Scrub_Seal_Specification.pdf

SCRUB SEAL:

(Rev. 11-7-25) SPI 6-30

Description

This provision covers the materials, equipment, construction and application procedures for a scrub seal treatment. The asphalt emulsion shall be a cationic polymer-modified rejuvenating emulsion, applied with an asphalt distributor, and scrubbed into the pavement with a trailer sled of nylon bristle broom heads. The coarse aggregate should be applied with a chip seal spreader.

Materials

Item Section Aggregates for Asphalt Surface Treatment 1012-2 Emulsified Asphalt, Grade CMS-1PC 1020-3 Fine Aggregate 1014-1 Mineral Filler 1012-1(D) Water 1024-4

Polymer Modified Rejuvenating Asphalt Emulsion, Grade CMS-1PC, should meet the requirements in Section 5 of AASHTO M 345 “Standard Specifications for Materials for Emulsified Asphalt Scrub Seal”.

Equipment

Use asphalt application equipment that meets Article 600-5.

Apply aggregate using a self-propelled, pneumatic-tire aggregate spreader capable of maintaining a specified rate with a uniform application for the width of asphalt material being covered. Tailgate spreaders will not be permitted. Areas that are inaccessible to the aggregate spreader shall be covered by hand spreading or other acceptable methods.

Scrub emulsion with an emulsion broom sled frame constructed of metal. The emulsion broom sled shall be attached to and pulled by the distributor truck. The emulsion broom sled must be equipped with a means of raising and lowering the emulsion broom sled at desired points. It shall be towable in the elevated position. The broom sled assembly shall be adjustable so that it does not push the emulsion off the roadway surface or outside the framework of the broom sled. The main body of the emulsion broom sled shall have a minimum frame size of 6.5 feet wide and 10 feet long. The maximum transverse rigid frame width at any point shall not exceed 6.75 feet. The nearest and furthest members, paralleling the back of the spreader truck, and diagonal members shall be equipped with street brooms. The leading member and the trailing member shall have brooms heads angled at 10 to 15 degrees off the centerline of the supporting member. The diagonal members shall have broom heads attached in line with the centerline of the supporting member.

Each individual street broom attached to the emulsion broom sled assembly shall be 3.5 inches wide x 6.5 inches high x 16 inches long and have stiff nylon bristles. Bristle height is to be maintained at a minimum of five inches (5”). The emulsion broom shall be equipped with hinged wing assemblies attached to the main body not to exceed 4.5 feet per side, with diagonals and equipped with street brooms. Broom heads should be maintained in good working condition.

Broom heads that are excessively worn or clogged or that cannot facilitate movement of emulsion through the bristles should be replaced.

at least 5 inches and maintained in a manner which facilitates movement of the emulsion between the bristles

Scrub Seal Mix Design The contractor shall submit a Mix Design for the Scrub Seal to the Pavement Preservation Engineer at the Materials and Tests Unit for review. It shall include material sources, application rates of stone and asphalt emulsion, total binder %, binder specific gravity and aggregate size and gradation. A JMF will be issued upon review and acceptance by the Materials and Tests Unit.

MATERIAL APPLICATION RATES AND TEMPERATURES

Type of Coat Aggregate Type Aggregate

Target Rate A

(Lbs/Sy)

Emulsion Target Rate B, C

(Gal/Sy) Scrub Seal 78M

A. Aggregate Target Rates have +/- 2.0 lbs/sy tolerance limit.

B. The Grade of Asphalt Emulsion shall be CMS-1PC.

C. Emulsion Target Rates have +/- 0.05 gal/sy tolerance.

D. Design Application rates are a starting point. Actual application rates will vary within the tolerances based on specific road conditions.

Weather and Seasonal Limitations

Do not place scrub seal treatment between October 15 and April 1. Apply scrub seal only when the surface to be treated is dry and when the air or surface temperatures measured at the location of the AST operation away from artificial heat, is 55°F and rising. Do not place AST when the air temperature is 98°F and rising. When placing a scrub seal that is to be immediately overlaid with asphalt plant mix, the seasonal and temperature limitations of Article 610-4 shall apply. Do not apply asphalt material when the weather is foggy or rainy.

