WBM ROADSWBM ROADS

Dr. B.SRIDHAR

TYPES OF HIGHWAY CONSTRUCTIONTYPES OF HIGHWAY CONSTRUCTION

The highways types are classified as below

* Earth and gravel roads

* Soil stabilized roads

* Water bound macadam (WBM)

* Bituminous roads

* Cement Concrete roads

PAVEMENT TYPESPAVEMENT TYPES

The selection of base course and the surface course depends upon the following factors:

* Type and intensity of traffic

* Funds available

* Subgrade soil and drainage conditions

* Availability of construction materials at site

* Climatic conditions

* Plants and equipment available

* Time available

The highway construction project may be broadly divided in two phases

* Earthwork and preparation of subgrade

* Pavement structure

WBM ROADSWBM ROADS• By John Macadam• Made of crushed or broken aggregate

mechanically interlocked by rolling and the voids filled with screening and binding material with the assistance of water

• Used as a Sub-base, base course or surface course

• Thickness ranges from 10 to 7.5 cm depending on the size and gradation of the aggregates used

SPECIFICATIONSSPECIFICATIONS

Type of Course aggregates• Generally consists of hard varieties of crushed

aggregates or broken stones

Property

Requirements for pavement layer

Sub-base Base course Surfacing course

Los angeles abrasion 60 50 40

Impact value 50 40 30

Flakiness index - 15 15

Size and grading requirements of coarse Size and grading requirements of coarse aggregateaggregate

Grading No. Size range,mm Sieve size mm % passing the sieve by wt.

1 90 to 40 100

80

63

40

20

100

65-85

25-60

0-15

0-5

2 63 to 40 80

63

50

40

20

100

90-100

30-70

0-15

0-5

3 50 to 20 63

50

40

20

10

100

95-100

35-70

0-10

0-5

SCREENINGSSCREENINGS

Used to fill up the voids in the compacted layer of coarse aggregates

Non plastic materials like Moorum or gravel

LL < 20%

PI < 6%

* Portion of material passing 0.075 mm < 10%

The grading requirements of screenings for The grading requirements of screenings for WBM construction WBM construction

Grading Size of screening

Mm

Sieve size mm

% passing the sieve, wt

A 12.5 12.5

10.0

4.75

0.15

100

90-100

10-30

0-8

B 10.0 10.0

4.75

0.15

100

85-100

10-30

Binding materialBinding material

• Fine grained material is used to prevent ravelling of the stones.

• P.I 4 % – 9% for surface course• P.I < 6 % for base course

Note: If the screenings used consists of crushable material like moorum or soft gravel, there is no need to apply binding material.

Construction procedureConstruction procedure

Preparation of foundation for receiving the WBM course

Provision of Lateral confinementSpreading of Coarse aggregatesRollingApplication of screeningsSprinkling and GroutingApplication of Binding MaterialSetting and Drying