If you decide to use concrete, you should know that there are different qualities of concrete you can order. As usual the higher quality cost more.
It has been 40 years since I worked for a cement company so my information may be dated, but back then:
The first thing to look at is how many sacks per yard. A high quality cement would be 8 and 1/2 sacks per yard or even 9. But do not stop there regarding quality, when it is a location where it will end up being exposed to temperature below freezing. There are chemicals that are added to cement that is used for bridges and when all of those chemicals are added it is called bridge mix. There is a chemical that retards how long the cement takes to harden. Making it harden slower results in a stronger concrete. There is a chemical that makes it produce small air bubbles in the concrete that gives the cement room to expand or contract without cracking. And there is a chemical that makes it retain moisture during hardening. If cement becomes too dry as it hardens that reduces it finished strength.
Any cement company that supplies cement to state highway construction probably has supplied cement for construction of a bridge. While the specifications do vary from state to state even with states in the same latitude that have the same winter weather, in general bridge mix is a very good quality cement that will not easily crack because of freeze - thaw cycles, and is stronger in general and less likely to crack. It will also last a very long time. If it were me, I would ask them if they make a bridge mix, and then get into details of how many sacks per yard, and each of the chemicals referring to what those chemicals do when talking about them.
If you go with a high quality bridge mix, be sure to broom in surface texture when you finish leveling it out. With the high sacks to yard ratio it is easy to have it end up with a smooth finish that can be to slippery to walk on in the winter without broom texture.
The other down side is that once it cures if you ever have to remove it, or sand it with a cement finishing machine to reduce the height in some area some, it will be very difficult to work with because it is much stronger.
Sure you want a good base with good drainage. And while laying cement is not something that I got into, rebar arrangements are usually used for a good pad. Talk to someone more knowledgeable than me about the installation. But if you want a cement that will not crack and will last for a very long time, go with a bridge mix.
