MANUAL 4 - Construction Industry Development Board

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MANUAL 4 – BITUMINOUS PAVEMENT SEALS
5.3.3 Prime coat
It is claimed that Otta seals do not require primed surfaces on which they are to be
constructed (except in the case of calcareous material).
On labour-intensive projects, where the work proceeds relatively slowly and the constructed
base may be opened to traffic for extended periods, it is recommended that the base be
primed, using an inverted emulsion prime at the maximum rate of 0,7 litres/m 2 , depending
on porosity/absorption of the base.
The prime can be applied with the motorised hand sprayer as the work proceeds and so
protect the base or open the base to light traffic.
If the base is an ETB, a diluted emulsion can be used instead of the inverted prime.
5.4 Use of pan and cylinder to determine aggregate application rate for
Otta seal
5.4.1 General
The pan and cylinder method is a quick manner of determining the ALD (average least
dimension) of the aggregate, i.e. by placing the aggregate in the pan, shoulder to shoulder,
pouring this quantity of aggregate into the cylinder using a graduated scale measuring the
depth of aggregate in the cylinder. (Figure 4.18)
This depth of aggregate equates to the ALD of the stone and, if divided by 1 000, gives the
rate of application in m 3 /m 2 required for the aggregate.
This procedure is applicable for normal seals for determining the ALDs.
5.4.2 Use for Otta seal
The pan and cylinder is eminently suitable for determining the rate of application of the
aggregate for Otta seals as follows:
• Fill the pan with the approved graded stone to a depth required in the field, e.g.
16 mm or 19 mm and how it should look after application – before rolling.
• Pour the contents in the pan into the cylinder, carefully without spilling any of the
aggregate.
• Drop the cylinder three or four times from a height of 50 mm onto a firm surface to
settle the contents. Level off the top of the surface on which you place the graduated
scale.
• Read off the remaining height on the graduated scale and this reading will give the
theoretical ALD/or thickness of the layer as placed in the pan and required in the field,
e.g. 20,6 mm.
• By dividing this reading on the graduated scale by 1 000, the rate of application in
m 3 /m 2 is established.
e.g. 20,6 mm 3 1 m 3 1 m = 0,0206 m 3 /m 2
1 000
• From this required rate of application, the spotting distances can be calculated for the
known half width of the road.
IMPLEMENTING EMPLOYMENT INTENSIVE ROAD WORKS 88