Prepared by : Engr. Md. Abdul Majid. Regional Engineer, Kabul.
NEEPRA, UNOPS
IntroductionWhen single application of bituminous material and
cover by the aggregate is called Single Bituminous Surface
Treatment (SBST).
When double application of bituminous material and covered by
the aggregate is called Double Bituminous Surface Treatment
(DBST)
Materials for surface Treatment
Generally two types of material required for DBST work A.
Bituminous Material B. AggregateA. Bituminous Material : The
materials shall be penetration grade bitumen (80/100 grade bitumen
blended with 5% - 10% Kerosene) Before use , bitumen should be
checked in laboratory either it is satisfied the specification or
not.
B. Aggregate : The aggregate shall be crushed stone or crushed
gravel of single size. 1st layer material size is bigger than 2nd
layer material. The nominal size of chipping selected for the 2nd
layer shall then be about half the normal size of the 1st layer to
promote good interlock between the layers. i.e. 1st layer 20mm,
then 2nd layer will be 10mm. 1st layer 14mm, then 2nd layer 7mm
.
Requirement of Aggregate:The crushed stone aggregate shall
conform to the following quality:a) The Flakiness index shall not
more then 35%.b) The Aggregate Crushing value shall be less than
30%.c) Ten percent fines shall more than 175 KN.d) Loss of sodium
sulphate soundness less than 10%e) 75% of particles shall have at
least two broken faces.
Gradation of Aggregate:
Standard Specification of DBST work.
Construction Method:1. Weather limitations : The ambient temp.
shall be at least 15 degree C. 2. Cleaning and Preparation of
Surface : 3. Application of Bituminous materials. 4. Spreading of
Stone chips: 5. Rolling : 6. Opening to Traffic.
