Designing and Proportioning Normal Concrete Mixtures
ACI 211
ACI 211A Properly Proportioned Concrete Mix Should Posses These
Qualities.Acceptable Workability of Freshly Mixed
ConcreteDurability, Strength and Uniform Appearance of the Hardened
ConcreteEconomy
SLUMPNormally specifiedChoice based type of construction shown
on Table 9-6
Slump
WATER CONTENTApproximation based on slump, maximum size of the
coarse aggregate, and type of concrete (air-entrained, or non
air-entrained)- see Table 9-5Air contents for AE concrete are
normally specified but can also be determined by exposure
conditions based on Table 9-5
WATER-TO-CEMENT RATIOConcrete strength is specified by the
design engineer.Based on specified concrete strength and type of
concrete (AE or non AE) see Table 9-3.W/C ratio may be modified due
to certain environmental conditionssee Tables 9-1 and 9-2.Concrete
strength may also be modified due to special conditions-see Table
9-11
Water/Cement Ratio
Cementitious ContentCement Content = Recommended water content
(Table 9-5) / the recommended water-to-cement ratio (Table 9-3 or
9-1 or 9-2)Cementitious Material = Portland cement, fly ash, blast
furnace slag, and silica fume.
Coarse and Fine Aggregate ContentsHow much does 1 cy of portland
cement concrete (PCC) weigh?What is the volume of 1 cy of PCC?
COARSE AGGREGATECoarse aggregate size specifiedDetermination of
VOLUME of CA recommended per unit volume of concreteVolume based on
maximum size of CA and fineness modulus of sand Table 9-4Weight of
CA = volume of CA x dry rodded unit weight of CA x 27 cf.
Volume Formulas Vol. of water = wt. of water/62.4 pcfVolume of
portland cement = wt. of PC/(3.15 x 62.4)Vol. of CA = wt. of
CA/(SG(ca) x 62.4)Volume of Air = (%Air content x 100)/27
FINE AGGREGATEFine Aggregate Content = 27 cu. ft. - Volume of
water - Volume of Cement - Volume of Coarse Aggregate Volume of
AirWeight of FA = volume of FA x specific gravity of FA x 62.4
Dry Weights vs. Actual WeightsBatch weights calculated from
volumes assume dry CA and dry FA.Actual weight of CA and FA are NOT
dryAdjustment based on moisture contents for both CA and FA.Dont
forget about correcting for water content also.
Trial BatchSlump should be within -inch of maximum design
value.Air content should be within 0.5% of maximum design
value.Avg. required compressive strength (psi) @ 28 days must be
equal to or greater than: f(cr) = f(c) + 1.34Sf(cr) = f(c) + 2.33S
-500
