Multiple Stress Creep Recovery (MSCR) Test: Jnr, Grades

Many highway agencies now rely on the multiple stress creep recovery (MSCR) test to judge whether an asphalt binder will hold up against rutting in summer heat. It runs on the same dynamic shear rheometer used for regular PG grading, but instead of wiggling the sample gently, it pushes on it in short bursts and then watches how much of the deformation springs back. The leftover, unrecovered part is what turns into ruts in a hot wheel path. This guide covers what the test does, how Jnr and percent recovery are calculated, what the S, H, V and E traffic grades mean, and how to read a result on a binder certificate.

The short answer

What it is: a creep-and-recovery test on short-term aged binder, run in a dynamic shear rheometer at the high pavement temperature for the job’s climate.
Standards: AASHTO T 350 is the test method and AASHTO M 332 is the grading specification that uses it. Both started as provisional standards (TP 70 and MP 19).
Loading: 1 second of constant shear stress followed by 9 seconds of rest, repeated 10 times at 0.1 kPa and then 10 more times at 3.2 kPa.
Key results: non-recoverable creep compliance (Jnr), percent recovery, and the change in Jnr between the two stress levels (Jnr_diff).
Grade limits in M 332: Jnr at 3.2 kPa of 4.5 kPa⁻¹ or less for S, 2.0 for H, 1.0 for V and 0.5 for E, with Jnr_diff no more than 75%.
Big change: heavier traffic is handled by asking for a lower Jnr at the same climate temperature, not by testing at a hotter temperature.

Why the MSCR test replaced the old rutting check

The original Superpave high-temperature check is G*/sin δ, measured with a small oscillating strain in the DSR. That works reasonably for plain binders, but polymer-modified binders behave differently. At tiny strains the polymer network barely engages, so the old parameter mostly sees the polymer as something that stiffens the asphalt, not as the rubbery, elastic network it becomes under a real truck tire.

The MSCR test applies much larger stress and strain, which brings that elastic behavior into play. Full-scale results drove the change. In its 2011 tech brief, the Federal Highway Administration reported that at its Accelerated Loading Facility, rutting on sections built with a dozen neat and modified binders lined up poorly with G*/sin δ (an R² of about 0.13) and much better with Jnr (an R² of about 0.82). Test sections on I-55 in Mississippi showed the same pattern over six years of traffic.

A practical bonus is that the same test also shows whether a binder actually contains a working elastomer. Agencies that once needed extra tests such as elastic recovery, force ductility or toughness and tenacity to confirm polymer modification can read much of that from the MSCR recovery data.

How the test works

This is an outline to help you read results, not a substitute for AASHTO T 350.

Age the binder. The sample is residue from the rolling thin-film oven, which mimics the hardening that happens during mixing and paving.
Mount it in the DSR using the same plate setup as the regular high-temperature test, and bring it to the test temperature. That temperature is the high climate grade for the project, such as 58°C or 64°C.
Run 10 cycles at 0.1 kPa. Each cycle is a 1-second creep load followed by a 9-second recovery period with no load.
Run 10 cycles at 3.2 kPa. Same timing, about 32 times the stress, which is closer to what a heavy wheel does on a hot day.
Calculate recovery and non-recoverable compliance for each cycle and average each stress level.

The whole sequence takes 200 seconds of loading and rest once the sample is at temperature, so a lab can grade a binder quickly once the RTFO aging is done.

The numbers it produces

Non-recoverable creep compliance, Jnr

At the end of each 10-second cycle, some of the strain has come back and some has not. Jnr is the strain that stays, divided by the stress that caused it:

Jnr = unrecovered strain ÷ applied stress (units of kPa⁻¹)

The 10 cycle values at each stress are averaged to give Jnr_0.1 and Jnr_3.2. A lower Jnr means less permanent deformation per load, which points to better rut resistance. The 3.2 kPa value is the one graded against the traffic limits.

Percent recovery, R

Percent recovery compares how much strain came back with the peak strain reached during the 1-second load:

R = (recovered strain ÷ peak strain) × 100

Plain asphalt usually recovers very little at 3.2 kPa. A well-blended elastomer such as SBS can recover a large share, acting a bit like a rubber band. The FHWA brief gives an example using two binders with the same base asphalt and the same 4% SBS content: one blended with an ill-suited polymer and no high-shear mixing recovered about 19%, while one with a better-matched polymer and high-shear mixing recovered about 40%, even though their conventional PG grades were nearly identical.

Stress sensitivity, Jnr_diff

Jnr_diff = (Jnr_3.2 − Jnr_0.1) ÷ Jnr_0.1 × 100

This shows how much worse the binder gets when the stress jumps. A big jump suggests the binder could be unexpectedly sensitive to heavy loads or a hotter-than-normal stretch of weather. M 332 caps it at 75%.

