GOVERNMENT OF TELANGANA STATE
OFFICE OF THE DEPUTY EXECUTIVE ENGINEER (PR) Vig & QC
SUB-DIVISION, NALGONDA.
Cir.No.AEE/SDBC/VQC Nlg/2015.Dated: 16.02.2015.
Sub:- SDBC - Construction of Semi-Dense Bituminous Concrete
Layer as per IRC Codes, MoRTH Specifications are communicated for
better understanding - Reg.
* * *
It is a known fact that the Panchayat Raj Engineers are new to
the construction of Semi-Dense Bituminous Concrete Layer. Till now
we are exposed to only BT Surface Dressing, OGPC, Seal coat and the
SDBC is a new concept to us. Hence to guide the PR Engineers the
specifications, design, construction, quality control in execution
of SDBC pavement layer are here with communicated for better
understanding and quality execution.
Preamble::The Semi-dense bituminous concrete shall be used as a
wearing course only and shall not be laid directly over WBM or any
granular base but to be laid on a previously prepared bituminous
bound surface. Being high cost specification SDBC mixes should be
properly designed for satisfactory performance and durability. It
can be constructed in a single or multiple layers ranging from 25mm
to 100mm in thickness. The SDBC is based on a controlled mix. The
density achievement is the basis in execution of SDBC and voids in
the mix should any cost well with in 3 to 5%.
General guideline for Semi Dense Bituminous Concrete.The work
consists of construction, in a single or multiple layers of
bituminous concrete prepared as per specified job mixed formula, on
previously prepared bituminous base.INGREDIENTS::The Semi-dense
bituminous concrete mix shall consist of binder, coarse aggregate,
fine aggregate and filler in suitable proportions.
Bitumen:
The bitumen shall be paving bitumen of Penetration Grade shall
comply with I.S. 73-1992 Specification for Paving Bitumen.The
bitumen shall be paving bitumen of penetration grade / Viscosity
grade with the range of 30/40 to 80/100 or ( VG 40 to VG 10 ). The
grading of bitumen is changed from Penetration Grade to Viscosity
Grade vide IS 73-2006 to improve the quality of Bitumen. The
variability in performance at high temperature can be addressed by
adopting a viscosity graded bitumen specification (based on
viscosity at 60 C ) in lieu of the current penetration graded
specification (based on penetration at 25C ), which differs in
properties at high temperature.
Bitumen can be classified into four types based on viscosity as
given below.
INDIAN BITUMEN SPECIFICATIONS AS PER IS 73:2006
Sl.NoCharacteristicUnitVG10VG20VG30VG40Test Method
1Absolute viscosity at 60C , minPoises800150024003200IS
1206(Part 2) : 1978 II)
2Kinematic viscosity at 135C , mincst250300350400IS 1206(Part 3)
: 1978
3Flash Point, Cleveland open cup, min.C 220220220220IS 1209 :
1978
4
Solubility in Trichloroethylene, %min% wt99999999IS 1216 :
1978
5
Penetration at 25C , 100 gm, 5 sec.1/10 mm80 to 10060 to 8050 to
7040 to 60IS 1203 : 1978
6Softening Point, minC 40454750IS 1205 : 1978
7Tests on residue from thin film oven test / RTFOT
a) Viscosity ratio at 60C , max4444IS 1206(Part 2) : 1978
b) Ductility at 25C after thin film oven test, minCm75504025IS
1208 : 1978
VG-10 BITUMEN: VG-10 is widely used in spraying applications
such as surface-dressing and paving in very cold climate in lieu of
old 80/100 Penetration grade. It is also used to manufacture
Bitumen Emulsion and Modified Bitumen products.
VG-20 BITUMEN: VG-20 is used for paving in cold climate &
high altitude regions.
