SpecificGravity(RelativeDensity)ofaBlendedAggregateThespecificgravityofablendedaggregate isnotsimplytheweightedaverageofthespecificgravitiesoftheindividualcomponents.Toderiveanappropriateequation,letsassumeablendoftwoaggregates(AandB).Theweightoftheblendisgivenby

blend A BW W W andthevolumeoccupiedbytheindividualparticlesoftheblendisgivenby

blend A BV V V Theweightandvolumeoftheaggregateparticlesarerelatedthroughspecificgravity:

agg

aggs w

WV

G

LetGA,GB,andGblendbe the specific gravitiesofmaterialsA andB and theblend.Then thevolumeequationabovecanberewrittenas

blend A B

blend w A w B w

W W WG G G

MultiplyingthroughbywanddividingthroughbyWblendleaves

1 A blend B blendblend A B

W W W WG G G

If the aggregate is being blended by weight, then WA/Wblend is the fraction of the blendcontributedbymaterialA(call itfA)andWB/Wblend isthefractionoftheblendcontributedbymaterialB(callitfB).Theequationabovecanthereforebewrittenas

1 A Bblend A B

f fG G G

So the inverse of the specific gravity of the blend is equal to theweighted average of theinversesofthespecificgravitiesofthecomponents.Forexample,of25%MaterialAand75%MaterialBhasaspecificgravitygivenby

1 0.25 0.75blend A BG G G

Whatwouldhappenifweblendtheaggregatebyvolumeinsteadofweight?