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
TYPES OF BASES AND SURFACE COURSES (BITUMINOUS) 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 Surface Dressing with Precoated Aggregate
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 mm
Recycling of Bituminous Pavement
BITUMINOUS MIX DESIGN (JOB MIX FORMULA)
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 Workability during construction
MARSHALL STABILITY TEST
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
MODIFIED MARSHALL TEST 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 respectively.
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. Bitumen content: 3% to 7.5% with increment of 0.5%
Tests
Specific gravity of Compacted Specimens:
Gt = 100 / (W1/G1 + W2/G2
+ W3/G3 + W4/G4 ) 2
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
Vv, % = 100(Gt – Gb)/ Gt Vb, % = Gb * W4/ G4 VMA, % = Vv + Vb VFB, % = 100 * Vb/ 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, % VFB = voids filled with bitumen, %
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 factor is applied.
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, Vv, VFB and VMA are computed from formula.
Optimum Bitumen Content
B0 = (B1 + B2 + B3)/ 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 simultaneously fulfilled.
JOB MIX FORMULA
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 construction, is called Job Mix Formula.
VISCOSITY GRADED (VG) BITUMENS AND THEIR GENERAL APPLICATIONS 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
SELECTION CRITERIA FOR GRADE OF MODIFIED BITUMEN
Lowest Daily Mean Highest Daily Mean Air Temperature, °C Air Temperature, Less than 20°C 20 to 30°C More than 30°C °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
PHYSICAL PROPERTIES OF COARSE AGGREGATE 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
Water Sensitivity
Retained Tensile strength
Min 80%
ASHTO 283
GRADING REQUIREMENT OF MINERAL FILLER IS Sieve (mm)
Cumulative % passing by weight of total aggregate
0.6
100
0.3
95 – 100
0.075
85 – 100
AGGREGATE GRADING AND BITUMEN CONTENT Specification
DBM
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)
SDBC
BC
Cumulative percent by weight of total aggregate passing
45
100
37.5
95 – 100
100
26.5
63 – 93
90 – 100
19
-
71 – 95
100
13.2
55 – 75
56 – 80
90 – 100
9.5
-
-
4.75
38 – 54
2.36
100 90 – 100
100
100
59 – 79
90 – 100
70 – 90
90 – 100
52 – 72
70 – 88
38 – 54
35 – 51
35 – 51
35 – 55
53 – 71
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
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%
9 – 19
TRRL METHOD, HER MAJESTY’S LONDON
PERMISSIBLE VARIATION FROM THE JOB MIX FORMULA 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
MIXING, LAYING AND ROLLING TEMPERATURES FOR DENSE MIXTURES (°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.
REQUIREMENT OF THE DENSE GRADED BITUMINOUS MIX USING VISCOSITY-GRADED (VG) PAVING/ MODIFIED BITUMEN Properties
Viscosity Grade Paving Bitumen
Modified Bitumen Hot climate
Test Method
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 65 – 75
% Voids filled with bitumen (VFB) Tensile Strength Ratio Coating of Aggregate Particles with bitumen
MS-2, ASTM D2041
80% (Minimum)
MS – 2 AASHTO T283
95% (Minimum)
IS: 6241
% VOIDS IN MINERAL AGGREGATE, 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
RECOMMENDED TYPE AND THICKNESS OF BITUMINOUS 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
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
25mm Bituminous Concrete (BC)
L,M and H
>5<10
40mm BC
L,M and H
≥10
50mm BC
L,M and H
≥100
2.
3.
Bituminous Macadam base/binder course
Dense Bituminous Macadam
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 be provided directly over manually laid granular bases.
CRITERIA FOR THE SELECTION OF GRADE OF BITUMEN FOR BITUMINOUS COURSES (IRC:372001) 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
Cold
Any
Mastic Asphalt
30/ 40 (VG-40)
SELECTION CRITERIA FOR VISCOSITY-GRADED (VG) PAVING BITUMEN BASED ON CLIMATIC CONDITIONS (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
-10°C or lower
VG- 10
VG- 10
VG- 20
TYPES OF DENSE GRADED BITUMINOUS MIXES, THEIR MIXES, THEIR USE, NUMBER OF LAYERS AND LAYER THICKNESS Specification
Purpose
Number of Layers
Thickness of each Layer
Dense Bituminous Base/ Binder Single or Macadam (DBM) Course/ Overlay for Multiple Strengthening
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
MAXIMUM 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
MAXIMUM PERMISSIBLE VALUES OF ROUGHNESS (MM/ KM) FOR SURFACE WITH DENSE GRADED BITUMINOUS MIXES S. 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
CONTROL TESTS FOR DENSE GRADED BITUMINOUS MIXES AND THEIR MINIMUM FREQUENCY S. 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.
16.
Density of compacted layer
One test per 700 sqmtr area.
MANUAL FOR CONSTRUCTION AND SUPERVISION OF BITUMINOUS WORKS (IRC)
BITUMINOUS PAVEMENT LAYERS Sprayed or Penetration Layer Systems Pre-mixed Aggregate and Bitumen Mixtures
SPRAYED OR PENETRATION LAYER SYSTEMS
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 superimposed bituminous layer
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. It is an alternative of a premix seal coat.
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 pavement damaged by rain and flood.
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 constructions.
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 finished surface dressing.
PRE-MIXED AGGREGATES AND BITUMEN MIXTURES
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 immediately after mixing on previously prepared base.
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 to heavy traffic.
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 relatively lower traffic in terms of msa<10.
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 highway, msa>10.
Open-graded Premix Surfacing (Clause 511)
Open graded Premix surfacing is a thin carpet. It is generally 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
It serves as a thin wearing course for lightly trafficked roads.
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 over which it is laid and is needed only for open graded PMC.
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 high volume of traffic, bus stops, junctions or on bridge decks.
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. It may also be used on top of a single coat surface dressing.
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. For maintenance operation in high rainfall zones.
THANKS!!! Open for discussion.