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Chapter – 01; AGGREGATES

Aggregate

In civil engineering the term aggregate means a mass of crushed stone, gravel,

sand etc., predominantly composed of individual particles, but is some cases

including clays .The largest particle size in aggregates may have a diameter as

large as 150 mm (6 in., and the smallest particle can be as !ne as 5 to 10

microns.

There are two main uses of aggregates in Civil Engineering:

"s an underlying material for foundations and pavements

"s ingredients in #ortland cement and asphalt concretes.

Four General Sie Chara!teristi!s of Aggregates:

$ourse aggregates% "ggregate particles that are retained on &.'5 mm

sieve (o.&. " &.'5 mm sieve has openings e)ual to &.'5 mm bet*een

the sieve *ires. " o. & sieve has four openings per linear inch. The &.'5

mm sieve is the metric e)uivalent to a o. & sieve.

+ine aggregates% #articles that pass a &.'5 mm sieve (o. &

a-imum aggregate size% ne sieve size larger than the nominal

ma-imum aggregate size.

ominal ma-imum aggregate size% ne size larger than the !rst sieve to

retain more than 10 percent of the aggregates.

Aggregate Sour!es:

"atural Sour!es for aggregates include gravel pits, river run deposits,

and roc/ )uarries. enerally, gravel comes from pits and river deposits

*here as crushed stones are the result of processing roc/s from )uarries.

2sually, gravel deposits must also be crushed to obtain the needed size

distribution, shapes, and te-ture.

#anufa!ture$ aggregates can use slag *aste from iron and steel mills

and e-panded shale and clays to produced light*eight aggregates.

3eavy*eight concrete, used for radiation shields, can use steel slag and

bearings for aggregates. 4tyrofoam beads can be used as an aggregate

in light*eight concrete used for insulation. atural light *eight

aggregates includes pumice, scoria, volcanic cinders, tu, and diatomite.



Aggregate %roperties

&' %arti!le Shapes an$ Surfa!e Te(ture

T*o considerations in the shape of the material%

1. "ngularity. +la/iness

enerally, angular and rough7te-tured aggregates produced bul/ materials

*ith higher stability than rounded, smooth 8 te-ture aggregates. 3o*ever,

the angular aggregates *ill be more di9cult to *or/ into place than rounded

aggregates, since their shapes ma/e it di9cult for them to slide across each

other.

#article 4hapes of $oarse "ggregates

Te-ture of $oarse "ggregate

"ggregates *ith a rough te-ture are more di9cult to compact into a dense

con!guration than smooth aggregates. :ough te-ture generally improves

bonding and increase interparticle friction. In general, natural gravel and sand

have a smooth te-ture, *hereas crushed aggregates have rough te-ture. 4ince

stability of portland cement concrete is mostly developed by the cementingaction of the portland cement and by the aggregate interloc/, it is desirable to

use rounded and smooth aggregate particle to improve the *or/ability of fresh

concrete during mi-ing. 3o*ever, the stability of asphalt concrete and base

courses is mostly developed by aggregate interloc/. Therefore, angular and

rough particles are desirable for asphalt concrete and base courses in order to

increase the stability of the materials in the !eld.



#article 4hape and Te-ture of +ine "ggregate

The volume of the !ne aggregate is calculated by dividing the *eight of the !ne

aggregate by its bul/ density. The higher the amount of void content, the more

the angular and rougher *ill be the surface te-ture of the !ne aggregate.

&&' Soun$ness an$ )ura*ilit+

The ability of aggregate to *ithstand *eathering is de!ned as soundness or

durability. "ggregates used in various civil engineering applications must besound and durable, particularly if the structure is sub;ected to severe

climatic conditions.

In the #hilippines, *ater freezing is not a problem therefore, *e *ill not

discuss the soundness test ("4T $<<

&&& Toughness, -ar$ness, an$ A*rasion Resistan!e

The ability of aggregates to resist damaging eect of load is related to the

hardness of the aggregate particles and is describe as the toughness or

abrasion resistance.

The =os "ngeles abrasion test ("4T $1>1, $5>5 evaluates the aggregates

toughness and abrasion resistance. In this test, aggregates blended to a

!-ed size distribution and are placed in a large steel drum *ith standard

sized steel balls that act as abrasive charge.

The drum is rotated, typically for 500 revolutions. The material is recovered

from the machine and passed through a sieve that retains all material. The

percent *eight loss is the =" abrasion number. This is an empirical test that

is, the test results do not have a scienti!c basis and are meaningful only

*hen local e-perience de!nes acceptance criteria.

&&&' A*sorption

There is no speci!c level of aggregate absorption that is desirable for

aggregates used in portland cement concrete, but aggregate absorption



must be evaluated to determine the

appropriate amount of *ater to mi- into

the concrete.

"bsorption is also important for asphalt

concrete, since absorbed asphalt is notavailable to act as a binder, ma/ing the

mi- less economical. =o*7absorption

aggregates are desirable for asphalt

concrete.

.) / ?one @ry means the

aggregate contains no moisture

Air )r+ / The aggregates may have some moisture but thesaturation state is not )uanti!ed

SS) A 4aturated 4urface @ry condition, the aggregateBs void are !lled

*ith moisture but the main surface area of the particle is dry.

