FAQ

Below are questions that have appeared in the past on the "Frequently Asked Questions" page.

1. Can I compete with the many ready mix producers in my region?

2. Is mobile-mixed concrete as good as ready-mix?

3. How do I prevent my auger from getting stalled by hardened concrete?

4. What's the best way to add calcium chloride?

1. I am interested in getting into the concrete business, but we have so many ready mix producers in my region that I wonder if I can compete using a mobile mixer.

Answer: One of the primary reasons many volumetric mixer owners are successful is that they do not compete with the ready mix producer, but instead service a portion of the marketplace that is avoided by these producers. Short loads, 5 cubic yards or less, are the most difficult jobs for a ready mix producer to accomplish. He must either send out a partially loaded unit, divide a load in half with the hope the second delivery is not delayed at all, or charge the end user a minimum - which means he has paid for material that is driving away in the drum. Volumetric mixers are ideally suited for this market. There is no need to send out a partially loaded unit since the concrete is produced when it is needed, where it is needed, and in the amount needed. The customer does not need to worry if he has calculated the size of his order exactly, since the material is produced at the time of delivery. He does not have to be concerned about the properties of the concrete - any mix desired can be provided. And he does not have to pay for material he did not need. He can have exactly as much or little as needed. There will always be a market for service that provides the customer with what he wants, when he wants it, and in the amount that he wants.

2. I have been involved in the concrete industry for 20 years, both in finishing and selling. I am interested in mobile mixers, but am concerned about the quality of the product. Is it as good as ready-mix?

Answer: Your concern is one that we often hear, especially from people who have only known concrete produced remotely and delivered in large quantities. Volumetric mobile mixers have been around for over 30 years, and have been used in every application imaginable. The concrete that they produce is equal in every way to that delivered by barrel trucks, and will often exceed the stated strength of the mix design simply because it is fresh. Volumetric mixers are used on federal and state DOT projects across the US, as well as bridge overlays.

One of the first things that the newly formed VMMB has done is develop a set of standards for the manufacture of volumetric mixers. Units having the VMMB rating plate will have met all of the manufacturing limits, and passed all of the uniformity tests required by ASTM C-685, the standard written for concrete made by volumetric mixers. The tests include slump, air entrainment, percentage of aggregate, unit density and compressive strength. This means that the concrete produced by these machines can meet any mix design requested, and do so consistently.

3. When I am producing concrete at a job site, the contractor will constantly ask me to stop and start. I run into problems when they stop me with a full auger, and then work on spreading what is already produced, or take a break. Some of these breaks can last 15 to 20 minutes. How can I keep my auger from getting stalled by hardened material?

Answer: The best way to keep your material from hardening is to not let the auger sit full. Many contractors are used to barrel trucks, which can continue to remix the concrete through many setting cycles, preventing hardening, but also reducing strength gain. When you are producing concrete, know how much material your auger holds, and stop the material feed when you see that an auger full of concrete is all that is needed to fill the area or wheelbarrow. Let your auger empty completely. If the contractor wants a little more, run your material feed again for a few seconds. Remember that you can always produce more, but you cannot produce less. This procedure will not only prevent material hardening in the auger, but will also keep the waste to a minimum, resulting in savings for everyone.

4. What is the best possible way to add calcium chloride to concrete in a volumetric mixer? I don't think that throwing it into the auger dry is the answer, and mixing it in the water system can't be good for the tank or the pipes. What's the solution?

Answer: The best way is by using an admix system. Different manufacturers of calcium chloride have largely different amounts of liquid that has to be added to get your 1% or 2% of calcium. Most volumetric mixer manufacturers have a system that will handle this additive. You have a choice of using a flow control system or a peristaltic system. Most flow control systems use a pump or a pressure tank, the operator adjusting the flow through a calibrated tube. Peristaltic systems use a tube and roller pump that puts out the exact amount of fluid per each pump revolution. Peristaltic pumps run in time with the cement drive system and you should make sure that you have a pump big enough to add all the calcium that you want. The amount of mixture you add can be changed by changing the tube size, changing the speed of the pump, or some have adjustable flow rates. With any of these systems you get an accurate amount of chemical when you want it and it is much better than using a coffee can or adding it to your water and not being able to make adjustments for the changing weather of the day.