How is a bridge built if cement does not dry in water?
Cement is a dry powder that reacts with water, hardening and acquiring resistance. The problem is that the greater the amount of water for the amount of cement (the so-called water/cement ratio), the lower the strength of the concrete. Who says that is the Abrams Law. For this and other reasons (such as salts and organic matter in the water) we cannot let the cement come into contact with the water.
To build a bridge, temporary structures called cofferdams are used, which hold the water.
In the photo, we have a cofferdam made of metal sheets. They are driven into the bottom of the river/sea and the water is pumped out. If the soil is very permeable, a very large amount of water will continue to enter the bottom, and it will be necessary to continue pumping throughout the work.