What is Bleeding in Asphalt Pavement?

Bleeding is a pavement distress in which a film of asphalt binder on the surface makes it shiny, glass-like and often sticky. It is also called flushing.

Bleeding, flushing and fattening up

The terms name the same condition. The Texas DOT says that excess binder exudes upward onto the surface and gives the black, frequently sticky surface called flushing, bleeding or fattening up. The FAA, the PAVER manual and the FHWA LTPP manual use the word bleeding. This page uses bleeding.

The PAVER manual names “asphalt cement or tars” as the binder that is in excess. A “bleeding tar” is the same distress. It is a binder film on top of the pavement.

What it looks like

The FAA describes bleeding as a film of bituminous material. The film makes a shiny, glass-like, reflecting surface that usually becomes quite sticky. FHWA describes it as excess binder on the surface, usually in the wheel paths. The Texas DOT shows the same pattern on a seal coat, with flushing in the wheel paths.

How to tell bleeding from similar surface conditions

• Polished aggregate. Bleeding is too much binder on the surface. FHWA describes polished aggregate as surface binder worn away to expose coarse aggregate. The conditions are opposite. PAVER says that if bleeding is counted, polished aggregate is not counted in the same area.
• Fog seals and slurry seals. FHWA says that these preventive treatments can look like bleeding. Note them, but do not rate them as bleeding.
• Rubber deposits and spilled oil. AC 150/5380-6C lists rubber deposits, oil spills and other contaminants as separate causes of lower skid resistance. Continuous fuel or oil spillage also softens the asphalt.

Bleeding compared with abrasion

Bleeding puts too much binder on the surface. Abrasion wears the surface away. The causes are opposite, and a runway has the same worry in both cases, which is lost skid resistance.

AC 150/5380-6C lists both under loss of skid resistance in flexible pavement. It ties bleeding to too much binder, low air voids or too heavy a tack coat. On asphalt, traffic wear shows as polished aggregate. Repeated traffic causes it, and little rough or angular aggregate stands above the binder.

PAVER rates bleeding (42) and polished aggregate (51) as separate distresses. It does not count them in the same area.

Causes

The FAA gives these causes:

• Too much asphalt binder in the mix.
• Too few air voids in the mix.
• An excessive tack coat before the HMA surface is placed.

In hot weather the binder fills the voids of the mix and then expands onto the surface. Cold weather does not reverse this. The binder stays on the surface and more of it collects.

For seal coats and surface treatments, the Texas DOT names too much binder as one of the most common defects.

How a new pavement can resist bleeding

The causes show where the control is. The mix needs the right binder content and enough air voids. The tack coat needs the right amount.

FAA Item P-401 sets design air voids of 3.5 percent for asphalt mix, tested to ASTM D3203. It accepts a lot when the total-mix air voids are between 2.0 and 5.0 percent (Table 5). Item P-603 covers the emulsified asphalt tack coat. It applies the tack coat uniformly, at a rate that the project representative approves before use.

Why it matters

Extensive bleeding may severely reduce skid resistance. The Texas DOT also says that flushing can lead to a loss of skid resistance. The FAA says bleeding may be a precursor to other surface deformities, such as rutting and wash-boarding.

How it is rated

The PAVER manual for asphalt airfields lists bleeding as distress 42. It defines no degrees of severity. The inspector notes bleeding when it is extensive enough to reduce skid resistance, and measures the area in square feet or square meters.

FHWA lists bleeding as distress type 11 in the LTPP manual. It marks the severity levels as not applicable. It says that bleeding indicates potential mixture-related performance problems. It records the area in square meters.

Bleeding on an airfield

ICAO Annex 14 Volume I requires a State to specify a minimum friction level for a paved runway. The runway must stay at or above that level. The State requires regular friction measurement with a continuous friction measuring device. Maintenance action must come before the level falls below the minimum (10.2.3, 10.2.4 and 10.2.7).

A bleeding runway can lose friction. An inspector finds bleeding by sight and records the area. The sight check does not give the skid resistance. AC 150/5380-6C says that visual observation during a pavement inspection is an inadequate predictor of skid resistance. It sends the friction survey to AC 150/5320-12, which sets the frequency and procedures.

Repair

The FAA lists these actions for bleeding:

• Blot the surface with sand and remove the sand before aircraft operations resume.
• For excessive bleeding, remove and replace the pavement.

AC 150/5320-6G lists profile milling as a repair for bleeding. A leveling course of suitable asphalt mix follows the milling. AC 150/5320-12C describes a thin milling pass of 1/8 to 3/16 inch (3.2 to 4.8 mm). It greatly increases the friction coefficient of a pavement that bleeding or rubber buildup contaminates.