Sampling Asphalt Mixtures

Loose asphalt mixture is sampled for binder content, gradation, maximum specific gravity and laboratory-compacted volumetrics. Like aggregate, it segregates when it is dumped, conveyed and spread, and it also cools, so a sample has to be taken quickly from a place that represents the mix and kept hot until it is split. The national practices are AASHTO R 97 for sampling (long numbered T 168) and AASHTO R 47 for reducing samples to test size (Texas DOT, 2026¹).

Sampling Locations

Specifications say where samples are taken. Each location has trade-offs:

• Plant discharge or silo. A sampling device passed through the full stream at the plant gives a sample that represents production, before any segregation in hauling or placing. It doesn't reflect what happens after the mix leaves the plant.
• Haul truck. Sampling from the truck bed is quick but needs care. The surface of a load is often coarse, so increments are taken from several places in the load, below the surface, after removing the top layer. Climbing on loaded trucks is a fall hazard, and many agencies now restrict it or require a sampling platform.
• Behind the paver, before compaction. This is the closest sample to the pavement itself. The common approach is the plate method: a metal plate, with a wire attached to find it, is placed on the existing surface ahead of the paver. After the paver passes, the plate is located, the full depth of the mat is cut around its edges and lifted with the mix on it. The hole is filled with fresh mix. Shovel sampling of the full depth of the uncompacted mat is an alternative where allowed.
• Windrow. Where a pickup machine feeds the paver from a windrow, the windrow can be sampled across its full cross section.

Whichever location is used, the time or tonnage and the spot within the truck or lane should be chosen randomly, not picked by eye (see Acceptance Plan Basics). Texas, for example, selects the sample's tonnage within each sublot from random numbers (Texas DOT, 2016²).

Sample Size and Containers

The field sample must be large enough for every test that will be run, with enough left for a retained or dispute portion; test methods give minimum masses that depend on the nominal maximum aggregate size. Samples are carried in clean, sturdy containers that hold heat, such as insulated boxes or metal buckets with lids, and labeled with the mix, lot and sublot, location, time and sampler (California Department of Transportation, 2022³).

Reducing the Sample

R 47 describes how to split a hot field sample down to test portions:

• Mechanical splitter. A riffle splitter sized for asphalt mixture, heated so the mix doesn't stick, divides the sample evenly. Pour it in uniformly across the chutes.
• Quartering. On a clean, heated, nonabsorbent surface, mix the sample, form it into a cone, flatten it, and cut it into four equal parts. Keep two opposite quarters.
• Incremental method. Some agencies allow forming the sample into a loaf and taking increments across it.

The mix must stay warm enough to work but should not be reheated more than the method allows, because reheating ages the binder and can change binder content, volumetric and performance test results. Hitting an exact mass by adding or removing material is not allowed (Western Alliance for Quality Transportation Construction, 2025⁴).

Things That Go Wrong

• Sampling only the top of a truck load, which is often the coarsest.
• Letting the sample cool, then reheating it repeatedly.
• Splitting on a cold surface, which leaves binder and fines behind.
• Picking the "worst-looking" or "best-looking" spot instead of a random one.

Related Articles

• Binder Content
• Theoretical Maximum Specific Gravity
• Segregation & Temperature Differentials

Standard Practices

• AASHTO R 97: Sampling asphalt mixtures
• AASHTO R 47: Reducing samples of asphalt mixtures to testing size

@misc{pavint-sampling-asphalt-mixtures,
  author = {{Pavement Interactive}},
  title = {Sampling Asphalt Mixtures},
  year = {2026},
  publisher = {HeadLight},
  howpublished = {\url{https://pavementinteractive.org/reference-desk/testing/sampling/sampling-asphalt-mixtures/}},
  note = {Accessed [date]}
}