Fatty Road Surface Defects in the road ( bleeding )
Bleeding or Fatty Surface is a surface of the pavement having a thin film of free bituminous binder on the topmost road surface, which creates a shiny, glass-like reflecting surface of bituminous pavement. Such a film of binders tends to become soft in hot weather and slippery in cold and wet weather. Types of vehicles leaving their impression. Hence develop low skid resistance on a bituminous surface leading to an unsafe road. Normally such type of flexible pavement failure appears along the wheel path. Sometimes it also appears at isolated locations, specific pavement lanes or on the entire carriageway.
Measurement of Severity level of Bleeding
- Low severity: isolated spots area measuring less than 5 m2 bleeding area and total area less than 1%
- Medium Severity: In case bleeding area more than 1% but less than 5% of the total area.
- High Severity: In such a case, the bleeding area exceeds 5% of the total area
Causes of Bleeding or Fatty Surface
- Excessive binder and erratic mix design.
- Wax in bitumen or other composition defects.
- Lower voids in hot mix and overloading of axles.
- Use of flaky and elongated particles.
- Excessive application of binder in surface dressing
- Use of high binder in tack coat and prime coat.
- Selection of incorrect binder and grade.
- High pavement temperature.
Treatment of Bleeding with Low , Medium and high severity ( road surface defects )
Low severity: can be corrected by applying heated coarse sand (passing 1.18 mm sieve) to blot up excess bitumen followed by light rolling.
Medium severity: surface may be corrected by application of bituminous pre-coated chips(heated): Passing 4.75 and retained over 1.18 mm and generally applied in a single layer followed by light rolling. But in case of the thickness of the bleeding surface is less than 1 mm, the treatment described in low severity is sufficient.
- High Severity: The effected portion shall be milled out and repaired with a hot or cold mix of the desired quality. Or Re-laid the milled material after mixing with fresh aggregates. Otherwise replaced with an open-graded premix carpet with low bitumen content.
Smooth Surface type flexible pavement failure
A smooth surface type of flexible pavement failure is defined as a surface having a very low skid resistance and becomes slippery when wet. Such a condition is hazardous, on the gradients, bends, and intersections.
Measurement of Severity level of Smooth Surface
The severity level of smooth surface may be defined by skid number by BPT
- Good and Safe Surface: Skid Number > 50
- Low severity Surface: skid number between 45-50
- Medium severity surface: Skid number between 35-45
- High severity surface: Skid number below 35
Causes of the smooth surface
After repeated traffic, the polishing of aggregates occurs, or uses of excessive binder in the mix
Treatment of the smooth surface
The rectification consists of resurfacing with a surface dressing , premix carpet ,thin BC layer or micro surfacing depending upon the type of existing surface. Care should be taken to select aggregates which have proven non -polishing characteristics.
Streaking is the appearance of alternate lean and rich lines of bitumen on the surface either in liner direction or in the longitudinal direction.
Causes of Streaking
- The surface of pavement in alternate longitudinal strips contains different quantities of bitumen. May be due to the non-uniform application of bitumen.
- Improper adjustment in spraying equipment
Treatment of Streaking road surface defects
- To remove the streaked surface and replace it with a new surface.
- It is better to prevent streaking than to correct it.
- Whenever mechanical equipment is used for spraying of bitumen, the distributor should be carefully calibrated
- The skilled operator should be deployed
Hungry surface means when loss of bitumen and fines from the surface and the appearance of dry surface with fine top down cracks. It is the most common road surface defects
Causes of Hungry Surface
- One of the reasons for such type of flexible pavement failure is the use of less bitumen in the bituminous Sometimes absorptive aggregates are there which may absorb the bitumen. Or it may be the use of bitumen with high asphaltenes / Polar aromatics.
Treatments of Hungry Surface
- Application of Fog seal, liquid surface rejuvenators, Slurry seal, micro surfacing or Thin overlays.