DESIGN OF BITUMINOUS MIXES FOR BM,
DBM, SDBC, BC
ETC
.
By
B.L.RAWAT
B.E.(HONS.), M.E.(HONS.),MBA
EXECUTIVE ENGINEER (BUILDING CELL) PWD, CE OFFICE, JAIPUR
T
YPES
OF
B
ASES
AND
S
URFACE
C
OURSES
(B
ITUMINOUS
)
Prime Coat
Tack Coat
Bituminous Macadam
Grade 1 Grade 2
Bituminous Penetration Macadam
For 50 mm thick For 75 mm thick
Built-up Spray Grout
Dense Bituminous Macadam
Surface Dressing
Single Coat
Double Coat
Open Graded Premix Carpet
Mix Seal Surfacing
Type A
Type B
Semi-Dense Bituminous Concrete
Grade 1 Grade 2 Grade 3 Bituminous Concrete
Seal Coat
Liquid Seal Premixed Seal Bitumen Mastic
Slurry Seal
3 mm 1.5 mmB
ITUMINOUS
M
IX
D
ESIGN
(J
OB
M
IX
F
ORMULA
)
Marshall Stability Test
Marshall Stability Test adopted by US Corps of Engineers is a semi-confined compression test which is
comparable to a triaxial test with a cell pressure of about 0.7 kg/sqcm.
Hveem Stabilometer and Cohesiometer Tests
Hveem Stabilometer embodies main characteristics of triaxial test. It requires kneading compactor.
Types of Bituminous Mixes
Dense graded Open graded
Desirable Properties
Stability: resistance to deformation
Density: degree of compaction
Durability: resistance against weathering
Flexibility: extent of deformation before failure
Resistance to skidding
M
ARSHALL
S
TABILITY
T
EST
The Marshall Test is made to obtain optimum binder
content for the type of aggregate mix and traffic intensity.
This stability test is applicable to hot-mix design using
bitumen and aggregates with maximum size of 25mm.
Stability: The Marshall Stability of the mix is defined as a
maximum load carried by a compacted specimen at a standard test temperature at 60°C and at the rate of 5 cm per minute.
Flow value: The flow value is the deformation the
Marshall test specimen undergoes during the loading, upto the maximum load, in 0.25 mm units.
Design Steps
Select grading to be used.
Select aggregates to be employed in the mix.
Determine the proportion of each aggregate required to produce the design grading.
Determine the specific gravity
Make up the trial specimens with varying bitumen contents.
Determine the specific gravity of each compacted specimen.
Make stability tests on the specimen.
Calculate the percentage of voids, VMA and the percent VFB in each specimen.
Select the optimum bitumen content.
Check the values of Marshall Stability, Flow, Voids in total mix, VFB with optimum bitumen content.
Apparatus
Marshall Mould: Cylindrical moulds of 10 cm diameter, 7.5 cm height with interchangeable base plate and
collar.
Sample Extractor: a jack or compression machine
Hammer: 8.8 cm diameter, 4.5 kg weight, free fall 45.7 cm.
Breaking Head
Loading Machine: movement at the rate of 5 cm per minute, proving ring of 5 tonne capacity.
Flow Meter: least count of 0.025 mm.
Oven, Hot Plate, Mixing Apparatus, Water Bath, Thermometer
M
ODIFIED
M
ARSHALL
T
EST
Asphalt Institute Manual MS-2 and ASTM D5581.
Used where maximum size of aggregate is more
than 26.5 mm.
Mould diameter: 150 mm.
When the modified Marshall test is used, the
specified minimum stability values and the specified
flow values shall be multiplied by 2.25 and 1.5
Preparation of Test Specimen
Aggregate: 1200 gm, heated to temperature of 175° to 190°C.
Mould Assembly and Rammer: pre-heated: 100° to 145°C. Bitumen: heated 121° to 138°C. Mixing temperature VG-10 or 80/100 grade: 154°C. VG-20 or 60/70 grade: 160°C. Compaction
50 blows on either side, for medium traffic roads 75 blows on either side, for heavy traffic roads Compaction temperature
VG-10 or 80/100 grade: 138°C. VG-20 or 60/70 grade: 149°C.
