Chapter II Concrete Making Materials - Mert Yücel...

CIV415 CONCRETE TECHNOLOGY

Chapter II

Concrete Making Materials “Aggregates”

Assist.Prof.Dr. Mert Yücel YARDIMCI

Advanced Concrete Technology - Zongjun Li 1

Concrete


Concrete is a composite material…

Aggregates with different sizes are surrounded by cement paste

Cement paste Aggregates Fine (d≤4mm), Coarse (4≤d≤25mm)

• Cement • Cementitious materials (Puzolans) • Water • Chemical admixtures

Concrete with crushed stone aggregates

Aggregates


• Aggregates constitute a skeleton of concrete. • Occupy approx. 60 – 75 % of the volume of conventional

concrete. • Affect fresh and hardened state properties of concrete. • Physical, thermal, and, sometimes, chemical properties

can influence the performance of concrete .

• Serve as an inexpensive filler. • Provides high volume stability in concrete by restricting

shrinkage of the cement paste to a certain extent.


Effects of Aggregates

Aggregate in fresh and plastic concrete: The behavior of fresh concrete, such as fluidity, cohesiveness, and rheological behavior, is largely influenced by the amount, type, surface texture, and size gradation of the aggregate. The selection of aggregate has to meet the requirement of the end use, i.e., what type of structure to be built.

Dmax should be approprate!


Aggregate in hardened concrete: Although there is little chemical reaction between the aggregate and cement paste, the aggregate contributes many qualities to the hardened concrete. In addition to reducing the cost, aggregate in concrete can reduce the shrinkage and creep of cement paste. Aggregates have a big influence on stiffness, unit weight, strength, thermal properties, bond, and wear resistance of concrete.

Effects of Aggregates

Classification of Aggregates


Classification criteria:

• Size • Source • Unit weight

Classification in accordance with SIZE


Coarse Aggregate • Aggregates retained on a No. 4 (4.75-mm)

sieve are classified as COARSE (ASTM) • Size of aggregate ranges from 5 to 150

mm. • For normal concrete used for structural

members such as beams and columns, the maximum size of coarse aggregate is about 25 mm.

Fine Aggregate • Aggregates passing through a No. 4 (4.75-

mm), retaining No.200 (75 µm) sieve are classified as FINE (ASTM)

• River sand is the most commonly used fine aggregate.

• Crushed rock fines can be used as fine aggregate.


Classification in accordance with SOURCE

Natural aggregates: This kind of aggregate such as sand and gravel is taken from natural deposits without changing the nature during production.

Manufactured (synthetic) aggregates : These kinds of aggregate are manmade materials, resulting from products or by-products of industry. Some examples are blast furnace slag and lightweight aggregate.

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Aggregate Sources

• Natural:

– natural sand & gravel pits, river rock

– quarries (crushed aggregates)

• Manufactured & recycled materials:

– pulverized concrete & asphalt

– steel mill slag

– steel slugs

– expanded clay and shale

– styrofoam

Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc.


Ultra-lightweight aggregate: • Unit weight of such aggregates is less than 500 kg/m3

• Expanded perlite and foam plastic are the examples. • The concrete made of ultra-lightweight aggregates has a bulk density from 800 to 1100 kg/m3

depending on the volume fraction of aggregate. • Such a concrete can be used only as nonstructural members, like partition walls.

Lightweight aggregate: • The unit weight of such aggregates is between 500 and 1120 kg/m3 • Blast-furnace slag, volcanic pumice, and expanded clay. • The concrete made of lightweight aggregate has a bulk density between 1200 and 1800 kg/m3

• Such concrete can be either a structural member or nonstructural member, depending what type of aggregate is used.

Classification in accordance with UNIT WEIGHT


Normal-weight aggregate: • An aggregate with a unit weight of 1520–1680 kg/m3. • Sand, gravel, and crushed rock belong to this category. • Concrete made with this type of aggregate has a bulk density of 2300–2400 kg/m3.

• It is the main concrete used to produce important structural members. Heavy-weight aggregate: • If the unit weight of aggregate is greater than 2100 kg/m3, it is • classified as heavy-weight aggregate. • Materials used as heavy-weight aggregate are iron ore, crashed steel pieces, and

magnesite limonite. • The bulk density of the corresponding concrete is greater than 3200 kg/m3 and can

reach 4000 kg/m3. • This kind of concrete has special usage, like radiation shields in nuclear power

plants, hospitals, and laboratories. • It can also be used as sound-shielding material.

Classification in accordance with UNIT WEIGHT

Properties of Aggregate


The moisture condition defines the presence and amount of water in the pores and on the surface of the aggregate.

• Oven Dry • Air Dry • Saturated Surface Dry • Wet

When aggregate is under either the OD or AD condition, it will absorb water during the concrete mixing process until the internal pores are fully filled with water.

