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OCR for page 44
44
100
80
% of Respondents
60
40
20
0
ASTM Weight Diff. Volume Diff. Not Checked Other
D2995
Responses
Figure 45. Methods to verify tack application rate.
Uniformity of the Applied Tack Coat to fix non-uniformity is taken); 17% do nothing. The results
are illustrated in Figure 48.
Most of the respondents, 66%, indicated that the require-
ment to have the entire surface covered with tack coat material
was the main specification to check for uniformity (see Fig- 4.1.4Findings Related to Tack
ure 46). The second most-used requirement was to ensure Coat Application
that no nozzles are completely or partially blocked, 34%. The
Pavement Failures Related to Improper
remaining options ranged from 13% to 26%.
Tack Rate/Material
More than half of the respondents (56%) reported that
they do not change their application rate due to any factor. The respondents reported slippage and delamination of the
Almost all of the remaining 44% of respondents who change pavement surface layer as approximately equal to results from
their application rate changed them based on the condition poor tack coat type or application, 89% and 87%, respec-
of the pavement surface. The remaining of the conditions tively. Fatigue cracking was the only other type of failure that
ranged between 0% and 10% (see Figure 47). received over 25% of the responses. Other types of failures
included shoving, bottom up stripping due to water intrusion,
and flushing/bleeding due to excessive tacking (see Figure 49).
Remedy for Non-uniform Tack Coat Application
Out of the responses compiled, 70% require the contractor
Lab/Field Test Methods to Determine
to reapply the tack coat material. Of those responses, 70%
the Interface Bond Strength
require a lower application rate for the reapplication. The
remaining respondents who require reapplication of the tack The vast majority of the respondents, 92%, indicated that no
coat material either applied the same rate, or they did not testing is performed to measure the bond strength between
specify which approach was taken. Two percent asked the pavement layers. Eight percent of the agencies indicated that
contractor not to do it on the next pass (and no other action testing is performed on the pavement interface. The traction
100
80
% of Respondents
60
40
20
0
Pavement Percentage No Blocked Proper Proper Not Checked
Covered Covered Nozzles Nozzle Height
Angle
Responses
Figure 46. Methods for assurance of tack coverage.