Compacted thickness: 63.5 ± 3.0 mm.
Tests
Specific gravity of Compacted Specimens:
G
t =100
/ (W
1/G
1 +W
2/G
2 +W
3/G
3 +W
4/G
42)
where W1 = percent by weight of coarse aggregates
W2 = percent by weight of fine aggregate
W3 = percent by weight of filler
W4 = percent by weight of bitumen in total mix
G1, G2 and G3 are apparent specific gravity
values of coarse aggregates, fine aggregates and filler and G4 is the specific gravity of bitumen.
Density and Void Analysis
V
v, % = 100(G
t– G
b)/ G
tV
b, % = G
b* W
4/ G
4VMA, % = V
v+ V
b
VFB, % = 100 * V
b/ VMA
where Gb = bulk density of a specimen
Gt = theoretical specific gravity mixture
Vv = air voids in the mix, %
Vb = volume of bitumen
VMA = voids in mineral aggregate, %
Marshall Stability and Flow Values
The specimen is kept immersed under water at 60°C ± 1°C for 30 to 40 mins.
Placed in test head and maximum load before failure is noted.
Flow value at failure is noted.
Correction in thickness if specimen not exactly 63.5 mm.
Correction Factors
Volume of Specimen in cubcm Approximate Thickness of Specimen (mm) Correction Factors 457 – 470 57.1 1.1.9 471 – 482 58.7 1.14 483 – 495 60.3 1.09 496 – 508 61.9 1.04 509 – 522 63.5 1.00 523 – 535 65.1 0.96 536 – 546 66.7 0.93 547 – 549 68.3 0.89 560 – 573 69.9 0.86
Determination of Optimum Bitumen Content
Five graphs are plotted with values of bitumen content against the values of:
Density Gb, g/cubcm
Marshall stability S, kg
Voids in total mix Vv, %
Flow value F, 0.25 mm units
Voids filled with bitumen VFB, %
Bulk density, Stability and Flow are measured
whereas percentage air voids, V
v,VFB and VMA are
Optimum Bitumen Content
B
0= (B
1+ B
2+ B
3)/ 3
where,
B1 = bitumen content corresponding to maximum density.
B2 = bitumen content corresponding to maximum stability
B3 = bitumen content corresponding to specified voids
content, Vv
Value of flow and VFB are found from graphs, corresponding to
B0. All the design values of Marshall Stability, Flow, Voids and
VFB are checked at the B0 with the specific design requirement
of the mix.
If mix designed does not fulfill any one or more of the design
requirements, the gradation of aggregates or filler content or bitumen content or combination of these are altered and the design tests are repeated till all the requirements are
J
OB
M
IX
F
ORMULA
The proportion in which the different aggregates, filler
and bitumen are to be mixed are specified by weight
or by volume for implementation during the
V
ISCOSITY
G
RADED
(VG) B
ITUMENS
AND
THEIR
G
ENERAL
A
PPLICATIONS
Viscosity Grade General Applications
VG-40
(40-60 penetration)
Use in highly stressed areas such as those in intersections, near toll booths, and truck parking lots in lieu of old 30/ 40 penetration grade VG- 30
(50-70 penetration)
Use for paving in most of India in lieu of old 60/ 70 penetration grade VG- 20
(60-80 penetration)
Use for paving in cold climate, high altitude regions of North India
