example 18.5 determining a suitable binder grade

8/13/2019 Example 18.5 Determining a Suitable Binder Grade

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Example 18.5 Determining a Suitable Binder Grade

- Correct for slow moving traffic: Move binder one grade higher. For

minimum 50 percent reliability, binder if PG 64-16. For minimum of 98

percent reliability, binder is PG 70-16.

- Correct for ESAL > 30 x 108 . Move binder one grade higher. For minimum

50 percent reliability, binder is PG 70-16. for minimum 98 percent reliability,

binder is PG 76-16.


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Table 18.13 Section of Asphalt Binder Performance Grades on the Basis of

Climate, Traffic Speed, and Traffic Volume


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1. Select the types of loading.

2. Move horizontally to the high pavement design temperature.

3. Move down the low pavement design temperature.

4. Identify the Binder Grade.

5. ESALS > 107consider increase of one high temperature grade. ESALS > 3 x 102

increase one high temperature grade.

Example:

Standing load, high design temperature

Low design temperature = - 25oC

Grade = PG 70-28


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Table 18.14 Coarse Aggregate Angularity Criteria


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The clay content is defined as the percentage of clayey material in the

portion of aggregate passing through the 4.75-mm sieve. It is obtained by

conducting the AASHTO T176 designated test Plastic Fines in Graded Aggregates

and Soils by Use of Sand Equivalent Test.

Tapping Bottom of

Cylinder

ApparatusManually-Operated Shaker

Irrigation Clay Reading


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Table 18.17 Clay Content Criteria

Table 18.17 gives minimum allowable values for sand equivalent for

different traffic loads.

Traffic, Million ESALs Sand Equivalent

Minimum, Percent

< 0.3 40

< 1 40

< 3 40

< 10 45

< 30 45< 100 50

100 50


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Gradation. The distribution of aggregate particle sizes for a given blend of

aggregate mixture is known as the design aggregate structure. The gradation

system used for Superpave is based on the 0.45 gradation plot. In order to

understand the gradation system used, it is first necessary to define certain

gradation terms that the Superpave system uses. These are maximum sizes,

nominal maximum sizes and maximum density gradation.

Maximum size is defined is one sieve larger than the nominal maximum size, and

the nominal maximum size is one sieve larger than the first sieve that retains more

than 10 percent of the aggregate. Five mixture gradations are specified in the

Superpave system, as shown in Table 18.18.

Maximum density gradationis obtained when the aggregate particles fit together

in their densest form. An important characteristic of the 0.45 power plot is that

the maximum density gradation for a sample of soil is given by the straight line

joining the maximum size and the origin (Figure 18.16).


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An acceptable aggregate gradation is defined by specifying control points on the

maximum density gradation chart for the smallest sieve size (0.075 mm), the

nominal maximum size, and an intermediate size sieve (2.36 mm). An acceptable

soil blend therefore should have maximum density gradation line that lies within

these control points.

Table 18.18 Superpave Mixture Gradation


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18.6.2 Volumetric Trial Mixture Design

This consists of:

Selection of design aggregate structure

Determining trial percentage of asphalt binder for each trial aggregate blend

Evaluating trial mix designs

Obtaining design asphalt binder content


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Determining Trial Percentage of

Asphalt Binder for each Trial Aggregate Blend


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example 18.5 determining a suitable binder grade

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