Seal Coating

What was the cause of the failure?Sponsored by: Minnesota LTAP Center

Presented by: Michael Marti, P.E.SRF Consulting Group, Inc.

Dan Wegman, P.E.SemMaterials

Minnesota has a Great Resource!

• Minnesota Seal Coat Handbook• Updated in 2006

– FAQ– Trails– Specification guidelines

• Available from Mn/DOT Maplewood Lab

Mn/DOT Research Services

What can make a chip seal fail?

• Rain or wet surface• Cool Temperatures• Dirty Rock• Bad Emulsion

• Low Shot Rate• Poor Workmanship

• High Traffic Count • Not Enough Rolling

• 2 of the above = 50% chance of failure

• 3 of the above = 100% chance of failure

Weather, weather, weather!

Most chip seal failures are a result of poor weather during construction

Condition of Aggregate

Aggregate should not be too dusty or

too wet or it won’t stick.

Shot Rate Depends Upon. . .

• Aggregate Size

• Aggregate Porosity

• Old Surface Condition– dry? – flushed?

• Traffic

• Weather!

Workmanship

• Equipment calibrated?• Spray bar set right?• Chips spread at the right amount & time?• Rolling, Rolling, Rolling• The whole crew on the same page

Nozzle Angle Setting = 15 - 30°

Spray bar Axis

Proper nozzle angle setting

Single

Double

Triple

Coverage

Workmanship & Equipment:Spray bar height for the right coverage

Traffic control

• No traffic before rolling

• Lower traffic speed until seal is cured

• Pilot car - Keep wayward traffic under control!