Aggregate Ug

7/29/2019 Aggregate Ug

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Dr. Kimberly KurtisSchool of Civil Engineering

Georgia Institute of TechnologyAtlanta, Geo rgia

Aggregate

Sand, gravel, crushed stone

Recycled concrete,

manufactured aggregate,crushed slag, iron ore

Much less expensive than

portland cement

Provides stability to asphalt

concrete and portland cementconcrete

Try to use as much aggregate as

possible for economy

- 60-80% agg in PCC

- ~90% agg in ACC

Aggregate is NOT just an inert filler

Aggregate properties influence:

Workability

Strength

Stiffness

Creep and shrinkage

Durability

Before we discuss how aggregate influences the properties ofconcrete, its worthwhile to examine intrinsic aggregate

properties

Sources of Natural Aggregate

Igneous - formed by cooling of molten rock matter either aboveor below the earths surface; phase separation occurs during

cooling, and crystals form in either a crystalline or glassymatrix; size of the grains is dependent on the rate of cooling.

Sedimentary - formed by consolidation of deposits of theproducts of weathering and erosion of existing rocks

Metamorphic - formed through the application of heat and

pressure to sedimentary or igneous rocks

Concrete Aggregates

Minerals Rocks

Aggregate Geology

Concrete Aggregates

Minerals Rocks

Quartz

Opal

Feldspar Mica

Calcite

Dolomite

Gypsum

Pyrite

Magnetite

Dolomite CaMg(CO3)2, a basic constituent of

sedimentary carbonate rocks (dolomites and

dolomitic limestones)

Aggregate Geology


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Concrete Aggregates

Minerals Rocks

(Generally composed ofseveral minerals)

Aggregate Geology

Concrete Aggregates

Minerals Rocks


Igneous

Granite

Diorite

Gabbro

Volcanic glass

Basalt

Granite typic ally composed of quartz,feldspar, mica & a few other minerals

Aggregate Geology

Concrete Aggregates

Minerals Rocks


Igneous Sedimentary

Granite

Diorite

Gabbro

Volcanic glass

Basalt

Quartzite

Graywacke

Limestone

Dolomite

Shale Chert

Limestone typical ly composed of

calcite, dolomite, and minor amounts of

quartz, feldspar and clay

Aggregate Geology

Concrete Aggregates

Minerals Rocks


Igneous Sedimentary Metamorphic

Granite

Diorite

Gabbro

Volcanic glass

Basalt

Quartzite

Graywacke

Limestone

Dolomite

Shale Chert

Marble

Metaquartzite

Slate

Schist

Gneiss Serpentine

Gneiss typi cally composed of feldspar

and mica, and may contain minor amounts

of other minerals.

Aggregate Geology

Other types of aggregate used in North America include:

Crushed air-cooled

blast-furnace slag

Natural & manufactured

lightweight aggregate

Manufactured

sand

Heavyweight

aggregate

Recycled-

concrete

aggregate


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Important Aggregate Characteristics?

Strength? Elastic modulus?

Toughness?

Hardness?

Size?

Size distribution?

Shape?

Texture?

Porosity?

Pore structure?

Composition?

Hardness/Abrasion Resistance

Abrasion resistance o f aggregate

Often use as a general indicator of quality

Essential for heavy-duty floors or pavements

Low abrasion resistance may result in breakdown of

aggregate during mixing and increase in fines

Los Angeles Abrasion Test (ASTM C 131 & C 535)

Aggregate sample and steel balls placed in

a drum shelf in drum lifts and drops

aggregate and balls

Breakdown due to abrasion and impact

determined by mass loss

Test results do not show a clear correlation

with abrasion of concrete

Skid Resistance

Skid resistance of aggregate

Siliceous content of fine aggregate ? 25%

Siliceous content = insolubleresidue after treatment with HCl

acid

Shape

Shape

Flat & elongated particles

Should be avoided

< 15% by mass

Ratio of length to width or thickness larger than 5:1

Texture


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Moisture Content

Aggregate contains no

moisture (pores are empty)

