ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 376

aggregate properties and using a series of charts to estimate the design as-
phalt content (The Asphalt Institute 1995).
Three cylindrical specimens 102 mm (4 in.) in diameter and 63.5 mm
(2.5 in.) high are prepared, using the California kneading compactor (Figure
9.25) according to ASTM D1561. Three asphalt contents near the estimated
design value are used to fabricate the specimens. The Hveem stability of the
specimens is determined using the Hveem stabilometer (Figure 9.35), ac-
cording to ASTM D1560. The Hveem stabilometer is a device that allows for
the application of a lateral pressure on the specimen while applying vertical
load using a compression machine.
As in the Marshall method, the bulk specific gravity, theoretical maxi-
mum specific gravity, percent air voids (VTM), and density of all specimens
are determined. The Hveem stability, density, and air voids are tabulated
and plotted versus asphalt content. The optimum asphalt content for the de-
sign mix should be the highest asphalt content the mix will accommodate
without reducing the stability or void content below the minimum values
required by the design criteria.
The laboratory-developed mixture design forms the basis for the initial
JMF. The initial JMF should be adjusted to consider the slight differences be-
tween the laboratory-supplied aggregates and those used in the field.

■ Evaluation of Moisture Susceptibility

Since loss of bond between asphalt and aggregates ( stripping ) has become a
significant form of asphalt pavement distress, several methods have been de-
veloped for evaluating the susceptibility of a mix to water damage. Most of
the popular methods require the specimens to be at the optimum asphalt
content and mix gradation.

9.9.7

FIGURE 9.35 Hveem sta-

bilometer.