“Cellular Concrete was used on Florida State Road 50 last week and is half the weight of compacted soil.”

image00In early November 2016, I was privileged to visit the construction site of one of the first uses of cellular lightweight concrete backfill in the State of Florida. The widening of State Road 50 in Ocoee, Florida – just north of Orlando – made it necessary to cross a low area with significant organic soil deposits, i.e., too thick to de-muck. Typically, building anything over organic deposits has risks of low strength and/or excessive settlement. There had obviously been a long-term settlement problem with the original road – we found about 14 inches of asphalt in one exposed area (see Photo 1), meaning that asphalt had been added to the road time and again to hold the elevation or correct other problems over time.

So after installing a sheetpile wall to minimize the disturbance to the adjacent wetland area, and removing some peat and muck, backfilling took place using a 60 PCF mixture of cement, sand, water, and … well, bubbles (Photo 2).

But not just any bubbles, these are processed on-site using an aeration machine that mixes water and a special polymer that makes the bubbles “resilient”, according to Nico Sutmoller, representative with Aerix Industries, the patent holder of this technology. Bubbles mix intimately with the other ingredients and hold their shape for several hours, until the concrete has begun to harden. In this process, concrete shrinks and finally bursts the bubbles. But what remains (in this case) is about 50% bubbles and 50% grout. In the above photo, you can see the voids left over from bubbles on a hardened piece of grout I grabbed at the site.

The contractor, MixOnSite – a national expert in placing lightweight cellular concrete – was installing the lightweight backfill in 2 to 3 image01foot thick lifts, to a maximum thickness of about 10 feet at this site.  Although the lightweight concrete will cure/harden over time and hold its own vertical side slope, tiebacks were used (Photo 3) along with the permanent sheetpile wall to make sure the road performs well for a long, long time.

image02This technologically advanced lightweight backfill solution was designed by FDOT District 5 geotechnical staff. The original geotechnical investigation was completed by Terracon. The design engineer for this roadway widening project was AECOM, and construction monitoring is being completed by CDM Smith. The general contractor on the site is Lane Construction.

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Larry Madrid, P.E., D.GE., F.ASCE is President of Madrid Engineering Group, Inc. and loves cool construction materials technology. He can be messaged via LinkedIN, or via email at:  larrymadrid@madridengineering.com