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 25°C ), which differs in properties at high temperature.

Bitumen can be classified into four types based on viscosity as given below.

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) VISCOSITY

INDIAN BITUMEN SPECIFICATIONS AS PER IS 73:2006Sl.N

o Characteristic Unit VG10 VG20 VG30 VG40 Test Method

1Absolute viscosity at

60°C , minPoises 800 1500 2400 3200

IS 1206(Part 2) : 1978 II)

2Kinematic viscosity

at 135°C , mincst 250 300 350 400

IS 1206(Part 3) : 1978

3Flash Point,

Cleveland open cup, min.

°C 220 220 220 220IS 1209 :

1978

4Solubility in

Trichloroethylene, %min

% wt 99 99 99 99IS 1216 :

1978

5 Penetration at 25°C , 100 gm, 5 sec.

1/10 mm80 to 100

60 to 80

50 to 70

40 to 60

IS 1203 : 1978

6 Softening Point, min °C 40 45 47 50IS 1205 :

1978

7 Tests on residue from thin film oven test / RTFOT

a) Viscosity ratio at 60°C , max

4 4 4 4IS 1206(Part

2) : 1978

b) Ductility at 25°C after thin film oven

test, minCm 75 50 40 25

IS 1208 : 1978

b) 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 135°C is a fair indicator of the ability of the bitumen to coat the aggregate properly. The values are i) Absolute Viscosity at 60°C Min. for VG-30 -2400 poises, (ii) Kinematic Viscosity at 135°C 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 135°C 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 47°C 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 25°C 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 25°C 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 220°C.

Coarse A ggregates : : 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 A ggregates : : 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.

1 0.600 mm 100

2 0.300mm 95-100

3 0.075mm 85-100

Composition of Semi- dense bituminous concrete pavement layers

( TABLE 500-15 of MoRTH 3rd Edn/ MOST Table 500-20 ) Grading-I

Sl.No. IS Sieve % Passing Remarks

1. 13.2 mm 100 Coarse Aggregates

2. 11.2 mm 88-100

3. 5.6 mm 42-64

4. 2.8 mm 22-38

5. 710 micron 11-24

Fine Aggregates6. 355 micron 7-18

7. 180 micron 5-13

8 90 micron 3-9 Filler

As per Approved Data:The gradation of aggregates is considered as follows in the approved data:

13.20 – 10 mm chips 20%10 mm to 5 mm chips 38%

Less than 5 mm chips 40%Filler-cement) 2%.

Job M ix F ormula ::

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 60°C, Flow = 2-4mm, Air Voids = 3-6%. The Job mix formula for SDBC should be in accordance with clause 511.3 of Ministry’s 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.

Property Test Specification

1. Cleanliness (dust) Grain size analysis Max 5% passing 0.075mm sieve

2. Particle shape Flakiness and Elongation Index (Combined)

Max 30%

3. Strength*Los Angeles Abrasion Value Max 35%

Aggregate Impact Value Max 27%

4. Polishing Polish stone Value Min 55

5. Durability

Soundness:

Sodium Sulphate Magnesium Sulphate

Max 12%Max 18%

6. Water Absorption Water absorption Max 2%

7. Stripping Coating & Stripping of Bitumen Aggregate Mixtures

Minimum retained coating 95%

8. Water Sensit ivity

Retained Tensile Strength Min 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 60°C 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 Sample Standard

1. Minimum Stability (kN at 60°C) 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 Voids 3 -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 <3% lead to rutting and shoving of the asphalt mixture.

Laying::

If the existing base is extremely irregular and wavy, it may be considered worth to lay a bituminous leveling course (Profile correction course) of adequate thickness to avoid an excessive use of the costly surface course.

The surface shall be thoroughly swept clean by mechanical broom and dust removed by compressed air.

Semi dense bitumen concrete carpet shall not be laid during rainy weather, or when the base/binder course is damp or wet and temp below 15°C.

The temperature of the mix at the time of laying shall not exceed 160°C and

shall not be less than 120°C.

A tack coat at the rate of 2.5 to 3.0 kg of bitumen per 10 sqm shall be given over a bituminous base or binder course. The rate of spread of Bitumen can be tested by a square plate of 200 x 200 x 3 mm thick laid on road surface before applying tack coat and weighing the same after applying tack coat.

