How long to let a concrete walkway cure

Question

I poured a concrete walkway in my back yard three days ago, and I've kept it wet, under plastic since then. Today, I removed the forms, packed sand around the edges (because I had a pile laying around, and to make weeding easier), wet it thoroughly and put the plastic back on. I know that 28 days is the standard for 99% strength, but my plan is to cure it for 7 days. [We're expecting a week of rain in a few days, so curing will continue then without my help.]

Given the time and cost of this project (relative to just making a gravel path), and what I've read about the importance of curing concrete, it makes perfect sense to me to cover it and just let it do its thing for a while.

My question: Am I babying this walkway too much, or more than normal? Every person I've mentioned the wet/plastic treatment to has questioned me, as though it is somehow unusual or unnecessary.

[My process, in case it is relevant: I used 3 inches of compacted 3/4 minus gravel, steel mesh elevated a few inches above the gravel, and poured 4 inches of 3500 psi concrete. I edged it and added expansion grooves every 5 feet.]

Answer 1

That's built as solid as my parents' driveway. As a walkway, I'd say it's solid and probably ready for use now, but curing it for the additional 4 days could make it more durable and less likely to chip and spall later.

A friend's neighbor poured a 3" thick dog run, then let his dog on it the next day. He later poured an additional 3" slab of the same construction, but kept it wet for 10 days. The fresh slab cracked and chipped within 2 years. The cured slab didn't show a mark even 5 years later.

Answer 2

The purpose of protecting the surface from drying out is to prevent plastic shrinkage cracks and is generally only an issue during the start of the curing process. Plastic shrinkage cracks occur if water evoraporates to quickly from the concrete, and the easiest solution is to cover the concrete with plastic. Adding water usually isn't necessary if you fix the plastic sheet at the edges, but it makes perfect sense to do so in some weather conditions.

There is a lot of guidance on how long to protect the surface to be found, and it varies a lot depending on concrete type and surface temperature and how large crack widths you can tolerate etc., from 1 day to 30 days, but generally speaking 1 week will cover the majority of cases just fine. I don't have enough information to give a specific advice on the protection time, but what you're doing sounds quite sensible to me.

Plastic shrinkage cracks are generally not very deep, so they don't hurt the lifetime of the structure all that much, but they aren't exactly pretty.