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Dr. Wasala Bandara
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Road Making Materials
Aggregate
Fine Course
Bitumen
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In road construction are
Crushed rock (from quarry)
Stream gravel
Concrete construction debris
Hard materials like broken pieces of tiles from tile industry
Slag (Slag is a waste product in metal extraction)
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Rock drill machines can be either hand held jack hammers or rig mounted
Jack hammers are light weight. They are
generally employed in drilling holes up to 38 mm
diameter and are powered by compressed air
Jack hammers
Handles
Hammer Head
Chuck
Drill Rod
Drill Bit
The main action of rock drills is to provide impact, thrust and rotation to a
drill rod attached to the drill
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Drilling rig
Can drill longer holes (100 m) with bigger diameter
(50mm, above 100 mm)
Rig mounted rock drills
The rig mounted rock
drills can be driven by
compressed air or by
hydraulic power.
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The rock cuttings are removed by flushing
Flushing is done by forcing water and/or
compressed air down the whole through
the drill rods and the drill bit
The cuttings are brought out of the hole
along the annular space between the drill
rod and the wall
Flushing medium also cools the bit during
drilling
Use of water in the flushing suppresses
the rock dust created in the process of
drilling
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The drilling machines can also be classified by theirdrilling actions into two main groups.
Drilling Machines
Percussiondrilling
machines
Rotary drillingmachines
Thrust, Impact
and Rotation
Only thrust and
rotation
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There are many types of drill bit used in rock drillingThe selection mainly depends on the drilling machine used, thediameter of the drilled holes and the required production rates
Chisel bit
Position of chisel bit
and the zone of rock
crushed at the first
impact
1st Zone of
crushed rock
Position of chisel bit
and the zone of
broken rock at the
second impact
2nd
Zone of
crushed rock
Position of chisel bit
and the zone of
broken rock at the
third impact
3
rd
Zone ofcrushed rock
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4-point cross-type bit Diamond bit
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Button bit
• Button bit diameters range from 100 mm to 225 mm
• Drill heads with many roller cutters are used for very large diameter drilling above
225 mm up to about 1500 mm
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Drilling Rates
• Dependent on:
•Rock Hardness
•Drill Type and Energy
•Type of Drill Bit
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Mixture of chemical compounds which rapidly decompose,instantly releasing large quantity of energy in form of
heated gas at a high pressure
An explosive should essentially contain a combustible
substance and an oxygen supplier
A good example is a mixture of carbon, sulphur and
sodium nitrate in black powder • Sodium nitrate provides oxygen
• Carbon and sulphur burn in oxygen and produce large
quantities of gases at high temperature and pressure
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List of ingredients in commercially available explosivesIngredients Chemical formula Function
Ethylene glycol dinitrate C2H4(NO3)2 Explosive base: lowers freezing point
Nitrocellulose (guncotton) C6H7(NO3)3O2 Explosive base; gelatinizing agent
Nitro-glycerine Nitrostarch C3H5(NO3)3
Explosive base
Explosive base; “non headache”
explosives
Trrinitroluene(TNT) C7H5N3O6 Explosive base
Metallic Powder Al
Fuel-sensitizer; used in high density
slurriesBlack Powder NaNO3+C+S Explosive base; deflagratesPentaerythritoltetranitrate
(PETN)C5H8N4O12
Explosive base; caps, detonating
cord
Ammonium nitrate NH4NO3 Explosive base; oxygen carrier
Liquid oxygen O2 Oxygen carrier
Sodium nitrate NaNO3Oxygen carrier; reduces freezing
point
Potassium nitrate KNO3 Oxygen carrier
Ground coal C Combustible, or fuelCharcoal C Combustible, or fuel
Paraffin CnH2n+ 2 Combustible, or fuel
Sulphur S Combustible, or fuel
Fuel oil (CH3)2(CH2)n Combustible, or fuel
Wood pulp (C6H10O5)n Combustible; absorbent
Lampblack C Combustible
Kieselguhr SIO2 Absorbent; prevents caking
Chalk CaCO3 Antacid
Calcium carbonate CaCO3 Antacid
Sodium chloride NaCl Flame depressant (permissibleexplosive)
