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3.0 ROAD CONSTRUCTION TECHNOLOGY

Er. Sabin Pokhrel

3.5 Construction of Bituminous Pavements

■ Roads in which bitumen is used as binder is termed as bituminous

pavement.

■ Stage development can be adopted depending on traffic demands

■ Bitumen content over optimum value is harmful reducing strength and

stability

3.5 Construction of Bituminous Pavements

■ Optimum binder content is determined by: surface area of aggregates

and techniques of construction.

■ Bituminous aggregate mixtures during mixing and compaction

operations are major issues.

3.5.1 Types of Bituminous Construction of Roads

■ 1. Classification based on Construction Technique

– Interface Treatments

– Surface dressing and seal coat

– Grouted or penetration macadam

– Premix Construction


■ 2. Classification based on temperature of Binder

– Hot mix

– Cold mix (Cutback and Emulsion)


■ 3. Classification based on method of mixing

– Road Mix method

– Central plant mix method


■ 4. Classification based on texture exhibited by compacted layers

– Open graded (Premixed Carpet)

– Dense Graded (Bituminous Concrete)


■ Binders may be road tars, cutback, emulsions etc.

■ Choice depends upon type of construction, technique, equipments

availability, climatic conditions etc.


■ Bituminous Concrete: mixture of controlled graded coarse aggregate

and bitumen.

■ Mastic Asphalt: mixture of bitumen, fine aggregates and fillers.

■ Rolled or Sheet Asphalt: mixture of bitumen and sand without any

coarse aggregates.


■ Hot mix method: binder and aggregate both heated before use

■ Cold Mix Method: Binder and aggregates not heated.

■ Road Mix: materials mixed at road side

■ Central Plant Mix: hot mix plant is situated centrally to the length of the road.

3.5.2 Interface Treatment

■ When a bituminous wearing surface is to be placed upon a previously

untreated compacted foundation layer such as earth, WBM, gravel etc.

it is necessary to bond the new surface with existing surface

developed with a bituminous material is known as interface

treatment.

3.5.2 Interface Treatment

■ TYPES:

■ Prime coat

■ Tack coat

Prime Coat

■ First application of low viscosity liquid bituminous material

■ Functions:

– Bond between base and the wearing surface

– Sealing of pore and capillary voids, water proofing

– Binding loose aggregates on existing surface

Prime Coat

■ Bituminous primer of suitable grade or viscosity is chosen and

sprayed uniformly at the rate of 7.3~14.6 kg/10 sq.m area depending

on porosity

■ Curing for at least 24 hrs is done

■ No traffic is allowed during the curing period

Prime Coat

Tack Coat

■ Single initial application of bituminous material on existing pavement

surface relatively impervious.

■ Applied with higher viscosity bituminous material

■ Generally hot bitumen at the rate of 4.9~9.8 kg/ 10 sq. m.

■ Ensures adhesion between existing surface and new bituminous

surface.

Tack Coat

3.5.3 Bituminous Surface Dressing

■ Bituminous Surface dressing refers to thin surface coverings of

bituminous layer and mineral aggregate.

■ It prevents removal of binding materials from WBM

Types:

■ Single coat Surface Dressing

■ Double Coat Surface Dressing

Single coat Surface Dressing

■ Single application of thin layer of bitumen followed by cover materials

of specified size stone aggregate, compacted by rollers

Double Coat Surface Dressing

➢ In this type of surface treatment, immediately after laying the first coat, second application of binder is applied and followed by uniform spreading of cover materials of smaller sized aggregate and then rolled.

Functions:

✓ To provide a dust free pavement surface over a base course in dry weather and mud free pavement in wet weather.

✓ To provide a waterproof layer and to prevent infiltration of surface water.

Construction steps of Double coat surface dressing

■ Preparation of existing surface

■ Application of binder

■ Application of stone chippings

■ Rolling

■ Application of binder and stone chipping for second coat

■ Finishing and opening of traffic

Sheet Asphalt

■ Carpet of sand-bitumen mix of compacted thickness 25 mm without coarse

aggregate

■ Materials used are sand,filler and bitumen

■ It is called as rolled asphalt in Britian

■ It is usually laid over cement concrete pavement to provide an excellent riding

surface

Mastic Asphalt

■ Mixture of bitumen, fine aggregate and filler in suitable proportion yielding a void

less and impermeable mass.