VG-10
(80-100 penetration)
Use in spraying applications and for paving in very cold climate in lieu of old 80/ 100 penetration grade
S
ELECTION
C
RITERIA
FOR
G
RADE
OF
M
ODIFIED
B
ITUMEN
Lowest Daily Mean Air Temperature, °C
Highest Daily Mean Air Temperature, °C
Less than 20°C 20 to 30°C More than 30°C More than -10°C PMB/ NRMB 120 CRMB 50 PMB/ NRMB 70 CRMB 55 PMB/ NRMB 40 CRMB 60 -10°C or lower PMB/ NRMB 120 CBMB 50 PMB/ NRMB 120 CRMB 50 PMB/ NRMB 70 CRMB 55
P
HYSICAL
P
ROPERTIES
OF
C
OARSE
A
GGREGATE
Property Test Requirement Test method
Cleanliness Grain size analysis Max. 5% passing 0.075mm
IS: 2386 Part I
Particle Shape Flakiness and Elongation Index
Max. 35% IS: 2386 Part I
Strength Los Angeles Abrasion Value BC- Max. 30% Others- Max. 35%
IS: 2386 Part IV
Aggregate Impact Value BC- Max. 24% IS: 2386 Part IV Others- Max. 27%
Polishing Polished Stone Value Min. 55 IS: 2386 Part IV Soundness (Either Sodium or Magnesium Sulphate) – 5 cycles
Sodium Sulphate Max. 12% IS: 2386 Part V Magnesium Sulphate Max. 18% IS: 2386 Part V Water Absorption Water Absorption Max. 2% IS: 2386 Part III Stripping Coating and Stripping of
Bitumen Aggregate Mixtures
Min. Retained Coating 95%
IS: 6241
G
RADING
R
EQUIREMENT
OF
M
INERAL
F
ILLER
IS Sieve (mm) Cumulative % passing by weight of total aggregate
0.6 100
0.3 95 – 100 0.075 85 – 100
A
GGREGATE
G
RADING
AND
B
ITUMEN
C
ONTENT
Specification DBM SDBC BC Grading 1 2 1 2 1 2 Normal maximum aggregate size 37.5 mm 26.5 mm 13.2 mm 9.5 mm 19 mm 13.2 mm Layer thickness 75–100 mm 50 – 75 mm 40 mm 25 mm 50 mm 25/ 40 mm IS Sieve size (mm) Cumulative percent by weight of total aggregate passing45 100 37.5 95 – 100 100 26.5 63 – 93 90 – 100 100 19 - 71 – 95 100 90 – 100 100 13.2 55 – 75 56 – 80 90 – 100 100 59 – 79 90 – 100 9.5 - - 70 – 90 90 – 100 52 – 72 70 – 88 4.75 38 – 54 38 – 54 35 – 51 35 – 51 35 – 55 53 – 71 2.36 28 – 42 28 – 42 24 – 39 24 – 39 28 – 44 42 – 58 1.18 - - 15 – 30 20 – 34 34 – 48 0.6 - - 15 – 27 26 – 38 0.3 7 – 21 7 – 21 9 – 19 10 – 20 18 – 28 0.15 - - 5 – 13 12 – 20 0.075 2 – 8 2 – 8 3 – 8 3 – 8 2 – 8 4 – 10 Bitumen content (Min) 4% 4.5% 4.5% 5% 5.2% 5.4%
P
ERMISSIBLE
V
ARIATION
FROM
THE
J
OB
M
IX
F
ORMULA
Description Permissible Variation
DBM SDBC/ BC Aggregate passing 19 mm or larger ± 8% ± 7% 13.2 mm/ 9.5 mm ± 7% ± 6% 4.75 mm ± 6% ± 5% 2.36 mm, 1.18 mm, 0.6 mm ± 5% ± 4% 0.3 mm, 0.15 mm ± 4% ± 3% 0.075 mm ± 2% ± 1.5% Binder Course ± 0.3% ± 0.3% Mixing Temperature ± 10°C ± 10°C
M
IXING, L
AYING ANDR
OLLINGT
EMPERATURES FORD
ENSEM
IXTURES(°C)
Bitumen Viscosity Grade Bitumen Aggregate Aggregate Temperature Mixed Material Temperature Laying Temperature Rolling Temperature VG – 40 160 – 170 160 – 175 160 – 170 150 Min. 100 Min. VG – 30 150 – 165 150 – 170 150 – 165 140 Min. 90 Min. VG – 20 145 – 165 145 – 170 145 – 165 135 Min. 85 Min. VG – 10 140 – 160 140 – 165 140 – 160 130 Min. 80 Min.
