# Properties of a Lightweight Fly Ash-Slag Alkali-Activated Concrete with Three Strength Grades
## 3 Experimental Results
### Fracture Properties  
Table 6 summarized the fracture characteristics of AAC and OPC concrete obtained in terms of fracture energy, fracture toughness and characteristic length. Figure 8 presents the average load displacement curves and load-CMOD curves of the OPC concrete and AAC beams with three identical samples in each group. As shown in Figure 8a, the load-displacement curves and load-CMOD curves of the AAC were of similar shape as those of the OPC concrete. However, when the OPC in NOPC and LOPC was replaced by blended FA-BFSP, the peak load was improved with the activation of the SS and SH solution. For example, the peak load increased from 5.385 kN in the NOPC specimen to 6.444 kN in the NAAC specimen of a similar grade, and the peak load increased from 4.698 kN in the LOPC specimen to 5.559 kN in the LAAC specimen of a similar grade. Besides, in case of the AAC specimens, the pre-peak slopes of the load-displacement curves were slightly steeper, and the deformations at the peak load were slightly larger than that of the OPC concrete. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type** & \(\delta_{0}\) **(mm)** & \(P_{\text{max}}\) **(N)** & \(G_{\text{F}}\) **(N/m)** & \(K_{\text{IC}}\) **(MPa\(\cdot\)m\({}^{1/2}\))** & \(l_{\text{ch}}\) **(mm)** \\ \hline NOPC & 0.61 & 5385 & 139 & 0.72 & 318 \\ LOPC & 0.48 & 4698 & 98 & 0.63 & 174 \\ NAAC-1 & 0.55 & 4679 & 121 & 0.62 & 275 \\ NAAC-2 & 0.53 & 6444 & 137 & 0.86 & 215 \\ NAAC-3 & 0.42 & 7680 & 154 & 1.02 & 187 \\ LAAC-1 & 0.59 & 3574 & 93 & 0.48 & 192 \\ LAAC-2 & 0.52 & 4385 & 96 & 0.58 & 186 \\ LAAC-3 & 0.42 & 5559 & 100 & 0.74 & 150 \\ \hline \hline \end{tabular} \(\delta_{0}\) represents the displacement at the failure load.  
\end{table} 
Table 6: Fracture parameters of the mixtures. Figure 7: Typical splitting surfaces of cube specimens: (**a**) NOPC; (**b**) LOPC; (**c**) NAAC; (**d**) LAAC. As demonstrated in Figure 8b,c, the slope of the linear branches of the load-displacement curves and load-CMOD curves and peak load increased with the strength for both the NAAC and LAAC. In addition, the strength grade of the AAC had little effect on the curvature of the post-peak curve; that is, with the increase in strength grade, the brittleness of the AAC increased slightly. However, the influence of the coarse aggregate type on the shape of the load deflection curve was greater than that of the binder type. The peak load and pre-peak slopes of the load-deflection curves of the LOPC and LAAC specimens with sintered fly ash LWAs were significantly lower than those of the NOPC and NAAC specimens with NWAs. The slopes of the post-peak curves of the LOPC and LAAC were steeper than those of the NOPC and NAAC. The literature [7,18] reported that, compared with OPC concrete, a thermally cured FA-based AAC exhibited a higher peak load and steeper slope in the post-peak curve. [PERSON] et al. [19] stated that an ambient-cured BFSP-blended fly ash AAC showed a slightly higher peak load and almost similar post-peak behavior, as compared to a similar grade OPC concrete. [PERSON] et al. [20] found that the peak  
Figure 8: Load–displacement curves and load–CMOD curves of the tested beams: (a) different mixture; (b) NAAC; (c) LAAC. load of an AAC in a three-point fracture tests was higher than that of an OPC concrete with a strength grade of C30; while the strength grade was C70, the peak load of the AAC in three-point fracture tests was less than that of its cement counterpart. The above literature further showed that the impact of binder type on the fracture properties of AAC was not as significant as that of the coarse aggregate type.