Crack in the DECK at shallow end

[Marin]

You either have ground movement cracking the concrete, or the handrail anchors weren't properly surrounded with decking.
Do you have a decorative overlay on the deck, or is it bare concrete? Either way a patch will show, some worse than others.
If the handrail seems stable and you just want to keep water/ice from creating further damage, you're best (read easiest) bet is a rubberized seam sealant. Home Depot carries SikaFlex, I believe they have grey and tan. It's the consistency of syrup, therefore self-leveling, so be careful with it. If the crack is deep you'll want to fill it with sand to within an inch of the top. That should keep for a while, even with usual ground movement and concrete expansion/contraction.
If the rail is wobbly, I'd say you have an insufficient base and need to dig out the anchors. Replace them with new and put some good concrete around them. When I core drill into a deck for new rails, or dig out and replace old anchors, I fill the area around the anchors with hydraulic cement. It dries fast (good for keeping the anchors true) and hard. If you have to replace the anchors let me know and I'll fill you in on making a jig to keep the anchors spaced correctly and level.

[Bosco390]

Thanks, Marin!!.... the handrail is solid as a rock, and the crack seems to worsen only during winter when moisture gets in and freezes. I have tried to fill with rubberized liquid patch as you speak of in the past, but I think the crack is really deep, and the fluid just seeps down and never fills... perhaps a hole completely through? Regardless, I had NOT thought of attempting fill with sand first, and will most certainly try that. I am also debating using 2-part epoxy to fill the crack. I recall doing some boat repair years ago, and spilling some of the epoxy I was using for resin... it was there on the garage floor for years unscathed until I worked on getting rid of it. We'll see.

Thanks so much for the reply!!!

[Marin]

You're welcome.

Self leveling seam sealant will find every pinhole and sink into it. That's why we use sand to backfill and not backer rod.

My only reservation about the 2-part epoxy is that it isn't flexible. When the deck expands and contracts it will crack again. The seam sealant will allow for some movement.