Plastic shrinkage and rain check for flatwork. Evaporation rate from the ACI 305 nomograph (Menzel–Uno equation) and rain chance, now and hour by hour from the National Weather Service forecast.
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Pour location
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Plastic shrinkage cracking
–lb/ft²/hr
Enter a pour location above, or set the conditions by hand under Conditions.
Estimate only, not a guarantee. Cracking can occur at any rate.
Rain · next 6 hours
Next 6 hours
Plastic shrinkage cracking
Evaporation rateNightCautionLimit
Rain chance
Under 20%20% or more50% or more, likely
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Load a location to see the hourly outlook.
Concrete temperature
Conditions
Or try a scenario
°F
%
mph
Forecast wind is measured at 33 ft. ACI uses wind about 20 in. above the slab, roughly two-thirds of the forecast. This applies to the readout and every hour in the outlook. Turn it off for a handheld reading at the slab, or to stay conservative.
°F
Controlling plastic shrinkage cracking
In the mix
Monofilament microfibers: hold the surface together while it's still plastic.
Straight cement, no fly ash: sets sooner, so less time to crack.