R
EQUIREMENT OF THED
ENSEG
RADEDB
ITUMINOUSM
IXUSING
V
ISCOSITY-G
RADED(VG) P
AVING/ M
ODIFIEDB
ITUMENProperties Viscosity Grade Paving Bitumen
Modified Bitumen Test Method
Hot climate Cold climate Compaction level
(Number of blows)
75 blows on each face of the specimen Minimum stability
(kN at 60°C)
9.0 12 10 AASHTO T245
Marshall flow (mm) 2 – 4 2.5 – 4 3.5 – 5 AASHTO T245 Marshall Quotient
(stability/ flow)
2 – 5 2.5 – 5
% Air Voids 3 – 5 MS-2, ASTM D2041
% Voids filled with bitumen (VFB)
65 – 75 MS – 2
Tensile Strength Ratio 80% (Minimum) AASHTO T283 Coating of Aggregate
Particles with bitumen
% V
OIDS INM
INERALA
GGREGATE, VMA
Nominal Maximum Particle Size (mm)
Min. % VMA related to designed % air voids
3 4 5 9.5 14 15 16 13.2 13 14 15 19.0 12 13 14 26.5 11 12 13 37.5 10 11 12
R
ECOMMENDED TYPE AND THICKNESS OFB
ITUMINOUS WEARING COURSES UNDER DIFFERENT SITUATIONS(IRC:37:2001)
Sl. No. Type of Base/Binder course Type of Bituminous Wearing Course Annual Rainfall L: <1500 mm M: 1500-3000 mm H: >3000 mm Design traffic (msa) 1. WBM,WMM, Crushed Macadam, Built up Spray Grout 20 mm PMC with sand seal coat L and M <10.0 20 mm PMC with liquid seal coat L, M and H <10.0 20 mm MSS Type ‘A’ or ‘B’ L,M and H <10.0 2. Bituminous Macadam base/binder course 25mm SDBC L,M and H <10.0 20 mm PMC with liquid seal coat L,M and H <10.0 20 mm MSS Type ‘A’ or ‘B’ L,M and H <10.0 3. Dense Bituminous Macadam 25mm Bituminous Concrete (BC) L,M and H >5<10 40mm BC L,M and H ≥10 50mm BC L,M and H ≥100
In applying the above recommendations, the following
points should be kept in view:
In case where a pavement is decided to be developed in
stages, the surfacing should correspond to that for the
design stage.
As far as possible, wearing course amenable to laying
with paver-finisher should be adopted over paver-finished
base/binder course.
Expensive surfacing like, Bituminous Concrete should not
C
RITERIA
FOR
THE
SELECTION
OF
GRADE
OF
B
ITUMEN
FOR
B
ITUMINOUS
C
OURSES
(IRC:37-2001)
Climate Traffic(CVD) Bituminous Course
Grade of
Bitumen to be used
Hot Any BM, BPM, BUSG 60/70 (VG-20) Moderate/Cold Any BM, BPM, BUSG 80/100 (VG-10) Any Heavy Loads,
Expressways, Urban Roads
DBM, SDBC, BC 60/70 (VG-20)
Hot/ Moderate Any Premix Carpet 50/60 (VG-30) or 60/70 (VG-20) Cold Any Premix Carpet 80/100 (VG-10) Hot/ Moderate Any Mastic Asphalt 15±5
S
ELECTIONC
RITERIA FORV
ISCOSITY-G
RADED(VG)
P
AVINGB
ITUMENB
ASED ONC
LIMATICC
ONDITIONS(IRC:111:2009)
Lowest Daily Mean Air Temperature, °C
Highest Daily Mean Air Temperature, °C
Less than 20°C 20 to 30°C More than 30°C More than -10° VG-10 VG- 20 VG- 30
T
YPES OFD
ENSEG
RADEDB
ITUMINOUSM
IXES,
THEIRM
IXES,
THEIRU
SE, N
UMBER OFL
AYERS ANDL
AYERT
HICKNESSSpecification Purpose Number of Layers Thickness of each Layer Dense Bituminous Macadam (DBM) Base/ Binder
Course/ Overlay for Strengthening Single or Multiple 50 mm – 100 mm Semi- Dense Bituminous Concrete (SDBC)
Wearing Course Single 25 mm – 40 mm
Bituminous Concrete (BC)
Wearing Course Single 25 mm/ 40 mm/ 50 mm
M
AXIMUM
PERMISSIBLE
FREQUENCY
OF
UNEVENNESS
Type of surface Unevenness, mm
Max. no. of Surface Unevenness
NH/ SH MDR and others Semi-Dense Bituminous Concrete (SDBC) 4 – 6 20 40 Bituminous Concrete (BC) 3 – 5 15 30
M
AXIMUM PERMISSIBLE VALUES OF ROUGHNESS(
MM/
KM)
FOR SURFACE WITHD
ENSEG
RADEDB
ITUMINOUSM
IXESS. No. Type of surface Condition of Road Surface ( mm/ km)
Good Average Poor 1. SDBC < 2500 2500 – 3500 > 3500 2. BC < 2500 2000 – 3000 > 3000
C
ONTROL TESTS FORD
ENSEG
RADEDB
ITUMINOUSM
IXES AND THEIRM
INIMUMF
REQUENCYS. No. Test Frequency
1. Quality of binder Number of samples per lot and tests as per IS:73 or IRC:SP: 53
2. Aggregate impact value/ Los Angeles Abrasion value
One test per 350 mtr cube of aggregate for each source and whenever there is change in the quality of
aggregate.
