Several variations can be used with the chip seal to address some of the previously noted problems.

Koch Industries, Perspection Inc.

Informations

• Publié par: Chyok
• Nombre de lectures: 10
• Langue: English

Extrait

Chip Seals - Special Techniques
Chip seals are a cost-effective pavement maintenance
application. When designed and constructed properly, they
usually perform very well on highways. Chip seals increase
Chip Seal skid resistance, fix distressed surfaces, and prolong the lives
of structurally sound pavements. However, in certain situations chip seals have had some limitations, including:
• limited life or premature failure if not properly designed or constructed,
• potential windshield damage from loose chips,
• increased tire noise, and
• prolonged traffic disruption during construction and curing.
With proper techniques, these problems can be avoided. Some special techniques and the solutions they provide
include:
• double or triple chip seals - increased service life
• modified binders - shorter closure time, better chip retention, increased service life
• precoated aggregate - shorter closure time, better chip retention, blacker color
• sand seals - less raveling and shelling
• sandwich seals - longer service life, seals flushed pavements, improved skid resistance,
appropriate for higher traffic volume roads
• cape seals - fewer loose aggregates, less tire noise, longer service life, appropriate for higher
traffic volume roads
Double or Triple Chip Seals
A chip seal is an application of asphalt followed by an
application of chips. A double chip seal repeats the same
Double Chip Sealprocedure using lower emulsion and aggregate application
rates, and the second aggregate is smaller sized than the first. Similarly, a triple seal is a third application of
both asphalt and a still smaller aggregate. The surface layer thickness is determined by the aggregate size used in
the first course. By using a smaller sized aggregate in the second layer, the voids in the first layer are filled in.
Normally the top size of the aggregate laid first is at least twice as large as the second aggregate. The smaller
aggregate on top helps “lock in” the first. When using multiple chip seal applications, the first layer should be
cured before application of the second layer.
Multiple chip seals cost about 1 1/2 to 2 1/2 times more than single chip seals. However, they usually give
more than twice the service life of single chip seals.
Modified Binders
Many states, such as Arizona, Texas, New Mexico, Michigan and Oregon, use polymer modified emulsions to
chip seal their roads. The use of polymer modified emulsions allows for chip sealing on high traffic volume
roads, which was not typically done in the past. The two biggest advantages of polymer modified binders for
chip seals are fewer early failures (because of the early chip retention), and longer time intervals between
needed repairs (cutting down on user delay costs).
Precoated AggregatePrecoated aggregates are used by some states such as Illinois, Oregon, Pennsylvania, Texas, Utah, Virginia and
Arizona. Usually, the aggregate is run through a hot mix plant with asphalt cement or a slow-setting emulsion
to produce an asphalt content of about 0.5 to 1% by weight of chips.
Precoating can tie up dust and improve adhesion between aggregate and binder. Early adhesion of the chips and
the binder is a major advantage on busy roads, because traffic is disrupted less when the road is re-opened more
quickly. Precoating the aggregate also gives the road a blacker finish, which is pleasing to the driving public.
However, precoating adds to the cost, and, if not designed properly, the precoated aggregates may delay the
break time of some emulsions. When correctly precoated, the aggregate particles should not stick to each other
and should flow readily through spreaders.
Sand Seals
A sand seal is an application of asphalt followed by a sand cover aggregate. The sand or stone screenings
2should be 1/4” (6.25 mm sieve) or smaller, and applied at a rate of about 10 to 15 lb/SY (5 to 8 kg/m ). The
binder used for sand seals is usually a rapid setting (anionic or cationic) or a medium setting (anionic or high-
2float) emulsion, and is applied at a rate varying from 0.15 to 0.20 gal/SY (0.7 to 0.9 liters/m ). The application
rate depends on the texture of the existing surface, local conditions, and traffic.
A sand seal is essentially the same as chip seal, except that finer aggregate is used as cover. The finer aggregate
has less chance of causing damage to passing vehicles than larger chips. The sand does not give the same skid
resistance and durability of the larger aggregates used in chip seals. While applied most commonly to low-
volume roads, some agencies have applied sand seals on moderate- to high-volume roads and have reported
good performance.
Sandwich Seals
In a sandwich seal, an aggregate is spread first,
followed by emulsion, followed by a second
Sandwich Sealapplication of aggregate; The seal, then, is a binder
sandwiched between two layers of aggregate. In this process, one-sized aggregates No. 4 to 3/8” (4.75 to 9.5
mm) are spread on a clean and dry pavement at a rate of about 80% of the amount needed to provide coverage at
one stone thickness. The aggregate is then rolled and followed by an asphalt emulsion applied at a rate of 1.2 to
1.5 times that normally used for a conventional single chip seal. A second course of one-sized No. 8 to No. 4
(2.36 to 4.75 mm) aggregate is then applied and rolled. The smaller, second aggregate locks the larger
aggregate in place. Different aggregate sizes may be chosen for a specific project, but the ratio of sizes is
important.
Before applying the sandwich seal, the existing pavement must be clean and dry. All aggregates used in the
sandwich seal application should be clean and free of dust. A light-weight steel roller may be used to seat the
first layer of aggregate. A slow-moving pneumatic roller is used to compact the top aggregate layer.
Sandwich seals are used for sealing high-traffic pavements and flushed pavements. The initial application of
aggregate prevents an asphalt rich surface from flushing or bleeding through the new seal. It also improves skid
resistance. Sandwich seals have approximately the same service life as the double chip seal, but can be more
economical because there is only one application of binder. Best results are obtained with a polymer modified
rapid setting emulsion, because of the early chip retention and the elasticity and durability of the modified
binder.Cape Seals
A cape seal is chip seal topped with a slurry seal or micro-surfacing. The name is derived from the Cape
Province of South Africa where it was originally developed. A single chip seal is applied and allowed to cure 4
to 10 days before applying the slurry seal. During that time, the surface should be regularly broomed so the
slurry will adhere well. After the chip seal has been cured, the slurry seal is applied to fill the voids between the
cover stones. After applying the slurry seal, traffic should be detoured for about 2 hours in warm weather, and 6
to 12 hours or more in cool weather. For a 1/2” (12.5 mm) thick layer, the emulsion is applied at a rate of about
2 20.3 to 0.45 gal/SY (1.4 to 2.0 l/m ), the chip at a rate of 25 to 30 lbs/SY (14 to 16 kg/m ), and the slurry
2mixture (usually Type I) at a rate of 6 to 10 lbs./SY (3 to 5.5 kg/m ).
The cape seal provides a dense surface with improved skid resistance and a relatively long service life. The
slurry on the surface prevents the shelling of and damage done by loose cover stones. These properties make
cape seals very suitable for high traffic volume roads. One of the limitations of the cape seal, however, is the
need to restrict traffic flow twice during the construction of the seal.
Sealing for Success
In any paving project, proper material selection, design, and construction practices, including adequate traffic
control, are an important part of the success.