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2013FallShotcreteEMag

Volumetric Batching of Wet-mix Shotcrete By Mason Guarino Fcess. Everyone that has experience with it cubic yards per hour (yd3/h). However, theirVolumetric batch plants are often marketedby production rate per hour in cubic yards or-or decades, volumetric batching has beencommonplace in the dry-mix shotcrete pro knows it is fairly easy, convenient, and reliable marketing of yd3/h is based on a much different and allows for ultimate material control. Main- mixture design than that of a normal shotcrete taining the trucks and equipment can be costly, mixture design. Their yd3/h is based on a mixture but the expenses are easily covered by the less- design with less cement and a higher slump. This expensive material, less wasted material, and means that if you want to be able to batch at a any downtime or frustration with ready-mix speed of 20 yd3/h (15 m3/h), you will need to companies. South Shore Gunite Pools & Spas, have a more in-depth conversation with the Inc. (SSG), has been using volumetric batch manufacturer. I have found that aiming for trucks since 2000 in the dry-mix process, so batching at 20 yd3/h works best and gives you when SSG decided to venture into the wet-mix options to adjust speed by starting and stopping. industry, it seemed like a no-brainer, as we Many batch plants are advertising their per-hour already had a volumetric batch plant capable of rate with a 5.5 cement bag mixture. Wet-mix producing concrete for the wet-mix process. shotcrete more commonly has an 8 bag or higher After some trial and error and research, we were per cubic yard mixture. This is easy to overcome able to successfully produce wet-mix shotcrete by letting the manufacturer know that you need material with our volumetric batch plant, place more cement delivered faster than the standard it into our pump, shoot it into place, and achieve model provides. You may want to specify a little compressive strengths of up to 6000 psi (41 MPa) higher rate than your standard mixture so there in 28 days. is an option to increase production. Additionally, the mix auger is typically sized to accommodate Selecting the Proper Volumetric a 5 to 6 in. (125 to 150 mm) slump material. With shotcrete, we are commonly looking for a 2 to Batching machine 4 in. (50 to 100 mm) slump, so the mix auger When making wet-mix shotcrete material with will need to have more power than provided in a volumetric batch plant, you first need to deter- a smaller stock machine. Larger stock machines mine your desired expectations of the machine. may have sufficient power to handle the lower Some questions you should ask yourself are: How slumps, but it should be discussed with the fast do you want to produce wet-mix material? manufacturer before you find yourself unable to What is your desired mixture design? How do you mix and convey your thicker shotcrete material want to control the water and admixtures? Do you to the pump. If you plan to run a large truck- want to set up a silo and machinery for continuous mounted volumetric batch machine, this will batching or do you want to run back and forth to typically have plenty of power to get the job reload the batch plant? All of these are important done. Smaller and stand-alone rigs may not have factors in determining the type of machinery that the necessary power out of the factory. will live up to your expectations. I will also address how we use our machinery, calibrating mixture Design and Batching the machine, and some of the advantages over conventional ready mixed concrete. Once started, considerations we learned a lot about what our machine was and Mixture designs for volumetric batch plants was not capable of. We had to modify certain are not the same as ready mixed, plant-batched things to get it to run the way we would have liked mixture designs. A volumetric batch plant typi- it to run right from the factory. These things could cally has some limitations. Some of the limita- have been avoided if I had known what to discuss tions I have found relate directly to two of the with the manufacturer beforehand. more favorable additives we use in wet-mix 18 Shotcrete • Fall 2013


2013FallShotcreteEMag
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