The underwater placement of concrete is often required for the repair of marine and hydraulic structures damaged by abrasion-erosion, frost damage, corrosion, sulphate attack, etc. Such repair can be carried out without dewatering to reduce the cost of repair and any interruption in the operation of the facility, resulting in considerable savings. Underwater concrete placement is also used in the construction of new structures, such as in cofferdam bases and bridge foundations. Underwater-cast concrete must be proportioned to be highly flowable in order to spread into place without consolidation and must exhibit adequate stability to reduce segregation and water dilution and develop a homogeneous structure with adequate mechanical properties and durability. Such concrete should spread from the discharge location under its own weight and form relatively flat repair surfaces. This is especially important given the lower unit weight of the concrete in water that results in a lower shear stress needed to ensure high deformability.

The required stability of fresh concrete depends on the rheological properties and placement conditions. With the increased consistency necessary to ensure proper spread of the cast concrete away from the placement point and around various obstacles and reinforcement, there is an increased risk of segregation and washout. Such stability must be high when the concrete is subjected to some free fall in water, as when the concrete is used for the repair of relatively shallow areas that make it impossible to ensure that the bottom of the placement device remains immersed in freshly cast concrete. The risk of water dilution also increases when the concrete is cast in circulating water. Dropping a highly workable concrete, even a short distance, through moving water can lead to a significant level of water dilution that can negatively impact mechanical properties and durability.

AWAs are incorporated to enhance the resistance of fresh concrete to water erosion, segregation. The majority of AWAs consist of water-soluble polymers.

The specific advantages of AWA underwater concrete include the following:
Compared to ordinary concrete, antiwashout underwater concrete is highly resistant to the washing action of water and rarely separates, even when dropped through water.
Its yield stress is small and its viscosity high, so the concrete components don’t segregate and it displays high fluidity.
As a result of the high fluidity, its self-leveling ability is improved.
Almost no bleeding occurs.
The properties required for underwater concrete placed by conventional tremie, pump with free fall and skips are:
specified strength and durabilty
self-compaction
self-levelling or flow resistance (depending on placing conditions)
washout resistance
cohesive to reduce segregation.