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Elongation Index and Length Gauge
The Elongation Index is a crucial measure used to determine the proportion of elongated, or flaky, particles in a sample of coarse aggregate. The shape of aggregate particles is a significant factor in the workability and stability of asphalt and concrete mixes. Excessively elongated particles can lead to poor compaction, reduced strength, and higher void content.
To determine the Elongation Index, a specialized tool known as a Length Gauge is used. This device is designed for the precise measurement of aggregate particles.
Key Features of the Length Gauge:
- Construction: The gauge features a series of stainless steel pins precisely mounted on a durable, brushed aluminum base. This robust construction ensures accuracy and longevity, even with frequent use in a lab or field setting.
- Measurement Slots: It includes six labeled openings, each corresponding to a specific sieve size fraction for particles below 50mm. These slots are calibrated to represent 1.8 times the mean dimension of the aggregate particles for that fraction.
- Easy Identification: The sieve fraction ranges are clearly stamped onto the base next to each corresponding measurement slot, allowing for quick and error-free sorting.
How to Calculate the Elongation Index:
- A representative sample of aggregate is first sieved into the standard size fractions.
- Particles from each fraction are then tested with the Length Gauge. A particle is considered elongated if its greatest dimension (length) prevents it from passing through the corresponding slot on the gauge.
- The total mass of these elongated particles is weighed.
- The Elongation Index is calculated by expressing the mass of the elongated particles as a percentage of the total mass of the initial sample.
Compliance:
This testing procedure and the equipment specifications meet the requirements of the following standard test method:
- BS 812: Testing aggregates. Method for determination of particle shape. Elongation index of coarse aggregate.