Rolling & Compaction::

Initially the rolling shall be with 8-10 T smooth wheeled roller, Intermediate with vibratory roller or 12-15T pneumatic tyred roller and finish rolling with 6-8 Tonnes smooth wheeled tandem rollers.

The each pass of the roller shall overlap the preceding one by half the width of the rear wheel.

Rolling shall be continued till the desired density of not less than 98% of the lab design density is achieved and all roller marks are eliminated.

Rolling operation shall be completed in every respect before the temperature of the mix falls below 80°C.

After the mix is compacted, the thickness laid may be checked by a scaled needle. The lesser thickness shall be corrected immediately. This shall also be correlated with the measured area of the surface laid and the total plant output of the mix in tonne.

For every 5oo Sqm or less of compacted surface, on field density test should be conducted to determine the density of mix as laid and shall not be less than 98% of the lab density.

Factors Influencing Compaction of Asphalt mixes

1) Type of Aggregates2) Shape of Aggregates3) Grading of mix4) Residual moisture content in aggregates5) Binder content6) Viscosity of binder7) Temperature of mix during compaction

Note: The first six requirements are taken care in the mix design, leaving temperature of compaction as the single most important affecting the final result.

Opening to Traffic::

The newly laid surface shall not be open to traffic for at least 24 hours after laying and the completion of compaction, without the express approval of the Engineer in writing.

General Guidelines:1) Loose thickness of BT – 37mm2) Compacted Thickness of BT-25mm3) Camber of BT Surface – 3.50%i.e., 65mm or 2.5’’ level difference between edge and center shall be provided. 4) Super-elevation of 7% shall be provided on curves, i.e., about 262mm (10.5’’) level difference between edge to edge sloping downward shall be maintained in a width of 3.75m and for extra width the level difference shall be increased accordingly.

5) Compaction is to be checked by sand replacement method. The Density of the compacted BT layer should not be less than 2.30 gms /cc i.e.,-2308 Kg/cum6) Wt.of Sample in a pit of 15cm x 15cm size min. – 1298 gms7) Wt.of Bitumen in a pit of 15cm x 15cm size min. – 58.44 gms8)Mixing Temperature - 150°C -165°C, Laying Temperature-130°C -160°C, Rolling Temperature-90°C -100°C min.

QUALITY CONTROLS::Periodic check of the aggregates at the gradation control unit or at the hot bin gates should be made to see that the proportion of the aggregates as specified in the designed job mix formula is complied with. The physical properties as required in table 3 shall be determined as the rate of one test each for every 50-100 cum of aggregates.Periodic check on penetration and softening point of the binder should be done as specified in IS 1203 & 1205.The aggregate temperature at the end dryer should be checked periodically and never exceed 163°C. A tolerance upto 10°C on the lower side may be permitted.The bitumen temperature should be well within the limits specified. The viscosity of heated bitumen shall be between 150 and 300 centi stokes for which normal temperature range for paving bitumen is 150°C to 177°C.At no time the difference in temperature between aggregates and bitumen should exceed 14°C.Atleast one sample for every 100t of bituminous mix discharged at the pugmill chute or a minimum of one sample per plant per day shall be collected and the following tests done.

a) 3 Marshall specimens shall be compacted and tested for the average stability, flow, voids content and density. The value should closely follow the lab design values.

b) Bitumen shall be extracted from about 1000gm of the mix and bitumen content is determined.

c) A sieve analysis of the aggregates after the bitumen is extracted shall be done and the gradation determined.

The permissible variation of the individual percentages of the various ingredients in the actual mix from the job mix formula shall be within the limits indicated below.

PERMISSIBLE VARIATIONS FROM THE JOB MIX FORMULA ( MoRTH TABLE 500-13)

S.No Description of IngredientPermissible variation by

weight of Total Mix ( in %)1 Aggregate passing 13.2mm or larger sieve ± 8%

2Aggregate passing 11.2mm sieve or 5.6mm sieve

± 7%

3 Aggregate passing 2.8mm sieve or 1.4mm sieve ± 6%4 Aggregate passing 710 µ sieve or 355 µ sieve ± 5%5 Aggregate passing 180 µ or sieve ± 4%6 Aggregate passing 90 µ sieve ± 3%7 Bitumen Content ± 0.3%8 Mixing Temperature ± 10%

Surface Finish and Quality ControlThe longitudinal profile of the finished surface shall be treated with a straight

edge 4.50m long parallel to the center line and the transverse profile with a camber template. Any irregularity greater than 6mm shall be corrected.