■ It has a property of self-healing of cracks without bleeding

■ It is mostly used on the surfaces on bridge deck slab,etc

Seal Coat

■ Very thin surface treatment or single coat surface dressing, either applied as a final step in new surface or existing surfaces which are worn out.

■ Premixed sand bitumen (Hot Mix) is commonly used over premixed carpet.

■ Purpose:

– Seal against ingress of water

– Increase resistance to skid

– Increase strength and bearing capacity of existing surface

Otta Seal

■ Bituminous surfacing consisting of graded aggregates ranging from

natural gravel to crushed rock combined with soft binders with or

without sand cover seal.

■ Single otta seal with or without sand cover seal with aggregate grading

open, medium or dense

■ Double otta seal with or without sand cover seal with aggregate

grading open, medium or dense

Otta Seal

■ Materials:

– Bitumen

– Aggregate: clean strong hard and durable

■ LAA value 40% max

■ Aggregate impact value 30% max

■ Flakiness index 30% max

■ PI <5% preferable

■ Gradation as per specification either open, medium or dense

Otta Seal

■ Coarse Sand: Clean, hard and durable

– Gradation all passes from 6.7mm

Otta Seal

■ Equipments:

– Storage tank with bitumen heating device

– Mechanical Broom or hand brushes

– Air Compressor

– Bitumen Distributor

– Aggregate Spreader

– Pneumatic Rollers

Otta Seal

■ Construction Steps:

■ Preparation and intensive cleaning of existing surface by mechanical broom or hand brushes

■ Application of prime coat

■ Spreading of binder

■ Spreading of aggregate of specified grading

■ Rolling by 2 pneumatic rollers at a min. wt. 12t or more with minimum of 15 passes

Otta Seal

■ Apply one pass with 10~12 t static steel roller to improve the

embedment of larger aggregate

■ For first 2 days after sealing, extensive rolling shall be applied by

pneumatic roller with minimum of 15 passes daily

■ Spreading of binder

■ Spreading of sand

Otta seal

■ Rolling with pneumatic roller and curing the surface till four weeks

■ After 8~12 weeks second coat is executed with all the above steps

Otta Seal

■ Quality control

– Conditions of the equipments

– Temperature of binder

– Penetration, viscosity and ductility test on binder

– Gradation, LAA, ACV, AIV, FI, PI test on aggregates

– Rate of application of binder and aggregates

Otta Seal

■ Precautions:

– Equipments should be in perfect running condition

– Coordination between labors, equipments and supervisor should

be excellent

– Caring immediate post construction, traffic management, follow-

up inspection

Grouted or Penetration Macadam

■ In penetration macadam construction , high viscosity bitumen is sprayed in fairly large quantity after the aggregates are spread and compacted.

■ The bitumen penetrates into the voids from the surface of compacted aggregate thus filling up a part of the voids and binding the stone aggregates together.

■ It is used as a base or binder course

Types:

a)Full Grout

b)Semi Grout

➢ When the bitumen penetrates to the full depth of compacted aggregate, it is called

full grout and when it penetrates up to about half the depth, it is called semi grout.

➢ Full grout is adopted in the regions of heavy rainfall and semi grout is adopted in the

regions of moderate rainfall and traffic.

➢ The construction of penetration macadam is recommended for thickness of 50-75

mm.

Bituminous Concrete

■ It consists of dense grading of coarse aggregate, fine aggregate and mineral filler

coated with bitumen binder.

■ The thickness depends upon the traffic intensity and quality of base course and

ranges from 40 to 75 mm.

■ This kind of surfacing is more durable, have better riding quality and more load

carrying capacity.

Bitumen Bound Macadam

■ It consists of one or more course of compacted coarse aggregate

premixed with a bituminous binder and laid immediately after mixing

and then compacted.

■ When this layer is exposed as a surface course, at least a seal coat is

necessary.

■ It is laid with usual thickness of 5-7.5 cm

Construction procedure of bituminous bound macadam

■ Preparation of Underlying layer

■ Application of tack coat or prime coat

■ Premix preparation

■ Placement

■ Rolling and finishing

Bituminous Carpet

■ Bituminous premixed carpet is prepared from stone chippings 10 mm and 12 mm

size, premixed with bitumen or tar binder and compacted to the thickness usually 2-

2.5 cm

■ It is covered by premixed sand bitumen seal coat before opening to traffic

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