Section 4: Flexible Base Overlay and Flexible Base Thickening
4.1 Flexible Base Overlay
The flexible base overlay has been used as an intermediate
layer of a new structure, placed directly on top of an old structure.
The primary purpose, in addition to increasing structure, has been
to resist the propagation of reflective cracks from the old structure.
The existing structure still offers good/uniform support. A suitable
surface designed for the expected traffic loading must also be planned.
As such, this type of rehabilitation can increase the overall highway
profile considerably. The material proposed for the new flexible
base should be evaluated for moisture susceptibility and durability;
trapping moisture in the flexible base overlay between the old highway
surface and the new surface must be avoided.
4.2 Flexible Base Thickening
Flexible base thickening can be used to improve the structural
capacity of low to moderate volume highways. This technique can
be used where there are low levels of existing structural damage,
the existing base is uniform, and the subgrade offers good (> 15
ksi) support. The new base material should be of equal or higher
quality than the existing base; where this is not the case, it is
essential that the new material be thoroughly blended with the existing
base. When the materials are blended, cutting into the subgrade
must be avoided. This subject was explored as a part of research project
0-4182. Field performances were evaluated in
“Field Performance and Design Recommendations
for Full Depth Recycling in Texas.”