- Concrete Curing Home
- What curing does to the concrete
- Curing Methods
- How do we cure: The three basic methods
- When do we cure: Timing it right
- Methods for Curing Colored Concrete
- Related Information:
- Properly curing concrete slabs
- Curing colored concrete
- Proper curing techniques for concrete driveways
- How to fix common curing problems: Expert advice from Chris Sullivan
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When is the Right Time to Cure Concrete?
So the objective is to keep our young and impressionable concrete damp and at the right temperature (ideally between 50 and 85 F). The most frequently overlooked curing aspect is keeping exposed concrete surfaces moist while they are hydrating. Most concrete, especially most decorative concrete, will have plenty of water initially in the mix to completely hydrate the cement. The problem is that if the exposed surfaces dry out then the concrete can't hydrate and our young concrete ends up with very sensitive skin—easily scratched and sometimes actually dusty.
There are three phases of curing and the length of time each lasts depends on the concrete and the environmental conditions. Check out Figure 1.6 in ACI 308, Guide to Curing Concrete, to see how this works:
Keeping the concrete surface wet for 7 days is still the best way to cure concrete.PNA Construction Technologies
- When concrete is first placed for a slab, bleed water rises as the concrete mixture settles. During this period (initial set), if the bleed water is evaporating from the surface faster than it is rising out of the concrete then you need to do some initial curing or else you are likely to end up with plastic shrinkage cracks. To know if that's necessary, you need to know the evaporation rate (see below).
- Between initial set and final set, intermediate curing would be needed if the finishing (or stamping) is complete prior to final set.
- After final set, you need to do final curing.
During initial set, the rate at which the bleed water evaporates depends on a combination of factors: air temperature and humidity, concrete temperature, and wind velocity. The classic, and still best way to estimate the rate of evaporation is the Menzel/NRMCA nomograph—an easy-to-use chart that combines all of these factors. You can get this nomongraph out of ACI 308 or it's also available in an excellent piece in the March 2007 Concrete International, "Estimating Evaporation Rates to Prevent Plastic Shrinkage Cracking." You can also estimate evaporation rates using a free online program developed by Luke Snell and Amir Munir.
So you use these methods to figure out how fast the bleed water is evaporating--if it's greater than 0.2 pounds per square foot per hour, then initial curing is necessary because the concrete will be drying out. In the next section we'll discuss how to do initial curing.
After initial set, the concrete surface still needs moisture and now there's no bleed water. This is when you really need to cure the concrete. You need to assume that your concrete needs to be cured—it does! You don't want your perfect baby concrete to turn into a juvenile delinquent, do you?