Cantabro Test: Abrasion Loss for Open-Graded Asphalt
The Cantabro test measures how easily a compacted asphalt specimen sheds stone when it is knocked around. It is the go-to durability check for open-graded friction courses and porous asphalt, where raveling is the main way these mixes fail. The method is simple: weigh the specimen, tumble it in a drum, weigh it again.
Asphalt tonnage calculator →How the test works
- Standard: ASTM D7064 (for open-graded friction course mix design) and similar agency methods.
- Specimen: a gyratory-compacted cylinder, usually 150 mm across, at the design air voids for the open-graded mix.
- Equipment: the same Los Angeles abrasion drum used for aggregate testing, but with no steel balls.
- Run: 300 revolutions at the drum's normal speed of about 30 to 33 rpm, at a controlled room temperature, typically 25 °C.
- Result: Cantabro loss = 100 × (initial mass − final mass) ÷ initial mass.
Worked example (made-up numbers)
A specimen weighs 4,820 g before tumbling and 4,190 g after. Loss = 100 × (4,820 − 4,190) ÷ 4,820 = 13.1 percent. If the agency limit is 15 percent unaged, the mix passes. A second specimen aged before testing loses 19.4 percent; whether that passes depends on the aged limit in the spec.
Typical limits
Agencies set their own numbers, but many open-graded specifications cap unaged loss somewhere around 15 to 20 percent and add a separate, sometimes looser, limit for aged specimens. Some also run the test after moisture conditioning. Check the governing spec before you design.
Why open-graded mixes need it
Open-graded mixes are built with a gap in the gradation so water drains through the layer. That gives them voids of roughly 15 to 20 percent or more and relatively few stone-on-stone contacts. When the binder ages or the mix is under-asphalted, tires pluck stones out of the surface. The Cantabro drum imitates that plucking. For background, see open-graded friction course and porous asphalt.
Balancing Cantabro against draindown
The easy fix for high loss is more binder, but open-graded mixes also have to pass a draindown test, which checks that binder does not run off the stone in the truck. The usual answer is binder plus help:
- Polymer-modified binder for stronger, stickier films.
- Cellulose or mineral fibers to hold thicker films without draindown.
- Hydrated lime in some specs, which can help both durability and moisture resistance.
Cantabro vs LA abrasion
The LA abrasion test uses the same drum but tests loose aggregate with steel balls to measure how hard the stone is. The Cantabro test checks the compacted mix, so it measures how well the binder holds the stone together. A mix can use hard stone and still fail Cantabro if it is short on binder.
Where you will see it
Mostly on highway open-graded friction courses, airport friction courses and porous parking areas. If you are pricing your own porous or standard driveway mix, figure tons from area and depth with the asphalt tonnage calculator.
Questions people ask
What is the Cantabro test?
A durability test where compacted asphalt specimens are tumbled in a Los Angeles abrasion drum without the steel balls and weighed before and after to find the percent mass loss.
How many revolutions are used in the Cantabro test?
300 revolutions, at the drum's usual speed of roughly 30 to 33 revolutions per minute.
What is a passing Cantabro loss?
Limits vary by agency. Many open-graded specifications cap unaged loss somewhere around 15 to 20 percent and set a separate limit for aged specimens.
Why is the Cantabro test used for porous mixes?
Open-graded and porous mixes have few contact points and thin binder films, so raveling is their main failure mode. The tumbling test imitates that loss of stone.
Can the Cantabro test be used on dense mixes?
Some researchers use it as a quick durability index for dense-graded mixes too, but it is mainly specified for open-graded friction courses and porous asphalt.
What lowers Cantabro loss?
More binder, polymer-modified binder, fibers to hold the binder in place, sound aggregate and good compaction of the specimen.
Related guides
- Open-graded friction course
- Porous asphalt
- LA abrasion test
- Stone mastic asphalt
- Asphalt testing basics
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