Hveem Stabilometer: How the Hveem Stability Test Works

The Hveem stabilometer is the heart of the Hveem mix design method, the system California used to design asphalt mixes for most of the twentieth century. Instead of crushing a sample until it fails, it asks a gentler question: when you push down on this mix, how much does it try to squeeze out sideways? A mix that acts like a liquid passes the vertical load straight to the sides. A stable mix carries it through stone-on-stone contact and pushes back very little.

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Quick facts

Standards: AASHTO T 246 (stabilometer and cohesiometer) and AASHTO T 247 (sample compaction with the California kneading compactor).
Specimen: 4 in. (102 mm) across, about 2.5 in. (64 mm) tall.
Test temperature: 60 degrees C (140 degrees F).
Result: stabilometer value S, on a scale of 0 to 90.
Typical minimums: 30, 35 and 37 for light, medium and heavy traffic.

A little history

In the late 1920s California built many rural roads with "oil mixes", blends of aggregate and liquid asphalt spread by blade and compacted by traffic. There was no way to design them. Francis Hveem, then a resident engineer with the California Division of Highways, worked out how to pick the oil content from the aggregate's surface area. He noticed that smooth, glassy stone deformed while rough stone held up, and built the stabilometer to measure that difference. He then designed the kneading compactor, because lab samples made by other methods did not match field cores.

How samples are made

Trial mixes at several binder contents are compacted in the California kneading compactor. A shield-shaped tamper foot strikes the mix near the edge while the mould turns a sixth of a revolution between blows. That kneading action lines up the particles more like a roller does in the field than a flat hammer blow. Each specimen is then warmed to 60 degrees C for testing.

How the stabilometer test runs

Calibrate. With a metal calibration cylinder in place, set the liquid pressure to 5 psi and check that about two turns of the pump take it to 100 psi.
Load the sample. Push the hot specimen from its mould into the rubber sleeve and set a follower on top.
Apply vertical load. Press down at 0.05 in. per minute, reading the side pressure at set loads up to 6,000 lbf. The reading at 5,000 lbf, a vertical pressure of 400 psi, is the one used.
Measure displacement. Drop the load to about 1,000 lbf, set the side pressure back to 5 psi, then count pump turns to raise it to 100 psi. That count, D, reflects how much the sample deforms.
Calculate S. Correct for height if the specimen is not close to 2.5 in.

The formula

S = 22.2 ÷ [(Ph × D) ÷ (Pv − Ph) + 0.222]

Pv is the vertical pressure (400 psi), Ph is the horizontal pressure read at that load and D is the turns count. If Ph equalled Pv, as in a liquid, S would be zero. If the sample transmitted no side pressure at all, S would be 90.

Made-up example: Ph = 40 psi and D = 3.0 turns. (40 × 3.0) ÷ (400 − 40) = 120 ÷ 360 ≈ 0.333. Add 0.222 to get 0.555. S = 22.2 ÷ 0.555 = 40, which clears even the heavy-traffic minimum.

Picking the binder content

Hveem's idea was to use as much binder as possible for durability without letting stability drop below the minimum. Stability falls as binder rises, and air voids drop. The designer plots both against binder content and picks the highest binder that still meets the stability minimum and void target, which is about 4%.

The cohesiometer

The method originally had a second device that bent the tested specimen as a beam to measure cohesion, meant to predict raveling. Hot mixes rarely failed it, so it fell out of use.

Hveem vs Marshall vs Superpave

The Marshall test loads a sample on its side until it breaks and records peak load and flow. The Hveem test measures a stiffness-like value without breaking the sample. Both were largely replaced in the US by Superpave volumetric design, often paired with a rutting check such as the Hamburg wheel tracking test. The stabilometer lives on in the R-value test for soils and aggregate base.

Questions people ask

What is the Hveem stabilometer?

It is a triaxial-type device that holds a compacted asphalt sample inside a rubber sleeve surrounded by liquid. When a vertical load is applied, the liquid pressure shows how much the sample pushes sideways. Less sideways push means a more stable mix.

Who developed the Hveem method?

Francis Hveem, an engineer with the California Division of Highways, developed it in the late 1920s and 1930s. California and several other western states used it for decades.

What is a good Hveem stability value?

Asphalt Institute criteria list minimum stabilometer values of 30 for light traffic, 35 for medium traffic and 37 for heavy traffic, with air voids around 4%.

How is the stabilometer value calculated?

S = 22.2 / [(Ph x D) / (Pv - Ph) + 0.222], where Pv is the vertical pressure (400 psi at a 5,000 lbf load), Ph is the horizontal pressure read at that point, and D is the displacement measured in pump turns.

What temperature is the test run at?

The sample is brought to 60 degrees C (140 degrees F), the same temperature at which hot-weather rutting is a concern.

Is the Hveem method still used?

Most agencies now use Superpave volumetric design, but the stabilometer still turns up in some western state specifications and research. The same device is also used for the R-value test on soils and base.

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