Surface Evenness SDBC Course::

The surface unevenness of completed SDBC course in longitudinal and transverse directions shall be with in the limits specified in Table 1 & 2 of IRC:SP:16-2004 “Guidelines for Surface Evenness of Highway Pavements".

Permissible Surface Unevenness for SDBC

Sl.No.

Description of Layer Longitudinal Profile measured with a 3-Metre Straight Edge

Transverse Profile

Max.Permissible Surface Un-evenness.

Maximum No. Of undulations

permitted in any 300M length.

Max. Permissible variation from

specified profile under camber

template.1 SDBC 6 mm 40 Nos 4 mm

RECOVERIES::

Recovery for Shortfall in Thickness / Quantity / Weight for all items of road works (Vide Govt. in PR&RD Dept Memo No.15320/VIG.I/2005-1, dated 12.5.2006)

Shortfall in Thickness / Quantity / Weight

Recovery

Upto 10% Twice the Agr. Rates10-20% Thrice the Agr. Rates

>20 Rejection & Redone.

Responsibility for the lapses:

If Average of all Deficiencies found ResponsibleMore than 10% AEEMore than 15% AEE & DyEEMore than 20% AEE , DyEE & EE

All the Field Officers are requested to go through the above instructions and it is expected a flawless systematic process of SDBC Construction meticulously, here after in respect of all items involved in the process of SDBC construction..

( Neelakanteshwar Yedla)

neelakantyedla@gmail.com Dy. Executive Engineer,

(PR) Vig& QC Sub-Division, Nalgonda.

Encl:-1) IRC 95-1987 Code on SDBC.2) HP Bitumen Handbook

To,The Executive Engineer (PR) PIU Nalgonda, PRI Miryalaguda with a request to communicate the same to all field Engineers under their control.Copy to all DyEE’s /AEE’s through EE’s concerned.C/S to the Executive Engineer (PR) Vig & QC Division Mahbubnagar/Hyderabad for favour of information.

SEMI DENSE BITUMINOUS CONCRETE

Calculation of loose thickness (approximate ) as per data

Out put as per data = 195.00 cumCorresponding area for 25mm thickness, for 195 cum = 195.00/0.025

= 7800.00 SqmVolume of aggregate as per data = 286.50 cumHence loose thickness = 286.50/7800 = 0.03673 m (or) Loose thickness = 36.73 mm

Calculation of weight of sample for pit size of 0.15m x 0.15m for 25mm thickness ( approximate ) as per data

Volume of mix as per data =195.00 cumWeight of mix as per data = 450tonnes (or) 450000 kgsDensity of mix = 450 / 195 =2307.69 kg/cumWeight of sample excavated from pit size 0.15m x 0.15m = 0.15 x 0.15 x 0.025 x 2307.69 = 1298.08 gmsWeight of metal chips excavated from pit size 0.15m x 0.15m = 0.15 x 0.15 x 0.03673 x 1500 = 1239.64Hence weight of bitumen = 1298.08 - 1239.64 Weight of bitumen for 25mm thick = 58.44 gms or 4.50 % of BT

Calculation of Filler material (Cement) (approximate ) as per data

Corresponding area for 25mm thickness, for 195 cum = 195.00/0.025 = 7800.00 Sqm

= 7800 / 3.75 Length = 2080 mts

As per data weight of aggregate = 450-20.25 = 429.75 tonnesAs per data Filler material = 2% by weight of aggregate = 429.75 x 2 /100 = 8.95 MT or 8595 Kgs or 171.90 bags = 171.90/2.080 = 82.64 bags per KMCement ( Filler material) Rate (appx.) Rs 300/- per bag Works out to = 82.64 x 300 = Rs 24792/KM Note :- These calculations are approximate and prepared for guidance to field staff, however actual calculations shall be based on the design mix.

