Water Displacement on a Pipe Fill

Two common applications for cellular concrete are annular grouting, and pipe abandonment. In both of those situations there is a potential for water to be present in the space to be filled, so the question arises; can a 30 PCF cellular concrete can actually displace water? Because the density of 30 PCF cellular is half the weight of water, the default answer is no. However there are a number of other factors and physics at play as to whether or not this is actually achievable; pipe diameter, material density being pumped in, pumping rate, to name a couple.

With this demo we used a 16” diameter pipe, 20’ long that was filled with water and showed, as we have before, that a material lighter than water can in fact displace it. We used one our CT-100D machines to pump in 35PCF material and filled pipe with the cellular concrete.  It would be typical to push clean water out of the vent pipe, followed by cellular concrete. In this demo this didn’t happen, however after a minute or two of pushing material out of the vent the density was checked and was 36 PCF. This seemingly indicated that the water had been in fact pushed out, with very little wash out.  A final verification was done one week later by cutting the pipe in sections to check for any voids where water would not have pushed out by the cellular concrete. As seen in the photos, the was very little of the pipe that did not get filled.

Lift Height Test

Because cellular concrete is used in many mass void fill applications, the maximum lift height, or pour depth, is a question that arises often. Being able to pour a deeper lift typically means being able to place more material at a time, which increases efficiency and productivity. It’s not uncommon to see specs written that limit lift heights to two or three feet. The limiting factor is the foam concentrate used to produce the foam.  Generally, a stronger more durable foam will be able to withstand a deeper lift, at any given density. A foam that isn’t up to the task will oftentimes collapse upon itself, reducing yield and increasing density. Collapsed foam is sometimes referred to as shrink, however they are two different things. On any given pour a half to one inch of shrink may be common, however when foam fails and collapses, up to 80% of the material volume may be lost.

In this demo we stood a 24” diameter X 8’ long pipe, on end and filled it with 30 PCF cellular concrete.  The G2 control on CT-100D was set to produce 2.5 PCF foam at a 45:1 water to concentrate ratio. Foam density and water concentrate ratio are critical in terms of ensuring that the foam being produced will have the integrity to meet the application.  After dealing with a couple small leaks on the side of the used pipe, the material was topped off within about three inches of the top and left to  set and cure. Heavy rain showers within a couple hours did create about a half inch of “knock down”, otherwise the material was able to set without any collapse or shrink issues.  After a week, we sectioned the pipe to check for any density changes from the top of the fill to the bottom, indicating any segregation issues. Be on the lookout for a video for more in depth information on the results.