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Rock blasting is carried out using explosives from two or more of the types
a) High power explosives
b) Detonators – plain or electrical
c) Blasting agents
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Velocity of Detonation (VOD)- How long it takes to get the chemical reaction
completed and energy released
Type of explosivesHigh explosivesHigh VOD, detonated with shock wave propagation associated with gas
expansion
For example: dynamite, water gels, emulsion
Low explosivesLow VOD, deflagrated with gas expansion onlyFor example: such as black powder
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• Detonators are used for the initiation of an explosivecharge
• They are made of high heat sensitive explosives and
can be set off by fire (flame)
•The explosion caused by them is capable of initiatingthe explosion of High explosives
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The blasting agents are cheap and safe to handle
FUSE WIRE
SHOT
EXPTODER
STEMMING
BLASTING
AGENT
(ANFO)
PRIMER
(Gelignite or
Dynamite)
DETONATOR
The safest blasting agent ANFO is a mixture of
ammonium nitrate and
fuel oil
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ANFO blasting agents
3NH4NO3 + CH2 →CO2 + 7H2O + 3N2+ heat
m.w. 3 (80.1gm) +(14gm) = 254.3gm
NH4NO3 = 94.5%
CH2 = 5.5%
ammonium fuel oil
nitrate
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hb = length of bottom charge
(qbk kg/m)
hp = length of
column charge
(qpk kg/m)
ho = length ofstemming
u = under drilling
1
3
VV V V V
K = Bench
Height
Free Face
V
E
E
E E
B = B e
n c h W i d t h
K Vertical height of bench in (m) ho Length of stemming (m)
B Bench width (m) hb Length of bottom charge (m)
V Practical burden (m) hp Length of column charge (m)
E Practical hole spacing (m) qbk Charge concentration of bottom charge (m)
u Depth of under drilling (m) qpk Charge concentration of column charge (m)H Length of entire hole (m)
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C - ground factor
d - blast hole diameter = × (m)
= 0.3 × (m)
1) Maximum burden ()
2) Under-drilling ()
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3) Length of entire hole (H)
= + (m) = ( + ) × 1.05 (m)
For vertical hole For inclined hole
K
H =
( K +
u )
u
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4) Faulty drilling factor (F)
= 0.05 + 0.03 × (m)
5 cm setting error
Hole with 5 cm setting error
Hole with 5 cm setting error
+ 3% deviation (worst
possible)
F = FAULTY DRILLING FACTOR
F=.05+.03H
Vmax
Vmax
Intended hole
V
Hole should
start here
V = Vmax - F
H
F
5) Practical burden (V)
= (m)
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6) Practical hole spacing (E)
= 1.25 × (m)
7) Length of stemming (ℎ)
ℎ = (m)
8) Length of bottom charge (ℎ)
ℎ = 1.3 × (m)
9) Length of column charge (ℎ)
ℎ = (ℎ + ℎ) (m)
Inert material
(rock dust, sand,
clay, saw dust)
Explosive
Explosive
Stemmingh0
hp
hb
H
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10) Density of bottom charge (): is in meters
= .4
4 × × (kg/m) P- Density of explosive (kg/m3)
11) Density of column charge ()
= 0.5 × (kg/m)
12) Total bottom charge per hole ()
= × ℎ (kg)
13) Total column charge per hole ()
= × ℎ (kg)
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14) Total charge per hole ()
= + (kg)
15) Specific charge q
Specific charge =
× × (kg/m3)
16) Specific charge
Specific charge =
× × ×(−)(kg/m3)
Where KxVxE is the volume of rock broken per hole
Generally for bench blasting q is around 400 g/m 3
Where KxVxEx(nbh-1) is the total volume of rock broken per blast. Also note that B=E X (nbh-1)
hb = length of bottom charge
(qbk kg/m)
hp = length of
column charge
(qpk kg/m)
ho = length of
stemming
u = under drilling
1
3
V V V V V
K = Bench
Height
Free Face
V
E
E
E E
B = B e
n c h W i d t h
The specific charge for the whole blast with nbh holes per row given by:
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Crushing is necessary to reduce further the size of particles
created by blasting
The blasting products vary in size from large boulders to fine
fragments
Large boulders are subject to secondary blasting and therock less than 1200mm can be reduced in size by crushing
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Crushers
Hammer
mills
Jaw
crushers
Gyratory
crushers
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A Hammer mill consists of heavy steel hammers hung bysteel chains or steel plate
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The crushing action takes place
between two jaws with manganesesteel liners
One jaw is fixed while the other is
movable.
