Ultra-thin layer Asphalt Ultra-thin layer Asphalt workshopsworkshops

May 2002May 2002

Scope of workshopsScope of workshops

To discuss concerns with UTLAs. To discuss concerns with UTLAs. Initially defined as <25 mm (but Initially defined as <25 mm (but consideration should be given to consideration should be given to thicknesses of up to 30 mm)thicknesses of up to 30 mm)

Provide solutions to address the Provide solutions to address the concernsconcerns

Two workshopsTwo workshops• Suppliers/contractorsSuppliers/contractors• Clients/consultantsClients/consultants

ConclusionsConclusions

Performance expectations and design Performance expectations and design parameters for UTLAs vary widelyparameters for UTLAs vary widely

4 different types were identified4 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 Confusion about the different types of UTLAsUTLAs

Main ConcernsMain Concerns

CompactionCompaction Inexperience with the use of UTLAsInexperience with the use of UTLAs Inappropriate pavement designsInappropriate pavement designs Inappropriate mix designsInappropriate mix designs Inappropriate specifications Inappropriate specifications

New findingsNew findings

Widespread confusion about the different Widespread confusion about the different types of UTLAstypes of UTLAs

The extent of engineering compromise The extent of engineering compromise which occurs in some applicationswhich occurs in some applications

The problems with rapid cooling in all The problems with rapid cooling in all seasons in SAseasons in SA

The need to provide for inexperienced The need to provide for inexperienced supervisors and designers in the futuresupervisors and designers in the future

Suggested actionsSuggested actions To redefine UTLA as “various asphalt To redefine UTLA as “various asphalt

gradings with a layer thickness of 30mm gradings with a layer thickness of 30mm or less”or less”

Develop new guidelines covering the Develop new guidelines covering the identified needs of basic construction identified needs of basic construction supervision and a generic functional layer supervision and a generic functional layer (in residential areas)(in residential areas)

Thin layer performance asphalts were Thin layer performance asphalts were deemed to be proprietary products and deemed to be proprietary products and outside the scope of such a guidelineoutside the scope of such a guideline

Area for considerationArea for considerationRisk profile

ThicknessStructural Functional

High Med Low High Med Low

50 mm

40

30

20 X X

10 X X

0 X X