Evaluation of Engineered Cementitious Composite for Underwater Applications: Washout Resistance and Flowability

This study investigates the fresh properties and washout resistance of Engineered Cementitious Composite Underwater Concrete (ECCUWC) incorporating varying dosages of Anti-Washout Admixtures (AWAs) and Polyvinyl Alcohol (PVA) fibres. The aim is to optimize mix design to achieve sufficient flowability while minimizing material loss under submerged conditions. Twenty ECCUWC mixtures were prepared with a constant fly ash (FA) content of 25% by mass of cement and a fixed water-to-binder ratio of 0.40, while systematically varying AWA (0.5% to 1.1%) and PVA fibre content (1.0% to 1.75%). Fresh properties and washout resistance were evaluated through slump flow, V-funnel (at air and underwater), turbidity, and pH stability tests. The results showed that increasing AWA content significantly improved cohesion, resulting in reduced slump flow and turbidity values. The mixture containing 1.1% AWA and 1.75% PVA exhibited the best overall performance, achieving a slump flow of 240 mm, minimal washout loss of 2.1%, and turbidity as low as 58 NTU. Mixtures with 0.7% and 0.9% AWA also performed well, maintaining high flowability and reduced turbidity. The optimized range of 0.7–1.1% AWA and 1.5–1.75% PVA was found to provide the best balance between workability and stability. These findings contribute to the development of sustainable, non-dispersive ECCUWC mixes that meet the stringent requirements of underwater construction, particularly in marine and hydraulic environments where conventional concrete typically underperforms due to washout and poor cohesiveness.