# Effect of Different Gradings of Lightweight Aggregates on the Properties of Concrete
## 2 Experimental Investigation
### Mix Design Methodology  
An optimization of a lightweight concrete (LWC) mixture is not so simple because this type of concrete is very sensitive to any change in its components that affect its stability and properties significantly. One important target of this study is to minimize the density of the material. For this purpose, increasing the lightweight aggregate content, which is the lightest component in the concrete mixture, is a good option to reduce the material density; this can be achieved by applying a dense \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Material** & **Co** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **SO\({}_{3}\)** & **Cl** & **Specific Density** & **Surface Area (cm\({}^{2}\)/g)** \\ \hline Cement [wt \%] & 54.8 & 23.7 & 8.8 & 1.46 & 5.21 & 0.3 & 0.59 & 2.4 & - & 3.05 & 3860 \\ Silica fume [wt \%] & 0.2 & 98.4 & 0.2 & 0.01 & 0.1 & 0.15 & 0.2 & 0.1 & 0.01 & 2.2 & 200,000 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical and physical properties of cement and silica fume [wt %]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material** & **Bulk Density** & **Specific Density** & **Crushing Resistance * (MPa)** & **Water Absorption ** **[wt \%]** \\ \hline Liaver(r) & & & & & **60 min** & **24 h** \\
0.5–1.0 & 250 & 450 & 2.6 & 12.08 & 21.8 \\ Liaver(r) & & & & & & & \\
1.0–2.0 & 220 & 330 & 2.4 & 13.96 & 26.5 \\ Liaver(r) & & & & & & & \\
2.0–4.0 & 190 & 310 & 2.2 & 11.5 & 27.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical properties of the lightweight aggregates (LWA). Figure 1: Expanded glass aggregate (Liaver®) and its microscopy images. packing concept without a negative effect on the material properties. The idea of this concept is that if a large volume of aggregate can be efficiently packed in a certain volume, then the gaps between the aggregates can be minimized, and thereby the required paste to fill the gaps is considerably decreased [27]. In this study, LWC mixture proportions are selected based on the granular optimization of solid materials by means of the Andreasen and Andersen model [20] as:  
\[P(D)=\frac{D^{q}-D_{min}^{q}}{D_{max}^{q}-D_{min}^{q}}, \tag{1}\]  
where \(P(D)\) is the total fraction passing through a sieve with the particle size \(D\). \(D_{max}\) is the maximum particle size, \(D_{min}\) is the minimum particle size, and \(q\) is the distribution factor [17; 28]. There are several suggestions on the selection of the \(q\) value. Some researchers found that \(q\) = 0.37 gives the optimal packing [23; 29], while others suggested that \(q\) = 0.28 is the ideal case [30; 31]. The factor \(q\) can be experimentally determined, and it depends upon the size and shape of the particles. Higher values of \(q\) lead to coarse mixtures with lower fine content; however, lower values lead to mixtures with higher fine materials content. [PERSON] et al. [32] used \(q\) = 0.37 to develop ultra-lightweight concrete and claimed that this value can give the optimal packing for self-compacting concrete. In this study, four different values of \(q\) (0.23, 0.25, 0.30, and 0.45) are used to investigate the effect of the grading on the material properties, and the specimens with different \(q\)-values are denoted here as LW 23, LW 25, LW 30 and LW 45, respectively. The proportions of different aggregate sizes are presented in Figure 2 and Table 3. All mixes have the same cementitious material compositions, and the mix proportions of the  
Contrary to normal aggregates, the water absorption of LWA is a considerable factor that affects the workability of LWC significantly. It has a negative effect on the concrete workability, especially with transport concrete, which should be workable for a long time.