1、Standard Practice for Emulsified Asphalt Scrub Seal Design AASHTO Designation: PP 91-181Technical 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
2、TS-5b PP 91-1 AASHTO Standard Practice for Emulsified Asphalt Scrub Seal Design AASHTO Designation: PP 91-181Technical Section: 5b, Bridge and Pavement Preservation Release: Group 1 (April) 1. SCOPE 1.1. This standard practice determines application quantities for applying aggregate and emulsified a
3、sphalt 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 pne
4、umatic tire compactor. There is the option of including a fog seal to help with chip retention. 2. REFERENCED STANDARDS 2.1. AASHTO Standards: M 140, Emulsified Asphalt M 208, Cationic Emulsified Asphalt M 316, Polymer-Modified Emulsified Asphalt T 11, Materials Finer Than 75-m (No. 200) Sieve in Mi
5、neral Aggregates by Washing T 19M/T 19, Bulk Density (“Unit Weight”) and Voids in Aggregate T 27, Sieve Analysis of Fine and Coarse Aggregates T 84, Specific Gravity and Absorption of Fine Aggregate T 85, Specific Gravity and Absorption of Coarse Aggregate 2.2. State Agency Guidance Documents: Minne
6、sota Seal Coat Handbook (2006, Minnesota DOT) Minnesota Pavement Distress Manual (2003, Minnesota DOT) 2.3. Federal Lands Highway (FLH) Standard: FLH T 508, Flakiness Index Value 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a vio
7、lation of applicable law.TS-5b PP 91-2 AASHTO 3. TERMINOLOGY 3.1. Definitions: 3.1.1. average least dimensionreduction of median particle size to account for flat particles by using flakiness index. Represents the sealcoat thickness in the wheel path where traffic forces flat aggregate to orient on
8、its flattest side. 3.1.2. badly pocked, porous, oxidizedsevere raveling of surface with much cracking. 3.1.3. flushed-bleedingfree asphalt on the pavement surface with little or no texture. 3.1.4. median particle sizetheoretical aggregate size that corresponds to 50 percent passing on the gradation
9、curve. 3.1.5. medium crackingmedium severity transverse, longitudinal, and/or 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 1 to 3 ft in width, also falls under this
10、 distress category. 3.1.6. severe crackinghigh 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
11、 treatments on pavements with severe cracking distress. 3.1.7. slight crackingsingle or well-spaced low severity transverse or longitudinal cracks. Also includes low severity longitudinal joint cracking. 3.1.8. slightly pocked, porous, oxidizedraveling beginning to show with moderate cracking. 3.1.9
12、. smooth, non-poroussome free asphalt on the pavement surface, but with some cracking. 4. SIGNIFICANCE AND USE 4.1. This standard practice may be used to determine the quantities of materials required for the construction of emulsified asphalt scrub seals. Practitioners may select one of the two des
13、ign 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. 5. SCRUB SEAL DESIGN REQUIREMENTS 5.1. Materials: 5.1.1. Scrub SealEmulsified asphalt and aggregat
14、e used in the design shall meet the requirements specified by the Owner Agency and shall be representative of the materials used for the project. 5.1.2. Fog Seal (Optional)Common emulsified asphalt grades for fog seal include CSS-1, CSS-1h, SS-1, SS-1h, and CQS-1h. Materials shall meet the requireme
15、nts 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. 2018 by the American Association of State Highway and Transportation Officials. All rights rese
16、rved. Duplication is a violation of applicable law.TS-5b PP 91-3 AASHTO 5.2. Design Methods for Selection of Initial Emulsion and Aggregate Application Rates: 5.2.1. All design work will be carried out using aggregate either directly from the job site stockpile or equivalent material from the same s
17、ource and having substantially the same material properties. 5.2.2. Modified Kirby Design Method: 5.2.2.1. Aggregate Application Rate: 5.2.2.1.1. Fabricate a board measuring 3 ft by 11/2ft. A 3/4-in. thick particle board works well for this item. Attach 1 in. by 2 in. pine wood strips to the edge of
18、 the board to create a raised edge. 5.2.2.1.2. Weigh the completed board and record the weight in pounds. 5.2.2.1.3. Place the aggregate to be used on the project on the board. The quantity will vary depending on the gradation, shape, and crushed content of the aggregate, but should be no less than