Moisture Content (MC) of Aggregate


Wstock is the weight of aggregate in the stock condition. WOD the weight of oven-dried aggregates. WSSD is the weight of aggregate in the SSD condition.

Absorption capability of an aggregate is defined as the total amount of

water that can be taken by an aggregate from the OD to the SSD condition.

What is the importance of moisture content and water absorption capacity of aggregates?


In designing a concrete mix, the moisture content usually uses the SSD condition as a reference, because it is an equilibrium condition at which the aggregate will neither absorb water nor give up water to the paste.

If the MCSSD value is positive, it means that the aggregate is under a surface moisture condition. If it is negative, it means that the pores in the aggregate are only partly filled with water.

The amount of water used for mixing concrete has to be adjusted according to the MCSSD value in order to keep a correct w/c ratio, especially for a high-strength concrete in which a small w/c ratio is used, and the amount of adjusted water involved in MC can easily be a large portion of the total amount of water in the mixture.

Density and Specific Gravity


Since aggregates are porous materials, even a single piece of aggregate contains both solid material volume and pores volume. Hence, two types of aggregate density are defined: Density (D) and Bulk Density (BD)

Density (D) is defined as the weight per unit volume of solid material only, excluding the pores volume inside a single aggregate:

Bulk density (BD) is defined as the weight per unit volume of both solid material and the pores volume inside a single aggregate:


Density and Specific Gravity Specific gravity (SG) is a ratio of density or bulk density of aggregate to density of water. As second definition; SG is the mass of a given substance per unit mass of an equal volume of water.

Depending on the definition of volume, the specific gravity can be divided into absolute specific gravity (ASG) and bulk specific gravity (BSG).


Density and Specific Gravity • In practice, the BSG value is the realistic one to use since the effective

volume that an aggregate occupies in concrete includes its internal pores. • The BSG of most rocks is in the range of 2.5 to 2.8. • The BSG can be determined using the so-called displacement method. • In this method, Archimedes’ principle is utilized. • The weight of aggregate is first measured in air, e.g., under the SSD

condition, and is denoted as WSSD in air. Then, the weight of the sample is measured in water, denoted as WSSD in water.

where Wdisplacement is the weight of water displaced by the aggregates

Unit Weight


• The unit weight is defined as the weight per unit bulk volume for bulk aggregates.

• The bulk volume also includes the space among the particles.

According to the weight measured at different conditions, the unit weight can be divided into UW(SSD) and UW(OD):

The percentage of spacing (voids) among the aggregates can be calculated as

Geological Classifications

• Igneous

• Sedimentary

• Metamorphic

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

• Check physical, chemical, and mechanical properties, supplemented by mineralogical examination.

• Historical performance in a similar design. Mamlouk/Zaniewski, Materials for Civil and

Construction Engineers, Third Edition.

Copyright © 2011 Pearson Education, Inc.

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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

Mamlouk/Zaniewski, Materials for Civil and



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Aggregate Sizes • Coarse aggregate material retained

on a sieve with 4.75 mm openings

• Fine aggregate material passing a sieve with 4.75 mm openings

• Traditional – Maximum aggregate size – the

largest sieve size that allows all the aggregates to pass

– Nominal maximum aggregate size – the first sieve to retain some aggregate, generally less than 10%

• Superpave – Maximum aggregate size – one

sieve size larger than the nominal maximum aggregate size

– Nominal maximum aggregate size – one sieve larger that the first sieve to retain more than 10% of the aggregate

4.75mm

1”

#4 sieve =

four openings/linear

inch Mamlouk/Zaniewski, Materials for Civil and



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Aggregate Mining

Quarry

Sand from river deposit




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Aggregate Properties • Shape and texture • Soundness • Toughness • Absorption • Specific gravity • Strength and modulus • Gradation • Deleterious materials and cleanness • Alkaline reactivity • Affinity for asphalt

Typical source properties

Needed for PCC and HMA

mix design




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Particle Shape & Surface Texture

• Shape = angular, rounded, flaky, or elongated

• Flaky and elongated are bad because of easy breakage

and difficulty compacting in thin asphalt layers

– High friction (angular, rough) for strength & stability of

asphalt

– Low friction (rounded, smooth) for workability of concrete




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Angular Rounded Flaky

Elongated Flaky & Elongated




http://pavementinteractive.org/index.php?title=Image:Flat_elongated.jpg

http://pavementinteractive.org/index.php?title=Image:Flat_elongated.jpg

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Coarse Aggregates Particle Shape Evaluation

• Shape – Flat and elongated test

Flat and elongated device

Flat

Elongated

Flat and Elongated




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Coarse Aggregates Particle Shape & Surface Texture Evaluation

• Texture and angularity – fractured faces

• Visual inspection to determine the percent of aggregates with:

