Module II : Analysis and design of concrete pavements
Lecture 1 : Pavement Materials
 

Foamed bituminous mix

  • Foamed bituminous mix (FBM) is a foamed mixture of air, water and bitumen. It is produced by injecting very small quantity of water into the hot bitumen, resulting in spontaneous foaming and temporary alteration of the physical properties of the bitumen. Figure-8 represents schematically the manufacture of FBM.
  • Although the foamed bitumen technology was developed more than forty years ago, it is now gaining popularity owing to its good performance, ease of construction and compatibility with a wide range of aggregate types (Transportek 1998).
  • Usage of FBM results in reduction in binder content and transportation costs, as it requires less binder and water than other types of cold mixing methods.
  • FBM can be compacted immediately and can carry traffic almost immediately after compaction is completed ( Jenkins et al., 2003 ).
  • The strength characteristics of FBMs are highly moisture dependent. This is because of the relatively low binder content and high void content of foamed bituminous mixes.
  • FBMs are not as temperature susceptible as HBM. Since larger aggregates are not coated with binder, the friction between the aggregates is maintained at higher temperatures.
  • Foamed bitumen can achieve stiffness comparable to those of cement-treated materials, with the added advantages of flexibility and fatigue resistance (Ramanujam and Kendall, 1999).
  • FBMs usually lack resistance to abrasion and raveling and are not suitable for wearing/friction course applications.

Figure - 8 Schematic presentation of FBM manufacture ( Romanoschi 2003 )

Some specific situations where use of foamed bitumen technology can be considered are:

•  A pavement which has been repeatedly patched to the extent that pavement repairs are no longer cost effective.

•  A weak granular base overlies a reasonably strong subgrade.

•  Granular base too thin to consider using cementitious binders.

•  Can be effectively used in desert road stabilization etc. (Jenkins et al., 2003).

Relatively high cost, requirement of specific equipment for mix production, sensitivity to aggregate grading and stripping risk are some of the disadvantages with the foamed bituminous mix ( Jenkins et al., 2003 ).

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
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