VG-30 BITUMEN: VG-30 is primarily used to construct extra heavy
duty Bitumen pavements that need to endure substantial traffic
loads. It can be used in lieu of 60/70 Penetration grade. VG-40
BITUMEN: VG-40 is used in highly stressed areas such as
intersections, near toll booths and truck parking lots in lieu of
old 30/40 Penetration grade. Due to its higher viscosity, stiffer
Bitumen mixes can be produced to improve resistance to shoving and
other problems associated with higher temperature and heavy traffic
loads.IMPORTANT TESTS ON BITUMEN
a) VISCOSITYb) SOFTENING POINTc) PENETRATION TEST at 25 degree
Cd) DUCTILITY TESTe) FLASH POINT TESTf) SOLUBILITY TEST
VISCOSITY: It is an internal friction. The C.G.S. unit for the
viscosity is poise. It can be measured in lab by the following
equipments.a) capillary viscometer i) Cannon Manning Viscometerii)
Asphalt Institute Vacuum Viscometeriii) Tar Viscometer b) Cup
Viscometer c) Tar viscometer
Viscosity at 135C is a fair indicator of the ability of the
bitumen to coat the aggregate properly. The values are i) Absolute
Viscosity at 60C Min. for VG-30 -2400 poises, (ii) Kinematic
Viscosity at 135C Min. for VG-30 -350 cst. Too viscous bitumen
would result in inadequate and non uniform coating of the
aggregates. Very low viscosity would again result in inadequate
coating as the bitumen will tend to bleed. Therefore viscosity at
135C is a true reflection of quality of bond that is likely to be
formed with the aggregates.
SOFTENING POINT: The softening point is a empirical test and
denotes the temperature at which bitumen would behave more like a
liquid and less like a solid under standard conditions of heating
and loading. In this test a standard ring and ball apparatus is
used. The sample is taken in a standard mould and standard weights
( in the form of steel balls ) are placed on it. The system is then
heated in a water bath at a standard rate. The temperature at which
the bitumen coated steel ball touches the bottom of the beaker is
called the softening point temperature. The softening point test is
a very important as it is a fair indicator of melting point of
bitumen. Bitumen with lower softening point tends to melt on the
road in summer and start flowing under the impact of temperature
and traffic. Subsequently when bitumen cools at night the road
surface losses its original shape and becomes wavy. This mode of
failure of road due to bitumen is referred to as failure by
rutting.Bitumen with higher softening point, melt at higher
temperature and have better rutting resistance. The values of
softening point for VG-30 is 47C min. PENETRATION TEST : The
penetration of a bitumen material is the distance in 10th of
millimeter that a standard needle will penetrate vertically into a
sample of the material under standard conditions of temperature,
load and time i.e penetration at 25 degree C , 100gms(sample) , 5
seconds (load applied).The values of Penetration at 25C for VG-30
is 50-70. DUCTILITY TEST: Ductility test is an empirical test which
measures the cohesive strength of the bitumen. In this test a
standard size of bitumen sample is maintained at a constant
temperature. The sample is pulled at a constant rate and at a
constant temperature, the length at which the sample breaks is
called the ductility of the sample.The values of Ductility at 25C
for VG-30 is min 40 cm.
FLASH POINT TEST: Flash point test measures the flammability of
Bitumen.The values of Flash Point for VG-30 is min 220C.
Coarse Aggregates :: The coarse aggregate for semi-dense bitumen
concrete should satisfy the criteria laid in MoRTH Table 500-14.
Aggregate gradation is indicated in MoRTH Table 500-15 and the SDBC
should satisfy the Marshall requirement indicated in MoRTH Table
500-15.Fine Aggregates :: The fine aggregate shall be the fraction
passing the 2.36mm and retained on the 0.075 mm sieve consisting of
crusher run screening, natural sand or mixture of both.Fillers ::
The filler requirement normally met from material passing 90 sieve
in fine aggregates. If the filler material is deficient extra
filler shall be added. The filler shall be stone dust, hydrated
lime, fly ash or cement etc.,free from organic impurities. The
grading requirement of mineral filler shall be as given in the
table.( TABLE 500-9 of MoRTH )Sl.No.IS SieveCumulative % by Wt. of
total aggregates.
