AASHTO PP 90-2018 Standard Practice for Sand Seal Design.pdf

1、Standard Practice for Sand Seal Design AASHTO Designation: PP 90-181Technical Section: 5b, Bridge and Pavement Preservation Release: Group 1 (April) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-5b PP 90-1 AASHTO

2、 Standard Practice for Sand Seal Design AASHTO Designation: PP 90-181Technical Section: 5b, Bridge and Pavement Preservation Release: Group 1 (April) 1. SCOPE 1.1. This standard determines application quantities for applied graded cover aggregate and emulsified asphalt for sand seals on properly pre

3、pared bituminous streets. A sand seal is the application of emulsified asphalt following immediately by an application of a single layer of fine graded cover aggregate. The seal may be applied in multiple lifts depending on traffic demands and existing road surface conditions. 2. REFERENCED STANDARD

4、S 2.1. AASHTO Standard: MP 27, Materials for Emulsified Asphalt Chip Seals 3. TERMINOLOGY 3.1. Definitions: 3.1.1. badly pocked, porous, oxidizedsevere raveling of surface with much texture. 3.1.2. flushed-bleedingfree asphalt on the pavement surface with little or no texture. 3.1.3. slightly pocked

5、, porous, oxidizedraveling beginning to show with moderate texture. 3.1.4. slightly porous, slightly oxidizedlittle or no free asphalt on the surface with noticeable but low texture. 3.1.5. smooth, non-poroussignificant free asphalt on the pavement surface, but with noticeable but low texture. 4. SI

6、GNIFICANCE AND USE 4.1. This standard practice may be used to determine the quantities of materials required for the construction of emulsified asphalt sand seals. 4.2. Sand seal is recommended for low volume roads of less than 750 ADT. For use on compacted bases, a prime coat should be applied to t

7、he base prior to application of the sand seal. As an initial 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5b PP 90-2 AASHTO seal on a road base, more than one sand seal application may be necessar

8、y to obtain the expected seal lifespan. 4.3. For multi-layer application of sand seals, the road should remain open to traffic for 4 to 8 weeks between successive applications. 5. EMULSIFIED ASPHALT SAND SEAL DESIGN REQUIREMENTS 5.1. MethodSand seal is intended to be an economical and simple preserv

9、ation alternative for low volume roads where high quality materials may not be available. As such, the design method is semi-empirical. Several factors will influence the selection of emulsified asphalt spray rates and cover aggregate application rates. 5.2. Material Quantities: 5.2.1. Emulsified as

10、phalt application rate shall be in the range of 0.91 to 1.36 l/m2(0.20 to 0.30 gal/yd2). Cover aggregate shall be spread in the range of 6.51 to 13.6 kg/m2(12 to 25 lb/yd2). The Contractor shall use lab tests to design specific material quantities to meet existing field conditions. Variation in mate

11、rial quantities shall be made without adjustment to contract unit price. 5.2.2. Emulsified asphalt and aggregate used in the design shall meet MP 27 unless otherwise specified by the Owner Agency. The following material and jobsite conditions shall be considered in determination of variances from th

12、e center of the suggested emulsified asphalt and cover aggregate application rates. 5.2.3. TrafficSand seals are intended for low speed, low volume roads, generally less than 750 ADT. Higher traffic counts will require use of coarser aggregate gradations in conjunction with a decrease in emulsified

13、asphalt application rate. Depending on anticipate traffic types and speeds, use of angular high friction aggregate may be required. 5.2.4. Substrate Surface ConditionThe application rate of emulsified asphalt is impacted by the condition of the surface onto which the sand seal is applied. The existi

14、ng surface should be swept clean prior to application of sand seal. A porous surface will require a higher rate, and a smooth surface will require a lower rate. Table 1 indicates adjustments to emulsified asphalt application rates that can be made to the general emulsified asphalt application rate r

15、ecommendations in Sections 5.3.1 and 5.3.2 based on the observed condition of the substrate. Table 1Emulsified Asphalt Application Rate Adjustment for Substrate Surface Condition Existing Surface Condition Correction Factor, l/m2(gal/yd2) Flushed-bleeding 0.19 (0.06) Smooth, non-porous 0.09 (0.03) S

16、lightly porous, slightly oxidized 0.00 Slightly pocked, porous, oxidized +0.09 (0.03) Badly pocked, porous, oxidized +0.19 (0.06) 5.2.5. Aggregate CharacteristicsAggregate gradation will impact binder demand. Fine gradations require higher emulsified asphalt application rates. If the aggregate conta

17、ins significant quantities of flattened or elongated particles, the emulsified asphalt application rate should be adjusted downward. Aggregates with a high percentage passing No. 200 sieve or with low sand equivalent values will require increased emulsified asphalt application rates. 2018 by the Ame

18、rican Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5b PP 90-3 AASHTO 5.2.6. Adhesion of Binder Residue to AggregateThe specified emulsion class must be compatible with the project aggregate source. An aggregate from a

19、 predominantly calcareous mineral source such as limestone or dolomite will require an anionic type emulsified asphalt. A predominantly siliceous sourced aggregate will require a cationic type emulsified asphalt. If the aggregate mineralogy and emulsifier asphalt class are not matched as indicated,

20、an adhesion additive should be incorporated into the emulsified asphalt formulation to compensate. The compatibility of the emulsified asphalt with the project aggregate should be verified by a stripping test. 5.3. Selection of Emulsified Asphalt and Cover Aggregate Application RatesBased on the cho

21、sen aggregate gradation, use the center point values in Sections 5.3.1 and 5.3.2 to determine starting values. Adjust the values as recommended in Sections 5.2.1 through 5.2.4. 5.3.1. Smaller Gradations (Type I and II)0.40 to 0.60 L/m2(0.13 to 0.19 gal/yd2) emulsified asphalt application rate and 6.

22、0 to 9.0 kg/m2(11.1 to 16.6 lb/yd2) cover aggregate application rate. 5.3.2. Larger Gradations (Type II and III)0.60 to 0.80 L/m2(0.19 to 0.25 gal/yd2) emulsified asphalt application rate and 9.0 to 12.0 kg/m2(16.6 to 22.1 lb/yd2) cover aggregate application rate. 6. REPORT 6.1. Report the following

23、: 6.1.1. Aggregate spread rate in kilograms per square meter (pounds per square yard) to the nearest 0.1 kg/m2(0.2 lb/yd2). 6.1.2. Emulsified asphalt spray rate in liters per square meter (gallons per square yard) to the nearest 0.01 l/m2(0.002 gal/yd2). 7. KEYWORDS 7.1. Aggregate; emulsified asphalt; sand seal. 1This provisional standard was first published in 2018. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.