Ready Mix concrete is proportioned in a concrete batch plant according to any number of set recipes. The concrete is then mixed and delivered to the desired location via truck mounted mixers. Using a good quality batch process and good quality equipment can result in a precise mixture.
The early ready mix concrete plants started to appear sometime in the 1930's. There was a significant expansion of concrete plants in the 1960's. In 1961 Milton Zimmerman started supplying and then designing his own conrete batch plants. Construction Machinery Canada Inc. is now the third generation of Zimmerman's to continue in this field.
Concrete starts life as cement, aggregates and water. The aggregates are typically varying sizes of sand and gravel depending on the mix design. Ready Mix trucks are filled at a concrete batch plant like the basic version seen to the right. A long aggregate conveyor (seen in the back) fills overhead storage bins (seen on the right). A weigh batcher hanging below the overhead bins weighs a batch and then drops the material on to a truck charging conveyor (between the storage bins and the silo) which loads into the ready mix truck. Meanwhile the cement is being weighed in the cement batcher hanging below the cement silo (on the left) and above the discharge of the truck loading conveyor. A ready mix truck will then back up underneath the silo and recieve the materials. The water can be either weighed or metered at the same time and discharged into the truck at specified times to prevent balling of the cement. A small amount of water is kept behind until after loading the truck to help wash out the discharge point of the plant and the loading point of each truck. From start to finish loading a truck takes approximately 5-10 minutes depending on the design of the ready mix plant.
A typical mix will comprise of about 60 to 75 percent aggregates (mix of sand and stone), 10 to 25 percent is cement and 15 to 20 percent is water.
There are several other more advanced and faster plants that can be seen here, also designed by CMC.
Each batch of concrete can be made to order in both size and type. In Canada the typical size of a full load batch is between 7 and 9 cuM. Some trucks are capable of carrying up to 11 cuM. However many roadways have weight restrictions that limit the over all mass that can be carried per axle of the vehicle, especially during spring and fall when the ground is soft.
When choosing a concrete mix design the formula will depend on the needs of the project in terms of the required strength, the weather conditions it will be exposed to, the final appearance, the cost of various additives, building codes and local legislation.