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

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

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

Table 9.4

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/ft 3
• 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
Table 9.5
1” Slump

Step #2: Determine Mixing Water and Air Content
Weight of Water = 250 lbs/yd 3
Volume of Water = 250 lbs/yd 3 = 4 ft 3
62.4 lbs/ft 3
Volume of Water = 4 ft 3 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

W/C= Wt. of Water
Wt. of Cement
Wt. of Cement = 250 lbs/yd 3
.40
=625 lbs/yd 3
Volume of Cement = 625 lbs/yd 3 (Concrete)
3.15 x 62.4 lbs/ft 3
SG Cement
Volume of Cement = 3.18 ft 3 per cubic yard of concrete

Table 9.4

Step #6: Coarse Agg. Content
Weight (Dry) =.71 x 27 ft 3 /yd 3 x 100 lb/ft 3 = 1,917 lbs
Dry Rodded Unit Wt of Stone
Volume = 1,917 lbs = 11.46 ft 3
2.68 x 62.4 lbs/ft 3
SG Stone

Step #7: Fine Agg. Content
27 ft 3
4 ft 3
Cubic Yard of Concrete
Water
1.49 ft 3 Air (.055 x 27 ft 3 )
3.18 ft 3 Cement
11.46 ft 3 Stone
6.87 ft 3 Sand
Wt of Sand (Dry) = 6.87 ft 3 x 2.64 x 62.4 lbs/ft 3 = 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
1% Moisture
Wt of Sand (Wet) =1,131.7 lbs x 1.05= 1,188.3 lbs
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
Dry Wt.
Moisture Absorption
Water from Sand= 1,131.7 lbs x (.05-.007) = 48.66 lbs
Dry Wt.
Moisture Absorption
Water = 250 lbs – 9.59 lbs – 48.66 lbs = 191.75 lbs

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