CON 124Basic Concrete Mix Design Proportioning

Session 4Proportioning Methods

Methods for Proportioning Concrete Mixtures

Water-cement ratio method

Weight method

Absolute volume method

Field experience (statistical data)

Trial mixtures

Design of Concrete Mixtures Establishment of specific concrete

characteristics Relative Density (Specific Gravity) Absolute volume calculation (27 Cubic Ft) Durability Issues

Selection of proportions of available materials to produce concrete of required properties, with the greatest economy

Concrete Mixture Design from Field Data

Strength-Test Data Standard Deviations show mixture is

acceptable Durability aspects must be met Statistical data should represent the same

material, proportions, and concreting conditions

Proportioning Data for Proposed Work

Concrete Strength within 7MPa (1000 psi) Data should represent at least 30 consecutive tests or two

groups representing of consecutive tests totaling at least 30 tests (average of two cylinders)

If data between 15-29 tests, an adjusted Std. Dev. (S) is multiplied by modification factor from Table 11

Modified Std. Dev. (S) is then used in equations 1-3 from Table 12

When field strength test records do not meet the above, then the required average strength of concrete can be obtained from Table 13 (Table 9-11)

Proportioning from Field Data

Number of testsModification factor for

standard deviationLess than 15 see next slide

15 1.1620 1.0825 1.03

30 or more 1.00

Modification Factor for Standard Deviation ( 30 Tests)

Table 11: Modification factor for standard deviation when less than 30 tests are available. Interpolated for design mixtures modified standard deviation to be used to determine required average strength. Adapted from ACI 318.

Proportioning from Field Data Required Strength When Data Are Available to Establish a

Standard Deviation

Specified compressive strength, f'c, psi

Required average compressive strength, f'cr, psi

5000f'cr = f'c+ 1.34sf'cr = f'c + 2.33s - 500

Use larger value

Over 5000f'cr = f'c+ 1.34sf'cr = 0.90f'c + 2.33s

Use larger value Inch-Pound

Table 12: Required Average Compressive Strength When Data Are Available to Establish a Standard Deviation (Inch-Pound)Adapted from ACI 318.

Proportioning from Field Data Required Strength When Data Are Not Available

to Establish a Standard Deviation

Specified compressive strength, f'c, psi

Required average compressive strength, f'cr, psi

Less than 3000 f'c + 1000

3000 to 5000 f'c + 1200

Over 5000 1.10f'c + 700

Inch-PoundTable 13: (Inch-Pound Units). Required Average Compressive Strength When Data Are Not Available to Establish a Standard DeviationAdapted from ACI 318.

Proportioning by Trial Mixtures Trial batching verifies that a concrete mixture meets

design requirements prior to use in construction. The trial mixtures should use the same materials

proposed for the work. Three mixtures with three different water-cementing

materials ratios or cementing materials contents should be made.

The trial mixtures should have a slump and air content within ±20 mm (±0.75 in.) and ± 0.5%, respectively, of the maximum permitted.

Three cylinders for each water-cementing materials ratio should be tested at 28 days.

Proportioning by Trial Mixtures Approved mixture must meet required average

compressive strength Three trial mixtures using three different water to

cementing materials ratios Slump and Air Content within +/- 20 mm(+/- 0.75 in.) and

+/- 0.5% Cylinders cured as per ASTM C192 (AASHTO T126)

Plot water to cementing ratio to strength curve Test the properties of the newly proportioned

mixture

Proportioning Concrete Ingredients

Arbitrary assignment (1:2:3), volumetric Void Ratio Fineness Modulus Surface Area of Aggregates Cement Content Best approach

Select proportions based on past experience Reliable test data established relationship between

strength and water to cementing materials ratio

Plotting of Water to Cementing Ratio to Compressive Strength

Satisfactory Job Mixture Required Strength Minimum Cementing Materials Content or Maximum

Water to Cementing Materials Ratio Nominal Maximum Size Aggregate Necessary Amounts of Fine and Coarse Aggregate

(saturated surface dry condition, SSD) Air Content Desired Slump

Saturated Surface-Dry Density (SSD-Density)

where

DSSD is density in the SSD condition

M1 is the SSD mass in air, kg (lb)

M2 is the apparent mass immersed in water, kg (lb)

is the density of water, 1000 kg/m3 (62.4 lb/ft3)

21

1

MM

MDSSD

Slump Test

Slump test for consistency of concrete. Left figure illustrates a lower slump, right figure a higher slump.

Air Content

Pressure methodASTM C 231(AASHTO T 152)

Volumetric methodASTM C 173(AASHTO T 196)

Air indicator method AASHTO T 199

Tests, Measurements, Calculations

Tests for slump, air content, and temperature on trial mixture

Density (Unit Weight) and Yield Absolute Volume

Density (Unit Weight), Yield

• In accordance with ASTM C138• Density (Unit Weight): Pounds/Cubic ft• Yield: Cubic Feet• Calculation, Dividing total mass of materials

batched to density of freshly mixed concrete

Density (Unit Weight) and YieldFresh concrete is measured in a container of known volume to determine density (unit weight)• Scale must be sensitive to 0.3% of

anticipated mass of sample and container

• Size of container varies according to the size of the aggregate, the 7-L (25-ft3) air meter container for up tp 25-mm (1-in.) nominal max. size aggregate: 14-L (0.5 ft3) container for aggregates up to 50 mm (2-in.)

• Container should be calibrated at least annually (ASTM C 1077)

Density (Unit Weight) and Yield

ASTM C 138

(AASHTO T 121)Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete

ASTM C 1040 (AASHTO T 271)

• Density of Unhardened and Hardened Concrete in Place By Nuclear Methods

Absolute Volume

• Volume of a granular material is the volume of the solid matter in the particles without volume of air spaces

• Yield of freshly mixed concrete is equal to the sum of the absolute volumes of the concrete ingredients

Proportioning Concrete Mixtures

Absolute Volume Method

Dry Rodded Density Absolute Volume Density

Proportioning Concrete Mixtures

Absolute Volume Method

Abs Vol Density = Weight/Volume (no voids)

Specific Gravity = Abs Vol Density / Density of Water

Vol

Proportioning Concrete Mixtures

Absolute Volume Method

Abs Vol=Wt/(Specific Gravity x Density of Water)

Weight=Abs Vol x Specific Gravity x Density of Water

Density of Water = 62.4 lbs per cu ft ( @ 40C)

Material Density Values

• Portland Cement Relative Density (Specific Gravity) value: 3.15

• Blended Cements Relative Density Ranges: 2.90 to 3.15

• Fly Ash Relative Density value: 1.9 to2.8• Slag Relative Density value: 2.85 to 2.95• Water Relative Density value: 1.0• Normal Aggregates Relative Density value: 2.4

to 2.9

Design Review Flowchart

Design Review Flowchart

Design Review Flowchart

Design Review Flowchart

Questions?Email cemtek@netzero.net