–no fractured faces

–one fractured face

–more than one fractured face




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Soundness & Durability Resist weathering

– water freezing in voids fractures & disintegrates aggregates

– Test method uses “salt solution” to simulate freezing

•Prepare sample

minimum mass

specified gradation

Soak the samples to magnesium

sulfate or sodium sulfate

solutions for 16 hrs – dry 4 hrs

Repeat cycle 5 times

Measure gradation

http://pavementinteractive.org/index.php?title=Image:Chemicals_and_basket.jpg

http://pavementinteractive.org/index.php?title=Image:Before_after_soundness_test.jpg

http://pavementinteractive.org/index.php?title=Image:Before_after_soundness_test.jpg

Toughness & Abrasion Resistance – Resist load damage

• During construction

• Traffic loads

– LA abrasion test

•Prepare sample

•Minimum mass original

•Specified gradation

•Charge drum w/ sample

•Steel spheres

•500 revolutions

•Sieve

Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc. 29

http://pavementinteractive.org/index.php?title=Image:Abrasion_equipment.jpg

http://pavementinteractive.org/index.php?title=Image:Before_after.jpg

http://pavementinteractive.org/index.php?title=Image:Before_after.jpg

http://pavementinteractive.org/index.php?title=Image:Abrasion.gif

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Bone dry –

dried in oven

to constant mass

Internal impervious voids

Air dry –

moisture condition

state undefined

Saturated surface dry –

moisture condition

state undefined

Moist –

moisture condition

state undefined

Voids partially filled

Ws Wm WSSD=Ws+Wp Wm

Free moisture

Moisture content

100s

sm

W

WWM

Absorption

100s

sSSD

W

WWM

Moisture content

100s

sm

W

WWM

Absorption is the moisture content when the aggregates are in the SSD condition

Free moisture is the moisture content in excess of the SSD condition.

A

Percent free moisture = M - A Important for proportioning concrete

negative free moisture – aggregates will absorb water

positive free moisture – aggregates will release water

Aggregate Moisture States

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Specific Gravity • The mass of a material divided by the mass of water whose volume is equal to the

volume of the material at a specific temperature, or

– G = r / rw

– rw = density of water at specified temperature

– @ 4C, rw is:

• 1000 kg/m3 = 1 g/ml = 1 g/cc

• 62.4 lb/ft3 (remember to stay consistent with force and mass units for

measurements and the issue of force and mass will go away as G is a ratio)

Mass Solid

Volume

Mass Water

Volume

G =




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Determining Specific Gravity

Mass Solid

Volume

Mass Water

Volume

Mass Solid

Mass Water

Mass Solid

Mass Water

Determine by weighing in air

Determine by

(weight in air - weight in water)




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Why Weight in Water?

Mass in air SG = Mass in air + Mass water - Mass in water

V = 400 ml

M = 400 g

+

V = 250 ml

M = 500 g

=

V = 650ml

M = 900 g

=

V = 400 ml

M = 650 g

-

V = 250 ml

M = 250 g

500 500 SG = = = 2 500+400 - 650 250

= value from

direct solution

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Effects of Voids

• Voids on the surface of aggregates create multiple definitions of specific gravity

–Apparent

–Bulk, Dry

–Bulk, SSD




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Apparent Specific Gravity

Gsa =

Mass, oven dry agg

Vol of agg

Apparent

Functional definition Volume of aggregate

Stone




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Bulk Specific Gravity, Dry

Gsb = Mass, oven dry

Vol of agg. + surface voids

Vol. of water-perm. voids

Surface Voids Functional definition

Bulk

Stone

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Bulk Specific Gravity, ssd (saturated surface dry)

Gs,bssd =

Mass, SSD

Vol of agg. + surface voids

Vol. of water-perm. voids

Surface Voids Functional definition

Bulk, saturated surface dry

Stone

Used for concrete

mix design

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Coarse Aggregate Specific Gravity by the Book

(ASTM C127)

Dry then saturate the aggregates

Dry to SSD condition and weigh

Measure submerged weight

Measure dry weight Mamlouk/Zaniewski, Materials for Civil and



http://pavementinteractive.org/index.php?title=Image:Casg.jpg

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Fine Aggregate Specific Gravity by the Book

(ASTM C128) Pycnometer used for FA

Specific Gravity

http://pavementinteractive.org/index.php?title=Image:Fasg.jpg

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Bulk Unit Weight & Voids in Aggregates

• Previous treatment of specific gravity and unit weight were for aggregate particles.

• The voids considered were for the voids at the surface of the particles.

• Sometimes we need to know the mass or weight of aggregate required to fill a volume, e.g. the volume of coarse aggregate in a cubic yard of concrete.

• Bulk unit weight is the weight of aggregate required to fill a “unit” volume. Typical units are cubic meters and cubic feet.