Aggregate contains some moisture,

but is not saturated (pores are

partially filled)

Aggregate is satu rated (pores are

filled), but there is no free water onthe surface

Aggregate is satu rated (pores a re

filled), and there is an excess of

water on the surface

Saturated surface

dry (SSD)

Aggregate is satu rated (pores are

filled), but there is no free water onthe surface

Aggregate absorption capacity = moisture content at SSD

(% mass of dry aggregate)

Absorption capacity (AC) of coarse aggregate = 0.2 to 4%

Absorption capacity (AC) of fine aggregate = 0.2 to 2%

Moisture content (MC) of coarse aggregate = 0.5 to 2%

Moisture content (MC) of fine aggregate = 2 to 6%

ASTM C 70, C 127, C 128 & C 566

Moisture Content and Absorption

Moisture Content and Absorption Capacity

MC (%) = (Magg-MOD)/ MODx100

AC (%) = (MSSD-MOD)/ MODx100

If MCAC,

If MC=AC,

Bulking is the increase in total

volume of moist fine aggregate

over the same mass dry

Bulking of Sand

Bulking of Sand

Stockpile

dry

Stockpile

partiallysaturated

Stockpile

saturated

Specific Gravity

SGagg= (mass of agg)/(mass of equal volume of water)

=(density of solid part of agg)/(density of water)

Because aggregates contain internal voids and are expected

to contain some water-filled voids in concrete, bulk specific

gravity is used.

BSG is different from SG because it is based on the mass

of the SSD aggregrate, rather than the mass of the mineral

material only

BSG = (density of agg including solids and internal

voids)/(density of water)

2.4-2.9 are typical values for normal weight aggregate


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Specific Gravity and Density

For portland cement concrete, specific gravity is usually determined for

aggregate in SSD condition:

ASTM C 127 Standard Test Method for Specific Gravity and

Absorption of Coarse Aggregate

ASTM C 128 Standard Test Method for Specific Gravity andAbsorption of Fine Aggregate

S.G.SSD = S.G.oven dry X100 + AC

100

(where ACis the aggregate

absorption capacity

expressed as a percentage)

Density for aggregate, as with all materials, is:

Aggregate density = relative density (S.G.) X density of wat er

Affects density of concrete and dead load of structure

Also called dry rodded unit weight

Agg mass/(Vol of agg + voids between), when compacted in astandard way

Void content =30 to 45% for coarse aggregate

40 to 50% for fine aggregate

Normal weight 75-110pcf

Lightweight < 70pcf

Heavy weight > 150 pcf

Bulk Density

ASTM C 29 Standard Test Method for

Bulk Density (Unit Weight) and Voids in

Aggregate

Aggregate Gradation

Particle sizes of aggregate in concrete typically range from < 150 ? m

(0.006 in) to > 20 mm ( in)

Aggregate grading by sieve analysis

ASTM C 136

AASHTO T 27

CS A A 23 .2-2A

Gradation

Sieve Designation and Opening Sizes

Designation

3" 3.000 in 75.0 mm

2-1/2" 2.500 in 63.0 mm

2" 2.000 in 50.0 mm

1-1/2" 1.500 in 38.1 mm

1" 1.000 in 25.0 mm

3/4" 0.750 in 19.0 mm

1/2" 0.500 in 12.5 mm

3/8" 0.375 in 9.5 mm

# 4 0.1870 in 4.750 mm

# 8 0.0937 in 2.200 mm

# 16 0.0469 in 1.180 mm

# 30 0.0234 in 0.600 mm

# 50 0.0117 in 0.300 mm

# 100 0.0059 in 0.150 mm

# 200 0.0029 in 0.075 mm

Nominal Opening

CoarseSieves

FineSieves

10012060.9Total

01.2138.8Pan

69.224.92999.21/2 in

33.435.84318.83/8 in

1.21.4165.4No. 16

2.55.0599.8No. 8

7.525.93119.1No. 4

94.06.0719.83/4 in

10000.01 in

% Passing% RetainedMass Retained(lb)

