Appendix E 1.4 Ambient Conditions
For most SAM applications, the pavement and air temperatures need to be above 20 °C, and higher still where wind chill is expected to cool the binder quickly after spraying. Wind chill will cause the binder to ‘skin’ more quickly and this will delay, or prevent, wetting and adhesion.
The presence of moisture in any form should be avoided, and less risk taken with respect to expected changes in weather conditions. The SAM should be sprayed only on a dry pavement surface, using only dry precoated aggregate to ensure good results. This may require the aggregate stockpile to be covered with plastic or a similar waterproofing material.
Concrete and timber bridge decks will require priming with a light grade of cutback bitumen prior to the application of a modified binder seal to ensure proper bonding. The presence of certain curing compounds (chlorinated rubber, hydrocarbon resin) on concrete bridge decks can cause bonding problems and must be removed prior to application of the prime and/or seal coat. If in doubt, compatibility with the primer and/or modified binder should be investigated.
Warm and dry weather conditions before and after application of the PMB or multigrade bitumen seal are desirable. Subsequent cold and/or wet weather may result in the aggregate stripping if the adhesive bond is not adequate.
Ambient conditions are less critical for SAMI applications where an asphalt overlay is to be applied without trafficking of the SAMI.