PennDOT Bulletin 27

CT-16-001 Step 2

**Replace the existing Appendix E in Bulletin 27 with the following:**

Appendix - E

**Pennsylvania Design Method ****for Seal Coats and Surface Treatments**

## Bituminous Seal Coat Design Basis

Pennsylvania 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.

### A.Materials Needed

#### 1)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).

### B.Information Needed

#### 1)Average Daily Traffic(From plan data, PENNDOT RMS data, or the District Traffic Unit)

#### 2)Aggregate Gradation (The aggregate producer should provide the average gradation for the aggregate that will be used on the project.)

#### 3)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.)

#### 4)Type of Binder (Use an Asphalt Emulsion or Performance Graded (PG)Asphalt)

#### 5)Type of Aggregate (Limestone / Dolomite, Gravel, Slag)

#### 6)Residual Asphalt in the emulsified or cutback asphalt (For emulsified asphalt the minimum residual asphalt is 65%. (Use 67% as a default) For PGasphalt, the residual is 100 %.)

#### 7)The Roadway Surface Condition for the Subject Roadway (As outlined below)

##### a)Black, flushed asphalt–The majority of the surface is asphalt covered and smooth with little aggregate visible

##### b)Smooth, non-porous – The surface is uniform and shows no signs of raveling or oxidation.

##### c)Slightly porous and oxidized–Beginning oxidation and some loss of surface aggregate.

##### d)Slightly pocked, porous and oxidized – widespread loss of fine and course aggregate and oxidized appearance.

##### e)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.

### C.Design Procedure for Single Application (Seal Coat)

#### 1)Emulsion Binder Application Design

The binder application rateis 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 asother factors like traffic volumes. The equation used in Pennsylvania for determining the seal coat binder application rate is shown below.

Where:

B = Binder Application Rate at 60° F, (gal/sy)

Ma = Median Size of Aggregate (inches)

T = Traffic Volume Factor

SC = Surface Condition Factor

Ab = 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 **

Where:

BF = Binder application rate at field temperatures

B = Binder Application Rate at 60° F

TF = 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.

##### a)Plot the average gradation information obtained from the quarry on the .45-powergradation chart. (Figure – 1)

##### b)Extend the horizontal line at the 50 percent passing mark until it intersects the gradation line.

##### c)Project a vertical line downward from the intersection of the 50 percent line and the gradation line until it crosses the millimeter scale.

##### d)Convert the millimeter reading to inches by dividing the reading by 25.4 mm/inch.

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PennDOT Bulletin 27

CT-16-001 Step 2

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PennDOT Bulletin 27

CT-16-001 Step 2

**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)

ADT / 0-100 / 101-500 / 501-1000 / 1001-2000 / >2000Correction Factor / 0.85 / 0.75 / 0.70 / 0.65 / 0.60

**Figure 2, Traffic Volume Factor**

**Surface 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 surfaceand the asphalt absorbed by the roadway itself.These conditions canreduce 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 Texture**/

**Surface Condition Factor (SC)**

Black, flushed asphalt / -0.03

Smooth, non-porous / 0.00

Slightly porous & oxidized / +0.03

Slightly pocked, porous & oxidized / +0.06

Badly pocked, porous & oxidized / +0.09

**Figure 3, Surface Condition Factors**

**Aggregate Absorption Factor (Ab)**

TheAggregate 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 Type /**Absorption Factor (Ab)**

Slag or Absorptive Gravel* / +0.03

All other Types / 0.00

*Note – For very absorptive aggregate (over 2.0%),a higher absorption factor may be considered based on field experience.

**Figure4, Aggregate Absorption Factor**

#### 2)Cover Aggregate Quantity Design

The 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.

Where:

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 Type / Percent Waste /**Waste Factor (E)**

Low Volume, Rural & Residential (< 500 ADT) / 5 / 1.05

Higher Volume (500 to 3000 ADT) / 10 / 1.10

Highways (>3000 ADT) / 15 / 1.15

**Figure5, Waste Factor for Traffic Whip-off **

Design Procedure Notes

The 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.

### D.Design Procedure for Double Application (Surface Treatment)

#### 1)Emulsion Binder Application Design

The equations used in Pennsylvania for determining the double application seal coat binder application rates are shown below.

