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Chip Seal is an application of a bituminous binder covered with an application of clean graded aggregate to an existing asphalt surface. It is also known as armor coat, bituminous sealing or seal coat, to name a few. The binders may be emulsions, paving grade asphalt cements, and modified versions of each being modified with various polymers such as latex, tire and natural rubbers.
The aggregates commonly vary in size from a maximum of 5/8 of an inch to a minimum of ¼ inch with less than 5% passing the No. 4 screen. Aggregate must be durable with the use of crushed stone, gravels or manufactured aggregates. Aggregates may be pre-coated with a small % of asphalt cement when used with hot asphalt binders. Chip Seal has been used in various forms since at least the early 1900’s. The quality has improved over the years with better binder technology, cleaner aggregates, and improved equipment and a better understanding of how the materials perform together.
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By making use of the best local aggregates with the most compatible binders while considering climate, traffic count and type to maximize results with awareness of cost with the funds that are available. Once the binder and aggregate are selected there are procedures to determine the rates of application for each.
The binder is applied by an asphalt distributor which has the capability of applying the design rate at the desired width. The binder application is followed by a mechanical aggregate spreader that is also capable of applying a design rate at the desired width. Then rolling is performed with pneumatic rollers to set the cover aggregate into the binder. Finally, if there is any loose aggregate, it is removed by a rotary broom.
There are virtually an unlimited number of Chip Seal combinations depending on what type of binder and aggregate are available. Chip Seal is normally one application but can be applied in double or even triple applications if needed. Multiple applications commonly use different sizes of aggregates to help “lock” the applications together.
Chip Seal is a comparatively low cost method of maintaining an asphalt surface indefinitely that can make use of local materials, and be performed by contract or by using local maintenance personnel. Traffic can be back on the road in minutes. A finished Chip Seal is very pleasing in appearance and traffic markings show up very well.