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Jaw crushers are used, where crusher gape is
more important than the capacity
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Gyratory crushers on the other hand have low tendency toproduce flaky and elongated products. The crushing
surfaces are curved.
It consists of a conical, suspended crushing head
Gyratory crushers are used, where high capacity
is required
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Jaw crusher Gyratory crushers
Crushes on half cycle Crushes on full cycle
Installation cost is high Installation cost is low
Capital & Maintenance cost isless
Capital & Maintenance cost ismore
Perform better on clayey,
plastic material
Particularly suitable for hard,
abrasive material
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40Bins
Feed
R o t a t i n g D r u
m
Perforations
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The quality of an aggregate is affected by the production
process in that:
(a)Decomposed or inferior rock can find its way into the crushers, which can
be eliminated by screening. If a considerable amount of clay is present
washing of the aggregates may be necessary. Contamination affects both
strength and adhesive qualities of aggregates.
(b)Higher reduction of the crushing plant can result in flaky or elongated
particles. The reduction ratio is the ratio of the size of feed to the size of
product. Experience shows that reduction ratio should be less than 4%.
(c) Excess of undersize materials can be caused by overloading the screens.
Flaky and elongated aggregates can contain more fines (undersize) than
the cubical aggregates.
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Fine Aggregate
aggregate particles mainly between the 4.75 mm size and the 75um sieveCoarse Aggregate
aggregate particles mainly larger than 4.75 mm
Pit Run
aggregate from a sand or gravel pit with no processing
Crushed Gravel
pit gravel (or sand) that has been put through a crusher either to break therounded gravel particles into smaller sizes or to produce rougher surfaces
Crushed Rock
aggregate from the crushing of bedrock. All particles are angular and not
rounded as in gravel
Screenings
chips, dust, powder that are produced from crushingConcrete Sand
sand that has been washed to remove dust and fines
Fines
silt, clay, or dust particles smaller than 75um usually the undesirable
impurities in aggregates
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The aggregates used in pavement construction should have
the following qualities:a) Hard (strength) enough to withstand the load of traffic and rolling equipment
b) Resistant to abrasion and weathering
c) Non slipping (skid resistance)
d) Angular (friction between particles)
e) Well graded (packing)
Aggregate Testing
Descriptive test Non-destructive test Durability test
A visual examination of an aggregate
and then describing the shape of and
the surface texture of the particles
• Rounded
• Irregular
• Angular
• Elongated
• Gradation testso sieve analysis
• Shape testso Flakiness index
o Elongation index
• Abrasion testso The aggregate abrasion test
o The accelerated polishing test
• Toughness testso Aggregate crushing test
o Ten percent fines test
o Aggregate impact testo Specific gravity test
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FlatElongated Angular Round
A visual examination of an aggregate and then describing the shape of and the surface texture of the particles
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A process in which an aggregate is
separated into its various sizes by
passing it through screens of various size
openings for the purpose of determining
the distribution of the quantities
separated
BS 812-103.1:1985
Sieve tests (BS 812-103.1:1985)
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Importance of sieving Grain size distribution for highway bases and asphalt mixes that will
provide a dense strong mixture
Ensure that the voids between the larger particles are filled with
medium particles. The remaining voids are filled with still smallerparticles until the smallest voids are filled with a small amount of fines.