Binder for Application 1:

Binder for Application 2:

Binder Total:

Binder Application Rate per AggregateSize:

and

Where:

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 smallaggregate (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)

TheAggregate 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 Type / Absorption Factor (Ab)Slag or Absorptive Gravel (*) / +0.06

All other Types / 0.00

*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 Factor

Temperature 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) / 150 / 155 / 160 / (Recommended)

165 / 170 / 175

TF Asphalt Temp. Factor / 1.027 / 1.028 / 1.030 / 1.031 / 1.033 / 1.034

Figure 7, Temperature Adjustment Factor

#### 2)CoverAggregate Quantity Design

The 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 layerof AASHTO No. 67 aggregate uses no waste factor for traffic whip-off)

First Aggregate Application (AASHTO No. 67)

Second AggregateApplication (AASHTO No. 8)

Where:

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 ofSeal Coats and Surface Treatments

### Example 1 - Design for Single Application (Seal Coat)

#### 1)Single Application Aggregate Median Size of Aggregate (Ma):

Sieve / Material onSieve(lb.) / Cumulative

Weight passing (lb.) / Total

%passing

½” / 0 / 12 / 100

3/8” / 1.8 / 10.2 / 85

No.4 / 8.4 / 1.8 / 15

No.8 / 1.4 / 0.4 / 3

No.200 / 0.4 / --- / ---

Plot 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.

Information Needed for the Design:

Data / English UnitsMedian Size of Aggregate / 0.27 inches

Loose Unit Weight of Aggregate / 100 lb/ft3

Average Daily Traffic / 600

Roadway Surface Condition / Slightly Pocked, Porous and Oxidized

Residual Asphalt % in Binder / 67%

Type of Aggregate

(Limestone, Gravel, Slag, ) / Limestone

Field emulsion application Temperature / 165°F

2)Emulsion Binder Application Design

Equation:

B = 0.41 gal/yd2

Where:

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 ApplicationRate at Field Application Temperatures

Equation:

BF = B x TF

BF = 0.41 x 1.031

BF = 0.42 gal/yd2

Where:

BF = Binder Application Rate at Field Temperatures

B = Binder Application Rate at 60°F

TF = Temperature Adjustment Factor (See Figure 7)

3)Cover Aggregate Application Rate

Equation:

C = 0.75 x Wl x Ma x E

C = 0.75 x 100 x 0.27 x 1.1

C = 22.3 lb/yd2

Where:

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 ApplicationAggregate Median Size of Aggregate (Ma):

AASHTO No.8 Aggregate

Sieve / Material onSieve(lb.) / Cumulative

Weight passing (lb.) / Total

%passing

½” / 0 / 12.0 / 100

3/8” / 1.8 / 10.2 / 85

No.4 / 8.4 / 1.8 / 15

No.8 / 1.4 / 0.4 / 3

No.200 / 0.4 / --- / ---

AASHTO No.67 Aggregate

Sieve / Material onSieve(lb.) / Cumulative

Weight passing (lb.) / Total

%passing

1” / 0 / 24 / 100

3/4” / 1 / 23 / 96

3/8” / 12.2 / 10.8 / 45

No.4 / 9.4 / 1.4 / 6

No.8 / 0.9 / 0.5 / 2

Plot the total percent passingvalues 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.

Information needed for the design:

Data / English UnitsMedian Size of Aggregate

(AASHTO #8) / 0.27 inches

Median Size of Aggregate

(AASHTO #67) / 0.4 inches

Loose Unit Weight of Aggregate / 100 lb/ft3

Average Daily Traffic / 600

Roadway Surface Condition / Slightly Pocked, Porous and Oxidized

Residual Asphalt % in Binder / 67%

Type of Aggregate

(Limestone, Gravel, Slag, ) / Limestone

Field Emulsion Application Temperature / 165°F

2)Emulsion Binder Application Design

Equations:

and

= 0.47gal/ yd2 and = 0.32gal/ yd2

Therefore: BT = (0.47+0.32+ 0.06+ 0.0) x 1.031 = 0.88gal/ yd2

Where:

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)

Binder Application 1:

Bap1 = 0.4 x BT = 0.4 x 0.88= 0.35 gal/ yd2

Binder Application 2:

Bap2= 0.6 x BT = 0.6 x 0.88= 0.53 gal/ yd2

3)Cover Aggregate Application Rate

First Aggregate Application (AASHTO No. 67)

C = 0.75 x Wl x Ma

C = 0.75 x 100 x 0.4 = 30 lb/yd2

Second Aggregate Application (AASHTO No. 8)

C = 0.75 x Wl x Ma x E

C = 0.75 x 100 x 0.27 x 1.1 = 22.3 lb/yd2

Where:

C = Cover Aggregate Application Rate (lb / sy)

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)

## References

1)N.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.

2)David W. Janisch, Frank S. Gaillard, Revised by Thomas J. Wood Minnesota Seal Coat Handbook 2006, Minnesota Department of Transportation, St. Paul MN, 2006.

3)Chip Seal Best Practices, TRB, National Cooperative Highway Research Program, Synthesis 342, Washington, D.C., 2005.

Hyperlink for seal coat design spreadsheet

Hyperlink for surface treatment design spreadsheet

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