I poured a sidewalk up to the house last year and it started flaking and coming apart in places. I think some of the gravel/sand I got might have had salt in it. A guy who works for highways gave it to me. Anyway Im getting ready to pour another layer on top of the existing concrete and dont know what is the best way to make sure it binds to the old stuff. A guy told me that there is some kind of chemical you can paint on the old concrete that will help it bind. I cant find anything online? Im going to use the ready mixed stuff this time.

There is a product from Sacrete that works OK, or look at Sikadur hi mod 32
is alot better

Latex bonding agent may help https://www.homedepot.com/p/SikaLat...e-and-Acrylic-Fortifier-187782/202521398

I can't help on the bonding agent. However if you put ice melt on the concrete it will do the same. Make sure to thoroughly clean it before re-pouring. in case that is the issue.
Best probably break it up and replace it

I wouldn't waste money on an overlay for exterior concrete. The freeze thaw cycle will have it off in a couple years. Take it out and repour with a better mix

^^^ sounds like your concrete was burnt.

You could bury the existing sidewalk with a few inches of compacted gravel and then frame and pour the new concrete. That way you would not have to do any demolition and haul away. Once the new concrete has well cured, you could grade your yard to it, so that it's not raised up so much.

Keith

Acryl 60 is what we used to use but that was interior work

Take the time to remove the old sidewalk, even if you put on some kind of binder or fortifier the old is compromised and may flake off under the binder. Freeze thaw cycles will have the 2 separated and coming apart anyway.
If you finished the first sidewalk your self and do not have any training then get a helper who has. Without the knowledge of how and when to get the finish on the pour you can have problems like spalling.

No bonding agents will help if the top is popping off, bust it out and repour.