Prepared by Marcia C. Belcher Construction Engineering Technology MIX PROPORTIONING Prepared by Marcia C. Belcher Construction Engineering Technology

Design Consideration: Obtaining Good Workability

Design Consideration: Obtaining Good Workability

Obtaining Good Workability

Obtaining Good Workability

Design Consideration: Prevent Segregation & Bleeding

Well Graded Aggregates Will Reduce Segregation & Bleeding Well Graded Poorly Graded

Measuring Workability: Slump

The Slump Cone

Concrete Construction Approximate Required Slump Values (PCA) Concrete Construction Slump (Max.) Slump (Min.) Reinforced foundation walls/footings 3 in 1 in Plain footings and substructure walls Beams & reinforced walls 4 in Building columns Pavement & slabs Mass concrete 2 in

Economics of Mix Design Goals: Maximize strength = minimize water = control bleeding & segregation Reduce Cost = use largest gravel possible for the job = minimize paste requirement Provide good durability = use well graded aggregates = maximize void packing = reduced segregation

Cost Comparison of Constituents

Guidelines We Use For Mix Design PCA Manual Tables for w/c ratio based on compressive strength requirement & slump (workability) Volume of stone required based on max. agg. size and sand fineness. Water required based on max. agg. size, slump & w/c ratio (compressive strength)

Design Method We Will Use: Absolute Volume Method Assumes no air voids in concrete Amount of concrete is sum of solid volumes: 1 CUBIC YARD Cement Sand Coarse aggregate Water Air

WATER CORRECTION Any water content in aggregates above SSD water content must be subtracted from the water requirements Any water requirement of aggregates (below the SSD water content) must be added to the water requirements

Material Values & Constants Needed For Design: SSD (Absorption) of Sand Unit Weight & SG of Sand SSD (Absorption) of Stone Unit Weight & SG of Stone Density of Cement = 195 pcf SG Cement = 3.15 Density of Water = 62.4 pcf 1 Cubic Foot Water = 7.48 gal 1 Gal. Water = 8.34 lbs

ACI Standard Mix Design Method The standard ACI mix design procedure can be divided up into 8 basic steps: Choice of slump Maximum aggregate size selection Mixing water and air content selection Water-cement ratio Cement content Coarse aggregate content Fine aggregate content Adjustments for aggregate moisture

Step #1: Select Slump Table 9.6

Step #2: Determine Mixing Water and Air Content Table 9.5

Step #3: Max. Agg. Size Check DEFINITION: Nominal maximum aggregate size is the largest sieve that retains some of the aggregate particles. ACI Limits: 1/3 of the slab depth 3/4 of the minimum clear space between bars/form 1/5 minimum dimension of non-reinforced member Aggregate larger than these dimensions may be difficult to consolidate and compact resulting in a honeycombed structure or large air pockets.

Step #4: Select W/C Ratio Table 9.3

Step #5: Cement Content The calculated cement amount is based on the selected mixing water content and water-cement ratio. W/C= Wt. of Water Wt. of Cement

Step #6: Coarse Agg. Content Table 9.4

Step #7: Fine Agg. Content

Step #8: Batch Weight & Water Adjustment Aggregate weights.  Aggregate volumes are calculated based on oven dry unit weights, but aggregate is batched in the field by actual weight.  Any moisture in the stockpiled aggregate will increase its weight. Without correcting for this, the batched aggregate volumes will be incorrect. Amount of mixing water.  If the batched aggregate is anything but saturated surface dry it will absorb water (if dry) or give up water (if wet) to the cement paste.  This causes a net change in the amount of water available in the mix and must be compensated for by adjusting the amount of mixing water added.

Mix Design Example: 10” Thick Unreinforced Pavement Slab

Properties of Concrete Specified By Engineer: Slump =1.0 inch 28-day strength of 5000 psi Air content: 4.5 - 6.5 percent

Information About Materials: Coarse aggregate we are using (ODOT #467): nominal maximum size = 1.5 inch (see Agg. Size Table) dry-rodded weight = 100 lb/ft3 specific gravity = 2.68 moisture content = 1.0 percent absorption = 0.5 percent Fine aggregate: fineness modulus = 2.80 specific gravity = 2.64 moisture content = 5 percent absorption = 0.7 percent

WE ARE DESIGNING BATCH WEIGHTS FOR ONE CUBIC YARD Step #1: Select Slump Engineer Specified 1” (correlates w/table) Table 9.6

Step #2: Determine Mixing Water and Air Content 1.5” Stone Table 9.5 1” Slump

Step #2: Determine Mixing Water and Air Content Weight of Water = 250 lbs/yd3 Volume of Water = 250 lbs/yd3 = 4 ft3 62.4 lbs/ft3 Volume of Water = 4 ft3 per cubic yard of concrete

Step #3: Max. Agg. Size Check ACI Limits: 1/3 of the slab depth 10”/3 = 3.33 inches > 1.5” OK

Step #4: Select W/C Ratio Table 9.3

Step #5: Cement Content W/C= Wt. of Water Wt. of Cement Wt. of Cement = 250 lbs/yd3 .40 =625 lbs/yd3 Volume of Cement = 625 lbs/yd3 (Concrete) 3.15 x 62.4 lbs/ft3 Volume of Cement = 3.18 ft3 per cubic yard of concrete SG Cement

Step #6: Coarse Agg. Content Table 9.4

Dry Rodded Unit Wt of Stone Step #6: Coarse Agg. Content Weight (Dry) =.71 x 27 ft3/yd3 x 100 lb/ft3 = 1,917 lbs Volume = 1,917 lbs = 11.46 ft3 2.68 x 62.4 lbs/ft3 Dry Rodded Unit Wt of Stone SG Stone

Step #7: Fine Agg. Content 27 ft3 Cubic Yard of Concrete 4 ft3 Water 1.49 ft3 Air (.055 x 27 ft3) 3.18 ft3 Cement 11.46 ft3 Stone 6.87 ft3 Sand Wt of Sand(Dry) = 6.87 ft3 x 2.64 x 62.4 lbs/ft3 = 1,131.7 lbs. SG Sand

Step #8: Aggregate Batch Weights & Water Adjustment Since there is moisture in both coarse & fine aggregate, their batch weights must be adjusted Wt of Stone(Wet) = 1,917 lbs x 1.01= 1,936.2 lbs Wt of Sand(Wet) =1,131.7 lbs x 1.05= 1,188.3 lbs 1% Moisture 5% Moisture

Step #8: Aggregate Batch Weights & Water Adjustment Mixing water needs to be adjusted. Both the coarse and fine aggregate are wet of SSD and will contribute water to the cement paste. Water from Stone = 1,917 lbs. x (.01-.005) = 9.59 lbs Water from Sand= 1,131.7 lbs x (.05-.007) = 48.66 lbs Water = 250 lbs – 9.59 lbs – 48.66 lbs = 191.75 lbs Dry Wt. Moisture Absorption Dry Wt. Moisture Absorption

Final Batch Wts. (1 Cubic Yard) Water 191.75 lbs = 23 gallons Cement 625 lbs Stone 1,936.2 lbs Sand 1,188.3 lbs