Dense Bituminous Macadam (DBM) is a binder course used for roads with more number of heavy commercial vehicles and a close-graded premix material having a voids content of 5-10 per cent.

1. Dense Bituminous Macadam

2. Presentation Outline:
• Introduction
• Why DBM?
• Design Criteria
• Materials
• Construction
• References

3. Introduction:
• Dense Bituminous Macadam (DBM) is a binder course used
for roads with more number of heavy commercial vehicles
and a close-graded premix material having a voids content of
5-10 per cent.

4. Why DBM?
• This material has increased in popularity due to durable
surface which performs almost well as in all situations.
• Suitable for all pavement layers and for all traffic conditions.
• DBM provides a good quality smooth surface and improved
skid resistance.

5. DESIGN CRITERIA(IRC:94-1996):
• Due to high cost of DBM it should be properly designed
according to standard design method so as to satisfy certain
criteria needed to assure adequate stability and durability.
SR No. Designation Requirement
(I) Number of Compaction blows on each end of
Marshall specimen
75
(II) Marshall Stability in Kg.(Minimum) 340
(III) Marshall flow in mm 2-4
(IV) VMA 5-10
(V) VFB 55-75
(VI) Bitumen content percent by weight of total mix 4.5-6.0

6. MATERIALS:
• In order to satisfy Design criteria, DBM mix shall consists of
Coarse Aggregate, Fine Aggregate and filler in suitable
proportions with required binder content.
• Proper Blend of aggregates should be done to so that final
gradation will satisfy either two limits according to thickness
in following table.

7. CONTI..
Sieve Size(mm)
Grading Number
1(For Layer thickness
≤50mm)
2(For Layer thickness
≥50mm)
(Percentage Passing)
37.5 - 100
26.5 100 85-100
19 85-100 71-95
13.2 63-82 58-82
9.5 52-74 52-72
4.75 39-54 35-50
2.36 28-43 28-43
0.60 15-27 15-27
0.3 7-21 7-21
0.15 5-15 5-15
0.075 2-8 2-8

8. Coarse Aggregate (retained on 2.36mm sieve):
• Preferably it should be hydrophobic and of low porosity.
• If hydrophilic aggregates are to be used the bitumen shall be
treated with antistripping agents.
• In case of more porous aggregates extra bitumen for
absorption by aggregates shall be provided to satisfy design
criteria.

9. CONTI..
Test Maximum percent
Aggregate impact value 35
Los Angeles Abrasion Value 40
Flakiness Index 35
Stripping Value 25
Soundness:
I)Loss with sodium sulphate-5 cycles
II)Loss with Magnesium sulphate-5
cycles
12
18
Water Absorption 2

10. Fine Aggregate (passing on 2.36mm and
retained on 75µm):
• Crushed Screenings, natural sand or mixture of both.
• Shall be clean, hard, durable dry and free from organic
substances.
Filler (passing 75 µm):
• Stone dust, cement, hydrated lime, fly ash or other non-
plastic mineral matter.
• Normally Filler requirement is met by the material passing
through 75 µm sieve in fine aggregate, if fine aggregate is
deficient then extra filler is added. Extra filler should be as
following:

11. CONTI..
Sieve % passing
600 µm 100
150 µm At least 90
75 µm >70
BITUMEN:
• The bitumen shall be viscosity grade paving bitumen
complying with the Indian Standard specification IS:73.

12. JOB MIX FORMULA:
• While the laboratory mix design gives the different
proportions of the mineral aggregate combinations in terms
of individual sieve sizes, for actual operational purposes in the
field, blending of two or more sizes of aggregate in terms of
weight or volume would be necessary.
• This blending ratio can be on a weight basis by giving percent
weight of the CA, FA and filler needed to give the aggregate
gradation.
• It can also be proportioned on a volumetric basis based on
the unit weight or bulk density of the aggregate supplied.

13. CONTI..
• The mineral aggregate content with Optimum Binder Content
as determined in the laboratory constitutes the job-mix
formula.
• Mix design shall be carried out, based on a correct and truly
representative sample of the materials that will actually be
used in the specific construction project.

14. CONSTRUCTION:
– PREPARATION OF BASE:
• The base on which dense bituminous macadam is to be laid
shall be prepared to the specified dimensions.
• The surface shall be thoroughly swept and free from dust and
other materials.
• If the base is irregular and wavy then proper corrective course
of adequate thickness is provided to rectify the profile.

15. CONTI..
• After that Tack coat(asphalt applied before a road is laid to
form an adhesive bond) is provided as per type of surface as
follows:
Rate Surface
6 to 7.5 Kg per 10 square meter Dry
5 to 5.5 Kg per 10 square meter Normal bituminous surface
7.5 to 10 Kg per 10 square meter Non-bituminous surface

16. CONTI..
- PREPARATION OF MIX:
• Preparation of mix is carried out in Hot Mix Plant of adequate
capacity.
• Plant may be either batch type or a continuous type.

17. CONTI..
-SPREADING OF THE MIX:
• The Mix shall be transported by tipper truck and spreading
done by mechanical paver.
• It should be spread in such a manner that after compacting
required thickness binder course is uniformly laid.

18. CONTI..
-COMPACTION:
• The Mix after spreading shall be compacted by rolling by a set
of rollers at a speed not more than 5km/hour.
• Typical roller position used in compaction is:
1) Initial or break down rolling » By 8 to 12 tonnes, three
wheel steel roller

19. CONTI..
2) Intermediate rolling
» By 15 to 30 tonnes,
smooth wheel pneumatic
roller
3) Finished rolling
» By 8 to 10 tonnes,
tandem roller

20. CONTI..
• Wheel of rollers should be kept moist to prevent the mix from
adhering to them. Rolling shall commence from longitudinally
from edge and proceed towards centre. Rolling shall be
continued till desired density is achieved.

21. CONTI..
-OPENING TO TRAFFIC:
• Traffic can be allowed after completion of the final rolling
when the mix has cooled down to the surrounding
temperature.

22. REFERENCES:
• IRC 94-1986 : Specification for Dense Bituminous
Macadam
• MORTH(5th Revision):SPECIFICATIONS FOR ROAD
AND BRIDGE WORK
• pavementinteractive.org
• pavingexpert.com