Stage 7: Selecting an Optimum Content of Binder

Stone Matrix Asphalt. Theory and Practice

After the selection of an optimum aggregate mix, the amount of binder should be selected in such a manner that the desired content of air voids in a compacted SMA

TABLE 7.1

Requirements for a Laboratory-Compacted SMA Binder Mixture Using a Marshall Hammer or superpave Gyratory compactora

property

requirement

Notes

Minimum content of binder,

>6.0

Before adjustment of aggregate density

% (m/m)

Content of air voids in a

>4.0

Usually 3.5-4.0

compacted sample, % (v/v)

Voids in a mineral aggregate VMA, % (v/v)

>17.0

Quantity required at production in an asphalt plant; in fact it should be slightly higher in a laboratory, min. 17.5%-18.0%

VCAMIX

<vcadrc

Appropriate filling volume among coarse particles and stone-to-stone contact are guaranteed

Marshall stability, kN

>6.2

Suggested, not required, quantity applies only to samples compacted with a Marshall hammer

Water resistance, TSR, %

>70

Test after AASHTO T283 (see Chapter 12)

Drain-off at the production

<0.3

Test after AASHTO T305 (see Chapter 8)

temperature in an asphalt plant, % (m/m)

Note: TSR = Tensile Strength Ratio a Based on NAPA SMA Guidelines QIS 122.

sample is available. To achieve this objective, a series of samples with different amounts of binder (usually three points) should be produced, guided by the results achieved in the previous tests with an initially assumed quantity of binder. In reality, 12 samples should be made—four for each point of binder content. Having deter­mined the bulk density and maximum density and calculated the air void content, a target quantity of binder should be selected so that the content of air voids is in the 3.5-4.0% (v/v) range.

The final amount of binder is selected based on test results. The selected SMA composition should be subjected to further testing. The final requirements are dem­onstrated in Table 7.1.



Related Posts:

Updated: 15 ноября, 2015 — 5:05 пп