salt water proofing

Q. I will be building a small boat dock landing at my land block which has a tidal river passing through.
I was thinking of using PVC culvert pipe as a form to pour the concrete into when building the support piles.
to add strength I will put chemically rust proofed reinforcing rod into the form before the concrete is poured.

My question is.....Is there a special cement that needs to be used for this kind of project...

A. When concrete is repeatedly exposed to salt water with alternate periods of evaporation, salt crystals are left behind in the concrete pores and surface. These crystals can then re-hydrate when exposed to moisture causing them to grow in size thereby exerting forces that can break up the concrete.

A good quality concrete mix (4000 psi.)with the appropriate amount of cement can create a strong concrete surface and minimize salt attack. You can also treat concrete with a penetrating concrete sealer specifically designed for this purpose to minimize or eliminate water absorption thereby minimizing deterioration of the concrete by the salt water.