## 5 Conclusions  
This paper investigates the bond behavior of reinforced fly ash-based geopolymer concrete using experimental work, simulation analysis, and theoretical work. To evaluate the bond behavior, experiments were conducted using 150 \(\times\) 300 mm cylindrical specimens with and without rebar cured in an oven at 60 \({}^{\circ}\)C for 4, 8 and 12 h. Numerical analysis was then performed to compare and verify the bond behavior based on bond stress slip relationships The crucial points of this research are the following:  
1. The bond strength of reinforced fly ash-based geopolymer concrete increases about 1.97 to 2.56 times with the increase of compressive strength from 20.33 MPa to 41.12 MPa. By comparison, with the different components of the geopolymer binder, the microstructure of specimens shows other behavior. Even the samples have similar compressive strength values. The bond strength shows a significant difference. There is a need for studies to focus more on the effect of components of geopolymer binder and curing condition on bond strength of reinforced geopolymer concrete in the future.
2. For the geopolymer concrete with the curing time of 8 and 12 h, the bond strength of reinforced geopolymer concrete rises when the \(c/d_{b}\) ratio varies from 3.25 to 4.19. Then, the bond strength decreases with the increase of \(c/d_{b}\) ratio from 4.19 to 5.75 whereas the bond strength of geopolymer concrete with a shorter curing time, 4 h, has the opposite tendency.
3. The bond behavior of the reinforced fly ash-based geopolymer concrete is well correlating with simulation analytical using ABAQUS/CAE tool. However, this behavior is quite dissimilar with the data computed from the fib model.
4. The bond-slip relationship of reinforced geopolymer concrete could be predicted using the proposed expression. This proposed formulation can be used to predict  
Figure 13: Failure mode of specimens: (**a**) splitting failure of concrete; (**b**) concrete cracking; (**c**) inside failure specimens; (**d**) damage initiation criteria in ABAQUS (a value of one indicates that the bond fails).  
the bond slip behavior of reinforced fly ash-based geopolymer concrete for practical purposes.
* The numerical parametric study is performed with two variables, namely the compressive strength of geopolymer concrete and the concrete cover. The bond strength increases considerably with the rise of concrete compressive strength, while a reverse trend is observed in case of the values of bond slips at maximum bond stress. For the influence of the concrete cover, the results revealed that the thickness cover slightly influence the bond strength. These results are consistent with those observed in the experiments.  
In the future work, the authors are working on investigating the bond behavior of reinforced geopolymer concrete under the corrosion conditions. The performance of ribbed steel bar would be evaluated by using proposed modelling in this study and experiment.  
Conceptualization, K.T.N. and T.A.L.; methodology, T.N.N.; software, K.T.N.; validation, T.A.L. and T.N.N.; formal analysis, T.A.L.; investigation, K.T.N.; writing--original draft preparation, K.T.N.; writing--review and editing, T.A.L.; visualization, K.T.N.; supervision, T.A.L.; project administration, K.T.N.; funding acquisition, T.A.L. All authors have read and agreed to the published version of the manuscript.  
This research is funded by Vietnam National University Ho Chi Minh City (VNU-HCM) under grant number B2020-20-01.  
The authors