MANUAL 4 - Construction Industry Development Board

MANUAL 4 – BITUMINOUS PAVEMENT SEALS
6.4 Application of binder for the seal
6.4.1 Types of binder
Emulsions are ideal for manual application as they do not have to be heated to temperatures
of 130°C – 140°C as is the case for penetration bitumen.
As they contain 35 – 40% water, the problem of over application, resulting in bleeding of the
surface is overcome to a large extent.
The following binders can be used for seal work:
• Anionic spray grade emulsion (60% bitumen and 40% water).
The viscosity of this binder is lower than the viscosity of a cationic emulsion, and the
rate of application for a tack coat reduces to approximately 0,7 to 0,8 litres per m 2
before the binder tends to flow, even when minimum gradients pertain.
Generally they do not require heating unless the air temperature at the time of
spraying is below 20 – 25°C.
• Cationic spray grade emulsion ( 65% bitumen and 35% water).
This emulsion is ideal for seal work. In cool weather it is advisable to heat the emulsion
with a low flame to 50°C.
Note
The flow properties of this emulsion are better than Anionic emulsions.
It is essential when using Cationic emulsion for the equipment to be thoroughly cleaned
out of any Anionic emulsion. The equipment must be flushed out with water and paraffin.
When heating Cationic emulsion, care must be taken to heat it with burners on a low
flame, The temperature to which it is heated must not exceed 50°C.
6.4.2 Rate of application of binder
The amount of binder that is required per m 2 is dependent on the size of aggregate to be
used (e.g. less binder is required for a 13 mm aggregate than for a 19 mm aggregate) and the
spacing between the aggregate.
It is therefore essential to determine the ALD of the stone before the quantity of binder can
be determined.
The amount of 60% or 65% emulsion for a single seal can be determined from Graph 4.2.
IMPLEMENTING EMPLOYMENT INTENSIVE ROAD WORKS 69
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