Cover Image

Not for Sale

View/Hide Left Panel
Click for next page ( 66

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 65
65 60 50 40 Frequency, Percent 30 20 10 0 9 10 12 15 18 20 30 Loss, Percent Magnesium Sodium Figure 28. Frequency distribution of sulfate soundness specifications. freeze-thaw testing. Equipment currently available to easily Of the responding agencies, 25% differentiate between conduct freeze-thaw testing in the laboratory was not avail- coarse- and fine-graded Superpave mixes. Pavement perme- able when the soundness test was developed (115). ability has been a concern with some coarse-graded Superpave The distribution of soundness specifications for coarse mixes. However, only two agencies specify different in-place aggregate is shown in Figure 28. A maximum allowable loss pavement densities for coarse- and fine-graded Superpave of less than 12% is specified by 53% of the agencies specify- mixes. In addition, Florida DOT includes permeability speci- ing sodium sulfate soundness. There is little consensus on the fications for coarse- and fine-graded mixes. Two other states criteria for magnesium sulfate soundness, with values rang- have permeability specifications for use during design, and ing from 12% to 30% loss. four states are considering permeability specifications. 3.4.2 Aggregate Specific Gravity 3.4 MIX DESIGN PROPERTIES The Superpave method specifies the use of the dry bulk 3.4.1 Gradation aggregate specific gravity for the calculation of VMA. Of the responding agencies, 89% use dry bulk specific gravity to Superpave gradation control consists of control points calculate VMA. Four agencies (9%) use the aggregate effec- on four sieve sizes: the maximum aggregate size, NMAS, tive specific gravity to calculate VMA. The effective gravity 2.36-mm (No. 8) sieve, and 0.075-mm (No. 200) sieve. Of the is determined using the HMA maximum specific gravity or responding agencies, 33% have altered the Superpave grada- rice value, asphalt content, and binder specific gravity. The tion bands. In some cases, these changes are as simple as effective specific gravity is always larger than the bulk spe- adding additional control points between the sieves specified cific gravity and, therefore, results in a larger calculated VMA. by the Superpave method or altering the range for the percent The use of the effective aggregate specific gravity to calcu- passing the 0.075-mm (No. 200) sieve. In other cases, agen- late VMA includes the volume of absorbed asphalt as part of cies have tightened the Superpave gradation bands to pro- the void volume between particles. One agency uses the appar- duce mixes that more closely resemble dense-graded mixes ent specific gravity to calculate VMA. This would result in a used prior to Superpave. One agency has modified the Super- larger calculated VMA then would be determined using either pave gradation bands to include the 16.0-mm sieve, used the bulk or effective aggregate gravities. One state does not prior to the introduction of the Superpave method. calculate VMA.