ACI Concrete Mix DesignN.C. DEPARTMENT OF TRANSPORTATIONMATERIALS AND TESTS UNITCONCRETE CERTIFICATION SCHOOL
Design ProcessDetermine the quantities of fine and coarse aggregate necessary to provide concrete meeting the requirement of he specifications using the absolute volume basis.Submit mix designs for each class of concrete to be used in the work. Pg 78
DesignSubmit mix designs in terms of saturated surface dry weights on M&T form 312U at least 35 days prior to using the proposed mix.Adjust batch proportions to compensate for surface moisture contained in the aggregates at the time of batching.
DesignChanges in the saturated surface dry mix proportions will not be permitted unless revised mix designs have been submitted to the Engineer and have been determined to be acceptable for use.
DesignAccompany Form 312U with a listing of laboratory test results of aggregate gradation, air content, slump, and compressive strength.List the compressive strength of at least three 6 x 12 or 4 x 8 cylinders at the age of 7 and 28 days.
DesignWhen the combination of materials is such that the compressive strength and/ or workable slump can not be obtained at the minimum specified cement content with the maximum allowable water-cement ratio, increase the cement at non cost to the Department by whatever amount is required without exceeding the allowable W/C ratio.Pg 79
DesignAcceptance of the mix design does not relieve the Contractor of the responsibility to furnish an end product meeting specifications requirements.
ACI Concrete Mix DesignThe NC DOH has adopted the ACI absolute volume method of design and requires this method be used in the design of all concrete mixes.
Remember:Absolute Volume= Weight / (SG x 62.4)Pg 80
Mix Design ProcessBefore calculations can begin on a concrete mix design, some info has to be supplied.Class of concrete to be designedType of placement, vibrated or non vibratedFine aggregatesSpecific GravityFineness ModulusPg 81
DesignCoarse aggregatesNominal maximum size of aggregateSpecific GravityDry-rodded unit weightRounded or angular aggregate N.C. SpecificationsMin. Cement content, W/C ratio, air content, Nom. Maximum aggregate size
ACI Table 5.3.6Volume of Coarse Aggregate Per Unit of Volume of ConcretePg 85
Nominal Max size of aggregate
Volume of Dry-rodded coarse aggregate* per unit Volume of Concrete for Different Fineness Moduli of Sand
Fineness Modulus of Sand
5 Basic IngredientsCementFine AggregateCoarse AggregateWaterAirThe combined total absolute volume should be 27 cubic feetPg 87
Mix Design WorksheetsFine Aggregate Data
Coarse Aggregate Data
ACI Table 5.3.6
Example, pg 83Using information provided, design a NCDOT Class A mix.
Max W/C ratio
Nom Max size
FM of sand
CementCement amount is determined from Table 1000-1 based on the class of concrete specified, vibrated or non vibrated.
Max W/C RatioMaximum water cement ratio is based on aggregate shape.Air entrained concrete has a different ratio than non air entrained concrete.
WaterThe amount of cement and the W/C ratio are used to determine the quantity of water.
AggregateThe aggregate data sheets are used to get the FM of he sand, SG of sand and stone, and the dry rodded unit weight of the stone.
= 2.87 cuft/cuyd
315 x 62.4
Water 564 x .488 = 275 = 33.0 gallons8.33
33.0 = 4.40 cu.ft./ cu.yd.7.5
Air.06 x 27 cu.ft. = 1.62 cu.ft./cu.yd.
Because air does not have a SG, the 6% volume that is displace by air is used.
Coarse AggregateUse ACI Table 5.3.6 to determine the % of the concrete mix that should be coarse aggregate. Use the nominal maximum size aggregate and the fineness modulus of the sand to determine the %.Pg 85
Use ACI Table 5.3.6 to determine that 62% of the mix must be dry rodded coarse aggregate..062 x 27 cu.ft. = 16.74 cu.ft/cu.yd.16.74 x 104.0 pcf = 1741 Lbs of stone1741 / (2.86 x 62.4) = 9.76 cu.ft./ cu.yd
Fine AggregateTotal the absolute volumes of the other materials
Determine the volume of the fine aggregate27.00 cu.ft.- 18.65 cu.ft 8.35 cu.ft.weight of sand required is8.35 cu ft x 2.63 x 62.4 = 1370 Lbs
ACI Worksheet ExampleFine AggCoarse AggTable 5.3.6Table 1000-1
Problem 1Class AAvib AESand-LilesvilleStone-Matthews QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1Pg 105
Problem 2Class Avib AESand-Emery PitStone-Kannapolis QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1Pg 106
Problem 3Class AAvib AESand-Great PitStone-Crabtree QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1
Problem 4Class Bnonvib AESand-Boone QStone-Mt Airy QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1
Problem 5Class AvibAESand-Johnsonville PitStone-Greystone QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1
Problem 6Class BvibAESand-Candor PitStone-North QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1
Problem 7Class AAvibAESand-Pageland QStone-Matthews QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1
Problem 8Class BnonvibAESand-Lilesville PitStone-Elkin QFine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1
Mix Designs Using Fly AshFly Ash may be substituted for Portland cement up to 20% by weight of the required cement.Substitute at the rate of at least 1.2 pounds of Fly Ash per pound of cement.Pg 97
Maximum Water - Cementitious Material Ratio Table
Example pg 91Design a Class A Fly Ash mix using the South McDowell Q # 57 stone and Rocky River sand. Substitute Fly Ash for 20% of the cement. Use 1.5 gallons less than the max water.
CementMultiply 20% times the 564 pounds of cement for Class A to get 112.8 pounds. Subtract from original cement pounds to get 451 pounds. (564 X .20) - 113 = 451 pounds of cement
Fly AshMultiply 112.8 times 1.2 to get 135 pounds of Fly Ash.112.8 X 1.2 = 135 pounds of Fly Ash
WaterMultiply max W/C ratio of .512 times the total amount of cementitious material. (.512 X 586) / 8.33 - 1.5 = 34.5 gallons
The design process for the remaining components remains the same.
Problem 9 Fly AshClass AAvibAE Fly AshSand-Great PitStone-Greystone Q20% replacement SG Fly Ash 2.26Fine agg wkstCoarse agg wkstTable 5.3.1Table 1000-1Fly Ash wkst
Problem 9 Cement and Fly Ash quantity
Cement 639 x .20 = 128639 -128 = 511 Lbs Cement
Fly Ash 18 x 1.2 = 154 Lbs Fly Ash
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