Double Bituminous Surface Treatment

 

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