Primary Resource
Before writing a specification for your micro surfacing project, review the Recommended Performance Guideline for Micro Surfacing (A143) provided by the International Slurry Surfacing Association (ISSA). This resource will help in design, testing, quality control, measurement and payment procedures for your project.
Note: It is important to keep in mind that ISSA provides recommended guidelines, not specifications. There are many important factors to consider after reviewing A143, and your project may demand specific processes and measurements from the guidelines.
Helpful Guidelines
Use ISSA A143 and the following statements to inform decisions and provide support when writing a final specification for your micro surfacing treatment:
- Determine if any changes are required to the specifications as stated for the asphalt emulsion and aggregate AASHTO/ASTM specifications.
- State the storage limitations for the asphalt emulsion.
- Determine if screening of the aggregate will be required.
Screen the material immediately prior to loading the nurse truck/mobile support unit. This way, there is no possibility of contamination when re-handling the material.
State the Type of micro surfacing to be applied: Type II or Type III.
- Type II is generally quieter and smoother.
- Type III is typically used when a high skid resistance is required, or when placing a rut fill or leveling course.
- Note: Many state specifications call out their own specific micro surfacing aggregate types that are different from ISSA’s.
Determine the application rate to be applied:
- An application rate must be specified based on the traffic level and expectations of the treatment.
- General guidelines for application rate:
- Specify at the higher end of the range for high traffic roads to provide more of a wearing surface.
- Specify at the higher end of the range for very rough pavements, as the voids will require more material.
- Specify at the lower end of the range for pavements with a consistent profile, or a smooth surface.
- Specify at the lower end of the range to save money.
- Note: The roughness of the pavement being surfaced is a factor in the proper application rate (rougher surface requires more material to fill the voids).
- Note: The application rate of micro surfacing is always specified in lbs/square yard or kg/square meter, as the irregular surface finish does not allow an accurate thickness measurement.
Do not specify an application rate for rut filling or a leveling course, as it is impractical to measure the ruts and low spots to know how much material will be required. Rut filling is typically paid by the ton.
State if the project will include a leveling course or rut filling. If ruts are present, the depth of the rut will dictate the use of a rut box or constructing a leveling course.
Determine specific requirements for the spreader box, such as a fixed width spreader box or a variable width spreader box. If a specific secondary strikeoff is required, it must be stated.
State if the project requires a calibration in the presence of an inspector, or will a previous calibration suffice. If a previous calibration is used, state the time limitation (for example, calibration must have been performed with the same materials in the last three months).
Require a recalibration when material changes, conveyor seals and/or, emulsion pumps have been replaced.
Require the contractor to perform a calibration with the inspector on site, with the specific materials for the job. This step has a high potential for increasing the quality of the job.
State the specific instructions related to notification.
The agency can provide early notification by website, newspapers, signs and/or door hangers. The contractor can notify by signs and/or door hangers the day before and the day of the application.
Determine if a tack coat will be required.
- Tack coat is required on extremely dry asphalt surfaces and all concrete and brick surfaces.
Speak with nearby agencies and local contractors to determine the normal practice in the area. Note that quality can be achieved on good asphalt surfaces either way, but the mix design must be prepared knowing if the pavement will receive a tack coat.
Determine if crack sealing will be performed before the application of micro surfacing. If so, state whether it is part of the micro surfacing contract, or a separate contract. If crack sealing is performed, state how much time must be allowed between the crack sealing and micro surfacing operations.
Ensure crack sealing material is not excessive, as it can be picked up by the micro surfacing paver tires and spreader box runners.
Determine if a test strip is required.
Determine if rolling will be required on the project. Rolling is generally required on airports.
To increase the longevity of the micro surfacing application, roll parking lots, cul-de-sacs, and other pavements that will not receive regular traffic.
State specifically how the project will be measured for payment.
Determine if a pre-bid meeting be held to discuss the specifications.
Additional Resources
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