pre-cast mixer styles with cellular, foamed concrete

[MDGREENWRLD]

The options that exist for pre-cast, wet processes include A) horizontal shaft, B) pan and C) planetary style mixers. The cost of these options increase from A) to C). Our application is a low-density (65 pcf) mix that has a need to fold cellular foam into the mix at the last step. When initial set time is important for mold break out, it has been my thought that a planetary (counter-current) mixer will "excite" and energize the mix fastest. Does anyone have direct experience with this in production? I assume that all styles of mixers will work to some degree, and that the mixing time is the greatest variable.

 

[concretemasonry]

From a practical standpoint, there are several factors to consider regarding the process of mixing:

1. What type of cement? Type I, Type III or Type ??/specialty. Often, heated mixing water can easily accelerate the concrete setting in a plant setting with uniform controlled temperature monitoring.

2. For aggregate in the concrete mix, what is the aggregate type? Many types are light and friable and cannot stand time durations from initial contact with moisture and may have varying amount of resistance to abrasion before breaking down prematurely due to friction and impact.

Obviously, there are differences between the slower horizontal mixers and the pan and planetary mixers that break materials down faster. Many plant operations use a Type III or a specialty blend if the volumes are sufficient to maintain a supply and maximize production.

The maintenance costs also vary widely with horizontal shaft or drum mixers very often operate 24/7/365 with little maintenance/plate replacement or down time and annual maintenance can be easily schedules. The more violent, aggressive mixing systems requiring impact usually have much higher wear and more unpredictable maintenance cycles.

Look at what other people use for similar applications and there usually no secrets in the industry because hardware like mixers, is selected based on the manufacturing process and products required. The biggest economic and quality demons come from starting and stopping operations that are geared for hours, shifts, weeks, or months compared to a continuous operation. A 24/7 situation for many weeks makes quality and uniformity a piece of cake.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[MDGREENWRLD]

Dick,

We are using Type I. There is no coarse aggregate in the mix - only sand. Unfortunately, I have little knowledge of what others are using in similar applications. Our plant will be set up in the Caribbean, and I anticipate only running the mixer one shift per day. Your input on the maintenance costs is helpful.