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

Number 0 and 1 are of very low consistency and are fluid at ordinary temperatures and flow like
oil. Number 2 and 3 are thicker and flow slowly at ordinary room temperatures. Number 4 and 5
are thick and sticky almost semi solid and poured with difficulty until heated.
Cutback bitumen is used for cold mix specifications as it will coat cold chippings in drum
mixers, unlike a straight run bitumen a cutback does not harden too rapidly on contact with cold
aggregate.
Bitumen Emulsions: - bitumen emulsified in water is called bitumen emulsion. Bitumen blended
with petroleum distillate is known as cutback bitumen.
Bitumen emulsions are chocolate brown colour. If mixed with petrol, kerosene, or diesel oil,
globules of water will appear. Emulsions have the advantage that they can be applied cold and
can be used on damp surface and wet aggregate although they are not always successful if laid
in wet weather. Cutback can be used when the road surface and also the aggregate are dry.)
Emulsions are not as competent, especially under heavy traffic as hot bitumen, and should be
used with discretion. They are not also cheap in real cost as about half the volume is water.
(Emulsion contain water cutbacks contain solvent.)
There are three grades of emulsions - (i) Quick breaking or rapid setting (RS), (ii) Medium
breaking or medium setting (MS) and (iii) Slow braking or Slow setting (SS). (The terms curing or
cutting are also used instead of setting and breaking). The time taken for breaking of an emulsion
is the measure of its grade and the type of work which to be used.
In order to decide whether the sample is suitable for surface dressing or grouting for coated
macadam or for soil stabilization it is necessary to know whether it is breaking or slow breaking.
The breaking rate can be assessed as follows:
Put some clean gravel or crushed stone into a pan and try to mix the emulsion with it
using a metal spoon. a fast breaking emulsion cannot be mixed in this way as it breaks gumming
up the spoon with bitumen. While a slow breaking emulsion will mix perfectly coating the spoon
the pan and aggregate,
Normally two types of bitumen emulsions are used for road work in INDIA -(i) quick
braking and (ii) slow breaking quick breaking emulsions are used for surface painting tack, c oats,
seals coats, and grouting. The emulsions for such works should have minimum 50% of bitumen
content slow breaking emulsion are used for pre mixing and patch repairs during wet weather.
This emulsion should have min: 60 per cent of bitumen content.
Bitumen emulsion is applied at atmospheric temperature but no work should be carried
out in frosty weather as emulsion is liable to be adversely affected by frost. Not work should be
undertaken when it is actually raining.
501.2.2. Coarse Aggregates: The coarse aggregates shall consist of crushed rock, crushed
gravel or other hard material retained on the 2.36 mm sieve. They shall be clean, hard, and
durable, of cubical shape, free from dust, organic or other deleterious matter. Where the
Contractor’s selected source of aggregates have poor affinity for bitumen, as a condition for the
approval of that source, the bitumen shall be treated with approved anti -stripping agents, as per
the manufacturer’s recommendations, without additional payment. Before approval of the source
the aggregates shall be tested for stripping. The aggregates shall satisfy the physical
requirements set forth in the individual relevant clause for the material in question. Where
crushed gravel is proposed for use as aggregate, not less than 90% by weight of the crushed
material retained on the 4.75 mm sieve shall have at least two fractured faces.
501.2.3. Fine Aggregates: Fine aggregates shall consist of crushed or naturally occurring
material, or a combination of the two, passing 2.36mm sieve and retained on the 75 micron sieve.
They shall be clean, hard, durable, dry and free from dust, organic or other deleterious matter.