Highway Engineering Design_Material Testing

8/17/2019 Highway Engineering Design_Material Testing

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Dr. Wasala Bandara

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Road Making Materials

Aggregate

Fine Course

Bitumen

2


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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)

3


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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


and the zone of

broken rock at the

second impact

2nd

Zone of

crushed rock


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

BS 812-103.1:1985


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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

BS 812-103.1:1985


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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

BS 812-103.1:1985


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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

BS 812-103.1:1985


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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

BS 812-103.1:1985


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Computation

Chart for recording sieve analysis results

BS 812-103.1:1985


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Computation

BS 812-103.1:1985


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Computation

BS 812-103.1:1985


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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

BS 812-105.1:1989


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Apparatus

A sample divider -Size appropriate to the

maximum particle size

to be handled


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)

BS 812-105.1:1989


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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

BS 812-105.1:1989


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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%

BS 812-105.1:1989


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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

BS 812-105.2:1990


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Apparatus

A sample divider -Size appropriate to the

maximum particle size

to be handled


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

BS 812-105.2:1990


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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

BS 812-105.2:1990


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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 )

BS 812-105.2:1990


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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)

BS 812-105.2:1990


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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

BS 812-105.2:1990


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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


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

Highway Engineering Design_Material Testing

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