MANUAL 4 - Construction Industry Development Board

MANUAL 4 – BITUMINOUS PAVEMENT SEALS
Photo 4.22
• The mixing must produce a consistency which is creamy and although very soft when
dropped from the mixer into the wheelbarrow (Photo 4.23), it will fall in similar fashion
to fresh cow dung without splashing, with a tendency to flow outwards for some 60 to
70 mm.
Photo 4.23
• The inside of the drum must be continually inspected for caking at the bottom of
the drum. This will be evident when, after mixing for ± 2 min, a watery mixture of
emulsion and aggregate (poorly graded) appears to form.
Some of the aggregate will have caked at the bottom of the
drum.
Note
• This will occur if the operator has kept the drum in the
semi-vertical position for extended periods while mixing. To
rectify this situation, place the drum in the near horizontal
position and tap the base of the drum with a 2 kg hammer.
Immediately the cake will be released and the mixture will
revert to the creamy smooth mixture.
IMPLEMENTING EMPLOYMENT INTENSIVE ROAD WORKS 45
The operator of the concrete mixer is in charge of
the discharging operations and must ensure that the
barrows are correctly placed, so that when discharging
of the drum occurs, the slurry falls well within the bowl
of the barrow without any wastage or mess taking place
(Photo 4.23). Only half barrow loads must be discharged
and not full loads.
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