This doesn’t seem right. I thought wet concrete and cured concrete weighed nearly the same amount. That is, concrete doesn’t ‘‘dry’’ from water evaporating. Rather, the water reacts chemically with the cement to become a permanent part of the mix as it ‘‘cures’’.
And this doesn’t even begin to take into account the safety factor that should have been built into the design and for that matter the expected live load of a walkway - that is the weight of the people who would be using it once constructed.
For a walkway to collapse during the pour suggests to me a much bigger problem in design or construction than simply neglecting to consider any difference between wet and cured concrete.
Hopefully an expert in such things will ‘‘weigh’’ in here and set me straight if I’m off the mark. Here’s a quote from a previous thread concerning the weight of wet vs. cured concrete:
in this thread: weight of cement; cured vs dry - Factual Questions - Straight Dope Message Board
ETA: I see Chesire Human has posted in this thread - do I have a correct understanding of your post from the linked thread?