WATER BOUND MACADAM BASE
DESCRIPTION
This work shall consist of furnishing and placing one or more courses of clean
crushed stone base mechanically interlocked by rolling, and voids thereof filled
with screening and binding material with the assistance of water, laid on a
prepared subgrade, sub base, or existing pavement in conformity with the lines.
grades and cross-sections shown on the drawings.
Unless otherwise directed by the Engineer this item of work may be applied to
road structure or shoulders.
Coarse aggregates either crushed or broken stone shall conform to the quality
requirements as specified hereunder, except that no CBR testing will be required.
The gradation curve of the coarse aggregate shall be within the envelop limits
given below:-
Sieve Designation Percent Passing by weight
mm Inch Class A Class B Class C
102 (4") 100
89 (3.1/2:) 90 - 100
76 (3") - 100
63.5 (2.1 /2") 25 - 60 90 - 100 100
50 (2") - 25 - 75 90 - 100
37.5 ( 1.1 /2") 0 - 15 0 - 15 35 - 70
25 ( 1 ") - - 0 - 15
19 (3/4") 0-5 0-5 0-5
12.5 ( 1 /2") - - -
Fine aggregate (filler material or screenings) shall consist of crushed stone
screenings or any other fine material approved by the Engineer. It shall be free
from clay lumps, dirt and other objectionable material. The fine aggregate
shall be of the following gradation.
Sieve Designation
mm Inch Percent Passing by weight
9 3/8 100
4.35 No. 4 85-100
0.15 No. 100 10-30
The material passing No. 40 sieve shall have a liquid Limit of not more than twenty
five (25) and a Plasticity Index of not more than six (6).
Physical Requirements
The additional physical requirements of coarse aggregates for water
bound macadam will satisfy the following limits:-
a. Loss Angeles Abrasion Value Max 45%
b. Flakiness Index Max 15%
c. The loss when subject to five cycles of the Sodium
Sulphate
Soundness test (AASHTO T-104) shall be less than twelve (
12).
Binding Material
Binding material to prevent raveling of water bound macadam shall
consist of a fine grained material passing 100 percent through 425
micron sieve and
possessing PJ value orrourro nine (4:.HfWliell tt'fe ·watefBo-una
Macadam
(WBM) is to be used as a surfacing course, and upto 6 when WBM is
being
adopted as sub-base/base course with bituminous surfacing. If lime
stone
formations are available nearby, lime stones dust or as directed by
the
Engineer, may be used fully employed for this purpose.
CONSTRUCTION REQUIREMENTS Equipment
Any combination of machines or equipment that will produce the
results meeting these specifications may be used with the approval of the
Engineer. These include mechanical spreaders, water sprinklers and
rollers/compactors.
Structure Preparation
Preparation of surface for water bound macadam, shall be carried out in
the same manner as for aggregate base course item 202.3.1.
Where the existing road surface is black topped, 50 mm x 50 mm
furrows shall be cut in the existing surface at one (1) meter intervals at
forty five (45) degree to the centre line of the carriage-way before
proceeding with the laying of coarse aggregates.
Before starting with WBM Construction, necessary arrangements shall be
made for the lateral confinement of aggregates. One method is to
construct side shoulders in advance to a thickness corresponding to the
compacted layer of the WBM course. After shoulders are ready, there
inside edges may be trimmed vertical and the included area cleaned of
all spilled material thereby setting the stage for spread of coarse
aggregates. The practice of constructing WBM in a trench section
excavated in the finished formation must be avoided.
Spreading and Compaction
Crushed stone shall be deposited and spread on the prepared surface to the
proper depth so that the compacted layer will not exceed two and a half
(2.1/2) times the thickness of maximum aggregate size. Each layer shall be
inspected thoroughly before screenings are being applied. The surface shall be swept with mechanical or
rolling to detect high or hand brooms to aid spreading of the screenings.
spots. Crushed stones shall
be added or shifted When the interstices in the coarse aggregate are filled with screenings, the
.provide a true surface. surface shall be sprinkled with water until it is saturated. . The rolling,
course aggregate layer, after sprinkling and application of additional screenings shall continue until a grout
being laid to proper thickness,is formed that fills all the voids and forms a wave of grout in front of the
shall be lightly rolled sufficient
roller.
only to establish the required
grade and level of the stonesWhen more than one layer is required to complete the Macadam base
course to the thickness shown on the drawings, each layer shall be
Spreading of the coarse
constructed as before prescribed.
aggregates shall be followed
by rolling with a smooth wheel Construction Control Testing
roller weighing at least 10 tons.
Rolling shall begin at the lower
Tests for compliance with the requirements of Item 206.2 will be made as
edge of the shoulders to lock
often as deemed necessary and to the satisfaction of the Engineer.
the stones firmly at the edge,
then progress gradually
Maintenance
towards the centre line.
Rolling shall continue until
aggregate is well keyed The completed base course shall be maintained in an acceptable condition
does not creep ahead of until the necessary subsequent treatment is applied.
roller.
MEASUREMENT AND PAYMENT
In no case, shall coarse
aggregates be stored in heaps Measurement
directly on the area where
these are to be laid nor shall The quantity of Water Bound Macadam Base to be paid for shall be
the hauling over a partly measured by the theoretical volume in place, as shown on the Drawings or as
completed base be permitted directed and approved for construction by the Engineer, placed and
however dumpers shall accepted in the completed Waterbound Macadam Base Course. No allowance
will be given for materials placed outside the theoretical limits shown on the
allowed at the construction area
where the material will cross-sections.
spreaded quickly after dumping.
Payment
Following the initial rolling, The accepted quantities measured as provided above shall be paid for at the contract unit p
screenings shall be applied items listed below and shown in the Bill of Quantities, which price and payment shall cons
uniformly over the surface. watering, rolling, labour, equipment, tools and incidentals
rolling shall be continued while
