Example - 1 - APC



Replace the existing Appendix E in Bulletin 27 with the following:Appendix - EPennsylvania Design Method for Seal Coats and Surface TreatmentsBituminous Seal Coat Design BasisPennsylvania uses a modified version of a seal coat design method developed by N.W. McLeod and presented in The Proceedings of the Association of Asphalt Paving Technologies, Volume 38, 1969.Materials Needed1)One 50 lb sample of the aggregate to be used in the seal coat construction for compatibility testing in accordance with AASHTO T-59 (Coating ability and water resistance section -17) as specified in Publication 37 (Bulletin 25, Appendix A). Information NeededAverage Daily Traffic (From plan data, PENNDOT RMS data, or the District Traffic Unit) Aggregate Gradation (The aggregate producer should provide the average gradation for the aggregate that will be used on the project.) Loose Unit Weight of Aggregate (The aggregate producer should provide the loose unit weight, in accordance with AASHTO T 19, for the aggregate that will be used on the project.) Type of Binder (Use an Asphalt Emulsion or Performance Graded (PG) Asphalt) Type of Aggregate (Limestone / Dolomite, Gravel, Slag) Residual Asphalt in the emulsified or cutback asphalt (For emulsified asphalt the minimum residual asphalt is 65%. (Use 67% as a default) For PG asphalt, the residual is 100 %.) The Roadway Surface Condition for the Subject Roadway (As outlined below) Black, flushed asphalt – The majority of the surface is asphalt covered and smooth with little aggregate visible Smooth, non-porous – The surface is uniform and shows no signs of raveling or oxidation.Slightly porous and oxidized – Beginning oxidation and some loss of surface aggregate.Slightly pocked, porous and oxidized – widespread loss of fine and course aggregate and oxidized appearance.Badly pocked, porous and oxidized – beginning stages of raveling of the pavement surface and completely oxidized surface. This category should also be used for open graded surfaces like Cold in Place Recycling, freshly placed 19 mm Superpave, and FB mixes.Design Procedure for Single Application (Seal Coat)1)Emulsion Binder Application DesignThe binder application rate is the most important factor in seal coat performance. There needs to be enough asphalt to hold the cover aggregate in place but not enough to cover the aggregate after traffic has reoriented the aggregate. The binder application rate is affected by physical material factors like the size of the cover aggregate, and roadway surface conditions, as well as other factors like traffic volumes. The equation used in Pennsylvania for determining the seal coat binder application rate is shown below.B=1.122×MA×T+SC+AbRAWhere:B = Binder Application Rate at 60° F, (gal/sy)Ma = Median Size of Aggregate (inches)T = Traffic Volume FactorSC = Surface Condition FactorAb = Aggregate Absorption Factor (gal/sy)RA = Residual Asphalt in binder, in decimal percent (typically from 0.65 to 0.68)Binder Application Rate at Field Application Temperatures BF=B×TFWhere:BF = Binder application rate at field temperaturesB = Binder Application Rate at 60° FTF = Temperature Adjustment Factor (See Figure 7 below) Median Size Aggregate (Ma)The Median Size of Aggregate (Ma) is the theoretical sieve size through which 50 percent of the material of a sample of aggregate passes. The Median Size of Aggregate is determined manually by the following method.Plot the average gradation information obtained from the quarry on the .45-power gradation chart. (Figure – 1)Extend the horizontal line at the 50 percent passing mark until it intersects the gradation line.Project a vertical line downward from the intersection of the 50 percent line and the gradation line until it crosses the millimeter scale.Convert the millimeter reading to inches by dividing the reading by 25.4 mm/inch.Traffic Volume Factor (T)The Traffic Volume Factor (T) accounts for the effect of traffic volumes on achieving the final embedment of the seal coat aggregate. The factors associated with various