Marshall Stability, Flow, and Voids

V_{a} = 100 (1 - \frac{G _{mb}}{G _{mm}}) VFA = 100 \frac{VMA - V _{a}}{VMA}

Marshall stability is the maximum load on the compacted specimen; flow is the deformation at that load (typically 0.01 in units). Air voids V_a (VTM) come from bulk mix gravity Gmb and Rice maximum Gmm. VMA is voids in the mineral aggregate (air plus effective binder). VFA is the percent of VMA filled with asphalt. Typical design: V_a ≈ 3–5%, VFA ≈ 65–78%, flow 8–18, stability above a traffic-dependent minimum (50 vs 75 blows/face).

$Stability$ (lbf): Maximum Marshall load
$Flow$: Deformation at maximum load
$G_{mb}$: Bulk specific gravity of the mix
$G_{mm}$: Maximum theoretical specific gravity
$V_{a}$ (%): Air voids
$VMA$ (%): Voids in mineral aggregate
$VFA$ (%): Voids filled with asphalt

Step-by-step solved example

Marshall specimen: Gmb = 2.410, Gmm = 2.512, VMA = 15.0%. Find air voids and VFA.

Marshall volume: air, asphalt, and aggregate like a three-phase diagram.

1. Air voids
V_a = 100(1 − 2.410/2.512) = 100(1 − 0.9594) = 4.06%.
$V_{a} = 4.06%$
2. VFA
VFA = 100(15.0 − 4.06)/15.0 = 10.94/15.0 × 100 = 72.9%.
$VFA = 72.9%$

Answer: V_a = 4.06%, VFA = 72.9%

10 practice questions

0/10 correct

1.Marshall stability is

2.Marshall flow is

3.Air voids V_a equal

4.VFA is

5.VMA (voids in mineral aggregate) includes

6.Gmb = 2.35, Gmm = 2.50. V_a =

7.Air voids well above 5% generally

8.75 blows per face vs 50 blows is used for

9.VMA = 14%, V_a = 4%. VFA is nearest

10.Binder content that is too high typically gives