10.600 mm100
20.300mm95-100
30.075mm85-100
Composition of Semi- dense bituminous concrete pavement layers(
TABLE 500-15 of MoRTH 3rd Edn/ MOST Table 500-20 )
Grading-ISl.No.IS Sieve% PassingRemarks
1.13.2 mm100Coarse Aggregates
2.11.2 mm88-100
3.5.6 mm42-64
4.2.8 mm22-38
5.710 micron11-24
Fine Aggregates
6.355 micron7-18
7.180 micron5-13
890 micron3-9Filler
As per Approved Data:The gradation of aggregates is considered
as follows in the approved data:
13.20 10 mm chips20%
10 mm to 5 mm chips 38%
Less than 5 mm chips 40%
Filler-cement)2%.
Job Mix Formula:: Being high cost specification SDBC mixes
should be properly designed for satisfactory performance and
durability. Requirement of job mix formula is to give Optimum
Bitumen contents v/s Density and shall satify the Marshals values
of Min stability = 8.2 kN at 60C, Flow = 2-4mm, Air Voids = 3-6%.
The Job mix formula for SDBC should be in accordance with clause
511.3 of Ministrys specifications and should be designed in lab and
get approved from the Engineer-in-Charge before implementation. The
detailed procedure for Job Mix is annexed to this
circular.Gradation of Mix::The representative samples of the
aggregates shall be tested in the design lab and proper blend shall
be worked out so as the final composition shall satisfy gradation
set forth below.( IS:2386 Part 1 Wet sieving method ).
Requirements for the mixture: The quality requirements for
individual ingredients of the mixture shall meet the requirements
set out below.Physical Requirements for Coarse Aggregate ( TABLE
500-14 of MoRTH )S.No.PropertyTestSpecification
1.Cleanliness (dust)Grain size analysisMax 5% passing 0.075mm
sieve
2.Particle shapeFlakiness and Elongation Index (Combined)Max
30%
3.Strength*Los Angeles Abrasion ValueMax 35%
Aggregate Impact ValueMax 27%
4.PolishingPolish stone ValueMin 55
5.DurabilitySoundness:Sodium Sulphate Magnesium SulphateMax
12%Max 18%
6.Water AbsorptionWater absorptionMax 2%
7.StrippingCoating & Stripping of Bitumen Aggregate
MixturesMinimum retained coating 95%
8.Water SensitivityRetained Tensile StrengthMin 80%
MARSHALL TEST : The Marshall test consists of the manufacture of
cylindrical specimens 102 mm in diameter & 64 mm high by using
a standard compaction hammer and a cylindrical mould. The specimens
are tested for their resistance to deformation at 60C at a constant
rate of 50mm/min. in a testing rig. The top and bottom of the
specimen remain unconfined. The maximum load before failure is
called Marshall Stability and the amount of deformation of the
specimen before failure is known as Marshall Flow. The ratio of
stability to flow is called Marshall Quotient and is an indicator
of the materials resistance to permanent deformation.
Marshall Properties Requirements::
Being high cost specification SDBC mixes should be properly
designed for satisfactory performance and durability. The mix as
designed and laid should satisfy the requirements given in the
following table.
Marshall Properties Requirements for Semi-Dense Bituminous
Pavement Layers( TABLE 500-16 of MoRTH )
S.No.Requirement of property of mix from Marshall
SampleStandard
1.Minimum Stability (kN at 60C)8.2kN or 820kgs
2.Minimum flow (mm)2
3.Maximum flow (mm)4
4.Compaction level (No.of blows)75 blows on each of the two
faces of the specimen
5.Percent Air Voids3 -5
6.Percent Voids in mineral aggregate (VMA)13-15
7.Percent Voids filled with bitumen (VFB)65 -75
Reasons for Poor performance of Asphalt mixes,
1. Inadequate initial compaction making the mix vulnerable to
high secondary compaction under traffic.2. Relatively high asphalt
contents that permit the reduction of air voids to less than 3%
under secondary compaction, leading to rutting under heavy axle
loads when pavement temperatures rise in summer.3. Low asphalt
contents and high air voids in the mix leading to top-down
cracking, raveling and stripping making the mix less durable.4.
High voids >8% lead to permeability of water and air resulting
in water damage, oxidation, raveling, and cracking. Low voids