Concrete – Pouring concrete for fence posts in heavy rain

If it's too wet and water starts to accumulate in the foundation, you can end up with weakened concrete.

One of the key metrics for a concrete mix is the free water to cement ratio. If the water content is too low, you struggle to get it to compact properly , resulting in air voids, and weak concrete. If the water content is too high, the water can leave pores in the concrete, which also reduces the strength of the concrete.

If the temperature is low, the hydration reaction slows down. Further, if the temperature is too low, the water can freeze, which means that it is not available to hydrate the cement, again affecting the strength of the concrete.

Eight months later, here is my answer and update:

I called the my town's building division and determined the frost line for my region is 48". It wasn't possible for me to dig below 48", so I dug to the frost line and instead of using cement, I filled the hole with pea gravel (roughly three 0.5 cu ft bags), tamped it down with a 2x4, and topped with some of the soil I had removed when digging. My thought is the pea gravel will allow draingage, while still providing enough support for my narrow fence post. This might not work for larger posts.

So far, the fence post has been very sturdy and having gone through one winter, has not risen. I will report back if I find any issues with my solution, but so far, I'm satisfied with it.