Ensure maximum density and strength using a maximum density curve
The gradation controls the amount of binder used and
tight compaction of the aggregate
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Apparatus
sample divider- Appropriate to the
maximum particle size to be handled
ventilated oven - Thermostatically
controlled to maintain a temperature of105 ± 5 °C.
A balance - Suitable capacity
accurate to 0.1 % of the mass of
the test portion
A mechanical sieve shaker
Test sieves
Trays & Containers
BS 812-103.1:1985
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Test sieves
BS 812-103.1:1985
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Procedure
Part 1 - Washed sieve analysis Dry aggregate and determine mass
Wash and decant water through 0.075 mm sieve until water is clear
Dry aggregate to a constant mass
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Procedure
Part 2 - Mechanical sieve analysis Place dry aggregate in standard stack of sieves
Place sieve stack in mechanical shaker
Determine mass of aggregate retained on each sieve
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Computation
Sieve Mass Cumulative
(mm) Retained Mass Retained % Retained % Passing
(g)
9.5
4.75
2.36
1.18
0.60
0.30
0.150.075
Pan
0.0
6.5
127.4
103.4
72.8
64.2
60.083.0
22.4
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Computation
% Passing = Cum. Wt Retained
Original Dry Wt.* 100% Retained =
Cum. Wt Retained
Original Dry Wt.* 100 [ 1 - ]
Sieve Mass Cumulative
(mm) Retained Mass Retained % Retained % Passing
9.5
4.75
2.36
1.18
0.60
0.300.15
0.075
Pan
0.0
6.5
127.4
103.4
72.8
64.260.0
83.0
22.4
0.0
6.5
133.9
237.3
310.1
374.3
434.3
517.3
539.7
0.0
1.2
24.8
44.0
57.5
69.480.5
95.8
100.0
100.0
98.9
75.2
56.0
42.6
30.619.5
4.2
0.0
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Computation
Chart for recording sieve analysis results
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Computation
BS 812-103.1:1985
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Computation
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Computation
The coefficient of uniformity ,Cu is a crude shape parameter
The coefficient of curvature, Cc is a shape parameter
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Flakiness Index (BS 812-105.1:1989)
Flaky is the term applied to aggregate or chippings that are flat and thin
with respect to their length or width
Aggregate particles are classified as flaky when they have a thickness(smallest dimension) of less than 0.6 of their mean sieve size
The test is n ot app l icable to mater ial passing a 6.30mm BS test sieve or
retained on a 63.0mm BS test s ieve
Thickness gauge =3
5
Average sieve size
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Apparatus
A sample divider -Size appropriate to the
maximum particle size
to be handled
ventilated oven - Thermostatically
controlled to maintain a temperatureof 105 ± 5 °C.
A balance -
Suitable capacity
accurate to 0.1 %
of the mass of the
test portionA mechanical sieve shaker
Test sieves
Trays & Containers
A metal thickness gauge - The gauge
shall be made from1.5mm thickness
sheet steel
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BS 812-105.1:1989
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Procedure Carry out a sieve analysisDiscard all aggregates retained on the 63.0mm test sieve and all aggregate passing the
6.30mm test sieve
Weigh each of the individual size-fractions retained on the sieves,
other than the 63.0mm BS test sieve, and store them in separate
trays
From the sums of the masses of the fractions in the trays (M1),
calculate the individual percentage retained on each of the various
sieves. Discard any fraction whose mass is 5% or less of mass M1. Record the
mass remaining (M2 )
Gauge each fraction by Using the gauge, select the thickness gauge
appropriate to the size-fraction under test and gauge each particle of
that size-fraction separately by hand
Combine and weigh all the particles passing each of the gauges (M 3)
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Computation
Flakiness index =M3M2
M2- Total weight of the sample taken (greater than 5 % of the total mass)
M3- Total weight of passing through various thickness gauge
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ComputationSize of aggregate Weight of material Flaking Index
(%)
(individual
size)
BS test sieve nominal aperture sizeTotal
Retainedthickness
gauge
Passingthickness
gauge100% passing 100% retained
63.0 50.0
50.0 37.5
37.5 28.0
28.0 20.0
20.0 14.0 732.2 613.9 118.3
14.0 10.0 1166.5 1095.2 71.3
10.0 6.3 542.0 463.7 78.3
Total 2440.7 2172.8 267.9
Flakiness index =Total weight of material passing through various thickness gauge
Total weight of the sample taken (greater than 5 % of the total mass)
Flakiness index =267.9
2440.7X 100%
Flakiness index = 11%
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Elongation Index (BS 812-105.2:1990)
Aggregate particles are classified as elongated when they have a length
(greatest dimension) of more than 1.8 of their mean sieve size
The test is not applicable to material passing a 6.30 mm test sieve or retained ona 50.0 mm test sieve
Thickness gauge =9
5Average sieve size
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Apparatus
A sample divider -Size appropriate to the
maximum particle size
to be handled
ventilated oven - Thermostatically
controlled to maintain a temperatureof 105 ± 5 °C.