Sieve #

Sieve analysis for -in stone

Aggregate Gradation: Example

% passing 3/8-in. sieve = 100 0 6.0 24.9 35.8 = 33.4 %


6/8

Grading curve for -in stone

0

20

40

60

80

100

Sieve Size

PercentPassing

#16 #8 #4 3/8 in1/2 in

3/4 in1 in

1.5 in2 in

69.21/2 in

33.43/8 in

1.2No. 16

2.5No. 8

7.5No. 4

94.03/4 in

1001 in

% PassSieve #

Aggregate Gradation: Example

Reducing the paste content of concrete leads to:

Reduced cos t

Reduced temperature rise

Reduced shrinkage

Reduced permeability

Fine Aggregate

Particles which pass No. 4 (4.75mm) but are retained on

the No. 200 (75um)

Grading of fine aggregate affects workability and cost of

portland cement concrete

Fineness modulus (FM) is a measure of how fine a sand is

For a fine aggregate, FM is calculated from the cumulative

percentages of aggregate retained on sieves No.4,8, 16,30, 50, 100 divided by 100

Typical values for concrete sand are 2.3-3.1

Masonry sand is fine, FM ~1.8

Fineness Modulus

283100Total

-03Pan

97318150 ? m (No. 100)

792124300 ? m (No. 50)

554520600 ? m (No. 30)

3565201.18 mm (No. 16)

1585132.36 mm (No. 8)

29824.75 mm (No. 4)

010009.5 mm (3/8 in.)

Cumulative %

retained

Cumulative %

passing

% retainedSieve size

Fineness modulus, FM =283

100= 2. 83

Coarse Aggregate

Particles larger than 4.75mm (0.2), retained on No. 4 sieve

Typical size range 4.75-50mm (0.2-2)


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MSAMaximum Size Aggregate (MSA)

In general, coarse aggregate graded up to the largest size practical for

the job conditions provides the most economical mix.

Placement conditions dictate the following:

Dmax ? clear cover to steel

Dmax ? clear space between bars

Dmax ? 1/5 distance between forms

Dmax ? 1/3 thickness of slab

Dmax ? 1/3 hose diameter or 40 mm (1 in)

For high strength concrete typically ? 70 MPa (10,000 psi):

Use smaller maximum aggregate sizes

Use crushed-stone aggregate

Grading Adjustments

0

5

10

15

20

25

30

Sieve Size

PercentRetained

#16 #8 #4 3/8 in

1/2 in

3/4 in

1 in

1.5 in

2 in

#30#50#100

Combined Coarse (50%) & Fine (30%) + Intermediate (20%)

Optimized Grading

Grading Adjustments

Reject oversize and/or fines

Combine aggregate

Grading:

? ?vf)i(Pw)i=VfTPw,ave=(1)Pw,ave

Specific Gravity:

SGave= [? (Pw)i]/{[? (Pw)i/ SGi]}

Determine the gradation (based on % passing by weight) andspecific gravity of a 25%-75% blend of aggregates A and B,

with SG of 2.5 and 2.7 respectively.

% passing by weight % passing by weight

Sieve Agg A Agg B 25-75 Blend

in. 100

in. 98

3/8 in. 90

#4 75 100

#8 60 95

#16 45 90

#30 30 65

#50 15 45

#100 5 20

#200 1 5

Grading Adjustments: Example

0.25(100) + 0.75(100)=100

99

98

94

86

79

56

38

16

4

SG of blended agg = 100/[(25/2.5) + (75/2.7)] = 2.65

Deleterious Substances


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Components of Concrete

Aggregate - coarse and fine Water

Cement

Supplementary cementing materials (SCMs)

Chemical admixtures

Cement paste - cement and water, possibly with SCMs and/orchemical admixtures

Mortar - cement paste and sand, sometimes with lime (CaO)added to the cement

Water

Water used for concrete batching should be fit to drink

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