## 3 Results and Discussion
### Bending Properties  
The average values of bending strength (MOR) and modulus of elasticity (MOE) in the bending of LVL samples in both face and edge directions are presented in Figure 8. It is obvious that the type of additives in the geopolymer binder affected the bending properties of the LVL samples. Referring to Figure 8A, LVLs made of geopolymer binder with no additives had a face MOE and MOR of about 13,000 and 93 MPa, respectively. The face MOE was not considerably changed by using various additives in the binder formulation. The face MOR was significantly reduced with the addition of phenol in the binder formulation, whereas the face MOR was increased about 20% with the addition of the grafted silica fume. In other words, the lowest value of face MOR was observed with a 10 wt %  
Figure 7: Shear strength of the LVL samples using geopolymer binder mixed with various additives.  
phenol usage (72 MPa), and the highest belonged to the sample with 10 wt % grafted silica fume (112 MPa). This result is also consistent with the trend observed in bonding shear strength of LVL samples. As was shown above, the shear strength values of LVL samples made of geopolymer binder with phenol were also the smallest due to the higher binder viscosity [12; 30; 39].  
Referring to Figure 8B, the additives in the geopolymer binder also showed a significant influence on the edge bending properties. The lowest MOE belonged to the sample with 10 wt % phenol (4400 MPa), whereas the highest MOE was observed for the sample with 10 wt % grafted silica fume (5270 MPa). The differences in the values of edge MOE between the reference sample and those made of conventional and grafted silica fume were insignificant. The edge bending strength was increased by about 10% after adding grafted silica fume to the geopolymer binder formulation. This could be  
Figure 8: Bending properties in both face (**A**) and edge (**B**) direction of the LVL samples using geopolymer binder mixed with various additives. MOE: average values of modulus of elasticity; MOR: average values of bending strength.  
due to the improved adhesion mechanisms created between the geopolymer binder and the wood constituents using silica fume [9; 29].  
The failure modes analysis of the bending samples can also explain the effect of various additives on the bending properties of LVL samples. As stated in Figure 9, the common failure mode of bending samples was a delamination crack that extended longitudinally through the binder line of the LVL samples and significantly influenced the maximum failure load tolerance. This can diminish the bending strength of LVL samples. The bending failure was initiated in the wood layers of LVL samples made of geopolymer binder mixed with grafted silica fume (in both face and edge bending tests). This indicates the improved adhesion between the modified geopolymer binders with the wood constituents.  
The mean values obtained for bending strength and MOE of the LVL panels were higher than the limit values for the structural purpose solid wood panels (32 MPa for face MOR and 9000 MPa for face MOE) indicated in the European Standard of EN 13353 [43] for panels having a thicknesses of up to 20 mm.