traffic levels are as follow. (See Figure 2)ADT0-100101-500501-10001001-2000>2000Correction Factor0.850.750.700.650.60Figure 2, Traffic Volume FactorSurface Condition Factor (SC)The existing roadway Surface Condition Factor (SC) accounts for the binder that is lost because of the voids in the existing roadway surface and the asphalt absorbed by the roadway itself. These conditions can reduce the asphalt available for holding the aggregate on the roadway. The factors associated with various roadway condition levels are as follow. (See Figure 3)Existing Surface TextureSurface Condition Factor (SC)Black, flushed asphalt-0.03Smooth, non-porous0.00Slightly porous & oxidized+0.03Slightly pocked, porous & oxidized+0.06Badly pocked, porous & oxidized+0.09Figure 3, Surface Condition FactorsAggregate Absorption Factor (Ab)The Aggregate Absorption Factor (Ab) accounts for the asphalt that is absorbed by different kinds of aggregates at different rates. The factors associated with two different absorption rates in Pennsylvania are as follow. (See Figure 4)Aggregate TypeAbsorption Factor (Ab)Slag or Absorptive Gravel*+0.03All other Types0.00*Note – For very absorptive aggregate (over 2.0%), a higher absorption factor may be considered based on field experience.Figure 4, Aggregate Absorption Factor2)Cover Aggregate Quantity DesignThe Cover Aggregate Application rate is determined in order to result in an aggregate cover that is one stone thick. The amount of aggregate needed remains the same regardless of the pavement condition or binder type or application rate. The equation used in Pennsylvania for determining the seal coat aggregate application rate is shown below.C=0.75×W1×Ma×EWhere: C = Cover Aggregate Application Rate (lb / sy)Wl = Loose Unit Weight of the Aggregate (lb/ft3) (In accordance with AASHTO T 19, from the aggregate producer or District Materials Unit)Ma = Median Size of Aggregate (inches, as outlined above)E = Waste Factor for Traffic Whip-off (See Figure 5 for factors)Waste Factor for Traffic Whip-off (E)The Waste Factor for Traffic Whip-off (E) is a percentage of additional aggregate needed to account for aggregate that is thrown to the side of the road by passing vehicles. The amount of aggregate that is lost depends on traffic speed and number of vehicles. The factors recommended for different traffic level are as follow. (See Figure 5)Road TypePercent WasteWaste Factor (E)Low Volume, Rural & Residential (< 500 ADT)51.05Higher Volume (500 to 3000 ADT)101.10Highways (>3000 ADT)151.15Figure 5, Waste Factor for Traffic Whip-off Design Procedure NotesThe application rates computed in the design should be treated as a starting point for field application of aggregate and binder quantities. Field conditions may dictate that adjustments be made (especially to the binder application rate) because the design relies on several assumptions made during design. Field adjustments made should be documented and evaluated to gain experience with seal coating variables. Design Procedure for Double Application (Surface Treatment)1)Emulsion Binder Application DesignThe equations used in Pennsylvania for determining the double application seal coat binder application rates are shown below.Binder for Application 1:Bap1=0.4×BTBinder for Application 2:Bap2=0.6×BTBinder Total:BT=(B1+B2+SC+Ab)×TFBinder Application Rate per Aggregate Size:B1=0.785×Ma1RAandB2 =0.785 x Ma2RAWhere: B1 = Binder Application Rate of large aggregate (AASHTO No. 67), (gal/sy)B2 = Binder Application Rate of small aggregate (AASHTO No. 8), (gal/sy)Ma1 = Median Size of large aggregate (AASHTO No. 67), (inches)Ma2 = Median Size of small aggregate (AASHTO No. 8), (inches)RA = Residual Asphalt in binder, in decimal percent (typically from 0.65 to 0.68)SC = Surface Condition Factor (see Figure 3 above)Ab = Aggregate Absorption Factor (gal/sy) (Figure 6 below)TF = Temperature Adjustment Factor (See Figure 7 below) (Adjusts application rate from the 60° design rate to the 150° to 175° application rate)Double Application Aggregate Absorption Factor (Ab)The Aggregate Absorption Factor (Ab) accounts for the asphalt that is absorbed by different kinds of aggregates at different rates. The factors associated with two different absorption rates in Pennsylvania are as follow. (See Figure 6)Aggregate TypeAbsorption Factor (Ab)Slag or Absorptive Gravel (*)+0.06All other Types0.00*Note – If different aggregate types (one absorptive one not) are used for the #67 and #8 aggregate the factor should be reduced to 0.03. For very absorptive aggregate (over 2.0%), a higher absorption factor may be considered based on field experience.Figure 6, Aggregate Absorption FactorTemperature Adjustment Factor (TF)The Temperature Adjustment factor (TF) accounts for the volume change by the asphalt emulsion at the application temperature compared to 60°F.Temperature Adjustment Factor (TF)Application Temperature (°F)150155160(Recommended)165170175TF Asphalt Temp. Factor1.0271.0281.0301.0311.0331.034Figure 7, Temperature Adjustment Factor2)Cover Aggregate Quantity DesignThe Cover Aggregate Application rate for a double application (Surface Treatment) is determined in a similar manner as the single layer. The amount of aggregate needed remains the same regardless of the pavement condition, binder type or application rate. The equation used in Pennsylvania for determining the quantity of AASHTO No. 67 and AASHTO No. 8 aggregate is shown below. (Note that the first layer of AASHTO No. 67 aggregate uses no waste factor for traffic whip-off)First Aggregate Application (AASHTO No. 67)C=0.75×W1×MaSecond Aggregate Application (AASHTO No. 8)C=0.75×W1×Ma×EWhere: C = Cover Aggregate Application Rate (lb / sy)Wl = Loose Unit Weight of the Aggregate (lb/ft3) (In accordance with AASHTO T 19, from the aggregate producer or District Materials Unit)Ma = Median Size of Aggregate (inches,) (as outlined above)E = Waste Factor for Traffic Whip-off (See Figure 5 for factors)Design Examples of Seal Coats and Surface TreatmentsExample 1 - Design for Single Application (Seal Coat)1)Single Application Aggregate Median Size of Aggregate (Ma):SieveMaterial onSieve (lb.)CumulativeWeight passing (lb.)Total% passing?”0121003/8”1.810.285No.48.41.815No.81.40.43No.2000.4-------118745103568500Plot the total percent passing values with the corresponding Sieve sizes on the 45 power gradation chart and connect the points by straight lines to obtain the gradation line for each aggregate. From the intersection of the gradation line with the 50% passing line, draw a line vertically down to the millimeter scale and read the median size aggregate from the scale and convert it to inches if necessary (25.4 mm = 1 inch) as shown below.315806745455426.8 mm = 0.27 inches006.8 mm = 0.27 inches255333523177500028898856527800022771101136015001837690348234000871220385318000Information Needed for the Design:DataEnglish UnitsMedian Size of Aggregate0.27 inchesLoose Unit Weight of Aggregate 100 lb/ft3Average Daily Traffic600Roadway Surface ConditionSlightly Pocked, Porous and OxidizedResidual Asphalt % in Binder67%Type of Aggregate (Limestone, Gravel, Slag, )LimestoneField emulsion application Temperature165°F2)Emulsion Binder Application DesignEquation: B=1.122×Ma×T+SC+AbRAB=1.122×0.27×0.7+0.06+0.00.67B = 0.41 gal/yd2Where: B = Binder Application Rate at 60°F, (gal/sy)Ma = Median Size of Aggregate (inches)T = Traffic Volume Factor (See Figure 2)SC = Surface Condition Factor (See Figure 3)Ab = Aggregate Absorption Factor (gal/sy) (See Figure 4)RA = Residual Asphalt in binder, in decimal percent (typically from 0.65 to 0.68)Required Binder Application Rate at Field Application Temperatures Equation: BF = B x TF257694523656600BF = 0.41 x 1.031BF = 0.42 gal/yd2Where:BF = Binder Application Rate at Field TemperaturesB = Binder Application Rate at 60°F TF = Temperature Adjustment Factor (See Figure 7) 3)Cover Aggregate Application RateEquation: C = 0.75 x Wl x Ma x E266007322582900C = 0.75 x 100 x 0.27 x 1.1C = 22.3 lb/yd2Where:C = Cover Aggregate Application Rate (lb / sy)Wl = Loose Unit Weight of the Aggregate (lb/ft3) (In accordance with AASHTO T 19, from the aggregate producer or District Materials Unit)Ma = Median Size of Aggregate (inches) (as outlined above)E = Waste Factor for Traffic Whip-off (See Figure 5)Example 2 - Design for Double Application (Surface Treatment)1)Double Application Aggregate Median Size of Aggregate (Ma):AASHTO No# . 