| Construction
Operations: Weather and seasonal
limitations: The provisions of Clause 501.5.1
shall apply, except that laying shall not be
carried out when the air temperature at the
surface on which the Mastic Asphalt is to laid
is below 10’C.
Preparation of the base: The
base on which mastic asphalt is to be laid shall
be prepared, shaped and conditioned to the profile
required, in accordance with Clause 501 or 902
as appropriate or as directed by the Engineer.
In the case of a cement concrete base, the surface
shall be thoroughly power brushed clean and
free of dust and other deleterious matter. Under
no circumstances shall mastic asphalt be spread
on base containing a binder which might soften
under high application temperatures. If such
material exists, the same shall be cut out and
repaired before the mastic asphalt is laid.
Tack coat: A tack coat in
accordance with Clause 503 shall be applied
on the base or as directed by the Engineer.
Preparation of mastic asphalt:
Penetration of mastic asphalt consists of two
stages. The first stage shall be mixing of filler
and fine aggregates and then heating the mixture
to a temperature of 170’C to 210’C.
Required quantity of bitumen shall be heated
to 170’C to 180’C and added to the
heated aggregated. They shall be mixed and cooked
in an approved type of mechanically agitated
mastic cooker for some time till the materials
are thoroughly mixed. Initially the filler alone
is to be heated in the cooker for an hour and
then half the quantity of binder is added. After
heating and mixing for some time, the fine aggregates
and the balance of binder are to be added and
further cooked for about one hour. The second
stage is incorporation of coarse aggregates
and cooking the mixture for a total period of
3 hours. During cooking and mixing, care shall
be taken to ensure that the contents in the
cooker are at no time heated to a temperature
exceeding 210’C.
Where the material is not required for immediate
use it shall be cast into blocks consisting
of filler, fine aggregates and binder, but without
the addition of coarse aggregate, weighing about
25 Kgs each. Before use, these blocks shall
be reheated to a temperature of not less than
175’C and not more than 210’C, thoroughly
incorporated with the requisite quantity of
coarse aggregates and mixed continuously. Mixing
shall be continued until laying operations are
completed so as maintain the coarse aggregates
in suspension. At no stage during the process
of mixing shall the temperature exceed 210’C.
The mastic asphalt blocks (without coarse aggregate)
shall show on analysis a composition within
the limits.
The mixture shall be transported to the laying
site in a towed mixture transporter having arrangement
for stirring and keeping the mixture hot during
transportation.
Spreading: The mastic asphalt
shall be laid, normally in one coat, at a temperature
between 175.C and 210’C and spread uniformly
by hand using wooden floats or by machine on
the prepared and regulated surface. The thickness
of the mastic asphalt and the percentage of
added coarse aggregate shall be in accordance
with Table 500-30 or as specified by the Engineer.
Where necessary, battens of the requisite dimensions
should be employed. Any blow holes that appear
in the surface shall be punctured while the
material is hot, and the surface made good by
further floating.
Joints: All construction joints
shall be properly and truly made. These joints
shall be made by warming existing mastic asphalt
by the application of an excess quantity of
the hot mastic asphalt mixture which afterwards
shall be trimmed to leave it flush with the
surfaces on either side.
Surface finish: The mastic
asphalt surface can have poor skid resistance
after spreading, in order to provide resistance
to skidding, the mastic asphalt after spreading,
while still hot and in a plastic condition,
shall be covered with a layer of stone aggregate.
This aggregate shall be 13.2 mm size (passing
the 19.0 mm sieve and retained on the 9.5 mm
sieve) or 9.5 mm size (passing the 13.2 mm sieve
and retained on the 6.7 mm sieve) or 9.5 mm
size (passing the 13.2 mm sieve and retained
on the 6.7 mm sieve) subject to the approval
of the Engineer. Hard stone chips, complying
with the quality requirements of table 500-17,
shall be precoated with bitumen at the rate
of 2+- 0.4% of S-65 penetration grade. The addition
of 2% of filler complying with Table 500-9 may
be required to enable this quantity of binder
to be held without draining. The chips shall
then be applied at the rate of 0.005 cu.m. per
10sq.m. and rolled or otherwise pressed into
the surface of the mastic layer when the temperature
of the mastic asphalt is not less than 100’C.
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Mastic Asphalt Flooring
Binder:
Subject to the approval of the Engineer, the binder
shall be a paving grade bitumen meeting the specific
requirements.
Traffic
may be allowed after completion of the work
when the mastic asphalt temperature at the mid-depth
of the completed layer has cooled to the daytime
maximum ambient temperature.