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Materials in Civil Engineering BLENDING OF AGGREGATES

Prepared by:

Asst. Prof. Dr. Deprizon Syamsunur

UCSI University

INTRODUCTION

Aggregates blending is the mixing of two or more aggregates so as to obtain different aggregate properties.

NCAT 3

* Uniformly graded

- Few points of contact

- Poor interlock (shape dependent)

- High permeability

* Well graded - Good interlock

- Low permeability

* Gap graded

- Only limited sizes - Good interlock - Low permeability

Types of Gradations

NCAT 4

Aggregate Gradation

• Use 0.45 Power Gradation Chart

• Blend Size Definitions – maximum size

– nominal maximum size

• Gradation Limits – control points

– restricted zone

NCAT 5

Example: 4.75 mm sieve plots at (4.75)0.45 = 2.02

Sieve Size (mm) Raised to 0.45 Power

0

20

40

60

80

100

0 1 2 3 4

Percent Passing

0.45 Power Grading Chart

NCAT 6

0.45 Power Grading Chart

0 .075 .3 .6 1.18 2.36 4.75 9.5 12.5 19.0

Sieve Size (mm) Raised to 0.45 Power

0

20

40

60

80

100

maximum density line

Percent Passing

max size

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Sieve Analysis

• Concept — “If two orthogonal dimensions of a particle are greater than a given sieve, then the particle is retained on it”

• The intermediate dimension controls the sieve size on which the particle is retained

square opening

Di

Di = intermediate

dimension < diagonal opening

Gradation Repeatability – Limestone Sample 67

0

10

20

30

40

50

60

70

80

90

100

1.00 10.00 100.00

Sieve Sizes (mm)

Percen

t P

ass

ing

Blacksburg 67 Trial_1

Blacksburg 67 Trial_2

Blacksburg 67 Manual

0.075

0.15

0.3

0.6

1.18

2.36

4.75

9.5

12.5

19.0

25.0

REASONS FOR BLENDING

Reasons for blending

1. Obtain desirable gradation

2. Single natural or quarried material not

3. Economical to combine natural and process materials

NUMERICAL METHOD

Numerical method

1.Trial and error

2.Basic formula

BLENDING OF AGGREGATES

SIEVES SIZE ENGLISH VS METRIC

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EXAMPLE

SOLUTION

SPECIFIC GRAVITY OF AGGREGATE BLEND

• Once the percentages of the stockpiles have been established, the combined aggregate specific gravities can also be calculated

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Specific Gravity, G

• Ratio of the mass to volume of an object to that of water at the same temperature

Mass Solid

Volume

Mass Water

Volume

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Specific Gravity Tests for Aggregates

• Two tests are needed

– Coarse aggregate (retained on the 4.75 mm sieve)

– Fine aggregate (passing the 4.75 mm sieve)

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Coarse Aggregate Specific Gravity

• ASTM C127 – Dry aggregate

– Soak in water for 24 hours

– Decant water

– Use pre-dampened towel to get SSD condition

– Determine mass of SSD aggregate in bucket

– Determine mass under water

– Dry to constant mass

– Determine oven dry mass

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Coarse Aggregate Specific Gravity

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Coarse Aggregate Specific Gravity

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Coarse Aggregate Specific Gravity Calculations

• Gsb = A / (B - C) – A = mass oven dry

– B = mass SSD

– C = mass under water

• Gs,SSD = B / (B - C)

• Gsa = A / (A - C)

• Water absorption capacity, % – Absorption % = [(B - A) / A] * 100

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Fine Aggregate Specific Gravity • ASTM C128

– Dry aggregate

– Soak in water for 24 hours

– Spread out and dry to SSD

– Add 500 g of SSD aggregate to pycnometer of known volume

• Pre-filled with some water

– Add more water and agitate until air bubble have been removed

– Fill to line and determine the mass of the pycnometer, aggregate and water

– Empty aggregate into pan and dry to constant mass

– Determine oven dry mass

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Fine Aggregate Specific Gravity

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Fine Aggregate Specific Gravity

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FINE AGGREGATE SPECIFIC GRAVITY

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Fine Aggregate Specific Gravity Calculations

• Gsb = A / (B + S - C) – A = mass oven dry

– B = mass of pycnometer filled with water

– C = mass pycnometer, SSD aggregate and water

– S = mass SSD aggregate

• Gs,SSD = S / (B + S - C)

• Gsa = A / (B + A - C)

• Water absorption capacity, % – Absorption % = [(S - A) / A] * 100

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* Prevent segregation and contamination * Good stockpiling = uniform gradations

- Short drop distances - Minimize moving - Don't use "single cone" method - Separate stockpiles

Stockpiling

NCAT 28

Stockpiling

COMBINED SPECIFIC GRAVITY

EXAMPLE

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