In its simplest form, concrete is a mixture of paste and aggregates (sand & stone). The paste, composed of cement and water, coats the surface of the sand and coarse aggregates then binds them together into a rock-like mass known as concrete.
Within this process lies the key to a remarkable trait of concrete: it’s plastic and can be molded or formed into any shape when newly mixed, strong and durable when hardened. These qualities explain why one material, concrete, can build skyscrapers, bridges, pavements, roads, houses and dams.
Concrete mixtures can be designed to provide a wide range of mechanical and durability properties to meet the design requirements of a structure. The compressive strength of concrete is the most common performance measure used by the engineer in designing buildings and other structures. The compressive strength is measured by breaking concrete specimens in a compression testing machine. The compressive strength is calculated from the failure load divided by the cross-sectional area resisting the load and reported in units of newtons per metre. Concrete’s compressive strength requirements can vary from 12 newtons for residential concrete to 50 newtons and higher in commercial structures.
A volumetric concrete mixer (also known as volumetric mobile mixer) is a mixer on a truck or trailer that contains concrete ingredient materials and water to be mixed at the job site to produce the exact amount of concrete needed.
A volumetric concrete mixer produces concrete by proportioning the materials out over time by volume and relating that volume back to the materials specific weight. These materials are then dispensed into a mixing auger where they are completely mixed together and all the cement is able to come in contact with water to begin hydration as well as encapsulate the complete surfaces of any other material being added into the mix. The material is being added into the mix auger as if it were in handfuls at a time so the there is more than enough energy in the mix auger to ensure a complete and uniform mix by the time it comes out of the discharge end of the auger, which is typically only about 5-10 seconds.
When a volumetric mixer is delivered, part of the delivery process is training and calibration. The calibration process is vital and important part to ensure your mixer is producing what you want to produce. In essence, we are not so much calibrating the mixer as we are the materials. Every material has its own density or weight by volume. When a calibration is done this weight by volume is determined for each material and the info is inputted into the computer. Once this is complete it is then possible to get the volume settings needed to accurately produce the mix design specified.
The calibration process therefore should be down one to two times a year to see if there are any major variances as well as if a new supply of material has been selected as the density may be different.
The production rate can vary depending on the mix design. If you are producing at maximum speed a volumetric concrete mixer with a 24” wide conveyor belt and 12” mixing auger can produce concrete at a rate of 40 cubic metres to 60 cubic metres per hour.
Both a concrete plant with ready-mix drum trucks and volumetric concrete mixer produce quality concrete however, there are some distinct advantages to choosing a volumetric mixer.
i. Customer only pays for exactly what they need: Because the VCM is in essence a mobile concrete batching plant if the customer needs a little more or a little less then what they originally thought it is not a problem because production stops when the job is done. With Ready-mix drum trucks the customer has to make an accurate estimate of what is needed because it is batched and water is added at the plant then delivered to the site.
ii. Concrete is ALWAYS Fresh: With a VCM the concrete is made fresh every second as it is being produced so the newest concrete is what is being laid. With concrete from a drum truck the concrete coming out last is the oldest and may already be stiff.
iii. Small quantities are not a problem: With a VCM you can produce as little as a quarter of a cubic meter or yard of concrete and then pack up and go to another job. With traditional drum trucks, this becomes almost impossible and very uneconomical. After a small load, the drum truck also has to return to the plant to reload for the next job.
iv. Multiple mixes in one stop: With a VCM the operator can do a variety of concrete mixes in one stop. For instance, perhaps a sidewalk had to be removed to get at some utilities. A VCM could then produce some fill concrete to cover the utilities and bring the grade to underside of sidewalk slab height. Then the slab could be formed up and the VCM could produce the correct concrete for the sidewalk slab as well without have to return to the job site.
v. Time is not a factor: With a VCM the problem of time does exisht. Concrete in a delivered in a drum truck is exposed to water at the plant and is now perishable and the time to get it delivered and into position is less than 2 hours. With a VCM you can deliver concrete an infinite distance away. With a VCM you can be stuck in traffic and still deliver fresh concrete to the customer. With a VCM delays on the job are much less stressful.
vi. Evenings and Weekends: To open a traditional batch plant after hours or on the weekends can cost thousands of dollars and require a minimum quantity of concrete to be ordered. With a VCM anytime and any day is just like any other.
The standard that govern the quality of concrete produced by a volumetric concrete mixer may differ depending on who you are supplying. Some larger associations such as the House Builders Federation may require you and your machine to meet either of the compliance standards below. Baylynx mixers meet these standards.
If you are looking at getting into the concrete production business, you do not need to know anything about concrete. However, you do need to be willing to learn…a lot. As manufacturers of volumetric concrete mixers, we want our customers to succeed. We will come alongside you and share as much knowledge as we can as well as help set you up with a team of other suppliers you will need to make your business a success. We regularly hold concrete technical courses at our Runcorn factory where you are always welcome. Our aim is to equip you with the ability to produce many products from your mixer.