Project at a Glance

Material Density: 90-100 pcf
Base Slurry Mix Design: .60 water cement ratio

In early 2024 Richway worked with a customer on a project that utilized cellular concrete in a unique application; repairing lock and dams along the Mississippi river. Although the use of cellular concrete in this application is not new, it remains to be a comparatively unique use, and solution provided by cellular concrete.

Lock and Dam # 7 was constructed in the 1930’s. The guidewalls, which are extensions of the lock wall, provide guidance and mooring facilities outside of the lock chamber itself. The foundation of the walls were constructed using timber cribbing that had been pile driven into the river bed, and backfilled using large aggregate. Over decades of continuous water flow, from the river itself and boat propeller wash, large voids had been created within the foundation system.

To restore stability to the guidewalls, cellular concrete was chosen to fill in these large voids. To begin the project, an extensive formwork system was built and attached to the guidewalls, underneath the surface of the water. Using divers, cellular concrete was then pumped into the forms to fill in the open voids within the foundation system. A series of bulkhead/fill ports were designed into the formwork, which allowed material to be placed and also to observe when full.

Cellular concrete was chosen to reduce burden on the riverbed and keep subsidence to a minimum. However, the material still needed to be heavy enough to displace the water into which it was being pumped. Starting with a sanded mix that had a weight of about 135PCF, the grout was batched in ready mix trucks and foamed using a CFVT-20-SM, and then pumped as far as 700’ to the point of placement. To pump the material an S-tube piston pump was chosen, and as expected some air escaped between the cutter ring and S-tube, causing a variation between pre and post pump densities. Therefore, the cellular grout was foamed down to 85PCF as tested off the chute of the truck, and again tested daily to confirm that post pump density was in the 90-100PCF range, per spec.

In total, the project required approximately 750yds of cellular concrete that was placed over the course of about 15 days.

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