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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.