Cellular Concrete Question & Answers - Set Time

What  is the set time for cellular concrete?  

The set time for cellular concrete is typically a little longer compared to “normal” concrete, due to the surfactants used in producing the foam. However, like anything produced with Portland cement, there is a finite time for production and placement. Generally, we recommend that the working time be limited to about four hours once the Portland is mixed with water, or about three hours after the foam is added. After this much time, the material should be left alone to continue the set process. Continuing to pump or move the material can result in collapsing and failure of the material. However, the set time can vary depending on the application, jobsite conditions, and the use of either retarders or accelerators.

2019 Spring Demo Day Success

At each of our Demo Days, Richway tries to answer questions that you have about cellular concrete through demos and seminars. This spring at our demo day we showed water being displaced by cellular concrete and completed a lift height test.


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.    

Pumping Cellular Concrete Vertically

On numerous occasions we've been asked if you can pump cellular concrete vertically. You certainly can. We've had the opportunity to be a part of a large project in which we pumped cellular concrete 4 stories high. About 4000yds³ of 35 PCF material was placed to level floors on a old timber frame building that was being renovated for new commercial use. After the cellular concrete was placed at depths up to 6”, a lightweight concrete cap was placed on top as the final floor topping. On this project our CT-30G was used, which utilizes the continuous production method in which foam is injected and mixed inline on the discharge side of the slurry pump.

A subsequent question that gets asked once we tell people you can pump vertically is whether or not the material density will change pre pump to post pump. Yes, it can. If at all and how much depends on a number of factors; pump type, pump condition, hose size/length, production method (continuous or batch), and other factors. All of these factors apply to pumping horizontally as well.

Using the right equipment and the proper production method can make a huge difference in the success of a project. Using the continuous production method along with the right equipment is not only more efficient, it’s easier to maintain consistent material density. Essentially in this production method foam flow rate and slurry flow rate must be proportioned to obtain the desired density. Richway’s equipment gives operators the ability to monitor all of the necessary inputs to ensure consistent material density as line lengths, sizes, and elevations change. Additionally our design and level of integration means that you’ll get repeatable results too.

Check out this video to see learn more about the Multi-Story Floor Leveling Project.

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