A balance -
Suitable capacity
accurate to 0.1 %
of the mass of the
test portionA mechanical sieve shaker
Test sieves
Trays & Containers
Metal length gauge
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Preparation of test portion
Reduce the sample by the procedures described in clause 6 of BS812-
102:1989 to produce a test
Allowance for the later rejection of particles retained on a 50.0mm test
sieve and passing a 6.30mm test sieve
Dry the test portion by heating at a temperature of 105 ± 5°C to achieve a
dry mass which is constant to within0.1%. Allow to cool and weigh
Minimum mass of test portion
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Procedure
Carry out a sieve analysisDiscard all aggregates retained on the 50.0mm test sieve and all aggregate passing the
6.30mm test sieve
Weigh each of the individual size-fractions retained on the sieves,other than the 50.0mm test sieve, and store them in separate trays
From the sums of the masses of the fractions in the trays (M1),
calculate the individual percentage retained on each of the various
sieves. Discard any fraction whose mass is 5% or less of mass M1. Record themass remaining (M2 )
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Procedure
Gauge each fraction as follows. Select the length gauge appropriate
to the size fraction under test and gauge each particle separately by
hand
Elongated particles are those whose greatest dimension prevents
them from passing through the gauge, and these are placed to one
side
Combine and weigh all the particles remaining each of the gauges
(M 3)
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Computation
Elongation index =M3M2
M2- Total weight of the sample taken (greater than 5 % of the total mass)
M3- Total weight of martial retained on various length gauges
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Computation
Size of aggregate Weight of materialFlaking Index
(%) (individual
size)
BS test sieve nominal aperture sizeTotal
Retained length
gauge100% passing 100% retained
50.0 37.5
37.5 28.0
28.0 20.0
20.0 14.0 732.2 613.9
14.0 10.0 1166.5 1095.2
10.0 6.3 542.0 463.7
Total 2440.7 2172.8
Elongation index = Total weight of martial retained on various length gauges
Total weight of the sample taken (greater than 5 % of the total mass)
Elongation index =2172.8
2440.7X 100%
Elongation index = 89%
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Calculate the flakiness index and the elongation index of the aggregatesample shown in Table 1.