ANNEXURE - II

Job Mix Formula ( Cl.507.3.3 of MoRTH) :

The Contractor shall inform the Engineer in writing, at least 20 days before the start of the work, of the job mix formula proposed for use in the works, and shall give the following details:

(i) Source and location of all materials;(ii) Proportions of all materials expressed as follows where each is applicable

(a) Binder type, and percentage by weight of total mixture;(b) Coarse aggregate/Fine aggregate/Mineral filler as percentage by weight of total aggregate including mineral filler;

(iii) A single definite percentage passing each sieve for the mixed aggregate(iv) The individual gradings of the individual aggregate fractions, and the proportion

of each in the combined grading.(v) The results of tests enumerated in Table 500-11 as obtained by the Contractor;(vi) Where the mixer is a batch mixer, the individual weights of each type of

aggregate, and binder per batch,(vii) Test results of physical characteristics of aggregates to be used;(viii) Mixing temperature and compacting temperature.

While establishing the job mix formula, the Contractor shall ensure that it is based on a correct and truly representative sample of the materials that will actually be used in the work and that the mixture and its different ingredients satisfy the physical and strength requirements of these Specifications.

Approval of the job mix formula shall be based on independent testing by the Engineer for which samples of all ingredients of the mix shall be furnished by the Contractor as required by the Engineer.The approved job mix formula shall remain effective unless and until a revised Job Mix Formula is approved. Should a change in the source of materials be proposed, a new job mix formula shall be forwarded to the Engineer for approval before the placing of the material.

Plant trials - permissible variation in job mix formula:Once the laboratory job mix formula is approved, the Contractor shall carry out

plant trials at the mixer to establish that the plant can be set up to produce a uniform mix conforming to the approved job mix formula.

The permissible variations of the individual percentages of the various ingredients in the actual mix from the job mix formula to be used shall be within the limits as specified in Table 500- 13. These variations are intended to apply to individual specimens taken for quality control tests in accordance with Section 900.

Once the plant trials have demonstrated the capability of the plant, and the trials are approved, the laying operation may commence. Over the period of the first month of production for laying on the works, the Engineer shall require additional testing of the product to establish the reliability and consistency of the plant.

Laying Trials: Once the plant trials have been successfully completed and approved, the

Contractor shall carry out laying trials, to demonstrate that the proposed mix can be successfully laid, and compacted. The laying trial shall be carried out on a suitable area which is not to form part of the works, unless specifically approved in writing, by the Engineer. The area of the laying trials shall be a minimum of 100 sq. m. of construction similar to that of the project road, and it shall be in all respects, particularly compaction, the same as the project construction, on which the bituminous material is to be laid.

The Contractor shall previously inform the Engineer of the proposed method for laying and compacting the material. The plant trials shall then establish if the proposed laying plant, compaction plant, and methodology is capable of producing satisfactory results. The density of the finished paving layer shall be determined by taking cores, no sooner than 24 hours after laying, or by other approved method.Once the laying trials have been approved, the same plant and methodology shall be applied to the laying of the material on the project, and no variation of either shall be acceptable, unless approved in writing by the Engineer, who may at his discretion require further laying trials.

ANNEXURE - III

QUALITY CONTROL TESTS AND THEIR MINIMUM FREQUENCY FORSEMI DENSE BITUMINOUS CONCRETE

Sl.No

Test Frequency

1 Quality of Binder 2 Samples for Lot

2 Aggregate Impact Value1 test for 50cum of

aggregates3 Flakiness/Elongation Index of Aggregates -do-4 Stripping Value 1 Set of 3 Specimens5 Water absorption of Aggregates6 Sand equivalent test As required7 Stone polishing value As required8 Mix Grading 2 Tests for day9 Stability of Mix ( by Marshal Test) 2 Tests for day

10 Water Sensitivity of Mix As required11 Swell Test on the Mix As required

12Temperature of Binder, Aggregates at plant &

Mix at the time of laying and rolling.Regular Intervals

13 Binder Content1 Test for 400t. Min 2

Tests for day.

14 Gradation of Mix1 Test for 400t. Min 2

Tests for day.

15 Rate of spread of Mixed materialsRegular check on Wt.of

mix and thickness of layer.

16 Density of compacted layers 1 Test for 250 Sqm area