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Section 4: Flexible Base Overlay and Flexible Base Thickening

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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.

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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 TTI report 4182-1, “Field Performance and Design Recommendations for Full Depth Recycling in Texas.”

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