Highways Agency

Appendix 1 - Advice on temporary markings for thin surfaces - background

Observations on the M6

In recent years, a series of sections of the M6 in Cheshire and Lancashire have been laid with a variety of thin surfacing systems that have behaved differently in terms of the embedment of temporary road studs and the adherence of road marking tape.

The systems have been identified and some simple characteristics of the mixtures used have been obtained. These characteristics are nominal maximum aggregate size, the nominal layer thickness, the target binder content and whether modified or unmodified binder was used. These characteristics, together with the observed behaviour of temporary road markings, are given in Table A1.

* Studs fixed with thixotropic glue; only short lengths of transverse tape used, so adherence would have been more difficult than with longer lengths of longitudinal tape.

The characteristics of the thin surfacing systems are considered to be the type that can be readily attainable for any particular location.

Models to estimate performance

By comparing the characteristics, it is possible to produce models that estimate the performance of a thin surfacing system when temporary road markings are used. The embedment of studs is assumed to depend on the layer thickness (and hence the potential extent of any deformation) whilst the adherence of tapes is assumed to depend on the "stickiness" of the system, as indicated by the binder content and whether the binder is modified.

The data indicate a possible model for the embedment of temporary road studs could be that studs:

• can or will embed if the nominal layer depth is equal to or greater than 35 mm
• will not embed if the nominal layer depth is less than 35 mm

The data indicate that a possible model for the adhesion of road marking tape could be that tape:

• will debond if
  • the adjusted modified binder content is less than 4.9 %
  • the adjusted unmodified binder content is less than 6.0 %
• can debond if
  • the adjusted modified binder content equals 4.9 %
  • the adjusted unmodified binder content equals 6.0 %
• will adhere if
  • the adjusted modified binder content is greater than 4.9 %
  • the adjusted unmodified binder content is greater than 6.0%

where the adjusted binder content is the target binder content times cube root of the ratio of the maximum nominal aggregate size and 14 mm. This ratio is used to compensate for extra binder content needed to provide the same binder film thickness on finer aggregate skeletons.

A comparison of the observed and estimated behaviours is given in Table A2, with an overall accuracy of both models of 75 %. The limitations are the range of values where the estimated behaviour is uncertain.

However, the models are only indicative because they are based on relatively few subjective observations. Furthermore, they relate specifically to freshly laid asphalt surfacings, and may not be applicable to surfacings that have been in service for some time.