**4. Conclusions**

The use of concrete for underwater placement is a significant challenge due to washout effect as well as the presence of various ions in the water which can influence the properties of concrete. The present study analysed the strength, changes in water pH, and AAFA setting time when go through underwater placement in seawater and freshwater. The chemical composition of AAFA paste is analysed using XRF and EDS. The AAFA can be used as binder for underwater concrete without the addition of anti-washout admixture (AWA). The maximum compressive strength of 71.10 MPa was obtained from the specimens cast in seawater on 28th days. It demonstrates 12.11% of strength reduction compared to specimens cast in dry condition and according to JSCE standard, the AAFA specimens are qualified to use for underwater casting. It was found that the presence of Cl- ions in seawater leads to formation of calcium chloride (CaCl2) which acts as accelerator for early setting time and strength development.

**Author Contributions:** Conceptualization, investigation, formal analysis, and visualization, Z.Y.; Supervision, funding acquisition, and project administration, M.M.A.B.A.; writing—review and editing, Funding acquisition and project administration, L.-y.L.; formal analysis and data curation, D.D.B.N.; Conceptualization, methodology, writing—original draft preparation and resources, M.A.A.Z.H.; validation and writing—review and editing, A.V.S.; interpretation, visualization and validation (P.V.); data curation and visualization, R.A.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by ROYAL SOCIETY NEWTON-UNGKU OMAR FUND (grant number NI170199), EUROPEAN UNION (grant number H2020-MSCA-RISE-2015-689857-PRIGeoC) and publications grant of the Gheorghe Asachi Technical University of Iasi (TUIASI) project number GI/P38/2021.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
