# Particle Index

The particle index test provides a combined shape-texture characterization. This test requires that an aggregate sample be divided up into specific size fraction. Each size fraction is placed into a container in three layers.

- Canonical URL: https://pavementinteractive.org/reference-desk/testing/aggregate-tests/particle-index/
- Last updated: 2018-09-05
- Review: reviewed by licensed professional engineers on the previous Pavement Interactive site, where reviewers were not recorded by name
- Standards: ASTM D3398

## Description

The particle index test provides a combined shape-texture characterization. This test requires that an aggregate sample be divided up into specific size fraction. Each size fraction is placed into a container in three layers. This is done twice; the first time, each layer is compacted with 10 blows of a tamping rod, and the second time, each layer is compacted with 50 blows of a tamping rod. The particle index is computed from the following equation:

## Calculations

$$I_a = 1.25(V_{10}) - 0.25(V_{50}) - 32.0$$

where:

- $$I_a$$ = particle index
- $$V_{10}$$ = voids in aggregate compacted at 10 drops per layer
- $$V_{50}$$ = voids in aggregate compacted at 50 drops per layer

The overall sample particle index is computed as a weighted average of the individual size fraction particles indexes based on the size fraction weights. Aggregates composed of rounded, smooth particles may have a low particle index of around 6 or 7, while aggregates composed of angular, rough particles may have a high particle index of between 15 and 20 or more.

## Test Procedures

- ASTM D 3398: Index of Aggregate Particle Shape and Texture