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.

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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