CIM 3330 Hot Weather Concreting

Who is in Authority for hot weather concreting regulations?
Click the card to flip 👆
1 / 21
Terms in this set (21)
Who is in Authority for hot weather concreting regulations?
ACI 305 - Committee on Hot Weather Concreting

ACI 308 - Committee on Curing Concrete

ACI 224 - Committee on Control of Cracking in Concrete Structures

PCA - Portland Cement Association

NRMCA - National Ready Mixed Concrete Association
"Hot Weather" is defined by ACI 305 as any combination of the following conditions that tends to impair the quality of concrete:

-__________ ________ temperature

- ________ _________ temperature

-Low Relative ___________

-__________ speed

-solar _____________
High ambient

High concrete

humidity

wind

radiation
What two things happen to concrete in hot weather?
Increased rate of cement hydration

Increased evaporation rate
Increased rate of cement hydration can be counteracted with ____________ ______________.
retarding admixtures
Increased evaporation rate can be counteracted with ____________ ____________ and ___________ ____________.
Proper protection, curing techniques
Potential Problems Caused By Hot Weather:

-_____________ water demand

-slump loss

-_______________ set times

-Decreased 28 day strength

-Plastic shrinkage cracking

-_____________ shrinkage cracking

-Increased _______________ caused by high water content and inadequate curing.
Increased

reduced

drying

permeability
_______________ is the natural exit of water from concrete due to consolidation of materials shortly after placement.
bleeding
The rate of bleeding will be highest __________ after placement and will diminish to ___________ during setting.
shortly, zero
Initial bleeding rates are typically below _______lb/ft2/hr. Dense mixes incorporating high cement contents and low w/c ratios typically have low bleed rates.
0.2
When the ______________ rate exceeds the rate of _______________, the concrete surface dries before setting occurs. As surface drying occurs, surface shrinkage occurs. However, drying and shrinkage occur at a much slower rate near the core. Differential shrinkage between the core and the surface causes residual stresses that lead to _______________ shrinkage cracking.
Evaporation, bleeding, plastic
ACI, PCA, and NRMCA suggest that precautions should ALWAYS be taken to minimize the possibility of plastic shrinkage cracking when the evaporation rate reaches __________________, and should be considered at lower evaporation rates when dense mixes are used.0.2 lb/ft^2/hrThe Evaporation Formula is: E = (Tc^2.5 - rTa^2.5)(1+0.4V) x 10^-6 E = ______________ __________ (lb/ft2/hr) Tc = _____________ __________ (°F) Ta = _________ ______________ (°F) r = ___________ ____________ (%) divided by 100 V = ___________ __________ (mph)evaporation rate concrete temperature air temperature relative humidity wind speedMeasures to Reduce Evaporation: -Reduce concrete __________ -Protect surface from __________ -Raise relative __________ at concrete surface -Apply liquid evaporation __________ -Avoid _____________ weather conditionstemperature wind humidity reducer unfavorable____________ ____________ occurs over time after setting due to the loss of water. The amount of shrinkage is largely related to the volume of water in the mix. Shrinkage will cause stresses due to restraint. Excessive shrinkage will lead to cracking.Drying ShrinkageAfter reducing concrete temperature to protect from evaporation, ______________ will continue to rise after _________________.temperature, placementFor reducing evaporation, What can be used to protect the surface of concrete from wind?wind breaksFor evaporation, What can be used to raise relative humidity on the concrete surface?Foggers4 Ways to Protect Against Drying Shrinkage: -__________ water use -____________ (ACI suggests a minimum of 7 days) -Proper _________ spacingminimize, curing, jointASTM ______ states that immediately after molding, specimens shall be stored at a temperature range from _____ to _____ degrees Fahrenheit and in an environment preventing moisture loss for up to _____ hours. Storage temperature shall be recorded using minimum-maximum thermometer.C31, 60, 80, 48Hot weather requires the use of ______ ____________ admixtures. When using these admixtures, the surface must be protected from drying for a longer period of time because the core will be slower to set.set retardingSealing the surface of concrete _________ to the completion of bleeding will trap bleed water below the surface. The bleed water will eventually dry, leaving a very small _______ near the surface. This will result in surface ________________ in small areas (usually about 2 - 8 inches in diameter).prior, void, delaminating