Experiment! Reducing mixer truck charge times is easy and usually a forgotten advantage. Like mix designs, concrete batch plants come in many different flavors. Today’s automatic batch controller’s make it an easy adjustment.
Ironically most producers utilize the same discharge sequence.
“70 % head water into the mixer truck first, then release the aggregates, and when 30% of the aggregate has discharged will release cement.” But when you asked them why, the reply is typically ” that’s the way it has always been.”
A common problem of cement balls or packing is a unbalanced sequence of materials into the mixer truck. Too much head water in a drum, will allow the cement to skate across the water and then pack the blades. Try reducing the amount of head water to 55% and increase the aggregate amount to 40%. The point here is to have the volume of water lowered and aggregate falling into the incoming flow of cement to mix the cement with aggregate/sand instead of 100% water. Visually watching a mixer truck being charged up close will identify any discharge gremlins you might be working with; but please be safe and use the necessary respirator, eye and ear protection.
Who knows what you will discover.
Some producers have found a better delivered concrete mix by using the following sequence
1. Discharge 65 % of water into mixer truck, then stop.
2. Discharge 90% of aggregate at a rate of 425+ lbs per second. stop
3. Discharge 100% of cement (nothing else)at a rate of 100+ lbs. per second.
4. Release the final aggregates.
5. Release the remaining water with the remaining 90% of the aggregates.
Producers also found;
1. Creamier mix – cement was mixed straight into the sand 1st instead of seeing water.
2. Cleaner truck hopper, blades and bell.
3. Faster mixer truck feed rates. Truck charged time was reduced because material feed rates were increased with more room individually in the head box. I.e. the aggregate boot wasn’t expanding into the cement boot.
Try making the sequence change first by manually discharging the batchers. Use a average fleet mixer truck as your beta test, but don’t tell the mixer driver you are trying something different. Simply ask them when they return from the job site how the mix looked. You might be surprised by the results.
Tilt Mixer adjustments. On a finer scale, the above adjustments can also be used on a Central Mix plant. The difference of 1 second between materials, can have a big impact on how quickly you will be able to get an accurate slump reading.