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Case Category

Microsurfacing

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Micro surfacing

Description
What?
Microsurfacing is similar to slurry seal. It consists of the application of a mixture of water, asphalt emulsion, aggregate (very small crushed rock), and chemical additives to an existing asphalt concrete pavement surface. Polymer is commonly added to the asphalt emulsion to provide better mixture properties. The major difference between slurry seal and microsurfacing is in how they “break” or harden. Slurry relies on evaporation of the water in the asphalt emulsion. The asphalt emulsion used in microsurfacing contains chemical additives which allow it to break without relying on the sun or heat for evaporation to occur. Thus, microsurfacing is an application that hardens quicker than slurry seals and can be used when conditions would not allow slurry seal to be successfully placed. Streets that have a lot of shade and streets that have a lot of traffic are good candidates for microsurfacing.

Why?
Microsurfacing is applied in order to help preserve and protect the underlying pavement structure and provide a new driving surface. Roads chosen for microsurfacing application generally have low to moderate distress and narrow crack width.

When?
Microsurfacing is typically applied on an intermittent, project-specific basis. Location, weather, traffic loading, and pavement conditions are factors used to determine if a microsurfacing application is appropriate. Roadways for microsurfacing treatment are commonly those which have slight to moderate distress, no rutting, and generally narrow crack widths, and in which a microsurfacing treatment would help extend the pavement life until resurfacing becomes necessary. 

How?
Microsurfacing is commonly mixed in, and applied using, a purposely built truck, generally referred to as a “slurry paver.” Slurry paver  hold the aggregate (fine crushed rock), water, polymer modified emulsion, and other additives, which are mixed in the on-board mixer. The microsurfacing mixture flows out of the rear and onto the pavement within the confines of a rear-mounted box referred to as a “micro box.” This box contains an auger which turns to uniformly distribute the mixture across the width. Workers with squeegees follow behind and assist in spreading the mixture, correcting areas not properly covered, and keeping the mixture off of concrete improvements such as gutters.

A piece of burlap is often dragged behind with the goal of producing a smooth texture while applying the microsurfacing material. The texture of microsurfacing is different than that of asphalt pavement. The texture may have faint lines and be somewhat coarse. In addition, when the microsurfacing is first placed the surface is tender and can be marked up by sudden turning movements. These impressions on the pavement are temporary as seasonal weather and traffic smooth out these imperfections over time.

Once placed microsurfacing needs 1 to 2 hours to set or harden before the road is open for traffic.