Pavement Preservation Journal - Spring 2012 - (Page 19)

Enhanced Fog Seals Boost Chip Retention by Dean Yake A lthough chip seal applications are very cost effective treatments for pavement preservation, problems with aggregate retention and the public’s perception of their appearance continues to create further challenges for user agencies trying to stretch highway dollars. A fog seal treatment has been recognized to greatly enhance chip retention and to provide a hot-mix asphalt type appearance, but conventional asphalt emulsions for fog seals pose application and performance problems of their own. However, new materials now exist that can speed construction, boost performance, and prolong pavement life. That’s what the Sixth District of the Mississippi Department of Transportation found when it elected to use a high-performance polymer modified asphalt emulsion on a project that was initially let using CSS-1h as a fog seal treatment on a recently chip-sealed road near Biloxi. LockDown LD-7 on the first mile, and then proceeded to apply conventional CSS-1h on the second mile for the DOT’s evaluation. After reviewing the application and curing times for each emulsion, the DOT promptly changed the job and the whole road was fog-sealed with LD-7. FAST-CURING EMULSION LockDown LD-7 is a fast-curing asphalt emulsion produced from a durable, high-modulus asphalt. Because of its fast-curing behavior, construction time of the fog seal is minimized, resulting in a non-tracking, very durable, attractive asphalt seal. While LD-7 can be used in any type of fog seal application, it was primarily developed for fog seal over chip seal treatments. It has been applied on both new and aging seal coats to “lock down” aggregate, reducing vehicle damage and extending the chip seal’s life. Other benefits include reduced water intrusion and a longlasting black surface exhibiting improved striping contrast and driver visibility. Fog seals on chip seal pavements with LD-7 result in the appearance of a fresh hot mix asphalt overlay at a DEMYSTIFYING FOG SEALS A fog seal is a light application of a dilute asphalt emulsion used to coat an existing roadway. These treatments are applied to reduce pavement aging and oxidation, diminish raveling, decrease permeability, seal minor cracks, and improve overall roadway appearance. With a light application rate typically in the 0.08 to 0.20 gallons per square yard range, these treatments also are economical solutions for user agencies to address common problems and lengthen pavement life. Typical costs are between $0.17 and $0.22 per square yard for most fog seal applications. While the benefits of fog seals have long been realized, several complicating issues have been observed with traditional materials. In conventional fog seal applications, slow-set emulsions with ordinary asphalt binders have been utilized, and while these materials can be used in an effective fog seal, they tend to be slow curing, often exhibit tracking behavior, and are less durable than has been desired. Mississippi DOT realized these issues when a five-mile road that had recently been chip-sealed was designated to be fog-sealed with CSS-1h. The contractor, T.L. Wallace Co. — which had been using Blacklidge Emulsions Inc. as supplier of CRS-2P for the project — worked to set up a trial for Mississippi DOT using the high-performance emulsion, High-performance, polymer modified emulsion is placed as fog seal over freshly chip-sealed road for Mississippi DOT Spring 2012 pavement preservation journal 19 PHOTO CREDITS: Blacklidge Emulsions, Inc.

Table of Contents for the Digital Edition of Pavement Preservation Journal - Spring 2012

President’s Message
National Preservation Conference: Make Plans Now
Pavement Preservation is ‘Sustainable’ Choice
Deck Micro Surfacing Cuts Accidents, Wins Award
Enhanced Fog Seals Boost Chip Retention
Sophisticated ‘Seal Coats’ Enhance Texas DOT Pavement Preservation
Rejuvenating Treatment Preserves Runway, Grooving
Fine-Mill Pavements for Smooth Thin Overlays
Puerto Rico, Southeast States Focus on Preservation
Maryland Identifies Right Fix for Right Road, Right Time
‘Thin is In’ for New Texas Center Courses
Why to Cut Back on Cutback Asphalt
Test Sections Constructed at Virginia Smart Road
Ground Penetrating Radar Fills Gaps in PMS

Pavement Preservation Journal - Spring 2012