compared with those from the experiments.  
Figure 5 shows the results of elastic modulus and compressive strength of the LWC specimens obtained from the experiments and simulations. As can be seen in these figures, all the LWC samples produced here have the density less than 500 kg/m\({}^{3}\), which is consistent with the objective of this study. In Figures 5a,b, general trends of the mechanical properties are almost the same, although the differences in the elastic modulus are relatively larger than that of the compressive strength; the elastic modulus and the compressive strength of LW 30 are the largest among all cases, while those of LW 23 is the smallest. In addition, both properties tend to increase as the density of the specimen increases, except the case of LW 23. The differences between the experiments and simulations are mainly due to the assumption of the numerical model; all the aggregates in the virtual samples are set to be perfect spheres, and this will be discussed in detail in Section 4.3. Among the samples, LW 30 includes the largest proportion of fine aggregates (Liaver\({}^{\textregistered}\) 0.5-1.0 mm) and the smallest volume of coarse aggregates (Liaver\({}^{\textregistered}\) 2.0-4.0 mm). Comparing the mechanical properties of LW 23 and LW 45, which have similar experimental densities, the elastic modulus and the compressive strength are larger when the proportion of fine aggregates is larger; this denotes that the lightweight concrete can have improved mechanical properties by controlling the size distribution of LWAs.  
In general, it is well known that the compressive strength value is the main factor to evaluate the efficiency of normal weight concrete. However, in the case of LWC, not only compressive strength, but also a thermal insulation property should be considered for the concrete development. Thermal properties of cementitious materials are mainly controlled by the pore size distributions as well as the total pore volume, or in other words, by the dry density; therefore, in order to evaluate the performance of lightweight concrete, both density and compressive strength should be carefully considered. In this study, the following formula is used to calculate the efficiency factor [49]:  
\[F_{eff}=[F_{c}/(p/2.2)]^{2.5}, \tag{5}\]  
where \(F_{eff}\) is the efficiency factor, \(F_{c}\) is the compressive strength at 28 days [N/mm\({}^{2}\)], and \(p\) is the dry density of concrete in [t/m\({}^{3}\)]. It has been suggested that high performance LWC shows an efficiency factor higher than 70 [49]. By applying the formula, all four of the mixes have efficiency factors of 275-280, which are much higher than that of conventional high performance LWC. This can be explained by the high content of LWA due to applying the packing density concept. By increasing the  
Figure 5: Comparison of mechanical properties of the LWC samples: (**a**) elastic modulus; (**b**) compressive strength.  
LWA content, which is much lighter than cement and water, ultra LWC can be produced. In addition, by enhancing the packing of particles, the pores between the particles are minimized, and the required cement paste to fill these pores are also minimized.  
The results in Figure 5 demonstrate that all the samples, which are designed by considering the packing algorithm, have higher mechanical performances with lower densities than those of conventional LWC. In particular, the LWC specimen with a larger proportion of finer aggregates in the same volume of aggregates shows a higher elastic modulus as well as compressive strength, although the density of the specimen becomes larger when the proportion of finer aggregates increases.