DESCRIPTION OF DST/DOUBLE SURFACE
TREATMENT
Double
bituminous surface treatment is a term used to explain a common type of
pavement surfacing construction usually 3/4" thick layer which involves
two applications of asphalt binder material (bitumen) and mineral aggregate.
The bitumen is applied by a pressure distributor, followed immediately by an
application of mineral aggregate, and finished by rolling.
Double
surface treatment are generally necessary on untreated water-bound macadam
roads subject to heavy traffic .A semi grout with seal coat or thin carpet
should be preferred to two coats of surface dressing if cost is not
prohibitive. Where the road is rutted or there are depressions more than 6 mm
deep ,two coat dressing should be done.
The second
coat may be applied 24 hours after the first coat or an interval of several
months may elapse. The advantage of allowing an interval between each coat is
that the first coat will have time to settle down under traffic and show up
depressions which can be made up in the second coat, thus ensuring an even
surface. When an interval is to elapse between each application ,the second
method of construction is exactly the same as in the single coat work.
Materials and Procedures
After completion of Water-bound layer construction of DST
consists on following steps.
1) Cleaning of top surface of water-bound and
removal of loose particles of stone dust (used to fill the voids of water-bound
macadam layer).The cleaning should provide a clear sight of stone's top surface
not having dust or stone pieces.
2)After
cleaning water-bound surface we will apply emulsion of prime coat @ 0.09 kgs / sft of surface area of water-bound layer
3) In First
Coat 12MM OR 1/2 " SIZE crush stone will be used @0.05 cu.ft/ Sft of
Water-Bound, Including shower of bitumen @.09 Kgs/Sft covering 80 % height of 1/2" sized crush stones
and this will be the first layer of DST.
4) In Second
Coat/Renewal Coat 8 to 9 MM OR 3/8" SIZE crush stone will be used @0.03
cu.ft/ Sft of Water-Bound, Including shower of bitumen @.11 Kgs/Sft covering 80 % height of 1/2" sized crush stones
and this will be the first layer of DST.
Seal Coat
Surface
dressing (gritting)or seal coat is required over open textured carpets. Premixed seal using medium course sand or fine grit
32-Cft per every 1000 Sq.Ft and Bitumen 98 Kgs Per every 1000 Sq.ft