19、5 lb and no greater than 25 lb. Fit as many aggregate particles on the board within the confines of the edging as possible. The aggregate particles should not overlap each other and should be only one stone thick. 5.2.2.1.4. Reweigh the board containing the aggregate in pounds. Subtract the weight o
20、f the empty board from the weight of the board with aggregate. Multiply this value by 2. This is the quantity of aggregate to be used on the scrub seal in pounds per square yard. Record this quantity as Q. 5.2.3. Initial Emulsified Asphalt Application Rate: 5.2.3.1. Measure the aggregate dry loose u
21、nit weight (T 19M/T 19, Section 12 Shoveling Procedure) and aggregate dry bulk specific gravity (T 84 and T 85). Use contractor quality control data if available. 5.2.3.2. Estimate the initial emulsified asphalt application rate using Equation 1. This represents the amount of asphalt needed to fill
22、the voids between the aggregate particles to a specific embedment depth. 5.61 16.24Wed T VGAR += (1) where: A = emulsified asphalt quantity, gal/yd2; e = percent embedment from Figure 1 expressed as a decimal; d = 1.33 Q/W; Q = quantity of aggregate from the board test, lb/yd2; W = dry loose unit we
23、ight of aggregate, pcf; G = dry bulk specific gravity of aggregate; T = traffic correction factor from Table 1; V = pavement surface correction factor from Table 2; and R = emulsion residue, expressed as a decimal, e. g., 0.65 = 65 percent. The result of the calculation for Equation 1 is the estimat
24、ed emulsified asphalt spray rate. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-5b PP 91-4 AASHTO Table 1Traffic Correction Factor, T AADTa2000 Traffic Factor, T 0.85 0.75 0.70 0.65 0.60 Table 6Sur
25、face Condition FactorMcLeod Method Condition Example Correction (gal/yd2) Black, flushed asphalt N/A 0.01 to 0.06 Smooth, non-porous 0.00 Slightly porous and oxidized +0.03 Slightly pocked, porous, and oxidized +0.06 Badly pocked, porous, and oxidized +0.09 5.3.3. Determine the design emulsified asp
26、halt application rate, defined as the average of the wheelpath and non-wheelpath emulsion application rates. 5.4. Adjustment to Initial Emulsified Asphalt Application Rate: 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation
27、 of applicable law.TS-5b PP 91-7 AASHTO 5.4.1. Adjusted Emulsified Asphalt Application Rate (Adj. EAR)Increase the design emulsified asphalt application rate determined in Section 5.2.3 for the Kirby Method or Section 5.3.2 for the McLeod Method by multiplying the design application rate by the fact
28、ors provided in Table 7. Select distress level based on state highway agency practice for the project location. Table 7Emulsified Asphalt Application Rate Adjustments Based on Severity and Extent of Cracking Type and Amount of Cracking Added Emulsified Asphalt Slight 1.06 Moderate 1.10 Severe 1.20 5
29、.4.2. Maintain an application rate of target rate 0.05 gal/yd2. Adjust as needed according to project specific conditions. Note 2Typical field application rate is within the range of 0.32 gal/yd2 0.05 gal/yd2. Note 3Field adjustments to application rate can be made to ensure at least a 4-in. wave of
30、 emulsion remains in front of the lead broom. Note 4Severe cracking is indicative of a structural issue in the pavement that will not be fully addressed by selection of a maintenance treatment. Reduce expectations for extension in service life of the pavement when maintenance treatments are placed o
31、ver pavements with high extent/severity of cracking. 5.5. Adjustment to Aggregate Application Rate: 5.5.1. Extra Chips to Avoid Roller Pick-UpSome extra aggregate should be spread during scrub seal construction with emulsions than is actually needed to produce a one-stone layer. This extra material
32、is applied to aid in reducing the potential for chips to be picked up by pneumatic rollers during construction. The amount of excess material will vary, but should be approximately 5 to 10 percent and never more than 10 percent. Adjustment up or down is necessary based on when the rollers begin to p
33、ick up the chips. 5.6. Fog SealApply fog seal at a rate of 0.060.13 gal/SY or as required by agency specifications. 6. REPORT 6.1. Report the following: 6.1.1. Design method used. 6.1.2. Aggregate spread rate, Q, in pounds per square yard to the nearest 1.0 lb/yd2. 6.1.3. Report the adjusted emulsif
34、ied asphalt spray rate, Adj. EAR, in gallons per square yard to the nearest 0.01 gal/yd2. 7. KEYWORDS 7.1. Application rate; design; emulsified asphalt; fog seal; scrub 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.
