# Properties of a Lightweight Fly Ash-Slag Alkali-Activated Concrete with Three Strength Grades
## 2 Experimental Program  
### Materials and Sample Preparation  
FA, BFSP and Portland cement were utilized as the binder materials here. The CEM I 42.5 R-type cement, complying with Chinese standard GB/T 175-2007 [25], which has a 28-day strength of 46.7 MPa, was used for making the OPC concrete. Table 1 depicted the chemical compositions and physical properties of the binder materials. In this study, two kinds of coarse aggregates were used: lightweight sintered fly ash aggregates, which was used as the coarse aggregate for the LOPC and LAAC, and conventional limestone aggregates, which were employed as the coarse aggregate for the normal-weight ordinary Portland cement concrete (NOPC) and NAAC. Natural river sand with a fineness modulus of 2.4 was used as fine aggregates for all concrete mixtures. The particle size range, fineness modulus, specific gravity, water absorption, aggregate crushing value and cylinder compressive strength of the different aggregates were determined according to GB/T 17431-1998 [26] and listed in Table 2.  
The alkali activator solution was prepared by dissolving sodium hydroxide (SH) pellets of 99% purity in a sodium silicate (SS) solution plus additional water and retained for 24 h before use. The chemical composition of the Na\({}_{2}\)SiO\({}_{3}\) solution, as provided by the supplier, refers to the presence of 13.6% Na\({}_{2}\)O, 29.9% SiO\({}_{2}\) and 56.5% water by mass. The specific gravity and the modulus of the Na\({}_{2}\)SiO\({}_{3}\) solution is 1.35 and 3.0, respectively. Drinking tap water was used in all the concrete mixing, and a poly-carboxylate-type superplasticizer (SP) with a specific gravity of 1.18 and pH value of about 7 was used in the LOPC and LAAC mixtures to achieve the required workability. The main purpose of this study is to investigate the effect of the concrete and binder types on the mechanical and fracture properties of concrete. The water/binder (W/B) ratio by weight for the control group with the OPC binder was fixed at 0.48 (NOPC) and 0.30 (LOPC), respectively. A lower water/binder ratio was adopted for the OPC-based lightweight aggregate concrete because a higher water/binder ratio will result in floating and segregation of the lightweight aggregates (LWAs) in the vibration process. In the investigation of LOPC, the trial and error methods of modifying the SP dosage were employed until the required slump value was achieved. The term water/solid (W/S) ratio \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Chemical Composition (\%)**} & \multicolumn{3}{c}{**Blaine Fineness**} & \multirow{2}{*}{**Density**} & \multirow{2}{*}{**LOI** (\%)} \\ \cline{2-2} \cline{6-9}  & **SiO\({}_{2}\)** & & & & & & & \\ \hline FA & 49.10 & 26.70 & 6.96 & 9.67 & 1.37 & 3871 & 2.21 & 2.08 \\ BFSP & 32.28 & 13.80 & 47.85 & 0.74 & 3.73 & 3862 & 2.86 & 1.30 \\ Cement & 21.66 & 5.42 & 63.15 & 2.62 & 2.89 & 3110 & 3.14 & 1.63 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties and compositions of the pozzolanic materials. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Type**} & **Particle** & **Specific** & **24 h Water** & **Fineness** & **Aggregate Crushing** & **Cylinder** \\  & **Size (mm)** & **Gravity** & **Absorption (\%)** & **Modulus** & **Value (\%)** & **Compressive Strength (MPa)** \\ \hline Natural River & \(\leq\)5 & 2.67 & 1.2 & 2.7 & - & - \\ Sand & \(\leq\)5 & 2.64 & 0.83 & - & 23 & - \\ Limestone & 5–20 & 2.64 & 11.3 & - & 30 & 10.6 \\ Sintered Fly & 4–16 & 1.24 & 11.3 & - & 30 & 10.6 \\ Ash Ceramsite & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical properties of the coarse and fine aggregates. in AAC is defined as the ratio of the total mass of water in the mixture to the sum of the mass of the blended FA-BFSP binder material and SH and SS solids. The strength of the AAC and its cement counterpart depends on the W/S ratio and W/B ratio respectively.