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Research Report 576 Flushing in chipseals

Published: | Category: Activity management , Research programme , Research & reports | Audience: Road traffic engineers & consultants

This report details research carried out from 2012 to 2015 into chipseal flushing. The physical mechanisms causing flushing were investigated and a model was developed to predict the growth of flushing over the New Zealand state highway network.

Factors making a major contribution to flushing are:

  • aggregate abrasion and breakdown
  • compaction and reorientation of the seal layer under traffic
  • water venting and sub-surface stripping in seal layers.

Factors having no or making only a minor contribution to flushing are:

  • thermal expansion of the bitumen
  • excess bitumen application
  • binder viscosity.

Further work is needed to quantify the significance of chip embedment into the basecourse.

A two-part model using parameters in the NZ Transport Agency Long-Term Pavement Performance database was developed. The first part uses a logistic model to predict the onset of flushing and an accuracy of 74% when used to predict the initiation of flushing on a separate data set.

The second part uses a linear model to predict the rate of flushing progression. First-coat seals, and second and higher generation seals were modelled separately.

The linear model was statistically strong (R2 of 0.445 for first-coat seals and 0.628 for second and higher generation seals).

Keywords: bitumen bleeding, chipseals, chipseal flushing, deterioration modelling, sprayed seals, surface dressings

Publication details

  • Author:
  • Published: September 2015
  • Reference: 576
  • ISBN/ISSN: 978-0-478-44529-9