Batching and Mixing

By "batching" time, I am assuming you are not asking about "mixing" time. Batching is normally measured in cycle time. A batch cycle incliudes the weighing of aggregates, cement, pozzolans and the metering or weighing of admixtures and water. This weigh-up time is variable dependent on whether you use a single, cumulative weighing hopper or individual hoppers allowing simultaneous weigh-up. The size of the dosing gates, feed rates of materials, etc. are all factors.

The mixing time in a "premix" plant, or "central" mix plant, is dependent on whether a complete, ready to test mix is desired, or a "shrink" or "starter" mix is being completed for dust control or quality control reasons (initial water/cement ratio control), i.e., limiting variables in numerous transit mixer drums.

The former is commonly referred to as "compacted" concrete, and to attain a good throroughly mixed compacted product it will depend on the type of premixer used. Low-intensity drum type mixers may require upwards of 120 seconds of mixing, while high-intensity mixers such as a twin-shaft mixers may require only 30 seconds for compacted results and as little as 5-10 seconds for shrink mixing.

The discharge time of the mixer is dependent on the type of truck receiving the mixture and that truck's ability to accept the mixture. The type of mix will also impact discharge times--whether mixes flow or not--and keeping in mind that higher cement content mix designs and lower slump mix designs discharge much slower.

Average cycle times for a normal 10 yd truck load can vary from an absolute minumum of 60 seconds up to 5 minutes depending on the aforementioned factors.