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Procedure Aggregate Bulk Unit Weight

• Loose

– Shovel dry aggregate into container

– Limit drop < 2” above rim of

container

– Strike off aggregate level with top of

container

– Determine weight of aggregate in

container, WS

– Compute unit weight

• Compacted

– Shovel dry aggregate into container

• Fill to 1/3 of volume

• Rod 25 times

• Repeat 3x to fill container

• Strike off aggregate level with top of

container

– Determine weight of aggregate in

container, WS

– Compute unit weight




Aggregate Gradation

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Aggregate Sizes (Review) • Coarse aggregate material retained

on a sieve with 4.75 mm openings

• Fine aggregate material passing a sieve with 4.75 mm openings

– Maximum aggregate size – the largest sieve size that allows all the aggregates to pass

– Nominal maximum aggregate size – the first sieve to retain some aggregate, generally less than 10%

4.75mm 1”

#4 sieve = four openings/linear inch

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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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Sieve Size

Per

cen

t P

assi

ng

0

100

Straight line identifies maximum

density aggregate blend

But a special scale is needed

for the size axis

0.45 Power Graph




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Types of Gradation on 0.45 Power Graph




48

This blend of

aggregates results in

the maximum

weight of

aggregates that can

be placed in a

container.




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Fineness Modulus

• a measure of the gradation fineness

• used for

– Concrete mix design

– daily quality control for concrete mix design

• Ri = cumulative percent retained on sieve sequence

• #100, 50, 30, 16, 8, 4, and 3/8“ sieves

• range of 2.3 - 3.1 for fine aggregate types larger FM being coarser

aggregate

100 iR

FM




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Blending Aggregate Gradations Stockpile aggregates with limited size range controls segregation – determine blend of stockpiles to meet

required control points. Trial & Error Method

Pi = Ai a + Bi b + Ci c….

For sieve size i,

Pi = percent in the blend that passes sieve size i

Ai, Bi, Ci … = percent of each stockpile in the blend

a, b, c … = percent of stockpile A, B, C that passes sieve size i

• Use spreadsheet program for trial and error calculations




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Cumulative passing (%) TS 802 Recommended limits

Sieve size SAND I SAND II Coarse aggregate mixture low limit high limit

22.4 100 100 100 100.0 89 96

16 100 100 65 80.8 73 86

8 100 100 25 58.8 54 71

4 100 100 0 45.0 37 56

2 76 67 0 32.0 25 43

1 54 41 0 21.1 16 32

0.5 36 27 0 14.0 10 22

0.25 21 11 0 7.0 6 15

0.15 10 5 0 3.3 3 10

100.0

80.8

58.8

45.0

32.0

21.1

14.0

7.0 3.3

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100

Cu

mu

lati

ve p

assi

ng

(%)

Sieve size (mm, log scale)

Sand I

Sand II

Coarse Aggr.

low limit

high limit

MIXTURE

MIXTURE SAND I : 20 % SAND II: 25 % C.A. : 55 %

Cleanness and Deleterious Materials • Deleterious Substances

– Organic impurities

– Minus 0.075 mm (No. 200)

–Coal, lignite, or other low density materials

– Clay lumps and friable particles

– Soft particles

• Sand Equivalency Test

SE = hsand / hclay x 100

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Alkali-Aggregate Reactivity

• Silica in some agg. reacts with the alkalis (Na2O, K2O) in Portland Cement (especially in warm, humid climates) – excessive expansion – cracking – popouts

• Carbonates in aggregate can also react to a lesser extent

• Minimizing reactivity if a reactive aggregate must be used – Type II cement – minimizes alkali

content of P.C. – Keep concrete as dry as possible Fly

Ash (Pozzolans) reduce alkali reactivity (not too much)

– Sweetening – add crushed limestone to the aggregate




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Alkali-Aggregate Reactivity

• Tests

– ASTM C227 – tests expansion potential of

cement-agg. combination

• expansion of mortar bar at specific temp. &

humidity

–ASTM C289 – reactive silicates in agg.

–ASTM C586 – reactive carbonates in agg. Mamlouk/Zaniewski, Materials for Civil and



Handling Aggregates • Minimize segregation, degradation, and contamination

• Avoiding Segregation – separation into components with similar characteristics

– any movement of aggregates promotes segregation

• small drop height

• build stockpiles in multiple cones

– fractionalize stockpiles

• close to single size aggregates in each stockpile

• batch separately

• Avoiding degradation – small drop height

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Sampling Aggregates

Random and representative of entire stockpile

– sample from entire width of conveyor belts at several locations

– sample from top, middle, and bottom of stockpile at several locations around stockpile diameter

– use larger sample for testing larger max. size

• Sample splitting or quartering

– to reduce sample size from large stockpile to small 1-5 kg sample

Sample Splitter

Quartering Mamlouk/Zaniewski, Materials for Civil and



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