Softening Point of Bitumen: Ring and Ball Test Explained

The softening point of bitumen is one of the oldest and simplest numbers on a binder data sheet. Bitumen never melts at a single temperature the way ice does. It just keeps getting runnier as it warms. To put a usable number on that, labs use the ring and ball test, published as ASTM D36 and AASHTO T 53. The result helps classify a binder, check that deliveries match, and judge how likely the material is to flow on a hot day. This guide walks through how the test works, what values to expect and how to read them.

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Quick facts

Test names: ring and ball softening point; ASTM D36/D36M, AASHTO T 53, IS 1205 in India, EN 1427 in Europe.
Range covered by D36: about 30 to 157 degrees C (86 to 315 degrees F).
Heating rate: 5 degrees C per minute, held steady.
Result: the average of two readings, in degrees C or F.
Higher number: a harder binder that resists flow in summer heat.

Why bitumen needs a "softening point"

Asphalt binder is viscoelastic. Cold, it acts almost like a brittle solid; hot, it pours like thick syrup; in between it does a little of both. Since there is no sharp melting point, the only way to compare two binders is to agree on an arbitrary but tightly controlled test and report the temperature where a defined amount of softening happens. The ring and ball method does exactly that. Change the ring size, the ball weight or the heating speed and the number changes, which is why the standard pins all three down.

Equipment

Two shouldered brass rings that hold the bitumen disks.
A pair of steel balls, each 9.5 mm (3/8 inch) in diameter and weighing about 3.50 g.
Brass guides that keep each ball centered on its disk.
A ring holder that keeps the rings level, with a bottom plate 25 mm below them.
A heat-resistant glass beaker as the bath, a thermometer or sensor, and a hot plate or burner that can hold a steady rise.
Freshly boiled distilled water for softening points up to 80 degrees C, or USP glycerin above that.

How the ring and ball test runs

Prepare the sample. Heat the bitumen just enough to pour, avoiding local overheating, and fill both rings on a release-coated plate.
Cool and trim. Let the disks cool, then cut off the excess flush with the top of each ring.
Set up the bath. Place the rings, guides and thermometer in the holder and lower it into the liquid. For water baths the start is about 5 degrees C; glycerin baths start around 30 degrees C. Let the balls and sample reach that temperature.
Place the balls and heat. Set a ball in each guide and raise the bath temperature at 5 degrees C per minute.
Watch the drop. As the disks warm, each sags under its ball. Record the temperature the moment the bitumen-wrapped ball touches the plate 25 mm below.
Report. Average the two temperatures. If the pair is too far apart, the test is repeated.

The heating rate matters more than anything else. A faster rise reads high because the thermometer gets ahead of the sample. Labs reject runs where the rate drifts outside the allowed band.

Typical softening point values

Binder	Softening point (ring and ball)	Source of the figure
VG-30 (India)	47 degrees C minimum	IS 73 specification
60/70 penetration grade	About 49 to 56 degrees C	Common supplier data sheets
80/100 penetration grade	About 45 to 52 degrees C	Common supplier data sheets
35/50 (EN 12591)	50 to 58 degrees C	European paving grade table

Treat the supplier ranges as typical, not as a spec. The binding numbers are whatever your purchase specification or agency standard says.

What the number tells you

Grade check. A load that reads well off its usual softening point may be the wrong grade, a blend, or binder that was overheated in storage.
Hot-weather behavior. A low softening point warns of a binder that may bleed or rut when pavement surfaces get hot. For the related flow test at road temperatures, see our DSR guide.
Penetration index. Paired with the needle penetration test, the softening point is used to estimate how sensitive a binder is to temperature.
Polymer storage stability. For polymer modified asphalt, labs compare the softening point of the top and bottom of a stored tube to see whether the polymer is separating.

Softening point vs PG grade

On US highway work the binder is bought by performance grade, such as PG 64-22, which is set by rheometer and aging tests rather than by softening point. Our explainer on what PG 64-22 means covers that system. You will still see ring and ball results on modified binder sheets, roofing asphalt, crack sealants and on penetration or viscosity graded bitumen sold outside the US.

Does a homeowner need to care?

Rarely. On a driveway the plant picks the binder and the mix. What you control is thickness, base and timing. Use the driveway asphalt calculator for tonnage, size the stone under it with the asphalt base calculator, and if you reuse old pavement, the asphalt millings calculator handles that material.

Questions people ask

What is the softening point of bitumen?

It is the temperature at which a small disk of bitumen, warmed slowly in a liquid bath, gets soft enough that a steel ball resting on it sags through and drops 25 mm. Bitumen has no true melting point, so this fixed, repeatable test gives everyone the same reference temperature.

How is the ring and ball test done?

Two brass rings are filled with hot bitumen, cooled and trimmed. Each gets a 9.5 mm steel ball weighing about 3.5 g on top, and the assembly goes into water or glycerin that is heated at 5 degrees C per minute. The temperature when each ball touches the plate 25 mm below is recorded and the two readings are averaged.

What is a typical softening point for paving bitumen?

It depends on the grade. Indian standard IS 73 sets a minimum of 47 degrees C for VG-30. Supplier sheets for 60/70 penetration bitumen commonly list about 49 to 56 degrees C, and harder grades run higher. Polymer-modified binders can be well above these numbers.

Why does water or glycerin matter?

ASTM D36 uses freshly boiled distilled water for softening points from 30 to 80 degrees C and USP glycerin for higher ones, up to 157 degrees C. Water would boil before a very hard bitumen softened, so the higher-boiling liquid is needed for those samples.

Is a higher softening point better?

Higher means the binder resists flowing and rutting on hot days, which is good in a hot climate. But a binder that is too hard can crack in cold weather. The right value is the one that matches the climate and traffic the grade was chosen for.

Is the softening point used in PG grading?

Not directly. US highway agencies grade binder with the Superpave PG system, which relies on rheometer tests. Softening point is still run on penetration and viscosity grades, on roofing asphalt and on many modified binders, and it is used to check whether polymer separates in storage.

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