• 2001 BST Condition Report
• 2002 BST Condition Report
• 2002 Pavement Report
• Construction
• Distance Chart
• Engineering
• Permits
• Regulations
• Road Report
• Road Safety
• Shakwak Project
• Weight Restrictions
• Weigh Stations
• Yukon Road Map
• Links & Contacts

Contact Us:

Transportation Maintenance
Department of Highways and Public Works
Government of Yukon
Box 2703
Whitehorse, Yukon
Canada Y1A 2C6
 
Phone: (867) 456-7623
Toll free (In Yukon):
1-877-456-7623
Fax: (867) 667-3608
highways@gov.yk.ca

Updated Oct. 1, 2002

BST Road Surface Management System for Yukon Highways

1. INTRODUCTION

Bituminous Surface Treatments (BST) have been used on Yukon highways since the late 1970’s in order to provide an improved level of service to the traveling public. BST was initially used for dust control on gravel roads as an alternative to calcium chloride and has since been developed as an inexpensive paved surface on low volume roads and as a stage replacement for asphaltic concrete on fully designed pavement structures.

There are approximately 1,860 kilometers of BST on the Yukon territorial highway system. The system, at present, is expanding on an annual basis. In addition, the Alaska Highway through north-eastern British Columbia, which is owned and operated by the federal government, has a further 500 kilometers of BST. In order to maintain an acceptable level of service, these highway systems need continual rejuvenation requiring significant expenditures of maintenance dollars. The efficient expenditure of these funds can only be achieved through project prioritization based on accurate and consistent information on the condition of the BST road network. In order to achieve this objective, a comprehensive management system was developed.

2. CLASSES

The system divide the BST roads into three distinct classes as follows:

Class 1 includes all roads on which the BST has been applied to an unimproved road structure which has not been designed to any particular standard.

Class 2 includes roads on which a 75 to 150 mm thick layer of crushed gravel base course is placed on the sub grade prior to BST application.

Class 3 is comprised of roads with fully designed sub-base and base course layers on which BST has been applied as a substitute for hot-mix asphaltic concrete.

3. RATING

Annually a Transportation team travels all the BST roads in Northern BC and Yukon and rates each section on the following factors including ridescrore.

Raveling is the loss of cover aggregate from the BST surface through the action of traffic.

Bleeding is an excess of asphalt that has accumulated on the BST surface. When severe, this presents a safety concern as vehicles have a tendency to hydroplane on wet bleeding surfaces.

Rutting is the formation of depressions in the wheel path. When severe, water ponds in the ruts and steering is affected creating safety problems.

Subgrade failures are bearing capacity failures in the layers underlying the BST and base.

Shoulder disintegration refers to the disintegration of the BST surface starting at the shoulder edge and progressively working inwards.

Potholes refer to shallow failures in BST or base course as opposed to the sub grade failures mentioned above which are more deeply seated.

Cracking refers to transverse, longitudinal, or alligator cracking in the BST.

Patching refers to the amount of patching already carried out on the section.

Distortions refer to uneven aggregate embedment leading to a washboard surface.

Streaking refers to longitudinal streaks in the BST where there is uneven embedment of the aggregate in the longitudinal direction.

Sections generally are never longer than 10 kms and are always different for BST classes, or BST age. Once the ratings have been completed each individual rating is weighted (in a formula) based on the degree of distress it represents . i.e. sub grade failures have a weighting factor of 1.5 as compared to streaking which is weighted at 0.3. The data is compiled for each section and are overall rating or B.C.I. (Bituminous Condition Index) is calculated.

Maintenance and replacement decisions are based on the following
BCI ranges by BST class:

4. BST LIFE

There are many criteria that impact on the life of BST and the decision when to rip it up and replace it. The following shows average life of BST by class based on 2 different BCI criteria.

5. COSTS

The cost of applying BST varies depending on the geographical area being worked and the proximity of that area to emulsion supply and gravel resources. Generally speaking in the southern area of the Yukon (Whitehorse - South) BST costs approximately $2.00 M² or $21,000 per km (10.5 m wide surface). These costs do not include the aggregates another 20¢ - 25¢ per m² should be added for this purpose.

In the Western/Northern Yukon our BST costs approximately 1.80 m² or $18,900 per km (10.5 m wide surface) and again the aggregate costs need to be added.

One of the more significant costs in the management of BST is the ripping up of the old surface and preparation for the application of the new BST surface. It is our opinion that it is very important not to waste the old BST surface (asphalt and aggregate). The asphalt residue provides strength in the base and the aggregate costs money to produce and apply. Our focus has been to find cost effective methods to tear up the old BST surface and break it down to a workable size so that it can be reintegrated into the surface.

Our conventional method prior to 1994 was to rip up the BST using graders with rippers and/or scarifiers and work the material back and forth until broken up fine enough to lay. This cost approximately $18,000 per km.

In the summer of 1994, we experimented with two different processes for reclaiming old BST surface. The first was full depth reclamation using a reclaimer. This process cost approximately $8000.00 per km.

The second process incorporated a farm disc pulled by a D-7 dozer with a specially built ripper bar mounted on the ripper. This unit was followed by a steel drum elliott grid packer. This process proved to be very effective costing between $3500 - $5000 per km.

5. OVERLAYS

Prior to 1994 we overlayed existing BST surfaces if they cracked badly or showed excessive raveling and were not "badly" rutted. Our approximate costs to overlay were $11,000 per km. When comparing this to our cost of conventional rip and reshape (graders) of $18,000 per km and regular BST costs of $17,000 per km overlays looked very attractive. However, overlay is not a new surface that will last 10 - 12 more years on a class 3 for example. Its life span is linked directly to what the original BST and base are doing. In other words, overlays are cost effective in repairing a very minor band of BST distresses on newer BST’s.

Operationally we are doing less overlays due primarily to the reduced cost to rip and reshape and apply a new smooth distress free surface.

6. ANNUAL PROGRAM

Transportation Maintenance Branch applies approximately 200 kms of BST per year. This normally is broken down to 25 - 30 kms of BST on newly reconstructed road (excluding Shakwak program) and the remainder is replacing an already existing BST surface.

We presently crush approximately 200,000 M³ annually for maintenance purposes, of this, approximately 73,000 M³ is produced and used as BST aggregate. The remainder is sanding aggregate, resurfacing aggregate or base aggregate.

Here are some photos of our BST program
Click on the photo for a larger image.

Ripper and discer tear up the old road surface.

Discer grinding up the old road surface.

Oil distributor spreading oil on prepared gravel surface.

Chipper lining up to spread surface of crush gravel.

Chipper spreading gravel.

Gravel truck filling hopper on chipper.

Now we add compaction with a wobbly wheel packer,

And more compaction with drum packers.

Final product after two days and before sweeping.

Alaska Highway with new BST.