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Chip Seal – An affordable and effective surface treatment

 

Chip seal (also known as seal coat) is a layer of asphalt binder that is covered by embedded aggregate (one stone thick). On Grafton Rd, two coats are expected to be applied with primarily single surface application on the minor roads. Chip seal is often said to provide a more flexible surface treatment than asphalt and is typically preferred where the road base is poor.

 

Many jurisdictions use chip seal overtop existing pavement surfaces to reduce the formation of pavement distress as part of a regular 5 year pavement management program   In terms of unit rates, chip seal costs about $6.00/m2 for a double application and a double asphalt lift costs approximately $38.00/m2.

 

Chip seal provides many benefits to the road surface as it is somewhat flexible, and improves traction and resistance to skidding. In the past it has been assumed that a chip seal surface is inappropriate for a trunk route such as Grafton Rd., however in other jurisdictions this treatment method is used on high volume roads of greater than 20,000 vehicles per day.  Chip seal surface treatment has been used on the Island Highway and as well as the Coquihalla Highway.

 

The materials used will include Chip Seal Emulsified Asphalt binder with Anti-Strip Agent and Aggregate Placement (Double Coat) to the following specifications:

 

Emulsified Asphalt Binder:         HF-150AS – Anti-Strip

 

D” Chip Rock:                                Gradation specifications for local material are as follows:

 

Sieve Size  (mm)

CLASS: Mass Percent Passing

D-Spec

Test 1 - From Belt

Test 2-Composite

13.2

100

99.7

100

9.5

30-80

86

89.2

4.75

25-45

50.9

47.2

0.6

5-20

15.6

13.3

0.075

0-3

7.8

6.7

                                Source: BC Ministry of Transportation Specifications – 2006

                                Section 531 – Asphalt Surface Treatments

 

                                Notes:

                                1.  Table derived from Table 531 – E of the BC MoT Specifications

                                2.  Test 1 was samples from the screening belt

3.  Test 2  was sampled form a composite mix which was taken from the screening production pile

 

The chip material to be used has been subjected to a washed screen analysis.  The analysis of the locally sourced chip material indicated a slightly larger percentage of fine material.  As a result we are using an anti-strip additive in the mix and are considering the additional use of an added polymer.  On behalf of the Bowen Island Municipality, the oil manufacturer has conducted independent tests to ensure that the granular material is compatible with the oil mixture.  Test results have shown a 98% coating of the chip seal material which is considered excellent.

 

For more information regarding the 2009 Road Capital Upgrade Program, please refer to the Bowen Island Municipality – Public Works Report which was presented to Council on June 15, 2009.  This report may be viewed at the following link: http://bimbc.ca/files/embedded/090615COW3-1   

 



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