In Chicago cement generally goes through several freeze and thaw cycles each year. And along the thickness, and any re-bar enforcement, there is a wide range of strength that cement can have.
If the earth is very soft, you might want to pack it or have it packed down before putting in the cement. Some also use a layer of stone before the cement is put down.
In general cement from a cement truck (along with specifying how many yards, usually 2 to 8 yards per truck, but some places have larger trucks that can hold 10 or even 12 yards), cement is ordered by how many sacks of cement per yard.
There are also pumper cement trucks that can pump a cement to hard to reach locations. Cement from a pumper may not have the same size stones, and some may not have any stone.
In general, I assume you will be looking for cement from a cement truck that has a barrel that turns.
Low cost cement is usually something like six and a quarter sacks per yard. High quality cement like the cement used for a bridge is usually something like nine and a quarter sacks yard. Different states have different standards, but are in the same ball park, like one state may order 9.25 sacks per yard, another may order 9.5 sacks per yard, for bridges and overpasses.
Along with increasing the amount of cement per yard, high quality (super structure) or (bridge cement), is also made with special additives.
One of the additives causes the cement to take a long time to cure. Cement that cures over a long time is stronger than similar cement that was cured fast.
One of the additives causes the cement to retain moisture so it will not dry out too early during long curing.
One of these additives causes the cement to foam up so that when it dries there will be very small air bubbles through-out the cement. These very small air bubbles give the cement room to expand and contract during freeze-thaw cycles. And this prevents the cement from cracking.
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If you want a garage floor that will not crack because of freeze-thaw cycles, you might want to look into a cement mix similar to bridge cement, including the three special additives, to retard the cement so it takes a long time to cure, to cause the cement to stay moist during the long cure, and to cause the cement to foam up so that it has very small air bubbles that provide room for it to freeze and thaw.
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Also ALWAYS have the cement truck driver spin the cement barrel for five minutes at an increased engine speed, before you have any cement poured from the truck.
If the driver runs the barrel while traveling to you, more cement will be on one side of the truck than on the other side. This can cause the truck to flip if it makes a fast turn. Therefore even though it may have taken the driver something like a half hour to get to your location, do not assume he ran the barrel on the way there. And if he did not run it on the way to you, and you do not make him spin the barrel fast for five minutes, you may end up with too many stones in the last part of the batch, and too many stones towards the end of the mix can make it hard to get a good finish for the surface.
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Now days you can also order cement with colors added to it.
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And one last thing, if you do go with super-structure cement, be sure to have someone who knows how to finish the surface around to help shape the cement. Because this much stronger cement is really tough to grind to change the final surface once it dries.
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Finally, there is even a variance in the quality of the cement itself. Some cement manufacturers have long ago mined the good stuff from the site they are working. Others may have a site that has very good cement. So a cement made with X number of sacks from one site, might be somewhat different final strength than a similar cement made with the same number of sacks but made from cement that came from a different site.
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In general, high quality cement can cost about twice as much as low quality cement.