8 AggregateSieveMaterial onSieve (lb.)CumulativeWeight passing (lb.)Total% passing?”012.01003/8”1.810.285No.48.41.815No.81.40.43No.2000.4------AASHTO No# . 67 AggregateSieveMaterial onSieve (lb.)CumulativeWeight passing (lb.)Total% passing1”0241003/4”123963/8”12.210.845No.49.41.46No.80.90.52Plot the total percent passing values with the corresponding Sieve sizes on the 45 power gradation chart and connect the points by straight lines to obtain the gradation line for each aggregate. From the intersection of the gradation line with the 50% passing line, draw a line vertically down to the millimeter scale and read the median size aggregate from the scale and convert it to inches if necessary (25.4 mm = 1 inch) as shown below.6381751136015AASHTO No. 800AASHTO No. 833718502579370AASHTO No. 67 00AASHTO No. 67 297624523177500037350706527800028898857766050022771102493010001837690378714000638175389890000255333523177500028898856527800022771101136015001837690348234000871220385318000327660049530AASHTO No. 67 = 10.2mm = 0.4 inches00AASHTO No. 67 = 10.2mm = 0.4 inches297624569215AASHTO No. 8 = 6.8 mm = 0.27 inches00AASHTO No. 8 = 6.8 mm = 0.27 inchesInformation needed for the design:DataEnglish UnitsMedian Size of Aggregate (AASHTO #8)0.27 inchesMedian Size of Aggregate (AASHTO #67)0.4 inchesLoose Unit Weight of Aggregate 100 lb/ft3Average Daily Traffic600Roadway Surface ConditionSlightly Pocked, Porous and OxidizedResidual Asphalt % in Binder67%Type of Aggregate (Limestone, Gravel, Slag, )LimestoneField Emulsion Application Temperature165°F2)Emulsion Binder Application DesignEquations: BT=(B1+B2+SC+Ab)×TFB1=0.785×Ma1RAandB2 =0.785 x Ma2RAB1=0.785×0.40.67 = 0.47gal/ yd2 and B2 =0.785 x 0.270.67 = 0.32gal/ yd2 Therefore: BT = (0.47 + 0.32 + 0.06 + 0.0) x 1.031 = 0.88gal/ yd2Where: B1 = Binder Application Rate of large aggregate (AASHTO No. 67), (gal/sy)B2 = Binder Application Rate of small aggregate (AASHTO No. 8), (gal/sy)Ma1 = Median Size of large aggregate (AASHTO No. 67), (inches)Ma2 = Median Size of small aggregate (AASHTO No. 8), (inches)RA = Residual Asphalt in binder, in decimal percent (typically from 0.65 to 0.68)SC = Surface Condition Factor (see Figure 3 above)Ab = Aggregate Absorption Factor (gal/sy) (Figure 6 below)TF = Temperature Adjustment Factor (See Figure 7 below) (Adjusts application rate from the 60° design rate to the 150° to 175° application rate)381444527686000Binder Application 1:Bap1 = 0.4 x BT = 0.4 x 0.88 = 0.35 gal/ yd2379306726754700Binder Application 2: Bap2 = 0.6 x BT = 0.6 x 0.88 = 0.53 gal/ yd2 3)Cover Aggregate Application RateFirst Aggregate Application (AASHTO No. 67)366141026924000C = 0.75 x Wl x MaC = 0.75 x 100 x 0.4 = 30 lb/yd2Second Aggregate Application (AASHTO No. 8)379454824892000C = 0.75 x Wl x Ma x EC = 0.75 x 100 x 0.27 x 1.1 = 22.3 lb/yd2Where:C = Cover Aggregate Application Rate (lb / sy)Wl = Loose Unit Weight of the Aggregate (lb/ft3) (In accordance with AASHTO T 19, from the aggregate producer or District Materials Unit)Ma = Median Size of Aggregate (inches) (as outlined above)E = Waste Factor for Traffic Whip-off (See Figure 5)ReferencesN.W. McLeod A General Method of Design for Seal Coats and Surface Treatments, The Proceedings of the Association of Asphalt Paving Technologies, Volume 38, St. Paul MN 1969.David W. Janisch, Frank S. Gaillard, Revised by Thomas J. Wood Minnesota Seal Coat Handbook 2006, Minnesota Department of Transportation, St. Paul MN, 2006.Chip Seal Best Practices, TRB, National Cooperative Highway Research Program, Synthesis 342, Washington, D.C., 2005.Hyperlink for seal coat design spreadsheetHyperlink for surface treatment design spreadsheet ................
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