CE 308 - Lec 5 - Aggregates
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Transcript of CE 308 - Lec 5 - Aggregates
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MILITARY COLLEGE OF ENGINEERING
RISALPUR
CE 308 – PRC I - LECTURE 5
AGGREGATES
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AGGREGATE
According to ASTM 25 and D8: Aggregate is the granular
material, such as sand, gravel, crushed stone, crushed blast-furnaceslag, or construction and demolition waste that is used with a
cementing medium to roduce either concrete or mortar!
Coarse aggregate - articles larger than "!#5 mm $%o! " sieve& Fine aggregate - articles smaller than "!#5 mm but larger than
#5 'm $%o! 2(( sieve& ) *+cet Mass oncrete ) in $.5( mm&
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Aggregates ma/ divided into two categories deending on the
source : %atural aggregate
Artificial aggregate
%atural aggregates are usuall/ derived from natural sources andma/ have been naturall/ reduced to si0e $e!g! gravel or shingle& or
ma/ have to be reduced b/ crushing!
The most widel/ used artificial aggregates are clean bro1en bric1s
and air-cooled fresh blast-furnace-slag!
DEPENDING ON SOURCE
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DEPENDING ON SOURCE
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DEPENDING ON SOURCE
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SPECIFIC GRAVITY OF ROCKS
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ON BULK DENSITY
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ON BULK DENSITY
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ON SHAPE
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STRENGTH
The strength of concrete cannot e+ceed the strength of the
aggregate! n ractice, concrete strength is li1el/ to be much less than
the strength of the aggregate, because stress concentrations
are generated at the aggregate- cement aste interface
$nterfacial Transition 3one, T3& when stress is alied onconcrete!
4ea1 aggregates ma/ brea1 down during mi+ing, handling
and comaction!
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STRENGTH
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ABSORPTION AND POROSITY
The internal ore characteristics are ver/ imortant roerties of
aggregates! The si0e, the number , and the continuit/ of the ores through an aggregate article ma/ affect the strength of theaggregate, abrasion resistance, surface te+ture, secific gravit/,
bonding caabilities, and resistance to free0ing and thawing action!
Absortion relates to the articles abilit/ to ta1e in a li6uid!
7orosit/ is a ratio of the volume of the ores to the total volumeof the article!
7ermeabilit/ refers to the articles abilit/ to allow li6uids to ass through! f the roc1 ores are not connected, a roc1 ma/ havehigh orosit/ and low ermeabilit/!
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POROSITY AND PERMEABILITY
An aggregate can be ver/ orous but ver/ less ermeable
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ABSORPTION AND POROSITY
9ul1 Densit/ is the weight er unit of volume of a substance!
Secific gravit/ is the ratio of the densit/ of the substance to thedensit/ of water !
Moisture ontent is defined as the water in e+cess of the
saturated and surface-dr/ conditions!
Thus, the total water content of a moist aggregate is e6ual to thesum of absortion and moisture content!Aggregate e+osed to rain collects a considerable amount of
moisture on the surface of the articles, and, e+cet at the surface
of the stoc1ile, 1ees this moisture over long eriods!This is articularl/ true of fine aggregate, and the moisture
content must be allowed for in the calculation of batch 6uantities
and of the total water re6uirement of the mi+ during mi+ design!
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ABSORPTION
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ABSORPTION
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ABSORPTION
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BULKING OF SAND
n the case of sand, there is another effect of the resence of
moisture i!e! bul1ing, which is an increase in the volume of a given
mass of sand caused b/ the films of water ushing the sand
articles aart! 9ul1ing of sand affects the roortioning of materials b/
volume! n volume batching, bul1ing results in a smaller mass of sand
occu/ing the fi+ed volume of the measuring bo+!
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SOUNDNESS
A sound aggregate is able to resist stresses induced b/
environmental or climatic conditions! Some aggregates degrade or disintegrate under the action of
c/cles of free0ing and thawing or salt weathering! Suscetible aggregates are usuall/ micro orous, that is, the/
have high absortion arising from a large roortion of fine ores!
ree0ing or salt cr/stalli0ation can induce considerable
stresses in fine ores that ma/ lead to degradation!
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SOUNDNESS TEST
The Soundness Test determines
the resistance of aggregates to
disintegrate when e+osed to
solutions of Sodium Sulhate and
Magnesium Sulhate!
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IMPURITIES
Impurity Effect on fresh concrete Effect on hardened concrete
Chlorides Accelerate the set Damp patches and efflorescence
Sulfates Interference with hydration Cracking and spalling
Shells Reduce workability Damage to surface finish
Acid solublematerial in sand
NoneReduced skid resistance ofpavement
quality concreteAlkali reactivesilica
None Risk of alkali–silica reaction
Swelling clays Increased water demand Reduced strength
Reactive ironpyrites
ossible reduced yield !urface staining
Mica Increased water demand Reduced strength
Organic matter ossible retardation ossible reduced strength
Coal and lignite ossible retardation !urface staining" pop#outs
Soluble lead or
incossible retardation ossible reduced strength
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REACTIVE AGGREGATES
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REACTIVE AGGREGATES
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OTHER REQUIREMENTS
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