DIGEST 2006 - Sabita

peak value of 1,2 J/cm 2 . Typical
results appear in Figure 1.
(ii) Julian Wise and Derick
Pretorius conducted tests in 2003
to determine the shear force
required to dislodge a UTFC layer
from a continuously graded SABS
mix.
In summary the following
procedures were conducted:
• Base briquettes were
prepared in Marshall moulds
according to the SABS mix
specification, and compacted
to 88% and 90% respectively
of Rice, and allowed to cool;
• Bond coat applied on top of
SABS mix, followed by UTFC,
and compacted with 100
blows on one side only;
• Composite briquette pushed
partly out of mould to expose
joint;
• Load applied with a CBR
press to determine shear
force.
The effect of the bond coat
application rate on the
permeability of the SABS mix was
also evaluated. The results are
summarised in Table 1.
Handling
Unlike conventional tack coat
emulsions, bond coat emulsions
are very shear and temperature
sensitive, and should be handled
strictly in accordance to the
method prescribed by the
suppliers. These are generally
latex modified emulsions, which
are sensitive to pumping and
heating. Excessive pumping
and/or heating forms tough,
irreversible deposits, which can
block the very small nozzles used
by the integrated paver/sprayers.
This can often lead to extensive
delays on site. Special care should
thus be taken during loading,
heating and transfer operations to
prevent damage to the emulsion.
Bond strength
The bond between the overlaid
material and the existing surface
is a function of:
• Application rate: the quantity
of tack or bond coat required
is a function of the surface
texture of the overlaid
surface. Rough, milled
surfaces have a surface area
approximately 30% larger
Bond coat (l/m 2 )
Degree of
compaction
(% of Rice)
Average
Permeability
l/hr
Average
Tangential
Tension (kPa)
0.4 88 1.3 853
0.4 90 0.2 689
0.7 88 2.6 831
0.7 90 0.2 772
1.01 88 0.4 882
1.01 90 0 752
Table 1
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