Polymer-Modified Emulsified Asphalt. Micro surfacing ALWAYS contains polymer-modified emulsified asphalt.

Spreader Box Augers. While it is advantageous for all slurry surfacing system spreader boxes to contain augers, it is mandatory that micro surfacing spreader boxes contain them. Consideration may be given to the use of a variable-width spreader box to minimize overlap and assist the applicator working on variable width pavements.

Secondary Strike-Off. A secondary strike-off is integral to the makeup of a quality micro surfacing paver’s spreader box. It can correct drag marks, as well as improve the surface texture and surface aesthetics. The secondary strike-off mounts directly behind the primary strike-off and is in contact with the fresh mix. It removes most surface imperfections without requiring a person to remove them with a hand tool. The secondary strike-off does not remove the cause of the drag mark, so that still must be removed by hand. But it will correct the imperfections in the surface while the oversized aggregate is removed.

Scratch Coat. Scratch coats are only used with micro surfacing primarily to level pavements with longitudinal ruts less than 0.5 in (12.5 mm) deep. They may also be used to correct minor transverse irregularities that are narrower than the width of the spreader box or for structurally sound roads with surface distresses, such as raveling or weathering. When applying a scratch coat, a steel strike-off or strike-off of stiff rubber is substituted for the primary strike-off in the standard full-width micro surfacing spreader box. The rigid strike-off scratches over the high spots of the pavement, filling in the irregularities. The concept is to fill the depressed areas and leave minimal material on the high ridges. All scratch coat materials should cure under traffic for at least 24 hours before the final surface course is placed. Scratch coats are not a stand-alone application and should always be covered with a full-width micro surfacing pass.

Rut Filling. Rut filling should only be performed with micro surfacing and should only be used on stable ruts that have resulted from long-term traffic compaction rather than failures in the base or sub-base. If rutting is ongoing, the micro surfacing will not prevent its continued development. Rut filling is typically constructed with a Type III gradation. Deep ruts may require multiple lifts and asphalt content on the low side of the allowable range unless the existing pavement condition is dry and absorptive. Asphalt contents that are higher than necessary may create stability problems. Attempting to fill ruts with a surface course is not recommended. Ruts not filled using a separate rut-filling process will negatively affect surface course application rate and performance. A single rut of 0.25 in (6.4 mm) or less deformation will increase the total average surface course application rate as the rut must be filled to the level of the existing pavement during the application process. Ruts of 0.5 inch (12.5 mm) or more should be filled individually with a rut box, generally starting with the outside rut first and inside rut last.

Using various mix designs, techniques, and equipment, Micro Surfacing can be used successfully in these situations:

• In quick-traffic applications as thin as 3/8 inch (9.5mm), Micro Surfacing can increase skid resistance, color contrast, surface restoration, and service life to high-speed roadways (interstates and autobahns). Such projects are often reopened to traffic within an hour.
• Modern, continuous-load pavers can lay 500 tons of Micro Surfacing per day, with no long traffic delays. This equates to an average 6.6 lane miles (10.6 lane kilometers) per day for surfacing applications.
• On airfields, dense-graded Micro Surfacing produces a skid-resistant surface. Rolling should be considered for airport projects as they may not receive the desired traffic rolling to prevent aggregate from coming loose and causing potential damage. If rolling is specified, a rubber-tired roller should be used. This will allow the tires to knead the surface and compact all areas.
• As a thin, restorative surface source on urban arterials and heavy traffic intersections, Micro Surfacing does not alter drainage. There is no loss of curb reveal Micro Surfacing.
• Micro Surfacing is applied to problem sections of roads or runways to eliminate hydroplaning problems that occur during periods of rain. The Micro Surfacing can restore the proper surface profile and improve the surface texture, making the area safe to use.
• Because Micro Surfacing can be effectively applied to most surfaces at 3/8 inches (9.5mm) or less, more area per ton of mix is covered, resulting in cost-effective surfacing.
• Micro Surfacing creates a new, stable surface that is resistant to rutting and shoving in summer and to cracking in winter.
• Applied to both asphalt and Portland cement concrete surfaces (usually preceded by a tack coat on concrete), Micro Surfacing is often used to restore a skid-resistant surface to slick bridge decking with minimum added dead weight.
• Used as a scratch (leveling) course, to be followed by a surface course, Micro Surfacing can provide transverse surface leveling.
• Because of its quick-traffic properties, Micro Surfacing can be applied in a broad range of temperature and weather conditions, effectively lengthening the paving season. It is particularly suitable for night applications on heavy-traffic streets, highways, and airfields.
• Applied at ambient temperatures, Micro Surfacing has low energy requirements. And It is environmentally safe, emitting no pollutants.
• Micro Surfacing life expectancy usually exceeds seven years.
• Capable of filling wheel ruts up to 1-1/2 inches (38mm) deep when the pavement has stabilized and is not subject to plastic deformation, Micro Surfacing has the unique ability to solve this problem without milling. Deep ruts may require multiple lifts to be filled properly.

Successful Micro Surfacing incorporates carefully selected materials , proven mix design methodology, advanced technical specifications, and adherence to proper field application best practices (See the ISSA Design and Inspection Manual).

Micro Surfacing begins with the selection of high-quality materials – asphalt, aggregate, emulsifiers, water, and additives – which must meet project-dictated material specifications, as well as Micro Surfacing system performance requirements as defined by the project specifications.

The International Slurry Surfacing Association’s (ISSA) broad range of specialized mix design tests help to ensure that the mixture has these Micro Surfacing characteristics:

1. Is capable of being spread in various thick cross-sections (wedges, ruts, scratch course), which
2. After initial traffic consolidation, does not further compact (i.e. resists compaction) throughout the entire design tolerance range of asphalt content and variable thicknesses to be encountered, and
3. Maintains good macro-texture (high wet coefficient of friction) in variable thick sections throughout the service life of the Micro Surfacing.

Successful Micro Surfacing projects depend on strict adherence to technical specifications. Many project owners find it helpful to design their individual job specifications around those recommended by ISSA (Technical Bulletin A143) The resulting “mix design” and job specifications are carefully adhered to in the field, where ISSA member contractors use specialized job-calibrated equipment and thoroughly trained crews to maintain consistent quality control.