470ASPHALT SEAL COAT

470.1DESCRIPTION—This work is the application of emulsified asphalt, immediately followed by application

of coarse aggregate.

470.2MATERIAL—

Application Temperature F Class of Material Type of Material Minimum Maximum

RS-2P Polymer-Modified Emulsified Asphalt 140 175 CRS-2P Polymer-Modified Cationic Emulsified Asphalt 140 175 HFRS-2P Polymer-Modified High Float Emulsified Asphalt 140 175 RS-2(1) Emulsified Asphalt 140 175 CRS-2(1) Cationic Emulsified Asphalt 140 175 HFRS-2(1) High-Float Emulsified Asphalt 140 175

or a gradation listed in Table A and with the SRL designated in the Contract Item. Supply aggregate from a source listed in Bulletin 14. The Contractor may use an aggregate or blends of aggregates with an SRL equal to or better than that specified. Blends are 50% by weight of the two aggregates. Mix the aggregates using an approved method.

Table A Aggregate Gradations for Seal Coats Sieve Size Total Percent Passing Type SC-1(1) 12.5mm (1/2 inch) 100 9.5mm (3/8 inch) 90-100 6.25mm (1/4 inch) 0-70 4.75mm (No. 4) 0-25 2.36mm (No. 8) 0-5 75µm (No. 200) 0-1.0 Note: Material finer than 75µm (No. 200) sieve will be determined according to PTM No. 100. Aggregate is to meet the requirements of Table B, Type A specified in Section 703.2, except 703.2(c)3 flat and elongated particles must have a ratio of 1:3 (3:1) conforming to ASTM D4791, Method A.

470.3CONSTRUCTION—At least 2 weeks before the scheduled start work, submit a seal coat design for

the Representative’s review. Design the seal coat according to the method in Appendix E of Bulletin 27. If the source or gradation of aggregate changes or if type of asphalt changes, submit a new seal coat design.

cracks as specified in Section 469.

to allow satisfactory material penetration and adhesion and when the air, surface, and aggregate

temperatures are above 60F. Do not apply emulsified asphalt if, in the Representative's opinion, rain is imminent or if freezing temperatures are expected within 24 hours after application. Except when approved by the District Executive in writing, do not apply RS-2P or CRS-2P from September 15 to May 1 in Districts 1-0, 2-0, 3-0, 4-0, 9-0, 10-0, 11-0, 12-0, and 5-0 (Monroe, Carbon, and Schuylkill Counties only); and from October 1 to May 1 in Districts 6 -0, 8-0, and 5 -0 (Berks, Lehigh, and Northampton Counties only). Use a distributor as specified in Section 460.3(b). Use a rate of application within ±10% of the design rate. Determine the distributor application rate in the field according to PTM No. 747. If the Representative determines that the design application rate for the emulsified asphalt is too low or too high, the emulsified asphalt application rate may be adjusted in the field to account for unforeseen or changing conditions. For inaccessible areas, uniformly spread the emulsified asphalt over the surface using portable pressure units. The quantity of material placed at one time must be consistent with the facilities for handling, spreading, and rolling coarse aggregate, as well as the temperature of the surface and emulsified asphalt. Uniformly spread the emulsified asphalt at the junction of separate applications.

Avoid aggregates with excessive free moisture. Before spreading aggregate, verify the calibration of the spreader using a method acceptable to the Inspector-in-Charge. Immediately after applying the emulsified asphalt, uniformly spread a single layer of coarse aggregate at the design rate using a mechanical spreader capable of spreading 15 pounds per square yard to 25 pounds per square yard. Within 5 minutes after application of the emulsified asphalt begin rolling the aggregate with pneumatic-tire rollers, as specified in Section 108.05(c)3.f. Provide a sufficient number of rollers to roll the width of stone spread within 5 minutes after the start of rolling. Overlap each pass by 1 foot with the adjacent roller pass. Make a minimum of two roller passes over the aggregate between the wheel paths. Roll each pass at a speed of less than or equal to 10 miles per hour to prevent turning over aggregate. Use a contact pressure from 40 pounds per square inch to 50 pounds per square inch.

the material obtains adequate stability and adhesion and the material is sufficiently cured to prevent distortion, flushing of emulsified asphalt to surface, and loss of aggregate. Check the surface to ensure that the emulsified asphalt has set in shaded areas. Shaded areas may require longer set times. Provide sufficient flaggers and pilot vehicles to move traffic through the work zone or over the completed work at speeds that prevent aggregate distortion or pick -up. If needed, sweep the surface with a power broom to remove surplus aggregate before and after opening the road to traffic. Provide a shadow vehicle for sweeping operations after opening the road to traffic. Utilize only Waterborne Pavement Markings as specified in Section 962 on asphalt seal coats.

coat surface 1 day after completion of the seal coating operations and after final sweeping has been completed. If the surface of the seal coat aggregate is less than 50 percent embedded in the asphalt, the Representative may require the application of a fog seal as specified in Section 472.

470.4MEASUREMENT AND PAYMENT—