Aggregate Blending

Thursday February 22, 2018

Concrete

Cementitous

water & admixtures

GLUE!

Typical Components of Concrete

Fine aggregate

25%

coarse aggregate

45%

water & admixtures

15%

Cementitous

10%

air 5%

Characteristics of Aggregates• Gradation

• Specific Gravity

• Moisture Content

• Strength

• Freeze-thaw resistance

Cost & Availability

Curling/Warping

A Little Science

(Just a little, I promise)

Concrete water content vs. ultimate shrinkage

8

The Move to Larger Aggregate

• Many engineers are looking to use

– concrete with larger aggregates

– More aggregate in the mixture

Aggregates grading and size

effects A mixture of particle

sizes is more

efficient at filling

void space than all

particles of any one

size.

Larger maximum

sizes also help

graded aggregates

fill volume more

effectively.

Cubic Yard

3’

3’

3’

Volume =27cf Surface Area = 162 Sf

CUBIC YARD

3’

3’

3’

Volume = 27 cf Surface Area = 54 sf

Effects of aggregate grading on mixture paste fraction

Tools for analyzing combined aggregate grading

Coarseness Factor Chart

ACI 302

Individual Percent Retained

8-18

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

22%

24%

26%

28%

30%

2" 1.5" 1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200

ASTM Standard Sieve Size

Combined % Retained

Original Revised

0.45 Power Curve

1.5

"

1"

3/4

"

1/2

"

3/8

"

#4

#8

#16

#30

#50

#100

#200

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

ASTM Standard Sieve Size

0.45 Power Curve

Orig

Rev

0.45 Power Curve

Perc

ent P

assin

g

Oklahoma State University

8-18

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

22%

24%

26%

28%

30%

2" 1.5" 1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200

ASTM Standard Sieve Size

Combined % Retained

Original Revised

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

22%

24%

26%

28%

30%

2" 1.5" 1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200

ASTM Standard Sieve Size

Combined % Retained

Original Revised

Tools to Assist

• Shilestone Software

• Compass

• www.trantulacurve.com

• Make your own spreadsheet?

• But… Math is based on volume, not weight

Issues

CRT’s Opinion

• Larger top size

– Approximately 5% retained on the 1”

• Of all aggregates, not just the coarse

• Better graded

– No holes

Example

• The process works

• Example