Bridge Approach Void Filling

void filling below bridge approach with cellular concrete

Problem:

Large voids were discovered under a section of pile-supported bridge approach on a DOT project in North Carolina, requiring bridge approach void filling.  Tens of thousands of square yards of the adjacent roadway had been constructed over cellular concrete, so the DOT wanted to fill voids under this area of the bridge approach with cellular concrete.  Lightweight fill material was required to reduce future settlement due to extensive weak underlying soils.

Constraints:

Because these voids were discovered right before pavement overlay was to be done, mobilization and placement had to be fast.  To avoid any issues with buoyancy, the DOT specified that the fill material be at least 70PCF.

Solution:

Cellular concrete placement for bridge approach void filling.

Filling voids with cellular concrete.

While the overlying roadway pavements would have been more than enough to compensate for the buoyancy of geotechnical polyurethanes, polyurethane was ruled out as a solution for this project because of the density requirement.  Geotechnical polyurethane lightweight fills are around 2PCF.  

70PCF wet-cast density cellular concrete was identified as the most appropriate material to reduce costs & still meet the density requirement.  The lower density cellular concrete is made, the lower the unit cost for the same project volume.  This is because the most expensive part of the mix is the Portland cement.  The lower the mix density, the less cement in each cubic yard.

Results:

CJGeo mobilized a cellular concrete crew to Elizabeth City.  The original estimated volume of 100 cubic yards was met on the first day.  An additional 60 cubic yards of material were placed the second day.  Cellular concrete placement was done by gravity distribution through the expansion joints in the approach slabs and the cored holes left from installation of the micropiles for the pile supported roadway slabs.  

Immediately after completion of the cellular concrete placement, paving was done.  The bridge approach void filling was completed using non-pervious, 70PCF cellular concrete.