Volumetric Parameters

The volumetric relationship in an asphalt mixture is shown schematically in Figure 7.1 in German terms. Equations are based on TP A-08 2007 and Hutschenreuther and Woerner (2000).

Symbols in Figure 7.1 include the following:

Hbit = Volume of voids in compacted asphalt samples, % (v/v)

Bv = Binder volume, % (v/v)

Mv = Mineral aggregate volume, % (v/v)

HMbit = Voids in mineral aggregate (VMA), % (v/v)

Obviously, the sum of all the parts should equal 100%.

MV + BV + Hbit = 100%

The way of calculating volume parameters and defining them is outlined here.

Air voids

Aggregate volume

Mv

FIGURE 7.1 Volume relationship in an asphalt mixture according to terminology adopted in Germany. (From Graf, K., Splittmastixasphalt—Anwendung und Bewahrung. Rettenmaier Seminar eSeMA’06. Zakopane [Poland], 2006. With permission.)

The binder volume in an asphalt mixture

В = Binder content in the mixture, % (m/m)

pA = Bulk density of the asphalt mixture (sample), g/cm3

pB = Binder density at a temperature of 25°C, g/cm3

Volume of mineral aggregate

Pa (100 – В)

pR, M

pA = Bulk density of the asphalt mixture (sample), g/cm3 В = Binder content in the mixture, % (m/m) pRM = Density of the aggregate mix, g/cm3

Content of air voids in compacted asphalt mixture

Hbit = PR-bit Pa -100%

PR, bit

pA = Bulk density of the asphalt mixture (in German Raumdichte), g/cm3 pRbit = Maximum density of the asphalt mixture (in German Rohdichte), g/cm3

Air voids in compacted mineral aggregate (the hypothetical voids content)

HM, bit = Hbit + BV

Bv = Binder volume, % (v/v)

Hbit = Air voids in the compacted asphalt mixture, % (v/v) Voids filled with a binder

hfb = -^- • 100%

HM, bit

Bv = Binder volume, % (v/v) HM, bit = VMA, % (v/v)

7.1.3 Comments

• In most cases of designing an SMA, the steps described in Section 7.1.1 are sufficient.

• The void contents in compacted Marshall specimens after the application of various compactive efforts (2 x 50 and 2 x 75 blows [Graf, 2006]) have also been compared. For a designer, a large difference between samples of the same SMA mixture under different compactive efforts is an indicator of too high a compactability under the influence of an excessive effort. However, that practice has not been formalized.

• Some German engineers check the voids in mineral aggregate (HMbit) to find out if it is higher than 18% (v/v), as do their fellow U. S. engineers. However, this practice remains unsanctioned.