2011_AAPA_Study_Tour.. - Aapaq.org

6. Improving pavement performance - Questions & Responses AAPA 2011 Study Tour Group ReportPresentation by Kim JenkinsPoint of the hard binder was set between 55 and 71 degrees with Post RTFO bitumen expected tobe greater or equal to than the original SP value minus 2 degrees. The corresponding Viscosityrange for 15 to 25 grade bitumen is greater or equal to 550 .Q 9. What is the local experience with regards to early life skid resistance and permeability ofSMA? Do you apply grit and how do you prevent ingress of water into the pavement?What are your permeability and texture requirements?The availability of the Agrement South Africa certified Ultra Thin Friction Courses has reduced theuse of generic SMA with the functional benefits replaced by the properties of the UTFC.There does not appear to be any early life skid resistance issues for SMA mixes in South Africa and,where needed, they have wet weather advisory signage on the high speed national toll roads toreduce the traffic speed in wet conditions for all road surfacing types including concrete. Thesurface texture and PSV of the SMA are monitored to ensure satisfactory performance underheavy traffic.There have been some minor concerns with achieving compaction where rubber bitumen SMAmixes have been placed however concerns on the permeability of the SMA in general has not beenraised. The underlying asphalt pavements have not been reported to have been damaged bywater infiltration through the SMA surfacings.Gritting is not specified for SMA surfacings at present however work is being done on the nationalroad network with skid resistance assessment by SCRIM testing. It is unclearUnable to determine if permeability of the SMA has caused underlying pavement problems andthere is no requirement for waterproofing seal to be used under the SMA to address water ingressinto pavements.V4-2 Page 84