Micro Surfacing Construction

TEST STRIP

If required, a test strip should be placed in conditions similar to those that are expected to occur during the project.

FOG SPRAY (WATER)

• When the asphalt pavement is hot and dry, the surface should be fogged with water ahead of the spreader box.
• The rate of fog spray application is adjusted as the temperature, surface texture, humidity, and dryness of the pavement changes.
• Avoid pooling of water ahead of the spreader box.

APPLICATION RATES & COVERAGE

• The micro surfacing must have an appropriate consistency to meet the pavement owner’s requirements of texture and application rate.
• Application rates are effected by the gradation of the aggregate and the demand of the pavement surface. (For example, a very rough surface texture will require a certain amount of material to fill the voids, unlike a smooth, polished surface).
• Ensure that the pavement is completely covered. No lumps or unmixed aggregate can be deposited on the pavement.
• Drag marks are not acceptable.

HANDWORK

• Areas which cannot be accessed by the spreader box will need to be surfaced using hand squeegees. If necessary, the area to be hand worked should be lightly dampened prior to mix placement.
• As much as possible, handwork should exhibit the same finish as that applied by the spreader box, and should be completed prior to final surfacing with the spreader box.

JOINTS & EDGES

• Joints must be clean, without excess buildup, uncovered areas, or unsightly appearance.
• Longitudinal joints should be placed on lane lines.
• Partial width passes should only be used when necessary and should not be the last pass of any paved area.
• Overlaps must be kept to a minimum, as they will be noticeable upon completion of the project.
• Transverse joints are to be butt joints (not overlapped) to avoid creating a bump in the surface. The end of the first pass will be cut clean and square with a flat shovel, and the second pass will start with the primary strikeoff at this same point.
• The aesthetics of the project will improve greatly when lines at curbs, shoulders and intersections are kept straight.
• If necessary, a suitable material will be used to mask off the end of streets to provide straight lines.

RUT-FILLING

Ruts of 1/2 inch (0.6 cm) or greater in depth shall be filled with a rut-filling box. Ruts in excess of 1-1/2 inch (3.8 cm) in depth may require multiple applications with the rut-filling box. When rutting or deformation is less than 1/2 inch (0.6 cm), a full width leveling (scratch) course may be applied with the spreader box using a rigid strike-off.

MIXTURE STABILITY & CONSISTENCY

• The micro surfacing should be sufficiently stable, so that the mixture doesn’t prematurely break in the spreader box.
• The mixture should be homogeneous during and following mixing and spreading.
• It should be free of excess liquids, which create segregation of the aggregate.
• Do not spray additional water into the spreader box.
• The mixture of the mat must be consistent, not too wet.
• The texture should reveal larger stones in the mix.
• The surface produced by a finish course of micro surfacing will reflect the surface it is being applied to. If an increase in smoothness (with respect ot IRI) is required, a leveling (scratch) course is recommended.

For further information, please review ISSA’s web-based courses on micro surfacing.