Specification Part 3 - Road & Bridge Works - Urban Administration ...

(k) Use of Premix seal coat:- It is intended for sealing the voids in the bituminous surface over
which it is laid and is needed only for those surface, which are textured eg: an open graded
premix carpet.
(l) Use of Slurry seal: - Slurry seals can be used for both preventive and corrective maintenance
of aged bituminous surfaces and surface with fine cracks. They seal surface cracks, fill voids and
minor depressions, and provide a more even riding surface or base for further treatment. They
may also be used on top of single coat surface dressing.
(m)Use of bituminous cold mix (including gravel emulsion): designed cold mix:- Bituminous
cold mixes are used in situation where hot-mix plants are not readily available including for
working in remote areas and maintenance operations.
(n) Use of Bituminous cold mix (including gravel emulsion): recipe cold mix: - These
mixtures are considered suitable for use only for emergency and minor repair work and temporary
road surface improvement.
(o) Use of Modified binder: emerging materials:- The use of these material is expected to
result in an extended service life of bituminous pavement subjected to heavy traffic and in
extreme climate conditions, thus justifying the extra cost of adding modifier/fibers. other
advantages includes: lower temperature susceptibility, higher resistance to ageing, higher fatigue
life, higher resistance to cracking and better adhesion between aggregates and binder.
501.2. Materials
501.2.1. Binder:-
(a) Bitumen: - Bitumen is a petroleum product. The colour of bitumen is dark brown to black.
(b) Choice of binder: - Binders are manufacture in many different grades of consistency from
very fluid that pour at atmospheric temperature to hard material. The road engineer is presented
with a somewhat bewildering number of alternatives. The choice of a particular type or surfacing
material is determined by economic as well by technical consideration. There are always
movement in the road surface due to exposed to weather or for other reasons it become brittle at
low temperature high stresses are developed when movements occur and the bond between
adjacent stones can then be easily destroyed. To reduce the effect of hardening as soft a grade
of bitumen as practicable should be used without danger of the surface "pushing" or" waving".
Road surfacing vary widely in their texture in the more open textured type the bitumen
acts as an adhesive between stone and road or between stone and stone, and in the dense close
textured type the bitumen act in combination with the fine aggregate as a plastic mortar. These
binder are required to remain in a plastic condition so that the surfacing can accommodate itself
without cracking to small movements induce in the road by temperature variations, moisture
changes and traffic. Binder must also be sufficiently viscous and resilient possessing shock
absorbing qualities to resist the forces of the traffic (impact). Adhesion and viscosity are thus the
important physical properties of bitumen.
Bitumen is not suited to damp or water logged areas as regards road construction work.
The higher the viscosity the greater is the strength of the surfacing up to a limit when
viscosity reaches some high values it imparts brittleness to the material. The viscosity of the
binder should be selected according to the intensity of the traffic on the road and also the
temperature in which work is to be carried out. Low viscosity binder can be laid cold and high
viscosity binder has to be laid hot and is used in warmer weather. A more viscous binder is
specified for the more heavily trafficked roads to resist distortion under the intense traffic and
should be laid warm or hot within a few hours of manufactures. Where binders of relatively low
viscosity are used the resulting surfacing is initially soft and may be deformed if it receives traffic
immediately after being laid.
Adhesion: - The construction or maintenance of road/is primarily a problem of adhesion. Bitumen
adheres well to all stones normally used as road aggregates provided they are dry and not unduly
dusty. Moisture is the chief cause of stripping and swelling. Some stones have greater surface