AASHTO PP 91:18 (2020) Standard Practice for Emulsified Asphalt Scrub Seal Design

AASHTO PP 91:18 (2020) Standard Practice for Emulsified Asphalt Scrub Seal Design.
1.1. AASHTO PP 91 practice determines application quantities for applying aggregate and emulsified asphalt for scrub seals.
1.2. A scrub seal is a four-step process in which the application of emulsified asphalt is followed immediately by a scrub broom to push the emulsion into the cracks in the pavement, followed with an application of a single layer of cover aggregate, and then rolled with a pneumatic tire compactor. There is the option of including a fog seal to help with chip retention.
3.1.4. median particle size—theoretical aggregate size that corresponds to 50 percent passing on the gradation curve.
3.1.5. medium cracking—medium severity transverse, longitudinal, andlor longitudinal joint cracking. Spalling is observed at the crack edge and some cracks have begun to become interconnected. Block cracking, with cracks creating sections approximately I to 3 ft in width, also falls under this distress category.
3.1.6. severe cracking—high severity transverse, longitudinal, and/or longitudinal joint cracking. There is significant spalling at crack edges and cracks have become interconnected. Alligator cracking is also included in this distress category. Use caution in applying maintenance treatments on pavements with severe cracking distress.
3.1.7. slight cracking—single or well-spaced low severity transverse or longitudinal cracks. Also includes low severity longitudinal joint cracking.
3.1.8. slightly pocked, porous, oxidized—raveling beginning to show with moderate cracking.
3.1.9. smooth, non-porous—some free asphalt on the pavement surface, hut with some cracking.
SIGNIFICANCE AND USE
This standard practice may he used to determine the quantities of materials required for the construction of emulsified asphalt scrub seals. Practitioners may select one of the two design methods detailed in this practice.
4.2. The design practice is similar to those used for chip seals with adjustments made to account for the surface condition and cracking of the existing pavement.
SCRUB SEAL DESIGN REQUIREMENTS
Materials:
5.1.1. Scrub Sea/—Emulsified asphalt and aggregate used in the design shall meet the requirements
spccified by the Owner Agency and shall be representative of the materials used for the project.
5.1.2. Fog Seal (Optiona!)—Cornmon emulsitied asphalt grades for fog seal include CSS- I, CSS- I h, SS-l, SS-lh, and CQS-lh. Materials shall meet the requirements of M 140, M 208, or M 316. Other materials and specifications may be used at the request of the Owner Agency. For fog seal, the emulsified asphalt is usually diluted at a 1: 1 ratio with potable water.AASHTO PP 91 pdf download.