# Effect of Different Gradings of Lightweight Aggregates on the Properties of Concrete
## 5 Conclusions  
In this study, a series of ultra-lightweight concrete specimens less than 500 kg/m\({}^{3}\) densities are designed and produced, and their properties and characteristics are evaluated. An expanded glass, Liaver(r), is used as the lightweight aggregate, and different gradings for the lightweight aggregates are adopted to maximize the aggregate contents in the specimens. The effects of gradings on the concrete characteristics and properties are investigated. For the purpose, the virtual specimens that contain more than 70% of aggregates are modeled. The qualities and the characteristics of the specimens are examined using X-ray CT and the lineal-path function, which is a probabilistic description method.  
The material properties, such as elastic modulus, compressive strength, and thermal conductivity, are measured using experimental and numerical approaches. The conclusions of this study can be summarized as follows:  
* The obtained results show the effect of gradings and the packing algorithm on the material properties of lightweight aggregate concrete.
* All the specimens produced in this study show a higher performance than conventional lightweight concrete based on efficiency factors, while the specimen densities are lower than those of conventional concretes.
* When the volume content of the lightweight aggregates is the same, the lightweight concrete specimen with a larger proportion of finer aggregates shows a larger elastic modulus and compressive strength, while the thermal conductivity of the specimen is larger.
* Lightweight concrete with lower thermal conductivity, while minimizing the loss of mechanical properties, can be produced by using an appropriate grading, although the density of the specimen strongly affects the material properties and becomes larger when the proportion of finer aggregates increases.
* The X-ray CT imaging and the lineal-path function shows potential for examining the relative aggregate size in the concrete specimen.  
With the confirmation of the effect of the grading on the material properties, a more in-depth parametric study of different gradings as well as a packing algorithm would be required for further development of ultra-lightweight concrete with higher performance.  
Figure 9: \(L_{linu}\) for the LWC samples (note: the results of \(r/D\) range between 0 and 0.12 are only presented here.).  
**Acknowledgments:** The project is supported by the German Federal Ministry of Education and Research (BMBF, Project number: 13 XP5010B) and the German Academic Exchange Service (DAAD, Ref. no.: 91563255). This work is also supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1A6A3A03007804). In addition, the authors want to thank [PERSON] (Helmholtz Centre Berlin) for his assistance in X-ray CT imaging.  
**Author Contributions:** [PERSON] conceived and designed the experiments; and [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] contributed reagents/materials/analysis tools; and [PERSON], [PERSON] and [PERSON] wrote the paper.  
**Conflicts of Interest:** The authors declare no conflict of interest.