Sieve size (mm)Weight retained
(g)
Weight passing
through
Flakinessgauge (g)
Weight not retainedelongation gauge (g)100% passing
100%Retained
63.0 50.0 516550.0 37.5 4356 683 4256
37.5 28 3526 558 3301
28 20 2215 447 2058
20 14 1154 640 1029
14 10 570 128 481
10 6.3 350 63 326
AASHTO: T 85 (1996)
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This procedure covers the determination of specific gravity andabsorption of coarse aggregate in accordance with AASHTO: T 85
(1996)
Absorption – the increase in the mass of aggregate due to water being
absorbed into the pores of the material, but not including water adhering to the
outside surface of the particles, expressed as a percentage of the dry mass
Specific Gravity – the ratio of the mass, in air, of a volume of a material to the
mass of the same volume of gas-free distilled water at a stated temperature
Specific gravity is critical information for the Hot Mix Asphalt Design
Engineer. The value is used in calculating air voids, voids in mineral
aggregate (VMA), and voids filled by asphalt (VFA)
AASHTO: T 85 (1996)
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Moisture Conditions of Aggregates:
1. Oven dry- fully absorbent
2. Air dry- dry at the particle surface but containing some
interior moisture
3. Saturated surface dry (SSD) – neither absorbing water nor
contributing water to the concrete mixture
4. Wet or moist- containing an excess of moisture on thesurface
AASHTO: T 85 (1996)
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AASHTO: T 85 (1996)
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Apparatus
ventilated oven - Thermostatically
controlled to maintain a temperature
of 105 ± 5 °C.
Balance
Sample container
Suspension apparatus
with Water tank
Sieves
AASHTO: T 85 (1996)
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Procedure
Thoroughly mix the sample of aggregate and reduce it to the approximatequantity needed using the applicable procedures in T 248
Reject all material passing a 4.75-mm (No. 4) sieve by dry sieving and
thoroughly washing to remove dust or other coatings from the surface
Preparation of test portion
Dry the test sample to constant mass at a temperature of 110 ±5°C and cool
in air at room temperature for 1 to 3 hours. 2
Sink the aggregate in water at room temperature for a period of 15 to 19
hours
Remove the test sample from the water and roll it in a large absorbent cloth
until all visible films of water are removed (Wipe the larger particles individually)
AASHTO: T 85 (1996)
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Procedure
Determine the saturated surface dry (SSD) weigh of the sample (Designate
this mass as “B”)
Place the SSD test sample in the sample container and weigh it in water
maintained at 23.0 ±1.7°C (Shake the container to release entrapped air
before recording the weight) (Designate this submerged weight as “C”)
Remove the sample from the basket. Ensure all material has been removed
and place in a container of known mass
Dry the test sample to constant mass at a temperature of 110 ±5°C about
24hrs (Designate this mass as “A”)
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Bulk Dry Specific Gravity =A
(B-C)
A - Oven dry weight B = Saturated surface dry (SSD) weight C = Weight in water
Computation
Bulk Dry Specific Gravity
The ratio of the weight in air of a unit volume of aggregate at a stated
temperature to the weight in air of an equal volume of gas-free distilled water at
a stated temperature
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Bulk SSD Specific Gravity =B
(B-C)
B = Saturated surface dry (SSD) weight C = Weight in water
Computation
Bulk SSD Specific Gravity
The ratio of the weight in air of a unit volume of aggregate, INCLUDING the
weight of water within the voids filled to the extent achieved by submerging in
water for approximately 15 hours, to the weight in air of an equal volume of gas-
free distilled water at a stated temperature
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Apparent Specific Gravity =A
(A-C)
A - Oven dry weight C = Weight in water
Computation
Apparent Specific Gravity
The ratio of the weight in air of a unit volume of aggregate at a stated
temperature to the weight in air of an equal volume of gas-free distilled water at
a stated temperature
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Computation
Absorption
The increase in weight of aggregate due to water in the pores of the material, but
not including water adhering to the outside surface of the particles
Absorption = (B- A)
A
A - Oven dry weight B = Saturated surface dry (SSD) weight
X 100 %
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Bitumen is a black, oily, viscous material that isa naturally-occurring organic byproduct of decomposed organic materials.
