## 3 Results and Discussion
### Effects of Grout Annulus  
The laboratory results were also cross analyzed to explore the effects of grout annulus. In a similar manner, global and component behaviour was examined. When comparing \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Model** & **Unstandardized Coefficients** & **Standard Error** & **Standardized Coefficients** & **t** & \(\boldsymbol{p}\) \\ \hline H\({}_{\text{i}}\) & (Intercept) & –31.56 & 85.55 & & –0.37 & 0.780 \\ Average compression & strength of grout (MPa) & 4.24 & 2.10 & 0.27 & 2.02 & 0.059 \\ Rib spacing (mm) & –1.28 & 0.24 & –0.72 & –5.36 & \textless{}0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Coefficients for predicting LRFM. Figure 12: Effects of rib spacing on the shear stress and displacement profiles: (**A**) specimen D-1, (**B**) specimen D-3, (**C**) specimen D-5. the strength and failure modes of the specimens, which can be seen below in Table 8, it was observed that specimen D-1 failed in grout as opposed to shank. Visual inspection of the failure in the grout seemed to visually correspond to a reduction of confinement of the specimen, with cracking patterns resembling dilation slips failure; this can be seen in Figure 13. Figure 13 also highlights the observation of other cracking observed in specimens. Specim B-1-i and C-1 both had large voids and thus should have resulted in lower strength because of the reduction of bond length, and specimen B-1-ii failed in shank at similar loads. This suggests that a reduction in bond strength can be associated with very large grout annuli. In line with the literature [67; 68], it was expected that with increased grout annulus there would be a decrease in stiffness. However, no clear trends were observed across the data. Regression analysis could not be conducted as there were insufficient trends. When examining rib spacing 1, the axial deformation of the bar at 100 kN, B and C grout annuli (sizes) were stiffest. Although there were no clear trends when examining the effect of grout annulus on bond performance across the data and multiple linear regression of LRFM could not be conducted, there was some support for a trend with the unaltered commercially available bars. When analyzing the strain profiles, it appeared that the unaltered rebar in B and C grout annulus performed better than the smaller and larger annuli. These can be seen visually in Figure 11, comparing annulus A to B. For smaller loads, grout annulus A and D were more similar (this departure could potentially be caused by effects related to pipe deformation of the small pipe). Interestingly, beyond yield, it generally appeared that grout annulus C attenuated strain better than annulus B; this appeared to be caused by less rebar-grout debonding. However, when examining the strain at the free end, and the LRFM specimens in the grout, annulus B had better performance. However, the effects of the grout void could have impacted these results. When examining the shear profiles, A and D seemed to activate later and have lower values of shear stress even at higher displacement. Specim B-1-I had the highest shear stress. This can be seen in Figure 14.  
In summary, there was some support for the theory that the bond performance of an unaltered rebar could be increased with increased grout annuli within a set range. Performance effects of increased stiffness, higher LRFM and better strain attenuation were observed with the unaltered bar. This range of grout annulus sized at 8.4\(\times\) and 11.9\(\times\) average rib height agrees with the finding of numerical modelling by [PERSON], which suggested 9 times to 12 times rib height [69] and other research which suggested the benefits of increased grout annuli [5,9,70]. It should be noted that these trends were not seen globally across all the tested rib spacings.