Table of Contents

Appendix F 3.2 Adjustments to the Basic Voids Factor

The design voids factor, VF (L/m2/mm), is determined by adjusting the basic voids factor (Vf) to account for abnormal aggregate shape (Va) and effect of traffic (Vt). These factors may be positive or negative and are cumulative.

Adjustment for aggregate shape (Va)

Table F 1: Adjustment to basic voids factor for aggregate shape (Va)

Aggregate typeAggregate shapeFlakiness index (%)Shape adjustment Va
Crushed or partly crushedVery flaky> 35Considered too flaky and not recommended for sealing
Flaky26 to 35–0.01
Angular16 to 25Nil
Cubic10 to 15+0.01
Very cubic(1)< 10+0.02
Not crushedRoundedn.a+0.01
  1. Not recommended for bottom layer of D/D seal as insufficient angularity does not promote interlock with top layer.

Adjustment for traffic effects (Vt)

Table F 2: Adjustment (Vt) to basic voids factor for traffic effects

TrafficAdjustment to basic voids factor (L/m2/mm)
Flat or downhillSlow moving – climbing lanes
On overtaking lanes of multi-lane rural roads where traffic is mainly cars with ≤ 10% of HV+0.010.00n.a.n.a.
Non-trafficked areas such as shoulders, medians, parking areas+0.02n.a.n.a.n.a.
0 to 15 (EHV(%))Nil–0.01–0.01–0.02
16 to 25 EHV(%)–0.01–0.02–0.02–0.03
26 to 45 EHV(%)–0.02–0.03–0.03–0.04
46 to 65 EHV(%)–0.03–0.04–0.04–0.05
> 65 EHV(%)Use the process described in Section 5.2.7 for access roads to quarries, mining locations, etc.

n.a. Not applicable

EHV(%) Equivalent heavy vehicles, includes both standard heavy vehicles and large heavy vehicles (see Equation 2, Section 5.2.5).

* Channelisation – a system of controlling traffic by the introduction of an island or islands, or markings on a carriageway to direct traffic into predetermined paths, usually at an intersection or junction. This also applies to approaches to bridges and narrow culverts.