## 2 Materials and Experimental Methods
### Test Method  
Figure 1 shows the testing program used to investigate the bond behavior of reinforced geopolymer concrete, including the compressive strength test and pullout test. Three \(150\times 300\) mm specimens from each mixture group were prepared for the compression test. The compressive strength test applies a compressive axial load to the \(150\times 300\) mm cylinder specimens at rates ranging from 0.15 to 0.35 MPa/s, until failure occurs according to ASTM C39 [35].  
Several tests have been used to obtain the bond strength of reinforcing bar embedded in concrete. There are three kinds of specimens including beam-end specimens, beam with lap splices, and pullout specimens. In this research, the pullout testing was chosen to assess the bond strength of various rebars. A traditional pullout testing is given in Figure 2 and the loading rate is chosen at 1 mm/min. The samples of pullout testing are straightforwardly built and tested. This method has also been used to evaluate the bonds in concrete for many years. The results of the pullout test can be utilized to determine the bond strength of rebars in case the premature splitting of the surrounding specimens is innocent. Besides, when the relative bond resistance is allowed, this test is chosen as the most useful method for comparing the bond-slip curves of numerous types of rebars. Thus, the pullout test must be an acceptable method to determine the influence of many variables on bond behavior (for example, comparing the bond-slip relation of the different concrete mix proportions, sizes of rebar, and other factors with supplementary geopolymer concrete).  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Name**} & **CA** & **FA** & **Fly Ash** & \begin{tabular}{c} **Na2 SiO3** \\ **Solution** \\ **(kg)** \\ \end{tabular} & **AL/GS** & \begin{tabular}{c} **Superplasticizer** \\ **(kg)** \\ \end{tabular} & \begin{tabular}{c} **Description of** \\ **Mixtures** \\ \end{tabular} \\ \hline \
\begin{tabular}{c} GP1 \\ GP2 \\ GP3 \\ \end{tabular} & 1294 & 554 & 476 & 120 & 48 & 0.35 & 7 &
\begin{tabular}{c} Cured at 60 \({}^{\circ}\)C, 4 h \\ Cured at 60 \({}^{\circ}\)C, 8 h \\ Cured at 60 \({}^{\circ}\)C, 12 h \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mixture proportions of this research.  
Figure 1: Testing program of this research.  
The bond stress is calculated by assuming that the bond stress is uniformly distributed along the embed length of the bar:  
\[\tau_{\max}=\frac{P_{\max}}{\pi\cdot d_{b}\cdot l_{b}} \tag{1}\]  
where \(\tau_{\max}\) is the maximum bond stress, \(P_{\max}\) is the corresponding applied force at failure, \(d_{b}\) is the bar diameter, and \(l_{d}\) is the bar embedded length.  
In this research, the bond behavior of reinforced geopolymer concrete was evaluated by considering the effect of compressive strength (\(f^{\prime}_{c}\)) of geopolymer concrete, the concrete cover to bar diameter ratio (\(c/d_{b}\)) on the bond strength and bond-slip relation. Three diameters of reinforcing bars, as shown in Table 3, were used. The details of specimens are given in Table 4 and Figure 2. In this Table, the samples are named GPxRy, which GP stands for geopolymer concrete; x (1,2,3) is the number of mix proportion; R stands for reinforcing bar; and y (1,2,3) refers the diameter of reinforcing bar 12 mm, 16 mm, and 20 mm, respectively.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Rebar** & **Rib Height (mm)** & **Rib Spacing (mm)** \\ \hline d12 & 0.78 & 7.8 \\ d16 & 1.04 & 10.4 \\ d20 & 1.3 & 13 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Details of rebar.  
Figure 2: Schematic of typical pullout test.