3. Flakiness Index One test per 350 mtr cube of aggregate for each source and whenever there is change in the quality of
aggregate. 4. Soundness test (Sodium
and Magnesium Sulphate test)
1 test for each source and whenever there is change in the quality of aggregate.
5. Water absorption of aggregate
1 test for each source and whenever there is change in the quality of aggregate.
6. Sand equivalent test 1 test for each source and whenever there is change in the quality of aggregate.
7. Plasticity Index 1 test for each source and whenever there is change in the quality of aggregate.
S.No. Test Frequency
8. Polished stone value 1 test for each source and whenever there is change in the quality of aggregate.
9. Percent of fractured faces 1 test per 350 mtrcube of aggregate when crushed gravel is used.
10. Mix grading 1 test for individual constituent and mixed aggregate from dryer for each 400 tonnes of mix subject to minimum of 2 tests per day per plant.
11. Stability and voids analysis of mix including theoretical
maximum specific gravity of loose mix
3 tests for stability, flow value, density and void content for each 400 tonnes of mix subject to minimum of 2 tests per day per plant.
12. Moisture susceptibility of mix (AASHTO T283)
1 test for each mix type whenever there is change in the quality or source of coarse or fine aggregate. 13. Temperature of binder in boiler,
aggregate in dryer and mix at the time of laying and
compaction
At regular intervals
14. Binder content One set for each 400 tonnes of mix subject to minimum of 2 tests per day per plant.
15. Rate of spread of mix material After every 5th truck load.
MANUAL FOR CONSTRUCTION AND
SUPERVISION OF BITUMINOUS WORKS
(IRC)
B
ITUMINOUS
P
AVEMENT
L
AYERS
Sprayed or Penetration Layer Systems
S
PRAYED
OR
P
ENETRATION
L
AYER
S
YSTEMS
Prime Coat (Clause 502)
It is a low viscosity bituminous emulsion on untreated absorbent base in preparation for a bituminous course.
Uses
To plug the capillary voids
To coat and bond loose materials on the surface To harden or toughen the surface
To promote adhesion between the layer being primed and the
Tack Coat (Clause 503)
It’s a low viscosity liquid bituminous binder to an existing
bituminous surface.
Uses
It is used to ensure a bond between the new construction and
the old surface.
When an additional course is applied within a couple of days
on a freshly laid bituminous layer that has not been used by traffic or on an old bituminous rich surface in warm weather, the Tack Coat may be dispensed with.
Liquid Seal Coat (Clause 513)
It comprises of an application of a layer of bituminous binder over an existing bituminous surface, followed by a cover of stone chipping.
Uses
The application of Liquid Seal Coat over an existing
bituminous surface is for the purpose of sealing the voids in the bituminous surface.
Bituminous Penetration Macadam (Clause 505)
It is a compacted layer of coarse aggregates into which bituminous binder is introduced. The binder penetrates into the layer through the voids and binds the stone
aggregates. Key aggregates are spread on surface and rolled so as to fill in the surface voids in the coarse
aggregate layer.
Uses
It is not advocated for use in heavily trafficked situations. It is used in the remote area where it is difficult to transport
mixing and laying equipments.
It may be used as a temporary emergency material to repair a
Built-up spray grout (Clause 506)
It consists of two-layer composite construction of
compacted crushed coarse aggregate with application of bituminous binder after each layer and key
aggregates on top for the second layer.
