What temp was it that it froze I have used it at -20 degrees and it never froze but was more like a thick syrup. I know from everything I have read it will not freeze in non diluted condition but will turn very thick. Now if it was diluted it can freeze according to the water content. Now I did at one time get some premixed coolant that was only good for +10 which isn't very good for cooling systems.
here is a a excerpt from Prestone's web site
Q. What is the best antifreeze/coolant concentration for a vehicle? Can I use 100% antifreeze? A. We recommend that you use between a 50% and 70% concentration of antifreeze. At least 50% is necessary to give the adequate amount of corrosion protection, as well as freeze/boilover protection. However, we do not recommend more than 70% antifreeze. This would cause restriction of the heat transfer capabilities, corrosion protection, and freeze protection. The concentration of freeze/boilover protection of the antifreeze mixture can be checked using a Prestone® Antifreeze Coolant Tester.
This is from Peaks web site.
As the name implies the third main function of antifreeze is to protect the cooling system from freezing. The way to achieve maximum freeze protection differs between ethylene and propylene glycol. For ethylene glycol the maximum protection is at 67% ethylene glycol in water. A ethylene glycol solution of this concentration will freeze at -84° F (pure ethylene glycol freezes at 8° F). Propylene glycol does not freeze. It experiences a chemical phenomenon known as supercooling. For this reason there is no freezing point of pure PG. Due to the heat transfer and inhibitor activation reasons discussed above, PG antifreeze should also be maintained between 40% and 70% in water. Boil over protection with both glycols increases with glycol concentration.