b'YOUR TOOLKIT FOR BUILDING EXCELENCEhot and cold weather concreting is the desiredis found in ACI 306 R-16.Specific hot weather target temperature of the mixture when deliveredconcreting information is found in ACI 305 R-10. to the job site.Usually, normal concreting (ambientThe elapsed time between the addition of water to temperatures ideally between 50 and 70 F and up tothe concrete mixture and when concrete finishing 90 F) does not require any temperature modificationneeds to occur is very temperature dependent. ofmixturebecausethematerialsavailableatThis time period is difficult to predict because it concrete plant are not that much different than thedepends upon job site ambient temperature, relative temperatures at the job site.During cold weatherhumidity, and wind conditions.Final finishing concreting, concrete materials should be at least 50 Fgenerally begins when bleed water on the concrete when delivered to job site.A discussion focused onsurface has evaporated.A rule of thumb exists heating concrete materials is found in ACI 306 R-16.that says this time period reduces by about one-half Heated mixtures are achieved by heating water to 140when the temperature increases by 20 F.Similarly, F and/or heating aggregates to 60 F to ensure frozena 20 F ambient temperature decrease doubles the lumps are removed.No maximum temperaturetime period.So, in general, the placement needs limit is needed for a hot weather concrete mix asto be much faster during warm and hot weather long as other steps of proportioning, production,concreting while the placement and final finishing delivery, placing, consolidating, finishing, andof concrete in cold weather will take much longer. curing are satisfactorily completed (ACI 305 R-10). One of the major challenges with hot weather Concrete Placement concreting is the very rapid evaporation of bleed Concrete placement includes delivery, placement,water from the fresh concrete.Sometimes bleed consolidating and finishing.General placing,water will evaporate so quickly that the concrete consolidating,andfinishinginformationsurface will begin to dry before finishing has been isfoundinACI302.1R-15asChapter10.completed.Water needs to be added to keep Specificcoldweatherconcretinginformationthe surface moist during the consolidation and Photo 3: The timing and equipment used for finishing varies by project based on weather, concrete specifications, and desired final effects.continued on page: 18 FRAME BUILDER - OCT2020 / 17'