Cellular concrete is an excellent material for tunnel abandonment and abandonment of similar large structures.
Mix Design for Tunnel Abandonment
The typical cellular concrete mix design for tunnel abandonment is 30PCF wet cast density. This yields an average compressive strength of 140psi at 28 days. Each cubic yard in place contains 512 pounds of Portland cement, 256 pounds of water, and 20.3 cubic feet of preformed Aerlite foam. In situations where higher compressive strengths are required, higher density cellular concrete can be used. If exceptionally high strengths are needed, sanded mixes can be used, however sanded cellular concrete mixes don’t flow as well as neat mixes, which can require additional placement steps.
Placement Method for Tunnel Abandonment
Depending on the size of the tunnel being abandoned, material can either be gravity fed or placed by pumping. With gravity feeding, tremmie placement is relatively easy. For long or relatively flat structures, placement using pumps is generally optimal. Neat mix cellular concrete can easily be pumped farther than 1500LF.
Cellular concrete is economical for tunnel abandonment grouting because the majority of the mix is atmospheric air. Because cellular concrete can be easily pumped long distances, it is easy to install in hard to access locations and over long stretches.
Since tunnels and similar structures are generally high volume placements, continuous generation is the most typical method. With continuous generation, slurry is delivered to the jobsite in 5 to 8 yard loads, and pumped to a mixing chamber. Preformed cellular concrete foam is injected into the slurry stream in the mixing chamber. As the mixture passes out of the mixing chamber through the discharge hose, the slurry and preformed foam turn into a homogenous mixture of cellular concrete.
For small tunnel abandonment jobs, batch generation can be used for placing the cellular concrete.