It is similar to Penetration Macadam but with less interlock and binder.
Uses
It is used only for emergency repair work and other temporary
Surface Dressing (Clause 510)
A thin film of bituminous binder is sprayed onto the road surface, covered with a layer of stone chippings and
well rolled.
Uses
Used for relatively lightly trafficked roads, over gravel or other
untreated road bases to reduce dust nuisance.
To protect freshly laid WBM, WMM. It acts as a water-proof seal.
To increase the skid resistance of smooth surface. To act as a temporary bituminous surface on newly
constructed roads so as to allow for settlements due to traffic before costlier bituminous layers are provided.
Fog Spray (Clause 518)
A Fog Spray is a light application of a slow-setting emulsion diluted with water on an existing surface.
Uses
To renew an old bituminous surface that has become dry and
brittle with age.
To seal small cracks and surface voids
To inhibit ravelling and whip-off of chippings by traffic on newly
P
RE
-
MIXED
A
GGREGATES
AND
B
ITUMEN
M
IXTURES
Bituminous Macadam (Clause 504)
Types Open graded (Bituminous Macadam, BM)
Dense graded (Dense Bituminous Macadam, DBM) It consists of a graded aggregate coated with
bituminous binder. The main source of strength of mixer is from mechanical interlocking of aggregate particles and the cohesion imparted by binder.
Thickness varying from 50 to 100 mm.
Voids content can be as high as 20-25%.
Uses
A layer of BM serves as a base/ binder course, laid
Dense graded bituminous macadam (DBM) (Clause
507)
The stone aggregates are more closely graded. As a result the mixture is more dense.
Thickness varying from 50 to 200 mm.
Uses
DBM is used as a base/ binder course for pavement subjected
Semi-dense Bituminous Concrete (SDBC) (Clause
508)
The SDBC is a variant of BC, the difference being a lower binder content and the aggregate used being less dense graded. It is laid in a single course over a
previously prepared bituminous base.
Uses
It is used as a binder/ wearing course on roads carrying
Bituminous Concrete (BC) (Clause 509)
Bituminous Concrete layer consists of a thoroughly compacted dense graded bituminous mixture of very well graded course and fine aggregates with filler and relatively high amount of bitumen compared to DBM and SDBC.
Uses
BC layer serves as a wearing course for heavily trafficked
Open-graded Premix Surfacing (Clause 511)
Open graded Premix surfacing is a thin carpet. It isgenerally laid to a thickness of 20 mm. A seal coat is provided to render it less permeable to water.
Uses
It serves as a wearing course on lightly trafficked roads. For temporary improvement and maintenance.
Close-graded Premix Surfacing/ Mix Seal Surfacing
(MSS) (Clause 512)
It is a fairly open graded mix used as a thin carpet.
Thickness in the range of 12-40 mm.
It is a mix of PMC with seal coat. Construction in 1 operation.
Uses
Premix Seal Coat (Clause 513)
Premix Seal Coat is a thin application of a bituminous course over another bituminous surface.
Uses
It is intended for sealing the voids in the bituminous surface
Mastic Asphalt (Clause 515)
It is a mix of bitumen, mineral filler and fine aggregate.
Voidless compact mass.
It flows like viscous fluid at temperature of around 200°C.
Solidified into a dense mass on normal temperature.
No compaction is required.
Uses
Wearing course for heavy duty pavement, city streets carrying
Slurry Seal (Clause 516)
It is a mixture of well graded fine aggregate, cement filler, bituminous emulsion and additional water.
Uses
For preventive and corrective maintenance of aged bituminous
surfaces and surfaces with fine cracks.
Recycling of Bituminous Pavement (Clause 517)
In-situ recycling Central plant recycling
The process can be achieved by hot-mix or cold-mix technique.
Uses
Recycling of a bituminous pavement is the reuse, after some
processing, of a pavement material that has served its first intended purpose.
Advantage
Reduction in excess of height of pavement Effective use and conservation of materials Economy
Bituminous Cold Mix (Clause 519)
It consists of unheated aggregates and emulsified or cutback bitumen.
Uses
It is used in situations where hot-mix plant are not readily
available.
In remote areas.