Cement build up and possible remedy

[lkconcrete]

I drive and batch at a small precast plant. Have been getting cement stuck or packed in the drum right about 3/4 of the way down in the largest part of the drum.

We run a SCC mix with a fairly high cement content of 750lbs per yard at a .40 water ratio.

Have tried different batch sequences but keep getting the same result most of the time. Sometimes the truck will be clean inside and other times it will be stuck in that spot.

Right now I am cement first loading or "slurry mixing".
Sequence is:
Water with air admixture
Cement (this is mixed for one minute by its self)
Agg
Superplastizer in with the last of the sand
20 gallons washdown.
after all loading it is mixed for 75 to 100 revolutions at about 15rpms.

Have zero problems with mudballs or sand streaks, but the stuck cement builds up fast.

Since sometimes it's clean and sometimes it's not, I'm wondering if it doesn't have something to do with the amount of initial mix water since at times it can vary from 24 gallons per yard to about 34 gallons per yard depending on aggregate moisture.

I know our mix varies a lot from the standard redimix batch since it is so fluid and has more cement.

Any takes on this? willing to try anything at this point to remedy this.

[mxrdrver]

When U add water first, the entire inside of the drum is wet. Then when U drop the cement, the cement sticks to everything wet. Most batch plants add 70-80 of the water first, then blend the cement into the rock and sand as it's dropped into the drum. That way, the rock and sand carries the cement so there is less mess. Your fins will be cleaner and less of the cement residue will get all over the back of the truck.

[lkconcrete]

Going to try a few different loading sequences and see what the results are.

Anyone have an experience with "cement last" loading? If so what were the results?

[lkconcrete]

Made a batch yesterday.

Put most of the water up front.
put in 5000 lbs coarse agg
then ribboned in the cement with the agg
then finished it off with HRWR and 20 gallons that was held back for wash down

Result was the same. Good mud with no balling but again I have cement stuck in the same two spots about midway down the drum.

Will try something else. One thought I had is maybe it needs to mix longer before adding the plastisizer since nothing gets ground up once it gets too fluid.

Anyone else making SCC?