Cement is afraid of water and sun. When it comes into contact with water, it will agglomerate. Cement only needs moisture protection, but exposure in the hot sun is not good for cement bags.
If the unopened new cement is exposed to the sun, there is no problem. After all, it can be kept dry. Even if the sealed cement is exposed to the sun, it will be "broken" after a few days, which is invisible to the naked eye. However, if the same amount of river sand is mixed with water when it is first opened, its strength will become worse, and it will break when it solidifies. However, after the cement is exposed to the sun, the temperature will accelerate the hydration reaction of cement when it comes into contact with water.