Ultra-thin layer Asphalt workshops May 2002

Scope of workshops To discuss concerns with UTLAs. Initially defined as <25 mm (but consideration should be given to thicknesses of up to 30 mm) To discuss concerns with UTLAs. Initially defined as <25 mm (but consideration should be given to thicknesses of up to 30 mm) Provide solutions to address the concerns Provide solutions to address the concerns Two workshops Two workshops Suppliers/contractorsSuppliers/contractors Clients/consultantsClients/consultants

Conclusions Performance expectations and design parameters for UTLAs vary widely Performance expectations and design parameters for UTLAs vary widely 4 different types were identified 4 different types were identified Conventional asphalt (<30mm)Conventional asphalt (<30mm) Stone Mastic AsphaltStone Mastic Asphalt Thin layer performance asphaltThin layer performance asphalt Residential asphaltResidential asphalt Confusion about the different types of UTLAs Confusion about the different types of UTLAs

Main Concerns Compaction Compaction Inexperience with the use of UTLAs Inexperience with the use of UTLAs Inappropriate pavement designs Inappropriate pavement designs Inappropriate mix designs Inappropriate mix designs Inappropriate specifications Inappropriate specifications

New findings Widespread confusion about the different types of UTLAs Widespread confusion about the different types of UTLAs The extent of engineering compromise which occurs in some applications The extent of engineering compromise which occurs in some applications The problems with rapid cooling in all seasons in SA The problems with rapid cooling in all seasons in SA The need to provide for inexperienced supervisors and designers in the future The need to provide for inexperienced supervisors and designers in the future

Suggested actions To redefine UTLA as “various asphalt gradings with a layer thickness of 30mm or less” To redefine UTLA as “various asphalt gradings with a layer thickness of 30mm or less” Develop new guidelines covering the identified needs of basic construction supervision and a generic functional layer (in residential areas) Develop new guidelines covering the identified needs of basic construction supervision and a generic functional layer (in residential areas) Thin layer performance asphalts were deemed to be proprietary products and outside the scope of such a guideline Thin layer performance asphalts were deemed to be proprietary products and outside the scope of such a guideline

Area for consideration Risk profile Thickness StructuralFunctional HighMedLowHighMedLow 50 mm XX 10XX 0XX