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ce 4650 lec 11 Specific gavity
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Terms in this set (34)
Specific gravity
provides a relationship b/w mass and volume
- constant per specific material
SG weight indicator
Light weight < 2.4
Normal 2.4-2.8
Heavy >2.8
SG use
SG used as a tool to bridge b/w mass and volume
-Used to compute aggregate volume in Asphalt mis design
Bridge between mass and volume equation
G = (mass solid/volume)/(mass water/volume)
Sg formula
sg= weight of a unit volume of material/ weight of an equal volume of water at approximately 25C
G= mass/(volume*yw)
Density
Density = (yw) G
Each agg is made of
-mass
-Solid volume
>Pores: may or may not be accessible to water
Volume of agg particle
-Apparent volume(Vapp): volume of the solid mater and non accesible pores in the particle
-Bulk volume(Vbulk): Apparent volume plus the volume of the water accessible capilary pores
Mass of aggregate particles
-varies with moisture content
-stage of moisture content
Stages of moisture content
Wet
-aggregate is well soaked
-capillary pores saturated w/ water
-surface contains free moisture
Saturated Surface dry (SSD)
-aggregate is well soaked
-capillary pores saturated w/ water
-surface is dry (moisture wiped off)
air dry
-capillary pores are partially saturated
Oven dry (OD), (Dry)
-Capillary pores are dry
-place aggregate in oven to dry to constant weight
Weight of agg: SSD & Oven dry
Wssd: Weight of the aggregate particle in the SSD condition
Wod: Weight of agg particle in oven dry condition
Gxy
-x: indicates s for stone
-y indicates the volume type
-a: apparemt
-b:bulk
Mass Volume types
Mssd Mod
Vbulk Vapp
Gsb(OD)
Gsb(SSD)
Gsb(OD)=Wod/Vbulk
Gsb(SSD)=Wssd/Vbulk
Gsa(OD)
Gsa(SSD)
Gsa(OD)=Wod/Vapp
Gsa(SSD)=Wssd/Vapp
Water units
1gm = 1 cm^3
yw=1 g/cm^3
yw=62.4 lb/ft^3
volume measurements
-Volume is determined by volume of water it displaces
-Mass of water displaced by sample. Since 1 g water= 1 cm^3 water, this value also represents volume of water displaced by sample
Vbulk=(Wssd-Wsubmerged)/yw
Vapp=(Wod-Wsubmerged)/yw
Absorption
- absorption is single event
-Absorption%=(Wssd-Wod)/Wod*100
If absorption = 0
-There are no permeable pores
-Volumes are the same
-Gsb=Gse=Gsa
Moisture
-Moisture content is variable
-Moisture content%=(Ww-Wod/Wod)*100
Absorption/Moisture case 1
Mc> Abs
-There is a free surface moisture
-Free surface moisture= MC- Abs
Case 2
Mc<Abs
-The aggregate is in air dry condition
-Free moisture= (-) or <0
Case 3
MC=Abs
-Free moisture =0
3 types of agg SG: All have same mass,
Bulk specific gravity (Gsb)
Gsb
-Bulk Volume
-Vbulk=Overall volume of agg particle + the volume of permeable pores filled with water
-smallest G
Effective SG, Gse
Gse
-Effective volume
-excludes absorbed asphalt volume
Apparent SG, Gsa
-Apparent Volume
-Volume of aggregate particle
-Excludes absorbed water volume
Bulk SG
-SSD level: reached when the permeable pores are saturated and the surface is dry
-Gsb=(Dry mass/bulk vol)/1 g/cm^3
-=Ws/[Vs+Vpp] yw
apparent SG
-App volume = volume of solid agg particle only
-Gsa=(drymass/App vol)/1g/cm^3
-Gsa=Ws/([Vs]yw)
effective SG
-Eff vol=solid volume + volume of water permeable pores not filled with asphalt
Gse=Drymass/Eff vol/1g/cm^3
-Gse=Ws/{Vs+Vpp-Vap}*yw
Sg tests for aggs: Two test
-Specific gravity of coarse aggregate: retained on 4.75 mm sieve
-SG of fine agg: Passing the 4.75mm sieve
-Combine G's: weighted average
=p1+p2+p3/(p1/G1+P2/G2...
ASTM C127 coarse agg
-5kg on +no 4
-Dry agg to constant weight, soak in water 24 hours
-Determine weight under water= C
-use damp towel to get SSD condition
-Determine weight of SSD agg in bucket= B
-Dry to constant weight
-Determine oven dry mass= A
Coarse agg spec gravity
G=wt/V*yw
Gsb(Od)=A/(B-C)
A=weight of oven dry sample, gm
B=wt of sample in ssd condition
C=wt of SSD sample submerged in water, gm
Fine Agg SG: ASTM C128
A=wt of oven dry samp, gm
B=wt of pycnometer filled w/ water
C=wt of pycnometer, SSD aggregate, and water calibration to mark, mg
S=SSD agg wt
ASTM C128: dry agg until reaches SSD point
-dry mat slumps too much (<SSD)
-mat at SSD point will slump slightly
-Wet material does not slump at all
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