S, H, V and E traffic grades

Grade letter	Typical traffic in M 332	Jnr_3.2 max	Jnr_diff max
S (standard)	Under 10 million ESALs and normal speeds above 70 km/h	4.5 kPa⁻¹	75%
H (high)	10 to 30 million ESALs, or slow traffic at 20 to 70 km/h	2.0 kPa⁻¹	75%
V (very high)	More than 30 million ESALs, or standing traffic under 20 km/h	1.0 kPa⁻¹	75%
E (extremely high)	More than 30 million ESALs and standing traffic, such as toll plazas or ports	0.5 kPa⁻¹	75%

The letter goes between the two numbers of the PG grade. A binder sold as PG 64H-22 is tested at 64°C for rutting, meets the H limit for Jnr, and still has to pass the usual low-temperature checks for -22. M 332 notes that the specification describes “most situations,” so an agency can choose a different letter for a particular road. Early versions of the spec, as quoted in the 2011 FHWA brief, used a looser 4.0 kPa⁻¹ cutoff for S, so older documents may show that number.

Grade bumping, the old way and the new way

Under the traditional system, an agency expecting heavy or slow traffic in a PG 64 climate might ask for a PG 70 or PG 76 high grade. That forced a stiffer binder by testing it at a temperature the road would never actually reach, which can be misleading for polymer systems that soften fast as they heat up. Our explainer on what PG 76-22 means covers that older approach.

With MSCR grading, the test stays at the real climate temperature and the bar gets stricter instead. The same 64°C test can produce a 64S, 64H, 64V or 64E label depending on how low the Jnr is. That makes it easier to compare binders from different suppliers on the same footing.

Worked example: grading one binder

The readings below are made up for illustration; real results come from a lab report.

Climate high grade for the project: 64°C, so the test runs at 64°C.
Average unrecovered strain at 3.2 kPa: 4.8, which gives Jnr_3.2 = 4.8 ÷ 3.2 = 1.5 kPa⁻¹.
Average Jnr at 0.1 kPa: 1.2 kPa⁻¹.
Jnr_diff = (1.5 − 1.2) ÷ 1.2 × 100 = 25%, under the 75% cap.

1.5 is too high for V (1.0) or E (0.5) but under the H limit of 2.0, so the high-temperature part of the grade is 64H. If the low-temperature tests support -22, the binder is a PG 64H-22. To earn a V, the supplier would have to bring Jnr_3.2 down to 1.0 or lower, usually by adding more polymer or blending it better.

Is there a minimum percent recovery?

Not as a hard grading limit in the main M 332 table. The specification includes a nonmandatory appendix with a chart of percent recovery against Jnr. A point on or above the curve indicates the binder contains an acceptable elastomeric polymer, and an agency can require it in the purchase order. As a rough guide, the 2011 FHWA brief listed suggested minimum recoveries of 30% for a Jnr of 1.01 to 2.0, 35% for 0.51 to 1.0, 45% for 0.251 to 0.50 and 50% for 0.125 to 0.25. Many states write their own recovery requirement into their binder specs, so always check the local version.

Reading an MSCR result on a binder certificate

Check the test temperature. It should match the climate high grade in the name, not a bumped temperature.
Find Jnr at 3.2 kPa. That single number decides S, H, V or E.
Look at Jnr_diff. A value close to 75% means the binder is stress sensitive even if it passes.
Look at R at 3.2 kPa if you need proof of polymer modification.
Confirm the aging. MSCR results belong to RTFO residue; numbers from unaged binder are not comparable.

Why it matters on real jobs

Rutting shows up first where loads are heavy and slow: intersections, bus stops, truck lanes, ramps and parking areas where trucks sit. Those are exactly the places where an H, V or E binder earns its higher cost. For a typical home driveway, the binder grade is set by the local plant’s standard mix and the MSCR letter is rarely something you choose, but it helps to know why a commercial spec calls for one. If you are already seeing grooves in pavement, our guides to fixing ruts in an asphalt driveway, asphalt shoving and measuring ruts with a straightedge cover the field side.

Modified binders often travel with specialty mixes. See stone mastic asphalt, rubberized asphalt and open-graded friction course for where they are most common, and asphalt binder plus Superpave for the bigger picture. When you are ready to estimate material, the driveway asphalt calculator converts area and thickness to tons.

Questions people ask

What does the MSCR test measure?

It measures how much of the deformation in a hot, short-term aged binder sample stays after repeated one-second loads. The unrecovered part, reported as Jnr, signals rutting risk, and the recovered part shows how elastic the binder is.

What is a good Jnr value?

Lower is better for rut resistance. Under AASHTO M 332, Jnr at 3.2 kPa must be 4.5 kPa⁻¹ or less for an S grade, 2.0 for H, 1.0 for V and 0.5 for E, all measured at the project's climate high temperature.

What do S, H, V and E mean in a PG grade?

They are traffic designations: standard, high, very high and extremely high. A binder labeled PG 64V-22 was tested at 64°C and met the V limit for Jnr, which suits very heavy or very slow traffic.

Does the MSCR test replace G*/sin δ?

For agencies that adopt AASHTO M 332, yes for short-term aged binder. MSCR replaces the RTFO G*/sin δ rutting check, while the other parts of the PG system, including the low-temperature tests, stay in place.

What binder is used for MSCR testing?

Residue from the rolling thin-film oven, which represents binder after plant mixing and paving. That is the stage when a new pavement is most likely to rut.

What is Jnr difference?

It is the percent change in Jnr from the 0.1 kPa cycles to the 3.2 kPa cycles. M 332 limits it to 75% so that binders that get much worse under higher stress are screened out.

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