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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]
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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
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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
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FM Fi M d l
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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
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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=
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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
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Combined grading
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Calculation of combined grading
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Significance of aggregate grading
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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
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• 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
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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
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Bulk density
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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
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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
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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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