## 5 Conclusions  
The present study was designed to determine the effect of graphene oxide and fly ash, as well as provide an overview of the critical role of GO in cementitious materials in recent studies. This paper presents a concise summary of significant findings and potential future developments as follows:  
* The dispersion of GO in the mixture significantly affected the properties of the mortar, so the use of PCE and the mixing process should be experimented with to select the most suitable method.
* The addition of FA to the mortar mixture contributed to significantly improving the workability and reducing the unfavorable voids when the mortar hardens, leading to increased strength, both compressive and flexural. Fly ash, along with graphene oxide, exhibited a distinct benefit in mitigating the respective limitations of one another. It suggests that using FA is a cost-effective and efficient approach to attain the desired characteristics in cement-based materials.
* Although the results fluctuated differently compared to previous studies, the general trend was quite similar: the flexural strength had a higher growth rate than the compressive strength, and this also partly showed the superior properties of GO in the mixture.
* Within the scope of this study, the results show that 10 wt% FA and 0.036 wt% GO gave the best results not only in physical and mechanical properties but also in other necessary properties.
* At the same time, it also shows that by adding too much FA (up to 30 wt%) or increasing GO dosage to 0.05 wt%, the strength of the mortar mixtures tended to decrease.  
The scope of this study was limited in terms of using modern microstructure equipment for analysis, leading to reducing the visual picture of fly ash and the GO effect on mortar samples. In addition, some other properties of the mortar mixture need to be evaluated, such as tensile strength, shrinkage, and waterproofing ability. These limitations could be usefully explored in our future studies.  
Conceptualization, N.T.T.N., T.V.N., V.Q.V., M.Q.T., J.M. and S.N.D.; methodology, N.T.T.N., T.V.N., V.Q.V., M.Q.T., J.M., Y.X., K.K.N. and S.N.D.; software, N.T.T.N., T.V.N., M.Q.T., H.T.D. and K.K.N.; validation, N.T.T.N., T.V.N., M.Q.T., H.T.D. and K.K.N.; formal analysis, J.M., Y.X. and S.N.D.; investigation, N.T.T.N., T.V.N., V.Q.V., M.Q.T., J.M. and S.N.D.; resources, N.T.T.N., T.V.N., M.Q.T. and H.T.D.; data curation, N.T.T.N., T.V.N., M.Q.T. and H.T.D.; writing--original draft preparation, N.T.T.N., T.V.N., V.Q.V., Y.X., M.Q.T., H.T.D., J.M., K.K.N. and S.N.D.; writing--review and editing, N.T.T.N., Y.X., J.M. and S.N.D.; visualization, N.T.T.N., T.V.N., M.Q.T., H.T.D. and K.K.N.; supervision, Y.X., M.Q.T., J.M. and S.N.D.; project administration, Y.X., M.Q.T., J.M. and S.N.D.; funding acquisition, Y.X., M.Q.T., J.M. and S.N.D. All authors have read and agreed to the published version of the manuscript.  
This Research is funded by University of Transport Technology (UTT) under grant number DTTD2023-15.  
Not applicable.  
The data presented in this study are available on request from the corresponding author due to the host institution's rules.  
This Research is funded by University of Transport Technology (UTT) under grant number DTTD2023-15. The paper is supported by the Project to Attract Foreign Experts (G2023133018L) from the Ministry of Science and Technology of China. [PERSON] acknowledges the support by the doctoral grant reference PRT/BD/154268/2022, financed by Portuguese Foundation for Science and Technology (FCT), under the MIT Portugal Program (2022 MPP2030-FCT). The authors declare no conflicts of interest.