2 CE201 Aggregate v5

7/31/2019 2 CE201 Aggregate v5

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CE 201: Engineering Materials(Aggregates)

Dr. Md. Jahangir Alam

Associate ProfessorGeotechnical Engineering Division

Department of Civil Engineering,

BUET, Dhaka-1000

Email: [email protected]



Aggregates

• Granular material=sand, gravel, crushed stone (stone

chips), crushed brick (brick

chips), blast furnace slag, shingles

• 60-75% volume of concrete

• Affect workability of fresh

concrete, and properties of

hardened concrete

#200 (0.075 mm)

#4 (4.75 mm)

??????????

CA

FA

Silt and clay

Bring 3 Semi-log Graph Paper in the Next Class 2



Particle Size Distribution orGrain Size Distribution or

Grading of Aggregate

• Gradation curve or particle size distribution curve

can be obtained by

Let’s take a scale and startto measure dimensions of

particles.

R U Ready???

Sieve analysis

3



4



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FM Fi M d l



FM = Fineness Modulus

• FM = sum of the total percentages retained on each of a

specified series of sieves• Specified sieves or standard sieves for FM =

75.0, 37.5, 19.0, and 9.5 mm + No. 4, 8, 16, 30, 50, 100

• Bottom is No. 100, top is unlimited• Include whole range for summation???? 9



10



D = Well, C = Uniform, E = Gap

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Some Index Properties

• C….. Uniformly-graded soil• D …. Well-graded soil (Cu>4 for gravel, Cu>6 for

sand, Cc=1-3)

• E …. Gap-graded soil• D10, D30, D60 = ??

• D10 = Effective size, D50 = Mean diameter

• Coefficient of Uniformity,

• Coefficient of Curvature or

Coefficient of Gradation,

10

60

D

DC

u=

( )

6010

2

30

D D

DC

c=



0

20

40

60

80

100

0.01 0.1 1 10

P

e r c e n t F i n e r

( % )

Particle Size (mm)

Well Graded

0

20

40

60

80

100

0.01 0.1 1 10

P

e r c e n t F i n e r

( % )

Particle Size (mm)

Gap Graded

0

20

40

60

80

100

0.01 0.1 1 10

P e r c e n t F

i n e r ( % )

Particle Size (mm)

Uniformly Graded

Poorly Graded

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Combined grading



Combined grading

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Calculation of combined grading

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Significance of aggregate grading



Significance of aggregate grading(smooth, gap, poor, uniform)

• Need to know >>> well graded agg or smooth grading, gapgrading, uniform grading, poor grading

• Smooth grading => minimum void => less cement requirement to

fill void => cement paste can coat all particles• Poor grading => Harsh concrete mix

• Excessive fine aggregate => more surface area => more cement

• Maximum size of aggregate: larger => less cement requirement / But too many larger agg => more void unfilled by fine agg =>more cement paste requirement

• Who dictate nominal max size of agg? – Size and shape of concrete member

– Clear spacing between reinforcing bars

– Clear cover16



• Specific gravity?

• Four moisture conditions of aggregate – Damp or Wet or moist (more than 100%)

– Saturated surface dry (SSD) (100%)

– Air-dry (less than 100%) – Oven-dry or bone dry (0%)

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Specific gravity of aggregate



Specific gravity of aggregatePermeable pore or capillary pore

Impermeable pore

Capillary pores are interconnected and extended upto surface

• Absolute specific gravity

– All pores are excluded from V• Apparent specific gravity – Impermeable pores are included – Permeable pores are excluded from V

• Bulk specific gravity (OD weight is used) – All pores are included in V

• Bulk specific gravity SSD (SSD weight is

used)18

Bulk density



Bulk density• Loose or compacted (rodding, jigging)

• Batching by volume

• Bulk density = Mass/volume

– (volume includes all kind of voids; permeable, impermeable, inter-particle)

• Factors affecting the bulk density – Moisture content, FA+CA

– Grading, specific gravity, surface texture, shape and angularity

• Rodded bulk density = 1200 – 1760 kg/m3

– (75 – 110 lb/ft3)

• Absorption is based on OD weight

– (SSD-OD)*100/OD

• Surface moisture = Total – SSD

• Example 9, 12, 13, 14,

Absorption and surface moisture

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Examples explaining



Examples explaininguse of specific gravity and moisture content

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I m WATER?Made your

headache

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Harmful materials in aggregate



Harmful materials in aggregate

• Organic materials

• Silt, clay and other fine particles

• Salt

– Harmful effects• Interfere in hydration process of concrete

• Coatings prevents good bonding

• Make unsound (volume expansion after hardening)

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2 CE201 Aggregate v5