It is sticky, thick, Tar like form of petroleum
derived from polycyclic aeromatic hydrocarbon
83
General uses of Bitumen:
• Constructions of roads, runways and platforms
• Water proofing to prevent water seepage
• Canal lining to prevent erosion• Dump-proof courses for masonry
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Petroleum based bitumen (refinery bitumen) is largely
used in road construction in Sri Lanka
In the petroleum refinery
process in which the
residuum contains largely
the refinery bitumen
Bitumen
Bitumen
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Asphalts Tars Pitches
Natural
deposits
Petroleum
asphalts
Slow
curing
Medium
curing
Rapid
curing
Emulsifiers Stabilizer Rubber
Rock
asphalt
Native
asphalt
Asphalt
cement
Cut back
bitumen
Bitumen
Emulsion
Asphalts Tars Pitches
Natural
deposits
Petroleum
asphalts
Slow
curing
Medium
curing
Rapid
curing
Emulsifiers Stabilizer Rubber
Rock
asphalt
Native
asphalt
Asphalt
cement
Cut back
bitumen
Bitumen
Emulsion
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The most common bituminous materials are, as follows:
Asphalts (available as natural deposits or areproduced from petroleum processing)
Tars (obtained through the destructive distillation ofmaterials such as wood, coal, and shale, i.e., byheating wood or coal or shale in absence of air)
Pitches (obtained through further processing of tars)
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Asphalt cement (also called paving asphalt) are theprimary asphalt products produced by the distillation of crude oil.
At ambient temperatures asphalt cement is a black, sticky,semisolid and a highly viscous material
It is strong and durable cement with excellent adhesive andwaterproofing characteristics. It is also highly resistant tothe action of most acids, alkalis and salts
The largest use of asphalt cement is in the production of asphalt concrete, which is primarily used in the
construction of flexible pavements throughout the world The asphalt cement can readily be liquefied by applying
heat for mixing with mineral aggregates to produce asphaltconcrete
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Several standard grades of asphalt cement, based onconsistency, are available commercially
Two methods, viscosity and penetration are used toclassify asphalt cements into different grades, as follows:
The viscosity grades based on original asphalt cements(AC), as specified in ASTM D3381 are: AC – 5; AC – 10; AC –20; AC – 30; and AC – 40 (The numerical values indicateviscosity at 140 ºF in hundreds of poise)
The penetration grades, as specified in ASTM D946 are:200-300; 120-150; 85-100; 60-70; and 40-50 (higher thepenetration, the softer the asphalt cement, therefore, 40-50 isthe hardest grade and 200-300 is the softest grade
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Liquid asphalts or cutback asphalts are asphaltcements mixed with a solvent to reduce their viscosity to make them easier to use at ordinarytemperatures
They are commonly heated and then sprayed onaggregates
Upon evaporation of the solvent, they cure or hardenand cement the aggregate particles together
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Types and grades, as given below, are based on the type of solvent, which governs viscosity and the rates of evaporationand curing
Rapid-Curing (RC) - Produced by adding a light diluent of high volatility (generally gasoline or naphtha) to asphalt cement.These are used primarily for tack coat and surface treatments
Medium-Curing (MC) - Produced by adding a mediumdiluent of intermediate volatility (generally kerosene) to asphaltcement. These are generally used for prime coat, stockpilepatching mixtures, and road-mixing operations
Slow-Curing (SC) - Produced by adding oils of low volatility(generally diesel or other gas oils) to asphalt cement. They arealso called road oils. They are generally used for prime coat,stockpile-patching mixtures, and as dust palliatives
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Cutback asphalts are commercially available in differentgrades, as shown in the following Fig.:
A viscosity of 30 is more fluid than a viscosity of 3000
Prime coat is a coating applied directly to a prepared base before additional layers of support or coating are supplied. Prime coat asphalt preparation is a vital element, as itdirectly affects the shear strength of the final asphalt product.
