Owing　to　the　undrained　construction,　not　only　the　admixtures　but　also　the　hardening　process　is　believed　to　have　a　significant　effect　on　the　final　strength　of　non-dispersible　underwater　concrete　(UWC).　To　ensure　the　stability　and　workability　of　UWC,　this　paper　defined　the　hydration　stages　of　UWC　by　conducting　an　early-age　hydration　monitoring　experiment　based　on　PZT　(Piezoceramic　Lead-Zirconate-Titanate)　sensors　and　an　isothermal　calorimetry　experiment.　Additionally,　a　90-day　strength　gain　monitoring　experiment　and　a　compressive　strength　experiment　were　also　carried　out　to　establish　a　semi-empirical　strength　prediction　model,　which　can　be　utilized　to　assess　the　real　strength　of　UWC　by　substituting　the　monitoring　data　from　practical　structures.　With　practical　application　in　a　corroded　bridge　pier　strengthened　by　prefabricated　Basalt　FRP　(BFRP)　shell　and　UWC,　the　strength　prediction　model　presents　a　high　accuracy　on　the　prediction　of　hardening　strength　of　UWC,　and　all　the　indices　of　the　practical　bridge　pier　strengthened　by　BFRP　and　UWC　meet　with　the　design　codes.　This　indicates　that　the　strength　monitoring　approach　and　construction　quality　evaluation　method　can　apply　to　practical　underwater　structures.