Quote:
Originally Posted by cairnstone
At most 28 days, Bridges only get 7 days of wet cure. I'm surprised they used poly for this as considering the time of year and the availability of chemical curing agents that seal the concrete.
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All bridges? Fascinating. The engineers I work with never use these handy rules of thumb, instead, they make careful plans and then monitor things through field and lab testing. Maybe civil projects aren't so delicate and can just operate 'off the cuff.'
Yes there are chemicals that can be used to control all sorts of different aspects of concrete placement: curing agents, plasticizers, aeration controllers, etc. But using poly is not to speed up the curing time, but rather, to control the moisture levels near the surface (12-18") and to encourage the cure to take place evenly over the optimal period of time the engineering specifies. Accounting for atmospheric conditions is, of course, a main defining parameter.
The 28 day strength is also just one aspect. Generally speaking, all concrete reaches a 28 day strength, after which, further strength increases drop off quickly - though all concrete continues strengthening (growing the chemically induced bonds) forever (virtually). But, you need to control other aspects. Cracked and crumbly concrete also reaches a max at 28 days if you reduce the sample accordingly. The aim is to achieve a monolithic even strength throughout along with a monolithic surface that will work to refuse the entry of foreign materials (esp. water) over time.