The Volumetric Mixer Advantage
Innovative applications and additives are changing the concrete industry, as construction professionals find modern ways to use this ancient construction staple. With these new products comes the need for an equally advanced delivery solution.
The VMMB was organized in 1999. Its founders’ mission was to develop an equipment-rating standard for volumetric mixers and to promote education and professionalism for their manufacturers and operators.
Download the VMMB case study below to learn more about Volumetric Mixers.
Concrete Basics
Concrete is a mixture of paste and aggregate (sand and rock) when in its simplest form. Paste is composed of cement and water, which coats the surface of the sand and coarse aggregates and binds them together into a rock-like mass known as concrete.
Concrete is plastic and can be molded or formed into any shape when newly mixed because it is strong and durable when hardened. These qualities explain why concrete can build skyscrapers, bridges, sidewalks, and more.
Carefully proportioning and mixing the ingredients allows a mixer to create strong and durable concrete. Cement and water form a paste that surrounds and binds each particle of sand and stone. Through a chemical reaction of cement and water called hydration, the paste hardens and gains strength. A concrete mixture that does not have enough paste to fill all the voids between the aggregates will produce rough, honeycombed surfaces and porous concrete. An excessive amount of cement paste will be easy to place, but is uneconomical and more likely to crack.
The character of concrete is determined by the quality of paste. The strength of the paste, depends on the ratio of water to cement. The water/cement ration is the weight of the mixing water divided by the weight of the cement. High-quality concrete is produced by lowering the water/cement ratio as much as possible without sacrificing the workability of fresh concrete. Using less water produces higher-quality concrete which is consolidated and cured.
A properly designed concrete mixture possesses the desired workability for fresh concrete and the required durability and strength for hardened concrete. A mix, by volume, is about 10 – 15% cement, 60-75% aggregates, and 15-20% water. Entrained air bubbles in many concrete mixtures may also take up another 5-8%.
Besides Portland Cement, concrete may contain other cementitious materials including fly ash, ground slag and silica fume. Some of these cementitious materials are similar to the volcanic ashes that Romans mixed with lime to obtain their cement binder. Some of these Roman structures still exist today. The concrete industry uses these materials (which would normally be disposed in land-fill sites) to participate in the hydration-reaction and significantly improve the strength, permeability and durability of concrete.
Tips and Tricks
