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Slurry Seal
Slurry seal is a pavement preventive maintenance technique that is used to strengthen and extend pavement life. It involves placing a thin, asphalt-like layer of material over the top of pavement surfaces, including residential driveways, public roads, highways and airport runways.



It is primarily comprised of crushed aggregate, asphalt emulsion, cement and/or filler materials and water—which are all mixed together according to a laboratory’s design-mix formula to match the characteristics of the pavement being covered. The aggregate must be cleaned, crushed, durable, properly graded and uniform. The asphalt emulsion is a three-part system that consists of asphalt, water and emulsifier. It serves as a binder, holding the crushed aggregate together and adhering the new slurry surface to the old asphalt surface. Fillers, which can include cement, hydrated lime or aluminum sulfate liquid, are used in small quantities as stabilizers or chemical modifiers.

Slurry seal is a good solution for roads that are in the early stage of deterioration. If the pavement has major structural damage or large cracking, an asphalt overlay may be required instead. Prior to laying down the slurry seal, the street must be cleaned and removed of any debris. In many cases, a tack is laid down to help the new slurry seal material adhere to the existing surface. A specialized truck- or trailer-mounted slurry seal paver mixes all of the necessary ingredients and moves them into a spreader box that is connected to the back of the paver. The spreader box uses augers to continually mix the material before laying it in one smooth layer over the existing pavement. The slurry seal then sets and can be driven on upon the natural evaporation of water from the mix.

History of Slurry Seal
Slurry seal was first used in the early 1930s in Germany as a cold mix process. The Germans first used the “wet-mix-process” of very fine aggregate, asphalt binder and water in 1936 to strengthen the Berlin-Staaken Airport. The technique increased in popularity and was experimented with worldwide during the 1940s and early 1950s. In the 1950s, improved emulsifiers, continuous flow pavers and truck-mounted pavers made slurry seal a more durable and cost-effective solution to preserving roads.

Further advancements in mixing methods, emulsions and machinery have made slurry seal today's choice for highly durable, low cost paving and surface maintenance. As a treatment for most paved surfaces, slurry seal is now used extensively throughout the world. Local, state, and federal agencies—including the military—have a growing and ongoing commitment to the use of slurry seal in their maintenance programs, attesting to its effectiveness and affordability.

Benefits of Slurry Seal
Slurry seal provides a cost-effective way to preserve paved surfaces—costing up to two-thirds less than an asphalt overlay. Slurry seal also:

•	Extends the life of the pavement by up to seven or more years.

•	Provides a durable asphalt-like finish that sets in a few hours.

•	Extends pavement life by protecting it from oxidation, deterioration and water intrusion.

•	Provides a durable, all-weather, dust-free and non-bleeding surface.

•	Improves skid resistance and road handling characteristics without hazardous loose chips.

•	Corrects surface cracking, raveling and loss of matrix, while increasing water and air permeability, and traction.

•	Prevents surface distresses, deterioration and the effects of weathering when applied before problems occur.

•	Enhances the aesthetic value of the pavement by leaving a uniform black texture that can increase surrounding property values, marketing potential and buyer acceptance.

Types of Slurry Seal
Asphalt emulsion, fillers and water are mixed with one of three different grades of aggregate to create different slurry seal mixes—depending on the specifications of the job. Aggregate types include:

• Type I or #200 x 1/8 inches (3.2 mm): Fine aggregate for mixtures that are used for maximum crack penetration and sealing in low-density/low-wear traffic areas.

• Type II or #200 x 1/4 inches (6.4 mm): Typical aggregate that is most commonly used for moderate-to-heavy traffic areas. It seals, corrects moderate-to-severe raveling, oxidation and loss of matrix, and improves skid resistance.

• Type III or #200 x 3/8 inches (9.5 mm): Larger, coarse aggregate that is used to correct severe surface deterioration. It prevents hydroplaning and provides good skid resistance under very heavy traffic loads.

Other Forms of Pavement Maintenance
Pavement maintenance is a strategy used to apply cost-effective treatments to the surface of a structurally sound pavement. This preserves the pavement, minimizes life-cycle costs by slowing down deterioration, and maintains or improves the functional condition of it without increasing its structural capacity. It involves treating the pavement in the early stages of deterioration before it suffers major structural damage. Pavement maintenance has become increasingly popular among city, state and federal governments in the fight against damaged roads. Slurry seal is just one type of pavement maintenance. Some of the others include:

• Micro surfacing – A composition of polymer-modified asphalt emulsion and selected fine aggregate that sets in an hour or less. It is applied cold and can be placed in thicknesses up to 1.5 inches (38 mm). It is often used in areas when traffic needs to get on the road quickly and to fill in ruts.

• Chip seal – A seal coat that consists of a single application of asphalt followed immediately by a single application of cover aggregate. Excess cover aggregate is normally removed upon completion. This treatment weatherproofs and adds skid resistance properties that can be performed over base rock or pavement.

• Cape seal – Consists of a single application of chip seal followed with a single application of slurry seal or micro surfacing. This application is extremely cost-effective, giving the end user the best features of both treatments.

• Fog seal – A light treatment of diluted, fast-setting emulsified asphalt that is used to revive pavement. This is an inexpensive treatment that is best performed on newer pavements.

• Crack seal – The use of hot rubberized asphalt to fill in large cracks in deteriorated pavement. The cracks must first be cleaned out with compressed air before being filled.

• Seal coat – Application of one or two coats of emulsified filler based seal coat. This process seals the pavement and is aesthetically pleasing and extremely popular with shopping centers and playgrounds.