Cet A oist aggregates have moisture content in e-cess of the 44@

condition

Figure 1' Doids and moisture absorption of aggregates

The percent moisture content ($ in the aggregate can be calculated as%

4ample #roblem 1.1

" sample of sand has the follo*ing properties%

oist mass A 65. g

@ry mass A 5<E.E g

"bsorption A 1.6F



@etermine% (a Total moisture content, and (b free moisture content

&' Spe!i2! Gravit+

+our types of speci!c gravity are de!ned based on ho* voids in the

aggregate particles are considered. Three of these types are *idely

accepted%

"t present, there is no standard method for directly determining the

eective speci!c gravity of aggregates. The 2.4. $orps of Gngineers

has de!ned a method for determining the eective speci!c gravity of

aggregates that absorb more than .5F *ater.

Spe!i2! Gravit+ an$ a*sorption of Coarse Aggregates

Cith accordance to "4T $1'. In this procedure, a representative sample of

the aggregate is soa/ed for & hours and *eighed suspended in *ater. The

sample is then dried to the 44@ condition and *eighed. +inally, the sample is

dried to a constant *eight and *eighed. The speci!c gravity and absorption are

determined by

Spe!i2! Gravit+ an$ A*sorption of Fine Aggregates



Cith accordance *ith "4T $1<, a representative sample is soa/ed in *ater

for & hours and dried bac/ to the 44@ condition. " 5007g sample of the 44@

material is placed in a pycnometer, a constant volume Has/ *ater is added to

the constant volume mar/ on the pycnometer and the *eight is determined

again. The sample is then dried and the *eight is determined. The speci!c

gravity and absorption are determined by

&' 3ul4 5nit 6eight an$ oi$s in Aggregate

4ample problem 1.



$oarse aggregate is placed in a rigid buc/et and rodded *ith a tampering rod to

determined its unit *eight. The follo*ing data are obtained%

Dolume of buc/et A 1> ft>

Ceight of empty buc/et A 1<.5 lbs..

Ceight of buc/et !lled *ith dry rodded coarse aggregate A 55.E lbs.

a. $alculate the dry7rodded unit *eight

b. If the bul/ dry speci!c gravity of the aggregate is .6>0, calculate the

percent voids in the aggregate

"ns*er%

a. 11.> lb.ft> b. >1.5F

&&' Strength an$ #o$ulus

The strength if portland cement concrete and asphalt concrete cannot e-ceed

that of the aggregates. It is di9cult and rare to test the strength of aggregate

particles. $urrently, the test is mostly limited to research pro;ects.

&&&' Gra$ation

radation describes the particle size distribution of the aggregate. =argeaggregates are economically advantageous in portland cement and asphalt

concrete, as they have less surface area and, therefore, re)uire less binder.

4ieve "nalysis radation is evaluated by passing the aggregate through a

series of sieves.



Figure 1'7 4emi7log aggregate gradation chart sho*ing a gradation

e-ample

4ample #roblem 1.>

" sieve analysis test *as performed on a sample of !ne aggregate and

produced the follo*ing results%

$alculate the percent passing each sieve, and dra* a 0.&5 po*er gradationchart.

4ample #roblem 1.&

$alculate the !neness modulus of the sieve analysis results of sample

problem 1.>



Fineness #o$ulus

+ineness odulus is a measure of !ne aggregateBs gradation, and is used

primarily for portland cement concrete mi-. The !neness modulus is one7

hundredth of the sum of the cumulative percentage *eight retained. The

!neness modulus for !ne aggregate should be in the range of .> to >.1, *ith

a higher number being a coarser aggregate.

"ccording to the de!nition of !neness modulus, sieve .00 and 0.0'5 (o. 10

and 00 are not include in computing for !neness modulus of !ne aggregate.

&8' Cleanness an$ )eleterious #aterials

4ince aggregates are a natural product, there is the potential they can becontaminated by clay, shale, organic matter and other deleterious materials, such

as coal. " deleterious substance is any material adversely aects the )uality of

portland cement or asphalt concrete, deleterious substances are clay lumps, soft or

friable particles, and coatings. These substances decrease the adhesion bet*een

asphalt and aggregate particles.

The 4uperpave mi- design method re)uires use of the 4and G)uivalency test,

""43T TJ'6

8' Al4ali9Aggregate Rea!tivit+

4ome aggregates react *ith portland cement, harming the concrete structures. The

most common reaction is bet*een the active silica constituents of an aggregate and

the al/alis in cement. The al/ali7silica reactions results in e-cessive e-pansion,

crac/ing or pop7out in concrete.

Gvaluation for a potential al/ali7silica reactions%



1. +ield service history

. "4T $'

>. "4T $<E

&. "4T $5<6

$onstituents that can be added to reduced al/ali7silica reactivity%

1. +ly ash

. round granulated blast furnace slag

>. 4ilica fume

&. atural pozzolans

5. Keeping the concrete structure as dry as possible

6. :eplacing >0F of a reactive sand7gravel aggregate *ith crushed limestone

8&' Anit+ for Asphalt

"9nity means li/eness based on relationship or casual connection relationship by

marriage.

-)R.%-&<&C =water9loving> aggregates, such as silicates, have a greater

a9nity for *ater than for asphalt.

-)R.%-.3&) =water9repelling> aggregates have a greater a9nity for asphaltthan for *ater.

The mechanisms causing stripping are comple- and not fully understood .