Surface Preparation

Clean the surface to be treated of dust, dirt, clay, grass, and any other deleterious matter before application of the AST. Multiple passes of surface cleaning may take place as directed by the Engineer. Ensure that dust, dirt, clay, grass, and other deleterious materials are removed from cracks in pavement. Properly dispose of these materials as directed by the Engineer. Remove all raised pavement markers. Manholes, valve boxes, drop inlets and other service entrances shall be protected from the scrub seal by a suitable method.

Construction Methods

Robbie Robinson Can we get some wording to allow for some amount of judgement based on visuals in the field like: NOTE – The mix design is a starting point for field application. Emulsion and aggregate rates may need to be adjusted up or down, as necessary, to fill cracks in the existing pavement and to ensure no flushing occurs after rolling.

Lee, Garrett L Add some verbiage about contractor adjusting rates from road to road

Robbie Robinson Ensure that dust, dirt, clay, grass, and other deleterious materials are removed from cracks in pavement.

Lee, Garrett L Will be added

Demonstrate that all equipment has been calibrated in the presence of the Engineer. Once calibrated, pave a minimum 500-foot test section. If approved by the Engineer, the test section is incorporated into the production section. If the test section does not have a uniform coverage of asphalt emulsion and aggregate, submit a calibration plan to the Engineer with detailed information on equipment and a designated area for calibration. Perform calibration and construction of test strip at the beginning of the first day of production and then as directed by the Engineer.

A wave of asphalt emulsion should be present at the front of all the broom heads as the sled broom is pulled down the road. Adjust the emulsion application rate, broom sled weight distribution or ground speed if the wave is outspreading the broom or if the emulsion wave dissipates.

In cul-de-sacs and intersections, emulsion should be applied via hand wand. If the broom box is leaking emulsion, work should be stopped immediately, and the equipment corrected.

After the asphalt emulsion is applied by the distributor and scrub seal broom, apply the aggregate and roll the seal in accordance with Section 660-8(A) of the 2024 Standard Specifications. If a chip seal or fog seal layer is applied on top of the scrub seal layer, it should be done in accordance with Section 660 of the 2024 Standard Specifications.

Allow the Scrub Seal to sufficiently cure before traffic is allowed to drive on the seal. Excess aggregate should be removed from the road within 2-5 calendar days of scrub seal completion.

Temporary Traffic Control (TTC)

Follow TTC guidelines in Section 660-9.

Maintenance

Maintain the scrub seal treatment in an acceptable condition until final acceptance of the project.

Warranty

The Warranty outlined in Article 660-10 of the 2024 Standards and Specifications applies to all scrub seal treatments.

Adjustment for Emulsion for AST will be paid per the following formula:

A = B + ((D – C) / 235) 0.65

Where:

A = Adjusted Contract Unit Price of Emulsion for AST per gallon B = Contract Unit Price of Emulsion for AST per gallon C = Base Price Index of PG 64-22 per ton D = Monthly Average Terminal F.O.B. Selling Price for PG 64-22 per ton

See Price Adjustment – Asphalt Binder Special Provision found elsewhere in this proposal for the base price index of PG 64-22 per ton.

What constitutes an approval?

What happens when the test section is not approved?

Will multiple test sections be allowed?

How does the contractor proceed after a test section is not approved?

Lee, Garrett L A little more clarity here

Robbie Robinson Adjustments to the broom sled may be needed to ensure containment of the emulsion within the sled frame. Weight distribution of the broom sled is important to ensure uniform application of the emulsion and should be adjusted, as needed, so that all sections of the broom sled are showing a wave of emulsion in front of the broom heads.

Lee, Garrett L Not just the front of the broom, all areas of the broom

Loosen time and add “until sufficiently cured” on traffic opening

Measurement and Payment

Asphalt Surface Treatment: Scrub Seal. All AST will be measured and paid at the contract unit price per square yard. Payment at the above prices will be made for replacing any satisfactorily completed AST when such replacement has been made necessary by defects in subgrade or base constructed by others.

Emulsion for Asphalt Surface Treatment will be measured by the asphalt emulsion applied (gallons) and paid at the contract unit price per gallon, which price will be full compensation for all materials including modifiers and additives, labor, tools, equipment, and all other incidentals necessary to complete the work.

Payment will be made under:

Pay Item Pay Unit Asphalt Surface Treatment, Rejuvenating Scrub Seal Square Yard Emulsion for Asphalt Surface Treatment Gallon

Will the contractor be paid for actual emulsion used (gallon) or specified rate on the mix design?

Contractor gets paid on the actual amount of emulsion used. +/- 0.05 allows for road to road tweaks.