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Dr Rajib ChowdhuryDepartment of Civil Engineering

IIT Roorkee

Module CE-251

Building Materials,Construction and Estimation

Lecture 4: Aggregates

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Aggregate Sources

!

Natural:

" natural sand & gravel pits, river rock

" quarries (crushed)

! Manufactured & recycled materials:

"

steel mill slag

" steel slugs

" expanded shale

" styrofoam

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Geological Classifications

! Igneous

!

Sedimentary

!

Metamorphic

#

All three classes of rock are used successfully in CE applications.

# Check physical, chemical, and mechanical properties, supplemented bymineralogical examination.

# Historical performance in a similar design.

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Aggregate Uses

"

Under foundations and pavements" Stability

" Drainage

" As fillers

" Portland Cement Concrete

60-75% of volume

80-85% of weight

" Hot Mix Asphalt

80%-90% of volume

90-96% of weight

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Aggregate Sizes

! Coarse aggregate material

retained on a sieve with 4.75mm openings

! Fine aggregate materialpassing a sieve with 4.75mm openings

! Traditional

"

Maximum aggregate size thelargest sieve size that allows allthe aggregates to pass

" Nominal maximum aggregatesize the first sieve to retainsome aggregate, generally less

than 10%! Superpave

" Maximum aggregate size one

sieve size larger than the nominalmaximum aggregate size

" Nominal maximum aggregate

size one sieve larger that thefirst sieve to retain more than10% of the aggregate

4.75mm

#4 sieve =`four openings/

linear inch

1

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Aggregate Gradation

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Semi-Log graph

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Sample Problem

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Solution

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0.45 Power Graph

Sieve Size

PercentPassing

0

100

Straight line identifies maximumdensity aggregate blend

But a special scale is needed for the sizeaxis

Pi =100

di

D

!"#

$%&n

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0.45 Power Grading Chart

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0.45 Power Grading Chart

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Types of Gradation

Maximum Density Gradation: 0.45 Power Chart

High density gradation (Well Graded)

" has a good mix of all particle sizes which means the

aggregates use most of the volume and less cement or

asphalt is needed

One-size gradation (Uniform)

" all same size = nearly vertical curve

Gap-graded

" missing some sizes = nearly horizontal section of curve

Open-Graded"

missing small aggregates which fill in holes between larger

ones

" lower part of curve is skewed toward large sizes

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Effect of Amount of Fines on the Relative Propertiesof Aggregate Base Material

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Aggregate Mining

Quarry

Sand from river deposit