Which type of cement for saltwater environment?

[Boven_i_dramat]

Hello!
I have an old stone cist in Bohuslän where a number of stone blocks have fallen out and down to the bottom next to it. To prevent more blocks from doing that, I thought about filling the cavities around them with concrete. My question is which type of cement is best? The concrete will not be below the water surface but will be subjected to continuous splashing/spraying.

Thanks in advance!

 

[topmount]

In Fjällbacka, in the same type of environment above and below the water, I have used ordinary coarse concrete or cement (if you have access to gravel) with very good results.