Bitumen Coarse is the top layer of pavement and the layer that comes in direct contact with traffic. This layer should be able to withstand traffic and weather (High and low temperature, Rain) without exhibiting various distress like cracking, rutting etc. It may be composed of one or two layers as per the design.
- Bitumen Coarse provides structural support to the pavement surface.
- This layer also transmits the load to the subgrade and subbase layer (DBM, WMM, GSB).
Material Required for Bituminous Concrete
- Bitumen (Binder)
- Coarse Aggregate
- Fine Aggregate
- Anti-stripping agent
The individual specifications are already given in the last article of (DBM Layer).
Grading Requirement for DBM
|Nominal Aggregate Size||19mm||13.2mm|
|OBC||Min 5.2%||Min 5.4%|
|IS Sieve (mm)||Cumulative % by weight of total aggregate passing||Cumulative % by weight of total aggregate passing|
In case aggregate have specific gravity more than 2.7, minimum bitumen content can be reduced proportionally.
Grading Requirement for BC
Requirements of Fines in DBM:
Dense Bitumen Macadam (MORTH V):
|Layer Thickness||Fines Requirement (75 mic passing)||Remarks|
|40-50 mm||2-8 %||Grading 1 (MORTH V Table 500-17)|
|30-40 mm||4-10 %||Grading 2 (MORTH V Table 500-17)|
Plasticity Index≤ 4% Sand Equivalent Value < 50%
Quality Control Tests Required for Bitumen and Aggregate
Testing and frequency will be same as of DBM. Therefore we can refer to the given link.
Construction of BC Layer
Construction steps are same as given in DBM layer. Please refer to the link
- BC Productivity : 21000-25000 MT/month/team/day
- Paver Productivity : 50 m³/hr
- Roller productivity : 40 m³/hr