March 17, 2015

Most of us have been taught to add 80% of the head water first into the mixer truck, then start the aggregate, and after 30% of the aggregate start the cement. This is a common sequence for a dry concrete batch plant.

The problem is the discharging aggregate (375 lbs/sec) pinches off the cement boot and the cement (70 lbs/sec) slows down the aggregate discharge time. Cement dusting becomes a problem on higher sack loads.

If this sounds familiar, try the following;
65% of the water – stop.
90% of the aggregate (425+ lbs/sec) – stop.
100% of the cement (140+ lbs/sec).
Release the remaining aggregate and water for wash down.

Adjust the speed of the aggregate and cement rate for the maximum a mixer truck in your fleet can be charged.

3 advantages might happen;
1. The charge time is reduced by 25+%.
2. Cement Dusting is reduced.
3. Cement balls and packing is greatly reduced.

Most automatic batch controllers have several charging sequences that can be pre-programmed and tied to a specific mix design. Create a new sequence and experiment. A good test would be to make the change and not let the mixer truck driver know. Any feed back from the job site would be un-biased.