Tack coat is applied after the prime coat, to form an adhesive bond between the tackcoat and the next layer of coating
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Emulsified asphalts are increasingly being used in lieu of cutback asphalts for the following reasons:
Environmental regulations: Emulsions are relativelypollution free
Loss of high-energy products: When cutback asphaltscure, the diluents which are high energy, high price
products are wasted into atmosphere Safety: Emulsions are safe to use
Lower application temperature: Emulsions can beapplied at relatively low temperatures saving the fuel
costs. Emulsions can also be applied effectively to adamp pavement, whereas dry conditions are required for cutback asphalts
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Emulsified asphalt (also simply called emulsion) is a mixture of asphalt cement, water, and emulsifying agent
Because the asphalt cement will not dissolve in water,asphalt cement and water exist in separate phases asshown in the following figure:
To mix the asphalt cement with water, an emulsifying
agent (usually a type of soap) is added
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1. Colloid mill Method
2. High speed mixing method
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Process of manufacture of emulsified asphalt consists passing
the hot asphalt cement and water containing the emulsifyingagent under pressure through a colloid mill method
• The colloid mill breaks up
the asphalt cement and
disperses it, in the form of
very fine droplets, in thewater carrier
• The emulsified asphalt when
used, the emulsion sets as
the water evaporates
• The emulsion usually
contains 55-75% asphalt
cement and up to 3%
emulsifying agent, with
balance being water
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High speed mixing is a batch process in which hot
bitumen, hot water, emulsifier, and stabilizer are added
into a vessel and agitated using a high speed agitator
Bitumen
+
Water +
Emulsifier
+
Stabiliser
High speed
rotation
Agitator
Vessel
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Two most commonly used types of emulsified asphalts are
specified in ASTM D977 and ASTM D2397:
Anionic – electro-negatively charged asphalt droplets
Cationic – electro-positively charged asphalt droplets
Anionic emulsions adhere better to aggregate particleswith positive surface charges (e.g., limestone)
Cationic emulsions adhere better to aggregate particleswith negative surface charges (e.g., sandstone, quartz,siliceous gravel). Cationic emulsions also work better withwet aggregates and in colder weather
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Structure of Cationic Bitumen Emulsion
Asphalt particles have positive charge
Adhere better with negative particles (e.g., sandstone, quartz, siliceous
gravel)
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The anionic emulsified asphalts include Rapid Setting (RS),
Medium Setting (MS)
Slow Setting (SS)
as specified in ASTM D977
The cationic emulsified asphalts include
Rapid Setting (CRS)
Medium Setting (CMS)
Slow Setting (CSS)
as specified in ASTM D2397
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Selection and uses of emulsified asphalts are given in ASTMD3628. Generally, they are used as follows:
Type of emulsified
asphaltsUses
Rapid-setting Surface treatments and penetrationmacadam's
Medium-setting Open-graded cold asphalt-aggregate
mixtures
Slow-setting Track coat, fog seal, dense-graded coldasphalt-aggregate mixtures, and slurry
seals
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The amount of emulsifiers used in bitumen emulsions isbetween 0.5 to 1.0 %, which is just sufficient to preventcoagulation of globules
However, in some applications it is necessary to providebetter protection against coagulation
In such a case it is necessary to add a stabilizer, which canbe done during the manufacture of the emulsion or at alater stage
Commonly used stabilizers are casein and the potassium
soaps of tall oil (a liquid resin) or Vinsol resin
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Emulsions are classified into three groups according to theresistance to coagulation as follows
Labile emulsifiers – contain a minimum of emulsifierand moderately stable
Semi stable emulsions – are more highly stabilized
Fully stable emulsions – contain very highproportion of stabilizer
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A recent development in bitumen technology is the addition ofrubber to the bitumen mixtures to improve the performance of
resulting bitumen mixture
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Favourable effects of the presence of rubber in bituminousmaterials are:
1. A mixture of rubber – bitumen provides aggregate binding facility
2. Rubber bitumen reduces sensitivity to temperature changes of thebitumen.
3. Rubber increases softening point, viscosity, elasticity and cohesion
4. Loss of lighter fractions in bitumen though weathering is retarded
5. Bitumen mixtures containing rubber are more resilient and thereforecan absorb vibrations and traffic shock
6. Addition of vulcanized rubber in bitumen mixture can reduce reflectioncracking.
7. Adding 5.5 to 7.0 % rubber by weight of bitumen can reduce surfaceki i ld t t