505 - Chip Seals
GENERAL DESCRIPTION
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Definitions and Terms
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General Overview
Chip sealing is a common preventive maintenance activity across the State of Michigan. It involves spraying asphalt cement on the surface of an existing pavement followed by the application of a cover aggregate. The asphalt cement is emulsified (suspended in water) to allow for it to be applied without the addition of extreme heat. The cover aggregate is typically either naturally occurring gravel or crushed aggregate such as granite, quartzite, or trap rock (basalt), or limestone. Steel blast furnace slag is also used with great success.
Contractor Prequalification
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Code of Federal Regulation (CFR) / FHWA Regulations
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MATERIALS
The two main materials used in chip seal construction are the asphalt binder and the cover aggregate. The asphalt binder is typically an asphalt emulsion. The cover aggregate can be either natural or crushed. Asphalt Binder The most common asphalt binder used for chip seals in Michigan is an asphalt emulsion. MDOT has two Chip Seal Emulsions, CRS2M and CSEA.
Asphalt Emulsion
An asphalt emulsion consists of the following components:
- Asphalt Cement
- Water
- Emulsifying Agent (surfactant)
- Polymers
An asphalt emulsion is mostly asphalt cement, similar to that used in hot mix asphalt, with added latex or polymers for improved chip seal performance. Water is the second largest component and serves as the medium that suspends and transports asphalt particles. When the asphalt and water separate—changing the emulsion from brown to black—the emulsion is said to have “broken,” so aggregate chips must be applied and rolled quickly. A surfactant allows the asphalt to disperse into droplets by reducing surface tension and gives the emulsion its electrical charge. Because most aggregates in Michigan are negatively charged, cationic emulsions like CRS-2P and CSEA are used. After breaking, the asphalt settles to the pavement while the water rises and evaporates, leaving the asphalt behind.
CSEA vs CRS2M
CSEA is a more durable chip seal emulsion used on MDOT routes with higher volumes and in certain parts of the State. CSEA has higher residual asphalt content and higher toughness/tenacity with a higher elastic recovery which helps with repeated traffic loading. CSEA will contain higher polymer content than CRS-2M. CSEA will have a higher bond strength to the aggregate and will typically allow better results when opening to higher traffic.
Aggregate
Cover Aggregate The cover aggregate must be clean and dust free (≤2% retained on no. 200), uniform in size and hard so that it provides a tight, durable surface able to withstand the abuse of snowplows and vehicles. Aggregates used on MDOT Chip Seals are classified as either 34CS or CS-T. 34CS is a large gradation with some aggregate in the 3/8 with the majority being ¼ inch. CS-T is intended for the top course of double chip seals and has some ¼ inch stones but is mainly retained on the no. 4.
Pictures of Materials
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EQUIPMENT
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Description of Equipment Used
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Equipment Specifications
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Pictures of Equipment
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PRECONSTRUCTION
Submittals and Shop Drawings
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Permits
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Qualified Products List (QPL)
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Plant Inspections
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Contractor Submitted Plans/Procedures
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CONSTRUCTION
Construction Requirements/Procedures/Installation Methods
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Safety
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Productivity information/charts
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Items of Note
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Layout / Survey
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INSPECTION & TESTING
Inspection Procedures
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Special Attention Areas
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QA/QC Tests
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Lab Testing / Field Testing
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Rejection/Remedial Actions=
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MEASUREMENT, DOCMENTATION & PAYMENT
Measurement
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Documentation Requirements
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Basis of Payment
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LOCAL AGENCY PROJECTS
Only if applicable
RAIL PROJECTS
Only if applicable
GENERAL
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MATERIALS
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CONSTRUCTION
Double Chip Seal Seasonal Limitation
a. From June 1 to August 1 in the Upper Peninsula b. From May 15 to August 15 in the Lower Peninsula north of M-46 c. From May 15 to August 31 in the Lower Peninsula south of M-46
Longitudinal Construction Joints
Longitudinal Construction Joints in Double Chip Seal – Concern has been raised that the double chip seals are filling in centerline corrugations too much. As a result the special provision 20SP505(B) Warranty Work Requirements for Double Chip Seals contains language specifying that the base course of the chip seal will go up to the corrugations but not cover them. The top course will be the only one that will cover the corrugations.
Fog Seals
Chip Seals with Fog Seal - Delay times
As per spec, complete application of the fog seal within 48 hours of the application of chip seal, but not on the same day as the application of chip seal.
Because the fog seal prevents stone loss and also the temporary raised markings have taken a beating (especially on a double chip seal) the first application of pavement markings after a fog seal may be placed the next day.
MEASUREMENT AND PAYMENT
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