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MIX PROPORTIONING 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
Approximate Required Slump Values (PCA)
Concrete Construction
Slump (Max.) Slump (Min.)
Reinforced foundation walls/footings
3 in 1 in
Plain footings and substructure walls
3 in 1 in
Beams & reinforced walls 4 in 1 in
Building columns 4 in 1 in
Pavement & slabs 3 in 1 in
Mass concrete 2 in 1 in
Economics of Mix DesignGoals:
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 concreteAmount 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 SandUnit Weight & SG of SandSSD (Absorption) of StoneUnit Weight & SG of StoneDensity of Cement = 195 pcfSG Cement = 3.15Density of Water = 62.4 pcf1 Cubic Foot Water = 7.48 gal1 Gal. Water = 8.34 lbs
The standard ACI mix design procedure can be divided up into 8 basic steps:1. Choice of slump
2. Maximum aggregate size selection
3. Mixing water and air content selection
4. Water-cement ratio
5. Cement content
6. Coarse aggregate content
7. Fine aggregate content
8. Adjustments for aggregate moisture
ACI Standard Mix Design Method
Step #1: Select Slump
Table 9.6
Step #2: Determine Mixing Water and Air Content
Table 9.5
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 #3: Max. Agg. Size Check
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. ContentTable 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
Step #1: Select Slump
Engineer Specified 1” (correlates w/table)
Table 9.6
Step #2: Determine Mixing Water and Air Content
1.5” Stone
1” Slump
Table 9.5
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 #2: Determine Mixing Water and Air Content
ACI Limits:1/3 of the slab depth
10”/3 = 3.33 inches > 1.5” OK
Step #3: Max. Agg. Size Check
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. ContentTable 9.4
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
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
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
Step #8: Aggregate Batch Weights & Water Adjustment
MoistureDry Wt. 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
